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DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 2101 Synthesis, reactivity and structures of hafnium-containing homo- and hetero- (bi- and tri-) metallic alkoxides based on edge- and facesharing bioctahedral alkoxometalate ligands † Michael Veith,* Sanjay Mathur,* Charu Mathur and Volker Huch Institute of Inorganic Chemistry, University of Saarland, PO 151150, D-66041, Saarbrücken, Germany Using [{Hf(OPri)4(PriOH)}2] as a building-block precursor, a series of homo- and hetero-metallic alkoxides of hafnium has been prepared and characterised using elemental analyses, infrared, multinuclear (1H, 7Li, 13C and 113Cd) NMR and single-crystal X-ray diffraction studies.The solid-state structure of [Hf2(OPri)8(PriOH)2] 1 reveals an edge-shared bioctahedral structure with the co-ordinated alcohol forming a hydrogen bridge across the dinuclear unit. The reactions of 1 with other nitrogen- or oxygen-containing donors gave monosubstituted products of the general formula [Hf2(OPri)8(PriOH)L] (L = C5H5N 2 or C4H8O2 3) which retain the dinuclear edge-sharing bioctahedral structure as determined for 2 by X-ray crystallography.Compound 1 reacted (1 : 2) with LiBun or LiOPri to afford dimeric [{LiHf(OPri)5}2] 4. The molecular structure of 4 can be conceived as a dianionic [Hf2(OPri)10]22 unit that binds two Li1 one on each side of the Hf]Hf vector which are additionally co-ordinated by the bridging OPri groups to display a trigonal-pyramidal geometry at the lithium atoms.The Hf2O6Li2 core in 4 comprises two analogous seconorcubane subunits sharing a common face defined by a Hf2O2 ring. Equimolar reaction of CuCl2 and [KHf2(OPri)9] afforded the monomeric halide heterobimetallic derivative [CuHf2Cl(OPri)9] 5. Compound 5 is paramagnetic and follows Curie law behaviour as inferred by a variable-temperature 1H NMR study. In the solid state its molecular geometry could be formally seen as a tetradentate interaction of the distorted confacial bioctahedron [Hf2(OPri)9]2 with a CuCl1 fragment.Each Hf is six-co-ordinated; Cu is five-co-ordinated and displays a distorted trigonal-bipyramidal geometry. The reaction (1 : 1) of [CdHf2I(OPri)9] with KSr(OPri)3 produced a new heterotermetallic derivative [{[Cd(OPri)3]Sr[Hf2(OPri)9]}2] 6. This involves the switching of central metal atoms between the two precursors and the Hf2(OPri)9 unit in 6 binds to Sr rather than Cd as anticipated. The centrosymmetric dimeric form of 6 is made up of a [Sr(m-OPri)2Cd(m-OPri)2Cd(m-OPri)2Sr]21 spirocyclic unit capped at both the ends by [Hf2(OPri)9]2 moieties.There is continuing interest in heterometal alkoxides, in part, because large heterometal assemblies (metal–metal bonded or anion-bridged metal centres) can provide access to molecularbased systems displaying properties which may find applications in molecular electronics or optical switching devices.1 Among the tetravalent early transition metals the alkoxide chemistry of titanium and zirconium is most studied as shown by their frequent use as heterometal partners to a large number of metals throughout the Periodic Table.2 However, in contrast to titanium and zirconium, well characterised examples of hafnium are scarce, despite the fact that hafnium-containing ceramics, in view of their large relative permittivities, are finding increasing applications in the reliable production of ultralarge- scale integration (ULSI) memory devices.3 In earlier studies 4 the isopropoxides of some of the tetravalent metals (Sn, Zr, Hf and Ce) were suggested to be dimeric alcoholates of general formula [M2(OPri)8(PriOH)2] with an edge-sharing bioctahedral structure.This was later verified for Sn,5 Zr 6 and Ce6 by solid-state structural studies which additionally showed a trans positioning (across the M]M vector) of neutral (ROH) ligands and the existence of hydrogen bonding [R(M)O ? ? ?H? ? ?OR].In view of the increasing applications of hafnium-containing ceramics 7 and the dearth of data on synthetic and structural aspects of hafnium alkoxides, we initiated the present investigations on the synthesis, structure and reactivity of homo- and hetero-metal hafnium alkoxide derivatives. † Non-SI unit employed: Torr ª 133 Pa. Results and Discussion Syntheses and spectroscopic characterisation Owing to the presence of two neutral ligands, [Hf2(OPri)8- (PriOH)2] 1 is an interesting synthon since these ligands can be replaced with other donor molecules and in the absence of a donor ligand the co-ordinative unsaturation is expected to result in a structural change.Unless drastic conditions for expulsion are used, the co-ordinated alcohol in [M2(OPri)8(Pri- OH)2] derivatives shows a tendency for retention and samples of [Hf2(OPri)8(PriOH)2] heated in vacuum (30 min, 100 8C, 1022 Torr), when recrystallised from mixtures of toluene–pyridine and –1,4-dioxane, produced [Hf2(OPri)8(PriOH)(NC5H5)] 2 and [Hf2(OPri)8(PriOH)(O2C4H8)] 3, respectively (Scheme 1).However authentic samples of alcohol-free hafnium isopropoxide [Hf(OPri)4]n, as indicated by the analytical data and absence of OH stretching frequencies in the IR spectra, could be obtained on prolonged (>4 h) pumping of hafnium isopropoxide at higher temperatures (140 8C, 1022 Torr). Besides the characteristic stretching frequencies of metal-attached isopropoxy groups,4 the IR spectra (KBr and CDCl3) of 2 and 3 show broad OH stretching bands (see Experimental section) indicative of the hydrogen bonding present in both solution and solid state.The room-temperature 1H and 13C NMR spectra of 2 and 3 exhibit a single time-averaged environment for isopropyl groups suggesting a rapid exchange among different (bridging, terminal and neutral) types of ligands present in the molecule. As indicated by elemental analyses, cryoscopic and spectral studies, the formulation of 2 and 3 as [Hf2(OPri)8(PriOH)L]2102 J.Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 (i ) 2PriOH [Hf2(OPri)8(PriOH)L] L = C5H5N 2 or C4H8O2 3 [{Hf(OPri)4(PriOH)}2] 1 (ii ) 22 HOPri (HBu) [{LiHf(OPri)5}2] 4 Scheme 1 (i) L; (ii) 2 LiOPri (LiBun) (L = C5H5N 2 or C4H8O2 3) was supported by the single-crystal X-ray study performed on 2. Various attempts at an X-ray crystallographic analysis of compound 3 were not successful.In the light of the solid-state structure of compound 1 (see below), the edge-sharing octahedral framework can be viewed as a dianionic [Hf2(OPri)10]22 moiety which binds two H1 in a bidentate fashion. In order to replace this electrophile (H1) by any other monovalent cation the reaction of 1 was performed with LiBun or LiOPri to obtain dimeric [{LiHf(OPri)5}2] 4 (Scheme 1). In contrast to 1–3, compound 4 is stereochemically rigid and the ambient-temperature 1H NMR spectrum exhibits three overlapping doublets which could be resolved at 210 8C as three sets of signals in 2:2:1 intensity ratio, which is consistent with the solid-state structure of 4 showing three types of alkoxide ligands (Hf]OPri, Hf]m-OPri, Hf]m3-OPri]Li) and is also corroborated by 13C NMR spectral data (see Experimental section).The 7Li NMR spectrum in [2H8]toluene shows a sharp resonance at d 3.02. Molecular-weight studies performed in freezing benzene support the dimeric tendency (molecular complexity, h = 1.9) of 4.To explore the ligating behaviour of hafnium-based dinuclear alkoxometalate moieties toward bivalent cations, an anionexchange reaction was performed in benzene between anhydrous CuCl2 and [KHf2(OPri)9].8a The reaction mixture, after work-up, afforded a green solid in high yield (>90%) which could be crystallised from cold (0 8C) pentane as transparent green crystals of varying morphologies. The elemental analyses conform to the formulation [CuHf2Cl(OPri)9] 5.The presence of CuII imparts paramagnetic behaviour to 5 and the room-temperature 1H and 13C NMR spectra are not structurally diagnostic. The ambient-temperature 1H NMR spectrum however indicates a non-fluxional molecule with gem-dimethyl protons appearing as three broad doublets (d 0.92, 1.35 and 1.44); the methine protons are observed as two broad overlapping multiplets (d 4.27 and 4.70). Given the paramagnetism of 5 variable-temperature NMR studies were performed and the chemical shifts show a linear relationship with T21 which is in agreement with a simple Curie law.At 40 8C the methyl signal appears as two resonances which integrate approximately 4 : 5; the latter signal being sharper presumably corresponds to OPri groups experiencing less paramagnetic influence away from the copper centre (see below). A similar behaviour observed for the titanium analogue [CuTi2Cl(OPri)9] 8b has been detailed elsewhere. The heavy alkaline-earth elements are important constituents of a wide range of solid-state materials with diverse electronic and chemical properties including the high Tc superconductors (e.g.YBa2Cu3O72d,9 Bi2Sr2CaCu2O8 10) and pervoskite-based methane oxidation catalysts 11 (e.g. MM9O3: M = Ca, Sr or Ba; M9 = Ti, Zr, Hf or Ce). The controllable and easy incorporation of alkaline-earth metals in heterometallic systems is a challenge that is posed by the interplay of materials science and metal alkoxide chemistry.In analogy to KBa(OPri)3,12 used as a novel anion, [Ba(OPri)3]2, transfer reagent with halide heterobimetallic precursors [CdM2I(OPri)9] (M = Ti,8a Zr 12 or Hf 8a) for the facile and stoichiometrically precise incorporation of Ba21 in heteropolymetallic alkoxide assemblies [{[Cd(OPri)3]Ba[M2- (OPri)9]}2],8a,12 the strategy was examined for the incorporation of strontium which assumes significance since the alkoxides of heavy alkaline-earth metals are essential (owing to the size effect) constituents of conducting multimetallic ceramics, e.g.La22xSr2CuO4 13 and Bi2Sr2CaCu2O8.10 [{Hf(OPri)4(PriOH)}2] (i ) [KHf2(OPri)9] 1 (ii ) [{[Cd(OPri)3]Sr[Hf2(OPri)9]}2] (iii ) [CdHf2I(OPri)9] 6 Scheme 2 (i) KOPri; (ii) CdI2; (iii) KSr(OPri)3 An equimolar reaction of the recently reported [CdHf2I- (OPri)9] 8a with freshly synthesized [{KSr(OPri)3}n] in toluene afforded [{[Cd(OPri)3]Sr[Hf2(OPri)9]}2] 6 in almost quantitative yield (Scheme 2).The molecule 6 is stereochemically rigid and the room-temperature spectra (1H, 13C and 113Cd) are indicative of the structural pattern existing in solution. The 1H NMR spectrum exhibits six methyl signals in an intensity ratio 4:2:8:4:4:2 whereas the methine protons are observed as three overlapping septets that integrate 10:6:8. The 13C NMR spectrum displays five and six signals for the methine and methyl carbons in intensity ratios 8:2:4:4:6 and 6:4:4:4:2:4, respectively.The 113Cd NMR chemical shift (d 226.91) is comparable with the solution- and solid-state 113Cd NMR chemical shifts observed for four-co-ordinate cadmium in [{[Cd(OPri)3]- Ba[M2(OPri)9]}2] (M = Ti, Zr or Hf) 8a,12 derivatives. This along with the cryoscopic data supports the retention of the heterotermetallic nature and dimeric form of 6, as observed in the solid state (see below), in solution too. Solid-state and molecular structures Five hafnium isopropoxide derivatives have been characterised by single-crystal X-ray diffraction studies during this work. A summary of the data collection and crystallographic parameters are given in Table 8.