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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2141–2146 2141 Stabilisation of sodium complexes of 18-crown-6 by intramolecular hydrogen bonding † Jonathan W. Steed *a and Peter C. Junkb a Department of Chemistry, King’s College London, Strand, London, UK WC2R 2LS. E-mail: jon.steed@kcl.ac.uk. Fax: 144 171 848 2810 b Department of Chemistry, James Cook University, Townsville, Queensland, 4811, Australia Received 24th March 1999, Accepted 17th May 1999 Complexation of Na1 by 18-crown-6 within an aqueous medium resulted in the formation of the monohydrates [Na(18-crown-6)(H2O)(X)] (X = ClO4, NO3 or ReO4) in the presence of oxygen donor anions.All three complexes exhibit a significant intramolecular hydrogen bond between the co-ordinated water molecule and the crown ether as well as structure organising C–H ? ? ? O interactions. In the presence of anions with less aYnity for Na1, complexes of type [Na(18-crown-6)(H2O)2]X (X = N3 or I3) were formed.In the case of the azide both water molecules hydrogen bond strongly with the crown ligand giving rise to a highly unsymmetrical complex. In the triiodide more symmetrical intramolecular interactions are observed, as well as intermolecular water–crown hydrogen bonds. Reaction of NaBPh4 with 18-crown-6 in aqueous ethanol resulted in the formation of [Na2(18-crown- 6)2(H2O)3][BPh4]2 in which strong intramolecular hydrogen bonds are observed for both bridging and terminal water ligands in a similar fashion to the azide 4a.The bridging aqua ligands interact with both crown ether hydrogen bond acceptors. Introduction The early, and appealing, postulate that the selectivity of macrocyclic hosts such as the crown ethers for alkali metal cation guests depends largely upon the size match between ionic diameter and macrocycle cavity size has undergone a great deal of revision and elaboration since the discovery of these hosts in 1967.1 In particular, properties such as degree of preorganisation and the rigidity of the macrocycle have been shown to be crucial by wide ranging systematic studies.Factors such as cation charge, solvent and solvation free energy, chelate ring size and the number and type of donor groups are also highly important in determining host selectivity.2–6 The interplay of all of these considerations makes the isolation and study of particular aspects of cation co-ordination diYcult since the system must be viewed as a synergistic whole, particularly in the case of highly flexible molecules such as the crown ethers and related corands.We have recently begun a research programme aimed at the examination of the influence of non-covalent interactions, especially hydrogen bonds, on the structures and complexation behaviour of supramolecular systems.7–12 Such systems, notably those involving very weak interactions of the C–H ? ? ? X type 13–15 or with crystal engineering potential, are highly topical.16–24 In particular, we have found that systems which are either sterically or electronically mismatched have proved interesting by virtue of the distorted structures adopted in order to maximise the number of weak interactions stabilising the system as a whole.For example, the mismatched hydrogen bonded chain [UO2Cl2(H2O)3]16(15- crown-5)16 exhibits sixteen unique metal complexes and crown ethers before the pattern is able to repeat itself, as a consequence of the directionality of the multiple hydrogen bonds holding the complex together.7 In terms of electronically mismatched systems we have examined the binding of the soft metal ion Ag1 with the relatively hard ligand 15-crown-5 and substituted derivatives.8 In these cases, the degree of crown flexibility results in two packing modes characterised by the † 18-crown-6 = 1,4,7,10,13,16-Hexaoxacyclooctadecane.presence or absence of significant C–H ? ? ? O intermolecular hydrogen bonds.In view of the manifest selectivity of 18- crown-6 for K1 over all of the other alkali metals [log Ka (MeOH, 25 8C) 6.10, cf. 4.32, 5.35 and 4.62 for Na1, Rb1 and Cs1 respectively 2] we have chosen to investigate the structures of complexes of the non-complementary pair Na1/18-crown-6 prepared from a variety of solvents and in the presence of both hard and soft anions. Results and discussion Examination of the Cambridge Crystallographic database reveals a total of 52 structures containing Na1 complexes of 18-crown-6 or its derivatives, frequently acting as a counter ion to more “interesting” anions.25 Surprisingly, in the vast majority of cases, Na1 actually exhibits a good fit within the 18-crown-6 ring.In general, in relatively non-polar media such as tetrahydrofuran (thf), Na1 forms complexes of type [Na(18-crown- 6)(thf)2]1 1 in which the Na1 ion exhibits approximately equal equatorial bond distances to all six crown oxygen atoms of 2.76–2.80 Å, while thf molecules occupy axial co-ordination sites above and below the crown ether.The Othf–Na–Othf vector is essentially normal to the plane containing the six crown oxygen atoms, and exhibits a bond angle of 1808. The fact that 18- crown-6 is too large to bind Na1 is only evidenced by the rather long Na–O distances.26,27 In contrast, we find that in aqueous media, in the presence of O-donor anions, complexes of type [Na(18-crown-6)(H2O)(X)] (X = ClO4 2a; NO3 2b; or ReO4 2c) are formed in which the anion is co-ordinated to the hard, oxophilic Na1 cation.The crystal structure of the perchlorate complex 2a (Fig. 1; crystallographic data for all new complexes are summarised in Table 3) demonstrates a significantly distorted O3ClO–Na–OH2 bond angle of 163.18(8)8 and, in contrast to 1, the Na1 cation is situated significantly to one side of the macrocyclic cavity with Na–Ocrown distances ranging from 2.5871(17) to 3.1770(18) Å, Table 1.This highly unsymmetrical co-ordination is apparently a direct result of the presence of an intramolecular hydrogen bonding interaction between the coordinated water molecule and one of the crown oxygen atoms,2142 J. Chem. Soc., Dalton Trans., 1999, 2141–2146 O(1) ? ? ? O(5a) 2.919(3) Å; Fig. 1, Table 2. While this distance is at the longer end of the range normally observed for O–H ? ? ?O hydrogen bonds it must be remembered that this interaction forms part of a strained, non-covalent chelating system.The water molecule must balance its aYnity for both the crown oxygen atom and the sodium cation, while the whole system is limited by the flexibility of the crown ether. Clear evidence for the hydrogen bonded interaction comes from the positions of the water hydrogen atoms which were located experimentally, with H(2) directed towards the crown oxygen atom; H(2) ? ? ? O(5a) 2.16(5) Å, O–H ? ? ? O angle of 157(4)8. Indeed, in charged systems the basis of the strength–length analogy has recently been called into question.17 The remaining hydrogen atom of the water molecule is hydrogen bonded to the per- Fig. 1 Structure of [Na(18-crown-6)(H2O)(ClO4)] 2a, exhibiting an intramolecular hydrogen bond. Table 1 Selected distances (Å) for Na1 complexes of 18-crown-6 Complex 2a Na(1)–O(1) Na(1)–O(2) Na(1)–O(1a) Na(1)–O(2a) 2.345(2) 2.385(2) 2.6014(16) 2.5871(17) Na(1)–O(3a) Na(1)–O(4a) Na(1)–O(5a) Na(1)–O(6a) 2.6316(15) 2.8132(16) 3.1770(18) 2.9008(16) Complex 2b Na(1)–O(1) Na(1)–O(2) Na(1)–O(4) Na(1)–O(1a) Na(1)–O(2a) 2.4782(12) 2.5634(11) 2.3402(11) 2.6130(10) 2.5792(11) Na(1)–O(3a) Na(1)–O(4a) Na(1)–O(5a) Na(1)–O(6a) 2.4688(10) 2.5828(10) 3.2380(12) 3.6460(12) Complex 2c Na(1)–O(1) Na(1)–O(2) Na(1)–O(1a) Na(1)–O(2a) 2.365(7) 2.310(7) 2.698(8) 2.650(7) Na(1)–O(3a) Na(1)–O(4a) Na(1)–O(5a) Na(1)–O(6a) 2.643(6) 2.732(6) 2.970(6) 2.917(6) Complex 4a Na(1)–O(11) Na(1)–O(1) Na(1)–O(1a) Na(1)–O2(a) 2.296(4) 2.304(4) 2.430(2) 2.443(2) Na(1)–O(3a) Na(1)–O(1a)1 Na(1)–O(2a)1 Na(1)–O(3a)1 2.822(2) 3.225(2) 3.191(2) 2.757(2) Complex 4b Na(1)–O(1) Na(1)–O(1a) 2.322(2) 2.753(2) Na(1)–O(3a) Na(1)–O(2a) 2.765(2) 2.792(2) Complex 5 Na(1)–O(2)1 Na(1)–O(2) Na(1)–O(1) Na(1)–O(2a) 2.307(14) 2.383(15) 2.389(5) 2.851(4) Na(1)–O(3a) Na(1)–O(4a) Na(1)–O(5a) 2.394(4) 2.523(4) 2.696(4) Symmetry operator used to generate equivalent atoms: 1 2x 1 1, 2y 1 2, 2z 1 1.chlorate anion of an adjacent complex, to give an infinite hydrogen bonded chain.The complex is further stabilised by intramolecular C–H ? ? ? O interactions 15 between a non-coordinated oxygen atom of the perchlorate anion and the relatively acidic crown ethylenic backbone, with C(8a) ? ? ? O(5) 3.330(2) Å and a C–H ? ? ? O angle of 1478 (C–H distance normalised to 0.99 Å). The involvement of a water molecule in an intramolecular hydrogen bonding interaction is also present in a similar way in complexes 2b and 2c and clearly results in a significant stabilisation of the “[Na(18-crown-6)(H2O)]1” unit.In the case of complex 2b the Na1 cation is again forced to one side of the macrocyclic cavity in contrast to complexes such as 1 (Table 1), allowing the co-ordinated water molecule to approach a crown oxygen atom, O(4) ? ? ? O(6a) 3.1061(16) Å, Fig. 2. Also, as with 2a, the remaining water hydrogen atom interacts with an adjacent nitrate oxygen atom, O(4) ? ? ? O(3) 2.8275(15) Å.The nitrate anion is also able to form a further intramolecular C– H? ? ? O interaction, O(1) ? ? ? C(11) 3.309(2) Å, H(11a) ? ? ? O(1) 2.36 Å. Complex 2b diVers from 2a however in that the nitrate anion adopts a chelating co-ordination mode with Na–O distances of 2.4782(12) and 2.5634(11) Å, compared to a single short Na–OClO3 distance of 2.385(2) Å. This results in a greater steric demand on the face of the crown ether adjacent to the nitrate anion. This is apparently suYcient to result in a change in behaviour such that, in contrast to 2a, the intramolecular hydrogen bond to water now becomes much longer (and perhaps weaker) than the intermolecular interaction.Also, despite the similarity of the hydrogen bonded geometries, the crown conformation in 2b is entirely diVerent to that in 2a. In 2a the crown ether adopts a relatively flat conformation, similar to that observed in 1. In contrast the non-co-ordinated crown oxygen atoms O(5a) and O(6a) in compound 2b are signifi- cantly out of the plane of the remaining four.At first sight this is apparently in order to maximise the intramolecular hydrogen bonding to the co-ordinated water molecule. The fact that the Table 2 Selected hydrogen bond parameters (distances in Å, angles in 8) for Na1 complexes of 18-crown-6 D–H? ? ?A d(D–H) d(H ? ? ? A) d(D ? ? ? A) DHA Complex 2a O(1)–H(2) ? ? ? O(5a) a O(1)–H(1) ? ? ? O(4)1 0.80(5) 0.84(5) 2.16(5) 2.26(5) 2.919(3) 3.098(3) 157(4) 176(4) Complex 2b O(4)–H(42) ? ? ? O(6a) a O(4)–H(41) ? ? ? O(3)2 0.79(3) 0.89(2) 2.36(3) 1.95(2) 3.1061(16) 2.8275(15) 157(2) 170.1(18) Complex 2a a O(1) ? ? ? O(5a) a O(1) ? ? ? O(5) 3.136(6) 2.816(7) Complex 4a b O(1) ? ? ? O(1a) a O(11) ? ? ? O(2a) a O(1) ? ? ? N(3s) O(11) ? ? ? N(3s) 2.876(4) 2.889(4) 2.830(4) 2.866(4) Complex 4b O(1)–H(12) ? ? ? O(2a)3 O(1)–H(11) ? ? ? O(3a)4 0.77(7) 0.73(5) 2.25(6) 2.31(5) 2.842(3) 3.005(3) 135(6) 157(5) Complex 5 b O(1) ? ? ? O(1a) a O(2) ? ? ? O(4a) a 2.696(5) 2.741(18) Symmetry transformations used to generate equivalent atoms: 1 x 2 1– 2, y 1 1– 2, 2z 1 1– 2; 2 x 1 1– 2, 2y 1 3– 2, z 1 1– 2; 3 2x 1 1, 2y 1 2, 2z 1 1; 4 2x 1 1, y, 2z 1 3– 2.a Intramolecular hydrogen bond. b Hydrogen atoms not located.J. Chem. Soc., Dalton Trans., 1999, 2141–2146 2143 O–H? ? ? O distance is longer in 2b however points to a diVerent explanation. It is possible that the crown conformation is actually governed by the short C–H ? ? ? O interaction detailed above.By distorting in 2b, the crown is able to orientate a methylene group towards an oxygen atom of the co-ordinated nitrato ligand. Conversely, in compound 2a the perchlorate anion which acts as an acceptor of this ‘weak’ interaction is not chelating and is thus both further from the metal centre, and more conformationally mobile, hence much less crown distortion is required. In complex 2c the large ReO4 2 anion makes a very close approach to the Na1 cation, with Na–O(2) 2.310(7) Å, however the longer Re–O distances compared to the Cl–O bonds in 2a preclude the close approach of the crown ethylene backbone to the co-ordinated anion, and indeed the two materials are not isostructural, Fig. 3. The hydrogen bonding to water however is still present in the same way as for 2a and 2b. As for 2b the longer Owater ? ? ?Ocrown distances (Table 2) point to the dominance of intermolecular hydrogen bonding over intramolecular eVects, although the highly non-linear O(1)–Na–O(2) vector of 158.5(4)8 still indicates the presence of a significant intramolecular interaction.These results contrast significantly to the known structure of [Na(18-crown-6)(H2O)][SCN] 3 in which the SCN2 anion is not co-ordinated to the Na1 centre and the crown is significantly distorted in order to occupy the resulting vacant axial site with an etheric oxygen atom. The resulting conformation does not admit intramolecular hydrogen bonding and instead the apical water is hydrogen bonded solely to the N atoms of a pair of anions, which bridge between pairs of cations.28 Both intramolecular and intermolecular hydrogen bonding is observed, however, for the europium 15-crown-5 complex [Eu(15-crown- Fig. 2 Structure of [Na(18-crown-6)(H2O)(NO3)] 2b, exhibiting an intramolecular hydrogen bond. Fig. 3 Structure of [Na(18-crown-6)(H2O)(ReO4)] 2c, exhibiting an intramolecular hydrogen bond. 5)(H2O)2(NO3)3]?15-crown-5 in which the large Eu31 ion adopts a perching co-ordination mode which is much less geometrically restricting and binds to only two crown oxygen atoms. One europium-co-ordinated water molecule hydrogen bonds to two adjacent crown oxygen atoms with O ? ? ? O distances of 2.751 and 2.804 Å.29 In contrast to these hydrated species, in the KNO3 complex of 18-crown-6, the nitrato anion chelates one face of the K1 ion, which is situated slightly above the plane of the crown ether.No water is included in the structure.30 Clearly, the anions, X, are also involved in the co-ordination of the Na1 ion in complexes 2 and hence the structures of the 18-crown-6 complexes of relatively non-co-ordinating anions N3 2 and I3 2 were examined in anticipation of comparison with 3. However, the resulting species, [Na(18-crown-6)(H2O)2]X (X = N3 4a or I3 4b), exhibit two axially co-ordinated aqua ligands. In the case of 4a both water molecules take part in intramolecular hydrogen bonds of the type observed in complexes of type 2, with Owater ? ? ?Ocrown 2.882(5) Å and an extremely low Owater–Na–Owater angle of 131.4(2)8 (averages over two crystallographically independent molecules), Fig. 4. The sodium cation is forced far over onto one side of the crown in order to accommodate the pair of intramolecular hydrogen bonded interactions (Table 2) while the azide anion bridges via hydrogen bonding from one Na(H2O)2 1 unit to the next. Clearly the presence of two water molecules, coupled with the lower electronegativity of the N-acceptor anion, results in a significant increase in the importance of the intramolecular hydrogen bonding stabilisation. In the case of the analogous I3 2 complex 4b the low electronegativity of the iodine atoms in the anion results in no water–anion interaction whatsoever.Instead, the aqua ligands hydrogen bond to crown ether oxygen atoms both intramolecularly and intermolecularly, Ow ? ? ?Ocrown 2.842(3) and 3.005(3) Å, H ? ? ?Ocrown refined to 2.25(6) and 2.31(5) Å, respectively.This results in a linear O–Na–O vector which contrasts significantly with that in 4a and a much more symmetrical co-ordination of the Na1 ion within the crown, with slightly shorter distances to O(1a) and O(3a), 2.759(2) Å, than O(2a) [2.792(2) Å] which takes part in the intramolecular hydrogen bond. Fascinatingly, however, the Ow–Na–Ow vector is not normal to the crown ether plane, as in the case of 1, but intersects it an angle of 77.08 in order to maximise H2O? ? ?Ocrown hydrogen bonds, Fig. 5. A similar hydrogen bonded geometry has been observed for the Na(H2O)2 1 complex of 2,3,11,12-tetraphenyl-18-crown-6. This was suggested to arise from steric interactions with the phenyl groups. Its observation in 4b argues against this explanation.31 Fig. 4 Structure of [Na(18-crown-6)(H2O)2][N3] 4a showing two intramolecular hydrogen bonds.2144 J. Chem. Soc., Dalton Trans., 1999, 2141–2146 These results contrast with the structure of [Na(cis-anti-cisdicyclohexyl- 18-crown-6)(H2O)2]Br in which the Ow-Na–Ow is linear and orthogonal to the crown ether plane, with no short intramolecular contacts.32 The logarithm of the Na1 binding constant for this macrocycle in methanol at 25 8C is 3.68, markedly lower than that of 18-crown-6 itself (log Ka = 4.32).This suggests that the intramolecular hydrogen bonding interactions reported herein may be a non-negligible factor in the magnitude of the solution binding constants of these ligands for Na1.Clearly, however, the role of other well recognised factors, notably interactions with anions and orientation/ preorganisation of the etheric dipoles, are also crucial since the analogous dibenzo-18-crown-6 complex with Na(H2O)2 1 in the presence of Br2 also does not exhibit intramolecular hydrogen bonds,33 despite a log K1 value of 4.36 (methanol, 25 8C, picrate salt).2 In view of the interesting results obtained for the non-coordinating anions N3 2 and I3 2 in complexes 4 we also examined the 18-crown-6 complex of NaBPh4 in anticipation of confirming the geometry of the crown-co-ordinated Na(H2O)2 1 unit in the absence of significant interactions with the anions.Large, colourless crystals of composition Na?18-crown-6?1.5H2O were rapidly deposited from an ethanol–water solution (1 : 1 v/v). The crystal structure of this material proved fascinating although, reassuringly, consistent with the results described above.In fact the Na(crown) species was shown to be a binuclear dication containing one bridging and two terminal water molecules, Fig. 6, of overall formula [Na2(18-crown- 6)2(H2O)3][BPh4]2?EtOH 5. As with 4a the complex is disordered over two orientations of the Na1 and aqua ligands with the Na1 cations occupying either one side of the relatively symmetrical macrocyclic cavity or the other. The entire complex resides upon a crystallographic inversion centre.In both orientations, both the bridging and terminal aqua ligands engage in the expected intramolecular hydrogen bonding interactions, with relatively short O ? ? ? O contacts in the range 2.696(5)– 2.808(4) Å (Table 2). The sodium ions and their associated ligands may be regarded as a close analogy of azide complex 4a. In compound 4a the bridging aqua ligand O(2) is hydrogen bonded to the N3 2 anion. In 5 it is also co-ordinated to the second cation, Na(1), as well as hydrogen bonding to the second macrocycle. Unfortunately, the crystallographic disorder makes a detailed comparison of bond angles diYcult.This disorder apparently arises as a consequence of the ability to invert the entire Na2(H2O)3 21 unit within the symmetrical crown conformation, without materially aVecting the steric volume occupied by the whole binuclear complex. A key comparison which must be made in these systems is that between compounds 5 Fig. 5 Structure of [Na(18-crown-6)(H2O)2][I3] 4b showing intra- and inter-molecular hydrogen bonding. and 4b, both of which involve anions which do not significantly interact with the cationic complex. What is the reason for the formation of a bridged dimer in 5 and a mononuclear species in 4b? It is possible that the answer to this question lies in the steric bulk of the anions. The I3 2 anion is small enough to pack in channels in between a hydrogen bonded polymeric array of Na(H2O)2 1–crown complexes.In contrast the BPh4 2 anions arrange themselves in pairs, eVectively forming a vast cavity into which the Na2(18-crown-6)2(H2O)3 21 cation fits. As a further complication to this remarkable complex there are two entirely independent pairs of “anion sandwiched” Na2(18- crown-6)2(H2O)3 21 cations (both disordered as described above), which diVer in their orientation with respect to the anion-pair cavities, Fig. 7. The Na(1) dicationic complex apparently interacts with the BPh4 2 aryl groups solely via hydrophobic inclusion of the edge of the crown between pairs of phenyl groups.There are also interactions from the terminal water ligands to highly disordered ethanol molecules. In con- Fig. 6 Structure of the [Na2(18-crown-6)2(H2O)3]21 cation in complex 5, exhibiting intramolecular hydrogen bonds. Fig. 7 Crystal packing in [Na2(18-crown-6)2(H2O)3][BPh4]2?EtOH 5 showing the orientations of the two independent complexes.J.Chem. Soc., Dalton Trans., 1999, 2141–2146 2145 trast, the second dication engages in O–H ? ? ?p hydrogen bonds with oxygen ? ? ? centroid distances in the region of 3.3 Å with the second pair of anions. One possible explanation of this behaviour is that the incorporation of ethanol is necessary in order to hydrogen bond to the proton on the terminal aqua ligand, which is not intramolecularly hydrogen bonded to the crown. However, it appears that incorporation of two ethanol molecules would make the Na2(18-crown-6)2- (H2O)3 21 ? ? ? OHEt chain longer than the available space between the pair-wise (BPh4 2)2 cavities, causing ineYcient crystal packing.As a result the second cation is forced to engage in a weak O–H ? ? ?p interaction instead. Conclusion In terms of Na1 co-ordination, these results represent an extreme example of the second of the four possible modes of co-ordination of metal ions, which are too small to fit within a macrocyclic cavity (unsymmetrical co-ordination), outlined by Dunitz et al.34 They are of significance in the role of 18-crown-6 as a model for ionophore-mediated transport of Na1 and K1 ions across biological membranes, where the aqueous medium plays a significant role.The identification of this new kind of hydrogen bond in these complexes suggests a further contributing reason for decrease in selectivity of 18-crown-6 for K1 over Na1 in aqueous media, and gives insights into the high degree of solvent dependency of selectivity between diVerent metal ions by ligands such as the crown ethers.Perhaps even more importantly, the structure of complex 5 illustrates the extraordinary lengths to which Nature is willing to go in order to ensure that the number of intermolecular interactions is at a maximum. As our understanding of weak interactions in the solid state grows the key question seems in every case to be not “is an atom interacting with anything?”, but rather “what is it interacting with, and how may this interaction be maximised within the context of the rest of the structure?” Experimental Microanalyses were performed at University College London and at James Cook University.No precautions were taken to protect reaction mixtures from air or moisture and the majority of the products did not display significant moisture sensitivity when exposed to the atmosphere with the exception of complexes 2c and 4a which proved highly hygroscopic.Experimental conditions were designed to promote the formation of X-ray quality crystals and are unoptimised. Preparations [Na(18-crown-6)(H2O)(ClO4)] 2a. The salt NaClO4 (0.047 g, 0.38 mmol), was dissolved in water (5 cm3) and added to a solution of 18-crown-6 (0.1 g, 0.38 mmol) in water (5 cm3). The product deposited as colourless blocks upon slow evaporation of the solution over a period of one week. Yield 0.089 g, 0.22 mmol, 58%. Calc. for C12H26ClNaO11: C, 35.61; H, 6.47. Found: C, 35.5; H, 6.6%.[Na(18-crown-6)(H2O)(NO3)] 2b. The salt NaNO3 (0.032 g, 0.38 mmol) was dissolved in water (5 cm3) and added to a solution of 18-crown-6 (0.1 g, 0.38 mmol) in methanol (5 cm3). The product deposited as colourless blocks upon slow evaporation of the solution over a period of one week. Yield 0.088 g, 0.24 mmol, 62%. Calc. for C12H26NNaO10: C, 39.24; H, 7.13; N, 3.81. Found: C, 39.3; H, 7.5; N, 3.7%. [Na(18-crown-6)(H2O)(ReO4)] 2c.The salt NaReO4 (0.10 g, 0.38 mmol) was dissolved in water (10 cm3) and added to a solution of 18-crown-6 (0.1 g, 0.38 mmol) in methanol (10 cm3). The product deposited as colourless blocks upon slow evaporation of the solution over a period of one week. Yield 0.072 g, 0.13 mmol, 35%. Attempts to obtain reliable elemental analysis were frustrated by the compound’s extreme moisture sensitivity. [Na(18-crown-6)(H2O)][N3] 4a. The salt NaN3 (0.025 g, 0.38 mmol) was added to 18-crown-6 (0.1 g, 0.38 mmol) in a mixture of undried diethyl ether (5 cm3) and dichloromethane (5 cm3).The product deposited as colourless block over a period of twelve hours. Yield 0.09 g, 0.25 mmol, 65%. Attempts to obtain reliable elemental analysis were frustrated by the compound’s extreme moisture sensitivity. [Na(18-crown-6)(H2O)][I3] 4b. The salt NaI (0.057 g, 0.38 mmol) was dissolved in water (10 cm3) and added to a solution of 18-crown-6 (0.1 g, 0.38 mmol) in water (10 cm3).The product deposited long orange needles on slow evaporation of the solution over a period of six weeks. Yield: 0.027 g, 0.04 mmol, 10%. The I3 2 apparently arises as a consequence of the action of aerobic oxygen and light on the sample, which gradually turned from colourless to yellow during the course of the reaction. The limited availability of I3 2 accounts for both the low yield and long reaction time. Calc. for C12H28I3NaO8: C, 20.47; H, 4.01. Found: C, 22.0; H, 4.3%.[Na2(18-crown-6)2(H2O)3][BPh4]2?EtOH 5. The salt NaBPh4 (0.13 g, 0.38 mmol) was dissolved in ethanol (10 cm3) and added to a solution of 18-crown-6 (0.1 g, 0.38 mmol) in water (10 cm3). The product deposited as large colourless blocks on standing for twenty-four hours. Yield g, 0.15 mmol, 80%. The sample submitted for elemental analysis was powdered and allowed to stand in air for ca. one week resulting in loss of the ethanol solvent. Calc. for C72H70B2Na2O15: C, 68.25; H, 7.48.Found: C, 68.3; H, 7.6%. Crystallography Crystal data and data collection parameters are summarized in Table 3. Crystals were mounted using a fast setting epoxy resin on the end of a glass fibre and cooled on the diVractometer to the temperature stated. All crystallographic measurements were carried out with a Nonius KappaCCD equipped with graphite monochromated Mo-Ka radiation using f rotations with 28 frames and a detector to crystal distance of 25 mm. Integration was carried out by the program DENZO-SMN.35 Data sets were corrected for Lorentz-polarisation eVects and for the eVects of absorption using the program Scalepack.35 Structures were solved using the direct methods option of SHELXS 86 36 and developed using conventional alternating cycles of least squares refinement and Fourier-diVerence synthesis (SHELXL 97 37) with the aid of the program X-Seed.38 In general all nonhydrogen atoms were refined anisotropically, whilst hydrogen atoms were fixed in idealised positions and allowed to ride on the atom to which they were attached. Hydrogen atom thermal parameters were tied to those of the atom to which they were attached.In the case of compounds 2a, 2b and 4b water hydrogen atoms were located on the final Fourier-diVerence map and included within the model. It proved possible fully isotropically to refine them in these cases. Compounds 4a and 5 proved to exhibit a significant disorder taking the form of two separate positions each of 50% occupancy for all of the sodium cations and co-ordinated water.In addition, two of the four independent crown ethers in 5 also proved to be disordered, although this was modelled eVectively with each atom position showing clearly on Fourier-diVerence syntheses. All calculations were carried out either on a Silicon Graphics Indy R5000 workstation or an IBM-PC compatible personal computer. CCDC reference number 186/1472. See http://www.rsc.org/suppdata/dt/1999/2141/ for crystallographic files in .cif format.2146 J.Chem. Soc., Dalton Trans., 1999, 2141–2146 Table 3 Crystallographic data for new complexes 2a 2b 2c 4a 4b 5 Formula Formula weight/g mol21 T/8C Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 V/Å3 Z m/mm21 Reflections collected Independent reflections Parameters Goodness of fit of F2 Final R1, wR2, I > 2s(I) (all data) Largest diVerence peak/e Å23 C12H26ClNaO11 404.79 2100 Orthorhombic Pc21n 9.1846(3) 13.9712(5) 14.6305(3) 1877.38(10) 4 0.278 16095 3448 227 1.059 0.0298, 0.0745 0.0319, 0.0766 0.22 C12H26NNaO10 367.33 2100 Monoclinic P21/n 12.0590(4) 10.5053(3) 14.0593(5) 103.295(2) 1733.35(2) 4 0.142 14177 3381 226 1.056 0.0325, 0.0788 0.0398, 0.0837 0.17 C12H27NaO11Re 556.53 2150 Monoclinic P21/n 7.9787(12) 14.3770(6) 16.9546(8) 98.254(2) 1924.7(3) 4 6.386 16756 3648 227 1.077 0.0688, 0.1789 0.0716, 0.1831 4.33 a C12H26N3NaO8 365.36 2100 Triclinic P1� 9.5186(8) 10.4064(9) 11.0250(6) 67.825(2) 76.113(2) 67.551(2) 928.8(3) 2 0.127 5761 3388 245 1.063 0.0606, 0.1611 0.0892, 0.1824 0.410 C12H28I3NaO8 704.04 2150 Monoclinic C2/c 20.6803(8) 11.0480(5) 10.8675(3) 109.989(2) 2333.38(15) 4 4.066 10176 2241 121 1.082 0.0246, 0.0615 0.0266, 0.0628 0.951 C74H93B2Na2O15 1290.08 2150 Triclinic P1� 13.4119(9) 13.9456(10) 22.5930(17) 77.5320(2) 74.0820(2) 62.0940(2) 3572.1(4) 2 0.092 20041 11756 1052 1.024 0.0617, 0.1366 0.0950, 0.1540 0.832 a Close to metal atom.Acknowledgements We thank the EPSRC and King’s College London for funding of the diVractometer system. Grateful acknowledgement is also given to the NuYeld Foundation for the provision of computing equipment. References 1 C. J. Pedersen, J. Am. Chem. Soc., 1967, 89, 2495. 2 F. de Jong and D. N. Reinhoudt, Stability and Reactivity of Crown Ether Complexes, Academic Press, London, 1981. 3 G. Gokel, Crown Ethers and Cryptands, Royal Society of Chemistry, Cambridge, 1991. 4 R. M. Izatt, K. Pawlak and J. S. Bradshaw, Chem. Rev., 1991, 91, 1721. 5 F. Vögtle, Supramolecular Chemistry, Wiley, New York, 1991. 6 J. L. Atwood, J. E. D. Davies, D. D. MacNicol and F. Vögtle (Editors), Comprehensive Supramolecular Chemistry, Pergamon, Oxford, 1996, vol. 1. 7 J. W. Steed, H. Hassaballa and P. C. Junk, Chem. Commun., 1998, 577. 8 P. D. Prince, J. W. Steed and P. J. Cragg, Chem. Commun., 1999, in the press. 9 H. Hassaballa, J. W. Steed, P. C. Junk and M.R. J. Elsegood, Inorg. Chem., 1998, 4666. 10 J. W. Steed, P. C. Junk and B. J. McCool, J. Chem. Soc., Dalton Trans., 1998, 3417. 11 J. W. Steed and K. Johnson, J. Chem. Soc., Dalton Trans., 1998, 2601. 12 J. W. Steed and K. Johnson, J. Chem. Soc., Chem. Commun., 1998, 1479. 13 M. Mascal, Chem. Commun., 1998, 303. 14 R. Hunter, R. H. Haueisen and A. Irving, Angew. Chem., Int. Ed. Engl., 1994, 33, 566. 15 G. R. Desiraju, Acc. Chem. Res., 1996, 29, 441. 16 D. Braga, L. Maini and F. Grepioni, Angew. Chem., Int. Ed., 1998, 37, 2240. 17 D. Braga, F. Grepioni and J. J. Novoa, Chem. Commun., 1998, 1959. 18 D. Braga and F. Grepioni, Acc. Chem. Res., 1997, 30, 81. 19 B. M. Kariuki, K. D. M. Harris, D. Philp and J. M. A. Robinson, J. Am. Chem. Soc., 1997, 119, 12697. 20 N. N. L. Madhavi, A. K. Katz, H. L. Carrell, A. Nangia and G. R. Desiraju, Chem. Commun., 1997, 1953. 21 N. Yoshida, H. Oshio and T. Ito, Chem. Commun., 1998, 63. 22 K. N. Rose, L. J. Barbour, G. W. Orr and J. L. Atwood, Chem. Commun., 1998, 407. 23 K. N. Power, T. L. Hennigar and M. J. Zaworotko, Chem. Commun., 1998, 595. 24 J. P. Campbell, J.-W. Hwang, V. G. Young, Jr., R. B. von Dreele, C. J. Cramer and W. L. Gladfelter, J. Am. Chem. Soc., 1998, 120, 521. 25 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 31. 26 D. J. Darensbourg, C. G. Bauch and A. L. Rheingold, Inorg. Chem., 1987, 26, 977. 27 S. I. Bailey, L. M. Englehart, W.-P. Leung, C. L. R. M. Ritchie and A. H. White, J. Chem. Soc., Dalton Trans., 1985, 1747. 28 M. Dobler, J. D. Dunitz and P. Seiler, Actastallogr., Sect. B, 1974, 30, 2741. 29 M. Parvez, P. J. Breen and W. D. Horrocks, Jr., Lanth. Actin. Res., 1988, 2, 153. 30 J. W. Steed and P. C. Junk, unpublished work. 31 G. Weber, G. M. Sheldrick, T. Burgemeister, F. Dietl, A. Mannschreck and A. Merz, Tetrahedron, 1984, 40, 855. 32 M. Mercer and M. R. Truter, J. Chem. Soc., Dalton Trans., 1973, 2215. 33 M. A. Bush and M. R. Truter, J. Chem. Soc. B, 1971, 1440. 34 J. D. Dunitz, M. Dobler, P. Seiler and R. P. Phizackerley, Acta Crystallogr., Sect. B, 1974, 30, 2733. 35 Z. Otwinowski and W. Minor, Methods Enzymol., 1996, 276, 307. 36 G. M. Sheldrick, Acta Crystallogr., Sect. A., 1990, 46, 467. 37 G. M. Sheldrick, University of Göttingen, 1997. 38 L. J. Barbour, X-Seed, University of Missouri – Columbia, 1999. Paper 9/02358E

ISSN:1477-9226    

DOI:10.1039/a902358e

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2147–2149 2147 Synthesis and characterisation of the first unidimensional cobalt hydrogen phosphate, [H3N(CH2)3NH3][Co(HPO4)2] Andrew R. Cowley and Ann M. Chippindale * Chemical Crystallography Laboratory, University of Oxford, 9 Parks Road, Oxford, UK OX1 3PD Received 22nd February 1999, Accepted 19th May 1999 The first unidimensional organically templated cobalt hydrogenphosphate, [H3N(CH2)3NH3][Co(HPO4)2], has been synthesized at 433 K under solvothermal conditions in the presence of 1,3-diaminopropane and the structure determined at 150 K using single-crystal X-ray diVraction.The compound contains anionic chains of formula [Co(HPO4)2]22 constructed from edge-sharing 4-membered rings of alternating CoO4 and HPO4 tetrahedra from which hang additional “pendant” HPO4 groups. The chains, which are structurally similar to those found recently in unidimensional aluminophosphates, are held together by a network of hydrogen bonds involving both interchain and chain–diamine interactions.Introduction The considerable interest shown recently in the synthesis and characterisation of open-framework metal phosphates reflects their potential applications as molecular sieves, ion-exchange materials and heterogeneous catalysts. The use of organic amines in phosphate synthesis has led to a plethora of new materials with either 3- or lower-dimensional structures. The structure-directing properties of these amines are not as yet well understood and use of one amine can lead to the formation of a number of diVerent framework structures.This is clearly illustrated by 1,3-diaminopropane, which may form 3- dimensional structures including [H2N(CH2)3NH3][HAl3- P3O14]?H2O,1 [ H3N(CH2)3NH3][(VO)3(OH)2(H2O)2(PO4)2] 2 and [H3N(CH2)3NH3]2[Fe4(OH)3(HPO4)2(PO4)3]?xH2O,3 2-dimensional structures such as [H3N(CH2)3NH3]0.5[VO][VO4] 4 and [H3N(CH2)3NH3]0.5[Co(PO4)]?0.5H2O5 or unidimensional chain structures such as [H3N(CH2)3NH3][Ga(HPO4)(PO4)].6 In this paper we describe the use of 1,3-diaminopropane in the synthesis of the first organically templated unidimensional cobalt hydrogenphosphate, and the structural characterisation of this material using single-crystal X-ray diVraction.Experimental The compound [H3N(CH2)3NH3][Co(HPO4)2] was prepared under predominantly non-aqueous solvothermal conditions. The oxide CoO (0.4 g) was suspended in ethylene glycol (6 cm3) by stirring and 1,3-diaminopropane (1.5 cm3) added to act as structure-directing agent.The mixture was stirred until homogeneous and then aqueous H3PO4 (1.5 cm3, 85% by weight) added with further stirring to give a gel of overall composition CoO:20 HOC2H4OH: 3.4 H2N(CH2)3NH2 : 4.1 H3PO4 : 3.9 H2O. The gel was placed in a Teflon-lined stainless-steel autoclave and heated at 433 K for 7 d. The resulting solid product consisted of a biphasic mixture of deep-blue needles of the [H3N(CH2)3NH3][Co(HPO4)2] and colourless blocks.The latter were identified by single-crystal X-ray diVraction as the diammonium hydrogenphosphate hydrate [H3N(CH2)3NH3][HPO4]? H2O7 (monoclinic, space group P21/c, lattice parameters a = 6.9808(8), b = 16.724(1), c = 7.8550(7) Å, b = 113.657(9)8 at 200 K). The solid was washed with 3 × 20 cm3 glacial acetic acid and 3 × 20 cm3 methanol to remove the diammonium hydrogenphosphate hydrate and dried in air at 344 K.The resulting product was shown by powder X-ray diVraction (Fig. 1) to be monophasic. Combustion analysis results are C 10.78, H 4.70 and N 8.29% by weight, which are in good agreement with the values of C 11.02%, H 4.31% and N 8.57% calculated for the formula [H3N(CH2)3NH3][Co(HPO4)2]. Although stable indefinitely in dry air, a finely ground sample of the compound reacted rapidly with water at room temperature to form a palepink gelatinous solid which was shown to be amorphous by powder X-ray diVraction.An infrared spectrum of the compound (Perkin-Elmer 1710 FT spectrophotometer, KBr disc) showed a broad, strong absorption band in the range 3600–2300 cm21 and a number of sharp, medium-intensity bands in the range 1670–1170 cm21. Bands in the former region are compatible with OH, NH and CH stretching modes and in the latter with NH3, CH2 and OH deformation modes, consistent with the presence of H3N(CH2)3NH3 21 and OH groups. A single crystal suitable for X-ray diVraction study (size 0.06 × 0.12 × 0.40 mm) was selected from the as-synthesized material and mounted on a nylon fibre using a drop of perfluoropolyether oil.It was then rapidly cooled to 150 K in a flow of cold nitrogen using an Oxford Cryosystems CRYOSTREAM cooling system. Data were collected on an Enraf-Nonius DIP2020 diVractometer using graphite-monochromated Mo-Ka radiation (l = 0.71069 Å). Images were processed using the DENZO and SCALEPACK suite of programs.8 Data were corrected for Lorentz and polarisation eVects and a partial absorption correction applied by multiframe scaling of the image-plate data using equivalent reflections. The systematic absences in the data (h00, h odd; 0k0, k odd; 00l, l odd) indicated the space group to be P212121. 2030 Unique reflections were measured of which 1721 were observed with I > 3s(I). Full experimental information is given in Table 1. The structure was solved using direct methods (SIR92) 9 and all non-hydrogen atoms located.Framework hydrogen atoms were subsequently located in Fourier-diVerence maps and the hydrogen atoms of the diamine placed geometrically after each cycle of refinement. Full-matrix least-squares refinement on F of 153 parameters (atomic coordinates and anisotropic thermal parameters of non-hydrogen atoms, atomic coordinates only of hydroxyl hydrogen atoms) was carried out using the program CRYSTALS.10 A Chebychev 3-term polynomial weighting scheme was applied.The final residual electron densities were 20.789 and 0.671 e Å23. The crystal was found to be a racemic2148 J. Chem. Soc., Dalton Trans., 1999, 2147–2149 twin with twin ratio ca. 50%. Selected bond lengths and angles are given in Table 2. CCDC reference number 186/1474. See http://www.rsc.org/suppdata/dt/1999/2147/ for crystallographic files in .cif format. Discussion The structure consists of one-dimensional polymeric cobalt hydrogenphosphate anions of formula [Co(HPO4)2]22 running parallel to the a axis.The Co21 ions are tetrahedrally coordinated by four O atoms, which is consistent with the deepblue colour of the compound. The Co–O bond lengths (average 1.952 Å) are similar to those observed in other cobalt phosphates, for example, in [H3N(CH2)2NH3]0.5[Co(PO4)], Co–Oav 1.95 Å.11 The structure contains two crystallographically distinct HPO4 22 ions. One of the P–O distances of each PO4 tetrahedron is significantly longer than the other three (P(1)–O(1), Fig. 1 Powder X-ray diVraction pattern of a finely ground sample of the compound (Philips PW1700 diVractometer, graphite-monochromated Cu-Ka radiation). Fig. 2 View of one polymeric anion of the compound along the vector [011], showing zigzag chains of four-membered rings built from CoO4 and HP(1)O4 tetrahedra linked to pendant HP(2)O4 groups. Intra-chain hydrogen bonds are shown as dotted lines. Key: black circles, Co; grey circles, P; large white circles, O; small white circles, H.Drawing package ATOMS.12 1.565(3) and P(2)–O(5), 1.584(3) Å), suggesting that these O atoms are protonated. The presence of hydroxyl groups was confirmed by the observation of peaks in Fourier-diVerence maps close to O(1) and O(5) corresponding to the H atom positions. The CoO4 and HP(1)O4 units are linked alternately to form a zigzag “backbone” constructed from edge-sharing fourmembered rings of tetrahedra (Fig. 2). The HP(2)O4 group is bonded to these chains through only one bridging oxygen, O(6), to form “pendant” groups.In addition to the hydroxyl group, the pendant phosphorus carries two terminal oxygen atoms with P–O distances suYciently short to suggest the presence of some degree of multiple bonding (P(2)–O(7) and P(2)–O(8), 1.521(3) Å). The hydroxyl groups of the pendant HP(2)O4 units form intra-chain hydrogen bonds to bridging oxygen atoms of the backbone (O(5) ? ? ? O(2) = 2.654(4) Å) (Fig. 2) whilst the hydroxyl groups of the backbone HP(1)O4 units form interchain hydrogen bonds to P]] O oxygens of the pendant HP(2)O4 units (O(1) ? ? ? O(8) = 2.455(4) Å) (Fig. 3). In order to balance the charge of the polymeric anion, the organic counterion must be diprotonated. Each NH3 group forms three hydrogen bonds to O atoms of the anions (N ? ? ? O distances in the range 2.790(5) to 2.963(4) Å), thus forming a 3-dimensional network of hydrogen bonds between chains. Although this compound is the first reported example of a transition-metal phosphate containing this type of tetrahedronbased chain, similar one-dimensional structures have been observed previously in the two aluminophosphates [C10N2H9]- [Al(PO4)(H2PO4)] 13 and [H3N(CH2)2NH3][Al(PO4)(HPO4)].14 However, the chain packing and hydrogen-bonding schemes in the three materials are very diVerent, there being no direct interchain hydrogen bonding in either of the aluminophosphates.Although the present compound contains the same organic amine as the layered cobalt phosphate [H3N(CH2)3NH3]0.5- [Co(PO4)]?0.5H2O,5 there is no apparent structural relationship between the two materials.In contrast to the present compound, the layered material was prepared under aqueous conditions, illustrating the important role played by the solvent in directing framework formation in solvothermal syntheses. Fig. 3 View of the compound along the a axis showing the packing of [Co(HPO4)2]22 chains and charge-balancing [H3N(CH2)3NH3]21 cations.Inter-chain and amine–chain hydrogen bonds are shown as dotted lines. Hydrogen atoms have been omitted for clarity. Key: large black circles, Co; large grey circles, P; white circles, O; small grey circles, N, small black circles, C.J. Chem. Soc., Dalton Trans., 1999, 2147–2149 2149 One possible route to the synthesis of two- and threedimensional open-framework phases is the use of lowdimensional metal-phosphate precursors which contain structural elements present in the desired higher-dimensional framework. Examples of syntheses of novel aluminophosphate Table 1 Crystallographic data for [C3N2H12][Co(HPO4)2] Molecular formula Formula weight T/K Crystal system Space group a/Å b/Å c/Å U/Å3 Z m/mm21 Unique data Observed data with I > 3s(I) Merging R (%) R (%) Rw (%) C3H14CoN2O8P2 327.03 150 Orthorhombic P212121 5.210(1) 12.693(1) 15.518(1) 1026.1 4 2.01 2030 1721 4.50 3.24 3.70 Table 2 Selected bond lengths (Å) and angles (8) Co(1)–O(2) Co(1)–O(3) Co(1)–O(4) Co(1)–O(6) P(1)–O(1) P(1)–O(2) P(1)–O(3) P(1)–O(4) O(1)–H(1) O(2)–Co(1)–O(3) O(2)–Co(1)–O(4) O(3)–Co(1)–O(4) O(2)–Co(1)–O(6) O(3)–Co(1)–O(6) O(4)–Co(1)–O(6) O(1)–P(1)–O(2) O(1)–P(1)–O(3) O(2)–P(1)–O(3) O(1)–P(1)–O(4) O(2)–P(1)–O(4) O(3)–P(1)–O(4) N(1)–C(1)–C(2) C(1)–C(2)–C(3) 1.980(3) 1.945(2) 1.950(3) 1.933(3) 1.565(3) 1.537(3) 1.519(3) 1.523(3) 1.03(6) 108.7(1) 117.6(1) 109.0(1) 101.3(1) 112.6(1) 107.5(1) 105.8(2) 108.5(2) 111.7(1) 107.6(2) 111.4(2) 111.5(2) 110.2(3) 112.6(3) P(2)–O(5) P(2)–O(6) P(2)–O(7) P(2)–O(8) N(1)–C(1) N(2)–C(3) C(1)–C(2) C(2)–C(3) O(5)–H(2) O(5)–P(2)–O(6) O(5)–P(2)–O(7) O(6)–P(2)–O(7) O(5)–P(2)–O(8) O(6)–P(2)–O(8) O(7)–P(2)–O(8) Co(1)–O(2)–P(1) Co(1)–O(3)–P(1) Co(1)–O(4)–P(1) Co(1)–O(6)–P(2) P(1)–O(1)–H(1) P(2)–O(5)–H(2) C(2)–C(3)–N(2) 1.584(3) 1.510(3) 1.521(3) 1.521(3) 1.495(5) 1.492(5) 1.519(5) 1.508(6) 0.82(6) 110.1(2) 104.5(2) 112.7(2) 107.5(2) 110.2(2) 111.6(2) 127.4(2) 129.0(1) 126.7(2) 140.2(2) 113(3) 114(4) 111.5(3) frameworks by this method have previously been reported. For example the unidimensional material [C5H9NH3]5[Al3(PO4)4- (HPO4)] undergoes conversion into the layered phase [C5H9- NH3]2[Al2(PO4)2(HPO4)] on thermal treatment at 473K.15 The unidimensional cobalt hydrogenphosphate reported in this work may have potential utility in this role because the chain of edge-sharing four-membered rings which forms the “backbone” of the structure occurs as a structural element in many zeolite frameworks, e.g.gismondine and chabazite. Loss of the pendant phosphate groups and cross-linking of the chains might therefore result in formation of a 3-dimensional framework material. Work is in progress to study the eVects of thermal treatment on the compound. Acknowledgements A. R. C. would like to thank the Engineering and Physical Sciences Research Council for a studentship. References 1 S.Natarajan, J.-C. P. Gabrial and A. K. Cheetham, Chem. Commun., 1996, 1415. 2 V. Soghomonian, Q. Chen, R. C. Haushalter, J. Zubieta, C. J. O’Connor and Y.-S. Lee, Chem. Mater., 1993, 5, 1690. 3 K.-H. Lii and Y.-F. Huang, Chem. Commun., 1997, 839. 4 D. Riou and G. Férey, J. Solid State Chem., 1995, 120, 137. 5 J. R. D. DeBord, R. C. Haushalter and J. Zubieta, J. Solid State Chem., 1996, 125, 270. 6 T. Loiseau, F. Serpaggi and G. Férey, Chem. Commun., 1997, 1093. 7 S. Kamoun, A. Jouini and A. Daoud, Acta Crystallogr., Sect. C, 1991, 47, 117. 8 Z. Otwinowski and W. Minor, Methods Enzymol. 1997, 276. 9 A. Altomare, G. Cascarano, G. Giacovazzo, A. Guagliardi, M. C. Burla, G. Polidori and M. Camalli, J. Appl. Crystallogr., 1994, 27, 453. 10 D. J. Watkin, C. K. Prout, J. R. Carruthers and P. W. Betteridge, CRYSTALS User Guide, Chemical Crystallography Laboratory, University of Oxford, 1996. 11 J. Chen, R. H. Jones, S. Natarajan, M. B. Hursthouse and J. M. Thomas, Angew. Chem., Int. Ed. Engl., 1994, 33, 639. 12 ATOMS for Windows v3. 1, Shape Software, Kingsport, TN, 1997. 13 A. M. Chippindale and C. Turner, J. Solid State Chem., 1997, 128, 318. 14 I. D. Williams, J. Yu, Q. Gao, J. Chen and R. Xu, Chem. Commun., 1997, 1273. 15 S. Oliver, A. Kuperman, A. Lough and G. A. Ozin, Chem. Mater., 1996, 8, 2391. Paper 9/01469A