[{Hf(OPri)4(PriOH)}2] 1. Single crystals of compound 1 suitable for an X-ray diffraction study were grown from a cold (110 8C) isopropyl alcohol solution and are made up of discrete dimers of Hf(OPri)4?PriOH molecules (Fig. 1). Compound 1 crystallises ‡ in the triclinic space group P1� and the unit cell contains two crystallographically independent but structurally similar molecules of point group Ci (Fig. 1). Selected interatomic distances and angles for compound 1 are listed in Table 1. The central metal–oxygen unit is a planar rhombic Hf]O] Hf]O oxametallacycle lying on crystallographic inversion centres. Within the dimeric Hf2O10 unit, both the Hf atoms bonded to three terminal OPri, two bridging OPri and one terminal PriOH ligand show similar geometries, derived from a regular octahedron.The m-OPri ligands are situated nearly symmetrically between the two Hf atoms [Hf(1)]O(1) 2.148(6); Fig. 1 Two crystallographically independent molecules in the unit cell of [{Hf(OPri)4(PriOH)}2] 1. Hydrogen atoms of the isopropyl groups are omitted for clarity. Atoms designated with an ‘a’ are related by symmetry. The ‘bending’ of axial ligands (across the Hf]Hf vector) is indicative of the hydrogen bridges present between O(2) and O(4a) [O(4) and O(2a)] not shown ‡ The unit-cell constants given in ref. 6 do not match ours.J. Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 2103 Hf(1)]O(1a) 2.160(6) Å]; the oxygen atoms of bridging OPri groups are planar (sum of angles = 359.98) and have longer Hf]O contacts in comparison to the terminal Hf]O (1.93 Å) distances. The overall molecular structure, as observed for the analogous [M2(OPri)8(PriOH)2] (M = Sn, Zr or Ce) derivatives,5,6 is a distorted edge-sharing bioctahedron comprising a ‘(RO)2Hf- (m-OR)Hf(OR)2’ plane with trans alcohol ligands (axial) on each hafnium atom.It is noteworthy that the two molecules (A and B) present in the unit cell differ remarkably in Hf]O distances of the axial ROH and RO2 ligands [(molecule A: Hf(1)]O(2) 2.185, Hf(1)]O(4) 2.143 Å; molecule B: Hf(2)]O(8) 2.243, Hf(2)]O(9) 2.082 Å] whereas the Hf]O distances in the (RO)2Hf(m-OR)Hf(OR)2 plane are comparable (Table 1). However, the axial Hf]O bond lengths in both molecules are sufficiently different to distinguish between alkoxide (average 2.112 Å) and alcohol ligands (average 2.214 Å).Hydroxylic hydrogen atoms of the neutral (ROH) ligands could not be located crystallographically, however their presence can be inferred from the 1H NMR and Fourier-transform IR data. The distortion of Hf(1)]O(2) and Hf(1)]O(4) from regular octahedral geometry is consistent with the presence of a hydrogen bridge in the dimeric unit of 1. Despite the long non-bonded Hf ? ? ? Hf separation [3.463 (molecule A) and 3.468 Å (B)], the axial OR and ROH ligands are considerably bent (O ? ? ? O 2.78 Å) toward each other.The average Hf]Hf(a)]OPri and Hf] Hf(a)]O(H)Pri angles (Table 2), 83.3 and 78.88 respectively, indicate the asymmetric nature of the hydrogen bonding and also that the weakly bound (ROH) ligands bend more; the bending of axial ligands in [M2(OPri)8(PriOH)2] (M = Sn, Zr, Hf or Ce) derivatives seems to be prima facie evidence for hydrogen bonding since no such bending of ligands is observed in the structure of Nb2(OMe)10 14a and Nb2(OPri)10 14b which do not contain neutral ROH ligands.The exocyclic Hf]O]C angles are nearly linear (average 167.48) corroborating a strong OÆM p donation.15 The significant features of an edge-sharing bioctahedral unit present in [M2(OPri)8(PriOH)2] (M = Sn, Zr, Hf or Ce) derivatives are summarised in Table 2. There appears to be no significant correlation between the M ? ? ? M and O ? ? ? O distances with increasing metal(IV) size. However in view of the variation of O]M]M (81.1–85.38) and HO]M]M (80.9–71.48) angles it is conceivable that with increasing M ? ? ? M non-bonding separation the weakly co-ordinated ROH ligand shows an increased bending required for an effective hydrogen bonding since the O? ? ? O distances do not alter much (Table 2).Table 1 Selected bond lengths (Å) and angles (8) of compound 1 Molecule A Hf(1)]O(5) Hf(1)]O(4) Hf(1)]O(3) Hf(1)]O(2) Hf(1)]O(1) Hf(1)]O(1a) O(5)]Hf(1)]O(3) O(3)]Hf(1)]O(4) O(3)]Hf(1)]O(1) O(5)]Hf(1)]O(1a) O(4)]Hf(1)]O(1a) O(5)]Hf(1)]O(2) O(4)]Hf(1)]O(2) O(1a)]Hf(1)]O(2) O(5)]Hf(1)]O(4) O(5)]Hf(1)]O(1) O(4)]Hf(1)]O(1) O(3)]Hf(1)]O(1a) O(1)]Hf(1)]O(1a) O(3)]Hf(1)]O(2) O(1)]Hf(1)]O(2) Hf(1)]O(1)]Hf(1a) 1.932(8) 2.143(7) 1.938(8) 2.185(7) 2.148(6) 2.160(6) 97.5(4) 97.3(3) 95.1(3) 94.4(3) 83.3(3) 94.4(3) 161.6(3) 81.8(3) 97.4(4) 167.3(3) 83.1(3) 167.9(3) 73.0(3) 95.1(3) 82.4(3) 107.0(3) Molecule B Hf(2)]O(7) Hf(2)]O(6a) Hf(2)]O(8) Hf(2)]O(9) Hf(2)]O(10) Hf(2)]O(6) O(10)]Hf(2)]O(9) O(10)]Hf(2)]O(9) O(9)]Hf(2)]O(6a) O(7)]Hf(2)]O(6a) O(6a)]Hf(2)]O(6) O(7)]Hf(2)]O(6) O(6a)]Hf(2)]O(8) O(10)]Hf(2)]O(8) O(7)]Hf(2)]O(9) O(7)]Hf(2)]O(6a) O(10)]Hf(2)]O(6) O(9)]Hf(2)]O(6) O(10)]Hf(2)]O(8) O(9)]Hf(2)]O(8) O(6)]Hf(2)]O(8) Hf(2a)]O)]Hf(2) 1.944(7) 2.155(5) 2.243(7) 2.082(7) 1.911(8) 2.156(6) 99.6(3) 95.3(3) 86.5(3) 94.2(3) 72.9(2) 91.9(3) 79.1(2) 96.7(4) 99.9(3) 165.3(3) 166.8(3) 85.6(3) 92.1(3) 162.2(3) 80.2(2) 107.1(2) [Hf2(OPri)8(PriOH)(NC5H5)] 2.Crystals of compound 2 were grown from a toluene–pyridine solution at room temperature. The X-ray structural analysis confirmed the dimeric nature of this compound and a ball-and-stick view of the solidstate structure is shown in Fig. 2. Selected bond lengths and angles are summarised in Table 3. The centrosymmetry of the Hf2O2 core is not retained upon the reaction of the parent compound 1 with pyridine, as the stereoselective substitution of only one of the PriOH ligands by pyridine takes place.The configuration is similar to that of 1, viz. edge-sharing bioctahedral with the geometry around the hafnium atom being constituted by one neutral (PriOH/pyridine) and three exo- and two endo-cyclic anionic (OR2) ligands. In the solid state the molecules of 2 are stacked in a disordered manner and their superposition as shown in Fig. 2 does not allow a rigorous discussion of bond lengths and angles.However, the presence of hydrogen bonding trans to the disordered pyridine ligand is evident in the significant bending of the Hf]O(3) and Hf]O(3a) bonds. Fig. 2 Ball-and-stick view of [Hf2(OPri)8(PriOH)(NC5H5)] 2 with selected atom numbering. The lighter lines show the superposition of molecules. Hydrogen atoms are omitted for clarity Table 2 Typical interatomic distances (Å) and angles (8) found in the solid-state structures of [M2(OPri)8(PriOH)2] (M = Sn,5 Zr,6 Hf or Ce6) derivatives MIV (r/Å) Sn (0.71) Zr (0.80) Hf (0.86)* Ce (0.92) O? ? ? O in axial ligands 2.703 2.770 2.789 2.748 M? ? ? M vector 3.361 3.490 3.465 3.770 O]M]M 81.1 85.3 83.3 83.9 HO]M]M 80.9 75,9 78.8 71.4 * Average values for molecules A and B.Table 3 Selected bond lengths (Å) and angles (8) of compound 2 Hf]O(4) Hf]O(1a) Hf]O(1) Hf]O(5) O(4)]Hf]O(2) O(2)]Hf]O(5) O(2)]Hf]O(3) O(4)]Hf]O(1a) O(5)]Hf]O(1a) O(4)]Hf]O(1) O(5)]Hf]O(1) O(1a)]Hf]O(1) O(2)]Hf]N O(1a)]Hf]N Hf(a)]O(1)]Hf 1.929(6) 2.175(5) 2.178(5) 2.10(2) 99.3(3) 91.5(5) 92.7(2) 165.8(3) 94.2(4) 96.2(3) 89.7(5) 69.9(2) 92.1(5) 86.6(5) 108.6(2) Hf]O(2) Hf]O(3) Hf]N O(4)]Hf]O(5) O(4)]Hf]O(3) O(5)]Hf]O(3) O(2)]Hf]O(1a) O(3)]Hf]O(1a) O(2)]Hf]O(1) O(3)]Hf]O(1) O(4)]Hf]N O(3)]Hf]N O(1)]Hf]N 1.944(7) 2.154(6) 2.30(2) 88.6(4) 90.7(3) 175.8(5) 94.6(3) 85.5(2) 164.5(3) 86.2(2) 96.0(5) 171.0(5) 87.1(5)2104 J.Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 [{LiHf(OPri)5}2] 4.The compound of empirical formula LiHf(OPri)5 is dimeric in the solid state and possesses crystallographic Ci point symmetry. A ball-and-stick drawing of the molecular structure of 4 with the atom numbering scheme and an ORTEP16 plot emphasising the metal–oxygen core are shown in Fig. 3. The salient bond lengths and angles are summarised in Table 4. The overall molecular architecture is reminiscent of the solid-state structure of [Hf2(OPri)8(PriOH)2] 1 where the hydrogen atoms of the two trans PriOH ligands have been replaced by lithium atoms, but which are additionally coordinated by the bridging isopropoxo groups.The two hafnium Fig. 3 Ball-and-stick drawing of the dimeric [{LiHf(OPri)5}2] 4, omitting the hydrogen atoms and an ORTEP plot of the metal–oxygen core. Atoms designated with an ‘a’ are generated by symmetry operations I–IV given in Table 4 Table 4 Selected bond lengths (Å) and angles (8) of compound 4 Hf(1)]O(4) Hf(1)]O(3) Hf(1)]O(1) O(1)]Hf(1I) O(2)]LiIII O(3)]LiII Li]O(3IV) O(4)]Hf(1)]O(5) O(5)]Hf(1)]O(3) O(5)]Hf(1)]O(2) O(4)]Hf(1)]O(1) O(3)]Hf(1)]O(1) O(4)]Hf(1)]O(1I) O(3)]Hf(1)]O(1I) O(1)]Hf(1)]O(1I) Hf(1)]O(1)]Hf(1I) LiII]O(3)]Hf(1) O(2III)]Li]O(3IV) O(3IV)]Li]O(1IV) 1.938(8) 2.065(9) 2.226(8) 2.232(7) 1.85(3) 1.86(3) 1.86(3) 100.5(5) 92.9(4) 94.4(4) 96.7(3) 81.8(3) 160.7(4) 87.9(3) 64.9(3) 115.1(3) 98.5(10) 126(2) 91.4(12) Hf(1)]O(5) Hf(1)]O(2) Hf(1)]O(1I) O(1)]LiII Li]O(2III) Li]O(1IV) O(4)]Hf(1)]O(3) O(4)]Hf(1)]O(2) O(3)]Hf(1)]O(2) O(5)]Hf(1)]O(1) O(2)]Hf(1)]O(1) O(5)]Hf(1)]O(1I) O(2)]Hf(1)]O(1I) LiII]O(1)]Hf(1) LiII]O(1)]Hf(1I) LiIII]O(2)]Hf(1) O(2III)]Li]O(1IV) 1.936(9) 2.081(8) 2.232(7) 2.06(3) 1.85(3) 2.06(3) 95.2(4) 93.5(4) 167.5(3) 162.4(4) 88.2(3) 98.3(4) 81.0(3) 87.8(9) 88.3(9) 98.9(10) 91.2(12) Symmetry transformations used to generate equivalent atoms: I 2x, 2y, 2z 1 1; II x 2 1, y, z; III 2x 1 1, 2y, 2z 1 1; IV x 1 1, y, z.centres [Hf(1) and Hf(1a)] display a distorted-octahedral arrangement of ligands whereas the lithium atoms are located on the apices of the two distorted trigonal pyramids.The metal–oxygen core can be viewed as two analogous seconorcubane subunits sharing a common face, defined by the fourmembered Hf2O2 ring. The central unit resembles the known structures of [{MSn(OBut)3}2] (M = Li or Na) 17 and [{LiTi- (OPri)5}2],18 however, in contrast to the four-co-ordinated lithium atoms in [{LiSn(OBut)3}2] and [{LiTi(OPri)5}2], the lithium centres in 4 are three-co-ordinated.Despite the similarity in formulation and nature of the heterometal partners, the co-ordination geometries of the metal atoms in 4 are entirely different from that observed in [{LiTi(OPri)5}2]; Li and Hf are three- and six-co-ordinate in 4 in comparison to the four- and five-co-ordinate environments of Li and Ti in the latter case. This change in the ligand geometries is attributable to the pronounced tendency of larger tetravalent metals (Zr, Hf, Ce) to achieve six-co-ordination.Thus in 4 the co-ordination of O(1) and O(1a) to Li and Li(a), respectively, is sacrificed and the two oxygen atoms instead bind to the larger hafnium centres. Each hafnium possesses two terminal, two bridging (m) and two triply bridging (m3) isopropoxide ligands. Bond lengths from Hf to OPri increase in the order Hf]O (terminal) [1.935(8)–1.936(9) Å] < Hf]m-OLi [2.065(9)–2.081(8) Å] < Hf]m3-O [2.226(8)– 2.232(7) Å].The distortion in the octahedral environment of Hf is seen in the opening of the O(4)]Hf]O(5) angle [100.5(5)8] and narrowing of the O(3)]Hf(1)]O(2) angle [167.5(3)8] and is probably a combined effect of the steric demands of the isopropxy groups and the geometric constraints of the coordination environment about lithium. Lithium is bound by two bridging OPri groups in a symmetrical fashion [Li]O(3IV) 1.86(3) and Li]O(2III) 1.85(3) Å]; the Li]m3-O distance is 2.06(3) Å.Lithium although three-co-ordinate shows no significant C? ? ? Li contacts (shortest 2.932 Å) or any interaction in the typical range (1.85–2.40 Å) of agostic interactions. The Hf] O(terminal)]C angles (167.2–169.08) approach linearity. [CuHf2Cl(OPri)9] 5. Compound 5 crystallises as a monomer in the monoclinic space group P21/n. A ball-and-stick view of the solid-state structure is shown in Fig. 4 and pertinent bond distances and angles are given in Table 5.The molecule belongs to the class of halide heterobimetallic derivatives [CdM2I- (OPri)9] (M = Sn,19 Ti,8a Zr12 or Hf 8a) and [CuM2Cl(OPri)9] (M = Ti 8b or Zr 20) where the bivalent central metal atom is coordinated by the M2(OPri)9 2 confacial bioctahedral unit in a tetradentate manner. The heterometallic framework (CuHf2) of compound 5 forms an isosceles triangle (non-bonded Hf ? ? ? Cu and Hf ? ? ? Hf distances being 3.303 and 3.259 Å, respectively) held together by three doubly (m) bridging [O(2), O(4) and O(7)] and two triply (m3) bridging isopropoxo groups [O(1) and O(3)].Fig. 4 Ball-and-stick representation of the solid-state structure of [CuHf2Cl(OPri)9] 5 with the atom labelling scheme. Hydrogen atoms have been omitted for clarityJ. Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 2105 The constraints imposed in the formation of a chelating M2X9 bioctahedral sub-structure from an edge-sharing bioctahedron are evident in the distortion in geometries around two hafnium atoms [O(5)]Hf(1)]O(4) 106.6(4) and O(4)]Hf(1)]O(2) 139.6(4)8] when compared with the hafnium co-ordination in compound 1 (Table 1).The distorted trigonal-bipyramidal arrangement around Cu closely resembles the co-ordination sphere of Cd in [CdM2I(OPri)9] derivatives. The trigonal plane of 5 is composed of the atoms Cu, Cl, O(3) and O(5) with two large and one very acute trigonal angle (Table 5). Among the equatorial ligands [Cl, O(3) and O(5)], chloride is most tightly bound to copper since the Cu]O distance [average 2.185(9) Å] is longer than the copper contact to the much larger chloride ion [2.144(5) Å].However, the axial ligands [O(4) and O(7)] with bond lengths 2.001(10) and 2.008(10) Å are symmetrical. The metal–oxygen bond lengths in 5 follow the characteristic order (m3-OR > m-OR > terminal OR) observed in the heterometal derivatives based on M2(OR)9 fragments and corroborate the lengthening of M]O bonds with increased bridging of alkoxide oxygen atoms.Copper(II) being an odd-electron (d9) system is prone to Jahn–Teller distortion which makes the co-ordination flexible and both normal co-ordinated (Cu]L) and longer semico- ordinated (Cu ? ? ? L) bonds are possible.21 In an attempt to define precisely the copper co-ordination in compound 5, the copper–ligand distances and ligand–copper–ligand angles in a set of five-co-ordinated copper halide heterobimetallic derivatives [CuM2Cl(OPri)9] (M = Ti a, Zr b or Hf c) are assembled in Table 6.Among five-co-ordinate copper complexes of type CuL4L9 (cf. CuO4Cl in a–c) the observation of idealised square-pyrimidal (SPY) or trigonal-bipyramidal (TBPY) geometries is rather rare and often an intermediate arrangement is observed.21 The distorted-trigonal bipyramidal (TBPY) environment of copper in complexes a–c is most obvious in the bond angles in the equatorial plane which range from 70.8 to 145.98, showing Table 5 Pertinent bond lengths (Å) and angles (8) of compound 5 Hf(1)]O(6) Hf(1)]O(4) Hf(1)]O(1) Hf(2)]O(8) Hf(2)]O(7) Hf(2)]O(1) Cu]O(4) Cu]Cl Cu]O(3) O(6)]Hf(1)]O(5) O(5)]Hf(1)]O(4) O(5)]Hf(1)]O(2) O(6)]Hf(1)]O(1) O(4)]Hf(1)]O(1) O(6)]Hf(1)]O(3) O(4)]Hf(1)]O(3) O(1)]Hf(1)]O(3) O(9)]Hf(2)]O(7) O(9)]Hf(2)]O(2) O(8)]Hf(2)]O(1) O(7)]Hf(2)]O(1) O(8)]Hf(2)]O(3) O(7)]Hf(2)]O(3) O(1)]Hf(2)]O(3) O(4)]Cu]O(7) O(7)]Cu]Cl O(7)]Cu]O(1) O(4)]Cu]O(3) Cl]Cu]O(3) Hf(2)]O(1)]Hf(1) Hf(2)]O(3)]Hf(1) Cu]O(3)]Hf(1) Cu]O(4)]Hf(1) 1.926(11) 2.074(9) 2.211(8) 1.921(10) 2.081(10) 2.210(8) 2.001(10) 2.144(5) 2.187(9) 99.4(5) 106.6(4) 100.9(4) 164.0(4) 76.9(3) 93.7(4) 75.7(4) 70.5(3) 103.5(5) 102.7(5) 165.3(4) 75.6(4) 94.6(4) 75.7(4) 70.7(3) 150.8(4) 105.3(3) 77.6(4) 78.2(4) 142.6(4) 95.0(3) 94.1(3) 86.4(3) 95.8(4) Hf(1)]O(5) Hf(1)]O(2) Hf(1)]O(3) Hf(2)]O(9) Hf(2)]O(2) Hf(2)]O(3) Cu]O(7) Cu]O(1) O(6)]Hf(1)]O(4) O(6)]Hf(1)]O(2) O(4)]Hf(1)]O(2) O(5)]Hf(1)]O(1) O(2)]Hf(1)]O(1) O(5)]Hf(1)]O(3) O(2)]Hf(1)]O(3) O(8)]Hf(2)]O(9) O(8)]Hf(2)]O(2) O(7)]Hf(2)]O(2) O(9)]Hf(2)]O(1) O(2)]Hf(2)]O(1) O(9)]Hf(2)]O(3) O(2)]Hf(2)]O(3) O(8)]Hf(2)]O(7) O(4)]Cu]Cl O(4)]Cu]O(1) Cl]Cu]O(1) O(7)]Cu]O(3) O(1)]Cu]O(3) Hf(2)]O(2)]Hf(1) Cu]O(3)]Hf(2) Hf(2)]O(3)]Hf(1) Cu]O(7)]Hf(2) 1.932(10) 2.181(8) 2.233(8) 1.931(10) 2.143(9) 2.221(8) 2.008(10) 2.183(9) 101.8(5) 102.3(4) 139.6(4) 96.1(4) 71.1(3) 165.8(4) 70.8(3) 98.9(5) 102.8(4) 139.8(3) 95.7(4) 71.9(3) 166.2(4) 71.7(3) 102.7(5) 103.9(3) 79.0(4) 145.6(3) 78.0(4) 71.8(3) 97.8(3) 87.3(3) 94.1(3) 96.2(4) significant deviation from ideal 1208 angles.Also, the trans O]Cu]O angle (Table 6) in the three derivatives deviates (146.3– 150.88) from the ideal 1808 value. However a tetrahedral distortion which will elongate the Cu]Cl bond is not conceivable, rather the larger chloride ion is found to be the most tightly bound ligand to copper and the average Cu]m3-O distances in these derivatives are longer (b and c) or comparable (a) to the Cu]Cl contacts (Table 6).In all the derivatives the longer distances from copper to triply bridged (m3) oxygens (sum of their ionic radii = 2.07 Å) are associated with highly acute trigonal O]Cu]O angles (Table 6) reflecting the distortion from a TBPY arrangement. Further, the Cu]m3-O distances, in 5, are 0.16–0.18 Å longer than the symmetric Cu]m-O distances whereas the difference between Hf]m3-O and Hf]m-O distances is only 0.05 Å. In view of the observed bond anomalies, the copper co-ordination sphere in [CuHf2Cl(OPri)9] can be termed as ‘3 1 2’ with Cu]Cl, Cu]O(4) and Cu]O(7) being the stronger interactions and the co-ordination polyhedron of Cu21 can be conceived as an intermediate conformation between an elongated TBPY and compressed SPY geometry.[{ [Cd(OPri)3]Sr[Hf2(OPri)9] }2] 6. The formation of heterotermetallic frameworks [{[Cd(OPri)3]Ba[M2(OPri)9}2] (M = Ti, Zr or Hf) 8a,12 from iodide heterobimetallic derivatives [CdM2I(OPri)9] and KBa(OPri)3 is accompanied by a switching of central metal atoms between precursor molecules and has been attributed to the larger size and pronounced tendency of Ba21 to maximise its co-ordination number.A similar phenomenon has been observed in the isolation of 6 from [CdHf2I- (OPri)9] and KSr(OPri)3. Although Sr21 (1.18 Å) is significantly smaller than Ba21 (1.35 Å) it is large enough (cf. Cd21 0.99 Å) to induce a rearrangement of metals required in the constitution of the heterotermetallic assembly [{[Cd(OPri)3]Sr[Hf2- (OPri)9]}2].This strategy of incorporating Sr21 in molecular compounds has also been investigated with Ti and Zr as heterometal partners and the products obtained have been characterised by single-crystal X-ray crystallography.22 Compound 6 crystallises as a crystallographically imposed centrosymmetric dimer with a non-interacting benzene molecule in the crystal lattice. Selected bond lengths and angles are given in Table 7. The structural motif (Fig. 5) adopted is similar to the structures reported for barium derivatives. The overall molecule framework, when dissected formally, can be viewed as a [Sr(m-OPri)2Cd(m-OPri)2Cd(m-OPri)2Sr]21 spirocyclic cationic unit which is capped at both the ends by sequestering confacialbioctahedral Hf2(OPri)9 2 units. Alternatively in a triangular representation, which is obviously related to the barium derivatives, 6 can be viewed as a combination of two triangular [SrHf2(m3-OPri)2(m-OPri)3(OPri)4]1 units linked via a [(PriO)2Cd- (m-OPri)2Cd(OPri)2]22 unit.Each hafnium and strontium atom is six-co-ordinate while cadmium has a distorted-tetrahedral arrangement of ligands. The Cd–O(12a) distance [2.152(9) Å] is much shorter than an average Cd]O dative bond 23 and is comparable with the Cd]O(12) bond length (2.17 Å), in agreement with the observed dimeric structure of 6 and symmetrical bridging in the four-membered Cd(m-OPri)2Cd unit.The Hf]O distances of the Hf2(OPri)9 unit in 6 vary in the following order: Hf]m3-O]Hf (average 2.234 Å) > Hf]m-O]Hf (average 2.176 Å) > Hf]m-O]Sr (average 2.033 Å) > Hf]O (terminal) (average 1.916 Å). The short Hf]O terminal bonds (Table 7) associated with obtuse Hf]O]C angles (average 170.678) are typical of early transition-metal alkoxides. The co-ordination of strontium resembles a severely distorted octahedron with cis and trans angles ranging from 56.8 to 119.5 and 121.8(3) to L¢ Cu L L L L L = O; L¢ = Cl2106 J.Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 Table 6 Metrical comparison of copper–ligand bond distances and angles in a set of five-co-ordinate copper species [CuM2Cl(OPri)9] (M = Ti a,8b Zr b20 or Hf c) Bond length (Å) Axial Equatorial Angles (8) Complex abc Cu]O 2.007, 2.008 1.998, 1.999 2.001, 2.008 Cu]Cl 2.172 2.164 2.144 Cu]O 2.157, 2.149 2.207, 2.186 2.183, 2.187 Axial O]Cu]O 146.3 150.5 150.8 Trigonal 143.3, 145.9, 70.8 143.1, 145.6, 71.2 142.6, 145.6, 71.8 Table 7 Pertinent intratomic distance (Å) and angles (8) of compound 6 Hf(1)]O(6) Hf(1)]O(3) Hf(1)]O(2) Hf(2)]O(9) Hf(2)]O(4) Hf(2)]O(1) O(6)]Hf(1)]O(7) O(7)]Hf(1)]O(3) O(7)]Hf(1)]O(5) O(6)]Hf(1)]O(2) O(3)]Hf(1)]O(2) O(6)]Hf(1)]O(1) O(3)]Hf(1)]O(1) O(2)]Hf(1)]O(1) O(9)]Hf(2)]O(4) O(9)]Hf(2)]O(5) O(4)]Hf(2)]O(5) O(8)]Hf(2)]O(1) O(5)]Hf(2)]O(1) O(8)]Hf(2)]O(2) O(5)]Hf(2)]O(2) O(12a)]Cd]O(10) 1.918(10) 2.036(9) 2.225(9) 1.896(10) 2.030(9) 2.208(9) 99.5(6) 99.9(4) 100.6(4) 162.9(5) 81.5(3) 94.7(5) 82.2(3) 68.5(3) 98.7(5) 101.6(5) 149.5(4) 162.9(4) 72.8(3) 95.4(4) 73.0(3) 124.8(4) Hf(1)]O(7) Hf(1)]O(5) Hf(1)]O(1) Hf(2)]O(8) Hf(2)]O(5) Hf(2)]O(2) O(6)]Hf(1)]O(3) O(6)]Hf(1)]O(5) O(3)]Hf(1)]O(5) O(7)]Hf(1)]O(2) O(5)]Hf(1)]O(2) O(7)]Hf(1)]O(1) O(5)]Hf(1)]O(1) O(9)]Hf(2)]O(8) O(8)]Hf(2)]O(4) O(8)]Hf(2)]O(5) O(9)]Hf(2)]O(1) O(4)]Hf(2)]O(1) O(9)]Hf(2)]O(2) O(4)]Hf(2)]O(2) O(1)]Hf(2)]O(2) O(12a)]Cd]O(12) 1.934(10) 2.165(10) 2.249(8) 1.917(11) 2.187(10) 2.254(8) 99.8(5) 98.6(5) 149.7(4) 97.0(4) 74.1(4) 165.0(5) 72.4(3) 98.6(5) 102.3(5) 97.0(5) 97.0(4) 82.2(4) 165.6(4) 81.7(4) 68.7(3) 78.4(4) Cd]O(12a) Cd]O(12) Sr]O(11) Sr]O(3) Sr]O(1) O(12)]Cd(a) O(10)]Cd]O(12) O(10)]Cd]O(11) O(11)]Sr]O(10) O(10)]Sr]O(3) O(10)]Sr]O(4) O(11)]Sr]O(1) O(3)]Sr]O(1) O(11)]Sr]O(2) O(3)]Sr]O(2) O(1)]Sr]O(2) Hf(1)]O(1)]Sr Hf(2)]O(2)]Sr Hf(2)]O(4)]Sr Cd]O(10)]Sr Cd(a)]O(12)]Cd Cd]O(11)]Sr 2.152(9) 2.171(9) 2.406(9) 2.571(9) 2.642(8) 2.152(9) 120.7(4) 85.9(3) 75.5(3) 104.1(3) 119.5(3) 172.6(3) 65.5(3) 117.7(3) 64.5(3) 56.8(2) 93.6(3) 93.8(3) 100.7(4) 99.0(3) 101.6(4) 99.6(3) Cd]O(10) Cd]O(11) Sr]O(10) Sr]O(4) Sr]O(2) O(12a)]Cd]O(11) O(12)]Cd]O(11) O(11)]Sr]O(3) O(11)]Sr]O(4) O(3)]Sr]O(4) O(10)]Sr]O(1) O(4)]Sr]O(1) O(10)]Sr]O(2) O(4)]Sr]O(2) Hf(2)]O(1)]Hf(1) Hf(2)]O(1)]Sr