ISSN:1477-9226    

DOI:10.1039/a901469a

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2151–2157 2151 Synthesis, characterisation and polynuclearisation reaction of trans(S)-[Co(aminothiolate-N,S)2(en)]-type cobalt(III) complexes with 2-aminoethanethiolate, L-cysteinate and D-penicillaminate Toshiaki Yonemura,*a Zhi-Ping Bai,b Ken-ichi Okamoto,c Tomoharu Ama,a Hiroshi Kawaguchi,a Takaji Yasui a and Jinsai Hidaka d a Department of Material Science, Kochi University, Akebono-cho, Kochi 780-8520, Japan. E-mail: yonemura@cc.kochi-u.ac.jp b Co-ordination Chemistry Institute, Nanjing University; State Key Laboratory of Co-ordination Chemistry of Nanjing University, Nanjing, 210093, China c Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305-8571, Japan d Department of Industrial Chemistry, Kinki University in Kyushu, Iizuka, Fukuoka 820-8555, Japan Received 15th December 1998, Accepted 30th April 1999 The trans(S)-[Co(N)4(S)2]-type mononuclear complexes [Co(L)2(en)]1 or 2 (L = 2-aminoethanethiolate (aet) 1, L-cysteinate (L-cys) 3 or D-penicillaminate (3-sulfanyl-D-valinate) (D-pen) 5) were newly prepared by the reaction of trans-[CoCl2(en)2]1 with L at pH 8.5 and 25 8C.The crystal structure of 1 was determined by X-ray diVraction analysis. The geometry around the cobalt atom is approximately octahedral and two thiolate donor atoms in the aet ligands occupy trans positions to each other. Two Co–S bonds are lengthened by the double sulfur trans influence across the cobalt centre attributable to two thiolato sulfur donor atoms.The diastereomers of 3 and 5 were separated by the column chromatographic technique and characterised on the basis of their UV/Vis, CD and 13C NMR spectra. The LDD isomer of 5 (5ÀDD) is preferably formed by attractive (COO ? ? ? H–N–H) interactions. Though cis(S)- [Co(L)2(en)]1 or 2 (L = aet 2, L-cys 4 or D-pen 6) were also produced by the same preparative reaction, they could not be separated into the geometrical isomers because of very rapid isomerisation and/or polynuclearisation reaction during elution from the column.It is clear that all trans(S) complexes also show drastic and characteristic UV/Vis spectral changes with time in aqueous solutions and tend to isomerise to the cis(S) isomer, followed by the formation of S-bridged polynuclear complexes owing to both the double sulfur trans influence and high nucleophilicity of the thiolate donor atoms. The polynuclearisation reactions of the three trans(S) isomers proceed according to diVerent processes depending on their ligands.In the polynuclearisation reaction of 3, especially, the novel dinuclear complex LLLL-[Co{Co(L-cys-N,S)3}(L-cys-N,O,S)]22 7, which has not so far been identified in usual dinuclearisation reactions, was newly obtained. Introduction Metal thiolate co-ordination chemistry has experienced explosive development during the past two decades as a consequence of growing awareness of the occurrence of cysteine ligation in a variety of electron-transfer proteins, metalloenzymes and so on.However, only a few systematic studies have been reported for the properties of these complexes, because their syntheses are not generally trivial but complicated by diYculties inherent to thiolate co-ordination chemistry.1–3 Cobalt(III) complexes are appropriate to the investigation of the stereochemistry and spectroscopic properties of complexes with sulfur-containing aminocarboxylate ligands because cobalt(III) ions produce stable complexes with sulfur-containing ligands.2–8 So far, although a lot of cobalt(III) complexes with thiolate ligands have been reported with biochemical or structural interests, only one isomer has ever been preferentially isolated in many cases.The presence of two or more thiolate donor atoms in the co-ordination sphere induces an extreme specificity concerned with the formation of geometrical isomers.In general, cobalt(III) complexes containing two or three thiolate donor atoms take the cis(S) geometry as found in fac-[Co(L-N,S)3] [L = 2-aminoethanethiolate (aet), L-cysteinate (L-cys) or Dpenicillaminate (3-sulfanyl-D-valinate) (D-pen)] or bridge easily to other metal ions to form S-bridged polynuclear structures, which are stable enough in aqueous solution thus hampering the isolation of mononuclear species.2,3,9 However, the trans(S) isomers of [Co(N)4(S)2] and [Co(N)2(O)2(S)2] type were isolated by using a multidentate thiolate ligand such as endet = {2S(CH2)2N(CH3)CH2}2 in [Co(endet)(en)]1,10 an aromatic thiolate ligand such as 2-pyrimidinethiolate in[Co(pymt)2- (en)]1,11 a thioether and/or sulfinate ligand, such as L-methioninate in [Co(L-met)2],5 S-methyl-D-penicillaminate (smp) in [Co(D-smp)(D-psi)] (D-psi = 3-sulfino-D-valinate).12 It is diYcult to isolate the trans(S) isomer of the cobalt(III) complexes with two or three L-cysteine like aliphatic aminothiolate ligands.The first partial report of the crystal structure of the trans(S)- type cobalt(III) thiolato complex [Co(aet)2(en)]1 1 has been published as a preliminary communication.13 We report here the correct crystal structure of trans(S)-[Co(aet-N,S)2(en)]ClO4, and complete descriptions of the syntheses, separation of the diastereomers, structural characterisation and specific properties of trans(S)-[Co(aminothiolate-N,S)2(en)]-type complexes. The detailed investigations of these complexes will contribute significantly not only to our understanding of the mononuclear thiolato complexes but also to those of S-bridged di- and tri-nuclear complexes.Experimental Synthesis trans(S)- 1 and cis(S)-[Co(aet-N,S)2(en)]1 2. A solution of 2-aminoethanethiol hydrochloride (5.68 g, 50 mmol) in 20 cm32152 J. Chem. Soc., Dalton Trans., 1999, 2151–2157 of water was added to a solution of trans-[CoCl2(en)2]Cl14 (7.27 g, 25 mmol) in 50 cm3 of water.The mixed solution was adjusted to pH 8.5 and stirred at 25 8C for 1 h, whereupon it immediately turned from green to reddish brown. The reaction mixture was poured onto an SP-Sephadex C-25 column and separated into three bands, brownish violet (A-1), yellow (A-2) and greenish brown (A-3), in this elution order, by development with a 0.2 mol dm23 KCl aqueous solution. The formation ratio A-1 :A-2:A-3 was about 4:1:2. It was confirmed on the basis of the UV/Vis spectral data that the A-2 and A-3 bands contained [Co(aet)(en)2]2115 and trinuclear complex [Co3(aet-N,S)6]31,9 respectively.The A-1 band containing the desired complexes was circulated several times with the same eluent. It was separated into two bands, violet (1) and brown (2). The early violet eluate (1) was concentrated to a small volume with a rotary evaporator below 25 8C, and a large amount of methanol added to the concentrated solution to eliminate KCl. After the filtrate had again been concentrated to a small volume, a large amount of methanol was added to the concentrated solution to deposit a violet complex.The complex obtained as its chloride salt was dissolved in water and the resulting solution passed through a QAE-Sephadex column (ClO4 2 form) by elution with water in order to replace the Cl2 ion by ClO4 2. The eluate was concentrated to a small volume and allowed to stand in a refrigerator for a week. The resulting violet crystals were collected by filtration and dried in a silica gel desiccator.Yield: 0.2 g {Found: C, 19.57; H, 5.20; N, 15.14. Calc. for trans(S)-[Co(aet-N,S)2(en)]ClO4, C6H20ClCoN4O4S2: C, 19.44; H, 5.44; N, 15.11%}. NMR(13C, D2O): d 54.51 (CH2S), 47.63 (CH2NH2 of (en) and 30.15 (CH2NH2 of (aet). UV/Vis (H2O): l/nm (e/dm3 mol21 cm21) 548 (230), 448 (sh) (160), 324 (23000), 244 (sh) (2800) and 216 (sh) (13000). The late brown eluate (2) was treated with the same procedure. The separation of the geometrical isomer of 2 was attempted by the same column chromatographic method as that used for 1.However, it was not successful because of the formation of [Co3(aet-N,S)6]319 during the elution. The 13C NMR spectral measurements of the brown eluate 2 indicated that the complex contained two isomers (C1-cis(S) and C2-cis(S) were distinguished by the peak intensities). Yield: 0.9 g {Found: C, 19.33; H, 5.23; N, 14.92. Calc. for cis(S)-[Co(aet-N,S)2(en)]- ClO4, C6H20ClCoN4O4S2: C, 19.44; H, 5.44; N, 15.11%}.NMR(13C, D2O): d 52.85, 51.48 (CH2S), 48.38, 46.09 (CH2NH2 of en), 33.11, 30.73 (CH2NH2 of aet) for C1 isomer and 52.94 (CH2S), 47.61 (CH2NH2 of en) and 30.61 (CH2NH2 of aet) for C2 isomer. UV/Vis (H2O): l/nm (e/dm3 mol21 cm21) 574 (190), 444 (sh) (310), 380 (sh) (750), 334 (sh) (2800), 284 (15500), 266 (sh) (15000) and 216 (sh) (11000). trans(S)- 3 and cis(S)-[Co(L-cys-N,S)2(en)]2 4. These complexes were prepared by a method similar to that used for the aet complex, using 3.02 g (25 mmol) of L-cysteine. The reaction was carried out at 25 8C for 20 min.The reaction mixture was poured onto a QAE-Sephadex A-25 column and then separated into two bands, brownish violet (B-1) and greenish brown (B-2), in this elution order, by development with a 0.2 mol dm23 KCl aqueous solution. The formation ratio B-1 : B-2 was about 1 : 3. It was confirmed on the basis of the UV/Vis spectral data that the B-2 band contained trinuclear complexes, DLLLDLLL-, DLLLLLLL- and LLLLLLLL-[Co3(L-cys-N,S)6]32.2 The B-1 band containing the desired complexes was circulated several times.It was separated into two bands, violet (3) and brown (4). The resolution of the diastereomers of 3 was carried out by the column chromatographic method. As the band of 3 was circulated more than two times, it was separated into two bands, brownish violet (1)555 CD-3ÀLL, which showed a positive CD sign at 555 nm, and violet (2)555 CD-3ƒLL, which showed a negative one, in this order.The formation ratio of (1)555 CD-3ÀLL and (2)555 CD-3ƒLL was 27 : 73. The early eluate ((1)555 CD-3ÀLL) was concentrated to a small volume with a rotary evaporator below 25 8C, and a large amount of methanol added to the concentrated solution to eliminate KCl. After the filtrate was again concentrated to a small volume, a large amount of methanol was added. The brownish violet complex was deposited from the solution and collected by filtration. The complex obtained as its chloride salt was dissolved in water and the resulting solution passed through a SP-Sephadex C-25 column (Cs1 form) by elution with water in order to replace the K1 ion by Cs1.The eluate was concentrated to a small volume and methanol–ethanol (1 : 1) added till crystals deposited. The resulting brownish violet complex was collected by filtration and dried in a silica gel desiccator. The late eluate ((2)555 CD-3ƒLL) was treated in the same manner except that the complex was obtained as its potassium salt.Yield: 0.1 (1)555 CD-3ÀLL and 0.4 g (2)555 CD-3ƒLL. Found for (1)555 CD-Cs3ÀLL: C, 18.81; H, 4.81; N, 10.77. Calc. for (1)555 CD-LLL-trans(S)-Cs[Co(L-cys-N,S)2(en)], C8H18CoCsN4O4- S2?2.5H2O: C, 17.95; H, 4.33; N, 10.47%. NMR(13C, D2O): d 179.67 (COO), 69.00 (CH2S), 47.46 (CH2NH2 of en) and 34.26 (CH2NH2 of L-cys). UV/Vis (H2O): l/nm (e/dm3 mol21 cm21) 543 (190), 446 (sh) (230) and 326 (21900). CD (H2O): l/nm (De/dm3 mol21 cm21) 595 (11.50), 515 (11.85), 440 (sh) (10.5), 324 (221.20) and 214 (118.20).Found for (2)555 CDK3ƒLL: C, 21.72; H, 5.41; N, 12.55. Calc. for (2)555 CD-ƒLL-trans(S)- K[Co(L-cys-N,S)2(en)], C8H18CoKN4O4S2?3H2O: C, 21.33; H, 5.37; N, 12.44%. NMR(13C, D2O): d 69.28 (CH2S), 47.79 (CH2NH2 of en) and 34.05 (CH2NH2 of L-cys). UV/Vis (H2O): l/nm (e/dm3 mol21 cm21) 543 (190), 446 (sh) (190) and 326 (20000). CD (H2O): l/nm (De/dm3 mol21 cm21) 555 (22.50), 377 (12.60), 307 (11.80), 260 (sh) (12.0) and 234 (16.00).The late brown eluate (4) by treated with the same procedure as that used for the early eluate. However, the desired complex could not be isolated as crystals because it was thermally unstable and readily isomerised to the fac-[Co(L-cys-N,S)3]32 and polynuclear complexes during the repeated elution. Thus, the brown eluate (4) was used intact for measurements of the UV/Vis, CD and 13C NMR spectra and the plasma emission spectral analysis.trans(S)- 5 and cis(S)-[Co(D-pen-N,S)2(en)]2 6. These complexes were prepared by a method similar to that used for the L-cys complex, using 3.78 g (25 mmol) of D-penicillamine. The reaction was carried out at 25 8C for 2 h. On QAE-Sephadex the mixture was separated into three bands, brownish violet (C-1), green (C-2) and brownish green (C-3), in this elution order, by development with a 0.2 mol dm23 KCl aqueous solution. The formation ratio C-1 :C-2: C-3, was about 4:1:1.It was con- firmed on the basis of the UV/Vis spectral data that the C-2 and C-3 bands contained mono- and tri-nuclear complexes, [Co(Dpen- N,S)3]32 and [Co3(D-pen-N,S)6]32, respectively.3 The C-1 band containing the desired complexes was circulated several times. It was separated into three bands, violet (5), brown and dark brown (6). The second brown eluate showed an identical UV/Vis spectrum to that of trans(N)-[Co(D-pen-N,O,S)2]2.6 The resolution of the diastereomers of 5 was carried out by the column chromatographic method.The band containing 5 was separated into two bands, violet (2)535 CD-5ƒDD and brownish violet (1)535 CD-3ÀDD, in this order, by circulation more than two times. The formation ratio of (2)535 CD-5ƒDD and (1)535 CD-5ÀDD was 20 : 80. The cesium salts of those complexes were obtained by the same method as that used for the L-cys complex. Yield: 0.2 g (2)535 CD- 5ƒDD and 1.1 g (1)535 CD-5ÀDD. Found for (2)535 CD-Cs5ƒDD: C, 24.41; H, 5.62; N, 9.32.Calc. for (2)535 CD-DDD-trans(S)-Cs[Co(D-pen- N,S)2(en)], C12H26CoCsN4O4S2?3H2O: C, 24.01; H, 5.37; N, 9.33%. NMR(13C, D2O): d 177.76 (COO), 76.12 (CH), 50.31 (CS), 48.5 (CH2 of en), 34.25, 31.53 (CH3). UV/Vis (H2O): l/nm (e/dm3 mol21 cm21) 552(220), 392 (sh) (1600), 327 (22400) and 248 (sh) (6300). CD (H2O): l/nm (De/dm3 mol21 cm21) 535 (26.22), 420 (sh) (11.3), 322 (129.83), 270 (sh) (12.5), 240 (sh)J. Chem. Soc., Dalton Trans., 1999, 2151–2157 2153 (29.1) and 212 (225.22).Found for (1)535 CD-Cs5ÀDD: C, 23.63; H, 5.82; N, 9.03. Calc. for (1)535 CD-LDD-trans(S)-Cs[Co(D-pen- N,S)2(en)], C12H26CoCsN4O4S2?4H2O: C, 23.31; H, 5.54; N, 9.06%. NMR(13C, D2O): d 177.85 (COO), 77.89 (CH), 50.18 (CS), 47.7 (CH2 of en), 34.30, 31.93 (CH3). UV/Vis (H2O): l/nm (e/dm3 mol21 cm21) 550 (280), 423 (sh) (320) and 326 (21400), 244 (sh) (7900). CD (H2O): l/nm (De/dm3 mol21 cm21) 570 (12.69), 540 (sh) (12.3), 470 (sh) (20.5), 378 (22.55), 314 (23.79) and 236 (220.31).The late eluate containing complex 6 was concentrated to a small volume with a rotary evaporator below 20 8C. After the deposited KCl had been filtered oV, a small amount of ethanol and a large amount of acetone were added to the filtrate in an ice-bath. The resulting dark brown complex was collected by filtration, washed with acetone and diethyl ether, and then dried in a vacuum dessicator. The separation of the geometrical isomer of 6 was attempted by the same column chromatographic method as that used for 5.However, it was not successful because of the isomerisation to trans(N)-[Co(D-pen-N,O,S)2]26 during the repeated elution. The 1H and 13C NMR spectral measurements of the eluate (6) indicated that 6 contained two isomers (LDD-C1 and LDD-C2) of the four possible (LDD-C1, DDD-C1, LDD-C2 and DDD-C2). Yield: 0.7 g. Found for K6: C, 28.57; H, 6.37; N, 10.43. Calc. for cis(S)-K[Co(D-pen-N,S)2- (en)], C12H26CoKN4O4S2?3H2O?0.2C4H10O?0.2KCl: C, 28.53; H, 6.39; N, 10.44%.NMR(13C, D2O): d 179.04, 178.11 (COO), 76.59, 75.14 (CH), 52.51, 49.12 (CS), 48.78, 46.38 (CH2 of en), 33.61, 33.58, 31.22, 30.71 (CH3) for LDD-C1 isomer and 177.78 (COO), 77.65 (CH), 50.23 (CS), 47.72 (CH2 of en), 34.31, 31.98 (CH3) for LDD-C2 isomer. Isomerisation and polynuclearisation reactions of trans(S)-type complexes in the solution Each solution of trans(S)-[Co(aminothiolate-N,S)2(en)]1 or 2 (aminothiolate-N,S = aet, L-cys or D-pen) was allowed to stand at 22 or 50 8C under a nitrogen atmosphere, and its change with time was monitored by UV/Vis and CD spectral measurements.After 2 weeks the solution was diluted 10 times with deoxygenated water and poured onto a QAE-Sephadex A-25 (Cl2 form, 4 × 100 cm) or an SP-Sephadex C-25 (K1 form, 4 × 100 cm) column. The adsorbed band was eluted with a degassed 0.05 mol dm23 KCl aqueous solution. The chromatographic behaviours and UV/Vis and CD spectral data of the resulting eluates corresponded to those of the eluates obtained in the preparation of the complexes.Namely, four bands for the aet complex, trans(S)-1, cis(S)-2, [Co(aet)(en)2]21 and [Co3(aet- N,S)6]31, and five bands for the D-pen complex, trans(S)-5, cis(S)-6, [Co(D-pen-N,O,S)2]2, LDDD-[Co(D-pen-N,S)3]32 and LDDDDDDD-[Co3(D-pen-N,S)6]32, were obtained. On column chromatography of the L-cys complex, especially, besides the three eluates trans(S)-3, cis(S)-4 and LLLLLLLL- and LLLLDLLL- [Co3(L-cys-N,S)6]32 obtained in the preparation of the complexes, a new brown band appeared between the B-1 and B-2 bands.The UV/Vis, CD and 13C NMR spectral behaviours indicated that the brown band contained a dinuclear complex, LLLL-[Co{Co(L-cys-N,S)3}(L-cys-N,O,S)]22 7. The eluate from the brown band was concentrated to a small volume and filtered to remove KCl. The brown complex 7 was obtained on addition of acetone to the filtrate.Yield: 0.3 g. Found for K27: C, 19.53; H, 4.18; N, 7.43. Calc. for K2[Co{Co(L-cys-N,S)3}(L-cys- N,O,S)], C12H20Co2K2N4O8S4?5H2O?0.2C3H6O: C, 19.55; H, 4.06; N, 7.24%. NMR(13C, D2O): d 186.27, 179.7–179.4 (COO), 66.90, 64.53, 63.54, 63.31 (CH), 40.04, 37.88, 37.79, 30.46 (CH2S). UV/Vis (H2O): l/nm (e/dm3 mol21 cm21) 617 (sh) (630), 495 (sh) (2500), 448 (4200), 348 (sh) (10000), 316 (14100) and 262 (19500). CD (H2O): l/nm (De/dm3 mol21 cm21) 642 (14.35), 552 (211.36), 482 (15.70), 460 (sh) (14.7), 398 (15.55), 356 (19.91), 320 (sh) (20.5), 268 (229.86) and 232 (217.96).For the L-cys complex, the concentration of each eluate obtained from the chromatographic separation was determined by plasma emission spectral analysis. The amounts of the four isomers, trans(S)-3, cis(S)-[Co(L-cys-N,S)2(en)]2 4, [Co{Co(Lcys- N,S)3}(L-cys-N,O,S)]22 7 and [Co3(L-cys-N,S)6]32 in the eluate were estimated from curve analyses of the UV/Vis spectra. The concentration of each component in solution was determined at given times by calculation using a NEC PC-9801 VM computer using a least-squares linear method.In the curve analyses the spectral data at 81 points in the region of 400–240 nm (intervals of 2 nm) were used. Measurements The UV/Vis spectra of the complexes were recorded on a JASCO UVIDEC-610C or 670 spectrophotometer and the CD spectra on a JASCO J-600 or 720 spectropolarimeter. All the measurements were carried out in aqueous solutions at room temperature. The elemental analyses were performed by the Analysis Centre of the University of Tsukuba.The concentrations of cobalt in the complexes were determined by plasma emission spectral analysis with a Nippon Jarrel-Ash ICAP-575 ICP spectrophotometer. The 1H and 13C NMR spectra were recorded on a Bruker AM-500 spectrometer at the probe temperature in D2O. Sodium 4,4-dimethyl-4-silapentane-1- sulfonate (DSS) was used as an internal reference.Crystal structure determination Single-crystal X-ray diVraction experiments were performed on an Enraf-Nonius CAD4 diVractometer with graphitemonochromatized Mo-Ka radiation (l = 0.71073 Å). Crystallographic data for trans(S)-[Co(aet)2(en)]1 1 are summarised in Table 1. Unit cell parameters for a single crystal (0.38 × 0.40 × 0.45 mm) of 1 were determined by a least-squares refinement of 25 reflections in the range of 20 < 2q < 22. The structure was solved by direct methods and refined by full-matrix least-squares treatment on F.The non-hydrogen atoms were refined anisotropically. The hydrogen atoms were placed in calculated positions and refined as riding atoms (C–H = N–H 0.95 Å and B = 1.20 × value of riding atom). All the calculations were performed using the TEXSAN crystallographic software package.16 The largest parameter shifts were 0.02 times e.s.d. and |Dr|max in the final Fourier-diVerence maps were 0.3822, and 15 e Å23. CCDC reference number 186/1447.See http://www.rsc.org/suppdata/dt/1999/2151/ for crystallographic files in .cif format. Results and discussion Molecular structure Although we first considered the possibility of a monoclinic symmetry for complex 1 in the preliminary communication, Table 1 Crystallographic data for trans(S)-[Co(aet)2(en)]ClO4 1 Chemical formula M Crystal colour Crystal system Space group a/Å b/Å c/Å V/Å3 ZF (000) Dc/g cm23 m(Mo-Ka)/cm21 Reflections collected Observed reflections [I > 3sI ] RR9 C6H20ClCoN4O4S2 370.75 Purple Orthorhombic Fdd2 (no. 43) 10.5077(6) 17.108(1) 15.7022(6) 2822.7(2) 8 768 1.744 8.56 4312 3878 0.040 0.0642154 J. Chem. Soc., Dalton Trans., 1999, 2151–2157 further refinement showed that the orthorhombic space group Fdd2 fits much better to all observed reflections. A perspective drawing of the complex cation is given in Fig. 1, together with a numbering scheme. Selected bond distances and angles are listed in Table 2.The present complex adopts a six-co-ordinate structure and the co-ordination geometry around the Co atom is approximately octahedral CoN4S2. Two thiolato sulfur atoms of the aet ligands occupy trans positions to each other. Therefore, 1 is assigned to trans(S)-[Co(aet)2(en)]1. The Co–S1 distances (2.2871(4) Å) are longer than the Co–S distances of other complexes containing a co-ordinating aliphatic thiolate or thioether sulfur atom, such as 2.226 Å in [Co(aet)(en)2]21,15 2.267(10)Å in [Co(CH3S(CH2)2NH2)(en)2]31,17 2.239(1)Å in trans-[Co{CH3SCH(CH3)CO2}(tren)]21 (tren = tris(2-aminoethyl) amine),18 and 2.232(1)–2.244(2) Å in trans-[Co(ma or mta)(tren)]21 (ma = 2-sulfanyl-acetate and mta = 2-(methylsulfanyl) acetate).7,9 This indicates that the Co–S bonds are lengthened by the double sulfur trans influence due to two aliphatic thiolato-type sulfur donor atoms.As the other striking structural characters are almost the same as described previously, further detailed descriptions are omitted here.Structural assignment and properties Three geometrical isomers, trans(S), C2-cis(S) and C1-cis(S), are possible for [Co(aminothiolate-N,S)2(en)]-type complexes. The 13C NMR spectrum of 1 exhibits three peaks [d 54.51, 30.15 (aet) and 47.63 (en)] due to methylene carbons of each ligand. This indicates that 1 has a C2 symmetry. The UV/Vis spectral behaviour resembled those of other trans(S)-[Co(N)2(S)2(en)]- type complexes with pymt or endet ligands,10,11 giving a sharp d–d absorption band at (17–18) × 103 cm21 and a characteristic sulfur-to-cobalt charge transfer (SCCT) band at 31 × 103 cm21 (Fig. 2). These spectral behaviours provide useful information for structural assignment of the other trans(S)-type complexes. The UV/Vis spectra of 3 and 5 also show the d–d transition and intense SCCT bands in the same region as 1 does. The 13C NMR spectra revealed that 3 and 5 have C2 symmetry, because (2)555 CD-3ƒLL and (1)555 CD-3ÀLL exhibited four resonance lines due to the eight carbons, and (2)535 CD-5ƒDD and (1)535 CD-5ÀDD exhibited six Fig. 1 Molecular structure of trans(S)-[Co(aet)2(en)]ClO4 1. Hydrogen atoms have been omitted for clarity. Table 2 Selected bond distances (Å) and angles (8) for trans(S)- [Co(aet)2(en)]ClO4 1 Co–S(1) Co–N(1) Co–N(2) S(1)–C(1) S(1)–Co–S(1*) S(1)–Co–N(1) S(1)–Co–N(2) S(1)–Co–N(1*) S(1)–Co–N(2*) N(1)–Co–N(2) 2.2871(4) 1.975(2) 1.979(2) 1.817(2) 175.09(3) 90.77(4) 90.37(5) 85.81(4) 93.25(5) 91.73(7) N(2)–C(3) C(3)–C(3*) N(1)–C(2) C(1)–C(2) N(1)–Co–N(2*) N(2)–Co–N(2*) Co–N(1)–C(2) N(1)–Co–N(1*) Co–S(1)–C(1) Co–N(2)–C(3) 1.484(2) 1.509(4) 1.492(2) 1.508(3) 174.82(7) 84.98(10) 114.9(1) 91.8(1) 98.70(6) 109.3(1) resonance lines due to the twelve carbons.Therefore, these four complexes are assignable to trans(S)-[Co(aminothiolate-N,S)2- (en)]-type (aminothiolate = L-cys or D-pen) complexes. Two diastereomers, DLL (DDD) and LLL (LDD), are possible for each of 3 and 5.The CD spectrum of (2)535 CD-5ƒDD exhibits a negative band in the first absorption band region, while that of the (1)535 CD-5ÀDD has a positive band in that region (Fig. 2). Accordingly, (2)535 CD-5ƒDD and (1)535 CD-5ÀDD are assigned to (2)535 CD-DDDand (1)535 CD-LDD-trans(S)-[Co(D-pen)2(en)]2, respectively. In a similar manner, (1)555 CD-3ÀLL and (2)555 CD-3ƒLL are assigned to (1)555 CD-LLL- and (2)555 CD-DLL-trans(S)-[Co(L-cys)2(en)]2, respectively.In the first absorption band region of (2)555 CD-3ƒLL, two CD bands of the same 1 sign appeared. This agrees well with the pattern predicted from the CD spectra of the trans(N)- [Co(L-aminocarboxylate)2(ox)]2 and trans(O)-[Co(L-aminocarboxylato) 2(en)]1 complexes.20 On the contrary, (1)535 CD-5ÀLL shows only one CD band in the first absorption band region. This diVerence may be related to the UV/Vis spectral behaviour, which does not have the splitting in the first absorption band region, and attributed to the peculiar transition of the thiolate sulfur donor atom.The resonance peaks due to the methine and methylene carbons in isomers (2)555 CD-3ƒLL and (1)555 CD-3ÀLL showed almost the same chemical shift patterns. For the en moiety the resonance peaks due to the methylene carbons in (2)555 CD-3ƒLL and (1)555 CD- 3ÀLL have almost the same chemical shifts as those in 1. These facts suggest that (2)555 CD-3ƒLL and (1)555 CD-3ÀLL do not form any hydrogen bond in the solution.Thus the diVerence in the amounts between (2)555 CD-3ƒLL and (1)555 CD-3ÀLL (73 : 27) reflects the favourable equatorial orientation of the carboxylate and the steric repulsion between the methine and methylene groups on the L-cys ligands. The resonance peaks due to the methylene carbons in the en ligand in (2)535 CD-5ƒDD are shifted to lower magnetic field (ca. 1 ppm) compared to those in (1)535 CD-5ÀDD and the resonance peaks due to the methine carbons in (2)535 CD-5ƒDD are shifted to higher magnetic field (ca. 2 ppm) compared to those in (1)535 CD-5ÀDD. Similar trends are observed for the di- and trinuclear complexes [Co{Co(aminothiolate-N,S)3}(D-pen-N,O,S or dien)]0 or 22 and [Co3(aminothiolate-N,S)6]32 (aminothiolate- N,S = L-cys or D-pen).2,3 It is reasonable to consider that these shifts are aVected by the formation of the intramolecular hydrogen bond COO ? ? ? H–N–H. Molecular models of these Fig. 2 The UV/Vis and CD spectra of trans(S)-[Co(aet)2(en)]1 1 (——), DDD-trans(S)-[Co(D-pen-N,S)2(en)]2 5ƒDD (—-—) and LDDtrans( S)-[Co(D-pen-N,S)2(en)]2 5ÀDD (- - - - -).J.Chem. Soc., Dalton Trans., 1999, 2151–2157 2155 complexes suggest the formation of hydrogen bonds due to steric repulsion between the methyl protons on the D-pen ligands and the amine protons on the D-pen or en ligand. The formation ratio of (1)535 CD-5ÀDD : (2)535 CD-5ƒDD (80 : 20) slightly increased compared with (2)555 CD-3ƒLL : (1)555 CD-3ÀLL (73: 27) because of such structural stabilisation.On the other hand, the UV/Vis spectral pattern of complex 6 is quite similar to that of other cis(S)-[Co(N)2(S)2(en)]-type complexes, giving a characteristic broad SCCT band at 34 × 103 cm21.10 Further, the 13C NMR spectrum exhibits twelve intense resonance lines (d 30.71, 31.22, 33.58, 33.61, 46.38, 48.78, 49.12, 52.51, 75.14, 76.59, 178.11 and 179.04) and six weak ones (d 31.98, 34.31, 47.72, 50.23, 77.65 and 177.78). This suggests that 6 is a mixture of the C1-cis(S) (major) and C2-cis(S) (minor) isomers.The cis(S) isomers seem to take preferentially the absolute configuration LDD or DDD. The absolute configurations of the C1- and C2-cis(S) isomers containing 6 are more favourable to LDD configurations than DDD ones because of similar steric repulsion attributable to the methyl group in 5 and the repulsion between the unshared electron pairs on the sulfur donor atoms located in cis positions.3 The CD spectrum of 6 shows a relatively intense positive peak in the first absorption band region, suggesting that the configurations of the cis(S) isomers containing 6 are assignable to LDD.The C1-cis(S) isomer was formed in larger amount than the C2-cis(S) one. This fact may be explained as follows: in the C2-cis(S) isomer, the two sulfur donor atoms occupy trans positions to the two nitrogen atoms of the en ligand, so that the en ligand seems to become labilised by the structural trans eVect due to the sulfur donor atoms.This interpretation is consistent with the fact that cobalt(III) complexes with thiolate ligands prefer to the cis(S) geometry. The UV/Vis spectra of 2 and 4 are quite similar to that of cis(S)- [Co(D-pen-N,S)2(en)]2 6 over the whole region. They exhibit a broad SCCT band at 35 × 103 cm21 characteristic of cis(S)- [Co(N)2(S)2(en)]-type complexes.10 This suggests that 2 and 4 also adopt the cis(S) geometries of [Co(aet-N,S)2(en)]1 and [Co(L-cys-N,S)2(en)]2, respectively, contain two geometrical isomers, C1- and C2-cis(S), and each of the geometrical isomers in 4 consists of two diastereomers, LLL and DLL.Actually, the 13C NMR spectral measurements indicated that 2 and 4 contained two and four possible isomers, respectively. However, the desired complex could not be separated because it was thermally unstable and readily isomerised to the fac-[Co(L-cys- N,S)3]32 and polynuclear complexes during repeated elution.The UV/Vis spectrum of brown complex 7 shows d–d transition bands in the region (16–24) × 103 cm21 and intense bands due to the SCCT transition at ca. 38 × 103 cm21. Such spectral behaviour is quite similar to those of [Co{Co(aminothiolate- N,S)3}(D-pen-N,O,S or dien)]-type (aminothiolate = aet, L-cys or D-pen) dinuclear complexes.3 The 13C NMR shift pattern of 7 also resembles that of the latter complexes. Four resonance peaks due to the carboxylate carbon atoms of the L-cys ligands were observed in the d 186–179 region.The carbon resonance peaks appeared at d 186.27 and 179.7–179.4 for the co-ordinated and unco-ordinated carboxyl groups, respectively. A single resonance peak due to the methylene carbon atom is located relatively upfield (d 30.46) compared with those of the corresponding carbon atoms in the [Co(aminothiolate-N,S)3] moiety (d 40.04–37.79). These results suggest that three sulfur atoms in the L-cys ligands bridge two cobalt(III) ions, but a sulfur atom in one tridentate L-cys-N,O,S does not.The results from UV/Vis and NMR spectral measurements indicate that 7 is the dinuclear complex [Co{Co(L-cys-N,S)3}(L-cys-N,O,S)]22, having C1 symmetry. The CD spectral behaviour of 7 is similar to those of LLLL-[Co{Co(L-cys-N,S)3}(D-pen-N,O,S or dien)]22 or 0 and L-[Co{Co(aet-N,S)3}(D-pen-N,O,S)]1.3 The IR spectral measurement also supports this. Accordingly, it is suggested that 7 adopts a LLLL configuration.This complex containing L-cys- N,O,S as a tridentate ligand was not obtainable by the usual preparative method for the dinuclear complexes. Structural change of trans(S)-type complexes Fig. 3 shows the UV/Vis spectral changes of the trans(S) isomers in 0.1 mol dm23 KCl solution at 50 8C. The UV/Vis and CD spectra became approximately constant after 2 weeks. During this time course, clear-cut isosbestic and isodichroic points were not observed.The change in the absorption curve, in which the maximum of the SCCT band shifted to higher energy (from 327–324 to 291–284 nm), suggests that the cis(S) type isomers were formed. Moreover, Fig. 3 (a) and (b) show that the absorption intensities in the d–d transition region increased with time, accompanied by the production of di- and trinuclear complexes. These imply that the trans(S) isomer in the solution changes to several species, which were confirmed by the spectral data of the eluate from the column chromatographic separation [four eluates showing four diVerent spectra for aet and L-cys complexes and five eluates with five diVerent spectra for the D-pen complex] as described in the Experimental section.The observed and calculated curves of trans(S)-[Co(L-cys- N,S)2(en)]2 3 at 22 8C after 2 weeks were in good agreement. The calculated concentration–time dependencies are plotted in Fig. 4. The starting trans(S) isomer decreased during the monitored timescale, while the cis(S) isomer increased in concentration for the initial period and then (after ca. 250 h) the dinuclear and trinuclear complexes were formed. With time (after ca. 800 h) Fig. 3 The UV/Vis spectral changes of the complexes in 0.1 mol dm23 KCl solution at 50 8C measured at 12 or 6 h intervals: (a) trans(S)- [Co(aet)2(en)]1 1, (b) DLL-trans(S)-[Co(L-cys-N,S)2(en)]2 3ƒLL and (c) LDD-trans(S)-[Co(D-pen-N,S)2(en)]2 5ÀDD.2156 J. Chem. Soc., Dalton Trans., 1999, 2151–2157 the cis(S) isomer began to decrease and simultaneously the dinuclear and trinuclear complexes increased.The dinuclear complexes, LLLL-[Co{Co(L-cys-N,S)3}(L-cys-N,O,S)]22 7, finally became major species. In this case, the dinuclear complex 7 was selectively formed with only the LLLL configuration and the trinuclear complexes were formed with LLLLLLLL and LLLLDLLL (ca. 1 : 1) configurations; the reason for these selectivities is not clear at present.The isomerisation and polynuclearisation reactions of 3 are explained in Scheme 1. In the initial stage of the reaction (i), (ii) mononuclear complexes are formed. Path (i) is an equilibrium reaction because a small amount of trans(S) isomer was also obtained from the isomerisation reaction of the cis(S) one. The tris(L-cysteinato)cobalt(III) complex, fac-[Co- (L-cys-N,S)3]32, produced in path (ii) has high nucleophilicity, so in the final stage of the reaction the S-bridged di- and trinuclear complexes are mainly formed (iii), (iv).That is a reason why the pure trans(S) and cis(S) isomers were not isolated up to now. This is supported by a previous report that the S-bridged trinuclear complex [Co3(L-cys-N,S)6]32 was easily formed from fac-[Co(L-cys-N,S)3]32.2 Path (v) (the change between the di- and tri-nuclear complexes) did not occur under the present conditions. For the trans(S)-aet complex 1 a similar spectral change and column chromatographic separation were observed except that only trinuclear complex was formed in the polynuclearisation stage (of course the dinuclear complex is not formed because the aet ligand functions only as a didentate-N,S lig- Fig. 4 The changes of the isomer proportions in the isomerisation and polynuclearisation reactions of trans(S)-[Co(L-cys-N,S)2(en)]2 3 (0.05 mol dm23 KCl, 22 8C): trans(S)-[Co(L-cys-N,S)2(en)]2 (s), cis(S)-[Co- (L-cys-N,S)2(en)]2 (n), [Co{Co(L-cys-N,S)3}(L-cys-N,O,S)]22 (h), [Co3(L-cys-N,S)6]32 (d).and). In the isomerisation and polynuclearisation of trans(S)-Dpen complex 5, although the SCCT band shifts to higher energy, a drastic increase of the absorption intensities in the d–d transition region was not observed. These results suggest that the S-bridged di- and tri-nuclear complexes are diYcult to form, since the six methyl groups attached to the neighbouring carbon atoms of the co-ordinated sulfur atoms in the [Co- (D-pen-N,S)3] moiety are sterically bulky.Therefore, the mononuclear trans(N)-[Co(D-pen-N,O,S)2]2 complex, which has the minimum steric hindrance of all products, is produced as major species, and small amounts of LDDD-fac-[Co(D-pen-N,S)3]32 and LDDDDDDD-[Co3(D-pen-N,S)6]323 are formed in the final stage of this reaction. The result of the column chromatographic separation also supports this. Consequently, the isomerisation reactions of trans(S)-[Co(D-pen-N,S)2(en)]2 proceed through the paths shown in Scheme 2.UV/Vis Spectral behaviours of [Co(S)n(N)6-n]-type (n 5 1, 2 or 3) complexes Fig. 5 shows the UV/Vis spectra of mononuclear complexes, [Co(D-pen-N,S)(en)2]1,8 trans(S)-[Co(D-pen-N,S)2(en)]2 3, cis(S)-[Co(D-pen-N,S)2(en)]2 4 and fac-[Co(D-pen-N,S)3]32,3 which are of [Co(S)n(N)6-n] type (n = 1, 2 or 3). As the UV/Vis spectral patterns of the L-cys and D-pen complexes, trans(S)- or cis(S)-[Co(L-cys- or D-pen-N,S)2(en)]2 3–6, are also similar to one another, these can be compared with the same trans(S)- or cis(S)-[Co(N)4(S)2] system.It is known that the first absorption band (1A1g æÆ 1T1g transition of the complex for the Oh symmetry) splits clearly into two components for the trans(O)-[Co(N)4(O)2]- or trans(N)-[Co(N)2(O)4]-type complexes. This is the so-called Yamatera semiempirical rule which states that the position and shape of the d–d absorption band can be predicted from semiempirical calculation on the basis of molecular orbital theory.2 According to this treatment, the complexes adopting the same geometry are expected to show similar UV/Vis spectral behaviour.However, the present sulfur-atom containing trans(S)-[Co(D-pen- or L-cys-N,S)2(en)]2 complexes indicate a deviation from the rule, that is no clearly explicit splitting is observed for those complexes. The reason is that the splitting is so small because the ligand field strengths of nitrogen and sulfur are similar, and further it has not been clarified how the ligand field strength of thiolato sulfur compares with those of nitrogen and oxygen (N > S > O or S > N > O).3–10 Consequently, the geometrical structures of the complexes with thio- Scheme 1 Co N N N N S S COO– COO– Co S N N N N S COO– COO– Co S S N N N S COO– COO– –OOC Co S S S Co N N N –OOC COO– COO– Co S S S N N N COO– –OOC –OOC Co S N N N O S S N S Co COO– COO– COO– O trans(S) cis(S) fac(S) trinuclear complex (iii) (i) (iv) (v) dinuclear complex (ii)J.Chem. Soc., Dalton Trans., 1999, 2151–2157 2157 late sulfur-containing ligands cannot be determined from only the splitting patterns in their d–d absorption band region. The position and pattern of the SCCT bands commonly reflect the geometries such as cis(S) and trans(S) for cobalt(III) complexes containing two thiolate or thioether sulfur atoms. The cis(S) isomers of thiolato and thioether complexes exhibit intense broad SCCT bands in the region of (32–38) × 103 cm21 which are composed of more than two components.The trans(S) isomers exhibit an intense sharp band at lower energy (ca. 31 × 103 cm21). Of course, the present trans(S)-[Co(aet-, L-cys- or D-pen- N,S)2(en)]2 is also distinguishable from the cis(S) isomer on the basis of the UV/Vis spectral patterns in the SCCT band region (Fig. 5). Further, for the [Co(S)n(N)6-n]-type (n = 1–3) complexes (except the trans(S) isomer), we found that the SCCT band broadens (no explicit splitting), shifts to higher energy, and Fig. 5 The UV/Vis spectra of [Co(S)n(N)6-n]-type (n = 1–3) complexes: [Co(D-pen-N,S)(en)2]1 (——), trans(S)-[Co(D-pen-N,S)2(en)]2 (5) (– – –), cis(S)-[Co(D-pen-N,S)2(en)]2 6 (----) and fac-[Co(D-pen-N,S)3]32 (—-—). Scheme 2 Co N N N N S S –OOC Co S N N N N S –OOC –OOC Co N O S N O S O O –OOC trans(S) trans(N) cis(S) increases in intensity with n (1 to 3). This seems to depend on the number of the sulfur atoms co-ordinating to CoIII. Such spectral behaviours were also observed for all cobalt(III) complexes with the other thiolate ligands.Therefore, these facts suggest that the structures of the [Co(S)n(N)6-n]-type (n = 1–3) complexes are characterised by the position and intensity of the SCCT band in their UV/Vis spectra. Acknowledgements This work was supported by a Grant-in-Aid for Encouragement of Young Scientists (No. 08740522) from the Ministry of Education, Science, Sports and Culture, Japan. References 1 J.J. Mayerle, S. E. Denmark, B. V. DePamphilis, J. A. Ibers and R. H. Holm, J. Am. Chem. Soc., 1975, 97, 1032; R. W. Lane, J. A. Ibers, R. B. Frankel, G. C. Papaefthymiou and R. H. Holm, J. Am. Chem. Soc., 1977, 99, 84; P. de Meester and D. J. Hodgson, J. Am. Chem. Soc., 1977, 99, 101; H. M. Helis, P. de Meester and D. J. Hodgeson, J. Am. Chem. Soc., 1977, 99, 3309; G. J. Gainsford, W. G. Jackson and A. M. Sargeson, J. Am. Chem. Soc., 1977, 99, 2383; 1979, 101, 3966; N. Baidya, M.M. Olmstead and P. K. Mascharak, Inorg. Chem., 1989, 28, 3426; N. Baidya, D. Ndreu, M. M. Olmstead and P. K. Mascharak, Inorg. Chem., 1991, 30, 2448; I. E. Burgeson and N. M. Kostic, Inorg. Chem., 1991, 30, 4299; L. Zhu and N. M. Kostic, Inorg. Chem., 1992, 31, 3994. 2 K. Okamoto, S. Aizawa, T. Konno, H. Einaga and J. Hidaka, Bull. Chem. Soc. Jpn., 1986, 59, 3859; S. Aizawa, K. Okamoto, H. Einaga and J. Hidaka, Bull. Chem. Soc. Jpn., 1988, 61, 1601. 3 K. Okamoto, T. Yonemura, T. Konno and J. Hidaka, Bull. Chem. Soc. Jpn., 1992, 65, 794; T. Yonemura, S. Nakahira, T. Ama, H. Kawaguchi, T. Yasui, K. Okamoto and J. Hidaka, Bull. Chem. Soc. Jpn., 1995, 68, 2859. 4 V. M. Kothari and D. H. Busch, Inorg. Chem., 1969, 8, 2276; P. de Meester and D. J. Hodgson, J. Chem. Soc. Dalton Trans., 1976, 618; K. Wakayama, K. Okamoto, H. Einaga and J. Hidaka, Bull. Chem. Soc. Jpn., 1983, 56, 1995; K. Okamoto, M. Takaki, T. Yonemura, T. Konno and J. Hidaka, Inorg. Chim. Acta, 1990, 175, 31. 5 J. Hidaka, S. Yamada and Y. Shimura, Chem. Lett., 1974, 1487. 6 K. Okamoto, K. Wakayama, H. Einaga, S. Yamada and J. Hidaka, Bull. Chem. Soc. Jpn., 1983, 56, 165. 7 T. Yonemura, K. Shibuya, K. Okamoto, T. Ama, H. Kawaguchi and T. Yasui, Inorg. Chim. Acta, 1997, 260, 119. 8 H. C. Freeman, C. J. Moore and A. M. Sargeson, Inorg. Chem., 1978, 17, 3513. 9 G. R. Brubaker and B. E. Douglas, Inorg. Chem., 1967, 6, 1562. 10 K. Yamanari, N. Takeshita and Y. Shimura, Bull. Chem. Soc. Jpn., 1984, 57, 1227, 2852. 11 K. Yamanari, K. Okusako and S. Kaizaki, J. Chem. Soc., Dalton Trans., 1992, 1615. 12 T. Yonemura, T. Yasui, K. Okamoto and J. Hidaka, Acta Crystallogr., Sect. C, 1996, 52, 1390. 13 T. Yonemura, K. Okamoto, T. Ama, H. Kawaguchi and T. Yasui, Chem. Lett., 1993, 1123. 14 J. C. Bailar, Jr., Inorg. Synth., 1946, 2, 222. 15 R. C. Elder, L. R. Florian, R. E. Lake and A. M. Yacynych, Inorg. Chem., 1973, 12, 2690. 16 TEXSAN, Crystal Structure Analysis Package, Molecular Structure Corp., The Woodlands, TX, 1985 and 1992. 17 R. C. Elder, G. J. Kennard, M. D. Payne and E. Deutsch, Inorg. Chem., 1978, 17, 1296. 18 S. Ohba and Y. Saito, Acta Crystallogr., Sect. C, 1984, 40, 398. 19 The t-isomer has the S atom at the trans position to the tertiary amine of the tren ligand. 20 N. Matsuoka, J. Hidaka and Y. Shimura, Inorg. Chem., 1970, 9, 719; Bull. Chem. Soc. Jpn., 1972, 45, 2491, 1975, 48, 458. 21 H. Yamatera, Bull. Chem. Soc. Jpn., 1958, 31, 95; N. Matsuoka, J. Hidaka and Y. Shimura, Bull. Chem. Soc. Jpn., 1967, 40, 1868. Paper 8/09753D