Hf(1)]O(2)]Hf(2) Hf(1)]O(2)]Sr Hf(1)]O(3)]Sr Hf(1)]O(5)]Hf(2) 2.170(8) 2.172(9) 2.428(9) 2.610(10) 2.650(8) 124.1(3) 128.5(4) 117.9(3) 109.4(3) 121.8(3) 110.7(3) 64.2(3) 165.1(3) 64.5(3) 94.1(3) 95.1(3) 93.5(3) 94.0(3) 101.2(3) 97.1(4) 172.6(3)8, respectively.The Sr atom shows different contacts to two doubly bridging oxygen atoms [Sr]O(3) 2.571(9), Sr]O(4) 2.610(10) Å] while the Sr]m3-O distances are comparable [2.642(8) and 2.650(8) Å]. Conclusion We have used bioctahedral alkoxohafnate ligands [Hf2- (OPri)10]22 and [Hf2(OPri)9]2 with a variety of electrophiles (H1, Li1, Cu21 and Sr21) to prepare hafnium-containing homo- and hetero-metallic alkoxides.Subject to the ligand–electrophile stoichiometry, both edge-sharing (1, 2 and 4) and face-sharing (5 and 6) bioctahederal structures are observed. As a general feature, the present work demonstrates the preference of larger tetravalent early transition metals for six-co-ordination. Irrespective of the heterometal partner, hafnium atoms in all the structurally characterised derivatives are present in an octahedral geometry.The tendency of Hf IV to attain an octahedral surrounding of Fig. 5 Molecular structure of the centrosymmetric dimer [{[Cd- (OPri)3]Sr[Hf2(OPri)9]}2] 6 showing the atom labelling scheme used. Hydrogen atoms are not shown. Atoms designated with an ‘a’ are related by symmetry ligands is especially evident in the formation of compound 4 which in comparison to the titanium analogue [{LiTi- (OPri)5}2] 20 (Li, four-co-ordination; Ti, five-co-ordination) shows a different co-ordination environment for the metals, in 4, and a bond to Li (three-co-ordination) is sacrificed to satisfy the six-co-ordination of hafnium.This observation is strengthened in the easy formation and extraordinary stability of the bioctahedral [Hf2(OPri)9]2 unit (5 and 6). This unit could be considered as a ligand-deficient derivative of [Hf2(OPri)10]22 [leaving one of the hafnium(IV) centres five-co-ordinate] where, despite the geometric constraints imposed in the transformation of an edge-sharing bioctahedron (I) to a confacial bioctahedron (II), the two metals form an additional isopropoxo bridge to achieve the six-co-ordination. Experimental Reagents and general techniques All operations were carried out under a dry dinitrogen atmosphere with rigorous exclusion of oxygen and moisture.[2H6]- Benzene and [2H8]toluene were dried over molecular sieves and all other hydrocarbon solvents were distilled from lithium aluminium hydride and sodium–benzophenone.Isopropyl alcohol was dried by distillation from magnesium metal and aluminiumJ. Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 2107 triisopropoxide. Pyridine was distilled from KOH and stored over 0.4 Å molecular sieves. Cryoscopy (C6H6, 5 8C) was used to estimate the nuclearity of the new compounds. Metal and halogen contents were determined using established analytical procedures.24 The compound [Sr(OPri)2]n was obtained by the alcoholysis of [Sr{N(SiMe3)2}2(thf)2] (thf = tetrahydrofuran).25 Copper(II) chloride and CdI2 were dried by heating in vacuum and analysed for halogen contents before use.The NMR(1H, 7Li and 13C) spectra were obtained on a Bruker AC-200 spectrometer, IR spectra on a Bio-Rad FTS-165 spectrometer. The 7Li and 113Cd NMR chemical shifts are referenced externally to 0.1 mol dm23 solutions of LiCl and Cd(NO3)2 in D2O, respectively. Analyses (C, H and N) were performed using a LECO Elemental Analyser CHN 900.Preparations [Hf2(OPri)8(PriOH)2] 1. Hafnium isopropoxide 1 was synthesized following the literature method.4 Elemental and spectral (IR and NMR) analyses, performed to check the identity of the product, conform to the reported values 6 and hence are not reproduced. [Hf2(OPri)8(PriOH)(NC5H5)] 2. A crystalline sample of [Hf2(OPri)8(PriOH)2] (2.45 g, 2.57 mmol) was heated in vacuo (150 8C, 1022 Torr) for 30 min to obtain a viscous mass.The product was dissolved in toluene (10 cm3) and pyridine (2 cm3) was added. The solution was stirred for 1 h at 50 8C and left at room temperature overnight, when large rhombohedral crystals of compound 2 were formed. These were collected by decantation and dried in static vacuum. Yield: 1.35 g, 53% (Found: C, 39.5; H, 7.0; Hf, 35.95; N, 1.4. C32H68Hf2NO9 requires C, 39.7; H, 7.1; Hf, 36.9; N, 1.45%). NMR (CDCl3, 20 8C): 1H (200.13 MHz), d 9.11 (br, 2 H, o-H of py), 7.32 (m, 2 H, m-H of py), 7.27 (t, 1 H, p-H of py), 4.44 (m, 9 H, CH) and 1.16 (d, 54 H, J = 6 Hz, CH3); 13C-{1H} (50.3 MHz), d 151.40, 137.93, 123.59 (o-, p-, m-C of py), 69.53 (CH) and 26.80 (CH3).IR (CDCl3, cm21): 3154 [br, n(OH)], 1617m, 1479m, 1392s, 1330s, 1164s, 1027s, 848m, 813s, 774m and 665m. M: Found 1032; Calc. 968. [Hf2(OPri)8(PriOH)(O2C4H8)] 3. Compound 3 was synthesized in an analogous manner to that for 2 using [Hf2- (OPri)8(PriOH)2] (1.50 g, 1.57 mmol) and a toluene–1,4-dioxane mixture.Crystals were obtained from a concentrated solution at room temperature. Yield: 0.79 g, 51% (Found: C, 38.05; H, 7.2; Hf, 36.0. C31H70Hf2O11 requires C, 38.15; H, 7.25; Hf, 36.6%). NMR (C6D6, 20 8C): 1H (200.13 MHz), d 4.62 (m, 10 H, CH and OH), 3.67 (s, 8 H, CH2) and 1.16 (d, 54 H, J = 6 Hz, CH3); 13C-{1H} (50.3 MHz), d 69.51 (CH), 67.87 (CH2) and 26.34 (CH3). IR (CDCl3, cm21): 3154 [br, n(OH)], 1617s, 1440s, 1372m, 1332m, 1253w, 1152s, 1012s, 980m, 774m and 610s.M: Found 1103; Calc. 976. [{LiHf(OPri)5}2] 4. To a toluene (10 cm3) suspension of LiOPri (0.41 g, 6.21 mmol) was added a clear solution of [Hf2(OPri)8(PriOH)2] (2.94 g, 3.10 mmol) in hexane (20 cm3) and the resulting mixture stirred at room temperature. The clear solution obtained was heated at 50 8C for ª4 h and the volume reduced to ª15 cm3. The solution was cooled to 230 8C, producing colourless crystals overnight. A second crop was obtained by concentrating the mother-liquor. Yield: 1.01 g, 34% (Found: C, 37.0; H, 7.15; Hf, 36.9; Li, 1.4.C30H70Hf2Li2O10 requires C, 37.5; H, 7.3; Hf, 37.1; Li, 1.45%). NMR (C6D5CD3): 1H (200.13 MHz, 210 8C), d 4.71 (m, 3 H, J = 6, CH), 4.60 (spt, 2 H, J = 6, CH), 1.40 (d, 12 H, J = 6, CH3), 1.38 (d, 12 H, J = 6) and 1.32 (d, 6 H, J = 6 Hz); 13C-{1H} (50.3 MHz, 20 8C), d 69.95, 69.02, 67.68 (CH), 27.83, 27.66, 26.81 (CH3); 7Li (77.77 MHz, 20 8C), d 3.02. M: Found 916; Calc. 962. [CuHf2Cl(OPri)9)] 5. A benzene (20 cm3) solution of freshly sublimed [KHf2(OPri)9] (3.95 g, 4.26 mmol) was added to a benzene (15 cm3) suspension of finely divided anhydrous CuCl2 (0.58 g, 4.31 mmol) and the resulting mixture stirred at room temperature for ª6 h.Over a few hours the solution gained a green coloration and an off-white precipitate remained. The mixture was heated at 70 8C for 3 h and the KCl formed was filtered off. All solvent was removed in vacuo to obtain a green solid.Dissolving the solid in the minimum volume of pentane followed by cooling at 210 8C gave green transparent crystals of compound 5. Yield: 1.22 g, 29% (Found: C, 32.55; H, 6.2; Cl, 3.4; Hf, 35.85. C27H63ClCuHf2O9 requires C, 32.85; H, 6.4; Cl, 3.6; Hf, 36.15%). NMR (C6D5CD3): 1H (200.13 MHz, 20 8C), d 4.27–4.70 (br, 9 H, CH), 1.44 (br, 6 H, CH3), 1.35 (br, 12 H, CH3) and 0.92 (br, 36 H, CH3); (40 8C), d 4.79 (br, 9 H, CH), 1.64 (br, ª30 H, CH3) and 1.24 (br, 24 H, CH3); 13C-{1H} (50.3 MHz, 40 8C), d 68.96, 67.54 (CH), 27.83, 27.40 (CH3). M: Found 950; Calc. 988. [{[Cd(OPri)3]Sr[Hf2(OPri)9]}2] 6. (a) [{KSr(OPri)3}n]. Using freshly synthesized Sr(OPri)2 and KOPri, [{KSr(OPri)3}n] could be obtained by following the procedure described for KBa- (OPri)3 12 (Found: C, 35.15; H, 6.8; Sr, 29.0. C9H21KO3Sr requires C, 35.55; H, 6.95; Sr, 28.8%). NMR (C6D6, 20 8C): 1H (200.13 MHz), d 4.29 (m, 3 H, CH) and 1.35 (d, 18 H, CH3); 13C-{1H} (50.3 MHz), d 63.93 (CH) and 30.16 (CH3).The poor solubility of the compound precluded molecular-weight studies. (b) To a prestirred solution of KSr(OPri)3 (0.35 g, 1.16 mmol) in benzene (10 cm3) was added a solution of freshly sublimed [CdHf2I(OPri)9] (1.31 g, 1.16 mmol) in benzene (15 cm3) and the reaction mixture was stirred at room temperature for ª12 h. After filtration of Kl and removal of volatiles, compound 6 was recovered as a white solid in almost quantitative yield (1.43 g, 97%). It was redissolved in a mixture of toluene–pentane and kept at 0 8C when colourless plates were formed.Yield: 0.82 g, 56% (Found: C, 35.45; H, 6.55; Cd, 8.55; Hf, 34.15; Sr, 6.8. C78H174Cd2Hf4O24Sr2 requires C, 35.9; H, 6.7; Cd, 8.6; Hf, 27.35; Sr, 6.7%). NMR (20 8C, C6D5CD3): 1H (200.13 MHz), d 1.63 (d, 24 H, J = 6, CH3), 1.51 (d, 36 H, J = 6, CH3), 1.47 (d, 24 H, J = 6), 1.43 (d, 12 H, J = 6), 1.38 (d, 24 H, J = 6), 1.35 (d, 24 H, J = 6 Hz), CH protons observed as three overlapping septets centred at d 4.64, 4.54 and 4.48; 13C-{1H} (50.3 MHz), d 70.95, 69.53, 68.56, 67.94, 65.49 (CH), 30.47, 27.40, 26.77, 26.65, 26.49, 26.08 (CH3); 113Cd-{1H} (44.3 MHz), d 226.91.M: Found 2297; Calc. 2610. X-Ray crystallography Single crystals suitable for crystallography were selected from the bulk samples of compounds 1, 2 and 4–6 and transferred in an inert atmosphere to Lindemann capillaries of appropriate dimensions. The sealed capillaries were then mounted on the goniometer head of a four-circle (Siemens AED for 4–6) or an image-plate (Stoe IPDS for 1 and 2) diffractometer operating with graphite-monochromated Mo-Ka radiation (l = 0.710 73 Å) and the w–q scan technique (except in the case of 1 and 2).In each case the cell constants and orientation matrix for data collection were obtained from a least-squares refinement using the setting angles of 25 reflections. Data collection for all the compounds was performed at 293(2) K. Lorentz-polarisation and absorption corrections (semiempirical from y scans for 4– 6, numerical for 1 and 2) were applied to all the data.The structures were solved by a combination of direct methods (SHELXS 86) 26 and Fourier-difference techniques. The structures were refined (SHELXL 93)27 by full-matrix least-squares analysis on F with anisotropic displacement parameters for all nonhydrogen atoms. All hydrogen atoms except that of OH in compounds 1 and 2 were idealised (C]H 0.96 Å) and included in the final stage of refinements with fixed isotropic parameters.Weights {w = q/[s2(Fo 2) 1 (aP)2 1 bP 1 d 1 e sin q] where P = [max(0, Fo 2) 1 (1 2 f )Fc 2]} were included in the last refinement cycles.2108 J. Chem. Soc., Dalton Trans., 1997, Pages 2101–2108 Table 8 Summary of crystallographic data for compounds 1, 2 and 4–6 Empirical formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 ZF (000) Dc/g cm23 Crystal size/mm Standard reflections q Range/8 Reflections collected Independent reflections Observed reflections [I > 2s(I)] Goodness of fit on F2 Final R indices [I > 2s(I)] (all data) Largest difference peak and hole/e Å23 1 C30H70Hf2O10 947.84 Triclinic P1� 12.118(2) 12.212(2) 14.964(3) 80.69(3) 84.91(3) 88.89(3) 2176.6(7) 2 948 1.446 0.5 × 0.4 × 0.2 50–250 2.54–26.13 21 630 8013 6182 1.089 0.0655 0.0796 1.295, 22.545 2 C32H68Hf2NO9 967.85 Monoclinic C2/c 10.501(2) 18.076(4) 22.859(5) 90.94(3) 4338(2) 4 1932 1.482 0.3 × 0.2 × 0.15 50–200 2.25–24.13 10 197 3408 3016 1.053 0.0544 0.0594 1.602, 21.157 4 C30H70Hf2Li2O10 961.72 Triclinic P1� 9.963(2) 10.895(2) 12.123(2) 66.65(3) 68.21(3) 70.04(3) 1092.3(3) 1 480 1.462 0.4 × 0.3 × 0.25 3 1.90–22.49 2857 2857 2711 1.187 R1 = 0.0456 R1 = 0.0486 1.235, 21.576 5 C27H63ClCuHf2O9 987.74 Monoclinic P21 /n 9.778(2) 24.360(5) 16.826(3) 93.06(3) 4002.1(14) 4 1948 1.639 0.45 × 0.33 × 0.3 3 1.67–24.99 7261 7040 5586 1.151 R1 = 0.0725 R1 = 0.0940 1.236, 21.657 6 C78H174Cd2Hf4O24Sr2 2610.17 Monoclinic P21 /c 22.800(5) 12.894(3) 19.260(4) 96.20(3) 5629(2) 2 2588 1.540 0.5 × 0.3 × 0.15 3 1.80–22.50 8062 7346 5859 1.049 0.0694 0.0884 0.889, 21.439 Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/503.Acknowledgements We gratefully acknowledge the generous support of Deutsche Forschungsgemeinschaft under the framework of the programme SFB-277 and the Alexander von Humboldt Foundation, Germany for a research fellowship (to S. M.). References 1 G. J. Ashwell (Editor), Molecular Electronics, Wiley, New York, 1992. 2 R. C. Mehrotra, A. Singh and S. Sogani, Chem. Rev., 1994, 94, 1643; K. G. Caulton and L. G. Hubert-Pfalzgraf, Chem. Rev., 1990, 90, 969. 3 W. S. Rees, jun. (Editor), CVD of Non-metals, VCH, Weinheim, 1996. 4 D. C. Bradley, R. C. Mehrotra and D. P. Gaur, Metal Akoxides, Academic Press, London, 1978. 5 M. J. Hampden-Smith, T. A. Wark, A. Rheingold and J. C. Huffman, Can. J. Chem., 1991, 69, 121. 6 B. A. Vaartstra, J. C. Huffman, P. S. Gradeff, L. G. Hubert- Pfalzgraf, J. C. Daran, S. Parrand, K. Yunulu and K. G. Caulton, Inorg. Chem., 1990, 29, 3126. 7 C. Favotto, A. Margaillan and M. Roubin, Ann. Chim. (Paris), 1996, 21, 13. 8 M. Veith, S. Mathur and V. Huch, Inorg. Chem., (a) 1996, 35, 7295; (b) in the press. 9 H. Nagamoto, K. Amanuma, H. Nobutomo and H. Inoue, Chem. Lett, 1988, 2, 237. 10 H. Maeda, Y. Tanaka, M. Fukutomi and T. Asane, Jpn. J. Appl. Phys., 1988, 27, L209. 11 P. Pereira, S. H. Lee, G. A. Somaraji and H. Heinemann, Catal. Lett., 1990, 6, 255. 12 M. Veith, S. Mathur and V. Huch, J. Am. Chem. Soc., 1996, 118, 903. 13 R. J. Cava, R. B. van Dover, B. Batlagg and E. A. Rietman, Phys. Rev. Lett., 1987, 58, 408. 14 (a) A. A. Pinkerton, D. Schwarzenbach, L. G. Hubert-Pfalzgraf and J. G. Riess, Inorg. Chem., 1976, 15, 1196; (b) E. P. Turevskaya, N. Ya. Turova, A. V. Korolev, A. I. Yanovsky and Yu. T. Struchkov, Polyhedron, 1995, 14, 1531. 15 M. Chisholm and D. L. Clark, Comments Inorg. Chem., 1987, 6, 23. 16 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 17 M. Veith, Chem. Rev., 1990, 90, 3. 18 M. J. Hampden-Smith, D. S. Williams and A. L. Rheingold, Inorg. Chem., 1990, 29, 4076. 19 M. Veith, S. Mathur and V. Huch, J. Chem. Soc., Dalton Trans., 1996, 2485. 20 B. A. Vaartstra, J. A. Samuels, E. H. Barash, J. D. Martin, W. E. Streib, C. Gasser and K. G. Caulton, J. Organomet. Chem., 1993, 449, 191. 21 D. Reinen and C. Friebel, Inorg. Chem., 1984, 23, 791; J. D. Blanchette and R. D. Willett, Inorg. Chem., 1988, 27, 843. 22 M. Veith and S. Mathur, unpublished work. 23 S. C. Goel, M. Y. Chiang and W. E. Buhro, J. Am. Chem. Soc., 1991, 112, 6724. 24 A. I. Vogel, A Textbook of Quantitative Inorganic Analysis, Longmans, London, 1978. 25 M. Westerhausen, Inorg. Chem., 1991, 30, 96. 26 G. M. Sheldrick, SHELXS 86, Program for Crystal Structure Determination, University of Götting1986. 27 G. M. Sheldrick, SHELXS 93, Program for Crystal Structure Determination, University of Göttingen, 1993. Received 5th February 1997; Paper 7/00833C

ISSN:1477-9226    

DOI:10.1039/a700833c

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2103–2107 2103 Laser-induced photoacoustic calorimetric determination of enthalpy and volume changes in photolysis of 59-deoxyadenosylcobalamin and methylcobalamin Lai Bin Luo,a Gang Li,a Hui Lan Chen,*,†,a Shao Wei Fu b and Shu Yi Zhang b a State Key Laboratory and Institute of Coordination Chemistry, Department of Chemistry, Nanjing University, Nanjing 210093, P. R. China b Laboratory of Modern Acoustics and Institute of Acoustics, Nanjing University, Nanjing 210093, P.R. China Photolysis of 59-deoxy-59-adenosylcobalamin (AdoCbl) in neutral aqueous solution and methylcobalamin (MeCbl) in neutral and acid aqueous solution has been investigated using pulsed, time-resolved photoacoustic calorimetry in the temperature range 10–30 8C. The enthalpy changes for the above cobalamins, 129 ± 17, 163 ± 21 and 176 ± 23 kJ mol21, respectively, are consistent with the values obtained by thermolytic kinetic methods.The reaction volume changes for them, 6 ± 1, 2 ± 0.5 and 5 ± 1 ml mol21, respectively, are probably due to the conformational changes of the corrin ring and its side chains accompanying Co]C bond cleavage. Coenzyme B12 (59-deoxy-59-adenosylcobalamin, abbreviated AdoCbl, Fig. 1) is a cofactor in over a dozen enzymatic reactions, in which 1,2-intramolecular rearrangements of the substrates occur. The essential first step in the catalytic cycle of B12- dependent mutases is the homolytic cleavage of the Co]C bond to produce a 59-deoxy-59-adenosyl radical and paramagnetic cobalamin (B12r).1–4 While isolated AdoCbl undergoes slow thermolysis at ambient temperature (25 8C, k ª 10210 s21), the mutases can catalyze Co]C bond cleavage (e.g. 25 8C, k ª 102 s21) by about 12 orders of magnitude.5 How these enzymes accelerate rupture of the Co]C bond and achieve such a level is a focus-point in B12 chemistry.Knowledge of the Co]C bond dissociation energy (BDE) of AdoCbl and related organocobalt compounds, and the factors that influence such bond dissociation, may help to understand enzyme-induced bond weakening and dissociation. Since Finke 5 and Halpern6 accomplished the measurement of the cobalt–carbon BDE of AdoCbl by determining the kinetics of the thermal bond dissociation process, in which radical trap complexes were used to scavenge organic radicals, great eVorts have been devoted to the field.7–10 It has been revealed that there may be an interplay between the trans and steric influences of the axial Ado and 5,6-dimethylbenzimidazole (DMBz) ligand, and further, the steric rather than electronic eVects modulate the lability of the Co]C bond.5–11 Recently, Brown suggested that side chain thermal motions of the corrin ring might be an important source of entropic activation for the homolysis of such complexes.12 One hypothesis here, that of enzyme-induced corrin ‘butterfly’ or ‘upward’ conformational distortion with its resultant corrin ring– adenosyl steric interactions to ‘lift’ the adenosyl group from cobalt and otherwise distort it along the Co]C bond,4,11,13 has been accepted by bio-inorganic chemists but remains undemonstrated in the B12 enzymes themselves.The recent X-ray crystallographic structure determination for two B12-dependent enzymes, i.e. AdoCbl-dependent methylmalonyl-CoA14a and MeCbl-dependent methionine synthese,14b reveals that the cofactor is bonded in a DMBz base-oV form and the cobalt atom is co-ordinated via a long bond to a histidine residue from the protein.It has also been proposed that photo-induced homolysis is a consequence of the similar steric strain between † E-Mail: hlchen@nju.edu.cn the corrin ring and the Ado ligand.1,15–18 Crystallographic data for various enzyme-free cobalamins suggest that interaction of the corrin ring with axial Ado and DMBz bases causes ring pucker or distortion, i.e. upward folding of one side of the corrin ring.11a,19 However, quantitative data about the volume change accompanying the relaxation process of a sterically strained corrin ring during Co]C bond breaking were not determined.With the development of time-resolved photoacoustic calorimetry (PAC), it is now feasible to measure the dynamics of enthalpy and volume changes that accompany ligand dissociation and/or molecular movements in photoinduced chemical reactions.20–22 Since AdoCbl and alkylcobalamins undergo photo-induced Co]C bond homolysis to produce Cob(II)- alamin (B12r) and the corresponding alkyl radical, similar to many of the B12-dependent enzyme reactions, we adopted the PAC technique to assess volume changes resulting from the conformational changes in the corrin ring and enthalpy changes in the Co]C bond cleavage process.Methylcobalamin (MeCbl), another B12 coenzyme, is known to be biologically active and essential for human metabolism.1 We selected this molecule for investigation not only because of its natural occurrence as a cofactor for a methyltransferase Fig. 1 The structures of 59-deoxy-59-adenosylcobalamin and methylcobalamin N N Co H2N O NH2 O O H2N O NH2 N N NH2 O H2N O N N NH O O P O O O O HO HO R N N N N NH2 O H H HO OH f g a b c d e AdoCbl R = Me MeCbl R =2104 J. Chem. Soc., Dalton Trans., 1998, Pages 2103–2107 enzyme but also because CH3 is a small group and comparative information could be obtained facilitating the investigation into steric interaction and conformational changes of the corrin ring during Co]C bond cleavage.Experimental Samples 59-Deoxy-59-adenosylcobalamin was obtained from Aldrich and MeCbl prepared according to the literature.23 For PAC experiments, the concentrations of AdoCbl and MeCbl were 1.5 × 1025 M in neutral deionized water and in 0.05 M HCl aqueous solution. Potassium dichromate (AR) was used as a calorimetric reference.21a Apparatus and methods Details for a similar experimental system using pulsed PAC have been described previously.20–22 In our experiment a Q-switched Nd:YAG laser (Continuum NP70) operating at 10 Hz, 355 nm, pulse width 8 ns, and 15 mJ was used as the excitation source.The laser beam diameter was fixed by a 0.9 mm pinhole, which determined the time resolution to be equal to the travel time of the acoustic wave through the laser beam diameter (about 600 ns in the aqueous solutions). Temperature (10–30 8C) is kept constant within ±0.2 8C by using a thermostat and a thermoelement placed directly into the sample cell.Acoustic waves, an average of the signals from 100–200 pulse excitations, were detected by a 2 MHz PZT cylindrical tube transducer. The receiving area of this transducer is relatively enlarged, compared with a conventional PZT disk, and its receiving face just matches the cylindrical acoustic waveform in the whole circumferential space. The output voltage is ampli- fied by a HP-8847F and recorded on a HP-54510B instrument.The data were transferred to a personal computer where each acoustic wave was normalized to the laser energy measured by a transient radiometer (DigiRad. R-752 and P-444). Sample absorbances range from 0.2 to 0.3 at 355 nm (1 cm path length) and are matched to that of a calorimetric reference. The solutions are argon-saturated before pumping into the sample cell, and flow continuously during photolysis (see Scheme 1).Data analysis According to previous studies,20–22 the acoustic signal (S) results from expansion or contraction, i.e. the volume changes of the irradiated sample [equation (1) where the parameter K is a S = KDV (1) function of the instrument response]. There are two contributions to the overall volume changes. One is derived from the thermally induced volume change in the solution, DVth, which is related to the thermal expansion coeYcient (b) of the solvent and the heat capacity (Cp) of the