ISSN:1477-9226    

DOI:10.1039/a809753d

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2155–2162 2155 Molecular structures of tetraborane(10) derivatives: ab initio calculations for (CH3)2MB3H8 (M 5 B, Al, Ga or In) and gas-phase electron diVraction studies of (CH3)2AlB3H8 and (CH3)2GaB3H8 † Carole A. Morrison,a Bruce A. Smart,a Paul T. Brain,a David W. H. Rankin *,a and Anthony J. Downsb a Department of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, UK EH9 3JJ b Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK OX1 3QR Structural trends in the family of compounds (CH3)2MB3H8 (M = B, Al, Ga or In) have been investigated by ab initio molecular orbital calculations.In addition, the gas-phase molecular structures of (CH3)2AlB3H8 and (CH3)2GaB3H8 have been re-determined by gas-phase electron diVraction using the SARACEN method of structural analysis. Salient structural parameters (ra 0) for the aluminium and gallium compounds were found respectively to be: r[B(1) ? ? ? M(2)] 231.6(7), 234.2(8); r[B(1)]B(3)] 178.2(12), 178.9(23); r[B(1)]B(4)] 184.4(10), 184.3(23); r[B(1)]H(1,2)] 124.6(11), 121.6(18); r[M(2)]H(1,2)] 182.5(13), 186(6); r[B(1)]H(1,4)] 126.2(11), 122.9(18); r[B(4)]H(1,4)] 142.6(11), 140(3) pm; butterfly angle 123.8(20), 119.8(13)8.The introduction of the SARACEN method1,2 for the analysis of gas-phase electron diVraction (GED) data has led to a considerable improvement in the reliability and quality of structural refinements. In this method parameters which cannot be refined (both geometric and vibrational) are assigned restraints derived from an array of ab initio calculations. All geometric parameters and significant amplitudes of vibration are then refined as a matter of principle.The series of compounds under investigation in this paper is based on the compound tetraborane(10) with one terminal BH2 unit replaced by a M(CH3)2 unit (where M = B, Al, Ga or In).All four compounds have been investigated by ab initio calculations, and for (CH3)2AlB3H8 and (CH3)2GaB3H8 by electron diVraction. For these types of compound the structural information which can be obtained by electron diVraction alone is somewhat limited. The distances B]B, M]C and M]Hb are of similar length and therefore strongly correlated and, with the heavy atoms dominating the molecular scattering, locating the precise positions of the hydrogen atoms is a particularly diYcult exercise.Consequently, in the original refinements reported for these compounds,3 several parameters had to be fixed at assumed values and other assumptions had to be made to simplify the structural analysis. In addition, no reliable force fields were available to assess the eVects of vibration. Thus, the preliminary structures reported for these molecules are of a very basic nature. With the availability of ab initio harmonic force fields and the development of the SARACEN method much improved structures can now be secured.In addition to the new SARACEN refinements, the structural trends and similarities identified within the series (CH3)2- MB3H8 by ab initio calculations are also discussed. Finally, the calculated structure of (CH3)2InB3H8 is compared with the experimental structure found in the solid phase.4 This paper represents the final section of a structural exploration of † Supplementary data available: tables of ab initio geometries and energies and Cartesian coordinates from the 6-311G**/MP2 ab initio calculation for (CH3)2MB3H8 (M = B, Al, Ga or In), and final coordinates and least-squares correlation matrix for the SARACEN study of (CH3)2MB3H8 (M = Al or Ga).For direct electronic access see http:// www.rsc.org/suppdata/dt/1998/2155/, otherwise available from BLDSC (No. SUP 57391, 14 pp.) or the RSC Library. See Instructions for Authors, 1998, Issue 1 (http://www.rsc.org/dalton). tetraborane(10) derivatives, new molecular structures for the parent compound tetraborane(10) 2 and the derivative series H2MB3H8 (where M = Al, Ga and In) 5 having been published previously.Experimental (a) Ab initio calculations Theoretical methods. All calculations were carried out on a DEC Alpha APX 1000 workstation with the exception of the 6-31G*/MP2 and 6-311G**/MP2 (CH3)2InB3H8 calculations, which were carried out on the Rutherford Laboratory DEC Alpha 8400 5/300 workstation. The GAUSSIAN suite of programs was used throughout.6 Geometry optimisations.Details of the graded series of calculations performed for the dimethyl series of compounds are the same as for the hydride series reported in the preceding paper.5 It is noted that, as no standard basis set for indium is available beyond the 3-21G* level, the basis set of Huzinaga7 with an additional diVuse d-function (exponent 0.10), contracted to (21s, 17p, 1111d)/[15s, 12p, 711d], was used for all higher level calculations.It is also worth repeating the special treatment used to describe the 3d and 4d electrons of gallium and indium, respectively. The default setting in the GAUSSIAN program placed these orbitals in the core region. A close examination of the calculated orbital energies, however, clearly showed these orbitals to lie closer in energy to the outer valence orbitals, rather than the inner core orbitals. Calculations were therefore performed with these orbitals defined as valence.Calculations beyond the MP2 level of theory were not attempted as higher level calculations were expected to give rise to only small changes in geometry, based on the evidence obtained from the larger series of calculations performed on the hydride analogues.5 Frequency calculations. Frequency calculations were performed at the 6-31G*/SCF level for (CH3)2B4H8, (CH3)2AlB3H8 and (CH3)2GaB3H8, confirming Cs symmetry as a local minimum in each case. Performing the 6-31G*/SCF frequency calculation in Cs symmetry for (CH3)2InB3H8 gave rise to one imaginary frequency (at 25 cm21), indicating that the Cs2156 J. Chem.Soc., Dalton Trans., 1998, Pages 2155–2162 Table 1 GED data analysis parameters for (CH3)2AlB3H8 and (CH3)2GaB3H8 Camera distance/ Weighting functions/nm21 Correlation Scale Electron wavelength b/ Compound (CH3)2AlB3H8 (CH3)2GaB3H8 mm 128.16 285.06 128.45 285.06 Ds 4242 smin 72 24 68 24 sw1 92 42 100 44 sw2 280 130 230 130 smax 328 160 288 166 parameter 0.1908 0.2430 0.0999 0.2442 factor, ka 0.676(23) 0.882(17) 0.871(47) 0.850(38) pm 5.8720 5.1189 5.1336 5.0969 a Figures in parentheses are the estimated standard deviations.b Determined by reference to the scattering patterns of benzene vapour. geometry is not a local minimum on the potential energy surface at this level. However, lowering the symmetry to C1 resulted in the location of a local minimum less than 0.01 kJ mol21 below the Cs geometry at the 6-31G*/SCF level, with the two methyl groups rotated by only 78.It is not clear whether improvements in the theoretical treatment would lead to a Cs or a C1 minimum for this compound; however, it is clear that the potential-energy surface is very flat and that any distortion from Cs symmetry is small. For (CH3)2AlB3H8 and (CH3)2Ga- B3H8 the force fields described by Cartesian force constants at the 6-31G*/SCF level were transformed into ones described by a set of symmetry coordinates using the program ASYM40.8 Since no fully assigned vibrational spectra were available for these compounds, the force fields were adjusted using scaling factors of 0.94, 0.96 and 0.92 for bond stretches, angle bends and torsions, respectively.‡ (b) Gas-phase electron diVraction (GED) GED data.The new refinements for (CH3)2AlB3H8 and (CH3)2GaB3H8 reported here are based on the original data sets 3 recorded on the Edinburgh apparatus. As with H2GaB3H8 reported in the previous paper,5 these compounds were found to react with the photographic emulsion of the GED plates, giving rise to data with higher than usual noise levels.Standard programs9 were used for the data reduction with the scattering factors of Ross et al.10 The weighting points used in setting up the oV-diagonal weight matrices, the s ranges, scale factors, correlation parameters and electron wavelengths are given in Table 1. GED model. As both (CH3)2AlB3H8 and (CH3)2GaB3H8 possess Cs symmetry, the same set of geometric parameters was used to describe the two structures.The model used was essentially based on that for H2GaB3H8 5 with an additional two parameters [r(C]H) and angle H]C]M] to locate the positions of the hydrogen atoms in the two methyl groups attached to the M atom, which were assumed to possess local C3v symmetry (see Fig. 1). Thus, twenty-two geometric parameters are required to define the structures fully in Cs symmetry, as given in Table 2.It should be noted that the new model system incorporates an additional five geometric parameters, compared with the model used in the original refinement.3 These parameters allow a further five structural features to be investigated, namely the deviations of the bridging hydrogen atoms from the heavy-atom planes M(2)]B(1)]B(3) and B(1)]B(3)] B(4), the diVerences between the terminal B]Hendo/exo and M]Cendo/exo distances, and finally the tilting of the terminal BH2 unit towards or away from the heavy-atom cage.Analogous parameters have been introduced in the recent re-refinements of B4H10 2 and H2GaB3H8.5 The heavy cage atoms required four parameters to locate their positions: the weighted average and diVerence of the two B]B distances (p1,2), r[B(1) ? ? ? M(2)] (where M = Al or Ga) (p3) and the butterfly angle (p20) describing the angle between the ‡ Scaling constants as used in the force fields for B4H10 2 and for H2GaB3H8.5 planes B(1)]B(4)]B(3) and B(1)]M(2)]B(3).The remaining parameters locate the eight hydrogen atoms in the boron cage and the two methyl groups. Parameter p4 is defined as r[M(2)]H(1,2)], p5 as the weighted mean of all B]H distances in the molecule, and p6 as the average B]H bridging distance minus the average B]H terminal distance. Parameter p7 is the diVerence between the outer bridging distance B(4)]H(1,4) and the average of the two inner bridging distances B(1)]H(1,2) and B(1)]H(1,4); p8 is r[B(1)]H(1,4)] minus r[B(1)]H(1,2)]; p9 is the diVerence between rB(1)]H(1) and the average B]Hendo/exo distance, and p10 rB]Hendo minus rB]Hexo.Parameters p11 and p12 are defined as the average of, and diVerence between, the two M]C distances, respectively, and p13 is the distance C]H. The six bond-angle parameters required are B(3)]B(1)]H(1) (p14), C(2)endo]M(2)]C(2)exo (p15), H(4)endo]B(4)]H(4)exo (p16), the MC2 and BH2 tilt parameters (p17 and p18), defined as the angles between the bisectors of the C(2)endo]M(2)]C(2)exo and H(4)endo]B(4)]H(4)exo wing angles and the planes B(1)]M(2)] B(3) and B(1)]B(4)]B(3), respectively, with positive values indicating tilting into the heavy atom cage, and finally the angle H]C]M (p19).The last two parameters are the torsion angles, ‘H(1,2) dip’ and ‘H(1,4) dip’ (p21 and p22), which define the elevation of the H(1,2) and H(1,4) bridging atoms above the B(1)]M(2)]B(3) and B(1)]B(4)]B(3) planes, respectively [i.e.the angles between the two sets of planes B(1)]M(2)]B(3) and B(1)]M(2)]H(1,2), and B(1)]B(4)]B(3) and B(4)]B(1)] H(1,4)]. Results and Discussion (a) Ab initio calculations In light of the many calculations performed on this series of compounds the full set of results obtained is confined to SUP 57391 Tables 1–4. Results obtained from the highest level calculations, 6-311G**/MP2, are reported for all four compounds in Table 3 of this paper. A number of trends in geometry were observed to accompany improvements in basis set and level of theory, with the Fig. 1 Molecular framework of (CH3)2MB3H8 (M = B, Al, Ga or In)J. Chem. Soc., Dalton Trans., 1998, Pages 2155–2162 2157 most significant changes generally arising as a result of the introduction of electron correlation to the MP2 level. The main changes observed are summarised below. Cage structure. The sensitivity of the cage distances to improvements in basis set and level of theory showed many parallels to the cage distance in the H2MB3H8 series of derivatives reported in the previous paper.5 In particular, r[B(1)]B(3)] in both sets of derivatives lengthened on average less than 1 pm on improving the basis set from 6-31G* to 6-311G** at both the SCF and MP2 level.The r[B(1)]B(4)] distance was found to be more sensitive to change; it increased by about 1–1.5 pm at both SCF and MP2 levels for the boron, aluminium and indium analogues, and shortened by just over 3 pm at SCF (remaining largely unaVected at the MP2 level) for the two gallium compounds.This diVerence in behaviour for the gallium compounds can largely be attributed to the poor quality of the 6-31G* basis set, which is deficient in the number of basis functions describing the core region of such a large atom. The introduction of electron correlation had similar eVects for all four compounds in both series, with r[B(1)]B(3)] shortening by about 2 pm with both the 6-31G* and 6-311G** basis sets.In contrast, r[B(1)]B(4)] was found to be less aVected by electron correlation in the (CH3)2MB3H8 series than in the H2MB3H8 series. It shortened by 1–2 pm in (CH3)2B4H8 for Table 2 Geometric parameters (ra 0/pm, angles in 8) for the SARACEN refinements of (CH3)2AlB3H8 and (CH3)2GaB3H8 Results c Parameters a,b Me2AlB3H8 Me2GaB3H8 Independent p1 p2 p3 p4 p5 p6 p7 p8 p9 p10 p11 p12 p13 p14 p15 p16 p17 p18 p19 p20 p21 p22 av. r(B]B) diV.r(B]B) r[B(1) ? ? ? M(2)] r[M(2)]H(1,2)] av. r(B]H) av. r(B]Hb) 2 r(B]Ht) diV. [r(B]Hb)] (outer 2 inner) diV. [r(B]Hb)] (inner) r[B(1)]H(1)] 2 av. r[B(4)]Ht] diV. r(B]Ht) (endo 2 exo) av. r[M]C] diV. r(M]C) (endo 2 exo) r(C]H) B(3)]B(1)]H(1) C(2)endo]M(2)]C(2)exo H(4)endo]B(4)]H(4)exo MC2 tilt BH2 tilt H]C]M Butterfly angle H(1,2) dip H(1,4) dip 182.3(9) 6.1(13) 231.6(7) 182.5(13) 126.5(7) 11.6(12) 17.2(6) 1.6(13) 20.5(4) 0.2(1) 193.9(5) 0.2(1) 107.2(4) 112.3(12) 132.0(23) 118.5(13) 27.1(4) 0.7(13) 111.0(15) 123.8(20) 13.4(13) 1.5(16) 182.5(22) 5.3(13) 234.2(8) 186(6) 123.4(14) 11.6(18) 17(3) 1.3(13) 20.6(1) 0.3(3) 193.2(4) 0.3(3) 111.0(10) 111.6(13) 132.5(15) 118.5(13) 24.7(23) 0.5(21) 108.6(10) 119.8(13) 14.3(16) 20.2(21) Dependent B(1)]B(4)]B(3) B(1)]M(2)]B(3) r[B(1)]B(3)] r[B(1) ? ? ? B(4)] r[B(1)]H(1,4)] r[B(4)]H(1,4)] r[B(1)]H(1,2)] r[B(1)]H(1)] r[B(4)]H(4)endo] r[B(4)]H(4)exo] r[M(2)]C(2)endo] r[M(2)]C(2)exo] 57.8(4) 45.3(3) 178.2(12) 184.4(10) 126.2(11) 142.6(11) 124.6(11) 119.4(10) 119.8(10) 119.6(10) 194.0(5) 193.8(5) 58.1(5) 44.9(7) 178.9(23) 184.3(23) 122.9(18) 140(3) 121.6(18) 116.3(17) 116.8(17) 116.5(17) 193.4(4) 193.1(4) a For definition of parameters see the text; b = bridging, t = terminal.b For atom numbering see Fig. 1. c For details of the refinements see the text. Estimated standard deviations (e.s.d.s) obtained in the leastsquares refinement are given in parentheses. both basis sets (compared to 4–5 pm in B4H10), 4–5 pm in (CH3)2AlB3H8 (cf. 5–6 pm in H2AlB3H8), ca. 3 pm in (CH3)2- GaB3H8 (cf. 4–7 pm in H2GaB3H8), and 2–3 pm in (CH3)2- InB3H8 (3 pm in H2InB3H8) for both basis sets. The distance r(B ? ? ? M) was found to vary in a similar fashion for the two series of derivatives on improving the basis set from 6-31G* to 6-311G**, resulting in a lengthening at the SCF and MP2 levels. The two exceptions were r(B ? ? ? Al) and r(B ? ? ? In) which shorten by 0.7 pm and 2.4 pm, respectively, at the SCF level.Electron correlation at the MP2 level resulted in a shortening of the r(B ? ? ? M) distance in both series of derivatives. The eVect was more pronounced in the (CH3)2- MB3H8 series, with r(B ? ? ? M) shortening by ca. 11 pm in (CH3)2B4H8 for both basis sets (cf. 4–5 pm in B4H10); 3–5 pm in (CH3)2AlB3H8 (cf. 2–4 pm in H2AlB3H8); 7.5–10.5 pm in (CH3)2GaB3H8 (cf. 3–6.5 pm in H2GaB3H8), and 9–11 pm in (CH3)2InB3H8 (7–9 pm in H2InB3H8). Bridge region.Of the three B]H bridging distances, r[B(4)]H(1,4)] was observed to be the most sensitive to changes in theoretical method, with many changes paralleling those found for the H2MB3H8 series. In particular, improving the basis set from 6-31G* to 6-311G** resulted in a lengthening of all three B]H distances in the boron, aluminium and indium compounds in the two series by about 0.5 pm at both the SCF and MP2 levels. The analogous distances in the two gallium compounds behaved diVerently to the other members on the series, with r[B(1)]H(1,2)] increasing by about 1 pm, r[B(1)] H(1,4)] shortening by about 0.3 pm, and r[B(4)]H(1,4)] lengthening by about 3 pm at both the SCF and MP2 levels.Again, this diVerence in behaviour for the gallium compounds is principally a reflection of the poor quality of the 6-31G* basis set. The introduction of electron correlation at the MP2 level showed several similarities in the two sets of derivatives with, for example, the inner bridging distances r[B(1)]H(1,4)] lengthening and r[B(1)]H(1,2)] shortening on average by 1 pm for all compounds.The most significant diVerence between the two sets of derivatives relate to the two boron compounds using both basis sets; the outer bridging distance r[B(4)]H(1,4)] shortens by almost 5 pm in (CH3)2B4H8 compared to just 1 pm Table 3 Structural trends observed in the (CH3)2MB3H8 series (M = B, Al, Ga or In) by ab initio (6-311G**/MP2) calculations (re/pm, angles in 8) M Fragment Cage Bridge Terminal Parameter a Covalent radius c Ionic radius c Mulliken charge c r[B(1)]B(3)] r[B(1)]B(4)] r[B(1) ? ? ? M(2)] Butterfly angle r[B(1)]H(1,2)] r[M(2)]H(1,2)] r[B(1)]H(1,4)] r[B(4)]H(1,4)] B(1)]H(1,2)]M(2) H(1,4) dip H(1,2) dip r[M(2)]C(2)endo] r[M(2)]C(2)exo] r[B(4)]H(4)endo] r[B(4)]H(4)exo] r[B(1)]H(1)] C(2)endo]M(2)]C(2)exo H(4)endo]B(4)]H(4)exo B(3)]B(1)]H(1) B 88 — 10.2 173.5 185.3 189.9 120.8 124.1 145.4 125.8 141.8 89.2 10.6 11.0 160.3 159.3 119.4 119.0 118.4 119.0 118.7 114.3 Al 125 68 11.0 178.2 184.5 230.4 119.2 124.0 182.5 125.6 141.9 95.6 1.5 13.4 195.3 195.1 119.4 119.2 118.8 128.6 118.6 112.1 Ga 125 76 10.7 178.6 184.1 232.6 119.6 124.4 185.0 125.6 142.2 95.5 0.2 13.2 195.6 195.3 119.5 119.3 118.8 132.4 118.4 111.6 In b 140 94 11.3 179.7 183.5 256.3 120.2 124.4 205.2 125.7 142.4 99.1 3.3 15.4 217.2 216.9 119.6 119.4 119.0 137.2 118.3 111.1 a For definition of parameters see the text.b For In basis set used see the text.c Ref. 11.2158 J. Chem. Soc., Dalton Trans., 1998, Pages 2155–2162 in B4H10. In contrast, the r[B(4)]H(1,4)] distance shortens by 1–2 pm in the aluminium and gallium compounds in both series of derivatives and by ca. 3 pm in the two indium compounds on improving the level of theory from SCF to MP2 using 6-31G* or 6-311G** basis sets. The M]H bridging distance in the two derivative sets was also found to behave in a similar fashion, with r[Al(2)]H(1,2)] shortening by about 0.5 pm, r[Ga(2)]H(1,2)] shortening by an average of 5 pm, and r[In(2)]H(1,2)] shortening by about 1 pm on improvement of the basis set at both levels of theory.Electron correlation results in a change of less than 1 pm in r[M(2)] H(1,2)] (M = Al, Ga or In) irrespective of the basis set. Terminal region. The B]H terminal distances in all eight compounds were found to be largely insensitive to change, with all distances varying on average by less than 0.5 pm with improvements in basis set and less than 1 pm for improvements in the level of theory.Similarly the M]C distances were found to vary by no more than 0.6 pm for basis set improvement and less than 1 pm (M = B or Al) or 2 pm (M = Ga or In) with electron correlation. (b) Gas-phase electron diVraction (GED) In the original refinements of (CH3)2AlB3H8 and (CH3)2- GaB3H8 several structural assumptions had to be made since the amount of information that can be derived solely from the GED data is somewhat limited.3 In particular, the B]B, M]C and M]Hb distances, being of similar length, are all subject to strong correlation, and locating the hydrogen atoms is a particularly diYcult task as the heavy atoms dominate the molecular scattering.The following assumptions had to be made: (a) several parameters were fixed at values derived from the original B4H10 study,12 i.e. the two B]B distances, the angles B(3)]B(1)]H(1) and H(4)endo]B(4)]H(4)exo, the diVerence between the outer B(4)]H(1,4) and inner B(4)]H(1,4) bridging distances, and finally the diVerence between r[B(1)]H(1)] and the average B(4)]H(4)endo/exo distance; (b) the diVerence between the two inner B]Hb distances was set at zero; (c) the bridging hydrogen atoms were taken to lie in the heavy-atom planes B(1)]M(2)]B(3) and B(1)]B(4)]B(3); and finally (d) as no force field was available, vibrational amplitudes were fixed at values in line with those determined for the related molecules B4H10 11 and (CH3)2MBH4 (M = Al or Ga).13 In the earlier study 3 nine or ten of the seventeen geometric parameters used to describe the structures were successfully refined, along with three or four vibrational amplitudes.Final RG values recorded were 0.159 for (CH3)2AlB3H8 and 0.139 for (CH3)2GaB3H8. The structures deduced were largely in accord with those of similar compounds. However, with almost half of the geometric parameters fixed at assumed values, several severe structural assumptions made and the adoption of a very crude approximation concerning vibrational eVects, the quality of the original refinements was necessarily limited. As the SARACEN method allows the refinement of all geometric parameters and removes the need to make any structural assumptions in the GED model, a more flexible model can now be used, leading to much more reliable and realistic structures.In addition, the determination of reliable harmonic force fields by ab initio calculations removes the earlier assumptions concerning the eVects of vibration on the molecular structures.(CH3)2AlB3H8. The results obtained in the new refinement of the structure of (CH3)2AlB3H8 are given in Table 2. The radialdistribution curve [shown in Fig. 2(a)] is composed mainly of four peaks, with distances r[B(1) ? ? ? Al(2)], r[Al(2)]C(2)endo/exo], r[B(1)]B(2)] and r[B(1)]B(3)] forming the dominant features. The parameters p1 (the average B]B distance), p3 [rB(1) ? ? ? Al(2)], p5 (the average B]H distance), p11 (the average Al] Cendo/exo distance) could all be refined freely, together with p13 [r(C]H)] and p19 (Al]C]H) which, with multiplicities of six, would be expected to be well defined by the GED data.In addition, the angles C(2)endo]M(2)]C(2)exo (p15), MC2 tilt (p17) and the butterfly angle (p20) could also be refined to realistic values with reliable e.s.d.s. The remaining thirteen geometric parameters could be refined successfully only with the aid of flexible restraints (documented in Table 4) in accordance with the SARACEN method.§,¶ Four amplitudes of vibration, corresponding to distances u13[B(1) ? ? ? Al(2)], u17[B(1) ? ? ? C(2)endo], u18[B(1) ? ? ? C(2)exo] and u21[B(4) ? ? ? Al(2)] could be refined.With the inclusion of twelve vibrational amplitude restraints (given in Table 5), a further seventeen vibrational amplitudes yielded to refinement (see Table 6).Thus, all the amplitudes associated with distances contributing greater than 10% weighting of the most intense Fig. 2 Observed and final diVerence radial-distribution curves for (a) (CH3)2AlB3H8 and (b) (CH3)2GaB3H8. Before Fourier inversion the data were multiplied by s?exp[(20.000 02s2)/(ZM 2 fM)(ZB 2 fB)] (M = Al or Ga) § Each geometric restraint has a value and an uncertainty derived from the graded series of ab initio calculations. Absolute values are taken from the highest level calculation and uncertainties are estimated from values given by lower level calculations, or based on a working knowledge of the reliability of the calculations for electronically similar molecules. ¶ As a result of the large number of basis functions required to describe (CH3)2AlB3H8 and (CH3)2GaB3H8, it was not possible to perform calculations to a high enough level to display satisfactory convergence (see SUP 57391 Tables 2 and 3).However, the large array of calculations performed on the parent compound B4H10 (see previous paper),5 shows that the heavy cage atoms are much better described at the MP2 level of electron correlation than at the SCF level. Accordingly the uncertainty of 1 pm chosen for the cage parameter diV.r(B]B) (p2) for both refinements is based on the variation revealed in the B]B cage distances of B4H10 by calculations performed at the MP2 level and above. The derivation of the remaining geometric restraints is based on results obtained from the (CH3)2AlB3H8 and (CH3)2GaB3H8 series of calculations, and is documented in Table 4.J.Chem. Soc., Dalton Trans., 1998, Pages 2155–2162 2159 Table 4 Derivation of the geometric restraints used in the SARACEN refinements of (CH3)2AlB3H8 and (CH3)2GaB3H8 (r/pm, angles in 8) Basis set/level of theory Compound (CH3)2AlB3H8 (CH3)2GaB3H8 p2 p4 p6 p7 p8 p9 p10 p12 p14 p16 p18 p21 p22 p2 p4 p6 p7 p8 p9 p10 p12 p13 p14 p15 p16 p18 p21 p22 Parameter a diV.r(B]B) r[Al(2)]H(1,2)] av. B]Hb 2 av. B]Ht diV. [r(B]Hb)] (outer 2 inner) diV. [r(B]Hb)] (inner) r[B(1)]H(1)] 2 av. r[B(4)]Ht] diV. r(B]Ht) (endo 2 exo) diV. r(Al]C) (endo 2 exo) B(3)]B(1)]H(1) H(4)endo]B(4)]H(4)exo BH2 tilt H(1,2) dip H(1,4) dip diV. r(B]B) r[Ga(2)]H(1,2)] av. r(B]Hb) 2 av. r(B]Ht) diV. [r(B]Hb)] (outer 2 inner) diV. [r(B]Hb)] (inner) r[B(1)]H(1)] 2 av. r[B(4)]Ht] diV. r(B]Ht) (endo 2 exo) diV. r(Ga]C) (endo 2 exo) r(C]H) B(3)]B(1)]H(1) C(2)endo]Ga(2)]C(2)exo H(4)endo]B(4)]H(4)exo BH2 tilt H(1,2) dip H(1,4) dip 6-31G*/ SCF 8.7 182.1 11.9 17.8 1.4 20.1 0.2 0.2 113.2 119.3 0.4 13.2 0.5 10.6 190.2 10.8 14.8 1.6 20.1 0.0 0.0 108.6 112.2 129.9 119.1 2.2 12.8 2.0 6-311G**/ SCF 9.0 181.9 12.4 18.0 0.5 20.2 0.2 0.3 113.1 119.5 20.3 12.3 0.1 7.0 186.2 12.8 19.2 20.2 20.2 0.2 0.2 108.6 112.2 131.2 119.2 20.6 12.0 0.7 6-31G*/ MP2 6.0 183.2 10.7 16.6 1.6 20.6 0.2 0.3 112.3 117.7 0.0 14.0 0.2 6.1 190.7 10.2 14.7 2.0 20.5 0.1 0.1 109.4 110.9 131.2 117.3 2.2 14.0 2.8 6-311G**/ MP2 6.3 182.5 11.4 17.1 1.6 20.5 0.2 0.2 112.1 118.6 0.8 13.4 1.5 5.5 185.0 11.6 17.2 1.2 20.6 0.3 0.3 109.4 111.6 132.4 118.4 0.6 13.2 0.2 Value used 6.3(10) 182.5(10) 11.4(10) 17.1(5) 1.6(1) 20.5(1) 0.2(1) 0.2(1) 112.1(10) 118.6(10) 0.8(10) 13.4(10) 1.5(13) 5.5(10) 185.0(50) 11.6(14) 17.2(20) 1.2(10) 20.6(1) 0.3(2) 0.3(2) 109.4(15) 111.6(10) 132.4(12) 118.4(10) 0.6(16) 13.2(12) 0.2(16) a For definition of the parameters see the text.b For method of electron correlation used for Ga see the text.Table 5 Derivation of vibration amplitude restraints for the SARACEN studies of (CH3)2AlB3H8 and (CH3)2GaB3H8 Compound (CH3)2AlB3H8 (CH3)2GaB3H8 Parameter u1[B(1)]B(3)]/u12[B(1)]B(4)] u2[B(1)]H(1)] u3[B(1)]H(1,4)] u4[B(1)]H(1,2)] u5[B(4)]H(1,4)] u8[Al]C(2)endo]/u9[Al]C(2)exo] u10[Al]H(1,2)] u14[Al ? ? ? H(methyl)endo]/u15[Al ? ? ? H(methyl)exo] u16[C(2)endo]C(2)exo] u19[Al]H(1,4)]/u20[Al]H(1)] u22[B(4) ? ? ? C(2)endo] u23[B(4) ? ? ? C(2)exo] u1[B(1)]B(3)] u8[Ga(2)]C(2)endo]/u9[Ga(2)]C(2)exo] u12[B(1)]B(4)] u10[Ga(2)]H(1,2)] u14[Ga]H(methyl)endo]/u15[Ga]H(methyl)exo] u16[B(1)]C(2)endo]/u17[B(1)]C(2)exo] u18[Ga(2) ? ? ? H(1,4)] u19[Ga(2) ? ? ? H(1)] Value a 0.83 8.2 9.1 9.1 12.9 1.0 12.6 1.0 11.0 0.96 12.9 21.8 6.8 1.00 8.6 14.8 1.0 1.00 14.0 15.0 Uncertainty b 0.04 0.82 0.91 0.91 1.29 0.05 1.26 0.05 1.1 0.05 1.29 2.2 0.68 0.05 0.86 1.48 0.05 0.05 1.4 1.5 a Values for amplitude restraints calculated from 6-31G*/SCF force field.b Uncertainties are 5% of amplitude ratio, 10% of absolute values. feature in the radial-distribution curve were determined. Values for the amplitude restraints were calculated directly from the scaled 6-31G*/SCF force field, with uncertainty ranges of 5% adopted for amplitude ratios or 10% for absolute values. Direct amplitude restraints were found to be necessary in the case of u2[B(1)]H(1)], u3[B(1)]H(1,4)] and u4[B(1)]H(1,2)] as the normal practice of restraining ratios resulted in the return of unrealistic vibrational amplitude values in the least-squares refinement as a result of the high correlation eVects.Cage structure. The three cage distances r[B(1)]B(3)], r[B(1)]B(4)] and r[B(1) ? ? ? Al(2)] refined to final values of 178.2(12), 184.4(10) and 231.6(7) pm, respectively, compared with their 6-311G**/MP2 ab initio values of 178.2, 184.5 and 230.4 pm. The butterfly angle (p20) refined to 123.8(20)8, compared with its ab initio value of 119.28.Bridge region. The four bridging distances r[B(1)]H(1,4)], r[B(4)]H(1,4)], r[B(1)]H(1,2)] and r[Al(2)]H(1,2)] refined to 126.2(11), 142.6(11), 124.6(11) and 182.5(13) pm, respectively, in agreement with their 6-311G**/MP2 ab initio values to within one standard deviation. Terminal region. The three terminal B]H distances, r[B(1)] H(1)], r[B(4)]H(4)endo] and r[B(4)]H(4)exo], refined to 119.4(10), 119.8(10) and 119.6(10) pm, respectively, in agreement with their respective 6-311G**/MP2 ab initio values to within one2160 J.Chem. Soc., Dalton Trans., 1998, Pages 2155–2162 standard deviation. The final two terminal distances, r[Al]Cendo] and r[Al]Cexo], at 194.0(5) and 193.8(5) pm, are slightly shorter than their predicted ab initio values of 195.3 and 195.1 pm. Of the six angles required to define the locations of the terminal atoms four parameters (p14, p16, p18 and p19) all refined to values within one standard deviation of their ab initio values. Angle C(2)endo]Al(2)]C(2)exo (p15) refined to 132.0(23)8, within two e.s.d.s of its ab initio value of 128.68, and the AlC2 tilt angle (p17) refined to 27.1(4)8, compared with its ab initio value of 24.68, the negative value indicating a tilt out of the heavy atom cage.(CH3)2GaB3H8. The results obtained for the new refinement of the structure of (CH3)2GaB3H8 are also given in Table 2. The radial-distribution curve [given in Fig. 2(b)] shows many similarities to that characterising (CH3)2AlB3H8 [see Fig. 2(a)] resulting from the similarities in molecular structure. The main diVerence between the two curves relates to the relative contributions from distances associated with gallium compared with aluminium. With an atomic number more than twice that of aluminium, gallium contributes much more to the molecular scattering through the atom pairs it forms, and contributions from other atom pairs necessarily give rise to less structural information.Consequently, only seven of the twenty-two geometric parameters in (CH3)2GaB3H8 could be refined freely {viz. p1 av. r(B]B), p3 r[B(1) ? ? ? Ga(2)], p5 av. r(B]H), p11 av. r(Ga]Cendo/exo), p17 GaC2 tilt and p19 H]C]Ga}, compared with nine for (CH3)2AlB3H8. The derivation of the fifteen geometric restraints required to allow all the geometric parameters to refine is given in Table 4. Values adopted for the restraints were derived in the same way as for the aluminium analogue, with p2 [diV.r(B]B)] based on the large array of calculations performed on the parent compound B4H10.5 In addition, three amplitudes of vibration, u13[B(1) ? ? ? Ga(2)], u15[B(1) ? ? ? C(2)endo] and u16[B(1) ? ? ? C(2)exo], could be refined freely. A further nine were successfully refined with the inclusion of eight amplitude restraints (given in Table 5), resulting in the refinement of all amplitudes associated with distances contributing greater than 10% weighting of the most intense feature in the radial-distribution curve (see Table 7).Table 6 Selected bond distances (ra/pm) and amplitudes of vibration (u/pm) obtained from the SARACEN refinement of (CH3)2AlB3H8 i 123456789 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Atom pair B(1)]B(3) B(1)]H(1) B(1)]H(1,4) B(1)]H(1,2) B(4)]H(1,4) B(4)]H(4)endo B(4)]H(4)exo Al(2)]C(2)endo Al(2)]C(2)exo Al(2)]H(1,2) C]H(methyl) B(1)]B(4) B(1) ? ? ? Al(2) Al ? ? ? H(methyl)endo Al ? ? ? H(methyl)exo C(2)endo ? ? ? C(2)exo B(1) ? ? ? C(2)endo B(1) ? ? ? C(2)exo Al(2) ? ? ? H(1,4) Al(2) ? ? ? H(1) B(4) ? ? ? Al(2) B(4) ? ? ? C(2)endo B(4) ? ? ? C(2)exo Distance 178.7(12) 121.8(10) 128.2(11) 126.1(12) 143.9(11) 122.1(10) 122.3(10) 194.8(5) 194.5(5) 183.0(13) 108.7(4) 185.2(10) 231.6(7) 253(7) 253(7) 355(3) 366.5(22) 340(3) 325(3) 314.6(13) 331(3) 405(3) 480.6(17) Amplitudea,b 7.2(13) 7.8(10) 9.2(11) 9.0(11) 13.0(16) 8.3 fixed 8.3 fixed 6.4(5) 6.4(5) 12.7(16) 8.0(8) 8.7(16) 9.9(5) 22(4) 22(4) 10.9(14) 9.3(21) 9(4) 6(6) 7(6) 19(9) 13.8(14) 20.5(24) a Estimated standard deviations, obtained in the least-squares refinement, are given in parentheses. b Amplitudes which could not be refined are fixed at values derived from the 6-31G*/SCF scaled force field.Cage structure. The three cage distances r[B(1)]B(3)], r[B(1)]B(4)] and r[B(1) ? ? ? Ga(2)] refined to 178.9(23), 184.3(23) and 234.2(8) pm, respectively, compared with their 6- 311G**/MP2 ab initio values of 178.6, 184.1 and 232.6 pm.The small standard deviation for r[B(1) ? ? ? Ga(2)] reflects the dominant electron scattering properties of the gallium and boron atoms. The butterfly angle (p20) refined to 119.8(13)8, compared with its ab initio value of 119.68. Bridge region. The four bridging distances, r[B(1)]H(1,4)], r[B(4)]H(1,4)], r[B(1)]H(1,2)] and r[Ga(2)]H(1,2)], refined to 122.9(18), 140(3), 121.6(18) and 186(6) pm, respectively, in agreement with their 6-311G**/MP2 ab initio values to within one or two standard deviations.The distance Ga(2)]H(1,2), with a standard deviation of 6 pm, was found to be poorly defined by the GED data as a result of its closeness to the B]B distances. In the derivation of the restraint for this parameter [185(5) pm] it was necessary to stipulate a large uncertainty to allow for the significant variation that occurs in this bond length with improvements in basis set and level of theory (see Table 4).Although the restraint is very flexible, it enabled the Ga(2)]H(1,2) distance to be determined with much greater confidence than was possible using the GED data alone. Terminal region. The terminal B]H distances, r[B(1)]H(1)], r[B(4)]H(4)endo] and r[B(4)]H(4)exo], refined to 116.3(17), 116.8(17) and 116.5(17) pm, in agreement with their respective 6-311G**/MP2 ab initio values to within two standard deviations. The distances Ga]Cendo and Ga]Cexo [like r(Al]Cendo) and r(Al]Cexo) in (CH3)2AlB3H8] refined to values slightly shorter than their predicted ab initio values [193.4(4) and 193.1(4) pm by GED, 195.6 and 195.3 pm ab initio].Four of the six angles required to define the locations of the terminal atoms, p14–16 and p18, refined to values within one standard deviation of their 6-311G**/MP2 ab initio values. Parameters p17, MC2 tilt, and p19, H]C]Ga, refined freely to values of 24.7(23)8 and 108.6(10)8, compared with their ab initio values of 24.88 and 110.68.The RG factors recorded for these refinements were 0.081 [(CH3)2AlB3H8] and 0.111 [(CH3)2GaB3H8], the slightly high values being attributable to the rather high noise levels in the GED data resulting from fogging of the photographic plates by the (CH3)2MB3H8 vapours. With all twenty-two geometric parameters and all significant vibrational amplitudes refining, the structures are the best that can be obtained using all avail- Table 7 Selected bond distances (ra/pm) and amplitudes of vibration (u/pm) obtained from the SARACEN refinement of (CH3)2GaB3H8 i 123456789 10 11 12 13 14 15 16 17 18 19 20 Atom pair B(1)]B(3) B(1)]H(1) B(1)]H(1,4) B(1)]H(1,2) B(4)]H(1,4) B(4)]H(4)endo B(4)]H(4)exo Ga]C(2)endo Ga]C(2)exo Ga]H(1,2) C]H(methyl) B(1)]B(4) B(1) ? ? ? Ga Ga ? ? ? H(methyl)endo Ga ? ? ? H(methyl)exo B(1) ? ? ? C(2)endo B(1) ? ? ? C(2)exo Ga ? ? ? H(1,4) Ga ? ? ? H(1) B(4) ? ? ? Ga Distance 179.4(23) 118.5(17) 124.5(18) 123.7(19) 140(3) 119.4(17) 118.7(17) 194.1(4) 193.9(4) 186(6) 112.4(9) 185(23) 234.4(8) 253(7) 253(7) 364(5) 346(5) 321(3) 316.1(18) 328.0(15) Amplitudea,b 6.7(9) 8.3 fixed 9.0 fixed 9.2 fixed 13.9 fixed 8.3 fixed 8.3 fixed 5.9(7) 5.8(7) 15.3(19) 7.6 fixed 8.5(11) 7.5(9) 11(3) 11(3) 11(5) 12(6) 13.6(19) 14.6(20) 9.3(20) a Estimated standard deviations, obtained in the least-squares refinement, are given in parentheses. b Amplitudes which could not be refined are fixed at values derived from the 6-31G*/SCF scaled force field.J.Chem. Soc., Dalton Trans., 1998, Pages 2155–2162 2161 able data, both experimental and theoretical, and all standard deviations should be reliable estimates, free from systematic errors resulting from limitations of the model. A selection of bond distances (ra) and vibrational amplitudes (u) for (CH3)2- AlB3H8 and (CH3)2GaB3H8 are given in Tables 6 and 7, respectively. Cartesian coordinates and final least-squares covariance matrices can be found in SUP 57391.The final radialdistribution curves and combined molecular scattering curves are shown in Figs. 2 and 3, respectively. (c) Structural trends within the series (CH3)2MB3H8 predicted ab initio: the eVects of changing M The main structural changes predicted by the 6-311G**/MP2 ab initio calculations for the series of dimethyltetraborane(10) derivatives (CH3)2MB3H8 (M = B, Al, Ga or In) are given in Table 3. Many of the trends observed with this series parallel those found in the hydride series reported earlier, and can be summarised as follows.Changes in M]B/H distances. As with the hydride derivatives, 5 the increasing values of r[B(1) ? ? ? M(2)], r[M(2)] H(1,2)], on moving from B to In can be attributed largely to the increase in atomic (or ionic) radius of the atom M (see Table 3). Thus, significant changes in these bond distances occur on replacing boron with aluminium and gallium with indium, but small changes are also observed on replacing aluminium with gallium.As noted with the hydride series, a secondary factor may be the decrease in Mulliken charge calculated ab initio for atom M (also given in Table 3). As the oxidation state approaches 11 the system can be thought of as approaching the formulation [(CH3)2M]1[B3H8]2. This dissociation will result in r[B(1) ? ? ? M(2)] and r[M(2)]H(1,2)] increasing by an amount greater than the radius of atom M.Note: with the formal charge assignment on atom M in the dimethyl series being Fig. 3 Observed and final diVerence combined molecular scattering curves for (a) (CH3)2AlB3H8 and (b) (CH3)2GaB3H8. Theoretical data were used in the s ranges for which no experimental data are available closer to 11, the two distances are 1–4 pm longer compared to the hydride series. Angles correlated with atom M. The angle C(2)endo]M(2)] C(2)exo was found to widen in a manner largely correlating with the increasing size and decrease in charge calculated for atom M.With the formal Mulliken charge assignment on atom M approaching 11 (see Table 3), the C2M unit will tend towards a linear structure. It is interesting to note that as the charge assignment is much closer to 11 in the dimethyl series than in the hydride, the angle C(2)endo]M(2)]C(2)exo is wider than H(2)endo]M(2)]H(2)exo by 1–38. The bridging angle B(1)]H(1,2)] M(2) varied in accordance with the increasing distance B(1) ? ? ? M(2).This angle was found to be ca. 18 wider in the dimethyl than in the hydride series, which can be attributed to the longer B(1) ? ? ? M(2) distance observed in the dimethyl series, as described above. Changes in the B3H8 fragment. As with the hydride series, the distance B(1)]B(3) was found to be aVected by the size of the atom M, with a significant lengthening observed when B is replaced with Al, and a further slight lengthening when In replaces Ga.The distance was found to be less than 1 pm longer in the dimethyl series. The angle B(3)]B(1)]H(1) narrowed slightly on moving from B to In, possibly due to a correlation with r[B(1)]B(3)]. As observed with the hydrides, r[B(1)]B(4)] shortened slightly across the dimethyl series, which can be attributed to a greater Mulliken charge disparity between atoms B(1) and B(4) as M = B æÆ In, resulting in the distance shortening slightly due to a simple electrostatic force. The same general trend was observed in both sets of derivatives for the positions of the bridging hydrogen atoms above the BBB/M plane [the H(1,2) and H(1,4) dip angles], with a greater elevation of the bridging atoms above the B(1)]M(2)] B(3) plane [H(1,2) dip] than above the B(1)]B(4)]B(3) plane [H(1,4) dip].This observation was accounted for in the hydride series by the tilting of the wing units. In the dimethyl series the MC2 unit tilts || out of the cage by 58 (cf. hydride MH2 38) and the BH2 unit tilts into the cage by 18 (M = Al æÆ In), in accordance with the hydride series.Thus H(1,2) dip would be expected to be more pronounced in the dimethyl derivatives, and H(1,4) would be expected to be about the same for both sets of compounds. This was indeed found to be the case, with H(1,2) raised ca. 138 above the B(1)]M(2)]B(3) plane in the aluminium and gallium compounds (cf. ca. 10.58 in H2AlB3H8 and H2GaB3H8), rising to 158 in (CH3)2InB3H8 (cf. 148 in H2InB3H8).The variation in H(1,2) dip angles observed across the series can probably be attributed to the increase in size of atom M, with H(1,2) forced higher above the B(1)]M(2)]B(3) plane to relieve steric strain. The H(1,4) dip angle was found to be consistent in each series, with the only significant discrepancy of 10.68 in (CH3)2B4H8 vs. 8.48 in B4H10 explained by a H2B exo tilt of 24.48 in the former, compared with 22.48 in the latter, resulting in the higher elevation of the H(1,4) [and H(3,4)] atom in (CH3)2B4H8. Once again, the ab initio value obtained for the H(1,4) dip angle in (CH3)2GaB3H8, at just 0.28, appears to be anomalous compared with the rest of the series. However, a close scrutiny of the complete range of ab initio calculations carried out (see SUP 57391 Table 3) indicates a significant variation in this parameter from 0.2 to 2.88 which can be attributed mainly to improvements in basis set.An uncertainty of about 38 in the 6-311G**/MP2 value of 0.28 would make this parameter more consistent with the results obtained for the other members of the series.Distances and angles unchanged by atom M. The distances B(1)]H(1,4), B(4)]H(1,4) and B(1)]H(1,2) and angle H(4)endo] B(4)]H(4)exo an the butterfly angle were largely unaVected by || Wing tilts as described in GED model.2162 J. Chem. Soc., Dalton Trans., 1998, Pages 2155–2162 the identity of atom M. With reference to the corresponding hydrides, the butterfly angle for (CH3)2MB3H8 was found to be wider by ca. 48 when M = B, 38 when M = Al or Ga, and 18 when M = In. This widening can probably be attributed to reducing steric strain between the (CH3)endo group and H(4)endo. The eVect is dominant in the earlier members of the series where the distance between the two groups is smaller, resulting in a larger opening of the cage to accommodate the (CH3)endo group. (d) (CH3)2InB3H8: comparison of ab initio and X-ray diVraction molecular structures The final aspect of this work involved drawing a comparison between the molecular structure of (CH3)2InB3H8 deduced by ab initio calculations and the structure determined by X-ray diVraction (see Table 8).4 Ab initio calculations determine the molecular structure of one discrete molecule which, in the absence of GED or any other experimental structural results for the gaseous molecule, represents the closest approach to the gas-phase structure that can be achieved at the present time.A direct comparison of the geometric parameters obtained ab initio with those determined by X-ray diVraction of a single crystal is therefore expected to identify diVerences between the gas- and solid-phase structures. A word of caution should be entered, however, in making this type of comparison. DiVerences in molecular structure are to be expected as a consequence of the fundamental diVerences in the two techniques. Firstly, the definition of bond length is diVerent: ab initio methods calculate the diVerence between the positions of atomic nuclei whilst X-ray diVraction measures the diVerence between centres of electron density.Secondly, the ab initio geometry is a static, vibration-free equilibrium structure; the crystal structure, measured at 150 K,4 is subject to vibrational and librational averaging eVects. For these reasons only fairly gross structural diVerences between the two sets of results have been considered significant.The main structural diVerences, X-ray vs. ab initio, were found to centre around the indium atom, with (i) r[B(1) ? ? ? In(2)] approximately 20 pm longer, (ii) the internal cage angle H(1,2)]In(2)]H(2,3) approximately 158 narrower, and (iii) C(2)endo] In(2)]C(2)exo approximately 208 wider in the solid phase compared with the discrete structure calculated ab initio. Table 8 Comparison of some geometrical parameters for (CH3)2- InB3H8 (r/pm, angles in 8) Fragment Cage Bridge Terminal Parameter r[B(1)]B(3)] r[B(1)]B(4)] r[B(1) ? ? ? In(2)] Butterfly angle r[B(1)]H(1,4)] r[B(4)]H(1,4)] r[B(1)]H(1,2)] r[In(2)]H(1,2)] H(1,2) dip H(1,4) dip H(1,2)]In(2)]H(2,3) r[In(2)]C(2)endo] r[In(2)]C(2)exo] C(2)endo]In(2)]C(2)exo Ab initio 179.7 183.5 256.3 120.2 125.7 142.4 124.4 205.2 15.4 3.3 95.5 217.2 216.9 137.2 X-Ray diVraction (averaged values) a 178.4(8) 180.5(10) 274.4(11) 124(2) 115(4) 140(7) 112(5) 224(11) 14(3) 3(1) 81(2) 210.6(1) 210.5(1) 158.0(1) a See ref. 4. Two molecules, of C1 symmetry were located in the asymmetric unit. Parameters are averaged to Cs symmetry for direct comparison with the ab initio structure, and uncertainties are quoted to 1 s. The explanation for these structural diVerences is evident upon closer examination of the crystal structure: two neighbouring molecules interact with the indium centre through hydrogen H(1) atoms, eVectively increasing the co-ordination number of the indium centre from four to six.As a result of this change in co-ordination H(1,2)]In(2)]H(2,3) will narrow, r[B(1) ? ? ? In(2)] will lengthen to maintain the r[B(1)]B(3)] distance, and C(2)endo]In(2)]C(2)exo will widen to force the two methyl groups apart and thereby accommodate the two new co-ordinating species. In short, the changes reflect the greater ionic character of the compound in the crystal structure compared to that calculated, and the increased metallic character of the heavier Group 13 elements.Indium is characterised by adopting a high coordination number (typically six), and by forming solids with potential anionic partners manifesting increased ionic character. Acknowledgements We thank the EPSRC for the financial support of the Edinburgh Electron DiVraction Service (grant GR/K44411) and the Edinburgh ab initio facilities (grant GR/K04194). We also thank Drs. Simon Aldridge, John Dain and Simon Parsons for the parts they played in the experimental characterisation of the compounds (CH3)2MB3H8 (M = Al, Ga or In); and Dr. Lise Hedberg (Oregon State University) for providing us with a copy of the ASYM40 program. We are grateful to the Rutherford Laboratory for their generous allocation of time on the DEC Alpha 8400/300 workstation. Finally, we thank the University of Edinburgh for funding a research studentship for C. A. Morrison. References 1 A. J. Blake, P. T. Brain, H. McNab, J. Miller, C. A. Morrison, S. Parsons, D. W. H. Rankin, H. E. Robertson and B. A. Smart, J. Phys. Chem., 1996, 100, 12 280. 2 P. T. Brain, C. A. Morrison, S. Parsons and D. W. H. Rankin, J. Chem. Soc., Dalton Trans., 1996, 4589. 3 C. J. Dain, A. J. Downs and D. W. H. Rankin, J. Chem. Soc., Dalton Trans., 1981, 2465. 4 S. Aldridge, A. J. Downs and S. Parsons, Chem. Commun., 1996, 2055. 5 C. A. Morrison, B. A. Smart, P. T. Brain, C. R. Pulham, D. W. H. Rankin and A. J. Downs, preceding paper. 6 M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A. Petersson, J. A. Montogomery, K. Raghavachari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts, R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-Gordon, C. Gonzalez and J. A. Pople, GAUSSIAN 94, Revision C.2, Gaussian, Inc., Pittsburgh, PA, 1995. 7 S. Huzinaga and M. Klobukowski, J. Mol. Struct., 1988, 167, 1. 8 L. Hedberg and I. M. Mills, ASYM40 version 3.0, update of program ASYM20, J. Mol. Spectrosc., 1993, 160, 117. 9 A. S. F. Boyd, G. S. Laurenson and D. W. H. Rankin, J. Mol. Struct., 1981, 71, 113. 10 A. W. Ross, M. Fink and R. Hilderbrandt, International Tables for Crystallography, ed. A. J. C. Wilson, Kluwer, Dordrecht, Boston and London, 1992, vol. C, p. 245. 11 D. D. Ebbing, General Chemistry, ed. M. S. Wrighton, Houghton MiZin, Boston, 1987, ch. 7. 12 C. J. Dain, A. J. Downs, G. S. Laurenson and D. W. H. Rankin, J. Chem. Soc., Dalton Trans., 1981, 472. 13 M. T. Barlow, A. J. Downs, P. D. P. Thomas and D. W. H. Rankin, J. Chem. Soc., Dalton Trans., 1979, 1793. Received 24th February 1998; Paper 8/01554F