solution.The other may arise from the volume change between the products and reactants, DVr [equation (2), where r is the density of the solution, and DE S = K(DVth 1 DVr) = K[(b/Cpr)DE 1 DVr] (2) Scheme 1 Flowchart of solution for photoacoustic calorimetry is the thermal energy released to the medium upon decay]. A compound (K2Cr2O7) is used as the calorimetric reference. It converts the photon energy entirely into heat with no reaction volume change, i.e.DVr = 0. Therefore Sref = K(b/Cpr)Ehn. The ratio of the acoustic wave amplitudes of the sample to the calorimetric reference is then defined as f, expression (3), thus f = S/Sref = (DE/Ehn) 1 DVr/[(b/Cpr)Ehn] (3) giving equation (4). It is assumed that DE and DVr are Ehnf = DE 1 DVrCpr/b (4) independent of temperature. The intercept and slope of the linear plot of Ehnf vs. Cpr/b at diVerent temperatures yields DE and DVr, respectively. However, the quantum yield F of the photo-induced chemical reaction must be taken into account for the evaluation of DH and DVR.Therefore, the overall enthalpy and volume changes for a reaction are determined according to equations (5) and (6), respectively. DH = (Ehn 2 DE)/F (5) DVR = DVr/F (6) Results The photoacoustic signals for both AdoCbl and K2Cr2O7 (reference) in neutral aqueous solution at 10 8C are shown in Fig. 2. The relationship between the signals and the absorbed energy is linear within the range studied (Fig. 3), which eliminates the possibility of multi-photon eVect in solutions. The values of DE and DVr for each complex are obtained through equation (6). Plots of Ehnf vs. Cpr/b are shown in Fig. 4. Values of b, Cp and r at diVerent temperatures are according to the literature.24 The quantum yield values are 0.23 for base-on AdoCbl, 0.35 for base-on MeCbl and 0.50 for base-oV MeCbl respectively (see Discussion).15–18 From equations (6) and (7), the enthalpy and reaction volume changes are obtained.The associated enthalpies, Co]C BDEs and volume changes are given in Table 1. For comparison the data from thermolysis experiments are also listed. Discussion Reaction mechanism Alkylcobalamins exhibit a temperature-dependent axial-base equilibrium, i.e. the DMBz group is either co-ordinated to CoIII or not.1b The photochemical reactions in the system include Fig. 2 Photoacoustic signal of K2Cr2O7 (– – –) and 59-deoxy-59- adenosylcobalamin (–––) in neutral aqueous solution at 10 8C (both are 1.5 × 1025 M)J.Chem. Soc., Dalton Trans., 1998, Pages 2103–2107 2105 Co]C bond dissociation of both the six-co-ordinate base-on form and the five-co-ordinate unprotonated base-oV species. Studies of the temperature-dependent axial-base equilibrium indicate that base-on forms are predominant for AdoCbl and MeCbl in neutral aqueous solution at room-temperature (ca. 95 and 97% at 25 8C).5b,9b Acidification of MeCbl produces baseo V MeCbl where the DMBz group is not co-ordinated to CoIII and is protonated.The pKa of DMBz in MeCbl is 2.7. In 0.05 M HCl aqueous solution, the base-oV MeCbl is ca. 96%.25 Therefore, this study only considers the signal contribution from the base-on form of AdoCbl and MeCbl in neutral solution or the base-oV form of MeCbl in acidic solution. A mechanism for photolytic cleavage of the Co]C bond is proposed in Scheme 2.15 As Chen and Chance indicated,15 upon photolysis of AdoCbl and MeCbl, the excited Co*,C state can either relax to the Fig. 3 The relationship between signal amplitude and excitation energy of K2Cr2O7 and MeCbl (both are 1.5 × 1025 M) Fig. 4 Plots of Ehnf vs. Cpr/b for AdoCbl (n) and MeCbl (h) in neutral aqueous solution, and MeCbl (d) in 0.05 M HCl aqueous solution (all are 1.5 × 1025 M) Table 1 Data from photolysis of 59-deoxy-59-adenosylcobalamin and methylcobalamin by PAC DVr/ml mol21 DH/kJ mol21 BDE/kJ mol21 DH‡/kJ mol21 a BDE/kJ mol21 a AdoCbl 6 ± 1 129 ± 17 129 ± 17 138 ± 8b 125 ± 8b MeCbl (base-on) 2 ± 0.5 163 ± 21 163 ± 21 171 ± 13c 155 ± 13c MeCbl (base-oV) >5 ± 1 >176 ± 23 >176 ± 23 a Data obtained from thermolysis.b See ref. 5(b). c In ethane-1,2-diol, see ref. 9(b). ground state (k3 ª 3 × 1011 s21), or undergo cleavage to form a geminate pair (k1 ª 3 × 1012 s21).26 Although thermolysis of cobalamin can also form a geminate pair, the rate is low enough (ª10210 for AdoCbl and ª10213 s21 for MeCbl at 25 8C)5b,9b to be negligible. As discussed elsewhere, there is a solvent ‘cage’ for the radical pair.15,16,27 The caged geminate pair can either recombine to form the reactant or diVuse into the solvent to form free radicals.For AdoCbl and MeCbl geminate recombination rates in H2O (k4 ª 109 s21) are competitive with cage escape (k2 ª 1.8 × 109 s21).16,28 This means that CoII species and the free radical are the final products for our experimental time windows of ca. 100 ns. In the system, there are some radical side reactions, including hydrogen abstraction by the carbon radical from the solvent and/or the corrin ring (k = 102–104 s21),15b dimerization (k ª 1010 s21), cyclization (k = 104–105 s21 for Ado) and diVusional recombination, etc.5,15 Recombination of the methyl (109 M21 s21) and 59-deoxy-59-adenosyl (108–109 M21 s21) radicals with CoII is found to be near the diVusion-controlled limit in H2O.5,15 For the sample concentrations of about 1025 M, the concentration of the free radicals should be much less than 1025 M. Our investigations on photo-dissociation of the Co]C bond are not contaminated by artefactual side reactions.Quantum yields Quantum yields for AdoCbl and MeCbl have been investigated by several groups.14–17 Using nanosecond laser pulse with diVerence absorption spectra, Chen and Chance reported in 1990 that the nanosecond (ns) quantum yield of AdoCbl is 0.23 ± 0.04 and that there is no significant change in the quantum yield at two wavelengths (355 and 532 nm).15a Later, with a continuous-wave (CW) laser they measured the CW anaerobic quantum yield of AdoCbl (F = 0.20 ± 0.03, at 442 nm), which agrees with the ns quantum yield within experimental error.15b The measured CW anaerobic quantum yield of MeCbl (F = 0.35 ± 0.03, at 442 nm) 15b is in agreement with its investigation by Pratt and Whitear that gave a quantum yield of ca. 0.30 with no wavelength dependence.16 However, Endicott and Netzel obtained quantum yields of 0.16 ± 0.05 for MeCbl and 0.09 ± 0.035 for AdoCbl by a picosecond flash photolysis technique. 17 This result is consistent with that of Taylor et al.18 where they based their yields on continuous photolysis with O2 scavenging. Chen and Chance suggested that the lower quantum yields reported by Endicott’s group are probably due to a calculation from the single wavelength absorbance changes at the CoII peak absorbance and not taking into consideration the spectral overlap of various absorptions.Therefore, we adopt Chen’s quantum yields, 0.23 for AdoCbl and 0.35 for MeCbl. However, as there is only a qualitative quantum yield for baseo V MeCbl reported by Pratt 16 and Taylor,18 we use F < 0.5 in our calculations. Enthalpy change and Co]C bond dissociation energy (BDE) The enthalpy changes of photolysis for AdoCbl and MeCbl measured by PAC are given in Table 1. Since the apparent DH is a net enthalpy change from an excited state to forming a CoII species and a free radical, which are homolytic decomposition products of the Co]C bond within our experimental time-scale, the values of DH are equal to those of Co]C BDE themselves, and most of the error in the measurement (10–15%) reflects the uncertainty in the quantum yield data.Besides, data for thermolysis for AdoCbl and MeCbl determined by kinetic methods at 80–110 8C are also listed in Table 1. As discussed by Finke et al.Scheme 2 Co*,C (Co,C)geminate pair CoII + C k1 k2 k–2 k–1 k3 hn k4 Co—C2106 J. Chem. Soc., Dalton Trans., 1998, Pages 2103–2107 the enthalpy changes are contributed to from two components: (a) dissociation of the Co]C bond forming a geminate pair and (b) diVusion of the geminate pair from the ‘cage’ to solvent forming a free radical.27,29 The Co]C BDE is given by subtracting 13 kJ mol21 from the activation enthalpy.5b It has been found that our Co]C BDE values obtained from the PAC method at 10–30 8C are consistent with the previously literary values for thermolysis dissociation determined by kinetic methods at 80–110 8C.Furthermore, for base-oV MeCbl, there is no enthalpy change reported to date and it is even diYcult to obtain by the kinetic methods. We have for the first time estimated the enthalpy change and Co]C BDE of base-oV MeCbl by the PAC method to be >176 ± 23 kJ mol21. It is higher than that for the base-on form as expected.Volume changes A reaction volume change in solution has two components,20–22 (a) the solvation volume change associated with property changes in the surrounding medium, such as polarity, electrostriction, and dipole interactions, etc., and (b) the intrinsic volume change related to the size of the molecules or ions, for example, formation or destruction of empty space that is too small to be occupied by solvent molecules. Previous crystallographic 19,30,31 and 2-D NMR32 investigations of cobalamins indicate that the main molecular movements associated with the cleavage of the Co]C bond for alkylcobalamins include, (a) the diVusion of the organic radical into the solvent from the ‘cage’, (b) upward movement of the corrin ring, (c) the shifts of the corrin-ring side chains.During photolysis of AdoCbl and MeCbl, the volume changes attributed to the medium reorganization 20–22 invoked by the molecular movements as mentioned above should be presented.According to the X-ray diVraction investigation on five-coordinated B12r,31 the conformation of the corrin ring is upward with a folding angle 16.38, which is larger that in AdoCbl (13.38) and similar to that in MeCbl (15.88). The solvent molecule near the axial co-ordination site is ca. 3.42 Å from the center in B12r,31 which may form a small empty space, not occupied by the solvent molecule, around CoII. Therefore, in the process of Co]C bond cleavage, it can contribute to the positive volume changes. Our results have revealed that reaction volume changes for base-on AdoCbl (6 ± 1 ml mol21) is larger than for base-on MeCbl (2 ± 0.5 ml).Since the estimated radii for the Ado and Me radical are 6 and 1.1 Å, respectively, it is reasonable that the methyl radical is less interrupted by a solvent cage. Further, as discussed above, adenosyl is a bulky group, while methyl is small.11,15,19,32a Therefore conformational changes accompanying the cleavage of the Co]C bond and cage escape in AdoCbl should be larger than those in MeCbl.This gives rise to the reaction volume changes, both the solvational and the intrinsic volume changes for AdoCbl are larger. Unfortunately, there is no single-crystal diVraction structural information for base-oV B12r. We cannot make structure comparison between base-oV MeCbl and its photolytic product base-oV B12r. In the base-oV species, as the bulky DMBz is not co-ordinated to the cobalt atom, the folding angle would be markedly decreased, and also the corrin ring, as well as its side chain, in the base-oV form is much more flexible than that in the base-on form.9a,10b,11 It suggests that with the dissociation of the Me group, there is much more conformational change for base-oV MeCbl than for base-on MeCbl.This might contribute to the larger reaction volume change in photolysis of base-oV MeCbl (>5 ± 1 ml mol21). Conclusion This paper reports photoacoustic calorimetry studies in the temperature range 10–30 8C, used to measure the energy changes for photo-induced Co]C bond homolysis of two kinds of coenzyme B12.The resultant Co]C BDE values for AdoCbl and MeCbl in neutral water (base-on forms) are in good agreement with those obtained by kinetic methods at a higher temperature range (80–110 8C). Moreover, the Co]C BDE value of MeCbl in acid solution (base-oV form) has also been determined by the PAC method, which would be larger than that of the base-on form and probably have been diYcult to obtain by the kinetic method.This is the first time that the quantitative structural volume changes for the photolysis of two kinds of cobalamin derivatives using temperature-dependent PAC studies in neutral and acidic solution have been obtained. These volume changes were suggested to be due to conformational changes of the corrin ring and its side chains accompanying the cleavage of the Co]C bond. The values of such volume changes are in the following order: base-on AdoCbl > base-on MeCbl and baseo V MeCbl > base-on MeCbl. They reflect that the extent of the conformational changes depends on the bulkiness of the upper (a) ligand of the corrin or the co-ordination of the lower (b) nucleotide loop DMBz base with cobalt.The results give evidence about the flexing of the corrin ring, and the steric interactions between the corrin ring and the Ado group, which have been suggested to be important in enzyme-induced distortion and lability of the Co]C bond.Acknowledgements This work was supported by the National Natural Science Foundation of China and by the Laboratory of Modern Acoustic Foundation of Nanjing University, China. References 1 (a) D. Dolphin (Editor), B12, Wiley, New York, 1982; (b) J. M. Pratt, Inorganic Chemistry of Vitamin B12, Academic Press, New York, 1972. 2 J. Halpern, Science, 1985, 227, 869. 3 R. G. Finke, in Molecular Mechanisms in Bioorganic Processes, eds.C. Bleasdale and B. T. Golding, The Royal Society of Chemistry, Cambridge, 1990, p. 244; R. G. Finke, D. A. Schiraldi and B. J. Mayer, Coord. Chem. Rev., 1984, 54, 1. 4 L. G. Marzille, in Bioinorganic Catalysis, ed. J. Reedijk, Marcel Dekker, New York, 1993. 5 (a) R. G. Finke and B. P. Hay, Inorg. Chem., 1984, 23, 3041; 1985, 24, 1278; (b) B. P. Hay and R. G. Finke, J. Am. Chem. Soc., 1986, 108, 4820. 6 J. Halpern, S.-H. Kim and T. W. Leung, J.Am. Chem. Soc., 1984, 106, 8317; 1985, 107, 2199. 7 R. J. Blau and J. H. Espenson, J. Am. Chem. Soc., 1985, 107, 3530. 8 S.-H. Kim, H. L. Chen, N. Feilchenfeld and J. Halpern, J. Am. Chem. Soc., 1988, 110, 3120; M. K. Geno and J. Halpern, J. Am. Chem. Soc., 1987, 109, 1238. 9 (a) B. P. Hay and R. G. Finke, J. Am. Chem. Soc., 1987, 109, 8012; (b) B. D. Martin and R. G. Finke, J. Am. Chem. Soc., 1990, 112, 2419; 1992, 114, 585; (c) M. D. Waddington and R. G. Finke, J. Am. Chem.Soc., 1993, 115, 4629. 10 (a) K. L. Brown and H. B. Brooks, Inorg. Chem., 1991, 30, 3420; (b) K. L. Brown and D. R. Evans, Inorg. Chem., 1994, 33, 6380. 11 (a) V. B. Pett, M. N. Liebman, P. Murray-Rust, K. Prasad and J. P. Glusker, J. Am. Chem. Soc., 1987, 109, 3207; (b) D. W. Christianson and W. N. Lipscomb, J. Am. Chem. Soc., 1985, 107, 2682. 12 K. L. Brown, D. R. Evans, S. Cheng and D. W. Jacobsen, Inorg. Chem., 1996, 35, 217; K. L. Brown, S. Cheng and H. M. Marques, Inorg.Chem., 1995, 34, 3038; K. L. Brown, H. B. Brooks, D. Behnke and D. W. Jacobsen, J. Biol. Chem., 1991, 266, 6737; K. L. Brown, X. Zou and D. R. Evans, Inorg. Chem., 1994, 33, 5713. 13 J. Halpern, Pure Appl. Chem., 1983, 55, 1059; T. Toraya and A. Ishida, Biochemistry, 1988, 27, 7677; J. M. Pratt, Pure Appl. Chem., 1993, 65, 1513; M. D. Waddington and R. G. Finke, J. Am. Chem. Soc., 1993, 115, 4629. 14 (a) F. Mancia, N. H. Keep, A. Nakagawa, P. F. Leadlay, S. McSweeney, B.Rasmussen, P. Bösecke, O. Diat and P. R. Evans, Structure, 1996, 4, 339; (b) C. L. Drennan, S. Huang, J. T. Drummond, R. G. Matthews and M. L. Ludwing, Science, 1994, 266, 1669.J. Chem. Soc., Dalton Trans., 1998, Pages 2103–2107 2107 15 (a) E. Chen and M. R. Chance, J. Biol. Chem., 1990, 265, 12 987; (b) E. Chen and M. R. Chance, Biochemistry, 1993, 32, 1480 and refs. therein. 16 J. M. Pratt and B. R. S. Whitear, J. Chem. Soc. A, 1971, 252. 17 J. Endicott and T. Netzel, J.Am. Chem. Soc., 1979, 101, 4000. 18 R. Taylor, L. Smucker, M. L. Hanna and J. Gill, Arch. Biochem. Biophys., 1973, 156, 521. 19 P. G. Lenhert and D. C. Hodgkin, Nature (London), 1961, 192, 937; P. G. Lenhert, Proc. R. Soc. London, Ser. A, 1968, 303, 45; H. F. J. Savage, P. F. Lindley, J. L. Finney and P. A. Timmins, Acta Crystallogr., Sect. B, 1987, 43, 296. 20 K. S. Peters and G. J. Snyder, Science, 1988, 241, 1053; C. L. Norris and K. S. Peters, Biophys. J., 1993, 65, 1660; K.S. Peters, T. Watson and T. Logan, J. Am. Chem. Soc., 1992, 114, 4276; J. A. Westrick, K. S. Peters, J. D. Ropp and S. G. Sligar, Biochemistry, 1990, 29, 6741; J. A. Westrick, J. L. Goodman and K. S. Peters, Biochemistry, 1987, 26, 8313. 21 (a) S. E. Braslavsky and G. E. Heibel, Chem. Rev., 1992, 92, 1381; (b) J. L. Habib-Jiwan, A. K. Chibisov and S. E. Braslavsky, J. Phys. Chem., 1995, 99, 10 246; (c) I. Yruela, M. S. Churio, T. Gensch, S. E. Braslavsky and A. R. Holzwarth, J. Phys.Chem., 1994, 98, 12 789; (d ) M. S. Churio, K. P. Angermund and S. E. Braslavsky, J. Phys. Chem., 1994, 98, 1776; (e) P. J. Schulenberg, W. Gärtner and S. E. Braslavsky, J. Phys. Chem., 1995, 99, 9617; ( f ) M. E. Van Brederode, T. Gensch, W. D. HoV, K. J. Hellingwerf and S. E. Braslavsky, Biophys. J., 1995, 68, 1101; ( g) J. L. Habib-Jiwan, B. Wegewijs, M. T. Indelli, F. Scandola and S. E. Braslavsky, Recl. Trav. Chim. Pays-Bas., 1995, 114, 542. 22 R. R. Hung and J.J. Grabowski, J. Am. Chem. Soc., 1992, 114, 351; J. L. Goodman and M. S. Herman, Chem. Phys. Lett., 1989, 163, 417; M. S. Herman and J. L. Goodman, J. Am. Chem. Soc., 1989, 111, 1849. 23 D. Dolphin, Inorg. Synth., 1982, 20, 152. 24 R. C. Weast (Editor), CRC Handbook of Chemistry and Physics, CRC Press, Boca Raton, FL, 67th edn., 1986–1987. 25 D. Dolphin, A. W. Johnson and R. Rodrigo, R. Ann. N. Y. Acad. Sci., 1964, 112, 590. 26 P. A. Anfinrud, C. Hans and P. M. Hochstrasser, Proc. Natl. Acad. Sci. USA, 1989, 86, 8387; J. L. Martin, A. Migus, C. Poyart, Y. LeCarpentier, R. Astier and A. Antonetti, Proc. Natl. Acad. Sci. USA, 1983, 80, 173. 27 T. W. Koenig, B. P. Hay and R. G. Finke, Polyhedron, 1988, 7, 1499. 28 T. T. Tsou, M. Loots and J. Halpern, J. Am. Chem. Soc., 1982, 104, 623. 29 C. D. Garr and R. G. Finke, J. Am. Chem. Soc., 1992, 114, 10 440; Inorg. Chem., 1993, 32, 4414. 30 M. Rossi, J. P. Glusker, L. Randaccio, M. F. Summers, P. J. Toscano and L. G. Marzilli, J. Am. Chem. Soc., 1985, 107, 1729. 31 B. Kräutler, W. Keller and C. Kratky, J. Am. Chem. Soc., 1989, 11, 8936. 32 (a) M. F. Summers, L. G. Marzilli and A. Bax, J. Am. Chem. Soc., 1986, 108, 4285; (b) A. Bax, L. G. Marzilli and M. F. Summers, J. Am. Chem. Soc., 1987, 109, 566; (c) T. G. Pagano, P. G. Yohannes, B. P. Hay, J. R. Scott, R. G. Finke and L. G. Marzilli, J. Am. Chem. Soc., 1989, 111, 1484; (d ) T. G. Pagano, L. G. Marzilli, M. M. Flocco, C. Tsai, H. L. Carrell and J. P. Glusker, J. Am. Chem. Soc., 1991, 113, 531; (e) Y. W. Alelyunas, P. E. Fleming, R. G. Finke, T. G. Pagano and L. G. Marzilli, J. Am. Chem. Soc., 1991, 113, 3781; ( f ) A. Calafat and L. G. Marzilli, J. Am. Chem. Soc., 1993, 115, 9182. Received 1st December 1997; Paper 7/08644J © Copyright 1998 by the Royal Society of Chemistry

ISSN:1477-9226    

DOI:10.1039/a708644j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2109–2112 2109 Towards a model for the oxidized form of purple acid phosphatase: crystal structure and magnetic properties of a binuclear iron(III) complex containing phosphate ligands † Lihua Yin,a Peng Cheng,*,a Xinkan Yao b and Honggen Wang b a Department of Chemistry, Nankai University, Tianjin 300071, P. R. China b Central Laboratory, Nankai University, Tianjin 300071, P. R. China A novel binuclear iron(III) complex [{FeL[O2P(OPh)2]}2][ClO4]2 was synthesized and characterized by X-ray singlecrystal structure analysis, where HL is bis(benzimidazol-2-ylmethyl)(2-hydroxyethyl)amine. The crystals are triclinic, space group P1� , with a = 11.523(9), b = 11.809(6), c = 13.406(4) Å, a = 68.52(4), b = 71.41(5), g = 71.85(6)8 and Z = 1.The structure shows that the iron(III) ions are bridged by the oxygen atoms of two L ligands and a phosphate ligand is terminally co-ordinated to each iron(III). Magnetic susceptibility measurements in the range 4.2–300 K and subsequent calculations based on an isotropic Heisenberg model suggest antiferromagnetic coupling between the iron(III) ions with J = 217.5 cm21.The purple acid phosphatases (PAPs) are dinuclear iron enzymes (M 35 000–55 000) which catalyse the in vitro hydrolysis of phosphate esters (including nucleoside triphosphates) under acidic pH conditions.1–4 The purple, inactive forms of uteroferrin and of the phosphatase isolated from bovine spleen contain FeIII]FeIII units in their active sites.The centre of the catalytically active, pink species consists of a FeII]FeIII core. The oxidized form (purple) can be reduced in a one-electron process to the enzymatically active mixed-valence form (pink). The EPR, Mössbauer and magnetic properties of the two forms indicated that the iron centres are antiferromagnetically coupled in both oxidation states.5–9 The PAPs thus belong to a class of diiron proteins 2 which includes haemerythrin, 10,11 methane monooxygenase 12,13 and the R2 protein of ribonucleotide reductase.14 In this class of diiron proteins, suitable crystals of PAPs have yet to be obtained for X-ray crystallographic examination.Based on the spectroscopic, magnetic and EXAFS (extended X-ray absorption fine structure) investigations, the proposed structure of the active form of PAP from bovine spleen exhibits a terminally co-ordinated phosphate ligand 6,15,16 or phosphate bridging ligand.17 Very recently, Krebs and co-workers 18,19 reported the crystal structure of kidney bean purple acid phosphatase at 2.9 Å resolution.It contains one zinc(II) ion and one iron(III) ion and has a similar site to that in the mammalian FeII]FeIII purple acid phosphatase. The zinc(II) and iron(III) ions are 3.1 Å apart and bridged monodentately by the Asp-164 residue. The iron is further co-ordinated by the Tyr-167, His-325 and Asp-135, and the zinc by the His-286, His-323 and Asn-201 residues.The active-site structure supports a mechanism of phosphate ester hydrolysis involving nucleophilic attack on the phosphate group by an FeIII-co-ordinated hydroxide ion. Diiron-(II,III) and -(III,III) model compounds containing a bridging co-ordination of phosphate and phosphate ester have been synthesized and characterized in some cases.20–27 The diiron complexes with terminally co-ordinated phosphate ligands, however, are poorly understood.28 In this paper we report a novel binuclear iron(III) complex with terminally co-ordinated phosphate ligands, using the polydentate ligand bis(benzimidazol-2-ylmethyl)(2-hydroxyethyl)- amine.