ISSN:1477-9226    

DOI:10.1039/a801554f

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2159–2169 2159 Heterobimetallic alkoxysilyl cationic complexes: investigations into the displacement of a Ï-Á2-Si,O bridge by functional phosphine ligands Joël Blin,a Pierre Braunstein,a Jean Fischer,b Guido Kickelbick,c Michael Knorr,a Xavier Morise a and Tobias Wirth a a Laboratoire de Chimie de Coordination (UMR 7513 CNRS), Université Louis Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Cédex, France b Laboratoire de Cristallochimie et de Chimie Structurale (UMR 7513 CNRS), Université Louis Pasteur, 4 rue Blaise Pascal, F-67070 Strasbourg Cédex, France c Institut für Anorganische Chemie, Technische Universität Wien, Getreidemarkt 9/153, A-1060 Wien, Austria Received 13th January 1999, Accepted 5th May 1999 The lability of the SiOÆM interaction unique to some bimetallic complexes may confer hemilabile properties to the Si(OR)3 ligand and various bifunctional phosphines P–Z have been used in order to evaluate the possible competition for co-ordination between the bridging SiOÆM interaction and P–Z chelation.Thus, treatment of the heterobimetallic complexes [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppm)MCl] (M = Pd 4 or Pt 6; dppm = Ph2PCH2PPh2) and [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppa)PdCl] 5 (dppa = Ph2PNHPPh2) with TlPF6 in the presence of P–Z aVorded the corresponding cationic compounds [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppm)M(P–Z)PF6 (M = Pd 1 or Pt 3) and [(OC)3Fe{m-Si(OMe)2(OMe)}(m-dppa)Pd(P–Z)]PF6 2 (P–Z = Ph2PC6H4(o-OMe), a P{C6H4(o-OMe)}3, b Ph2PCH2C(O)Ph, c Ph2PCH2CH]] CH2, d Ph2P(CH2)2CN, e or Ph2PCH2C(O)NPh2, f ).These complexes are stabilized by the occurrence of a Fe–Si-OÆM four-membered ring and the pre-existent SiOÆM interaction in 4–6 was not displaced by the donor function of the incoming P–Z ligand. Complexes 1b and 1f were obtained as mixtures of two isomers, the P–Z ligands acting either as monodentate or as a P,O chelate. In the latter cases formation of fiveco- ordinated palladium species is proposed.Displacement of the SiOÆPd interaction originally present in 4 was observed when the diphosphines (Ph2P)2NR (R = Me or (CH2)3Si(OEt)3) were used, since the two phosphorus atoms co-ordinate to the Pd. Surprisingly these diphosphine ligands show diVerent co-ordination modes, depending on whether dppa or dppm is used as the assembling ligand. In the former case, chelation to the Pd is observed, which leads to complex [(OC)3{(MeO)3Si}Fe(m-dppa)Pd{Ph2PN(Me)PPh2}]PF6 2g, whereas in the latter case, oligomeric entities of the type [{(OC)3{(MeO)3Si}Fe(m-dppa)Pd[Ph2PN(R)PPh2]}n][PF6]n 1g,1h (n probably equals two) were formed.The molecular structures of [PdCl(dppm-P,P9){Ph2PC6H4(o-OMe)}]PF6 g and [Pd2Cl2(m-CO)- (m-dppm)2] 10, obtained during this work, have been determined by X-ray diVraction. Introduction During the past decades both complexes containing metal silicon bonds 1 and heteronuclear clusters 2 have attracted increasing attention owing to their fundamental interest and their catalytic and physico-chemical properties.With the objective of combining the potential of these two classes of compounds, we have investigated the synthesis and the reactivity of heterobimetallic complexes bearing a SiR3 ligand.3a This led to the discovery that a Si(OMe)3 unit, which was originally only known as a terminal ligand, could bridge two metal centres.3b,c We have synthesized a series of Fe–M heterobimetallic complexes of type A (M = Pd, Pt, Rh, In, Zn, Cd, etc.), which display a m-h2-Si,O bridge between the two metal centres.The bifunctional phosphine P–Y acts as an assembling ligand and thus contributes to the stabilization of the entire molecule.4 Surprisingly, the dative OÆM interaction is usually not displaced by two-electron donor ligands such as phosphines or amines. However, it is kinetically labile as shown by variable temperature 1H NMR experiments which revealed the hemilability of the Si(OMe)3 ligand.The equivalence of the OMe groups above the coalescence temperature results from rapid rotation of the ligand about the Fe–Si axis. This behaviour may represent an interesting tool for catalytic processes where the storage of a “masked” co-ordination site plays an important role. Indeed we have observed insertion reactions under mild conditions of small molecules such as CO, isocyanides or olefins into the Pd–C or Pt–C bond of such bimetallic complexes. 5 These reactions proceed via the following pattern: opening of the SiOÆPd interaction, co-ordination of the incoming substrate, cis migration, isomerization and closing of the Fe-Si- OÆPd ring. This is depicted in Scheme 1 in the case of CO insertion into a Pd–Me bond, followed by olefin insertion into the resulting palladium–acyl bond. Repetition of these successive steps results in sequential insertion of CO and olefins (OC)3Fe Ph2P Si Y MLn O MeO MeO Me M = Pd, Pt, Rh, In, Zn, Cd, etc.A CH2PPh2 (dppm), NHPPh2 (dppa), CH2C(O)Ph, 2-pyridine, etc. Y =2160 J. Chem. Soc., Dalton Trans., 1999, 2159–2169 leading to polyketone formation.3a,5a A related mechanism has also been proposed for the dehydrogenative coupling of stannanes catalysed by Fe–Pd complexes.6 The above observations prompted us to study the behaviour of the SiOÆPd interaction in the presence of various donor ligands which may compete with it.Infrared monitoring of the reactions in Scheme 1 has evidenced the formation of intermediates in which the oxygen atom of the ketone function of the growing chain co-ordinates to the palladium centre and generates a new Pd–C–C–C–O five membered ring.5a Thus we found it of interest to investigate whether similar displacements occur when ligands containing ketone or olefin functionalities, such as phosphines Ph2PCH2C(O)Ph c and Ph2PCH2CH]] CH2 d respectively, are present in the palladium co-ordination sphere.More generally we were interested in introducing in the coordination sphere of the metal M (Pd or Pt) nucleophilic functionalities Z which could potentially form a P,Z chelate, with retention or displacement of the SiOÆPd interaction. It was hoped that such studies could provide useful information about the chelate-assisted co-ordination of unsaturated functional groups which could also mimic the behaviour of substrates during catalytic cycles.We report here investigations on the synthesis and characterization of a series of cationic heterobimetallic Fe–Pd and Fe–Pt complexes 1–3 containing the closely related assembling ligands dppm and dppa (dppm = Ph2PCH2PPh2; dppa = Ph2PNHPPh2) and the functional phosphines P–Z shown below. Results and discussion The approach used for the preparation of the target complexes 1–3 is outlined in eqn. (1). It involves treatment of the corre- Scheme 1 (OC)3Fe Ph2P (MeO)2Si PPh2 Pd O Me Me (OC)3Fe (MeO)3Si Pd O Me C (OC)3Fe (MeO)3Si Pd Me (OC)3Fe (MeO)3Si Pd C Me O O Me Ph2P PPh2 (OC)3Fe (MeO)3Si Pd Me C O Ph2P PPh2 Ph2P PPh2 Ph2P PPh2 (OC)3Fe Pd (MeO)3Si Ph2P PPh2 O Me C O + CO norbornadiene + CO n cis-migration isomerization (OC)3Fe Ph2P Si X PPh2 M O MeO MeO P Z Me 1-3 4 X = CH2, M = Pd 5 X = NH, M = Pd 6 X = CH2, M = Pt ? + P–Z (1) TlPF6, - TlCl (OC)3Fe Ph2P Si X PPh2 M O MeO MeO Me Cl PF6 – sponding neutral chloro derivatives 4–6, which contain the m-h2-Si,O bridge between the metals, with TlPF6 in the presence of the appropriate P–Z phosphine. The driving force for this reaction is the formation of insoluble TlCl.The counter ion PF6 2 is a reliable probe in 31P-{1H} NMR spectroscopy (septuplet centered at ca. d 2144, JPF = ca. 700 Hz). Note that when silver salts were used as halide abstractors secondary reactions led to decomposition products such as [Fe(CO)3(dppm-P,P9)] or [Fe(CO)3(dppa-P,P9)]. Cationic complexes displaying a Ï-Á2-Si,O bridge Complexes with EPh3 (E 5 P or As) 7,8.We first prepared cations 7 and 8 from EPh3 (E = P or As) and 4 or 6 eqn. (2), in which the Fe–Si-OÆPd four-membered ring is retained. Thus their NMR and IR data could be used for comparison with those of complexes 1–3 and help determine the structures of the latter. Complex 7a has been obtained as a red-orange powder in an analytically pure form after a CH2Cl2 solution of 4 and PPh3 was treated with TlPF6, the volatiles removed in vacuo and the residue washed with Et2O and pentane. In addition to the characteristic PF6 2 signal (septuplet at d 2143.5, 1JPF = 710 Hz), the 31P-{1H} NMR spectrum consists of three doublets of doublets, the three phosphorus atoms being coupled to each other (Table 1, Fig. 1). The signals at lower field, d 41.4 and 31.0, are assigned by comparison with 4 to the P atoms of the dppm ligand, P(Fe) and P(Pd), respectively (213JPP = 45 Hz). The signal at d 21.5 is ascribed to the PPh3 ligand (Table 1).In the 1H NMR spectrum the methoxysilyl ligand gives rise to a very broad signal centered at d 3.47 as the result of its hemilability and the successive involvement of the diVerent oxygen atoms in co-ordination to the Pd. Upon cooling to 273 K, two (OC)3Fe Ph2P Si X PPh2 M O MeO MeO P Z Me 1 X = CH2, M = Pd 2 X = NH, M = Pd 3 X = CH2, M = Pt ? + Ph2P Ph2 P O Ph Ph2P O NPh2 Ph2P CN Ph2 P N PPh2 CH3 Ph2P OMe Ph2P N PPh2 (CH2)3Si(OEt)3 P OMe a c d g f e h b 3 P–Z = (OC)3Fe Ph2P Si PPh2 M O MeO MeO EPh3 Me (OC)3Fe Ph2P Si PPh2 M O MeO MeO Me Cl 7a M = Pd, E = P3 7b M = Pd, E = As 8a M = Pt, E = P3 8b M = Pt, E = As 4 M = Pd 6 M = Pt + CH2Cl2 –40 °C to RT 1 2 (2) TlPF6, EPh3 PF6 –J.Chem. Soc., Dalton Trans., 1999, 2159–2169 2161 Table 1 Selected 31P-{1H} NMR and IR data of cationic complexes 7 and 8 and their corresponding neutral complexes 4 and 6 Chemical shifts (J/Hz) Coupling constants/Hz Complex PFe a (JP-Pt) PM b (JP-Pt) PPh3 (JP-Pt) JP1–P2 JP1–P3 JP2–P3 n& (CO)c/cm21 4 7a 7b 6 8a 8b 48.0 41.4 40.1 52.9 44.5 (37) 44.4 (40) 34.9 31.0 30.2 7.7 (4756) 6.4 (4676) 5.3 (4593) 21.5 36.5 (2806) 55 45 47 47 39 42 16 13 42 12 1985m, 1925s, 1905s 2000s, 1950m, 1930s 2004s, 1950m, 1932s 1995m, 1935s, 1910s 2000s, 1947m, 1916s 2004s, 1954m, 1925s a P atom of the dppm ligand co-ordinated to the Fe.b P atom of the dppm ligand co-ordinated to the Pd in complex 7 or Pt in 8.c Recorded in CH2Cl2. signals are observed at d 3.40 and 3.71 with relative intensities of 2 : 1 (DG‡ = 55.6 ± 1.1 kJ mol21 for a coalescence temperature of 278 K). In the IR spectrum (CH2Cl2) three n(CO) absorptions typical for a meridional arrangement of the CO ligands around the iron centre are observed at 2000s, 1950m and 1930s cm21. These values are at higher wavenumbers than those of neutral 4, indicating that in 7a the eVect of the positive charge of the complex prevails over the donor properties of the PPh3 ligand (Table 1).Complex 7b displays a similar AX pattern in the 31P-{1H} NMR spectrum and its IR characteristics are similar to those of 7a. The 1H NMR spectrum of the former, however, shows for the methoxysilyl ligand two singlets at d 3.77 and 2.89 with relative intensities of 2 : 1, the latter being assigned to the three methyl protons of the OMe group co-ordinated to the Pd. In this complex rotation of the silyl ligand about the Fe–Si axis is therefore not observed on the NMR timescale at room temperature. It is interesting to contrast this behaviour with that of 7a and this may be due to the lower donor ability of AsPh3 vs.PPh3. The platinum complexes 8 exhibit IR spectra in the n(CO) region similar to those of their palladium counterparts 7, with absorption bands being at higher wavenumbers than in the case of the parent neutral complex 6 (Table 1). In the 31P-{1H} NMR spectrum of 8a the chemical shift of PPh3 is observed at lower field than in 7a (d 36.5 vs. 21.5) whereas the JP-P coupling constants are similar in both cases, except for Jcis between the two phosphorus atoms co-ordinated to M: 12 Hz for 8a (M = Pt) vs. 42 Hz in 7a (M = Pd). The 1JP-Pt coupling constants between the diVerent P atoms and Pt are very diVerent: 4676 Hz in the case of the P atom of the dppm ligand and 2806 Hz in the case of PPh3. This should be related to the fact that the former is trans to a relatively weak ligand whereas the latter phosphine experiences the trans influence of the metal–metal bond.In the 1H NMR spectra of 8a,8b the methoxy protons of the Si(OMe)3 unit give rise to two singlets in a 1 : 2 ratio, thus showing the Fig. 1 The 31P-{1H} NMR spectrum of the cation in complex 7a. rigidity of this ligand on the NMR timescale, as already observed for 6.3b Dppm–Fe–Pd and Fe–Pt complexes 1a and 3a with P–Z 5 Ph2PC6H4(o-OMe). We have been interested in preparing complexes 1a and 3a from Ph2PC6H4(o-OMe), since the methoxy donor function thus introduced in the co-ordination sphere of the palladium atom would be of a similar nature to that of the bridging alkoxysilyl ligand.Depending on whether or not the pre-existent Si–O bridge is retained, isomers a–g could be envisaged. In the case of isomer b, co-ordination of the oxygen atom of the anisyl group to the Pd or Pt would generate a five-membered ring expected to be thermodynamically more favorable than the Fe–Si–OÆPd four-membered ring retained in isomer a.Furthermore, the possibility of forming isomer g with a five-co-ordinated centre should also be considered (Scheme 2). Both the IR and NMR spectra of complex 1a show great similarities with those of 7a (see Tables 1–3). In the 31P-{1H} NMR spectrum the signal assigned to co-ordinated Ph2PC6- H4(o-OMe) occurs at d 14.7. Although it is at higher field than that of PPh3 in 7a (d 21.5), the diVerences in chemical shifts between “free” and co-ordinated ligands are similar: Dd = 127 and 130 for 7a and 1a, respectively.In the 1H NMR spectrum the four methoxy groups give rise to two signals at d 3.39 and 3.74, with relative intensities of 3 : 1. The latter is a sharp singlet, assigned to the methyl protons of the anisyl group which does not appear to chelate the Pd since the chemical shift is the same as for the free phosphine. The former signal is broad and ascribed to the three OMe groups of the silyl ligand, which appear equivalent on the NMR timescale, as the result of Scheme 2 (OC)3Fe Si M O MeO MeO P3Ph2 Me O Me (OC)3Fe (MeO)3Si M P3Ph2 O Me + + a b M = Pd, Pt Ph2P P2Ph2 1 Ph2P P2Ph2 1 (OC)3Fe Si M O MeO MeO P3Ph2 Me O Me + g Ph2P P2Ph2 12162 J.Chem. Soc., Dalton Trans., 1999, 2159–2169 the hemilabile behaviour of this ligand (see above). Variable temperature 1H NMR experiments confirmed these attributions: the signal at d 3.39, which is slightly shifted towards lower field upon cooling, splits into two signals at d 3.60 and 3.79, with relative intensities of 2 : 1, below coalescence temperature (245 K).The IR and NMR data are thus in favour of a structure for 1a similar to that of 7a and only isomer a is observed. Thus competition for co-ordination to palladium between the methoxy groups of the silyl ligand and that of the phosphine Ph2PC6H4(o-OMe) is not observed, the Fe–Si–OÆPd fourmembered ring remaining entropically favoured.Attempts to obtain suitable crystals of 1a for X-ray analysis led to the formation of decomposition products, amongst which the new cationic complex [PdCl(dppm-P,P9){Ph2PC6H4(o-OMe)}]PF6 9 and the known but not yet structurally characterized [Pd2Cl2(m-CO)(m-dppm)2] 10.7 Both these compounds have been isolated and structurally characterized (see below). The platinum complex 3a has also been prepared, from 6 and Ph2PC6H4(o-OMe), by using the method described above.Both the IR and NMR data (Tables 2 and 3), which are comparable to those of 1a and 8,8b, are consistent with this complex having a structure similar to that of 1a, with isomer a being the only one observed (Scheme 2). Note that when CO gas was passed through solutions of these complexes for 15 to 30 min the IR spectra in the n(CO) region were not modified; co-ordination of CO was not observed. This is similar to previous observations made on the neutral complexes 4–6.3 dppm Fe–Pd complex 1b with P–Z 5 P{C6H4(o-OMe)}3.In the n(CO) region the IR spectrum of complex 1b which contains the tris(o-anisyl)phosphine shows great similarities with that of 1a (Table 2). In the room temperature 31P-{1H} NMR spectrum two doublets of doublets are observed at d 40.5 (213JP1–P2 = 45 and 314JP1–P3 = 16 Hz) and 27.4 (2JP2–P3 = 37 Hz), which are ascribed to the P(Fe) and P(Pd) atoms of the dppm ligand, respectively. The signal corresponding to coordinated P{C6H4(o-OMe)}3 occurs as a very broad signal around d 0, which hardly emerges from the baseline and suggests a dynamic process.Upon cooling, a splitting of the above resonances was observed and signals corresponding to two isomers 1b and 1b9, in a 85 : 15 ratio, appeared below 263 K (Table 3, Fig. 2). Note that the 1H NMR spectrum contains complicated sets of signals, in the d 3.21–3.83 region, due to the numerous methoxy groups. More specific assignments were not attempted. We have previously reported that 213JP1–P2 values ranged from 40 to 56 Hz for bimetallic complexes stabilized by a Fe–Si- OÆM four-membered ring (M = Pd, Pt, etc.) and from 80 to 110 Hz in the absence of the latter (this has also been noticed in the present study, see below and Table 3).3,8 Thus, the observed Table 2 Selected IR data (cm21) for the cationic complexes 1 and 2a Complex n(CO), mer-Fe(CO)3 Other 1a 1b, 1b9 1c 1d 1e 1f, 1f9 1g 1h 2c 2g 3a 1995vs, 1941 (sh), 1918vs 1999vs, 1949 (sh), 1931vs b 2000vs, 1947 (sh), 1925vs 1992vs, 1944 (sh), 1918vs 2001vs, 1947 (sh), 1928vs 1992vs, 1945 (sh), 1925vs 1978vs, 1925 (sh), 1907vs 1977vs, 1924 (sh), 1908vs 2007vs, 1955 (sh), 1942vs 1977vs, 1924 (sh), 1907vs 1995vs, 1940 (sh), 1912vs 1670s c 2258wd 1659s,c 1591m,e 1555mc 1670s c a Recorded as KBr disk.b Recorded in CH2Cl2. c n(CO) vibration of the ketone/amide functionality. d n(C–N) vibration. e n(C–N) of the amide functionality. 213JP1–P2 values for the two isomers 1b (45 Hz) and 1b9 (44 Hz) are consistent with the presence of a SiOÆPd interaction in both cases.The only diVerence between the two 31P-{1H} NMR AMX spin systems concerns the chemical shifts assigned to the tris(o-anisyl)phosphine. In the case of the major isomer 1b, the Dd between “free” (d 239.5) and co-ordinated phosphine is 134.2 ppm. Since this downfield shift is in the same range as that observed for Ph2PC6H4(o-OMe) in 1a or for PPh3 in 7a, we suggest for 1b the same structure as for 1a and 7a, the tris(oanisyl) phosphine acting as a monodentate ligand eqn.(3). On the other hand, in the case of the minor isomer 1b9 the chemical shift of co-ordinated phosphine occurs at lower field than for 1b (Dd = 115.5 ppm). This suggests a diVerent co-ordination mode and a possible MeOÆPd interaction involving the phosphine ligand. Chelation of this phosphine to the Pd would generate a P–C–C–OÆPd five-membered ring, eqn. (3), which would contribute to the downfield shift observed.Thus a structure with two OÆPd interactions, involving both the phosphine and the silyl ligand, can be envisaged for 1b9. We have recently structurally characterized the bimetallic complex [(OC)3- Fe{m-Si(OMe)2(OMe)}(m-Ph2NHPPh2)Pd{C9H9NO3C(]] O)- Me}] B in which five-co-ordination of the palladium centre is achieved by dative interactions with the ketone function in the apical position of a square-based pyramid (C]] OÆPd 2.769(5) Å) and the alkoxysilyl ligand (SiOÆPd = 2.240(3) Å).5e Our structural proposal is also consistent with the fact that five- and even six-co-ordinate palladium centres have been reported and that phosphine ligands containing o-anisyl groups are commonly used as P,O chelating ligands 9 (see also below the crystal structure of 9).Although a crystal structure of complex 1b/1b9 is not available it is reasonable to assume that a species of type 1b9 best represents the static structure of this complex.Modeling studies with Chem3D (see Fig. 3) support this view and indicate that even a six-co-ordinated species might be envisaged since PdÆO distances of 2.553 and 2.825 Å are found (Fig. 3). This suggests a potential, incipient tridentate behaviour for ligand P{C6H4(o-OMe)}3. dppm and dppa Fe–Pd complexes 1c–1e and 2c. The cationic complexes 1c–1e have been obtained following the same procedure as that described above for the synthesis of 1a. On the basis of the IR and 31P-{1H} NMR data, which are given in Tables 2 and 3 respectively, it appears that the ketone or alkene (OC)3Fe Si Pd O MeO MeO P3{C6H4( o-OMe)}3 Me (OC)3Fe Si Pd O MeO MeO P3{C6H4( o-OMe)}2 Me O Me + 1b low temp.room temp + 1b' (3) Ph2P P2Ph2 1 Ph2P P2Ph2 1 PF6 – PF6 – (OC)3Fe Pd (MeO)2Si Ph2P PPh2 HN C Me O O OAc C O Me N BJ. Chem. Soc., Dalton Trans., 1999, 2159–2169 2163 Table 3 31P-{1H} NMR data (d, J/Hz) of cationic complexes a Fe M P3 P2 P1 P4 Complex P1 P2 P3 P4 213JP1 –P2 314JP1–P2 2JP2–P3 314JP1–P4 2JP2–P4 2JP3–P4 1a 1b b 1b9 b 1c 1d 1e 1f 1f9 1g 1h 2c 2g 3a 41.5 40.8 42.0 40.1 41.7 39.4 40.4 66.1 64.4 64.6 94.2 108.0 43.9 c 28.5 28.8 26.8 25.6 29.4 26.4 25.7 30.6 23.1 25.4 78.2 70.5 4.3 d 14.7 25.3 10.2 6.7 12.8 9.4 10.6 52.9 124.6 124.9 5.6 45.5 33.1 e 90.7 92.2 50.5 45 45 44 47 45 46 44 45 85 81 41 85 41 23 16 15 14 16 14 13 18 70 71 13 10 13 40 33 31 40 40 44 41 27 30 33 46 12 f 27 27 30 535 536 506 90 94 105 a In CD2Cl2; P1, P2, P3 and P4 refer to the diVerent phosphorus atoms in complexes 1 and 2.b Recorded at 243 K. c 1JP-Pt not observed. d 1JP-Pt = 4747 Hz. e 1JP-Pt = 2862 Hz. f Not observed. functionality does not co-ordinate to the palladium centre, neither by displacing the Fe–Si–OÆPd four-membered ring nor by giving a five-co-ordinated species. Indeed, in both cases, the 1H NMR spectrum shows two signals for the alkoxysilyl protons in a 2 : 1 ratio, indicating the non-equivalence of the OMe groups and the persistence of the SiO bridge between the Fe and Pd.For 1c the n(C]] O) absorption of the ketone function (1670 cm21) is identical to that of the free phosphine, whereas chelation of Ph2PCH2C(O)Ph to palladium usually causes a shift towards lower wavenumbers by ca. 100 cm21.10 Similarly the phosphinonitrile Ph2PCH2CH2CN behaves as a monodentate ligand in complex 1e in which the m-h2-Si,O bridge is retained. The n(CN) vibration is observed at the same value (2258 cm21) as for the unco-ordinated phosphine.In order to evaluate the influence of chemical modifications in the assembling ligand, we have prepared the Ph2PNHPPh2 (dppa) complex 2c, from 5 and Ph2PCH2C(O)Ph. The spectroscopic data are given in Tables 2 and 3. In the 31P-{1H} NMR spectrum the two signals at lower field d 94.2 and 78.2 are assigned to the P(Fe) and P(Pd) atoms of the dppa ligand, respectively. By comparison with neutral 5, a slight upfield shift of ca. 6 ppm is noticed for these two signals, as in the dppm series (Tables 1 and 3). In the IR spectrum, the n(C]] O) absorption of the ketone is observed at 1670 cm21, as for Ph2PCH2- Fig. 2 The 31P-{1H} NMR spectra of the cation in complex 1b/1b9 at (a) 298 K, (b) 243 K in CD2Cl2. C(O)Ph. Here again, the ketone functionality in 2c does not displace the SiOÆPd interaction. dppm Complex 1f (P–Z 5 Ph2PCH2C(O)NPh2). The NMR and IR data of cation 1f which contains a amidophosphine ligand being similar to those of 1c (Tables 2 and 3), we assume that their structures are comparable.However, 1f was accompanied by a second species 1f9 (ratio 1f : 1f9 = 70 :30) which displays in the 31P NMR spectrum a set of three doublets of doublets, at lower field than those of 1f (Table 3 and Fig. 4). The main feature is the large downfield shifts, compared with 1f, observed for the signals (a) of the P atom of the dppm ligand co-ordinated to the iron centre (125.7 ppm) and (b) of Ph2PCH2C(O)NPh2 (142.3 ppm).The IR spectrum shows an additional n(C]] O) vibration at 1555 cm21, which may be assigned to an amide function co-ordinated by its O atom to the electron deficient Pd.11 The 1H NMR spectrum of the mixture 1f, 1f9 contains three signals in a 4:1:1 ratio at d 3.74, 3.58 and 3.55, respectively, for the OMe protons. This would be consistent with the presence of two isomers containing a m-h2-Si,O bridging interaction. Therefore on the basis of the spectroscopic data, we propose that in 1f9 the functional phosphine ligand Ph2PCH2C(O)NPh2 Fig. 3 Chem3D model of complex 1b9 produced by using the following parameters inspired by the structure determination of [(OC)3- Fe{m-Si(OMe)2(OMe)}(m-dppm)PdSnPh3]3c or of 9 (for Pd–P(3)): Pd– P(2) 2.19, Pd–P(3) 2.370, Pd-Fe 2.670, Pd–O(1) 2.148, Pd–O(2) 2.825, Pd–O(3) 2.553, Fe–Si 2.260, Fe–P(1) 2.200, Si–O(1) 1.685, O(1)–C 1.38, O(2)–C 1.38, O(3)–C 1.38 Å; Si–Fe–P(1) 171.0, Si–O(1)–Pd 96.7, O(1)–Pd–P 175.0, Fe–Pd–P(2) 175.0, P(2)–Pd–P(3) 93.08.2164 J.Chem. Soc., Dalton Trans., 1999, 2159–2169 chelates the Pd and aVords a five-co-ordinated species. This is supported by observations made with related, structurally characterized Fe–Pd complexes in which a ketone function acts as a fifth ligand toward the Pd.5e Clearly, the protons of the SiOMe bridge are more sensitive to the change in co-ordination at the palladium than those of the other methoxy groups which resonate at d 3.74 in both cases.The two isomers 1f, 1f9 could not be separated, perhaps owing to the existence of an equilibrium of the type (4), which would be slow on the NMR timescale since no dynamic behaviour was observed by VT NMR within the stability range of the complex (<323 K). The contrasting behaviour of Ph2PCH2C(O)Ph and Ph2PCH2- C(O)NPh2 may be due to the slightly better donor properties of the amide vs. the ketone function.11 Cationic complexes in which the Ï-Á2-Si,O bridge is displaced dppm Complexes 1g,1h (P–Z 5 Ph2PN(R)PPh2).Diphosphines such as dppm or dppa also appeared to be interesting candidates for competition with the SiOÆPd bond. However, despite numerous attempts, reactions of complex 4 with dppm or dppa in the presence of an halide abstractor led to decomposition and/or mixtures of products; the desired complexes were not detected. Reasons for these observations remain speculative although in the case of dppa its low solubility may represent a drawback. In order to circumvent this problem we have used the more soluble N-methyl derivative (Ph2P)2NMe.Preliminary observations revealed that in the absence of halide abstractor complex 4 reacted with (Ph2P)2NMe to yield decomposition products, probably owing to displacement of the Pd-bound dppm P atom by (Ph2P)2NMe. In order to prevent this pathway, 4 was first treated with TlPF6 in acetonitrile, below 273 K, to generate in situ [(OC)3- Fe{m-Si(OMe)2(OMe)}(m-dppm)Pd(NCMe)]PF6 before the phosphine was added.The latter displaced the acetonitrile ligand, which aVorded 1g as the sole product (see Scheme 3). Its 31P-{1H} NMR spectrum shows, apart from the signal due to PF6 2, four signals, two for each of the diphosphine ligands. The pattern of these signals, doublets of doublets of doublets, indicates that all the phosphorus atoms are coupled to each other (Table 3, Fig. 5). The signals at d 124.6 (P3) and 90.7 (P4) are assigned to the P atoms of ligand (Ph2P)2NMe, whereas the two signals at higher field, d 64.4 (P1) and 23.1 (P2), are ascribed to the P atoms of the bridging dppm ligand, P(Fe) and P(Pd) respectively.In comparison with complexes 1a, 1c–1f, the P(Fe) Fig. 4 The 31P-{1H} NMR spectrum of the cation in complex 1f/1f9. (OC)3Fe Ph2P Si PPh2 Pd O MeO MeO Me O NPh2 Ph2 P (OC)3Fe Ph2P Si PPh2 Pd O MeO MeO Me O NPh2 Ph2 P + 1f 1f' + (4) ? signal is shifted towards lower field by ca. 24 ppm, whereas the P(Pd) signal is shifted in the opposite direction. These observations indicate for 1g a diVerent structure. The most striking feature is the very large JP-P value of 535 Hz between P2 and P4, which indicates a trans disposition of these two atoms. In the 1H NMR spectrum the nine methoxy protons appear equivalent since a sharp singlet is observed at d 3.59. In the IR spectrum of 1g the n(CO) vibrations occur at lower wavenumbers than for 1a, 1c–1f (Table 2), thus indicating a higher electron density in the former.This would be expected if the two phosphorus atoms of ligand (Ph2P)2NMe were co-ordinated to the Pd. On the basis of these spectroscopic data, we therefore conclude that the SiOÆPd interaction has been displaced. Nevertheless, a chelating co-ordination mode for (Ph2P)2NMe, as depicted in Scheme 3, is not corroborated by the observed 31P NMR chemical shifts (d 124.6 and 90.7). In such a case, these should be high field shifted in comparison to that of unco-ordinated (Ph2P)2NMe (d 72), owing to the chelate eVect.12 The data are more in accordance with a bridging co-ordination mode of ligand (Ph2P)2NMe between two Pd, one of the P atoms (P3) being trans to the Fe–Pd bond in one bimetallic unit, the other one (P4) being trans to the P2 atom of the dppm ligand in another bimetallic unit.The exact structure of 1g could not be determined by X-ray analysis, since, as for the other cationic bimetallic complexes described above, suitable crystals could not be obtained owing to slow decomposition in solution.However, mass spectroscopy using electrospray (1g) or FAB1 (1h) techniques showed the presence of isotopic patterns consistent with dinuclear Fe–Pd monocationic and tetranuclear Fe2Pd2 dicationic species. The latter is best explained by a dimeric form for these complexes (Scheme 3). Higher nuclearity cyclic species could be envisaged but were not detected.With the combined objectives of confirming the above observations and of obtaining complexes of potential use in sol–gel processes, we have prepared complex 1h from 4 and the phosphine (Ph2P)2N{(CH2)3Si(OEt)3}, following the same procedure as for 1g. Complex 1h was obtained as a burgundyred powder. Both its IR and NMR data are similar to those of Fig. 5 The 31P-{1H} NMR spectrum of the cation in complex 1g. Scheme 3 Representations of structures discussed for complexes 1g,1h (phenyl, carbonyl and methoxy groups have been omitted for clarity).Fe P1 Si P2 Pd P4 N P3 N P4 Fe P1 Si P2 Pd P3 Fe P1 Si P2 Pd P4 N P3 Me R R Chelate Dimeric form + 2+J. Chem. Soc., Dalton Trans., 1999, 2159–2169 2165 1g (Tables 2 and 3), thus indicating a similar structure (Scheme 3). The 1H NMR spectrum shows the expected signals for the (CH2)3Si(OEt)3 moiety. dppa Complex 2g (P–Z 5 Ph2PN(Me)PPh2). For comparison, we have also prepared the dppa analogue of complex 1g from 5 and phosphine (Ph2P)2NMe.The IR spectrum of this new complex is similar to that of 1g, 1h in the n(CO) region (Table 2). In the 31P-{1H} NMR spectrum the P(Fe) and P(Pd) signals of the bridging dppa ligand appeared at lower and higher field, respectively, than for 2c (Fig. 6). Similar trends were observed between the dppm complexes 1a, 1c–1f and 1g, 1h (see above). The similarity between the 213JP1-P2 values of 81–85 Hz for 2g and 1g, 1h is noteworthy and contrasts with those for the other cationic complexes where they range from 41 to 47 Hz.This would suggest the absence of a m-h2-Si,O bridge in the former, by analogy with observations made previously with related, neutral bimetallic complexes.3,8 Interestingly, the signals assigned to co-ordinated (Ph2P)2- NMe occurred at d 45.5 (P3) and 50.5 (P4) (Fig. 6), at high field compared to that of the “free” phosphine (d 72), and thus suggest a chelating co-ordination mode for this ligand.This contrasts with the situation in 1g where the phosphine does not chelate but acts as a bridging ligand. Furthermore, for both mononuclear neutral and cationic palladium complexes in which (Ph2P)2NMe has been found to chelate the metal centre, the 31P NMR chemical shifts also occurred in the d 40–50 region.13 That the JP1-P3 and JP2-P3 values are much smaller for 2g than for 1g, 1h (Table 3) is again consistent with diVerent structures for these complexes. The trans arrangement of P2 and P4 is confirmed by the large coupling constant between these two nuclei (506 Hz).Clearly, the co-ordination mode of (Ph2P)2NMe is strongly influenced by the nature of the assembling ligand (dppm or dppa). Unfortunately, the reactions of 5 with dppa or dppm carried out for comparison did not allow isolation of any well defined complex. Crystal structures of complexes 9 and 10 X-Ray quality crystals of complexes 9 and 10 were obtained from adventitious decomposition of 1a in a CH2Cl2–toluene– hexane mixture.However, 9 was then prepared in a rational way (62% yield) by treatment of a mixture of [PdCl2(dppm- P,P9)] and Ph2PC6H4(o-OMe) with TlPF6, eqn. (5), whereas 10 is easily prepared by carbonylation of [Pd2Cl2(m-dppm)2].7 The molecular structure of the cation of complex 9 is shown in Figs. 7 and 8 and selected bond distances and angles are listed in Table 4. The Pd atom has a square planar coordination environment involving the Cl and the three P atoms.The bond distances to Pd are in the normal range. The Pd–P(3) distance of 2.372(1) Å is slightly longer than the Pd–P(1) (2.281(1) Å) and Pd–P(2) (2.262(1) Å) distances involving the P (OC)3Fe P1 N P2 Pd P4 N P3 Me H PF6 – (MeO)3Si + Ph2P Ph2P Pd Cl Cl Ph2P Ph2P Ph2P O Me Cl Pd –TlPF6, a -40 °C to RT 9 + (5) PF6 – atoms of the chelating dppm ligand. The methoxy oxygen atom is oriented towards the metal centre, almost residing in an apical position, with a Pd–P(3)–C(38) angle of 108.8(1)8 and a P(3)–C(38)–C(39)–O(1) torsion angle of 1.0(5)8. This leads to a pseudo-five-co-ordinated palladium complex, with a long range Pd ? ? ? O interaction (3.172(3) Å).Although complex 10 has been known since 1978,7 it has not been characterized by X-ray diVraction. Its molecular structure is shown in Fig. 9 and belongs to the expected “A frame” type 15 in which the two palladium centres are held together by mutually trans dppm ligands and share a common carbonyl ligand.Selected bond angles and distances are given in Table 4 and lie within the range of those found for related systems such as [Pd2Cl2(m-CO)(dmpm)2] (dmpm = Me2PCH2PMe2),16 [Pd2Cl2(m-CO)(dam)2] (dam = Ph2AsCH2AsPh2),17 [Pd2Cl2- (m-SO)(dppm)2],17 [ Pd2{OC(O)CF3}2(m-CO)(dppm)2] 18 or [Pd2- Cl2(m-CH2)(dmpm)2].19 The Pd ? ? ? Pd separation of 3.190 Å suggests no direct metal–metal interaction. There is a slight deviation from square geometry around the almost planar Pd atoms, as shown by the P(1)–Pd(1)–P(3) and P(2)–Pd(2)–P(4) Fig. 6 The 31P-{1H} NMR spectrum of the cation in complex 2g (* denotes minor impurities). Fig. 7 An ORTEP14 view of the structure of the cation in complex 9. Thermal ellipsoids are drawn at the 50% probability level. Fig. 8 View of the palladium environment in complex 9 illustrating incipient five-co-ordination (see text).2166 J. Chem. Soc., Dalton Trans., 1999, 2159–2169 angles of 171.48(4) and 171.33(4)8, respectively.The bridging CO is symmetrically bound to the metal atoms, with bond distances Pd(1)–C(1) 1.974(4) and Pd(2)–C(1) 1.971(4) Å and bond angles Pd(1)–C(1)–O 125.27(5), Pd(2)–C(1)–O 126.79(5) and Pd(1)–C(1)–Pd(2) 107.93(5)8. The C(1)–O distance is 1.184(5) Å. The Pd–Cl distances of 2.445(1) and 2.427(1) Å are within the same range as those found in [Pd2Cl2(m-CO)- (dmpm)2] (2.444 and 2.446 Å)16 and [Pd2Cl2(m-CH2)(dmpm)2] (2.429 and 2.419 Å)19 and slightly longer than those in [Pd2Cl2(dpmMe)2] (dpmMe = Ph2PCH(Me)PPh2) (2.420 and 2.401 Å) in which the Cl atoms are trans to the Pd–Pd bond.20 Conclusion In order to study the availability of the masked co-ordination site on the palladium centre in bimetallic complexes containing a bridging m-h2-Si(OMe)3 ligand, such as 4 and 5, we have examined the behaviour of various donor functions held in proximity to the palladium centre by a phosphorus donor atom.We have found that donor functionalities such as methoxy, Fig. 9 An ORTEP view of the structure of complex 10. Thermal ellipsoids are drawn at the 30% probability level. Table 4 Selected bond distances (Å) and angles (8) for complexes 9 and 10 9 10 Pd–Cl Pd–P(1) Pd–P(2) Pd–P(3) P(1)–C(13) P(2)–C(13) C(39)–O O–C(44) Cl–Pd–P(1) Cl–Pd–P(2) Cl–Pd–P(3) P(1)–Pd–P(2) P(1)–Pd–P(3) P(2)–Pd–P(3) P(1)–C(13)–P(2) Pd–P(3)–C(38) C(38)–C(39)–O(1) C(39)–O(1)–C(44) 2.3344(8) 2.2804(7) 2.2617(7) 2.3724(7) 1.893(3) 1.835(3) 1.356(4) 1.413(5) 92.85(3) 166.18(3) 89.39(3) 73.34(3) 174.55(3) 104.34(3) 95.2(1) 108.76(3) 115.0(3) 120.3(3) Pd(1)–Cl(1) Pd(1)–C(1) Pd(1)–P(1) Pd(1)–P(3) Pd(2)–Cl(2) Pd(2)–C(1) Pd(2)–P(2) Pd(2)–P(4) C(1)–O Pd(1) ? ? ? Pd(2) Cl(1)–Pd(1)–C(1) P(1)–Pd(1)–Pd(3) Pd(1)–C(1)–O P(1)–Pd(1)–C(1) P(3)–Pd(1)–C(1) Cl(2)–Pd(2)–C(1) P(2)–Pd(2)–P(4) Pd(2)–C(1)–O P(2)–Pd(2)–C(1) P(4)–Pd(2)–C(1) Pd(1)–C(1)–Pd(2) 2.445(1) 1.974(4) 2.340(1) 2.341(1) 2.427(1) 1.971(4) 2.335(1) 2.336(1) 1.184(5) 3.190(4) 174.8(1) 171.48(4) 125.27(5) 86.5(1) 85.8(1) 178.8(1) 171.33(4) 126.79(5) 86.1(1) 87.1(1) 107.93(5) ketone, amide, olefin or nitrile, present in phosphines, do not displace the pre-existent Fe–Si–OÆPd four-membered ring. With the ligands tris(o-anisyl)phosphine and the amidophosphine Ph2PCH2C(O)NPh2, an additional interaction between an oxygen donor and palladium was evidenced, leading to incipient five- or even six-co-ordination in the case of P{C6H4- (o-OMe)}3.It is notable that the ligands (Ph2P)2NMe and (Ph2P)2- N{(CH2)3Si(OEt)3} are able to displace the SiOÆPd interaction.The nature of the resulting product depends upon the assembling ligand since with dppm these ligands assume a bridging behaviour whereas with dppa chelation is observed. These features might be related to the dppa ligand being less electron donating than dppm.4h Experimental General procedures All the reactions and manipulations were carried out under an inert atmosphere of purified nitrogen using standard Schlenk tube techniques.Nitrogen (Air liquide, R-grade) was passed through BASF R3-11 catalyst and 4 Å molecular sieves columns to remove residual oxygen and water. Solvents were dried and distilled under nitrogen before use: pentane, hexane and toluene over sodium, tetrahydrofuran and diethyl ether over sodium–benzophenone, acetonitrile and dichloromethane over calcium hydride. Elemental C, H and N analyses were performed by the Service de microanalyses du CNRS.Infrared spectra were recorded on a Bruker IFS 66 FT-IR spectrometer in the 4000–400 cm21 region and on a Bruker IFS 113V FT-IR spectrometer in the 500–90 cm21 region, 1H, 31P-{1H} and 13C- {1H} NMR spectra at 300.1, 121.5 and 75.5 MHz, respectively, on a Bruker AM300 instrument. Phosphorus chemical shifts were externally referenced to 85% H3PO4 in water with down- field chemical shifts reported as positive. Preparations The heterobimetallic complexes 4 and 63b and the ligands Ph2PCH2C(O)Ph,10 Ph2PCH2C(O)NPh2,11 (Ph2P)2NMe,21 (Ph2P)2N{(CH2)3Si(OEt)3} 22 and Ph2P(CH2)2CN23 were prepared according to published procedures. The ligand Ph2P{C6H4(o-OMe)} was obtained by treatment of Ph2PCl with MgBr{C6H4(o-OMe)} whereas P{C6H4(o-OMe)}3 was purchased from Lancaster Ltd and used without purification.[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd{Ph2P(C6H4[o- OMe])}]PF6 1a. A solution of complex 4 (225 mg, 0.286 mmol) and Ph2P{C6H4(o-OMe)} (87 mg, 0.300 mmol) in 20 ml of CH2Cl2 was stirred for 5 min at room temperature.It was then cooled to 230 8C and TlPF6 (120 mg, 0.343 mmol) added. The reaction mixture was allowed to return slowly to ambient under vigorous stirring. Meanwhile the initial orange colour turned dark red and TlCl precipitated. After filtration over a Celite pad, the solvent was removed under reduced pressure. The residue was washed with diethyl ether (2 × 20 ml) and pentane (2 × 20 ml) and then vacuum dried.Complex 1a was obtained as a red powder in 71% yield (240 mg) (Found: C, 50.64; H, 4.10. C50H48F6FeO7P4PdSi requires C, 50.50; H, 4.07%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.39 (s, 9 H, Si(OMe)3), 3.74 (s, 3 H, OMe phosphine), 4.33 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.5–7.5 (m, 34 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd{P(C6H4[o- OMe])3}]PF6 1b and 1b9. Treatment of complex 4 (100 mg, 0.13 mmol) with P{C6H4(o-OMe)}3 (50 mg, 0.14 mmol) and TlPF6 (52 mg, 0.15 mmol), according to the procedure described for 1a, aVorded a red powder, in 81% yield (132 mg) consisting of a mixture of 1b and 1b9 (see text) (Found: C, 47.96; H, 4.16.C52H42F6FeO9P4PdSi?CH2Cl2 requires C, 47.72;J. Chem. Soc., Dalton Trans., 1999, 2159–2169 2167 H, 4.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.21, 3.25, 3.40, 3.60, 3.75 and 3.83 (18 H, OMe), 4.15 (broad, 2 H, PCH2P) and 6.4–8.1 (m, 32 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd{Ph2PCH2C(O)- Ph}]PF6 1c.Complex 1c was prepared as described for 1a from 500 mg of 4 (0.635 mmol), 195 mg of Ph2PCH2C(O)Ph (0.640 mmol) and 250 mg of TlPF6 (0.716 mmol). It was obtained as a red-orange powder in 78% yield (595 mg) (Found: C, 51.11; H, 4.08. C51H48F6FeO7P4PdSi requires C, 51.00; H, 4.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.45 (s, 6 H, Si(OMe)2), 3.55 (d, 2 H, PCH2C(O), 2JPH = 11), 3.73 (s, 3 H, MeOÆPd), 4.26 (t, 2 H, PCH2P, 2JPH = 10 Hz) and 6.5–7.9 (m, 35 H, aromatics).[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(Ph2PCH2CH]] CH2)]PF6 1d. Complex 1d was prepared as described for 1a from 250 mg of 4 (0.317 mmol), 75 mg of Ph2PCH2CH]] CH2 (0.33 mmol) and 130 mg of TlPF6 (0.37 mmol). It was obtained as a burgundy-red powder in 75% yield (268 mg) (Found: C, 49.67; H, 4.02. C46H47F6FeO6P4PdSi requires C, 49.15; H, 4.21%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.56 (dd, 2 H, PCH2C, 2JPH = 8 or 6, 3JHH = 6 or 8 Hz), 3.50 (s, 3 H, MeOÆPd), 3.58 (s, 6 H, Si(OMe)2), 4.25 (t, 2 H, PCH2P, 2JPH = 11), 4.99 (dd, 1 H, CH]] CHAHB, 3JHHtrans = 18, 2JHAHB = 2.5), 5.16 (dd, 1 H, CH]] CHAHB, 3JHHcis = 11, 2JHAHB = 2.5 Hz), 5.63 (m, 1 H, CH]] ) and 6.8–7.8 (m, 30 H, aromatics).[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(Ph2PCH2CH2- CN)]PF6 1e. This complex was prepared as described for 1a from 250 mg of 4 (0.317 mmol), 79 mg of Ph2PCH2CH2CN (0.33 mmol) and 130 mg of TlPF6 (0.37 mmol). It was obtained as a red powder in 85% yield (320 mg) (Found: C, 48.91; H, 4.12; N 1.49.C46H45F6FeNO6P4PdSi requires C, 48.63; H, 3.99; N, 1.23%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 1.62 (m, 2 H, PCH2), 2.08 (m, 2 H, PCH2CH2), 3.49 (s, 6 H, Si(OMe)2), 3.57 (s, 3 H, MeOÆPd), 4.36 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 7.0–7.7 (m, 30 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)(Ï-dppm)Pd{Ph2PCH2C(O)- NPh2}]PF6 1f and 1f9. Treatment of 300 mg of complex 4 (0.38 mmol) with 154 mg of Ph2PCH2C(O)NPh2 (0.39 mmol) and 140 mg of TlPF6 (0.40 mmol), according to the procedure described for 1a, aVorded a red powder in 72% yield (353 mg) consisting of a mixture of 1f and 1f9 (see text) (Found: C, 53.14; H, 4.46; N, 1.23.C57H54F6FeNO7P4PdSi requires C, 52.94; H, 4.21; N, 1.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.45 (d, PCH2C(O), 2JPH = 7), 3.55 (s, OMe), 3.58 (s, OMe), 3.74 (s, OMe), 3.95 (t, PCH2P, 2JPH = 10), 4.08 (d, PCH2C(O), 2JPH = 10), 4.27 (t, PCH2P, 2JPH = 12 Hz) and 6.6–7.7 (m, 35 H, aromatics). [(OC)3{(MeO)3Si}Fe(Ï-dppm)Pd{Ph2PN(Me)PPh2}]n[PF6]m 1g.A solution of complex 4 (150 mg, 0.19 mmol) in 20 ml of MeCN was cooled to 240 8C and TlPF6 (70 mg, 0.20 mmol) added. The resulting suspension was stirred for 1 h while the temperature was maintained below 230 8C. Then solid (Ph2P)2NMe (80 mg, 0.20 mmol) was added, the temperature was allowed to warm to ambient and the mixture further stirred for 14 h. The initial orange-red colour turned dark red and TlCl precipitated. After filtration over a Celite pad, the solvent was removed under reduced pressure and the residue extracted with CH2Cl2.The filtrate was dried in vacuo, aVording a redbrown sticky material which was washed with diethyl ether (10 ml) and pentane (2 × 10 ml) and then vacuum dried. Complex 1g was obtained as a red-brown powder in 58% yield (143 mg) (Found: C, 49.50; H, 4.09; N, 1.27. C56H54F6FeNO6P5PdSi? CH2Cl2 requires C, 49.89; H, 4.20; N, 1.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.47 (s, 3 H, NMe), 3.59 (s, 9 H, Si(OMe)3), 3.74 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.6–7.9 (m, 40 H, aromatics).Mass spectrum (electrospray, acetonitrile, 40 V): m/z 1066.0 (M1 2 PF6 2 3CO, 100), 705.8 [2(M1) 2 2PF6 2 dppaMe 2 2Ph 2 5MeO 2 Me, 50] and 698.3 [2(M1) 2 2PF6 2 dppaMe 2 2Ph 2 5MeO 2 2Me, 27%]. [(OC)3{(MeO)3Si}Fe(Ï-dppm)Pd{Ph2PN(R)PPh2}]n[PF6]m 1h (R 5 (CH2)3Si(OEt)3). Complex 1h was obtained as described for 1g from 4 (102 mg, 0.13 mmol), (Ph2P)2N{(CH2)3Si(OEt)3} (77 mg, 0.13 mmol) and TlPF6 (49 mg, 0.14 mmol) as a burgundy-red powder in 58% yield (143 mg) (Found: C, 52.12; H, 5.20; N, 0.82.C64H72F6FeNO9P5PdSi requires C, 51.71; H, 4.88; N, 0.94%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 0.11 (m, 2 H, SiCH2), 0.93 (t, 9 H, 3JHH = 6 Hz, OCH2CH3), 1.12 (m, 2 H, SiCH2CH2), 2.82 (m, 2 H, NCH2), 3.43 (m, 15 H, Si(OMe)3 and SiOCH2), 3.88 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.5–7.9 (m, 40 H, aromatics). Mass spectrum (FAB1): m/z 2142 [2(M1 2 PF6 2 2(CH2)3Si(OEt)3 2 3MeO 2 Me, 13], 1284 (M1 2 PF6 2 2CO, 30), 1256 (M1 2 PF6 2 3CO, 100), 1207 (M1 2 PF6 2 2CO 2 Ph, 85), 1135 (M1 2 PF6 2 (CH2)3- Si(OEt)3, 15), 1079 (M1 2 PF6 2 (CH2)3Si(OEt)3 2 2CO, 25), 1002 (M1 2 PF6 2 (CH2)3Si(OEt)3 2 2CO 2 Ph, 34) and 997.7 [2(M1) 2 2PF6 2 2(CH2)3Si(OEt)3 2 3MeO 2 Me, 14%].[(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppa)Pd{Ph2PCH2C(O)- Ph}]PF6 2c. This complex was prepared as described for 1g from 100 mg of 5 (0.127 mmol), 39 mg of Ph2PCH2C(O)Ph (0.128 mmol) and 50 mg of TlPF6 (0.14 mmol).It was obtained as a red-brown powder in 76% yield (116 mg) (Found: C, 47.89; H, 3.83; N, 1.03. C50H47F6FeNO7P4PdSi?CH2Cl2 requires C, 47.59; H, 3.84; N, 1.09%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.45 (s, 6 H, Si(OMe)2), 3.65 (s, 3 H, MeOÆPd), 5.10 (broad, 1 H, NH) and 6.8–7.7 (m, 35 H, aromatics). [(OC)3{(MeO)3Si}Fe(Ï-dppa)Pd{Ph2PN(Me)PPh2}]PF6 2g. This complex was prepared as described for 1g from 100 mg of 5 (0.127 mmol), 52 mg of (Ph2P)2NMe (0.13 mmol), and 50 mg of TlPF6 (0.14 mmol).It was obtained as a red-brown powder in 66% yield (108 mg) (Found: C, 50.57; H, 4.04; N, 2.17. C55H53F6FeN2O6P5PdSi requires C, 50.92; H, 4.12; N, 2.16%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.10 (s, 3 H, NMe), 3.03 (s, 9 H, Si(OMe)3), 4.72 (broad, 1 H, NH) and 6.7–7.9 (m, 40 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pt{Ph2PC6H4(o- OMe)}]PF6 3a. This complex was prepared in a similar manner to 1a from 200 mg of 6 (0.228 mmol), 67 mg of Ph2P{C5H4- (o-OMe)} (0.23 mmol), and 87 mg of TlPF6 (0.25 mmol).It was obtained as a yellow-brown microcrystals in 79% yield (230 mg) (Found: C, 46.00; H, 3.75. C50H48F6FeO7P4PtSi?0.5CH2Cl2 requires C, 45.94; H, 3.74%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.88 (s, 3 H, MeOÆPt), 3.47 (s, 3 H, OMe phosphine), 3.73 (s, 6 H, Si(OMe)2), 3.96 (t, 2 H, PCH2P, JPH = 10 Hz) and 6.8–7.7 (m, 34 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppa)PdCl] 5. The hydrido complex [FeH{Si(OMe)3}(CO)3(dppa-P)] was formed in situ by photochemical oxidative addition of HSi(OMe)3 (1.15 ml, 9 mmol) to [Fe(CO)5] (0.4 ml, 3 mmol) in hexane (100 ml) followed by addition of 0.646 g (Ph2P)2NH (dppa, 2.8 mmol).This procedure is similar to that previously described for [FeH{Si(OMe)3}(CO)3(dppm-P)].4b Addition of NEt3 (0.4 ml, 0.28 mmol) caused precipitation of [HNEt3][Fe{Si(OMe)3}- (CO)3(dppa-P)]. The reaction mixture was kept at 220 8C for 2 d. The solvent was then decanted and the residue dried under reduced pressure and redissolved in dichloromethane.2168 J.Chem. Soc., Dalton Trans., 1999, 2159–2169 The solution was cooled to 230 8C and [PdCl2(COD)] (0.77 g, 2.7 mmol) added. After the solution had been stirred at room temperature for 1 h it was filtered through a 3 cm pad of silica and Celite. The solvent was then removed under reduced pressure and 5 was obtained as a yellow powder in 62% yield based on Pd (1.32 g) (Found: C, 45.48; H, 4.07; N, 1.80. C30H30ClFeNO6P2PdSi requires C, 45.71; H, 3.84; N, 1.78%).n(CO) (hexane) 2002s, 1955s and 1918w cm21. 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.70 (br, 9 H, Si(OMe)3) and 4.5 (br, NH). 31P-{1H} NMR (CD2Cl2, 121 MHz, 298 K): d 85.8 (d, 213JPP = 51, P(Pd)) and 100.8 (d, 213JPP = 51 Hz, P(Fe)). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(PPh3)]PF6 7a. This complex was prepared in a similar manner to 1a from 150 mg of 4 (0.19 mmol), 52 mg of PPh3 (0.20 mmol), and 76 mg of TlPF6 (0.22 mmol).It was obtained as a red powder in 80% yield (175 mg) (Found: C, 50.31; H, 4.08. C49H46F6FeO6P4PdSi requires C, 50.77; H, 4.00%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.47 (broad, 9 H, Si(OMe)3), 4.19 (t, 2 H, PCH2P, 2JPH = 10.5 Hz) and 6.8–7.9 (m, 35 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pd(AsPh3)]PF6 7b. This complex was prepared as described for 1a from 150 mg of 4 (0.19 mmol), 61 mg of AsPh3 (0.20 mmol), and 76 mg of TlPF6 (0.22 mmol). It was obtained as a red powder in 74% yield (170 mg) (Found: C, 48.65; H, 4.14. C49H46AsF6- FeO6P3PdSi requires C, 48.92; H, 3.85%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.89 (s, 3 H, MeOÆPd), 3.77 (s, 6 H, Si(OMe)2), 4.13 (t, 2 H, PCH2P, 2JPH = 10.5 Hz) and 7.0–7.9 (m, 35 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pt(PPh3)]PF6 8a. This complex was prepared as described for 1a from 200 mg of 6 (0.228 mmol), 60 mg of PPh3 (0.23 mmol), and 84 mg of TlPF6 (0.24 mmol). It was obtained as a yellow powder in 71% yield (200 mg) (Found: C, 47.42; H, 3.76.C49H46F6FeO6P4PtSi requires C, 47.17; H, 3.71%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 2.88 (s, 3 H, MeOÆPt), 3.79 (s, 6 H, Si(OMe)2), 3.94 (t, 2 H, PCH2P, 2JPH = 10.5 Hz) and 6.8–7.9 (m, 35 H, aromatics). [(OC)3Fe{Ï-Si(OMe)2(OMe)}(Ï-dppm)Pt(AsPh3)]PF6 8b. This complex was prepared as described for 1a from 200 mg of 6 (0.228 mmol), 70 mg of AsPh3 (0.23 mmol), and 84 mg of TlPF6 (0.24 mmol). It was obtained as a red powder in 77% yield (225 mg) (Found: C, 44.07; H, 3.19.C49H46AsF6- FeO6P3PtSi requires C, 43.62; H, 3.51%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.13 (s, 3 H, MeOÆPt), 3.81 (s, 6 H, Si(OMe)2), 3.95 (dd, 2 H, PCH2P, 2JPH = 9.8 and 11.2 Hz) and 7.0–7.8 (m, 35 H, aromatics). [PdCl(dppm-P,P9){Ph2P{C6H4(o-OMe)}]PF6 g. A mixture of 150 mg of [PdCl2(dppm-P,P9)] (0.267 mmol) and 78 mg of Ph2P{C6H4(o-OMe)} (0.267 mmol) in CH2Cl2 (20 ml) was cooled to 240 8C and treated with 95 mg of TlPF6 (0.27 mmol).The reaction mixture was allowed to warm to room temperature, stirred for 1 h at this temperature, filtered over a Celite pad and concentrated to ca. 3 ml. Addition of Et2O aVorded a yellow-orange precipitate. The solvent was removed via a canula and the residue washed with pentane (2 × 10 ml) and dried in vacuo. Complex g was obtained as a yellow-orange powder in 62% yield (160 mg) (Found: C, 54.96; H, 3.94. C44H39ClF6FeOP4Pd requires C, 54.85; H, 4.08%). 1H NMR (CD2Cl2, 300 MHz, 298 K): d 3.74 (s, 3 H, OMe), 3.79 (t, 2 H, PCH2P, 2JPH = 11 Hz) and 6.8–7.8 (m, 34 H, aromatics). 31P-{1H} NMR (CD2Cl2, 298 K): d 2143.6 (sept, PF6, 1JPF = 709), 248.2 (dd, dppm, P trans P, 2JPPtrans = 484, 2JPP = 81), 238.3 (d, dppm, P trans Cl, 2JPP = 81) and 16.04 (d, Ph2PC6H4(o-OMe), 2JPPtrans = 484 Hz). Collection of the X-ray data and structure determination for complexes 9 and 10 Single crystals suitable for X-ray diVraction were obtained from CH2Cl2–toluene–hexane. Data were collected on a Nonius MACH-3 diVractometer using Mo-Ka graphite monochromated radiation (l = 0.7107 Å), q–2q scans.The structures were solved using direct methods and refined against |F|. Absorption corrections were computed from the y scans of four reflections. For all computations; the Nonius MoLEN package 24 was used. Crystal data for complex 9. Yellow crystals, data collected at 293 K (crystal dimensions 0.35 × 0.40 × 0.40 mm): C44H39ClF6OP4Pd?C7H8, M = 1055.7, monoclinic, space group P21/c, a = 11.500(3), b = 20.814(6), c = 21.055(6) Å, b = 97.92(2)8, V = 4991.4 Å3, Z = 4, Dc = 1.405 g cm23, m(Mo-Ka) = 6.028 cm21.A total of 15846 reflections were collected, 2 < q < 308, 8137 having I > 3s(I). Absorption factors 0.98/ 1.00, 542 parameters. Final R(F) = 0.051, Rw(F = 0.080, Goodness of fit = 1.528, maximum residual electron density 1.26 e Å23. All non-hydrogen atoms were refined anisotropically with the exception of the toluene C atoms.The hydrogen atoms were introduced as fixed contributors (dC-H = 0.95 Å, BH = 1.3Bequiv(C) Å2); toluene protons were omitted. Crystal data for complex 10. Red crystals, data collected at 173 K (crystal dimensions 0.60 × 0.40 × 0.20 mm): C51H44OP4- Cl2Pd2?3CH2Cl2?H2O, M = 1353.3, tetragonal, space group P41, a = 21.171(6), c = 14.309(4) Å, V = 6413.4 Å3, Z = 4, Dc = 1.402 g cm23, m(Mo-Ka) = 10.228 cm21. A total of 9185 reflections were collected, 2 < q < 298, 7135 having I > 3s(I ).Absorption factors 0.89/1.00, 639 parameters. Final R(F) = 0.036, Rw(F) = 0.053, Goodness of fit = 1.167, maximum residual electron density 0.12 e Å23. All nonhydrogen atoms were refined anisotropically. The hydrogen atoms were introduced as fixed contributors (dC-H = 0.95 Å, BH = 1.3Bequiv(C) Å2); water protons were omitted. CCDC reference number 186/1457. See http://www.rsc.org/suppdata/dt/1999/2159/ for crystallographic files in .cif format.Acknowledgements We are grateful to T. Faure for preliminary studies on complex 1b and thank the SOCRATES Mobility Scheme between RWTH Aachen, Germany and Université Louis Pasteur, Strasbourg, France for a grant to T. W. We are grateful to the Centre National de la Recherche Scientifique for financial support and to Johnson Matthey plc for a generous loan of PdCl2. References 1 See for example: K. M. Mackay and B. K. Nicholson, in Comprehensive Organometallic Chemistry, eds. G.Wilkinson, F. G. A. Stone and E. W. Abel, Pergamon, Oxford, 1982, ch. 43; I. Ojima, in The Chemistry Organic Silicon Compounds, eds. S. Patai and Z. Rappoport, Wiley, Chichester, 1989, p. 1479; T. D. Tilley, in The Silicon–Heteroatom Bond, eds. S. Patai and Z. Rappoport, Wiley-Interscience, New York, 1991, pp. 245–309; C. Zybill, H. Handwecker and H. Friedrich, Adv. Organomet. Chem., 1994, 36, 229; P. Braunstein and M. Knorr, J. Organomet. Chem., 1995, 500, 21. 2 See for recent reviews: D.F. Shriver, H. D. Kaesz and R. D. Adams, in The Chemistry of Metal Cluster Complexes, VCH, Weinheim, 1990; G. Schmid, in Aspects of Homogeneous Catalysis, ed. R. Ugo, Kluwer, Dordrecht, 1990, vol. 7, pp. 1–36; P. Braunstein, New J. Chem., 1988, 12, 307; P. Braunstein and J. Rosé, in Stereochemistry of Organometallic and Inorganic Compounds, ed. I. Bernal, Elsevier, Amsterdam, 1989, vol. 3, ch. 1, pp. 3–138; P. Braunstein, in Perspectives in Coordination Chemistry, eds.A. F. Williams,J. Chem. Soc., Dalton Trans., 1999, 2159–2169 2169 C. Floriani and A. E. Merbach, VCH, Weinheim, 1992, pp. 67–107; P. Braunstein and J. Rosé, in Comprehensive Organometallic Chemistry II, Elsevier, New York, 1995, vol. 10, pp. 351–385; Heterometallic Clusters for Heterogeneous Catalysis, eds. R. D. Adams and F. A. Cotton, Wiley-VCH, New York, 1998, pp. 443–508; Metal Clusters in Chemistry, eds. P. Braunstein, L. A. Oro and P. R. Raithby, Wiley-VCH, Weinheim, 1999, in the press. 3 (a) P. Braunstein, M. Knorr and C. Stern, Coord. Chem. Rev., 1998, 178–180, 903 and refs. therein. (b) P. Braunstein, M. Knorr, A. Tiripicchio and M. Tiripicchio Camellini, Angew. Chem., Int. Ed. Engl., 1989, 28, 1361; (c) P. Braunstein, M. Knorr, H. Piana and U. Schubert, Organometallics, 1991, 10, 828. 4 (a) P. Braunstein, M. Knorr, E. Villarroya and J. Fischer, New J. Chem., 1989, 14, 583; (b) P. Braunstein, M. Knorr, U. Schubert, M. Lanfranchi and A.Tiripicchio, J. Chem. Soc., Dalton Trans., 1991, 1507; (c) P. Braunstein, M. Knorr, E. Villarroya, A. DeCian and J. Fischer, Organometallics, 1991, 10, 3714; (d ) F. Balegroune, P. Braunstein, L. Douce, Y. Dusausoy, D. Grandjean, M. Knorr and M. Strampfer, J. Cluster Sci., 1992, 3, 275; (e) P. Braunstein, L. Douce, M. Knorr, M. Strampfer, M. Lanfranchi and A. Tiripicchio, J. Chem. Soc., Dalton Trans., 1992, 331; ( f ) G. Reinhard, B. Hirle, U. Schubert, M. Knorr, P. Braunstein, A. DeCian and J. Fischer, Inorg. Chem., 1993, 32, 1656; ( g) P. Braunstein, M. Knorr, M. Strampfer, A. DeCian and J. Fischer, J. Chem. Soc., Dalton Trans., 1994, 117; (h) P. Braunstein, J. Durand, M. Knorr, X. Morise, R. Pugin, G. Kickelbick and U. Schubert, in preparation. 5 (a) P. Braunstein, M. Knorr and T. Stährfeldt, J. Chem. Soc., Chem. Commun., 1994, 1913; (b) P. Braunstein, T. Faure, M. Knorr, T. Stährfeldt, A. DeCian and J. Fischer, Gazz. Chim. Ital., 1995, 125, 35; (c) M. Knorr, P. Braunstein, A. DeCian and J. Fischer, Organometallics, 1995, 14, 1302; (d ) M. Knorr, C. Strohmann and P. Braunstein, Organometallics, 1996, 15, 5653; (e) P. Braunstein, M. Knorr, J. Cossy, C. Strohmann and P. Vogel, unpublished results. 6 P. Braunstein and X. Morise, Organometallics, 1998, 17, 540. 7 L. S. Benner and A. L. Balch, J. Am. Chem. Soc., 1978, 100, 6099. 8 P. Braunstein, T. Faure, M. Knorr, F. Balegroune and D. Grandjean, J. Organomet. Chem., 1993, 462, 271. 9 (a) K. R. Dunbar and J.-S. Sun, J. Chem. Soc., Chem. Commun., 1994, 2387 and refs. therein; (b) J.-S. Sun, C. E. Uzelmeier, D. L. Ward and K. R. Dunbar, Polyhedron, 1998, 17, 2049. 10 S.-E. Bouaoud, P. Braunstein, D. Grandjean, D. Matt and D. Nobel, Inorg. Chem., 1986, 25, 3765; P. Braunstein, D. Matt, D. Nobel, F. Balegroune, S.-E. Bouaoud, D. Grandjean and J. Fischer, J. Chem. Soc., Dalton Trans., 1998, 353. 11 J. Andrieu, P. Braunstein and A. D. Burrows, J. Chem. Res. (S), 1993, 380. 12 P. E. Garrou, Chem. Rev., 1981, 81, 229. 13 P. Braunstein and X. Morise, unpublished results. 14 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 15 C. P. Kubiak and R. Eisenberg, J. Am. Chem. Soc., 1977, 99, 6129. 16 M. L. Kullberg and C. P. Kubiak, Organometallics, 1984, 3, 632. 17 A. L. Balch, L. S. Benner and M. A. Olmstead, Inorg. Chem., 1979, 18, 2996. 18 D. J. Wink, B. T. Creagan and S. Lee, Inorg. Chim. Acta, 1991, 180, 183. 19 S. R. Klopfenstein, C. Kluwe, K. Kirschbaum and J. A. Davies, Can. J. Chem., 1996, 74, 2331. 20 C.-L. Lee, Y.-P. Yang, S. J. Rettig, B. R. James, D. A. Nelson and M. A. Lilga, Organometallics, 1986, 5, 2220. 21 F. T. Wang, J. Najdzionek, K. L. Leneker, H. Wassermen and D. M. Braitsch, Synth. React. Inorg. Metal-Org. Chem., 1978, 8, 119. 22 I. Bachert, P. Braunstein and R. Hasselbring, New J. Chem., 1996, 20, 993. 23 M. Habib, H. Trujillo, C. A. Alexander and B. N. StorhoV, Inorg. Chem., 1985, 24, 2344. 24 C. K. Fair, MOLEN, An Interactive Intelligent System for Crystal Structure Analysis, Nonius, Delft, 1990. Paper 9/00390H

ISSN:1477-9226    

DOI:10.1039/a900390h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 2163 Transition metal complexes containing the 1,2-dicarba-closododecaborane- 1,2-dithiolate ligand: crystal structures of [4-MeC5H4NMe]2[Pd(S2C2B10H10)I2], [NEt3H][Mo(Á5-C5H5)- (NO)(S2C2B10H10)I], [NBu4][Re(] O)(S2C2B10H10)2] and [4-MeC5H4NMe]2[{Mo(] O)(Ï-O)(S2C2B10H10)}2] James D. McKinney, Hongli Chen, Thomas A. Hamor, Keith Paxton and Christopher J.Jones*,† School of Chemistry, The University of Birmingham, Edgbaston, Birmingham, UK B15 2TT The dithiol ligand 1,2-dicarbaborane-1,2-dithiol, 1,2-(HS)2-1,2-C2B10H10 (H2cbdt), reacted with anhydrous PdI2 to form [Pd(cbdt)I2]22, isolated as its [4-MeC5H4NMe]1 salt 1 and with [{Mo(h5-C5H5)(NO)I2}2] in the presence of NEt3 to aVord the mononuclear complex [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] 2.Complete halide substitution occurred with [NBu4][Re(]] O)Cl4] to give [NBu4][Re(]] O)(cbdt)2] 3 and the reaction with MoCl5 in tetrahydrofuran aVorded the oxo-bridged molybdenum(V) dimer [4-MeC5H4NMe]2[Mo(]] O)(m-O)(cbdt)}2] 4 which is diamagnetic. The salts 1–4 have been characterised by single crystal X-ray diVraction studies. In all cases only very limited conjugation appears to occur between the sulfur atoms and the carbon atoms of the carbaborane cage, C]S bond lengths averaging 1.785 Å, slightly shorter than the pure single bond value.The electrochemical properties of the new complexes were investigated but no simple reversible electron transfer processes were observed. Complexes containing dithiolene ligands have played a well established role in modern co-ordination chemistry.1 Initially such complexes were of interest because of their novel electronic and magnetic properties and the extended redox series which were found for some dithiolene complexes.2 More recently this type of compound has become important in the study of new molecular materials.3 In particular dithiolene complexes, and related materials such as salts of [Ni(dmit)2]22, have been used to produce metal–organic materials which exhibit electrical conductivity 4 or third order non-linear optical properties.5 Another type of dithiolate ligand which may be of interest in the synthesis of new molecular materials is represented by 1,2-dicarbadodecaborane-1,2-dithiol 6 (H2cbdt).The chemistry of H2cbdt has been little studied, although complexes with Co21, Ni21 and Zn21 have been described previously7 and, more recently, a series of gold complexes has been reported.8 In order further to develop the known chemistry of H2cbdt, and assess its ability to form redox active transition metal complexes, we have examined its reactions with a selection of diVerent transition metal compounds.Results and Discussion Synthetic studies The synthetic approach adopted involved the direct reaction of S S S– S– pfdt2–, R = CF3 mnt2–, R = CN dmit2– tdt2– cbdt2– = C = BH R S– R S– S– S– S S– S– † E-Mail: c.j.jones@bham.ac.uk H2cbdt with the appropriate transition metal reagent followed, where necessary, by treatment with a suitable cation. The reaction products were characterised by IR and 11B NMR spectroscopy, positive and negative ion fast atom bombardment mass spectrometry (FABMS), elemental analyses and solution conductivity measurements.The reaction of H2cbdt with PdI2 followed by the addition of 4-MeC5H4NMe1 ions aVorded a product (1) which exhibits bands attributable to nmax(BH) in its IR spectrum and for which the 11B NMR spectrum indicates the presence of the ligand cbdt.The negative-ion FAB mass spectrum of 1 contains an ion at m/z = 674 attributable to {[4-MeC5H4NMe][Pd(cbdt)I2]}2 along with ions at m/z = 566 and 439 which correspond to {H- [Pd(cbdt)I2]}2 and [HPd(cbdt)I]2 respectively. The positive ion FAB mass spectrum contains an ion at m/z = 890 attributable to {[4-MeC5H4NMe]3[Pd(cbdt)I2]}1. These results indicate that substitution of the iodide ligands has not occurred and the elemental analyses are in accord with the formulation of 1 as [4-MeC5H4NMe]2[Pd(cbdt)I2] which has been confirmed by a single crystal X-ray diVraction study described below.The reactions between the binuclear complex [{Mo(h-C5H5)- (NO)I2}2] and thiols or dithiols are of interest since any of a variety of products may form depending on the nature of the thiolate ligand.9 The co-ordinatively unsaturated 16-electron complex [Mo(h5-C5H5)(NO)(SPh)2] may be obtained with PhSH9a but with mnt22 the seven-co-ordinate 18-electron complex [Mo(h5-C5H5)(NO)(mnt)I]2 is formed and with H2tdt or pfdt22 the binuclear complexes [{Mo(h5-C5H5)(NO)(L]L)}2] (L]L22 = tdt22 or pfdt22) are obtained.9b The reaction of H2cbdt with [{Mo(h5-C5H5)(NO)I2}2], in the presence of triethylamine, produced the salt [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] 2.The positive-ion FAB mass spectrum of 2 contains an ion at m/z = 102 which corresponds to the cation [NEt3H]1 and the highest mass ion appears at m/z = 729 which corresponds with the formula {[NEt3H]2[Mo(h5-C5H5)(NO)(cbdt)I]}1. The negative-ion FAB mass spectrum contains a highest mass ion cluster at m/z = 527 which corresponds to the formally sevenco- ordinate molybdenum complex [Mo(h5-C5H5)(NO)(cbdt)I]2. The solution conductivity and elemental analyses are consistent with the formulation of 2 as [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] which was confirmed by a single crystal X-ray diVraction study2164 J.Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 described below.In this reaction it appears that H2cbdt behaves more like mnt22 than H2tdt since a mononuclear iodo complex is obtained rather than a dimer in which both iodides have been replaced. In contrast to its cyclopentadienyl containing counterpart, the mononuclear co-ordinatively unsaturated complex [Mo(NO){HB(dmpz)3}I2] (dmpz = 3,5-dimethylpyrazolyl) reacts with PhSH or H2tdt to produce the mononuclear six-co-ordinate, formally 16-electron complexes [Mo(NO){HB(dmpz)3}(SPh)2] and [Mo(NO){HB(dmpz)3}- (tdt)] respectively.9c,10 However, under similar reaction conditions neither [Mo(NO){HB(dmpz)3}(cbdt)] nor [Mo(NO){HB- (dmpz)3(cbdt)I]2 could be obtained from H2cbdt and [Mo(NO){HB(dmpz)3}I2].This finding may result from the steric bulk of the HB(dmpz)3 ligand, which favours six-coordination, precluding the formation of a stable seven-coordinate complex.It is further likely that a pyrazolyl 3-methyl substituent or the HB(dmpz)3 ligand blocks binding of the bulky cbdt22 in the first instance, although the less sterically demanding chelate ligand tdt22 can be accommodated. The value of nmax(NO) for [NEt3H][Mo(h5-C5H5)(NO)(cbdt)I] was found to be 1639 cm21 which is comparable with respective values of 1640, 1630 and 1634 cm21 for [{Mo(h5-C5H5)- (NO)(tdt)}2], [Mo(h5-C5H5)(NO)(mnt)I]2 and [Mo(NO){HB- (dmpz)3}(tdt)].The reactions of H2cbdt with two higher oxidation state metal centres were also investigated. The complexes [NBu4]- [ReOCl4] 11 and MoCl5 were used as respective sources of ReV and MoV.The positive-ion FAB mass spectrum of the product from the reaction of H2cbdt with [NBu4][ReOCl4] contains an ion at m/z = 242 which corresponds to the cation [NBu4]1 and the negative-ion FAB mass spectrum contains a highest mass ion cluster at m/z = 615 which corresponds to [ReO(cbdt)2]2. The solution conductivity and elemental analyses of this salt are consistent with the formulation [NBu4][ReO(cbdt)2] 3 which was confirmed by a single crystal X-ray diVraction study described below.The formation of this product is in keeping with the general tendency of [ReOCl4]2 to form stable complexes with thiolate ligands.12 The IR spectrum of the 4- MeC5H5NMe1 salt of the product of the reaction between H2cbdt and MoCl5 in tetrahydrofuran contained strong bands attributable to nmax(BH).The negative-ion FAB mass spectrum contains a highest mass ion at m/z = 777 which corresponds to {[4-MeC5H4NMe][{MoO2(cbdt)}2]}2. An ion is also observed at m/z = 669 which corresponds to {H[{MoO2(cbdt)}2]}2. The positive-ion FAB mass spectrum contains a highest mass ion at m/z = 994 which corresponds to {[4-MeC5H4NMe]3[{MoO2- (cbdt)}2]}1.The solution conductivity of this salt is consistent with its formulation as a 2 : 1 electrolyte and the elemental analyses are consistent with the formulation [4-MeC5H4- NMe]2[{Mo(]] O)(m-O)(cbdt)}2] 4 which was confirmed by the single crystal X-ray diVraction study described below. It is possible that the formation of this complex results from hydrolysis during the purification process which is carried out in air.However, oxygen abstraction from the thf solvent is also possible as has been observed previously in the formation of [MoO{HB- (pz)3}Cl2] from MoCl5 and K[HB(pz)3] in thf.13 Structural studies All four complexes whose crystal structures have been determined contain as a common feature a metallo-1,2-dicarbadodecaborane- 1,2-dithiolate moiety.The B]B, B]C, C]C and C]S bond lengths agree closely, irrespective of the nature of the metal (Table 1). The overall mean values, 1.767, 1.720, 1.644 and 1.785 Å, respectively, are similar to the mean lengths of the corresponding bonds 1.778, 1.727, 1.632 and 1.781 Å measured 14 in C2B10S2C]] S and 1.775 and 1.716 Å given by Allen et al.15 for B]B and B]C bonds in comparable cage structures.The C]S bonds are only slightly shorter than the standard single bond value, indicating an only relatively small degree of p-electron delocalisation between the sulfur and the carborane cage (see Table 1). For comparison, C]S bond lengths in M(SC]] CS) (M = Pd, Mo or Re) moieties, which might be expected to show some electron delocalisation, average 16 1.709 [M = Pd (21 structures)], 1.733 [M = Mo (20 structures)] and 1.721 Å [M = Re (five structures)], some 0.05–0.08 Å smaller than our mean values, whereas in the saturated systems M(SC]CS) the C]S bond lengths average 16 1.828 Å for M = Pd (one structure), 1.816 for M = Mo (13 structures) and 1.826 Å for M = Re (five structures), approximately 0.04 Å greater than our mean values.This eVect can also be gauged by comparing the lengths of the C]S bonds in the bis(1,2-dithiooxalato)- oxorhenium(V) 17 and the bis(ethane-1,2-dithiolato)oxorhenium( V) 18 anions. In the former, which allows conjugation in the S]C]] O system, C]S bonds are in the range 1.730–1.766 Å, mean 1.742(8) Å, whereas in the latter, saturated system, C]S bonds are 1.795–1.849, mean 1.809 Å.Thus, for all three metals our C]S lengths are intermediate, but rather closer to the pure single bond value. Metal–sulfur lengths, however, do not show any systematic trend.In the palladium complex [4-MeC5H4NMe]2[PdII(cbdt)I2] 1, shown in Fig. 1, crystallographic mirror symmetry imposes a planar geometry on the metal co-ordination but deviations from a square planar geometry of up to 5.38 occur (see Table 2).The large I(2)]Pd]I(1) angle of 95.28(3)8 is presumably due to repulsion between the large iodide ligands. Similarly, in the crystal structure of [1,2-bis(phenylsulfanyl)benzene] diiodo palladium–diiodine,19 the I]Pd]I angle is 92.38 and the Pd]I and Pd]S bond lengths are 2.606 and 2.292 Å, respectively (cf. our values in Table 2). The structure of the anion [Mo(h5-C5H5)(NO)(cbdt)I]2 2 is shown in Fig. 2. If the cyclopentadienyl ligand is represented by its centroid (denoted Cn), the co-ordination geometry can be considered as very roughly approximating to trigonal bipyramidal. The axial angle I(1)]Mo]S(1) is 143.3(1)8 and the basal angles, involving Cn, N(1) and S(2), are in the range 117.4–124.98. In the somewhat analogous structures of (h5- cyclopentadienyl)[2-(1-dimethylamino)ethylphenyl-C,N]iodonitrosylmolybdenum20 and the closely related [Mo(h5-C5H5)- {C6H2(OCH2O)-2,3-CH2NMe2-6}(NO)I] 20 the geometry at molybdenum approximates to square pyramidal with the centroid of the cyclopentadienyl ring axial. The Mo]I bond Fig. 1 View of the dianion in compound 1 Table 1 Bond lengths (Å) for the carbaborane cage B]B B]C C]C S]C 1 1.765(3) a 1.713(9) d 1.638(10) 1.788(16) f 2 1.769(3) b 1.726(6) e 1.659(9) 1.783(3) f 3 1.770(2) c 1.717(5) a 1.636(7) f 1.790(2) d 4 1.765(3) b 1.723(4) e 1.652(7) 1.773(2) f a Mean of 16 values.b Mean of 21 values. c Mean of 42 values. d Mean of 4 values. e Mean of eight values. f Mean of two values.J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 2165 lengths in these structures at 2.857 and 2.870 Å are slightly longer than the corresponding length in 2 [2.844(1) Å], but the Mo]N(O) bonds, 1.770 and 1.775 Å, agree well with our value Fig. 2 View of the anion in compound 2 Table 2 Selected bond lengths (Å) and angles (8) involving the metal centres of the anions 1–4 [Pd(C2B10H10S2)I2]22 1 Pd]S(1) Pd]S(2) I(1)]Pd]I(2) I(1)]Pd]S(1) I(1)]Pd]S(2) I(2)]Pd]S(1) 2.268(2) 2.265(2) 95.28(3) 179.90(4) 85.95(5) 84.82(6) Pd]I(1) Pd]I(2) I(2)]Pd]S(2) S(1)]Pd]S(2) Pd]S(1)]C(1) Pd]S(2)]C(2) 2.625(1) 2.643(1) 178.77(5) 93.95(7) 104.7(3) 105.4(2) [Mo(h5-C5H5)(NO)(C2B10H10S2)I]2 2 a Mo]S(1) Mo]S(2) Mo]N Mo]I Mo]Cn N(1)]O I]Mo]S(1) I]Mo]S(2) I]Mo]N I]Mo]Cn S(1)]Mo]S(2) S(1)]Mo]N S(1)]Mo]Cn 2.477(2) 2.514(2) 1.768(6) 2.844(1) 2.050 1.200(7) 143.3(1) 73.9(1) 85.0(2) 107.8 81.4(1) 82.8(2) 108.6 Mo]C(3) Mo]C(4) Mo]C(5) Mo]C(6) Mo]C(7) S(2)]Mo]N S(2)]Mo]Cn N]Mo]Cn Mo]S(1)]C(1) Mo]S(2)]C(2) Mo]N]O 2.443(8) 2.394(8) 2.305(8) 2.313(7) 2.398(7) 117.6(2) 124.9 117.4 109.6(2) 108.4(2) 169.4(6) [Re(]] O)(C2B10H10S2)2]2 3 Re]S(1) Re]S(2) Re]S(19) S(1)]Re]S(2) S(1)]Re]S(19) S(1)]Re]S(29) S(1)]Re]O S(2)]Re]S(19) S(2)]Re]S(29) S(2)]Re]O 2.310(2) 2.314(2) 2.306(2) 87.9(1) 141.3(1) 79.9(1) 109.8(2) 81.1(1) 145.5(1) 107.4(2) Re]S(29) Re]O S(19)]Re]S(29) S(19)]Re]O S(29)]Re]O Re]S(1)]C(1) Re]S(2)]C(2) Re]S(19)]C(19) Re]S(29)]C(29) 2.323(2) 1.678(5) 88.5(1) 108.8(2) 107.1(2) 107.3(2) 107.8(2) 108.0(2) 107.7(2) [{Mo(]] O)(m-O)(C2B10H10S1)}2]22 4 b Mo]S(1) Mo]S(2) Mo]O(1) S(1)]Mo]S(2) S(1)]Mo]O(1) S(1)]Mo]O(2) S(1)]Mo]O(2*) S(2)]Mo]O(1) S(2)]Mo]O(2) S(2)]Mo]O(2*) 2.423(2) 2.424(1) 1.673(4) 85.3(1) 107.2(2) 139.4(1) 79.3(1) 104.5(1) 79.5(1) 144.1(1) Mo]O(2) Mo]O(2*) Mo]Mo* O(1)]Mo]O(2) O(1)]Mo]O(2*) O(2)]Mo]O(2*) Mo]S(1)]C(1) Mo]S(2)]C(2) Mo]O(2)]Mo* 1.933(4) 1.943(3) 2.565(1) 113.0(2) 110.9(2) 91.4(1) 105.2(2) 105.7(2) 82.9(1) a Cn denotes the centroid of the cyclopentadienyl ring. b Starred atoms are related to the corresponding unstarred ones by a crystallographic two-fold axis.of 1.768(6) Å. The Mo]S bonds in 2, mean 2.495(19) Å, are significantly longer than the mean length of 2.418 Å found for this bond in 13 structures containing the Mo(SCH2CH2S) fragment extracted from the CSD.16 The very long Mo]S(2) bond of 2.514(2) Å in 2 may be aVected by the translengthening influence of the cyclopentadienyl ring, angles C(5)]Mo]S(2) and C(6)]Mo]S(2), 146.6(2) and 145.9(3)8 respectively, involving the two shortest Mo]C distances (see Table 2).The flexibility of Mo]S bonds is however demonstrated by the range of lengths found,16 2.339–2.497 Å. The metal centres of both the anions 3 and 4 show approximate square pyramidal co-ordination. In [Re(]] O)(cbdt)2]2 3 (see Fig. 3) the rhenium atom lies 0.726(1) Å from the best plane of the four sulfur atoms, with the apical oxygen atom 2.404(6) Å from this plane on the same side as the rhenium. The Re]S bond lengths average 2.313(4) Å (see Table 2), in good agreement with those measured in two comparable square pyramidal Re(]] O)(SCHRCHRS)2 anions, mean 2.310 Å for both R = H18 and CO2H.21 The Re]O bonds are 1.742,18a 1.673 18b (two independent determinations) and 1.699 Å,21 compared to 1.678(5) Å in 3.The dimeric anion [{Mo(]] O)(m-O)(cbdt)}2]22 4 (Fig. 4) has crystallographic two-fold (C2) symmetry. Excluding the 2.565(1) Å Mo]Mo interaction, the square pyramidal coordination at molybdenum has the two sulfur atoms and the bridging oxygen atoms forming the basal plane (coplanar to within 0.045 Å), the Mo atom being displaced by 0.699(3) Å from this plane and the apical oxygen atom by 2.372(5) Å.The two edge-sharing, symmetry related pyramids are tilted by 25.4(1)8 with respect to one another. The Mo]S, Mo]O (bridging) and Mo]O (terminal) lengths are 2.424(1) (mean of two values), 1.938(5) (mean of two values) and 1.673(4) Å, respectively.In the di-m-oxo-bis[di(benzenethiolato)oxomolybdate(V)] dianion,22 which is based on the same central atomic configuration, mean bond lengths are Mo]S 2.447 Å, Mo]O (bridging) 1.937 Å and Mo]O (terminal) 1.677 Å, with a 278 angle between the basal planes of the molybdenum co-ordinating square pyramids, very similar to the situation in our structure (4). Five-co-ordinated rhenium in Re(]] O)S4 moieties and five-coordinated molybdenum in Mo(]] O)S2O2 moieties, whose structures are presently known,16 adopt, without exception, an essentially square pyramidal co-ordination geometry, with the doubly bonded oxygen ligand axial.The metal atom is displaced from the basal plane in the same direction as the apical Fig. 3 View of the anion in compound 3 Fig. 4 View of the dianion in compound 4 along the crystallographic two-fold symmetry axis.Starred atoms are related to the corresponding unstarred ones by the symmetry axis2166 J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 oxygen atom by 0.66–0.76 Å in the rhenium complexes 17,18,21,23 and by 0.66–0.73 Å in the molybdenum complexes,22,24 comfortably spanning our measured metal atom displacements from their respective basal planes.No abnormally close intermolecular contact distances are observed in any of the four structures. However, a significant intermolecular interaction occurs in compound 2 where there is a hydrogen bond between the triethylammonium ion and an iodine atom of the anionic complex, N ? ? ? I 3.795, H ? ? ? I 2.92 Å, and angle N]H? ? ? I 1638.Electrochemical studies Metal–1,2-dithiolene complexes often undergo sequential electron transfer reactions which are usually reversible.2 Electrochemical studies were carried out on the new carbaboranedithiolate complexes to establish whether they too would exhibit well defined electron transfer processes. The complexes [4-Me5H4NMe]2[Pd(cbdt)I2] and [NBu4][ReO(cbdt)2] did not undergo any well defined reduction or oxidation processes in the potential range 21.4 to 11.4 V vs.SCE. However, [NEt3H]- [Mo(h5-C5H5)(NO)(cbdt)I] oxidised at 10.61 V, although the process is electrochemically and chemically irreversible. These findings suggest that the carbaboranedithiolate ligand does not support the range of electron transfer processes found for complexes of dithiolene ligands.Conclusion The dithiol proligand H2cbdt has been found to react with several transition metal complexes. The heteroleptic complex [Pd(cbdt)I2]22 can be obtained from PdI2 but single crystal X-ray crystallography studies reveal no close intermolecular contacts or stacking of the {PdS2I2} moieties. The reaction of H2cbdt with [{Mo(h5-C5H5)(NO)I2}2] aVords the mononuclear complex [Mo(h5-C5H5)(NO)(cbdt)I]2 and, in this respect, cbdt22 behaves more like mnt22 than tdt22 which forms the dimer [{Mo(h5-C5H5)(NO)(tdt)}2]. The reaction with [ReOCl4]2 proceeds according to expectation aVording the five-co-ordinate rhenium(V) complex [ReO(cbdt)2]2.In the case of MoCl5 the reaction in thf involves oxygen abstraction, either from thf during the reaction or water during the purification procedure, and formation of the diamagnetic binuclear molybdenum(V) complex [{MoO(cbdt)(m-O)}2].The structural results suggest that cbdt22 behaves primarily as a dithiolate ligand with little delocalisation of charge between the cababorane cage, the sulfur donor atoms and the metal. The electrochemical behaviour of the new complexes suggests that the cbdt22 ligand is unable to support the rich electron transfer chemistry associated with dithiolene complexes.Experimental Reaction solvents were purified by distillation under nitrogen from standard drying agents before use. The reagents H2cbdt,6 [NBu4][ReVOCl4] 25 and [{Mo(h5-C5H5)(NO)I2}2] 26 were prepared by previously reported methods. All commercial reagents were pre-dried before use but were otherwise used as received.Reactions were carried out under an atmosphere of dry nitrogen but purification procedures were carried out in air. Column chromatography was carried out using silica gel (Merck; Kiesel gel 60, 70–230 mesh) or alumina (Merck, 70–230 mesh) with the eluents stated. The IR spectra were recorded from KBr discs using a Perkin-Elmer 1600 series FT-IR spectrophotometer, 11B NMR spectra at 86 MHz from dichloromethane or acetonitrile solutions using a JEOL GX270 spectrometer, 1H NMR 300 MHz spectra using a Bruker AC300 spectrometer and mass spectra using a Kratos MS80 instrument with positive or negative ion fast atom bombardment of a 3-nitrobenzyl alcohol matrix.Conductivity measurements were recorded from 1024 mol dm23 solutions of the new compounds in acetonitrile using a PTI 58 digital conductivity meter.Elemental analyses were performed by the Microanalytical Service, School of Chemistry, University of Birmingham or the Microanalytical Service, School of Chemistry, University of SheYeld. Preparations [4-MeC5H4NMe]2[Pd(cbdt)I2] 1. Palladium(II) iodide (0.36 g, 1.00 mmol) was dissolved in acetonitrile (10 cm3), the solution added dropwise to a solution of H2cbdt (0.21 g, 1.00 mmol) in acetonitrile (15 cm3) and the mixture stirred for 30 min at room temperature then heated under reflux for 16 h.The salt [4- MeC5H4NMe]I (0.47 g, 2.00 mmol) in acetonitrile (10 cm3) was added dropwise and the solution heated under reflux for 2 h. The solvent was removed in vacuo and the residue dissolved in dichloromethane (10 cm3), filtered, the solution warmed to 35 8C and hexane added until the product just started to precipitate.On standing a red crystalline solid was formed (0.65 g, 83%) (Found: C, 25.1; H, 3.95; N, 3.58. C16H30B10I2N2- PdS2 requires C, 24.6; H, 3.86; N, 3.58%), nmax(BH) 2566s cm21. 11B-{1H} NMR (CH2Cl2): d 219.82, 225.05, 227.64 and 230.17. 1H NMR (CD3CN): d 8.54 and 7.84 (2 H, d, J = 8; 2 H, d, J = 8 Hz, C5H4N), 4.24 (3 H, s, C5H4NCH3) and 2.63 (3 H, d, CH3C5H4N). Mass spectrum [m/z, I(%)]: positive-ion FAB, 890 (42) {[4-MeC5H4NMe]3[Pd(cbdt)I2]}1; 783 (100), {H[4- MeC5H4NMe]2[Pd(cbdt)I2]}1, negative-ion FAB, 674 (6), {[4-MeC5H4NMe][Pd(cbdt)I2]}2; 566 (10), {H[Pd(cbdt)I2]}2; 439 (55), {H[Pd(cbdt)I]}2.Lm 277 W cm2 mol21. [NEt3H][Mo(Á5-C5H5)(NO)(cbdt)I] 2. Triethylamine (0.061 g, 0.60 mmol) was added dropwise to a solution of H2cbdt (0.063 g, 0.30 mmol) in toluene (15 cm3) with stirring. A solution of [{Mo(h5-C5H5)(NO)I2}2] (0.164 g, 0.30 mmol) in toluene (10 cm3) was then added dropwise and the mixture heated under reflux for 16 h, the solvent evaporated in vacuo and the residue redissolved in dichloromethane (10 cm3).The solution was filtered, warmed to 35 8C and hexane added until the product just started to precipitate. On standing dark red crystals of the product were deposited (0.113 g, 60%) (Found: C, 25.3; H, 5.00; N, 4.35. C13H31B10IMoN2OS2 requires C, 24.9; H, 4.99; N, 4.47%). 1H NMR (CDCl3): d 5.94 (5 H, s, h-C5H5), 3.22 (6 H, q, J = 6, HNCH2CH3) and 2.45 (9 H, t, J = 6 Hz, HNCH2CH3).nmax(BH) 2568s, nmax(NO) 1639s cm21. Mass spectrum [m/z, I(%)]: positive-ion FAB, 729 (10), {H[Et3NH][Mo(h5-C5H5)- (NO)(cbdt)I]}1; negative-ion FAB, 524 (100), [Mo(h5-C5H5)- (NO)(cbdt)I]2; 494 (65), [Mo(h5-C5H5)(cbdt)I]2. Lm 143 W cm2 mol21. [NBu4][ReO(cbdt)2] 3. The salt [NBu4][ReOCl4] (0.07 g, 0.12 mmol) was dissolved in thf (10 cm3) and the solution added dropwise to a solution of H2cbdt (0.10 g, 0.48 mmol) in thf (15 cm3).The mixture was stirred vigorously for 30 min at room temperature during which time it changed from yellow to green. The mixture was then heated under reflux for 2 h. During this time it changed from green to bright yellow. The solvent was evaporated in vacuo and the residue recrystallised twice from dichloromethane–hexane to yield bright yellow crystals (0.087 g, 85%) (Found: C, 28.1; H, 6.75; N, 1.56.C20H56B20NOReS4 requires C, 28.0; H, 6.58; N, 1.56%); nmax(BH) 2583s, 2614, nmax (Re]] O) 980s cm21. 11B-{1H) NMR (CH2Cl2): d 219.86 (1B), 225.78 (4B), 226.99 (3B) and 229.07 (1B). Mass spectrum [m/z, I(%)]: positive-ion FAB 242 (100), [Bu4N]1; negative-ion FAB, 615 (100), [ReO(cbdt)2]2.Lm 160 W cm2 mol21. [4-MeC5H4NMe]2[{Mo(O)(Ï-O)(cbdt)}2] 4. A solution of H2cbdt (0.21 g, 1.00 mmol) in thf (20 cm3) was added dropwise to a suspension of MoCl5 (0.082 g, 0.30 mmol) in thf (15 cm3). The mixture was stirred vigorously for 30 min at room temperature then heated under reflux for 4 h to give a yellow solution.J. Chem. Soc., Dalton Trans., 1998, Pages 2163–2168 2167 Table 3 Crystallographic and experimental data for compounds 1–4 Formula M Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z Dc/g cm23 m(Mo-Ka)/mm21 Crystal size/mm q Range/8 Reflections measured (unique) Rint Variables Dr/e Å23 D/smax R, wR2 a w(a,b) b Observed reflections [I > 2s(I)] R[I > 2s(I)] 1 C2H10B10I2PdS2?2C7H10N 782.9 Orthorhomic Pbam 18.706(5) 20.764(5) 7.505(2) — 2915(1) 4 1.784 2.908 0.4 × 0.35 × 0.25 1.5–25.2 13 515 (2531) 0.1040 175 0.49, 20.79 0.001 0.0580, 0.1148 0.050, 0.82 2222 0.0415 2 C7H15B10IMoNOS2?C6H16N 626.5 Orthorhombic P212121 14.222(3) 16.514(3) 10.959(3) — 2574(1) 4 1.617 1.881 0.2 × 0.15 × 0.15 1.9–25.2 15 230 (4464) 0.0448 271 0.54, 20.50 0.002 0.0533, 0.0869 0.015, 7.40 4300 0.0494 3 C4H20B20OReS4?C16H36N 857.3 Monoclinic P21/n 10.989(2) 24.156(5) 16.069(4) 105.99(2) 4100(2) 4 1.389 3.188 0.2 × 0.2 × 0.15 1.6–25.2 15 875 (6259) 0.0430 424 0.47, 20.90 0.001 0.0623, 0.1058 0.024, 13.78 5649 0.0518 4 C4H20B20Mo2O4S4?2C7H10N 884.8 Orthorhombic P21212 12.226(4) 22.511(5) 7.215(4) — 1986(1) 2 1.480 0.872 0.35 × 0.3 × 0.3 3.3–25.3 4748 (2887) 0.0280 226 0.40, 20.64 0.001 0.0355, 0.0869 0.033, 3.18 2843 0.0345 a wR2 = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� .b w = 1/[s2(Fo 2) 1 (aP)2 1 bP] where P = (Fo 2 1 2Fc 2)/3. This was allowed to cool to room temperature before adding [4- MeC5H4NMe]I (0.24 g, 1.00 mmol) over a 10 min period and stirring the mixture for a further hour. The solvent was removed in vacuo and the residue dissolved in dichloromethane (10 cm3), filtered, the solution was warmed to 35 8C and hexane added until the product just started to precipitate.On standing a yellow crystalline solid deposited (0.144 g, 54%) (Found: C, 24.4; H, 4.42; N, 3.06. C9H20B10MoNO2S2 requires C, 24.4; H, 4.56; N, 3.17%); nmax(BH) 2575s, nmax(Mo]] O) 964s cm21. 11B-{1H} NMR (CH2Cl2): d 216.36, 223.38, 225.16 and 229.04. 1H NMR [(CD3)2CO]: d 8.85 and 8.01 (2 H, d, J = 3.9; 2 H, d, J = 3.9 Hz, C5H4N), 4.49 (3 H, s, C5H4NCH3) and 2.86 (3 H, d, CH3C5H4N).Mass spectrum [m/z, I(%)]: positive-ion FAB, 994 (17), {[4-MeC5H4NMe]3[{MoO(m-O)(cbdt)}2]}1; 850 (7), {[4-MeC5H4NMe]3[MoO(cbdt)2]}1; negative-ion FAB, 777 (32), {[4-MeC5H4NMe][{MoO(m-O)(cbdt)}2]}2, 669 (100), {H[{MoO(m-O)(cbdt)}2]}2; 525 (37), {H[MoO(cbdt)2]}2. Lm 260 W cm2 mol21.Crystallography Data for all four structures 1–4 were collected on a Rigaku Raxis II imaging plate area-detector diVractometer at 293(2) K using graphite-monochromated Mo-Ka radiation. The structures were determined by direct methods 27 and refined28 on F2 by full-matrix least squares with anisotropic displacement parameters for the non-hydrogen atoms. Hydrogen atoms were placed in calculated positions with isotropic displacement parameters.Specific absorption corrections were not applied since the crystals used were nearly equidimensional (see Table 3) and averaging of the symmetry-equivalent reflections largely compensates for any absorption eVects. Figures depicting the structures were prepared using ORTEP,29 the thermal ellipsoids being drawn at the 30% probability level.In compound 1 of the two dimethylpyridinium counter ions, one is disordered, so that the NMe and CMe moieties could not be distinguished; in the refinement the relevant ring atoms were treated as (��� N 1 ��� C). In 4 the dimethylpyridinium cation is similarly disordered, and was treated in the same way. The atoms of the triethylammonium counter ion in 2 exhibit high anisotropic displacement parameters and may also be aVected by disorder.CCDC reference number 186/1010. See http://www.rsc.org/suppdata/dt/1998/2163/ for crystallographic files in .cif format. Acknowledgements We are grateful to EPSRC for supporting this work through a studentship (J. D. McK.) and through research grant GR/ G44390. We also thank the EPSRC and the University of Birmingham for funds to purchase the R-Axis II diVractometer, and the British Council for a Sino-British Friendship Scholarship (to H. C.).References 1 U. T. Mueller-WesterhoV and B. Vance, in Comprehensive Coordination Chemistry, eds. R. D. Gillard, J. A. McCleverty and G. Wilkinson, Pergamon, Oxford, 1987, vol. 2, ch. 16.5, pp. 595–631. 2 J. A. McCleverty, Prog. Inorg.Chem., 1968, 10, 49; G. N. Schrauzer, Acc. Chem. Res., 1969, 2, 72. 3 T. Jørgensen, T. K. Hansen and J. Becher, Chem. Soc. Rev., 1994, 23, 41; T. K. Hansen and J. Becher, Adv. Mater., 1993, 5, 288; S. R. Marder, in Inorganic Materials, eds. D. W. Bruce and D. O’Hare, Wiley, New York, 1992, ch. 3; A. Kreif, Tetrahedron, 1986, 42, 1209; A. F. Garito and A. J. Heeger, Acc.Chem. Res., 1974, 7, 232. 4 (a) P. Cassoux and L. 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Zubieta, Inorg. Chim. Acta, 1982, 65, L223; P. J. Blower, J. R. Dilworth, J. P. Hutchinson, T. Nicholson and J. Zubieta, Inorg. Chim. Acta, 1984, 90, L27. 13 W. E. Cleland, K. M. Barnhart, K. Yamanouchi, D. Collison, F. E. Mabbs, R. B. Ortega and J.H. Enemark, Inorg. Chem., 1987, 26, 1017. 14 J. D. McKinney, T. A. Hamor, C. J. Jones and K. Paxton, Polyhedron, 1997, 16, 1819. 15 F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen and R. Taylor, J. Chem. Soc., Perkin Trans. 2, 1987, S1. 16 Cambridge Structural Database, Cambridge Crystallographic Data Centre, Cambridge, April 1997. 17 R. Mattes and H. Weber, Z.Anorg. Allg. Chem., 1981, 474, 216. 18 (a) P. J. Blower, J. R. Dilworth, J. P. Hutchinson, T. Nicholson and J. Zubieta, J. Chem. Soc., Dalton Trans., 1986, 1339; (b) W. Clegg, S. Boyde and C. D. Garner, Acta Crystallogr., Sect. C, 1988, 44, 172. 19 L. R. Gray, D. J. Gulliver, W. Levason and M. Webster, Acta Crystallogr., Sect. C, 1983, 39, 877 P. Urriolabeitia, A. de Cian and J. Fischer, J. Organomet. Chem., 1995, 494, 187. 21 J. Singh, A. K. Powell, S. E. M. Clarke and P. J. Blower, J. Chem. Soc., Chem. Commun., 1991, 1115. 22 I. G. Dance, A. G. Wedd and I. W. Boyd, Aust. J. Chem., 1978, 31, 519. 23 A. C. McDonell, T. W. Hambley, M. R. Snow and A. G. Wedd, Aust. J. Chem., 1983, 36, 253; T. Nicholson, P. Lombardi and J. Zubieta, Polyhedron, 1987, 6, 1577; G. Matsubayashi, T. Maikawa and M. Nakano, J. Chem. Soc., Dalton Trans., 1993, 2995; R. Hubener and U. Abram, Acta Crystallogr., Sect. C, 1993, 49, 1068; J. R. Dilworth, J. Hu, J. R. Miller, D. L. Hughes, J. A. Zubieta and Q. Chen, J. Chem. Soc., Dalton Trans., 1995, 3153. 24 P. L. Dahlstrom, J. R. Hyde, P. A. Vella and J. Zubieta, Inorg. Chem., 1982, 21, 927; V. Sanz, T. Picher, P. Palanca, P. Gomez-Romero, E. Llopis, J. A. Ramirez, D. Beltran and A. Cervilla, ibid., 1991, 30, 3113; D. Coucouvanis, S. Al-Ahmad, C. G. Kim, P. E. Mosier and J. W. Kampf, ibid., 1993, 32, 1533; C. G. Kim and Coucouvanis, ibid., 1993, 32, 1881; S. G. Jonasdottir, C. G. Kim and D. Coucouvanis, ibid., 1993, 32, 3591. 25 J. R. Dilworth, W. Hussain, A. J. Hutson, C. J. Jones and F. S. McQuillan, Inorg. Synth., 1996, 3, 257. 26 R. B. King, Inorg. Chem., 1967, 6, 30. 27 TEXSAN, version 1.6, Single Crystal Structure Analysis Software, Molecular Structure Corporation, Houston, TX, 1993. 28 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. 29 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. Received 31st March 1998; Paper 8/02446D

ISSN:1477-9226    

DOI:10.1039/a802446d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 2169 Fluxional rearrangements in molybdenum(0), tungsten(0) and rhenium(I) carbonyl complexes of 2,6-bis[(4S)-isopropyloxazolin-2-yl]- pyridine (L). Crystal structure of [Mo(CO)4L] ‡ Peter J. Heard *,†,a and Derek A. Tocher b a Department of Chemistry, Birkbeck College, Gordon House, 29 Gordon Square, London, UK WC1H 0PP b Department of Chemistry, University College London, Christopher Ingold Laboratories, 20 Gordon Street, London, UK WC1H 0AJ Treatment of the [ReX(CO)5] (X = Cl, Br or I) and [M(CO)4(pip)2] (M = Mo or W, pip = piperidine) compounds with the C2-symmetric ligand 2,6-bis[(4S)-isopropyloxazolin-2-yl]pyridine (L) yielded complexes of general formulae fac-[ReX(CO)3L] and cis-[M(CO)4L], in which the ligand is co-ordinated in a bidentate fashion.In solution these complexes undergo a fluxional process that exchanges the co-ordinated and pendant oxazoline rings. In the case of the M(CO)4 complexes all permutational isomers are equivalent.However, in the rhenium(I) complexes the lower symmetry of the metal moiety leads to the formation of chemically distinct species. The diVerent exchange pathways between these species gives rise to diVerent magnetisation transfers, providing a spectroscopic handle on the mechanism of the ligand rearrangement. The activation parameters have been evaluated by standard one-dimensional band shape analysis and by two-dimensional exchange spectroscopy; DG‡ (298 K) ª 52.0 and 62.6 kJ mol21, respectively for the complexes of Mo0 and W0 and is in the range 78.5–80.5 kJ mol21 for the rhenium(I) complexes.Complexes in which a meridional terdentate ligand has its bonding restricted to a bidentate mode of co-ordination are potentially fluxional.2 The classical example of this type of fluxionality is exhibited by bidentate complexes of 2,29:69,20- terpyridine (terpy), such as fac-[PtXMe3(terpy)] 3 and cis- [Mo(CO)4(terpy)].4 In these complexes the ligand oscillates between equivalent bidentate forms via a mechanism that appears to involve the ligand adopting a pseudo-terdentate bonding mode in the transition state.3,4 To gain further insight into the mechanism of this type of fluxional exchange, we investigated the analogous complexes of the C2 symmetric chiral ligand 2,6-bis[(4S)-methyloxazolin-2-yl]pyridine. The chiral centers on the ligand provide a spectroscopic handle on the mechanism, and it was shown that two independent exchange pathways were operative.1 The question now arises as to how the energetics of these fluxional pathways are aVected by the substituents on the oxazoline rings.To this end we now report on the solutionstate stereodynamics of the molybdenum(0), tungsten(0) and rhenium(I) carbonyl complexes of the ligand 2,6-bis[(4S)-isopropyloxazolin- 2-yl]pyridine (L), namely cis-[M(CO)4L] (M = Mo or W) and fac-[ReX(CO)3L] (X = Cl, Br or I).Experimental Syntheses All manipulations were performed under an atmosphere of dry, oxygen-free nitrogen, using standard Schlenk techniques.5 Solvents were dried 6 and degassed before use. The starting materials [M(CO)4(pip)2] (M = Mo or W, pip = piperidine) 7 and [ReX(CO)5] (X = Cl, Br or I) 8 and 2,6-bis-[(4S)-isopropyloxazolin- 2-yl]pyridine (L) 9 were prepared by standard literature methods. The three rhenium complexes were prepared similarly, as illustrated by the procedure given for [ReBr- † E-Mail: p.heard@chem.bbk.ac.uk ‡ Dynamic stereochemical rearrangements in ‘chiral-at-ligand’ complexes. Part 2.1 (CO)3L].The molybdenum and tungsten complexes were prepared as illustrated by the procedure for [Mo(CO)4L]. Analytical data for the complexes are reported in Table 1. {2,6-Bis[(4S)-isopropyloxazolin-2-yl]pyridine}bromotricarbonylrhenium( I). Pentacarbonylrhenium bromide (150 mg, 0.37 mmol) and 2,6-bis[(4S)-isopropyloxazolin-2-yl]pyridine (120 mg, 0.40 mmol) were refluxed in light petroleum (b.p. 60– 80 8C)–benzene (2 : 1 v/v, 30 cm3) for ca. 18 h. The solvents were then concentrated to dryness in vacuo, to yield an orange oil. Crystallisation from CH2Cl2–pentane gave 180 mg (75%) of [ReBr(CO)3L]. {2,6-Bis[(4S)-isopropyloxazolin-2-yl]pyridine}tetracarbonylmolybdenum( 0). The complex [Mo(CO)4(pip)2] (200 mg, 0.53 mmol) and 2,6-bis[(4S)-isopropyloxazolin-2-yl]pyridine (160 mg, 0.53 mmol) were stirred at ambient temperature for ca. 18 h in CH2Cl2 (20 cm3). The resulting red solution was concentrated to dryness in vacuo, and the solid residue recrystallised from CH2Cl2–pentane to yield 180 mg (67%) of crystalline, red [Mo(CO)4L]. Physical methods Infrared spectra were recorded in CH2Cl2 using matched KBr solution cells, on a Nicolet 205 FT spectrometer, operating in the region 4000–400 cm21. Fast atom bombardment mass spectra were obtained at the London School of Pharmacy on samples of the complexes in a matrix of 3-nitrobenzyl alcohol, on a VG Analytical ZAB-SE instrument, using Xe1 ion bombardment at 8 kV energy.Elemental analyses were carried out at University College London. Hydrogen-1 NMR spectra were recorded in (CDCl2)2, CD2Cl2 or CDCl3 on a Bruker AMX600 Fourier-transform spectrometer, at 600.13 MHz; chemical shifts are quoted relative to tetramethylsilane as an internal standard. Probe temperatures were controlled by a standard B-VT 2000 variable temperature unit; temperatures were checked against a standard sample of ethane-1,2-diol, and are considered accurate to2170 J.Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 Table 1 Analytical data for the complexes [M(CO)4L] (M = Mo or W) and [ReX(CO)3L] (X = Cl, Br or I) Yield a Analysis d (%) Complex [Mo(CO)4L] (%) 67 n(CO)b/cm21 1831, 1877, 1905, 2017 m/z c e C 49.15 (49.53) H 4.49 (4.55) N 8.22 (8.25) [W(CO)4L] 75 1829, 1873, 1893, 2009 598 (M), 569 (M 2 CO), 541 (M 2 2CO), 512 (M 2 3CO) 41.55 (42.23) 3.72 (3.88) 6.86 (7.04) [ReCl(CO)3L] 82 1901, 1921, 2026 608 (M), 579 (M 2 CO), 544 (M 2 Cl 2 CO) 39.24 (39.57) 3.77 (3.81) 6.81 (6.92) [ReBr(CO)3L] 75 1903, 1923, 2026 652 (M), 623 (M 2 CO), 595 (M 2 2CO), 572 (M 2 Br), 545 (M 2 Br 2 CO), 515 (M 2 Br 2 2CO) 36.56 (36.87) 3.20 (3.56) 6.19 (6.45) [ReI(CO)3L] 79 1906, 1924, 2025 699 (M), 671 (M 2 CO), 544 (M 2 I 2 CO) 34.47 (34.39) 3.21 (3.32) 5.97 (6.02) a Relative to [M(CO)4(pip)2] or [ReX(CO)5].b Recorded in CH2Cl2. c FAB mass spectral data. d Calculated values in parentheses. e No diagnostically useful spectrum obtained (see text). within ±1 8C. Band shape analyses of the variable temperature spectra were carried out using the iterative simulation program DNMR 5.10 Two-dimensional exchange (EXSY) spectra were obtained using the Bruker program NOESYST, that generates the pulse sequence D1–908–D0–908–D8–908–free induction decay. The relaxation delay, D1, was set at 2.0 s and the evolution time, D0, had an initial value of 3 ms.The mixing time, D8, was varied between 0.01 and 1.0 s, according to the complex and experimental temperature. Spectra were collected typically with 256 words of data in t1 and 4096 words of data in t2, and processed with 1024 words (data were forward linear predicted to 512 words, then zero-filled to 1024 words) in F1 and 2048 words in F2 (no zero filling). The spectral widths in F1 and F2 were ca. 9.6 ppm and sixteen scans were acquired for each of the 256 experiments.Rate data were extracted from the volume integrals of the resulting two-dimensional intensity matrix using the program D2DNMR.11 Activation parameters were calculated from a least-squares fit of the linearised Eyring equation, using the rate data obtained from the band shape analyses or the EXSY spectra. The errors quoted are those defined by Binsch and Kessler.12 Crystallography A single red crystal of [Mo(CO)4L] {L = 2,6-bis[(4S)-isopropyloxazolin- 2-yl]pyridine} with dimensions 0.66 × 0.46 × 0.40 mm was obtained as described, and mounted on a glass fibre.All geometric and intensity data were taken from this sample by an automatic four-circle Nicolet R3 mV diVractometer, using the w–2q technique, at 293(2) K. Three standard reflections (remeasured every 97 scans) showed no significant loss of intensity during data collection. Crystal data and data collection parameters. C21H23MoN3O6, M = 509.36, orthorhombic, space group P212121, Mo-Ka radiation (l = 0.710 73 Å), a = 9.519(2), b = 13.394(3), c = 18.316(4) Å, U = 2335.2(9) Å3, Z = 4, Dc = 1.449 g cm23, m = 0.60 mm21, F(000) = 1040, data collection range 5 < 2q < 508, 2353 unique reflections collected.Structure solution and refinement. Data were corrected for Lorentz-polarisation and absorption eVects (empirically; y scan method; maximum transmission 0.92, minimum transmission 0.78). The structure was solved by direct methods (SHELXS 86),13 and developed using alternate cycles of leastsquares refinement on F2 and Fourier-diVerence synthesis (SHELXL 93).14 Non-hydrogen atoms were refined anisotropically, and hydrogen atoms placed in idealised positions [r(C]H) = 0.96 Å] and assigned a common isotropic thermal parameter.The final cycle of least squares included 281 parameters for the 2350 variables. The final R and wR2 values were 0.0330 and 0.0774, respectively [I > 2s(I), 2096 data], 0.0426 and 0.0880, for all data. The absolute configuration was determined unambiguously using SHELXL 93 procedures; calculated Flack parameter = 0.02(7).CCDC reference number 186/1002. Results 2,6-Bis[(4S)-isopropyloxazolin-2-yl]pyridine 2,6-Bis[(4S)-isopropyloxazolin-2-yl]pyridine (L) was prepared as described previously,9 and its absolute configuration con- firmed by the crystal structure of [Mo(CO)4L] (see below). The full assignment of its 1H NMR spectrum L is necessary for the detailed analyses of the spectra of the complexes (see below); a discussion of this spectrum is therefore merited.The ambient temperature (298 K) 1H NMR spectrum of 2,6-bis[(4S)-isopropyloxazolin-2-yl]pyridine in CDCl3 shows signals in three regions. The isopropyl methyl environments are diastereotopic; thus the two equivalent isopropyl groups [free L has C2 symmetry (Fig. 1)] give rise to a pair doublets, at d 0.91 and 1.02 [3J(HHD) ª 6.8 Hz], due to the methyls, and a multiplet, at d 1.85, due to HD (see Fig. 1 for labeling), which also couples to HB of the oxazoline ring [3J(HH) = 6.4 Hz]. The oxazoline-ring hydrogen nuclides give rise to three signals in a 1:1:1 intensity ratio, in the region d 4.0–4.6: HB gives a complex multiplet due to coupling to HA, HC and HD, and HA and Fig. 1 The structures of the ligand 2,6-bis[(4S)-isopropyloxazolin- 2-yl]pyridine (L), and the complexes [M(CO)4L] and [ReX(CO)3L], showing the H nuclide labeling scheme.Note that the [ReX(CO)3L] complexes form two chemically distinct isomers, and the structure depicted is that of the major (‘trans’) isomer (see text) N O N N O Me2HC HA HC HB CMe2 HK HJ HD N JH LH HK O N HA HC HB M CO CO OC CO O N GH EH Me2CHH FH DHCMe2 N JH LH HK O N HA HC HB Re X CO OC CO O N GH EH Me2CHH FH DHCMe2 L M = Mo or W X = Cl, Br or I ' trans' isomerJ. Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 2171 Table 2 Proton NMR chemical shift data a for L and the complexes [M(CO)4L] and [ReX(CO)3L] d (oxazoline-H) Experimental co-ordinated ring unco-ordinated ring d (isopropyl-H) d (isopropyl-Me) c d (pyridine-H) Compoundb Ligand [Mo(CO)4L] [W(CO)4L] [ReCl(CO)3L] (major = 88, minor = 12) [ReBr(CO)3L] (major = 94, minor = 6) [ReI(CO)3L] (major = 96, minor = 4) conditions CDCl3, 298 K CD2Cl2, 200 K (CDCl2)2, 251 K (CDCl2)2, 298 K (CDCl2)2, 298 K (CDCl2)2, 298 K major 4.68 (HA) 4.43 (HB) 4.57 (HC) 4.69 (HA) 4.47 (HB) 4.59 (HC) 4.80 (HA) 4.51 (HB) 4.70 (HC) 4.81 (HA) 4.53 (HB) 4.71 (HC) 4.81 (HA) 4.55 (HB) 4.71 (HC) minor 4.63 (HB) 6.45 (HB) 4.50 (HB) 4.66,d 4.64 e major 4.51 (HA) 4.12 (HB) 4.21 (HC) 4.74 (HE) 4.31 (HF) 4.20 (HG) 4.75 (HE) 4.36 (HF) 4.20 (HG) 4.74 (HE) 4.28 (HF) 4.24 (HG) 4.76 (HE) 4.29 (HF) 4.26 (HG) 4.76 (HE) 4.30 (HF) 4.26 (HG) major 1.85 (HD) 1.86 (HH) 2.52 (HD) 1.89 (HH) 2.56 (HD) 1.92 (HH) 2.47 (HD) 1.93 (HH) 2.49 (HD) 1.95 (HH) 2.50 (HD) minor 2.59 (HD) 2.61 (HD) 2.62 (HD) major 0.91 1.02 0.74 (c) 0.92 (p) 0.95 (c) 0.99 (p) 0.75 (c) 0.92 (p) 0.95 (c) 0.97 (p) 0.91 (c) 0.98 (p) 1.01 (c) 1.06 (p) 0.92 (c) 0.99 (p) 1.03 (c) 1.07 (p) 0.92 (c) 0.99 (p) 1.03 (c) 1.07 (p) minor 0.92 0.99 1.04 0.93 1.01 1.05 0.94 0.95 1.05 major 7.84 (HJ) 8.19 (HK) 7.79 (HK or HL) 7.89 (HK or HL) 8.05 (HJ) 7.78 (HK or HL) 7.85 (HK or HL) 8.00 (HJ) 7.97 (HK or HL) 7.98 (HK or HL) 8.11 (HJ) 7.97 (HK or HL) 7.98 (HK or HL) 8.11 (HJ) 7.96 (HK or HL) 7.99 (HK or HL) 8.10 (HJ) minor 8.11 (HJ) 8.10 (HJ) 7.93 (HK or HL) 8.10 (HJ) a See Fig. 1 for labeling; not all minor isomer resonances observed (see text). b Populations (%) of the two isomers given in parentheses. c c = coordinated, p = pendant; assignment of minor isomer signals to the pendant and co-ordinated oxazoline rings is uncertain. d HC or HE of the minor isomer. e HC or HE of the minor isomer. Table 3 Proton NMR coupling constants a for L and the complexes [M(CO)4L] and [ReX(CO)3L] Coupling J(HAHB) J(HAHC) J(HBHC) J(HBHD) J(HDHMe) b J(HEHF) J(HEHG) J(HFHG) J(HFHH) J(HHHMe) c J(HJHK/HL) J(HKHL) Free L 9.7 7.8 8.4 6.4 6.8 7.7 [Mo(CO)4L] 10.4 9.1 7.1 3.3 6.9 10.2 8.2 8.5 6.7 6.8 8.0 0.9 [W(CO)4L] 10.4 8.8 6.5 3.1 7.1 10.1 8.2 8.2 6.1 6.7 7.8 1.3 [ReCl(CO)3L] 10.4 9.2 7.6 3.6 6.9 9.0 7.4 9.3 6.7 6.7 7.9 1.2 ReBr(CO)3L] 10.4 9.1 7.5 3.6 6.8 9.2 7.4 9.0 6.4 6.8 7.9 1.4 [ReI(CO)3L] 10.4 9.1 7.5 3.6 6.8 9.5 7.7 8.9 6.5 6.9 7.9 1.4 a Coupling constants in Hz; see Fig. 1 for labeling. Data for the [ReX(CO)3L] complexes refer to the major isomer only (see text).b Co-ordinated isopropyl-methyls (average coupling to the two diastereotopic methyls). c Unco-ordinated isopropyl-methyls (average coupling to the two diastereotopic methyls). HC give rise to a doublet of doublets and a triplet, respectively; there is no evidence of any long range couplings between HA and HD or HC and HD. The assignments of HA and HC were made on the same basis as our assignments of the corresponding signals in 2,6-bis[(4S)-methyloxazolin-2-yl]pyridine.1 Protons HK and HJ (pyridine H) give rise to a doublet and a triplet, respectively, in the region d 7.7–8.3.Hydrogen-1 NMR data are reported in Tables 2 and 3. Complexes [M(CO)4L] The two complexes [M(CO)4L] {M = Mo or W; L = 2,6-bis- [(4S)-isopropyloxazolin-2-yl]pyridine} were obtained as redbrown crystalline solids, as described. The infrared spectra (CH2Cl2 solution) each display four carbonyl stretching bands in the region 2020–1820 cm21, characteristic of a cis-M(CO)4 metal moiety,15 and the elemental analyses (Table 1) are consistent with the formula [M(CO)4L].Fast atom bombardment (FAB) mass spectrometry was carried out on both complexes. The tungsten complex displayed weak fragmentation peaks at m/z = 598 [W(CO)4L], 569 [W(CO)3L], 541 [W(CO)2L] and 512 [W(CO)L]; however, in the case of the molybdenum complex no diagnostically useful spectrum was obtained. NMR studies. The ambient temperature 1H NMR spectra of the complexes [M(CO)4L] (M = Mo or W) displayed highly exchange-broadened signals.This broadening disappeared on cooling, and well resolved spectra were obtained at ca. 200 K for the molybdenum complex and ca. 250 K for the tungsten complex. The spectra of the two complexes were similar, and the results obtained for the tungsten complex, [W(CO)4L], will serve to illustrate the analysis of the dynamic NMR problem. The 1H NMR spectrum of [W(CO)4L] at 251 K in (CDCl2)2 showed signals characteristic of the ligand acting in a (nonexchanging) bidentate bonding mode (Fig. 1). The spectrum (Fig. 2) displayed signals in three regions: (i) the isopropyl region (ca. d 0.7–2.6); (ii) the oxazoline-H region (ca. d 4.1–4.8); (iii) the pyridine-H region (ca. d 7.7–8.1). The isopropyl region of the spectrum displayed two pairs of doublets [3J(HH) ª 72172 J. Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 Hz], of equal intensity, due to two pairs of diastereotopic methyls, and two multiplets (also of equal intensity) due to the isopropyl hydrogens, HD and HH (Fig. 1). This points clearly to the ligand acting in an unsymmetrical bidentate bonding mode, with one oxazoline ring co-ordinated and the other uncoordinated. The assignment of the methyl signals to the two oxazoline rings was made on the assumption 16,17 that the chemical shift diVerence between the diastereotopic methyls of the co-ordinated ring would be greater than that between the diastereotopic methyls of the pendant ring.Thus the widely spaced pair of doublets was assigned to the isopropyl methyls of the co-ordinated oxazoline ring. The unsymmetrical bidentate bonding mode of the ligand renders all oxazoline-H nuclides inequivalent; thus the oxazoline-H region of the spectrum displays six equally intense signals. The signals can be assigned unambiguously to HE, HA, HC, HB, HF and HG, respectively, from high to low frequency by their relative chemical shifts [cf.free L spectrum (see above)] and their scalar couplings (1H]1H COSY experiment). The aromatic region of the spectrum displays a triplet, due HJ, and two doublets of doublets due to HK Fig. 2 The 600 MHz 1H NMR spectrum of [W(CO)4L] at 251 K, showing the oxazoline-H region. See Fig. 1 for labeling. The signals denoted * are due to decomposition and HL. Although it is not possible to distinguish unambiguously between HK and HL, this does not aVect the analysis of the dynamic NMR problem (see below).Hydrogen-1 NMR data are reported in Tables 2 and 3. On warming, fully revisable line shape changes were observed in all three regions of the spectrum (see above), due to the onset of a fluxional process on the NMR chemical shift timescale. The fluxional process leads to the exchange of analogous pairs of signals (e.g. HK/HL of the pyridine ring), clearly indicating an oscillation of the ligand between bidentate forms (Scheme 1).Four chemically indistinguishable permutational isomers, depicted in Scheme 1, exist in solution; these vary according to which oxazoline ring is co-ordinated, and the orientation of the isopropyl group of the co-ordinated oxazoline ring with respect to the axial M]CO groups. The fluxional process causes an interconversion of the isopropyl-Me and pyridine-H signals according to the dynamic spin systems 1 and 2, respectively (see Scheme 1 for H atom labeling).Since all four species are degenerate, the spin systems reduce to 3 and 4, respectively. The band shape changes associated with the isopropyl-methyl and pyridine-H signals were submitted to full analyses according to 3 and 4. Although [W(CO)4L] is thermally unstable, fourteen reliable fits were obtained for the isopropyl-Me signals, and seventeen reliable fits were obtained on the pyridine-H signals. Five of the seventeen fits for the pyridine-H signals are shown in Fig. 3. In the case of the molybdenum complex, [Mo(CO)4L], only the pyridine-H signals were submitted to a total band shape analysis, and a total of fifteen reliable fits were obtained. The Eyring activation parameters for both complexes are reported in Table 4. In analogous complexes of terpyridine, such as the tricarbonylrhenium( I) halide complexes, [ReX(CO)3(terpy)] (X = Cl, OPQR QRPO Q¢R¢O¢P¢ O¢P¢Q¢R¢ k1 k2 k4 k5 k3 k6 1 JKL JLK J¢L¢K¢ J¢K¢L¢ k1 k2 k4 k5 k3 k6 2 OPQR QRPO kobs JKL JLK kobs 3 4 Scheme 1 The four solution-state species of the complexes [M(CO)4L] (M = Mo or W, L9 = CO) and [ReX(CO)3L] (L9 = Cl, Br or I) and the interconversion pathways between them. The labels ‘cis’ and ‘trans’ refer to the orientation of the co-ordinated oxazoline ring isopropyl group with respect to the axial ligand, L9.Note that the ‘cis’ and ‘trans’ species are chemically equivalent in the [M(CO)4L] complexes (L = L9), but not in the [ReX(CO)3L] complexes (L � L9) 2N JH LH HK O N1 M L¢ CO OC CO O N3 HC MeP MeO 1 2 1 2 3 4 CH QMe RMe 3 ' trans' 2N JH LH HK O N3 M L¢ CO OC CO O N1 HC MeP MeO 3 4 3 2 1 2 CH QMe RMe 1 ' trans' k1 k3 k4 N2 HJ¢ HL¢ K¢H O 3N M L¢ CO CO OC HC 3 2 1 O 1N HC P¢Me O¢Me 3 4 MeQ¢ MeR¢ 1 2 ' cis' N2 HJ¢ HL¢ K¢H O 1N M L¢ CO CO OC HC 1 2 3 O 3N HC O¢Me P¢Me 2 1 MeQ¢ MeR¢ 3 4 ' cis' k6 k2 k5J.Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 2173 Table 4 Eyring activation parameters a for the complexes [M(CO)4L] and [ReX(CO)3L] Complex [Mo(CO)4L] [W(CO)4L] [W(CO)4L2] f [ReCl(CO)3L] [ReBr(CO)3L] [ReI(CO)3L] Fluxional process b ‘Tick-tock twist’ c ‘Tick-tock twist’ c ‘Tick-tock twist’ c ‘Tick-tock twist’ g ‘Tick-tock twist’ g ‘Tick-tock twist’ g DH‡/kJ mol21 55(1) 61.5(6) d 70(2) e 73(1) 71(1) 69.2(4) DS‡/J K21 mol21 10(4) 24(2) d 24(7) e 221(4) 232(4) 236(1) DG‡/kJ mol21 52.04(17) 62.53(3) d 62.69(8) e 62 78.98(5) 80.26(5) 79.79(1) a DG‡ quoted at 298 K; errors in parentheses. b See text.c Probable mechanism, see text. d From band shape analysis of the pyridine-H signals. e From band shape analysis of the isopropyl-Me signals. f L2 = 2,6-Bis[(4S)-methyloxazolin-2-yl]pyridine; DG‡ determined from band coalescence (pyridine- H signals), Tc ª 298 K; estimated error ca. ±10%. g Data refer to the major æÆ minor isomer process. Br or I), restricted rotation of pendant pyridine ring has been observed by low temperature NMR studies.18 Samples of the complexes, [M(CO)4L] (M = Mo or W) were therefore cooled to ca. 180 K (CD2Cl2 solution), to investigate the possibility of hindered rotation of the pendant oxazoline ring. However, the spectra remained essentially unchanged below the low temperature limit of the ligand fluxion (see above). It is possible that rotation about the C (pyridine)]C (oxazoline) bond is rapid (on the NMR timescale) at these temperatures; however, this is considered unlikely, and we tend to the view that the 1H NMR spectra are insensitive to the restricted motion as a consequence of the pendant oxazoline ring adopting either chemically indistinct rotamers, or a single rotameric form.This also appears to be the case in the rhenium(I) complexes, [ReX- (CO)3L] {X = Cl, Br or I; L = 2,6-bis[(4S)-isopropyloxazolin- 2-yl]pyridine} (see below). Attempts to isolate the analogous complexes of 2,6-bis[(4S)- methyloxazolin-2-yl]pyridine (L2), namely [M(CO)4L2] (M = Mo or W), and study their stereodynamics were frustrated by Fig. 3 Variable temperature and computer-simulated 1H NMR spectra of [W(CO)4L], showing the pyridine-H region.The ‘best-fit’ rate constants, kobs, for the ligand rearrangement are shown alongside. Rate data for the other temperatures are: kobs/s21 = 0.7 (255), 3.4 (266), 5.9 (271), 14.8 (281), 23.5 (286), 56.9 (296), 90.6 (301), 205 (311), 280 (316), 405 (321), 630 (327) and 890 (332 K). The signal denoted * is due to decomposition their instability.Infrared and 1H NMR spectroscopy indicated the formation of the desired species from reactions of the [M(CO)4(pip)2] compounds (M = Mo or W, pip = piperidine) with a stoichiometric quantity of the ligand; however analytically pure samples could not be obtained and the 1H NMR spectra were complicated by the presence of resonances due to decomposition products. An approximate value for the free energy of activation, DG‡, for the ligand fluxion was obtained for [W(CO)4L2], from coalescence temperature measurements (pyridine-H signals) (Table 4).However, no kinetic data could be obtained for the molybdenum complex [Mo(CO)4L2]. Crystal structure of [Mo(CO)4L]. The crystal structure of [Mo(CO)4L] was obtained primarily to verify the bidentate bonding mode of the ligand, and to confirm the absolute con- figuration of the ligand at C(1) and C(11). A view of the molecule showing the atom numbering scheme is shown in Fig. 4, and selected bond lengths and angles are reported in Table 5.Fig. 4 shows that the molecule has the expected cis-octahedral co-ordination geometry, with the ligand acting in a bidentate bonding mode. The geometry at the metal centre deviates somewhat from that of an idealised octahedron, due to the small bite angle of the ligand N(1)]Mo]N(2) 72.38The dihedral angle between the pendant ring and the plane containing N(1)]Mo]N(2) is 55.78, which compares to 76.2 and 52.98 respectively for the analogous dihedral angles in the complexes [ReCl(CO)3L2]1 and [ReBr(CO)3(terpy)].18 There are no signifi- cant diVerences in bond lengths between the pendant and coordinated oxazoline rings.The absolute configuration at C(1) (S) and C(11) (S) was confirmed. Complexes [ReX(CO)3L] The three complexes [ReX(CO)3L] {X = Cl, Br or I; L = 2,6-bis- [(4S)-isopropyloxazolin-2-yl]pyridine} were prepared as described (see above), and isolated as air-stable orange crystalline solids. The infrared spectra (CH2Cl2) of all three complexes display three bands in the carbonyl stretching region of the Fig. 4 Molecular structure of [Mo(CO)4L], showing the atom labeling scheme. Hydrogen atoms omitted for clarity2174 J. Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 spectrum characteristic of a fac-octahedron tricarbonyl coordination geometry.19 This clearly indicates that the ligand is bound in a bidentate fashion. Elemental analyses and FAB mass spectral data are also consistent with the presence of [ReX(CO)3L] (X = Cl, Br or I).Analytical data are reported in Table 1. NMR studies. The ambient temperature (298 K) 1H NMR spectra [(CDCl2)2 solution] of the complexes, displayed well resolved signals due to the presence of two isomers of widely diVering populations (see below). The spectra were essentially identical for the three complexes, and discussion of the chloro complex, [ReCl(CO)3L], will serve to illustrate the analysis of the problem. The 1H NMR spectrum of [ReCl(CO)3L] at 298 K displayed two sets of signals of diVerent intensities, due to the presence of two isomers, that vary according to the orientation of the coordinated oxazoline-isopropyl group with respect to the halogen [L9 (Scheme 1)]; the relative populations of the two species (see below) are 1 : 7.The assignment of the two sets of signals was made on the basis that the ‘cis’ isomer (Scheme 1) would be disfavoured on steric grounds. Although this hypothesis is supported by the decrease in the population of minor species with increasing size of the halogen (Table 2), some caution is necessary in this assignment because, in the analogous complexes of 2,6-bis[(4S)-methyloxazolin-2-yl]pyridine, the methyl group of the co-ordinated oxazoline is oriented ‘cis’ to the halogen in the solid state.1 This indicates that any steric interactions between the methyl and the halogen are minimal.However, it is thought likely that the increased steric requirements of the isopropyl group (compared to the Me group) in the present complexes would favour the ‘trans’ species; the latter was therefore assigned as the major isomer.The ‘static’ 1H NMR spectrum of [ReCl(CO)3L] was exactly analogous to that of [W(CO)4L] (see above), except for the presence of the additional signals due to the minor isomer, and spectral assignments were made similarly. A full assignment of minor isomer resonances was frustrated by the low population and the small chemical shift diVerences between the two sets of signals.The scalar couplings of the minor isomer were not measured, but are presumably similar to those of the major isomer (Table 3). The relative populations of the two isomers were determined by integration of isopropyl-H signals of the co-ordinated oxazoline rings. Hydrogen-1 NMR data for the complexes [ReX(CO)3L] (X = Cl, Br or I) are reported in Tables 2 and 3. On warming above ca. 310 K the signals due to the minor species quickly broadened, as a result of a dynamic chemical exchange process that involves an oscillation of the ligand between bidentate bonding modes (Scheme 1).As a consequence of the extensive overlap of the signals due to the two isomers (see above), the only signals amenable to analysis are those of the isopropyl-H nuclides. However, these signals cannot be accurately simulated because of their complexity. Table 5 Selected bond lengths (Å) and angles (8) for [Mo(CO)4L] Mo]C(21) Mo]C(31) Mo]C(41) Mo]C(51) Mo]N(1) Mo]N(2) C(31)]Mo]C(21) C(41)]Mo]C(51) C(21)]Mo]N(1) C(21)]Mo]N(2) C(31)]Mo]N(1) C(31)]Mo]N(2) N(1)]Mo]N(2) 1.963(7) 1.960(6) 2.050(7) 2.070(7) 2.284(4) 2.351(4) 86.8(3) 169.3(2) 174.4(2) 102.2(2) 98.7(2) 169.8(2) 72.3(2) N(1)]C(3) N(2)]C(4) N(3)]C(9) O(1)]C(3) O(2)]C(9) C(3)]C(4) C(3)]N(1)]Mo N(1)]C(3)]C(4) N(2)]C(4)]C(3) C(4)]N(2)]Mo N(1)]C(3)]O(1) N(3)]C(9)]O(2) C(1)]C(12)]C(13) 1.284(7) 1.365(7) 1.259(8) 1.343(7) 1.380(7) 1.486(9) 115.0(4) 122.3(5) 113.9(5) 113.8(4) 120.2(6) 119.3(5) 112.1(6) Kinetic data for the fluxional process were therefore obtained by two-dimensional exchange spectroscopy.Each isomer gives rise to a degenerate pair of (chemically indistinguishable) species in solution (Scheme 1); thus there are four species in solution, and three possible independent exchange pathways between them. Eight EXSY spectra were recorded at ca. 5 K intervals between 293 and 329 K (Table 6).Over this temperature range, exchange only occurs between the two isomers, along pathways k3 and k4 (Scheme 1); rates along the other two pathways, k1 (= k6) and k2 (= k5), are negligible (see below). This can be clearly seen in the two-dimensional EXSY spectrum of [ReCl(CO)3L] at 308 K (Fig. 5), where cross-peaks only occur between the signals of the pendant and co-ordinated isopropyl-H of diVerent isomers. Accurate rate data for the dynamic process were obtained from the EXSY spectra and are reported in Table 6.The Eyring activation parameters are in Table 4. In a previous study by our group on the analogous tricarbonylrhenium( I) halide complexes of 2,6-bis[(4S)-methyloxazolin- 2-yl]pyridine 1 it was shown that, at higher temperatures, the so-called ‘rotation’ pathway (see below) [pathway k1 (= k6), Scheme 1] was also operative. To investigate whether or not the ‘rotation’ pathway also occurs in the present complexes a full set of variable temperature 1H NMR spectra were acquired between ambient temperature (298 K) and ca. 410 K [the upper working limit for (CDCl2)2 solutions]. The spectra displayed the expected band shape changes due to the isomer exchange, but did not reveal any conclusive evidence of magnetisation transfer via pathway k1 (k6). However, some reversible broadening of the pyridine-H resonances, HK and HL that could be attributable to magnetisation transfer along k1 (k6), was observed as the high temperature limit was approached. A low temperature 1H NMR study (CD2Cl2 solution) was carried out, to investigate the possibility of restricted rotation of the pendant oxazoline ring about the C (pyridine)]C (oxazoline) bond.As in the molybdenum and tungsten complexes (see above), no evidence of any hindered rotation was observed. Again, this was attributed to the pendant oxazoline ring adopting either chemically indistinct rotamers, or a single rotameric form, rather than the rotation remaining rapid at low temper- Table 6 Two-dimensional EXSY data for the complexes [ReX(CO)3L] Complex [ReCl(CO)3L] [ReBr(CO)3L] [ReI(CO)3L] T/K 293 298 303 308 313 318 323 329 293 298 303 308 313 318 323 329 288 293 298 303 308 313 318 323 Mixing time, D8/s 1.000 0.650 0.400 0.250 0.150 0.100 0.060 0.035 0.900 0.300 0.150 0.100 0.060 0.090 0.020 0.010 1.000 0.600 0.300 0.180 0.100 0.060 0.035 0.022 k*/s21 0.049 0.094 0.154 0.242 0.372 0.624 0.933 1.487 0.031 0.054 0.082 0.145 0.225 0.372 0.496 0.829 0.024 0.040 0.063 0.103 0.163 0.262 0.403 0.596 * First-order rate constants for the major æÆ minor isomer fluxional process. Uncertainties are ca.±5%.J. Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 2175 atures (see above). This is also in accord with the results of a previous study on the tricarbonylrhenium(I) halide complexes of 2,6-bis[(4S)-methyloxazolin-2-yl]pyridine.1 Discussion Fluxional processes The two (generally accepted) possible mechanisms of the ligand fluxion in complexes of this type have been discussed previously, 1,3,4,18,20 and are depicted in Scheme 2. For the tricarbonylrhenium( I) halide complexes of 2,6-bis[(4S)-isopropyloxazolin- 2-yl]pyridine it is possible to distinguish between these two mechanisms because they give rise to diVerent, observable magnetisation transfers.1 Two-dimensional EXSY experiments (see above) reveal that the only observable magnetisation transfers occur along pathways k3 and k4, which are identical (Scheme 1).These two fluxional pathways arise as a consequence of the so called ‘tick-tock twist’ mechanism [Scheme 2 (ii)], indicating that this mechanism is operative in these complexes at moderate temperatures. In a previous study on the analogous complexes of 2,6-bis[(4S)-methyloxazolin-2-yl]pyridine,1 Fig. 5 Two-dimensional exchange spectrum of [ReCl(CO)3L] at 308 K, showing exchange between the co-ordinated and pendant isopropyl- H environments of the diVerent isomers band shape analysis of the oxazoline-Me signals indicated that the so-called ‘rotation’ mechanism [Scheme 2 (i)] was also operative at higher temperatures. There is some evidence to indicate that this mechanism might also occur at high temperatures (above ca. 400 K) in the present complexes (see above); however, since higher temperature studies were not attempted this could not be demonstrated conclusively. A third possible mechanism has been suggested by Rotondo et al.21 for the analogous ligand fluxion observed in squareplanar complexes of PdII and PtII with terpyridine, namely cis-[M(C6F5)2(terpy)].An equivalent mechanism can also be envisaged for octahedral complexes of the type reported here.1 Such a mechanism gives rise to the same magnetisation pathways as the ‘tick-tock twist’ mechanism (i.e. pathways k3 and k4, Scheme 1); however, if this mechanism were operative, free rotation about the M]N (pyridine) bond would be expected to occur in the intermediate.This would lead to observable magnetisation transfers along pathways k2 and k5. Rates along pathways k2 and k5 are clearly negligible at moderate temperatures (EXSY data), indicating that the ligand fluxion occurs via a ‘tick-tock twist’ mechanism rather than a ‘Rotondo-type’ mechanism. Entropy of activation data are consistent with this interpretation (see below). Since all four permutational isomers are degenerate in the [M(CO)4L] (M = Mo or W) complexes, the diVerent fluxional pathways cannot be diVerentiated; all give rise to the same 1H NMR magnetisation transfers. In principle, the presence (or otherwise) of the ‘tick-tock twist’ mechanism could be probed by 13C NMR studies; the equatorial M]CO environments would be exchanged if the ligand fluxion occurred via this mechanism.However, the instability of the complexes frustrated attempts to acquire 13C NMR spectra of suYcient quality to investigate the eVects of the fluxion on the M]CO signals.Since these complexes are closely analogous to the rhenium complexes, we tend to the opinion that the ‘tick-tock twist’ mechanism is likely to be operative. The possibility of the rotation mechanism also occurring is an intriguing one. Its contribution to the overall ligand rearrangement in complexes of the type reported here will (presumably) be influenced by the relative strengths of the M]N (oxazoline) bonds (see below).Molybdenum– and tungsten–nitrogen (oxazoline) bonds are expected to be weaker than the corresponding Re]N (oxazoline) bonds; the rate of exchange via the ‘rotation’ pathway might, therefore, be expected to be greater for the complexes of Mo and W than for Re. Thus, some contribution from the ‘rotation’ pathway to the observed rate constant, kobs, for the ligand fluxion in the [M(CO)4L] complexes cannot be ruled out, and further studies are necessary to probe this possibility; such studies are currently in progress in our laboratories.Activation parameters Examination of the activation parameters obtained for the complexes (Table 4) reveals several interesting points. Scheme 2 The two possible mechanisms of the fluxional processes in the complexes [M(CO)4L] and [ReX(CO)3L] 2N O N3 O N1 M L¢ CO OC CO 2N O N3 O N1 M L¢ CO OC CO 2N O N1 O N3 M L¢ CO OC CO 2N O N3 O N1 M L¢ CO OC CO 2N O N3 O N1 M L¢ CO OC CO N2 O 1N O 3N M L¢ CO CO OC Mechanism (i) 'Rotation' Mechanism (ii) 'Tick-tock twist'2176 J.Chem. Soc., Dalton Trans., 1998, Pages 2169–2176 (i) The trend in the free energy of activation, DG‡ (298 K), with respect to the metal moieties is ReI>W0>Mo0, which is in line with the trends reported previously for fluxional rearrangements of this type.4 However, the absolute magnitudes for DG‡ (298 K) are the highest reported thus far for these metals for this type of rearrangement.1,4,22 The high magnitudes for DG‡ presumably arise as a consequence of the formation of strong M]N (oxazoline) bonds.(ii) The free energies of activation for ‘tick-tock twist’ rearrangement in the [ReX(CO)3L] complexes are ca. 5.5 kJ mol21 higher than for the corresponding complexes of the ligand 2,6-bis[(4S)-methyloxazolin-2-yl]pyridine.1 This indicates that the Re]N (oxazoline) bond is several kJ mol21 stronger in the 4-isopropyloxazolinyl complexes than in the 4-methyloxazolinyl complexes, despite the increased steric requirements of the ligand.The formation of stronger Re]N (oxazoline) bonds in the present complexes presumably accounts for the negligible contribution of the ‘rotation’ mechanism (which necessarily involves its cleavage) to the overall stereodynamics. (ii) Although entropies of activation are subject to considerable errors, and should only be viewed with caution, it is apparent that DS‡ is negative for the rearrangement in the rhenium(I) complexes [DS‡(average) ª 230 J K21 mol21].This is consistent with a ‘tick-tock twist’ rather than a ‘Rotondo-type’ mechanism; the transition state in the ‘tick-tock twist’ mechanism is considerably more ordered than in the ‘Rotondo-type’ mechanism.1,21 For the M(CO)4 complexes, entropies of activation [DS‡(average) ª 10 J K21 mol21] are also in accord with an ordered transition state, indicating that the largest contribution to the observed rate constant (see above) comes from exchange along the ‘tick-tock twist’ pathways, k3 and k4 (Scheme 1).Acknowledgements P. J. H. is grateful to Birkbeck College, for financial support, and to the University of London Intercollegiate Research Service for access to the NMR facilities at Queen Mary and Westfield College. Dr. H. Toms and Mr. P. Haycock are acknowledged for the acquisition of the NMR spectra. References 1 Part 1, P. J. Heard and C. Jones, J. Chem. Soc., Dalton Trans., 1997, 1083. 2 E. W. Abel and K. G. Orrell, Encylcopedia of Inorganic Chemistry, ed. R. B. King, Wiley, New York, 1994, vol. 5. 3 E. W. Abel, V. S. Dimitrov, N. J. Long, K. G. Orrell, A. G. Osborne, V. S� ik, M. B. Hursthouse and M. A. Mazid, J. Chem. Soc., Dalton Trans., 1993, 291. 4 E. W. Abel, K. G. Orrell, A. G. Obsorne, H. M. Pain and V. S� ik, J. Chem. Soc., Dalton Trans., 1994, 111. 5 D. F. Shriver, Manipulation of Air-sensitive Compounds, McGraw- Hill, New York, 1969. 6 D. D. Perrin and W. L. F. Armarego, Purification of Laboratory Chemicals, Pergamon, Oxford, 1988. 7 D. J. Darensbourg and R. L. Kump, Inorg. Chem., 1978, 17, 2680. 8 S. P. Schmidt, W. C. Trogler and F. Basolo, Inorg. Synth., 1979, 28, 160. 9 H. Nishiyama, M. Kondo, T. Nakamura and K. Itoh, Organometallics, 1991, 10, 500. 10 D. S. Stephonson and G. Binsch, DNMR 5, Quantum Chemistry Program Exchange, Indiana University, 1978. 11 E. W. Abel, T. P. J. Coston, K. G. Orrell, V. S� ik and D. Stephenson, J. Magn. Reson., 1986, 70, 34. 12 G. Binsch and H. Kessler, Angew. Chem., Int. Ed. Engl., 1980, 19, 411. 13 G. M. Sheldrick, Acta. Crystallogr., Sect. A, 1990, 46, 467. 14 G. M. Sheldrick, SHELXL 93, University of Göttingen, 1993. 15 L. E. Orgel, Inorg. Chem., 1962, 1, 25. 16 H. Nishiyama, S. Yamaguchi, S.-B. Park and K. Itoh, Tetrahedron Asymmetry, 1993, 4, 143. 17 H. Nishiyama, S.-B. Park, M. Haga, K. Aoki and K. Itoh, Chem. Lett., 1991. 18 E. W. Abel, V. S. Dimitrov, N. J. Long, K. G. Orrell, A. G. Osborne, H. M. Pain, V. S� ik, M. B. Hursthouse and M. A. Mazid, J. Chem. Soc., Dalton Trans., 1993, 597. 19 D. A. Edwards and J. Marshalsea, J. Organomet. Chem., 1977, 131, 73. 20 E. W. Abel, A. Gelling, K. G. Orrell, A. G. Osborne and V. S� ik, Chem. Commun., 1996, 2329. 21 E. Rotondo, G. Giordano and D. Minniti, J. Chem. Soc., Dalton Trans., 1996, 253. 22 A. Gelling, K. G. Orrell, A. G. Osborne, V. S� ik, M. B. Hursthouse and S. J. Cole, J. Chem. Soc., Dalton Trans., 1996, 203. Received 13th February 1998; Paper 8/

ISSN:1477-9226    

DOI:10.1039/a801264d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2171–2175 2171 Synthesis and electrochemistry of [Pt(tame)2]41: crystallographic analysis of bis[1,1,1-tris(aminomethyl)ethane-N,N9]platinum(II) bis(tetrachlorozincate) dihydrate Kylie N. Brown,a David C. R. Hockless a and Alan M. Sargeson b a Research School of Chemistry, Australian National University, A.C.T., 0200 Australia b Chemistry Department, Australian National University, A.C.T., 0200 Australia Received 4th March 1999, Accepted 7th May 1999 Reaction of K2PtCl6 with the tripodal ligand tame [1,1,1-tris(aminomethyl)ethane] in dimethylformamide catalysed by K2PtCl4 aVorded the octahedral bis(tridentate ligand) [Pt(tame)2]41 ion.The cyclic voltammogram of [Pt(tame)2]41 in aqueous media showed an irreversible reduction of the six-co-ordinate platinum(IV) species to PtII and bulk electrochemical reduction of the [PtIV(tame)2]41 ion quantitatively produced a square planar platinum(II) complex [Pt(tame)2]21.Crystallographic analysis of the protonated complex [PtII(Htame)2][ZnCl4]2?2H2O, showed two dissociated nitrogen atoms on opposite sides of the PtN4 21 co-ordination plane which has typical PtII–N bond lengths (2.042(6) Å). The routes to the formation of the [PtIV(tame)2]41 ion and its reduced product are addressed. Introduction Platinum(IV) sarcophagine† cage complexes, namely [Pt(sep)]41, [Pt((NO2)2sar)]41, and [Pt((NHOH)2sar)]41, have been synthesized previously using [Pt(en)3]41 as a template,1 in analogy to the aqueous capping methods devised for [Co(en)3]31 encapsulation 2 (Scheme 1).It was also anticipated that the platinum(IV) cage complexes with expanded cavities, such as [Pt(tricosaneN6)]41, could be synthesized using the capping strategy described for [Rh(tricosaneN6)]31 complexes, where tris(propane-1,3-diamine)rhodium(III) ([Rh(tn)3]31) and [1,1,1- tris(5-amino-2-azapentyl)ethane]rhodium(III) ([Rh(stn)]31) ions were used as templates (Scheme 2).3 Since the anticipated PtIV– N bond length for the saturated PtN6 41 cage (ª 2.07 Å) is comparable to that of Rh–N in saturated RhN6 31 systems (2.09 Å),3 the synthesis of platinum(IV) tricosaneN6 complexes should be feasible using either [Pt(tn)3]41 or [Pt(stn)]41 complexes as templates.However, the syntheses of the necessary precursors for the platinum(IV) capping reactions, namely [Pt(tn)3]41 and [Pt(stn)]41, have not been reported and surprisingly attempts to synthesize the [Pt(tn)3]41 ion were not fruitful using modified syntheses which had been successful for [Pt(en)3]414 and [Pt(en)x- (pn)3 2 x]41 (x = 3, 2, 1 or 0).5 These routes produced mostly Scheme 1 Capping [Pt(en)3]41.(i) CH3NO2 or NH3, CH2O and base, in water. † Abbreviated ligand names used: sar, sarcophagine = 3,6,10,13,16,19- hexaazabicyclo[6.6.6]icosane; sep, sepulchrate = 1,3,6,8,10,13,16,19- octaazabicyclo[6.6.6]icosane; tricosaneN6 = 3,7,11,15,18,22-hexaazabicyclo[ 7.7.7]tricosane; Me5-tricosanetriimineN6 = 1,5,9,13,20-pentamethyl- 3,7,11,15,18,22-hexaazabicyclo[7.7.7]tricosa-3,14,18-triene; tame = 1,1,1-tris(aminomethyl)ethane; [9]aneN3 = 1,4,7-triazacyclononane; pn = propane-1,2-diamine. [Pt(tn)Cl2], [Pt(tn)2]21, trans-[Pt(tn)2Cl2]21 and red polymeric species of unknown constitution, regardless of the temperature and solvents including dimethylformamide, water, dimethyl sulfoxide and ethanol.In no case was the target [Pt(tn)3]41 ion isolated even after using ion-exchange chromatography.6 Similar attempts to synthesize [Pt(stn)]41 were also unsuccessful. Red oils were obtained when free stn was treated with K2[PtCl6] in the presence of K2[PtCl4] in a variety of solvents (e.g.water, DMF, DMSO, alcohols). NMR Spectroscopy and ion exchange chromatography also showed these oils to be complex mixtures. An alternative route to the synthesis of bicyclic platinum(IV) tricosaneN6 cage complexes was envisaged by strapping the template [Pt(tame)2]41 from top to bottom (Scheme 3).A precedent for such a path existed for the analogous cobalt(III) template, which when treated with formaldehyde and a range of aldehydes in acetonitrile gave the [Co(tricosanetriimineN6)]31 framework.7 The synthesis for the simple [Pt(tame)2]41 complex had not been reported, however, and this paper addresses its synthesis and redox properties. The tripodal tame ligand coordinates facially to the metal ion, in analogy to the [9]aneN3 and [9]aneS3 (trithiacyclononane) ligands, but is more flexible.Scheme 2 Capping [Rh(tn)3]31 and [Rh(stn)]31. (i) CH3NO2, CH2O and base, in water.2172 J. Chem. Soc., Dalton Trans., 1999, 2171–2175 The reactivities of the three bis(tridentate ligand) complexes are compared. Results and discussion A good yield of [Pt(tame)2]Cl4 (75%) was obtained after 40 h when free tame was added to a solution of K2[PtCl6] dissolved in warm dimethylformamide at 40 8C with a catalytic amount of K2[PtCl4].When the reaction was performed in ethanol and heated for three hours at 70 8C a slightly lower yield of the desired product was obtained. The 1H and 13C NMR spectra for [Pt(tame)2]Cl4 in D2O were consistent with that for an octahedral bis(tridentate ligand) complex with D3h symmetry. For example, the methyl, quaternary and methylene carbon atom resonances occurred respectively at d 21.80, 45.15 and 47.20 in D2O. The 195Pt coupling constants with the methylene and quaternary carbon atoms are typical for complexes of this type (2JPt–C = 8.4; 3JPt–C = 44.2 Hz, respectively).8 The nitrogen protons rapidly exchange with D2O and were not observed.This is consistent with the first pKa (7.0 ± 0.1) which is characteristic for simple hexaamine platinum(IV) complexes.9 The formation of the [Pt(tame)2]41 template is likely to be initiated by tame substitution at the catalytic platinum(II) ion to form a square planar complex, as outlined in Scheme 4.Oxidation by PtCl6 22 then takes place via a bridged intermediate, accompanied by co-ordination of the pendant amines on the two tame residues, to generate the six-co-ordinate hexaamine geometry preferred by PtIV. An equivalent amount of the catalyst PtCl4 22 ion is also regenerated. This proposal parallels the mechanism for ligand substitution about the platinum(IV) ion in the presence of PtII described previously for didentate ligands.10–13 It was hoped that the PtIV–PtIII couple would show a degree of reversibility, given the bis(tridentate ligand) nature of the complex.However, the cyclic voltammetry (CV) of the parent [Pt(tame)2]Cl4 in aqueous 1 M HClO4 using a hanging mercury drop electrode showed an irreversible electrochemical reduction wave at Epc = 10.02 V (vs. SHE, 100 mV s21, Fig. 1). The reduction potential was largely insensitive to electrolyte, acid and scan rate up to 0.5 V s21, and was slightly more positive than that for [Pt(en)3]41,1 presumably because of the larger bite size of the tame chelate.The response was also irreversible in acetone at 295 K, using edge-plane pyrolytic graphite and gold disc electrodes. No response was observed using a platinum disc electrode in acetone. Formation of the [Pt(tame)2]31 complex was not evident in either aqueous media or acetone. The response was also irreversible up to 5 V s21. The electrochemical data are attributed to a two-electron reduction of PtIV, accompanied by dissociation of two nitrogen donor atoms, to give a square planar platinum(II) complex as shown in Scheme 5.This is supported by the coulometric reduction of [Pt(tame)2]Cl4 at 20.80 V vs. SCE in 0.1 M CF3CO2H and also in 0.1 M NaClO4 using a mercury pool working electrode which clearly showed a two-electron process. The 1H and 13C NMR spectra of the bulk electrolysis product were relatively simple and indicated that only one product was formed. The microanalysis of the isolated Scheme 3 Strapping [Pt(tame)2]41 to form [Pt(Me5-tricosanetriimineN6)] 41.(i) CH3CH2CHO, CH2O and base, in acetonitrile. tetrachlorozincate salt also implied that the two dissociated amine groups were protonated. The 1H NMR spectrum of [PtII(Htame)2]Cl4 in D2O showed that the signals for the methylene protons on the dissociated strand of the tame ligand were poorly resolved, and vicinal platinum-195 coupling was not discernible. The splitting pattern of the methylene protons of the co-ordinated methylene amine strands was consistent with that expected for an AA9 system, presumably due to the less flexible environment induced by co-ordination.However, the configuration about the platinum(II) ion was not defined by the NMR data. Two amine donor groups clearly had dissociated cis or trans as a result of the reduction, to form a complex with either C2h or C2v Fig. 1 Cyclic voltammogram of [Pt(tame)2]41 in 1 M HClO4 (100 mV s21, vs.Ag–AgCl–KCl (sat.), hanging mercury drop electrode). Scheme 4 Proposed mechanism for [Pt(tame)2]41 synthesis (some amine protons have been omitted for clarity).J. Chem. Soc., Dalton Trans., 1999, 2171–2175 2173 symmetry respectively. However, both isomers would give rise to the same number of 13C signals and similar 1H NMR splitting patterns. An X-ray crystallographic analysis of a single crystal of the tetrachlorozincate salt of the product was therefore necessary to determine its structure. The structural analysis confirmed that two trans nitrogen atoms had dissociated. The ORTEP14 plot of the cation in [PtII(Htame)2][ZnCl4]2?2H2O is presented in Fig. 2. Similar trans stereochemistry has been observed for the two ligands in [Pt([9]aneN3H)2]41.15 The interatomic distances and angles are listed in Table 1 and other relevant crystallographic data are in Table 2. The Pt–N bond lengths are consistent with those of platinum(II) saturated amine complexes. The six-membered chelate rings of both tame residues are in a chair conformation with their dissociated pendant amines in equatorial positions and far from the feasible trans bonding sites on the Pt.Scheme 5 Electrochemical reduction of [PtIV(tame)2]41 (amine protons have been omitted for clarity). Fig. 2 An ORTEP diagram of the cation in [PtII(Htame)2][ZnCl4]2? 2H2O. Table 1 Selected interatomic distances (Å) and bond angles (8) for [PtII(Htame)2][ZnCl4]2?2H2O Pt(1)–N(1) Pt(1)–N(2) N(3)–C(5) C(2)–C(3) C(2)–C(5) N(1)–Pt(1)–N(1) N(1)–Pt(1)–N(2) Pt(1)–N(1)–C(3) C(1)–C(2)–C(3) C(1)–C(2)–C(5) C(3)–C(2)–C(5) N(1)–C(3)–C(2) N(3)–C(5)–C(2) 2.042(6) 2.042(6) 1.51(1) 1.53(1) 1.53(1) 180.0 87.9(3) 116.3(5) 111.8(7) 110.3(7) 108.8(6) 113.3(7) 115.1(7) N(1)–C(3) N(2)–C(4) C(1)–C(2) C(2)–C(4) N(1)–Pt(1)–N(2) N(2)–Pt(1)–N(2) Pt(1)–N(2)–C(4) C(1)–C(2)–C(4) C(3)–C(2)–C(4) C(4)–C(2)–C(5) N(2)–C(4)–C(2) 1.50(1) 1.49(1) 1.53(1) 1.53(1) 92.1(3) 180.0 118.6(5) 111.3(6) 110.0(6) 104.4(6) 114.6(7) It is not surprising that the two amine groups trans to each other dissociated during the reduction process since this is the pathway that requires the least rearrangement.It is also well known that square planar platinum(II) complexes interact weakly with most nucleophiles at these axial sites. It is instructive therefore to look at the reduction of the [Pt(en)3]41 ion. NMR Spectrometry was used to monitor the hydrogenation of [Pt(en)3]41 in the presence of Pd/C in 1 M DCl.The experiment was undertaken under acidic conditions in order to trap the dissociated amines and limit their reco-ordination to the platinum( II) centre. After 20 min of hydrogenation at pH ª 1 the 1H NMR spectrum showed four signals: three triplets at d 2.68 (ª 1 H), 3.11 (1 H) and 3.32 (1 H) and a singlet at d 3.38 (0.2 H). Four signals were observed in the 13C NMR spectrum at d 37.4, 40.1, 44.6 and 48.1.None of these spectra had signals consistent with those of the parent [Pt(en)3]41 ion, whose 1H and 13C resonances occur at d 3.26 and 49.4, respectively. These data are consistent with the sample containing mostly [Pt(en)- (NH2CH2CH2NH3)2]41 ion with about 20% [Pt(en)2]21 and free ethylenediamine: the triplet at d 2.68 is attributed to the methylene protons of the chelate in [Pt(en)(NH2CH2CH2NH3)2]41 and the two triplets at d 3.11 and 3.32 are attributed to the methylene protons of the unidentate ethylenediamine ligands.The singlet at d 3.38 is ascribed to the methylene protons of the dissociated and protonated ethylenediamine; the ethylenediamine protons of [Pt(en)2]21 (at d 2.65) overlap with those of the chelate in [Pt(en)(NH2CH2CH2NH3)2]41. Likewise, the assignment of the 13C spectrum is as follows: d 37.4 (free ethylenediamine), 40.1 and 44.6 (unidentate ethylenediamine) and 48.1 (didentate ethylenediamine for the [Pt(en)(NH2CH2CH2- NH3)2]41 ion overlapped with those of the [Pt(en)2]21 ion, d 47.6).The 1H and 13C NMR spectra of the products from the hydrogenation performed under neutral conditions were very diVerent. After 30 min of hydrogenation, followed by addition of DCl, only two major signals were evident in the 1H NMR spectrum, a triplet at d 2.67 and a singlet at d 3.39 and are attributed to [Pt(en)2]21 and protonated ethylenediamine, respectively. The 13C NMR spectrum also showed two major resonances, at d 47.6 ([Pt(en)2]21) and 37.4 (free ethylenediamine).However, in both the NMR spectra, signals of very low intensity were observed which were consistent with traces of the [Pt(en)(NH2CH2CH2NH3)2]41 ion. The implication of these two results is that PtIV will preferentially dissociate two trans groups. The formation of [Pt(en)2]21 and ethylenediamine in the neutral reduction may seem to be an exception to this requirement. However, this product almost certainly arises from rapid intramolecular amine addition, rearrangement and diamine dissociation in the initially formed complex [PtII(en)(NH2CH2CH2NH2)]21 ion.There will also be other occasions when such facile subsequent events obscure the initial product, particularly with multidentate systems.16 Formation of the platinum(III) ion was, likewise, not evident in attempts electrochemically to oxidise the platinum(II) Table 2 Crystal data for [PtII(Htame)2][ZnCl4]2?2H2O Chemical formula M Crystal system Space group a/Å b/Å c/Å b/8 V/Å3 Z m(Cu-Ka)/cm21 No.reflections measured unique Rint Residuals R, R9 C10H36Cl8N6O2PtZn2 881.91 Monoclinic P21/n (no. 14) 12.012(2) 10.194(2) 12.012(1) 112.276(7) 1361.1(3) 2 185.33 2284 2171 0.049 0.036, 0.0472174 J. Chem. Soc., Dalton Trans., 1999, 2171–2175 counterpart in aqueous media and in acetone, in contrast to the behaviour of the analogous [Pt([9]aneS3)2]31/21 couple in acetonitrile, where [Pt([9]aneS3)2]31 was produced from the bulk oxidation of [Pt([9]aneS3)2]21.17 The more polarisable sulfur donor atoms appear to help to stabilise PtIII.The diYculty in reco-ordinating nitrogen atoms compared to the sulfur atoms in the transformation from square planar PtII to octahedral PtIII might be explained by initial oxidation of the sulfur atoms followed by their intramolecular reduction by the platinum(II) ion to form PtIII. The same type of path is much less accessible for the nitrogen-containing ligands.Attempts chemically to generate the platinum(III) complex were also unsuccessful: the absorbance changes of a solution containing equimolar amounts of [PtII(Htame)2]Cl4 and the one electron oxidant ferrocenium tetrafluoroborate were negligible over 120 min at 298 K. The inability to regenerate the [PtIV(tame)2]41 from [PtII(Htame)2]41 was also evident when a solution of [PtII- (Htame)2]Cl4 in D2O was purged with oxygen for 3 d at 323 K. This behaviour, however, is not inconsistent with that of the similar complex [PtII([9]aneN3H)2]41 which took 20 h to oxidise to its related platinum(IV) hexaamine complex at 90 8C.15 The CV of the bulk-reduced [PtII(Htame)2]41 solution in 0.1 M aqueous NaClO4 showed an irreversible anodic response at 0.22 V vs.SCE using the edge-plane pyrolytic graphite electrode which disappeared after a second sweep. This is akin to passivation of the electrode which has been observed with more complicated platinum(II) tetraamine complexes.7,18 Bulk electrochemical oxidation of the same reduced solution using a carbon rod electrode at 0.4 V vs.SCE for 12 h was likewise unsuccessful: the 1H and 13C NMR spectra of the desalted electrolysed solution showed that no oxidation had occurred. It is not clear why the oxidation to reform the platinum(IV) hexaamine complex was unsuccessful, especially since the steric demands of the tame ligand are not high and access of oxidants is not hindered.It might be that eVective oxidation requires an inner-sphere pathway and the oxidants used here were not suitable. Despite the inability to regenerate the platinum(IV) hexaamine complex readily, it is clear that the synthetic pathway involves cycling between platinum-(II) and -(IV) species and this process requires further investigation. The use of the [Pt(tame)2]41 ion in encapsulation reactions will be described in subsequent publications. Experimental Syntheses All chemicals (AR grade) were used as received unless otherwise specified.Bio-Rad analytical grade Dowex 50W-X2 (200– 400 mesh, H1 form) was used in the cation exchange chromatography. All evaporations were conducted with Buchi rotatory evaporators at Torr ª 16–20 using a water-bath (< 50 8C). 1,1,1-Tris(aminomethyl)ethane (tame). The compound tame?3HCl (25.5 g) prepared as described previously19 was suspended in hot ethanol (1 L) and added slowly to a warm solution of NaOH (13.5 g) in ethanol (200 mL).The mixture was heated at reflux under a stream of nitrogen for 3 h. The ethanol was evaporated and the tame ligand extracted from the white residue using hot chloroform. The suspension was filtered and the solvent evaporated to yield a pale yellow oil. NMR (D2O): 1H, d 0.80 (s, 1 H, CH3) and 2.45 (s, 2 H, CH2); 13C, d 18.64 (CH3), 39.81 (quaternary carbon) and 45.64 (CH2). Bis[1,1,1-tris(aminomethyl)ethane-N,N9,N0]platinum(IV) tetrachloride monohydrate, [Pt(tame)2]Cl4?H2O.Free tame (2 equivalents, 1.0 g) was added dropwise to a stirring suspension of K2PtCl6 (2 g) in dimethylformamide (15 mL) in the dark; K2PtCl4 (ª 5 mg) was added to catalyse the reaction. A clear orange solution formed after the tame was added and within ª5 min a colourless precipitate was evident. The reaction was heated at 40 8C for 30 h. The reaction mixture was diluted to 500 mL with water, the pH adjusted to 4–5 with HCl and then the solution was sorbed onto a column (15 × 3 cm) of Dowex 50W-X2 cation exchange resin.The column was washed with water (500 mL) and 2 M HCl (500 mL) and the complex then eluted with 6 M HCl. Evaporation of the eluate to near dryness yielded a colourless powder which was filtered oV, washed with ethanol and then 2-propanol. The powder was dried in vacuo over molecular sieves. Yield: 75% (Calc. for C10H30Cl4N6Pt? H2O: C, 20.38; H, 5.47; Cl, 24.06; N, 14.26; Pt, 33.11. Found: C, 20.35; H, 5.71; Cl, 24.67; N, 14.13; Pt, 32.95%). pKa1 7.0 ± 0.1, pKa2 11 ± 0.1 at 25 8C (0.1 mmol titrated with 0.100 M NaOH in 10 mL H2O potentiometrically; data were analysed with SUPERQUAD).20 NMR (D2O): 1H, d 1.10 (s, 1 H, CH3) and 2.87 (t, 1 H, CH2, 3JPt–H = 10.3 Hz); 13C, d 21.80 (s, CH3), 45.15 (t, quaternary, 3JPt–C = 44.2) and 47.20 (t, CH2, 2JPt–C = 8.4 Hz).[PtII(Htame)2]Cl4. Controlled potential electrolysis of [Pt(tame)2]Cl4?H2O (207 mg) in 0.1 M NaClO4 (ª 20 mL) at 2800 mV vs.SCE using a mercury pool working electrode indicated that 1.96 electrons per platinum(IV) ion were consumed. After electrolysing for 12 h the solution was decanted. The mercury pool was rinsed three times with water ( ª10 ml). The combined washings and the electrolysed solution were loaded onto a 2 × 5 cm column of Dowex cation exchange resin which was then washed with water (500 mL), 1 M HCl (500 mL) and the product eluted with 6 M HCl. The 6 M eluate was evaporated to dryness to yield a cream-coloured powder (90%).Crystals of trans-[PtII(Htame)2][ZnCl4]2?2H2O were slowly grown from an aqueous solution containing two drops of a saturated solution of ZnCl2 in 4 M HCl. NMR (D2O): 1H, d 1.20 (s, 3 H, CH3), 2.74 (m, 4 H, CH2), 3.10 (s, 2 H, CH2), 5.08 (broad s, NH2) and 5.35 (broad s, NH2); 13C, d 18.4 (CH3), 37.3 (quaternary), 46.1 (CH2), 48.9 (CH2) and 49.2 (CH2). Hydrogenation of [Pt(en)3]Cl4. The complex [Pt(en)3]Cl4 (20 mg) was dissolved in 1 M DCl (0.7 mL) in an NMR tube and Pd/C catalyst (10%, ª3 mg) was introduced. The suspension was purged gently with hydrogen for 20 min and then with nitrogen for 5 min.The sample was sealed and centrifuged for 5 min before the 1H and 13C NMR spectra were acquired. Assignment of the signals was aided by doping the sample with ethylenediamine after the spectrum had been acquired and by comparing the NMR spectra of separate samples of the precursors and products in 1 M DCl.NMR (1 M DCl): 1H, d 2.68 (t, ª1 H, co-ordinated ethylenediamine of [Pt(en)(NH2CH2- CH2NH3)2]41, overlapping a small signal from [Pt(en)2]21), 3.11 (t, 1 H, unidentate ethylenediamine of [Pt(en)(NH2CH2CH2- NH3)2]41), 3.32 (t, 1 H, unidentate ethylenediamine of [Pt(en)- (NH2CH2CH2NH3)2]41) and 3.38 (s, 0.2 H, unco-ordinated ethylenediamine); 13C, d 37.4 (unco-ordinated ethylenediamine), 40.1 (unidentate ethylenediamine of [Pt(en)(NH2CH2CH2- NH3)2]41), 44.6 (unidentate ethylenediamine of [Pt(en)(NH2- CH2CH2NH3)2]41) and 48.1 (co-ordinated ethylenediamine of [Pt(en)(NH2CH2CH2NH3)2]41, overlapping a small signal from [Pt(en)2]21).The above procedure was repeated in neutral D2O, using 20 mg [Pt(en)3]Cl4 and hydrogenating for 30 min instead. Assignment of the signals was aided by doping the sample with ethylenediamine after the spectrum had been acquired and by comparing the NMR spectra of separate samples of the precursors and products in neutral D2O.NMR after acidification (ª 0.1 M DCl): 1H, d 2.67 (t, 2 H, [Pt(en)2]21) and 3.39 (s, 1 H, uncoordinated ethylenediamine); 13C, d 37.4 (unco-ordinated ethylenediamine) and 47.6 ([Pt(en)2]21). Physical methods All 1H and 13C NMR spectra were acquired using a Varian Gemini 300 MHz spectrometer and standard Varian software.J. Chem. Soc., Dalton Trans., 1999, 2171–2175 2175 The solvents D2O and DCl (Merck) were used without further purification. All spectra were referenced internally against 1,4-dioxane (d 3.744 vs.(CH3)4Si for the 1H NMR spectra and d 67.3 vs. (CH3)4Si for 13C NMR spectra).21 The electrolytes used in the aqueous electrochemistry were of AR grade. The electrolyte concentration was typically 0.1 or 1.0 M. The concentration of the electroactive species was ª1 mM. The samples were purged for ª15 min with a continuous flow of argon or nitrogen prior to data acquisition. Measurements were acquired under a blanket of dinitrogen or argon at ª293 ± 1 K unless otherwise specified.The cyclic voltammograms using a mercury drop working electrode were recorded using a Princeton Applied Research Model-170 Polarographic Analyser or Model-173 Universal Programmer in conjunction with a Model-175 Potentiostat/Galvanostat (PAR-175). Both systems were interfaced with a Hewlett-Packard 7046A (X,Y) plotter. The mercury electrode (Metrohm 663 VA stand with an RSC Model-411 interface unit) was generally used in the hanging mercury drop mode.The three-electrode configuration included an auxiliary electrode, which was a carbon rod (ª0.4 cm diameter, ª8 cm in length), and the reference electrode, which was either a Ag–AgCl–KCl(sat) (199 mV vs. SHE)22 or a saturated calomel electrode (SCE, 241 mV vs. SHE).22 Structure determination The X-ray crystallographic analysis of a single crystal of [Pt(Htame)2][ZnCl4]2?2H2O was made using a Rigaku AFC-6R diVractometer with graphite monochromated Cu-Ka (l= 1.54178 Å) radiation and a rotating anode generator.The data (Table 2) were collected using the w–2q scan technique to a maximum 2q value of 120.18. No decay correction was applied. The refinement reflections, 1799 [I > 3s(I )], were corrected for Lorentz-polarisation eVects. The structure was solved by direct methods23 and expanded using Fourier techniques.24 The nonhydrogen atoms were refined anisotropically. Hydrogen atoms were included but not refined. Neutral atom scattering factors were taken from Cromer and Waber.25 Anomalous dispersion eVects were included in Fcalc;26 the values for Df 9 and Df 0 were those of Creagh and McAuley.27 The values of the mass attenuation coeYcients were those of Creagh and Hubbel.28 CCDC reference number 186/1455.Acknowledgements This research was supported in part by the Australian Research Council. The authors are also grateful to the ANU Microanalytical Service and D. Bogsanyi for the pKa determination.References 1 H. A. Boucher, G. A. Lawrance, P. A. Lay, A. M. Sargeson, A. M. Bond, J. C. Sangster and J. C. Sullivan, J. Am. Chem. Soc., 1983, 105, 4562. 2 R. J. Geue, T. W. Hambley, J. M. Harrowfield, A. M. Sargeson and M. R. Snow, J. Am. Chem. Soc., 1984, 106, 5478 and refs. therein. 3 R. J. Geue, M. B. McDonnell, A. W. H. Mau, A. M. Sargeson and A. C. Willis, J. Chem. Soc., Chem. Commun., 1994, 664 and refs. therein. 4 D. C. Giedt and C. J. Nyman, Inorg. Synth., 1966, 8, 239. 5 F. P. Dwyer and A. M. Sargeson, J. Am. Chem. Soc., 1959, 81, 5272. 6 K. N. Brown, Ph.D. Thesis, Australian National University, 1994. 7 R. J. Geue, A. Höhn, S. F. Ralph, A. M. Sargeson and A. C. Willis, J. Chem. Soc., Chem. Commun., 1994, 1513. 8 P. A. Lay and A. M. Sargeson, Inorg. Chem., 1986, 25, 4801. 9 L. G. Sillén, Stability Constants of Metal-Ion Complexes. Section I: Inorganic Ligands, 2nd edn., Special Publication Number 17, The Chemical Society, London, 1964. 10 W. R.Mason, Coord. Chem. Rev., 1972, 7, 241. 11 A. Peloso, Coord. Chem. Rev., 1973, 10, 123 and refs. therein. 12 D. M. Roundhill, Comprehensive Coordination Chemistry, Pergamon, Oxford, 1987, vol. 5 and refs. therein. 13 F. R. Hartley, The Chemistry of Platinum and Palladium, Applied Science Publishers, London, 1973, p. 494 and refs. therein. 14 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 15 K. Wieghardt, M. Köppen, W. SwiridoV and J. Weiss, J. Chem. Soc., Dalton Trans., 1983, 1869. 16 K. N. Brown, R. J. Geue, T. W. Hambley, D. R. Hockless, A. D. Rae and A. M. Sargeson, J. Chem. Soc., Dalton Trans., submitted. 17 A. J. Blake, A. J. Holder, T. I. Hyde and M. Schröder, J. Chem. Soc., Chem. Commun., 1987, 987. 18 K. N. Brown, D. R. Hockless, A. M. Sargeson, F. Anson and C. Shi, unpublished work. 19 R. J. Geue and G. H. Searle, Aust. J. Chem., 1983, 36, 927. 20 P. Gans, A. Sabatini and A. Vacca, J. Chem. Soc., Dalton Trans., 1985, 1195. 21 E. Pretsch, T. Clerc, J. Seibl and W. Simon, Tables of Spectral Data for Structural Determinations of Organic Compounds, 2nd edn., Springer, Berlin, 1989. 22 D. R. Lide, CRC Handbook of Chemistry and Physics, 73rd edn., CRC Publishing Co., Boca Raton, FL, 1992–1993 and refs. therein. 23 A. Altomare, M. Cascarano, C. Giacovazzo and A. Guagliardi, J. Appl. Crystallogr., 1993, 26, 343. 24 P. T. Beurskens, G. Admiraal, G. Beurskens, W. P. Bosman, R. de Gelder, R. Israel and J. M. M. Smits, DIRDIF 94: The DIRDIF 94 program system, Technical Report of the Crystallography Laboratory, University of Nijmegen, 1994. 25 D. T. Cromer and J. T. Waber, International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, Table 2.2 A. 26 J. A. Ibers and W. C. Hamilton, Acta Crystallogr., 1964, 17, 781. 27 D. C. Creagh and W. J. McAuley, International Tables for Crystallography, Kluwer Academic Publishers, Boston, 1992, vol. C, Table 4.2.6.8, pp. 219–222. 28 D. C. Creagh and J. H. Hubbel, International Tables for Crystallography, Kluwer Academic Publishers, Boston, 1992, vol. C, Table 4.2.4.3, pp. 200–206. Paper 9/01725I

ISSN:1477-9226    

DOI:10.1039/a901725i

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2177–2182 2177 Enforcing geometrical constraints on metal complexes using biphenyl-based ligands: spontaneous reduction of copper(II) by sulfur-containing ligands Mitchell R. Malachowski,*a Mark Adams,a Nadia Elia,a Arnold L. Rheingold b and Richard S. Kelly c a Department of Chemistry, University of San Diego, San Diego, CA 92110, USA b Department of Chemistry and Biochemistry, University of Delaware, Newark, Delaware 19716, USA c Department of Chemistry, Merrimack College, North Andover, MA 01845, USA Received 7th January 1999, Accepted 3rd May 1999 Two biphenyl-based N2S2 ligands, 2,29-bis-(4-methylimidazol-5-yl)methylsulfanyl)biphenyl (N2S2-mim) and 2,29- bis(2-pyridylmethylsulfanyl)biphenyl (N2S2-mpy), have been synthesized and their complexation with copper(II) precursors studied.In order to assess whether the biphenyl ring is influencing the geometry around the copper atom, the NS ligand 1-methyl-4-(2-pyridylmethylsulfanyl)benzene (NS-mpy) and its copper complexes were prepared.The N4 ligand 2,29-bis-(2-pyridylmethylamino)biphenyl (N4-mpy) in which the sulfurs have been replaced by nitrogens also was prepared. Treatment of N4-mpy with copper(II) salts led to isolation of copper(II) complexes with the formula [Cu(N4-mpy)]X2 where X = ClO4 or BF4. These complexes were analysed by a combination of elemental analysis, IR spectroscopy, FAB MS and electrochemistry. Likewise, treatment of NS-mpy with copper(II) salts led to isolation of the copper(II) complexes [Cu(NS-mpy)2][ClO4]2 or [Cu(NS-mpy)2][BF4]2.In comparison to the results found for ligands N4-mpy and NS-mpy, treatment of N2S2-mim or N2S2-mpy with [Cu(H2O)6][ClO4]2 or [Cu(H2O)6][BF4]2 in MeOH led to spontaneous reduction to form the copper(I) complexes [Cu(N2S2-mim)]ClO4 [Cu(N2S2-mim)]BF4, [Cu(N2S2-mpy)]ClO4 and [Cu(N2S2-mpy)]BF4. The formulation of these complexes as copper(I) species was confirmed by analytical methods, and for [Cu(N2S2-mpy)]ClO4?MeCN by X-ray crystallography. The copper(I) ion is in a distorted tetrahedral environment ligated by two nitrogens and two thioethers from the ligand.Cyclic voltammetry shows [Cu(N2S2-mpy)]ClO4, [Cu(N4-mpy)][ClO4]2 and [Cu(NS-mpy)2][ClO4]2 undergo quasi-reversible one-electron processes with Eo9 is 10.77, 10.21 and 10.53 V vs. SCE. Controlling the geometry at a metal ion site is of fundamental importance in many areas of chemistry.The judicious choice of ligands which force metal ions into unusual geometries or which stabilize specific oxidation states are of interest in designing catalytic systems or in bioinorganic chemistry.1 Our current interest in synthesizing ligands of this type revolves around exploiting what is known about biological systems and utilizing this information to obtain synthetic systems with similar properties. As an example, blue copper proteins, such as plastocyanin and azurin, function as biological electron carriers.2 Crystallographic studies have shown that the active sites consist of a mononuclear copper(II) ion co-ordinated by two imidazoles, one thioether, and one thiolate. The geometry can be viewed as a distorted, flattened tetrahedron or as a trigonalplanar Cu(histidine)2(cysteine) unit with an additional methionine thioether apically bound.3 The blue copper proteins also have very positive reduction potentials showing their ability to stabilize the copper(I) form.Synthetic systems which incorporate the properties of the blue copper proteins require the preparation of tetradentate ligands which include both sulfur and nitrogen donors.4–7 In order to prevent disulfide formation or to reproduce the unusual distorted tetrahedral geometry, steric constraints often are built into the ligand sets or thioethers are used in place of the thiolate sulfur. As an example of a system which enforces tetrahedral geometry around copper, ligands with hindered pyrazolylborate moieties have been shown to recreate many of the properties of the naturally occurring compounds.6,7 Tetradentate ligands can be designed in a vast number of structural permutations and from a tremendous variety of motifs.Depending on the structural features of these ligands, they can be designed to force the resultant metal complexes into specific desired geometries. We particularly are interested in exploiting the properties of the biphenyl moiety in designing new ligand sets due to the fact that the two aromatic rings in the parent biphenyl are not coplanar, but instead have a dihedral angle between the rings of 428.A further increase in the dihedral angle between the rings can be anticipated if bulky substituents also are present on the rings due to the steric eVects of the substituents. Most importantly in our studies is the fact that substituents on the adjacent phenyl rings of the biphenyls will be forced out of plane and the resultant metal complexes modified from a planar-based geometry towards a more tetrahedral-like geometry.Metals such as copper(II), which have Jahn–Teller distortions present, prefer planar-based geometries so copper(II) complexes formed from these biphenyl-based ligands will have to balance the tension between the preferences of the ligand set with those of the metal ion. The use of biphenylbased ligands has resulted in the synthesis of a variety of metal complexes with interesting properties due to the presence of the biphenyl moiety 8–13 or dinaphthyl systems.14 As part of our eVorts towards synthesizing multidentate ligands and their copper complexes,15 we report here the synthesis of two N2S2 ligands, 2,29-bis-(4-methylimidazol-5- ylmethylsulfanyl)biphenyl (N2S2-mim) and 2,29-bis-(2-pyridylmethylsulfanyl) biphenyl (N2S2-mpy), and their complexation with copper(II) precursors. The electrochemical properties of the complexes were studied and the molecular structure of the [Cu(N2S2-mpy)]ClO4?CH3CN complex was determined by X-ray diVraction. In order to assess whether the biphenyl ring is2178 J.Chem. Soc., Dalton Trans., 1999, 2177–2182 influencing the geometry around the copper atom, we also have prepared the NS ligand, 1-methyl-4-(2-pyridylmethylsulfanyl)- benzene (NS-mpy), in which the biphenyl ring is absent along with its copper complexes. Additionally, we report the properties of the N4 ligand, 2,29-bis-(2-pyridylmethylamino)biphenyl (N4-mpy), in which the sulfurs have been replaced by nitrogens to determine how essential the sulfurs are to the properties of the complexes.Experimental General All reagents and solvents were purchased from commercial sources and used as received unless noted otherwise. 2,29- Disulfanyl-1,19-biphenyl and 2,29-diamino-1,19-biphenyl were prepared by the literature methods.16,17 Melting points were obtained with the use of a Fisher-Johns apparatus and are uncorrected.The C, H, and N chemical analyses were performed at Desert Analytical, Tucson, AZ. Metal contents were determined complexometrically by indirect titration with Na2H2edta and zinc acetate after destruction of the sample with concentrated nitric acid.18 The IR spectra were recorded on a Nicolet 5ZDX instrument, mass spectra at the Nebraska Center for Mass Spectrometry in Lincoln, NE, and 1H and 13C NMR on a Varian Unity 300 MHz instrument. Cyclic voltammetric data were collected using a Cypress Systems Model 1090 electrochemical analyzer (Cypress Systems, Lawrence, KS).All scans were done at 0.050 V s21 with 3 mm glassy carbon electrodes (BAS, West Lafayette, IN) in acetonitrile (Aldrich, 99.5% spectrophotometric grade) that contained 0.10 M tetrabutylammonium hexafluorophosphate (Aldrich, 98%) as the supporting electrolyte. The glassy carbon electrodes were polished with 0.3 and 0.05 mm alumina on microcloth pads (all Buehler, Lake BluV, IL), sonicated for 5 s in distilled water, and dried carefully before introduction into the electrochemical cell.A three-electrode system was used in all the measurements, with potentials recorded vs. a zero-leakage Ag1–AgCl reference electrode (SDR2, World Precision Instruments, Sarasota, FL). The potential of this reference was measured daily vs. an aqueous saturated calomel electrode (SCE) and an appropriate correction made so that the Eo9 values for each complex could be reported vs. SCE.A platinum wire served as the auxiliary electrode. The electrochemical cell consisted of a glass vial of ca. 10.0 cm3 volume with a fitted Teflon cap. All solutions were purged with solvent-saturated nitrogen prior to data collection. CAUTION. Although there were no incidents in our laboratory, transition metal perchlorates may explode violently. They should be prepared in small quantities and handled with care.S HN N S NH N S S N N HN HN N N S N N2S2-mim N2S2-mpy N4-mpy N, S-mpy Synthesis of ligands 2,29-Bis(4-methylimidazol-5-ylmethylsulfanyl)biphenyl (N2S2- mim). To acetic acid (250 cm3) was added 2,29-disulfanylbiphenyl (1.00 g, 4.6 mmol) and 4-methyl-5-imidazolemethanol hydrochloride (1.40 g, 9.2 mmol). The solution was refluxed for 4 h. Hot ethanol (15 cm3) was added and the solution cooled to room temperature. Sodium hydroxide (10 mol dm23) was added until the pH reached 8 and then water (50 cm3) was added.The yellowish precipitate that formed was collected and crystallized from ethyl acetate–hexane to give white crystals (1.32 g, 70.6%), mp 238–240 8C. Mass spectrum (FAB MS): m/z (relative intensity) 407 (12), 307 (10), 216 (14), 176 (10) and 133 (100). HRMS (FAB, m-nitrobenzyl alcohol): calc. for C22H23N4S2 ([M1H]1) 407.1364, found 407.1359. dH (CDCl3) 2.15 (6 H, s), 5.14 (4 H, s), 7.23–7.70 (8 H, m), 7.50 (2 H, s) and 9.26 (2 H, broad). 2,29-Bis(2-pyridylmethylsulfanyl)biphenyl (N2S2-mpy). To a solution of 2-chloromethylpyridine hydrochloride (1.50 g, 9.2 mmol) in water (50 cm3) was added a solution of 2,29- disulfanylbiphenyl (1.00 g, 4.6 mmol) in EtOH (50 cm3). After both reactants were completely dissolved, the solution was stirred for 5 min followed by the addition of 10 mol dm23 NaOH (1 cm3). The solution turned from clear to a light pink. It was refluxed and stirred for 24 h. After cooling to room temperature, the solvent was evaporated at reduced pressure.Light yellow crystals were obtained which were recrystallized from MeOH to give white crystals (1.57 g, 85.3%), mp 71– 72 8C, (lit.,12 70 8C). Mass spectrum (FAB MS): m/z (relative intensity) 401 (100), 308 (52), 276 (26) and 132 (78). HRMS (FAB): calc. for C24H21N2S2 ([M1H]1) 401.1068, found 401.1151. dH (CDCl3) 4.16 (4 H, s), 7.12–7.32 (8 H, m) and 7.36–7.55 (6 H, m), 8.48 (2 H, d) (Found: C, 71.40; H, 5.30; N, 6.80.C12H10NS requires C, 71.96; H, 5.04; N, 6.99%). 2,29-Bis(2-pyridylmethylamino)biphenyl (N4-mpy). To a solution of 2,29-diaminobiphenyl (1.0 g, 5.43 mmol) in EtOH (50 cm3) was added a solution of 2-chloromethylpyridine hydrochloride (3.56 g, 21.7 mmol) in water (15 cm3). A 10 mol dm23 NaOH solution was added dropwise to the solution until the pH reached 9. A change from a light yellow to a red-orange was observed at pH 8. The solution was stirred at room temperature and NaOH added over 5 d to maintain the pH at 8–9.During this time precipitation of an oV-white solid occurred. The reaction was complete when the pH no longer dropped below 8. The precipitate was collected by filtration and recrystallized from EtOH resulted in white crystals (1.51 g, 75.9%), mp 135–136 8C (lit.,8b 137 8C). Mass spectrum (FAB MS): m/z (relative intensity) 367 (100), 274 (35), 195 (23) and 180 (29). HRMS (FAB) calc. for C24H23N4 ([M 1 H]1) 366.1922, found 366.1923.dH (CDCl3) 1.62 (2 H, broad s), 4.48 (4 H, s), 6.61–6.83 (8 H, m), 7.04–8.50 (6 H, m) and 8.53 (2H, d) (Found: C, 79.00; H, 5.84; N, 15.62. C12H11N2 requires C, 78.65; H, 6.06; N, 15.28%). 1-Methyl-4-(2-pyridylmethylsulfanyl)benzene (NS-mpy). To a solution of p-thiocresol (3.61 g, 29.1 mmol) in 95% EtOH (75 cm3) was added 2-chloromethylpyridine hydrochloride (4.77 g, 29.1 mmol) dissolved in water (60 cm3). The mixture was stirred and refluxed for 24 h. The solution was extracted with CHCl3 (3 × 50 cm3) and the organic phase dried over Na2SO4, filtered, and the solvent evaporated under reduced pressure. The resultant oil was dissolved in hot ethyl acetate and hexane added to induce crystallization.Shiny white needle-like crystals appeared overnight (3.40 g, 54.3%), mp 183–185 8C. dH (CDCl3) 4.04 (2 H, s), 7.02–7.25 (4 H, m), 7.31–7.46 (3 H, m) and 8.08 (1 H, d) (Found: C, 72.18; H, 5.98; N, 6.77. C13H13NS requires C, 72.51; H, 6.10; N, 6.50%).J.Chem. Soc., Dalton Trans., 1999, 2177–2182 2179 Synthesis of copper complexes [Cu(N2S2-mim)]ClO4 1. A solution of N2S2-mim (0.10 g, 0.25 mmol) in MeOH (10 cm3) was treated with [Cu(H2O)6][ClO4]2 (0.093 g, 0.25 mmol) in MeOH (10 cm3), filtered and allowed to stand at room temperature whereupon colorless crystals precipitated over a period of two weeks. The crystals were collected and washed with cold MeOH. Mass spectrum (FAB MS): m/z (relative intensity) 469 (100), 406 (65), 311 (31), 186 (18) and 154 (29) (Found: C, 46.59; H, 4.36; Cu, 11.29; N, 10.01.C22H22ClCuN4O4S2 requires C, 46.39; H, 3.90; Cu, 11.16; N, 9.83%). [Cu(N2S2-mim)]BF4 2. A solution of N2S2-mim (0.10 g, 0.25 mmol) in MeOH (10 cm3) was treated with [Cu(H2O)6][BF4]2 (0.086 g, 0.25 mmol) in MeOH (10 cm3), filtered and allowed to stand at room temperature whereupon colorless crystals precipitated overnight. The crystals were collected and washed with cold MeOH. Mass spectrum (FAB MS): m/z (relative intensity) 469 (86), 406 (100), 311 (51) and 186 (15) (Found: C, 47.18; H, 3.65; Cu, 11.36; N, 10.32.C22H22BCuN4F4S2 requires C, 47.44; H, 3.99; Cu, 11.41; N, 10.06%). [Cu(N2S2-mpy)]ClO4 3. A solution of N2S2-mpy (0.10 g, 0.25 mmol) in MeOH (15 cm3) was added to a solution of [Cu(H2O)6][ClO4]2 (0.093 g, 0.25 mmol) in MeOH (10 cm3) turning from blue to pale yellow almost instantly. Colorless crystals formed over 48 h, were collected and washed with cold MeOH. Crystals suitable for determination were grown by vapor diVusion of diethyl ether into an MeCN solution of the complex.Mass spectrum (FAB MS): m/z (relative intensity) 565 (25), 563 (38), 464 (45), 401 (100), 364 (32), 307 (65) and 176 (52) (Found: C, 51.84; H, 3.63; N, 4.83. C24H20ClCuN2O4S2 requires C, 51.15; H, 3.58; N, 4.97%). [Cu(N2S2-mpy)]BF4 4. A solution of N2S2-mpy (0.10 g, 0.25 mmol) in MeOH (15 cm3) was added to a solution of [Cu(H2O)6][BF4]2 (0.086 g, 0.25 mmol) in MeOH (10 cm3) turning from light blue to colorless almost instantly.Colorless crystals formed overnight, were collected and washed with cold MeOH. Mass spectrum (FAB MS): m/z (relative intensity) 464 (35), 401 (100), 371 (27), 307 (76) and 176 (66) (Found: C, 52.46; H, 3.88; N, 4.91. C24H20BCuF4N2S2 requires C, 52.32; H, 3.67; N, 5.08%). [Cu(N4-mpy)][ClO4]2 5. A solution of N4-mpy (0.50 g, 1.4 mmol) in EtOH (25 cm3) was treated with [Cu(H2O)6][ClO4]2 (0.50 g, 1.4 mmol) in EtOH (25 cm3), filtered and allowed to stand at room temperature whereupon dark green crystals precipitated.Mass spectrum (FAB MS): m/z (relative intensity) 429 (38), 307 (28), 219 (7) and 154 (100) (Found: C, 45.59; H, 3.75; Cu, 10.45; N, 8.70. C24H22Cl2CuN4O8 requires C, 45.83; H, 3.53; Cu, 10.10; N, 8.90%). [Cu(N4-mpy)][BF4]2 6. A solution of N4-mpy (0.50 g, 1.4 mmol) in EtOH (25 cm3) was treated with [Cu(H2O)6][BF4]2 (0.47 g, 1.4 mmol) in EtOH (25 cm3), filtered and allowed to stand at room temperature whereupon green crystals precipitated.Mass spectrum (FAB MS): m/z (relative intensity) 429 (72), 307 (43), 219 (18) and 154 (100) (Found: C, 47.95; H, 3.83; Cu, 10.22; N, 9.09. C24H22B2CuF8N4 requires C, 47.75; H, 3.68; Cu, 10.53; N, 9.28%). [Cu(NS-mpy)2][ClO4]2 7. A solution of NS-mpy (0.30 g, 1.4 mmol) in absolute EtOH (10 cm3) was treated with [Cu(H2O)6]- [ClO4]2 (0.24 g, 0.70 mmol) in absolute EtOH (10 cm3), filtered and allowed to cool to room temperature.Large brown crystals formed which were filtered oV and washed with cold EtOH. Mass spectrum (FAB MS): m/z (relative intensity) 493 (23), 371 (8), 307 (31), 216 (32) and 154 (100) (Found: C, 45.05; H, 3.79; N, 4.04. C26H26Cl2CuN2O8S2 requires C, 45.60; H, 4.14; N, 4.13%). [Cu(NS-mpy)2][BF4]2 8. A solution of NS-mpy (0.30 g, 1.4 mmol) in absolute EtOH (10 cm3) was treated with [Cu(H2O)6][BF4]2 (0.24 g, 0.70 mmol) in absolute EtOH (10 cm3), filtered and allowed to cool to room temperature.Large brown crystals formed which were filtered oV and washed with cold EtOH. Mass spectrum (FAB MS): m/z (relative intensity) 493 (100), 310 (26), 278 (82) and 216 (77) (Found: C, 46.33; H, 3.78; N, 3.73. C26H26B2CuF8N2S2 requires C, 46.76; H, 3.93; N, 4.20%). Crystal structure determination for [Cu(N2S2-mpy)]ClO4?MeCN 3 Crystallographic data are collected in Table 1. Systematic absences in the diVraction data indicated either of the monoclinic space groups Cc or C2/c.Although the cation possesses nearly perfect twofold symmetry, only the non-centrosymmetric alternative can be stoichiometrically correct. In Cc the asymmetric unit consists of one copper(I) cation, one ClO4 2 counter ion and a molecule of acetonitrile, the recrystallization solvent. This choice is supported by the distribution of E values and by the chemically reasonable results of refinement. Corrections for absorption were made empirically. The structure was solved by direct methods and refined with all non-hydrogen atoms anisotropic.Hydrogen atoms were introduced as idealized contributions. At this point the refinement converged at R(F) = 12.6%, but diYculties in assigning the correct absolute structure led us to consider the possibility of racemic twinning. The inclusion of a racemic twin model in further refinement reduced R(F) to 4.4%. All computations used SHELXTL 5.03 software.19 CCDC reference number 186/1453.Results and discussion Synthesis The N2S2-mim ligand was prepared by treating 2,29-disulfanylbiphenyl with 4-methyl-5-imidazolemethanol hydrochloride. Imidazolylmethylation of thiols has been shown to occur for a variety of thiols,20 and we anticipated the procedure would lead smoothly to products here. The importance of this method in preference to others for incorporating imidazoles into multidentate ligands is that the imidazole ring is functionalized at the five position rather than the one or two position.Since the imidazole on histidine found in biological systems is also linked through this position, systems with this substitution pattern should have properties closer to the protein bound metalloproteins. The N2S2-mpy and NS-mpy ligands were synthesized using the substitution reaction between a thiol and 2-chloromethylpyridine under basic conditions; N2S2-mpy was reported previously by Serratrice and co-workers.12 The N4-mpy ligand was synthesized using the well known reaction between a primary amine and 2-chloromethylpyridine.In this case only one pyridylmethylene arm adds to each primary amine. This is probably a result of the precipitation of the product as it is formed under the reaction conditions used. This ligand previously was made via the reaction of 2,29-diaminobiphenyl with pyridine-2-carbaldehyde in the presence of zinc dust.8b Further condensation of the N4-mpy ligand with 2-chloromethylpyridine or other aromatic amines to form N6 ligands has been successful and will be reported elsewhere. Characterization of the ligands by a combination of 1H, 13C NMR, elemental analysis, fast atom bombardment or high resolution FAB MS confirmed the structures proposed.The complexes 1–8 were prepared in straightforward fashion from the appropriate ligand. Treatment of N4-mpy with copper(II) salts led to isolation of copper(II) complexes with the formula [Cu(N4-mpy)]X2 where X = ClO4 or BF4.These2180 J. Chem. Soc., Dalton Trans., 1999, 2177–2182 complexes were analysed by a combination of elemental analysis, IR spectroscopy, FAB MS and electrochemistry. Likewise, treatment of NS-mpy with copper(II) salts led to isolation of the copper(II) complexes [Cu(NS-mpy)2][ClO4]2 or [Cu- (NS-mpy)2][BF4]2. These complexes are formulated as being four-co-ordinate with two ligands per copper as evidenced by their mass spectra and elemental analysis data. In comparison to the results found for ligands N4-mpy and NS-mpy, treatment of the N2S2-mim or N2S2-mpy with [Cu(H2O)6][ClO4]2 or [Cu(H2O)6][BF4]2 in MeOH led to an immediate change in the solution from blue to very pale yellow signifying reduction of the oxidation state of the metal.Crystallization of the complexes led to isolation of colorless or oV- white crystals of [Cu(N2S2-mim)]ClO4 1, [Cu(N2S2-mim)]BF4 2, [Cu(N2S2-mpy)]ClO4 3, and [Cu(N2S2-mpy)]BF4 4. These complexes are air stable indefinitely.Their formulation as copper( I) species was confirmed by analytical methods, and for 3, by X-ray crystallography. Elemental analysis data were consistent with the presence of only one perchlorate or tetrafluoroborate counter ion in each. Serratrice and co-workers 12 previously had prepared 3 and saw a similar result. Repeated attempts to isolate X-ray quality crystals of 1 or 2 have been unsuccessful. Spontaneous reduction of CuII upon complexation to ligand sets typically occurs when sterically demanding ligands which contain sulfur are present.21–27 Addison and co-workers 21 have shown that in N2S2 macrocyclic ligands the ability of the ligand to provide a tetrahedral environment around CuI stabilizes that structure at the expense of the copper(II) form.A similar situtation exists here for complexes 1–4. The autoreduction process for N2S2 ligands with CuII is thought to occur through the copper-catalysed oxidation of the solvent or via ligand involvement of a sulfur radical cation.26,27 The solvent oxidation mechanism may be working in our case since changing the solvent from MeOH to MeCN slows down the reduction process.In MeCN the reaction mixture slowly becomes colorless over the course of 24 h rather than instantaneously as is found in MeOH. Structure of [Cu(N2S2-mpy)]ClO4?MeCN X-ray quality crystals of complex 3?MeCN were obtained by recrystallizing the complex from acetonitrile–diethyl ether.The complex crystallizes in the space group Cc. Crystal, data collection and refinement parameters are given in Table 1 and selected bond angles and lengths in Table 2. A view of the cationic portion of the complex is depicted in Fig. 1, including the atomic numbering scheme. The CuI is co-ordinated by two pyridyl nitrogens and two thioether sulfurs. The co-ordination geometry around the copper atom can best be described as distorted tetrahedral with the bond angles ranging from 87.5 to 136.38.Our goal was to enforce a tetrahedral geometry on the copper via the use of the N2S2-mpy biphenyl-based ligand and the crystallographic results confirm this approach. However, as noted above, the complex has stabilized itself by spontaneous Table 1 Crystallographic data for [Cu(N2S2-mpy)]ClO4?Me4CN 3 Formula Formula weight Crystal system Space group a, b, c/Å b/8 V/Å3, Z Dx/g cm23 m(Mo-Ka)/cm21 T/8C Reflections collected Independent reflections Transmission coeYcients R(F), R(wF2) (%) C26H23ClCuN3O4S2 604.58 Monoclinic Cc (no. 9) 14.0927(5), 14.0871(6), 13.7574(6) 105.1415(13) 2636.4(2), 4 1.523 11.3 250(2) 4510 3573 0.944–0.834 4.35, 10.12 reduction from CuII to CuI thereby minimizing the unfavorable steric constraints. The Cu–N bond lengths are essentially identical (1.966 and 1.967 Å) and fall within the norms for many other four-co-ordinated copper(I)-pyridine bond lengths.28 The Cu–S bond lengths (2.428 and 2.459 Å) also can be considered as normal.29 The flexibility of the biphenyl ring is manifested in the local geometry around the copper.One measure of the closeness of fit to a tetrahedron is the dihedral angle between the S(1)– Cu(1)–N(2) and S(2)–Cu(1)–N(1) planes (it would be 908 for an idealized tetrahedron). For complex 3?MeCN this value is 67.48. For other biphenyl-based copper(I) complexes this angle ranges from 55.1 to 91.78.9,10 A second measure of the tetrahedral nature of a complex is the dihedral “crossing” angle.For 3?MeCN the dihedral angle between the S(1)–C(12)–C(11)– N(2)–Cu–(1) plane and the S(2)–C(6)–C(5)–N(1)–Cu–(1) plane is 89.48. In other biphenyl-based copper(I) complexes, it varies from 48.9 to 74.98. Conformation changes also occur to the ligand upon complexation. Most notable is the dihedral angle of 838 found between the individual aromatic rings of the biphenyl moiety. This near perpendicular orientation of the rings shows how the biphenyl twists to generate the tetrahedron around the copper.This is the largest biphenyl dihedral angle reported for a copper(I) complex (between 61.6 and 73.98).9b,10 The non-planar nature of the rings and the ability of the ligand to twist out of planarity is a hallmark of biphenyl-based ligand sets. Mass spectra We have made extensive use of Fast Atom Bombardment Mass Spectrometry (FAB MS) in the analysis of copper(I) and copper(II) complexes for partial structure analysis.15 This technique has been used to help characterize complexes 1–8 by using both the molecular ion present and the fragmentation Fig. 1 Molecular structure and atom-labelling scheme for [Cu(N2S2- mpy)]ClO4?MeCN. Table 2 Selected bond lengths (Å) and bond angles (8) for [Cu(N2S2- mpy)]ClO4?MeCN 3 Cu(1)–N(1) Cu(1)–S(1) N(1)–Cu(1)–N(2) N(2)–Cu(1)–S(1) N(2)–Cu(1)–S(2) 1.966(6) 2.428(2) 136.3(2) 87.5(2) 116.76(13) Cu(1)–N(2) Cu(1)–S(2) N(1)–Cu(1)–S(1) N(1)–Cu(1)–S(2) S(1)–Cu(1)–S(2) 1.967(5) 2.459(2) 125.76(13) 86.52(14) 101.20(5) Dihedral angles Phenyl/phenyl 83.0 Mean Plane S(1)–C(12)–C(11)–N(2)–Cu(1) and mean plane S(2)–C(6)– C(5)–N(1)–Cu(1) 89.4 Plane S(1)–Cu(1)–N(2) and plane S(2)–Cu(1)–N(1) 67.4J. Chem.Soc., Dalton Trans., 1999, 2177–2182 2181 patterns obtained. The results indicate the presence of the intact cation in all cases. For example, it is found at m/z 469 for 1 and 464 for 3. The fragmentation patterns found for complexes 1–8 are also consistent with the presence of their respective ligands and counter ions.Electrochemistry The reduction potentials for complexes 3, 5, and 7 were measured by cyclic voltammetry in acetonitrile at a glassy carbon electrode. The results for the experiments are shown in Fig. 2. For a 0.38 mM solution of 3, two voltammetric waves were observed as the potential was swept in the anodic direction resulting in the oxidation of the copper(I) complex to CuII. The predominant wave has a value for Eo9 (taken as the average of the anodic and cathodic peak potentials) of 10.77 V vs.SCE. A value of 84 mV was observed for the peak separation, dEp, which is indicative of a quasi-reversible heterogeneous electron transfer. The ratio of the cathodic to anodic peak currents, ipc : ipa, was nearly 1 : 1, demonstrating that the oxidized form of the complex was stable on the timescale of the voltammetric experiment. This chemical reversibility, along with the very positive value for the oxidation potential, clearly illustrates the stability the N2S2-mpy ligand imparts to the copper(I) complex.The smaller of the two voltammetric waves, centered near 10.50 V, is thought to be the result of an impurity in the sample. The high oxidation potential for [Cu(N2S2-mpy)]ClO4 demonstrates the ease with which the complex can be reduced and is clearly a result of the biphenyl backbone and the sulfur donors. Indeed, the [Cu(N2S2-mpy)]ClO4 reproduces the very positive potentials found for the blue copper proteins.30 A cyclic voltammogram recorded for a 0.70 mM solution of complex 5 in acetonitrile is shown in Fig. 2. The potential was swept in the cathodic direction first with the reduction of CuII being observed at a value for Eo9 = 10.21 V vs. SCE. This is greater than 500 mV more cathodic than the reduction potential of 3 and shows the large eVect of replacing sulfur with nitrogen in this ligand. The value for DEp was 88 mV, very close to that observed for 3, demonstrating quasi-reversible kinetics for the electron transfer reaction.The ratio of the reverse to forward peak currents was again unity, indicative of the reversible regeneration of the original complex following reduction. The cyclic voltammetry of the copper(II) complex 7 (0.44 mM), prepared from two bidentate NS-mpy ligands, is chem- Fig. 2 Cyclic voltammograms recorded at a glassy carbon electrode in acetonitrile: (--) 0.38 mM solution of [Cu(N2S2-mpy)]ClO4 3, Eo9 = 10.77 V vs.SCE, DEp = 84 mV; (-) 0.70 mM solution of [Cu(N4- mpy)][ClO4]2 5, Eo9 = 10.21 V vs. SCE, DEp = 88 mV. The scan rate was 50 mV s21 and the supporting electrolyte 0.10 M tetrabutylammonium hexafluorophosphate solution in both cases. ically reversible (ipc : ipa = 1 : 1), with an Eo9 value of 10.53 V vs. SCE. This value is intermediate between those for 3 and 5. The value for DEp was found to be 124 mV, indicating that the electron transfer to 7 is the slowest of the three complexes, but still quasi-reversible.A comparison with the voltammogram for 3 demonstrates that the absence of the biphenyl moiety in 7 results in lessened stability for the 11 oxidation state for copper. Although this decrease in stability is not nearly as extreme as the 560 mV cathodic shift that results from the replacement of sulfur by nitrogen in 5, the presence of the biphenyl ring leads to a 0.24 V cathodic shift. The primary reason for this shift seems to be the ability of 3 to exist in a tetrahedral environment which stabilizes the copper(I) form.31 Conclusion We have probed the properties of copper complexes prepared from a series of related ligands which were designed to enforce geometrical constraints on the metal atom.Our original goal was to prepare ligands which would enforce tetrahedral geometry on metal ions through the use of the biphenyl backbone. In that respect, our original premise that the biphenyl moiety would impose this geometrical outcome has proven to be correct as evidenced by the single crystal structure analysis of 3?MeCN which revealed it to be in a pseudotetrahedral structure.However, in order to relieve the severe steric constraints placed on the copper(II) form, complexes 1–4 spontaneously reduced to CuI. In order to test whether the mere presence of two sulfur donors is enough to lead to the spontaneous reduction we prepared the bidentate NS-mpy analog of the N2S2- mpy ligand.When treated with copper(II) precursors isolation of copper(II) complexes was found. This result shows that the biphenyl backbone is necessary for the observed spontaneous reduction since the biphenyl is absent in the NS-mpy ligand. We also wanted to probe whether the sulfurs were essential for the reduction so we prepared the all nitrogen N4-mpy ligand. The spontaneous reduction found for complexes 1–4 does not occur when the sulfurs are replaced by nitrogen donors as in 5 and 6.Therefore, in ligands of this type, the presence of the sulfur donors and the biphenyl ring is necessary for the spontaneous reduction process. Cyclic voltammetry showed a significant positive shift of the CuII–CuI redox couple due to the presence of the sulfur donors or the biphenyl ring. It has previously been shown that the E1/2 values become more positive as the local geometry around the copper is changed from that of a distorted plane to a distorted tetrahedron.21 It is not surprising, then, that the Eo9 for [Cu(N2S2-mpy)]ClO4 is so positive as it includes sulfur donors and is forced into a tetrahedral environment.The synthesis of related ligands based on the biphenyl backbone are being pursued. Acknowledgements Acknowledgement is made to the donors of The Petroleum Research Fund, administered by the American Chemical Society, for partial support of this research (to M. R. M.). References 1 T.N. Sorrell, Tetrahedron, 1989, 45, 3. 2 P. M. Colman, H. C. Freeman, J. M. Guss, M. Murata, V. A. Norris, J. A. M. Ramshaw and M. P. Venkatappa, Nature (London), 1978, 272, 319; E. I. Solomon, J. W. Hare, D. M. Dooley, J. H. Dawson, P. J. Stephens and H. B. Gray, J. Am. Chem. Soc., 1980, 102, 168; J. S. Thompson, T. J. Marks and J. A. Ibers, J. Am. Chem. Soc., 1979, 101, 4180. 3 J. M. Guss and H. C. Freeman, J. Mol. Biol., 1983, 169, 521; E. T. Adman, R. E. Stenkamp, L. C.Sieker and L. H. Jensen, J. Mol. Biol., 1978, 123, 35; G. E. Norris, B. F. Anderson and E. N. Baker, J. Am. Chem. Soc., 1986, 108, 2784.2182 J. Chem. Soc., Dalton Trans., 1999, 2177–2182 4 E. Bouwman, W. L. Driessen and J. Reedijk, Coord. Chem. Rev., 1990, 104, 143. 5 L. Cassella, M. Gullotti, E. Suardi, M. Sisti, R. Pagliarin and P. Zanello, J. Chem. Soc., Dalton Trans., 1990, 2843. 6 N. Kitajima, K. Fujisawa and Y. Moro-oka, J. Am. Chem. Soc., 1990, 112, 3210. 7 N. Kitajima, K.Fujisawa, M. Tanalka and Y. Moro-oka, J. Am. Chem. Soc., 1992, 114, 9232. 8 (a) F. Lions and K. V. Martin, J. Am. Chem. Soc., 1957, 79, 1273; H. Goodwin and F. Lions, J. Am. Chem. Soc., 1960, 82, 5013; (c) T. P. Cheeseman, D. Hall and T. N. Waters, J. Chem. Soc. A, 1966, 1396. 9 (a) S. Knapp, T. P. Keenan, X. Zhang, J. Liu, J. A. Potenza and H. J. Schugar, Inorg. Chem., 1990, 29, 2189; (b) S. Knapp, T. P. Keenan, X. Zhang, R. Fikar, J. A. Potenza and H. J. Schugar, J.Am. Chem. Soc., 1990, 112, 3452; (c) S. Knapp, T. P. Keenan, X. Zhang, R. Fikar, J. A. Potenza and H. J. Schugar, J. Am. Chem. Soc., 1987, 109, 1882. 10 E. Muller, C. Piguet, G. Bernardinelli and A. F. Williams, Inorg. Chem., 1988, 27, 849; E. Muller, G. Bernardinelli and J. Reedijk, Inorg. Chem., 1996, 35, 192. 11 O. P. Anderson, J. Becher, H. Frydendahl, L. 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Kelly, A. L. Ferko and R. N. Hardin, Inorg. Chim. Acta, 1996, 249, 85; M. R. Malachowski, H.B. Huynh, L. J. Tomlinson and R. S. Kelly, J. Chem. Soc., Dalton Trans, 1995, 31; M. R. Malachowski, L. J. Tomlinson, M. J. Parker and J. D. Davis, Tetrahedron Lett., 1992, 33, 1395; M. R. Malachowski, M. G. Davidson and J. D. Davis, Inorg. Chim. Acta, 1992, 192, 157. 16 T. N. Sorrell and E. H. Cheesman, Synth. Commun., 1981, 11, 909. 17 L. R. Melby, J. Am. Chem. Soc., 1975, 97, 4044. 18 A. I. Vogel, Quantitative Inorganic Analysis, Longmans, London, 1961. 19 G. M. Sheldrick, SHELXTL 5.03, Bruker AXS, Madison, WI, 1988. 20 E. Bouwman and W. L. Driessen, Synth. Commun., 1988, 18, 1581. 21 K. K. Nanda, A. W. Addison, R. J. Butcher, M. R. McDevitt, T. N. Rao and E. Sinn, Inorg. Chem., 1997, 36, 134. 22 S. Kitagawa, M. Munakata and A. Higashi, Inorg. Chim. Acta, 1984, 84, 79. 23 T. Sakurai, M. Kimura and A. Nakahara, Bull. Chem. Soc. Jpn., 1981, 54, 2976. 24 J. M. Latour, D. Limosin and P. Rey, J. Chem. Soc., Chem. Commun., 1985, 464. 25 M. M. Olmstead, W. K. Musker and R. M. Kessler, Inorg. Chem., 1981, 20, 151. 26 A. Benzekri, C. Cartier, J. M. Latour, D. Limosin, P. Rey and M. Verdaguer, Inorg. Chim. Acta, 1996, 252, 413. 27 P. L. Verheijdt, J. G. Haasnoot and J. Reedijk, Inorg. Chim. Acta, 1983, 76, L43; P. J. M. W. L. Birker, J. Helder, G. Henkel, B. Krebs and J. Reedijk, Inorg. Chem., 1982, 21, 357; M. J. Schilstra, P. J. M. W. L. Birker, G. Verschoor and J. Reedijk, Inorg. Chem., 1982, 21, 2637. 28 N. Wei, N. N. Murthy, Z. Tyeklar and K. D. Karlin, Inorg. Chem., 1994, 33, 1177. 29 A. G. Orpen, L. Brammer, F. H. Allen, O. Kennard, D. G. Watson and R. Taylor, J. Chem. Soc., Dalton Trans., 1989, S1. 30 H. B. Gray, C. L. Cycle, D. M. Dooley, P. J. Grunthaner, J. W. Hare, R. A. Holwerda, J. V. McArdle, D. R. McMillan, J. Rawlings, R. C. Rosenberg, N. Sailasuta, E. I. Soloman, P. J. Stephens, S. Wherland and J. A. Wurzbach, In Bioinorganic Chemistry II, American Chemical Society, Washington, DC, 1977, p. 145. 31 J. R. Dorfman, R. D. Bereman and M. H. Whangbo, in Copper Coordination Chemistry: Biochemical and Inorganic Perspectives, eds. K. D. Karlin and J. Zubieta, Adenine, Guilderland, NY, 1983, p. 75. Paper 9/00223E

ISSN:1477-9226    

DOI:10.1039/a900223e

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2183–2187 2183 Synthesis and characterisation of silanol-functionalised dendrimers † Pamela I. Coupar, Paul-Alain JaVrès and Russell E. Morris* School of Chemistry, University of St. Andrews, St. Andrews, Fife, UK KY16 9ST. E-mail: rem1@st-and.ac.uk Received 12th March 1999, Accepted 19th May 1999 A number of carbosilane dendrimers derivatised on their external surface by silanol groups have been synthesized and characterised. The new molecules are prepared by repetitive hydrosilation/alkenylation reactions, and then careful hydrolysis of Si–Cl groups in one of two ways produces dendrimers with external Si–OH groups.Various molecules with three, four and eight vinyl groups were used as the starting molecules to produce dendrimers of diVerent sizes. The first-generation dendrimer based on a tetravinylsilane core has been characterised by single crystal X-ray diVraction. Introduction Since the first successful synthesis of a symmetrical branched dendrimer 1 this class of molecule has received considerable interest, with possible applications ranging from drug delivery agents, micelle mimics, nanoscale building blocks, high performance polymers and nanoscale reactors.2 The unusual architecture of these molecules leads to properties such as low intrinsic viscosity, high solubility and miscibility, and high reactivity (from the presence of many chain ends).An alternative application that has achieved some attention is that of catalysis,3–5 where dendrimers have some striking advantages over both homogeneous and heterogeneous catalysts.Homogeneous catalysts have a number of benefits over other types of catalysts (for example, faster kinetics, accessibility of the metal centre, etc.). However, a large drawback is that they are often diYcult to separate from the reaction mixture. Heterogeneous catalysts on the other hand are easy to separate from the reaction stream, but have the disadvantage that the catalytic sites are often inaccessible and that mass transport problems can decrease the activity of the catalysts.Dendritic catalysts lie at the interface between homogeneous and heterogeneous systems in that their size (>25 Å diameter) and their high shape persistence in solution (i.e. no reptation) will allow them to be separated from a solvent stream using ultrafiltration methods while their spheroidal shape will allow precise control over the number and location of the catalytic sites.This paper reports the synthesis and characterisation of new silanol-functionalised dendrimers. Our goal in preparing these molecules is to use them as mimics for silica surfaces by attaching catalytically active metal atoms to the silanol group. Silica is a well known support for many types of catalytically active centre, and recently Thomas and co-workers 6 have elegantly shown that organometallic chemistry can be used to ‘graft’ or ‘tether’ catalytic sites onto the inside surfaces of a mesoporous silica.This procedure has successfully been used in a number of ways, many of which are reviewed in the recent publication by Clark and MacQuarrie.7 In addition, Feher et al.8 have prepared a number of incompletely condensed polyhedral oligomeric silsesquioxane molecules made up of seven silicon atoms † Supplementary data available: detailed synthetic procedures for compounds 1–12.For direct electronic access see http://www.rsc.org/ suppdata/dt/1999/2183/, otherwise available from BLDSC (No. SUP 57564, 8 pp.) or the RSC Library. See Instructions for Authors, 1999, Issue 1 (http://www.rsc.org/dalton). at the corners of a cube, the last vertex being vacant. Three silanol groups point towards the empty corner of the cube and a number of metal atoms can then be tethered through these groups to produce catalytically active molecules. Van Santen and co-workers 9 have shown that capping the empty corner of the cube with titanium produces a species that is active for the epoxidation of a number of unsaturated hydrocarbons and, moreover, that none of the titanium is lost during the reaction.The silanol-functionalised dendrimers reported in this paper are related to these other types of silica mimics by having Si–OH units available at their surfaces for reaction with other species. Results and discussion Carbosilane dendrimer cores were synthesized according to the methods described previously,10–12 including some of our own previously published work in this area,13 using a repetitive procedure where hydrosilation of the exterior vinyl groups is followed by reaction with vinylmagnesium bromide. Once the required size of vinyl-derivatised dendrimer has been reached, hydrosilation with H(CH3)2SiCl in the presence of Karstedt’s catalyst (a platinum–divinylsiloxane complex) produces the monochlorosilane derivative regiospecifically on the terminal carbon of the vinyl group.Two methods were then used to synthesize the silanol-functionalised dendrimers (see Scheme 1). Method one involves the simple hydrolysis of the chloro group using water. To prevent condensation between the dendrimers this was accomplished with water as a fairly dilute solution in aniline. This method is successful for the firstgeneration dendrimers, although there are complications for the larger dendrimers leading to impure products.The second method involves the reduction of Si–Cl to Si–H using LiAlH4 and subsequent catalytic hydrolysis to Si–OH using water over palladium supported on carbon.14 This method is very clean and reasonably high yielding, and even though it involves an extra synthetic step produces comparable purity and yields to the first method, especially for the preparation of the larger silanol-functionalised dendrimers reported here where it is the method of choice.The methodology works equally well for dendrimers based on silane, cyclosiloxane and polyhedral oligomeric silsesquioxane cores. The dendrimers 1–6 were prepared successfully in this way and were characterised using 13C and 1H NMR, and CHN microanalysis. The first-generation dendrimer 1 was also unambiguously characterised by single-crystal X-ray diVraction. The2184 J. Chem. Soc., Dalton Trans., 1999, 2183–2187 intermediate silane (i.e. Si–H) functionalised dendrimers, 7–12, were also isolated and characterised by 13C and 1H NMR, and CHN microanalysis.For all these compounds, infrared spectroscopy showed a strong band at around 2120 cm21, which is the Si–H stretching vibration. This strong absorption together with the volume of H2 produced during the course of the reaction are useful indicators that can be used to follow the progress of the catalytic hydrolysis to silanol-functionalised dendrimers. Details of the synthesis and characterisation of Scheme 1 General synthetic scheme for silanol dendrimer preparation.Reagents and conditions: (i) HSi(CH3)2Cl–H2PtCl6 (see ref. 13); (ii) water, aniline in diethyl ether, 25 8C, 12 h; (iii) LiAlH4–diethyl ether, 25 8C, 15 h; (iv) water, Pd/C in 1,4-dioxane, 25 8C, 12 h. dendrimers 1–12 can be found in the Supplementary data. Of course, given the already demonstrated utility of the hydrosilation reaction in the preparation of dendrimers, these Si–H functionalised dendrimers should be themselves excellent synthetic platforms on which many new functionalised dendrimers could be based.Surprisingly, upon standing for 6 months in air the dendrimers show very little evidence for intermolecular condensation. The solubility of the dendrimers in methanol is similar to that of the freshly prepared samples and the CHN analysis results are within experimental error of those obtained originally. The crystal structure of dendrimer 1 (Fig. 1) confirms the molecular structure of the compound, and also that the synthetic procedure produces the expected functional transformations.As expected, the dendrimers pack in the solid state so that they are held together through the hydrogen bonds between silanol groups from diVerent molecules. This produces ‘channels’ in the structure lined by oxygen atoms as well as regions that only contain the van der Waals interactions between the methylene and methyl hydrogens. This can be most clearly seen in the view of the structure parallel to the crystallographic b axis shown in Fig. 2. The successful synthesis and characterisation of these new dendrimers oVers us the opportunity to use these molecules as mimics for silica surfaces by attaching chemical species to the external surfaces in the same way as that accomplished for silica surfaces, mesoporous silica and polyhedral oligomeric silsesquioxanes. Coupled with improved ultra- filtration techniques currently being developed, this may lead to a completely new class of homogeneous catalyst that can more easily be separated out of solution.The dendrimers based on polyhedral silsesquioxane cores are especially attractive for catalytic applications as they have a fairly high density of external sites that are all accessible for derivatisation. Further work aimed at functionalising the exterior surface of these molecules with catalytically active groups is currently underway. The dendrimers prepared in this work are monosilanols (i.e.there is only one hydroxyl group per silicon). However, the work of Roesky and co-workers 15 has shown that sterically hindered molecules, such as these dendrimers, can also be used to make di- and tri-silanols. We are also exploring the possibilities that the synthetic methods reported by Roesky can be applied to dendrimers of the type reported here. Experimental All manipulations were carried out under an atmosphere of argon.Solvents were dried according to established procedures. The starting materials for many of these syntheses have been reported in a previous paper.13 The buVer solution contained NaH2PO4?H2O (4.7 mmol l21) and NaOH (4 mmol l21). The 1H NMR spectra were recorded at 300.13 MHz and 13C NMR spectra at 75.47 MHz on a Bruker AM300 spectrometer operating in the Fourier transform mode with, for 13C spectra, noise proton decoupling. FTIR Spectra were recorded on a Perkin-Elmer 1710 spectrometer.Chemical analysis was accomplished by the University of St. Andrews Microanalysis service. Representative synthetic procedures (compounds 1, 5 and 11) Tetrakis[2-(hydroxydimethylsilyl)ethyl]silane 1. From tetrakis- [2-(chlorodimethylsilyl)ethyl]silane. A solution of tetrakis[2- (chlorodimethylsilyl)ethyl]silane (3.82 g, 7.3 mmol) in diethyl ether (50 ml) was added dropwise to a mixture of aniline (2.79 g, 30 mmol) and water (0.54 g, 30 mmol) in diethyl ether (100 ml).The solution was stirred at room temperature overnight. Diethyl ether (50 ml) was added and the anilinium salt removed by filtration. The filtrate was concentrated in vacuo andJ. Chem. Soc., Dalton Trans., 1999, 2183–2187 2185 the residue crystallised from diethyl ether–hexane. Compound 1 was obtained by filtration as a white solid (2.07 g, 64%). From tetrakis[2-(dimethylsilyl)ethyl]silane. A solution of tetrakis[2-(dimethylsilyl)ethyl]silane (0.3 g, 0.79 mmol) in 1,4- dioxane (15 ml) was added dropwise to a suspension of 5% palladium on charcoal (0.1 g) in a mixture of dioxane (5 ml) and buVer solution (0.5 ml).After the addition the solution was stirred at room temperature overnight, then filtered on Celite (THF as eluent) and the filtrate concentrated in vacuo. The residue (0.34 g) was crystallised from diethyl ether–hexane aVording compound 1 as a white solid (0.32 g, 91%) mp 129 8C (Found: C, 44.11 ; H, 10.43. C16H44O4Si5 requires C, 43.58 ; H, 10.06%). 1H NMR (CD3OD): d 0.27 (s, Si-CH3, 48 H), 0.70 (m, CH2, 32 H) and 5.07 (s, -OH, 8 H). 13C NMR (CD3OD): 20.84 (Si-CH3), 3.38 (CH2) and 11.06 (CH2). IR (KBr, disc): 3270vs, 2959m, 2910m, 1407m, 1250s, 1127s, 1068m, 868vs and 764s. 1,3,5,7,9,11,13,15-Octakis[2-(hydroxydimethylsilyl)ethyl]- pentacyclo[9.5.1.1 3,9.1 5,15.1 7,13]octasiloxane 5. A solution of 1,3,5,7,9,11,13,15-octakis[2-(dimethylsilyl)ethyl]pentacyclo- [9.5.1.1 3,9.1 5,15.1 7,13]octasiloxane 11 (0.36 g, 0.32 mmol) in 1,4- dioxane (25 ml) was added dropwise to a suspension of 10% palladium on charcoal (0.1 g) in a mixture of dioxane (5 ml) and a buVer solution (0.7 ml).After the addition the solution was stirred at room temperature overnight. The solution was filtered on Celite (THF as eluent) and the filtrate concentrated in vacuo. The viscous oil (0.48 g) was crystallised from ethyl acetate to give compound 5 as a white solid (0.26 g, 65%) (Found: C, 30.79 ; H, 6.89.C8H22O5Si4 requires C, 30.93 ; H, 7.14%). 1H NMR (CD3OD): d 0.29 (s br, Si-CH3, 48 H), 0.81 (m, CH2, 32 H) and 5.08 (s, -OH, 8 H). 13C NMR (CD3OD): d 21.61 (Si-CH3), 6.09 (CH2) and 9.70 (CH2). IR (KBr, disc): 3316vs, 2958m, 2895m, 1408m, 1253s, 1143vs, 868s, 757m, 632m, 536m and 470m.2186 J. Chem. Soc., Dalton Trans., 1999, 2183–2187 1,3,5,7,9,11,13,15-Octakis[2-(dimethylsilyl)ethyl]pentacyclo- [9.5.1.1 3,9.1 5,15.1 7,13]octasiloxane 11. A solution of 1,3,5,7, 9, 11, 13,15-octakis[2-(chlorodimethylsilyl)ethyl]pentacyclo[9.5.1.1 3,9. 15,15.1 7,13]octasiloxane (see ref. 13; 2.20 g, 1.58 mmol) in diethyl ether (100 ml) was added dropwise to a suspension of LiAlH4 (0.26 g, 6.8 mmol) in diethyl ether (80 ml). After additional stirring at room temperature for 15 h the solution was filtered on Celite. The filtrate was cautiously added to a mixture of hydrogen chloride (1 M in water, 100 ml) and ice. The organic layer was washed with brine (2 × 40 ml), dried over MgSO4 and concentrated.The residue (1.74 g) was recrystallised from acetone–ethanol aVording compound 11 as a white solid (1.07 g, 61%), mp 147 8C (Found: C, 34.09; H, 8.21. C8H22O3Si4 requires C, 34.49; H, 7.96%). 1H NMR (CDCl3): d 0.09 (d, 3JHH = 3.6 Hz, Si-CH3, 48 H), 0.63 (m, CH2, 32 H) and 3.87 (m, Si-H, 8 H). 13C NMR (CDCl3): d 24.80 (Si-CH3), 5.06 (CH2) and 5.68 (CH2). IR (KBr, disc): 2959m, 2923m, 2111vs (Si–H), 1407m, 1250s, 1145s, 1111vs, 888s, 836m, 806m, 720m, 625m, 545m and 470m.Spectroscopic data for other compounds 2–4, 6–10 and 12. Where no microanalysis results are given, NMR spectroscopy indicates that a small amount of solvent is trapped in the dendrimer. This is not an uncommon problem in dendrimer chemistry, especially for higher generations. Compound 2: 1H NMR (CD3OD) d 0.14 (s, Si-CH3, 3 H), 0.27 (s, Si-CH3, 16 H), 0.66 (m, CH2, 12 H) and 5.06 (s, OH, 3 H); 13C NMR (CD3OD) d 24.94 (Si-CH3), 0.42 (Si-CH3), 6.44 (CH2) and 12.24 (CH2).Compound 3 (Found: C, 37.18 H, 8.75. Calc: C, 36.99; H, 8.69%): 1H NMR (CD3OD) d 0.25 (s, CH3), 0.27–0.28 (d, CH3) and 0.66–0.73 (m, CH2); 13C NMR (CD3OD) d 23.25 (m, CH3), 21.1 (m, CH3), 9.53 (s, CH2) and 10.02 (s, CH2). Compound 4: 1H NMR (CD3OD) d 0.28 (s, Si-CH3, 72 H),J. Chem. Soc., Dalton Trans., 1999, 2183–2187 2187 0.64–0.75 (m, Si-CH2CH2SiCH2CH2Si, 64 H) and 5.05 (m, Si-OH, 12 H); 13C NMR (CD3OD) d 0.78 (Si-CH3), 4.66 (CH2), 5.30 (CH2), 5.83 (CH2) and 12.53 (CH2).Compound 6: 1H NMR (CD3OD) d 0.25 (s, Si-CH3, 24 H), 0.28 (s, Si-CH3, 96 H), 0.60–0.70 (m, CH2, 96 H) and 5.08 (s, Si-OH, 16 H); 13C NMR (CD3OD) d 0.78 (Si-CH3), 1.40 (Si-CH3), 6.51 (CH2), 6.77 (CH2), 7.02 (CH2) and 12.31 (CH2). Compound 7: 1H NMR (CDCl3) d 0.10 (d, 3JHH = 3.6 Hz, Si-CH3, 24 H), 0.50 (m, CH2CH2, 16 H) and 3.87 (m, Si-H, 4 H); 13C NMR (CDCl3) d 24.60 (Si-CH3), 3.63 (CH2) and 6.42 (CH2). Compound 9 (Found: C, 40.96; H, 9.7. Calc. C, 41.03; H, 9.64%): 1H NMR (CDCl3) d 3.8–3.9 (m, SiH, 1 H), 0.4–0.6 (m, CH2, 4H) and 0–0.1 (m, CH3); 13C NMR (CDCl3) d 9.764 (m, CH2), 5.466 (m, CH2), 21.557 (m, CH3) and 24.968 (m, CH3).Compound 10: 1H NMR (CDCl3) d 0.08 (d, 3JHH = 3.6 Hz, Fig. 1 Thermal ellipsoid plot of the crystal structure of compound 1 (ellipsoids at 50% probability). Fig. 2 Packing diagram of compound 1 viewed parallel to the crystallographic b axis. Oxygen atoms are shown as black spheres, silicon and carbon atoms as large and small grey spheres respectively.Si-CH3, 72 H), 0.49 (m, Si-CH2CH2SiCH2CH2Si, 64 H) and 3.86 (m, Si-H, 12 H); 13C NMR (CDCl3) d 24.77 (Si-CH3), 5.06 (CH2) and 5.68 (CH2). Compound 12: 1H NMR (CDCl3) d 2 0.04 (s, Si-CH3, 24 H), 0.08 (d, 3JHH = 3.6 Hz, Si-CH3, 96 H), 0.45–0.50 (m, CH2, 96 H) and 3.85 (m, Si–H, 16 H); 13C NMR (CDCl3) d 26.46 (Si-CH3), 24.77 (Si-CH3), 4.25 (CH2), 4.53 (CH2), 5.33 (CH2) and 6.33 (CH2). Single crystal X-ray diVraction Single crystal X-ray diVraction data for compound 1, C16H44O4Si5 (M= 444.98), recrystallised from a 50: 50 diethyl ether–hexane mixture, crystal size 0.4 × 0.4 × 0.1 mm, were collected on a Rigaku AFC7S four circle diVractometer employing Mo-Ka radiation at 220 K.The molecule crystallises in monoclinic space group P21/n (no. 14) with lattice parameters a = 10.00(2), b = 15.94(2), c = 17.49(1) Å, b = 92.4(1)8, V = 2785(7) Å3 with Z = 4, m = 2.71 mm21. The diVraction from the crystal was relatively weak and the reflections were rather irregularly shaped, this presumably accounts for the rather poor precision on the final unit cell refinement. The crystal showed almost no diVraction above 2q 408, but the final full-matrix least-squares refinement against F was successfully completed with R(F) = 0.038, R9(F) of 0.047 and goodness of fit of 2.4 against 2016 unique reflections (Rint = 0.02), of which 1521 were observed [I > 3s(I)].The silicon, carbon and oxygen atoms were refined with anisotropic thermal displacement parameters. The hydrogen atoms on the methylene units of the dendrimer arms were placed in geometrically reasonable positions.CCDC reference number 186/1475. See http://www.rsc.org/suppdata/dt/1999/2183/ for crystallographic files in .cif format. Acknowledgements We thank the Engineering and Physical Sciences Research Council for support and R. E. M. thanks the Royal Society for the provision of a University Research Fellowship. References 1 D. Tomalia and R. Dewald, US Pat., 4 507 466, 1985. 2 R. Dagani, Chem. Eng. News, 1996, 3 June, 30 and refs. therein. 3 D. Tomalia and P. Dvornic, Nature (London), 1994, 372, 617. 4 J. Knapen, A. W. van der Made, J. C. de Wilde, P. W. N. M van der Leeuwen, P. Wijkens, D. M. Grove and G. van Koten, Nature (London), 1994, 372, 659. 5 J. Haggin, Chem. Eng. News, 1995, 6 February, 26. 6 T. Maschmeyer, F. Rey, G. Sankar and J. M. Thomas, Nature (London), 1995, 378, 159. 7 J. H. Clark and D. J. MacQuarrie, Chem. Commun., 1998, 853. 8 F. J. Feher, T. A. Budzichowski, R. L. Blanski, K. J. Weller and J. W. Ziller, Organometallics, 1991, 10, 2526. 9 H. C. L. Abbenhuis, S. Krijnen and R. A. Van Santen, Chem. Commun., 1997, 331. 10 L. L. Zhou and J. Roovers, Macromolecules, 1993, 26, 963. 11 A. W. van der Made and P. W. N. M. van Leeuwen, J. Chem. Soc., Chem. Commun., 1992, 1400. 12 D. Seyferth, D. Y. Son, A. L. Rheingold and R. L. Ostrander, Organometallics, 1994, 13, 2683. 13 P.-A. JaVrès and R. E. Morris, J. Chem. Soc., Dalton. Trans. 1998, 2767. 14 G. H. Barnes and N. E. Daughenbaugh, J. Org. Chem., 1996, 885. 15 R. Murugavel, V. Chandrasekhar and H. W. Roesky, Acc. Chem. Res., 1996, 29, 183. Paper 9/01962F

ISSN:1477-9226    

DOI:10.1039/a901962f

出版商:RSC    

年代:1999

数据来源: RSC