† Non-SI unit employed: mB ª 9.27 × 10224 J T21. Experimental Bis(benzimidazol-2-ylmethyl)(2-hydroxyethyl)amine (HL) was synthesized by published procedures.29 All other chemicals used in this work were reagent grade and used as commercially obtained. Preparations Reaction of a 1:1:1 molar ratio (0.5 mmol) of bis(benzimidazol- 2-ylmethyl)(2-hydroxyethyl)amine, Fe(ClO4)3?9H2O and diphenyl phosphate in methanol (30 cm3) for 30 min afforded red microcrystals of [{FeL[O2P(OPh)2]}2][ClO4]2 (yield 80%) (Found: C, 49.1; H, 4.25; N, 10.15; P, 3.95.C60H56Cl2Fe2N10O18P2 requires C, 49.65; H, 3.85; N, 9.65; P, 4.25%). Red crystals suitable for X-ray single-crystal structure analysis were obtained by diffusion. Physical measurements The analyses (C, H, N, P) were performed at MHW laboratories (Phoenix, AZ, USA).The 1H NMR spectrum was recorded on an IBM AC300 spectrometer at 300 MHz and the chemical shifts (in ppm) were referenced to the residual protic solvent peak, the infrared spectrum on Perkin-Elmer 1800FT-IR spectrometer by using KBr pellets and electronic spectra (MeOH) on a Hitachi model 240 spectrometer at room temperature. Variable-temperature magnetic susceptibilities were measured on a vibrating-sample magnetometer, model CF-1, in the temperature range 4.2–300 K.Diamagnetic corrections were made with Pascal’s constants for all the substituent atoms,30 and the magnetic moments were calculated using the equation meff = 2.828(cT)� �� . The theoretical expression was fitted to the data by applying a least-squares refinement. X-Ray crystallography Details of crystal parameters, data collection and structure refinement are summarized in Table 1. The structure was solved by the direct methods (MULTAN 82).31 The iron atom positions were located in the initial E maps.The other nonhydrogen atoms were determined with successive Fourierdifference syntheses. Hydrogen atoms were not found. The final refinement (based on F) was by full-matrix least squares with unweighted and weighted agreement R factors of 0.058 and 0.063. The highest peak on the final Fourier-difference map had2110 J. Chem. Soc., Dalton Trans., 1997, Pages 2109–2112 Fig. 1 An ORTEP view of the complex with the atom numbering scheme the value of 0.44 e A23.All calculations were performed on PDP 11/44 and IBM 586 computers using the ORTEP program system 33 for molecular graphics. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/487.Results and Discussion Spectral characterization The IR spectrum of the complex showed n(P]] O) at 1202 cm21 and n(P]O]Ph) at 929 cm21, respectively. The strong absorption at 1100–1120 cm21 may be overlap of n(ClO4) and n(P]O). The n(NH) and n(C]] N) bands of benzimidazole are observed at 3450 and 1490 cm21. The bands at 745 and 532 cm21 should be assigned to nasym(Fe]O]Fe) and nsym(Fe]O]Fe), respectively. The 1H NMR spectrum of the complex measured in Me2SO solution exhibits paramagnetically shifted features.The sharp features at d 7.7 and 8.0 correspond to the protons of the benzene ring of diphenyl phosphate. The broad peaks at d 42.2 and 60.0 should be assigned to the protons of C(32)H and N(1)H of benzimidazole, which indicate that the N(2) nitrogen atoms are co-ordinated to iron(III) ions. The electronic spectrum of the complex in methanol shows absorption maxima at lmax = 214, 245, 270 and 451 nm (sh). An absorption maximum in the region of the charge-transfer transition of PAP (500–600 nm) could not be observed for the complex owing to the absence of phenolate oxygen donors.28 Crystal structure The complex [{FeL[O2P(OPh)2]}2][ClO4]2 crystallizes in the triclinic space group P1� .The structure of the cation of the complex and a stereoview of the unit cell are shown in Figs. 1 and 2, respectively. Selected bond lengths and angles are given in Table 2. The iron atoms in the centrosymmetric, binuclear structure are bridged by the oxygen atoms of the two L ligands.Each of these L ligands also binds one Fe atom through three nitrogen atoms (the tertiary N atom and one from each benzimidazole group) in a meridional mode. The very distorted octahedral coordination about the Fe atom is completed by the terminal binding of a phosphate ligand. The Fe ? ? ?Fe distance is 3.1, which is very similar to that in kidney bean PAP (3.1 Å),18 and bovine spleen enzyme (3.00 Å) 15 and uteroferrin (3.15 or 3.52 Å) 17 based on EXAFS studies.The complex exhibits a Fe ? ? ? P distance of 3.137 Å, which is about 0.21 Å shorter than that found in [Fe2Cl2{O2P(OPh)2}(tbpo)(MeOH)][ClO4]2?3Me- OH [Htbpo = N,N,N9,N9-tetrakis(benzimidazol-2-ylmethyl)-2- hydroxypropane-1,3-diamine] in which a phosphate ligand is terminally co-ordinated to iron(III) ion.28 This distance is also shorter than that in phosphate-bridged diiron(III) complexes and near to that in PAP from beef spleen (3.06 Å) 16 and uteroferrin (3.17 Å).17 Magnetic properties The variable-temperature susceptibility of the complex has been recorded in the region 4.2–300 K.The magnetic moment (meff) at room temperature is 6.22 mB. With lowering of the temperature, the magnetic moment of the complex decreases and reaches 0.64 mB at 8.7 K. This magnetic behaviour suggested that the operation of an antiferromagnetic spin exchange Fig. 2 Stereoview of the unit cellJ.Chem. Soc., Dalton Trans., 1997, Pages 2109–2112 2111 occurs in the complex. The magnetic data could be fitted on the basis of an isotropic Heisenberg model H = 22JS1S2 (S1 = S2 = 5– 2) [equation (1)], where A = 55 1 30 exp(210J/kT) 1 cm = 2Ng2b2 kT A B (1) 14 exp(218J/kT) 1 5 exp(224J/kT) 1 exp(228J/kT), B = 11 1 9 exp(210J/kT) 1 7 exp(218J/kT) 1 5 exp(224J/kT) 1 3 exp(228J/kT) 1 exp(230J/kT), cm is the molecular susceptibility and the other symbols have their usual meanings.The experimental data and fitted curves of magnetic susceptibilities and moments are shown in Fig. 3. The parameters found were J = 217.5 cm21 and g = 2.01. The agreement factor R, defined as S[(cm obs 2 cm calc)2/(cm obs)2], is 3.5 × 1023. The value of the exchange integral (217.5 cm21) is expected to fall in the range of m-alkoxo- or m-hydroxo-bridged binuclear iron(III) systems and slightly larger (absolute value) than the complex with a terminally co-ordinated phosphate ligand (213.7 cm21).28 The binuclear iron(III) complex, with a bis(alkoxo) bridge and the terminal monodentate phosphate ester ligands, is expected to be weakly antiferromagnetically coupled. This structural feature is actually of more interest regarding the co-ordination mode of the substrate to the reduced (FeIIFeIII) core of the enzyme, where monodentate ligation [to the iron(II) ion] seems likely, rather than to the oxidized (FeIII 2) form of the enzyme, for which most evidence favours a bidentate bridging co-ordination mode.The magnetic susceptibility results suggest that the amount of coupling may be an order of magnitude larger than that in magnetically coupled high-spin FeIIFeIII centres,6,8 but in Table 1 Crystallographic data and data-collection parameters for the complex Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 Crystal dimensions/mm Colour T/K Radiation (l/Å) Monochromator m/mm21 Absorption correction applied Transmission factors: min., max.Diffractometer Scan method h, k, l Limits qmax/8 Scan speed/8 min21 Programs used F(000) w Data collected Unique data Data with I > 3s(I) Rint No. variables Largest shift/e.s.d. in final cycle Rc R9 d C60H56Cl2Fe2N10O18P2 1449.72 Triclinic P1� 11.523(9) 11.809(6) 13.406(4) 68.52(4) 71.41(5) 71.85(6) 1569(2) 1 1.53 0.1 × 0.2 × 0.3 Purple 299 ± 1 Mo-Ka (0.710 73) Graphite 0.675 Empiricala 0.730, 1.192 Enraf-Nonius CAD4 w–2q 212 to 12, 213 to 13, 0–14 23 0.92–5.49 Enraf-Nonius SDP-PLUSb 746 1 for all observed reflections 4512 4082 1168 0.207 424 0.51 0.058 0.063 a See ref. 32. b See ref. 31. c R = S |Fo 2 Fc| /S|Fo|. d R9 = [Sw(|Fo 2 Fc|)2/ Sw|Fo|2]� �� ; w = 1/s2(Fo). agreement with the recent magnetic susceptibility studies on oxidized PAP from bovine spleen.34 Similarly, the bis(alkoxo) bridging is a reasonable model for the monodentate bridging carboxylate/bridging hydroxide unit that is probably present in the enzyme.Acknowledgements This work was supported by the National Natural Science Foundation of China. References 1 K. Doi, B. C. Antanaitis and P. Aisen, Struct. Bonding (Berlin), 1988, 70, 1. 2 L. Que, jun. and A. E. True, Prog. Inorg. Chem., 1990, 38, 97. 3 J. B. Vincent and B. A. Averill, FASEB J., 1990, 4, 3009. 4 R. G. Wilkin, Chem. Soc. Rev., 1992, 21, 171. 5 B. C. Antanaitis, P. Aisen and H. R. Lilienthal, J. Biol. Chem., 1983, 258, 3166. 6 B. A. Averill, J.C. Davis, S. Burman, T. Zirino, J. Sanders-Loehr, T. M. Loehr, J. T. Sage and P. G. Debrunner, J. Am. Chem. Soc., 1987, 109, 3760. 7 P. G. Debrunner, M. P. Hendrich, J. de Jersey, D. T. Keough, J. T. Sage and B. Zenner, Biochim. Biophys. Acta, 1983, 745, 103. 8 E. P. Day, S. S. Davis, J. Peterson, W. R. Dunham, J. J. Bonvoisin, R. H. Sands and L. Que, jun., J. Biol. Chem., 1988, 263, 15 561. 9 E. Sinn, C. J. O’Connor, J. de Jersey and B. Zerner, Inorg. Chim. Acta, 1983, 78, L13.Fig. 3 The experimental data and fitted curves of magnetic susceptibilities (s) and moments (d) of the complex Table 2 Selected bond distances (Å) and angles (8) Fe(1) ? ? ?Fe(1a) Fe(1)]O(4) Fe(1)]O(5) Fe(1)]N(4) P(1)]O(1) P(1)]O(3) 3.165 1.999(8) 2.055(8) 2.076(9) 1.58(1) 1.415(8) Fe(1) ? ? ? P(1) Fe(1)]O(5a) Fe(1)]N(2) Fe(1)]N(5) P(1)]O(2) P(1)]O(4) 3.137 1.910(7) 2.10(1) 2.34(1) 1.63(2) 1.426(9) O(4)]Fe(1)]O(5a) O(4)]Fe(1)]N(2) O(4)]Fe(1)]N(5) O(5a)]Fe(1)]N(2) O(5a)]Fe(1)]N(5) O(5)]Fe(1)]N(4) N(2)]Fe(1)]N(4) N(4)]Fe(1)]N(5) O(1)]P(1)]O(3) O(2)]P(1)]O(3) O(3)]P(1)]O(4) Fe(1)]O(4)]P(1) Fe(1)]O(5a)]C(4) Fe(1)]N(2)]C(37) Fe(1)]N(4)]C(47) Fe(1)]N(5)]C(2) 93.8(3) 89.8(3) 114.4(4) 109.6(4) 151.7(3) 90.2(3) 145.8(4) 74.9(4) 114.4(6) 108.8(6) 118.2(5) 131.9(5) 118.7(6) 115.7(8) 119.5(9) 111.2(7) O(4)]Fe(1)]O(5) O(4)]Fe(1)]N(4) O(5a)]Fe(1)]O(5) O(5a)]Fe(1)]N(4) O(5)]Fe(1)]N(2) O(5)]Fe(1)]N(5) N(2)]Fe(1)]N(5) O(1)]P(1)]O(2) O(1)]P(1)]O(4) O(2)]P(1)]O(4) Fe(1)]O(5a)]Fe(1a) Fe(1)]O(5a)]C(4a) Fe(1)]N(2)]C(31) Fe(1)]N(4)]C(41) Fe(1)]N(5)]C(1) Fe(1)]N(5)]C(3) 167.1(3) 88.8(3) 74.1(4) 104.7(4) 98.2(3) 77.6(3) 74.7(4) 98.5(6) 109.1(5) 105.8(6) 105.9(4) 134.3(6) 133.9(8) 129.9(9) 108.1(6) 103.5(7) Symmetry transformation: a 2x, 1 2 y, 1 2 z.2112 J.Chem. Soc., Dalton Trans., 1997, Pages 2109–2112 10 R. E. Stenkamp, L. C. Sieker and L. H. Jensen, J. Am. Chem. Soc., 1984, 106, 618. 11 S. Sheriff, W. A. Hendrickson and J. L.Smith, J. Mol. Biol., 1987, 197, 273. 12 B. G. Fox, W. A. Forland, J. E. Dege and J. D. Lipscomb, J. Biol. Chem., 1989, 264, 10 023. 13 A. C. Rosenzweig, C. A. Frederick, S. J. Lippard and P. Nordlund, Nature (London), 1993, 366, 537. 14 P. Nordlund, B.-M. Sjoberg and H. Eklund, Nature (London), 1990, 345, 593. 15 S. M. Kauzlarich, B. K. Teo, T. Zirino, S. Burman, J. C. Davis and B. A. Averill, Inorg. Chem., 1986, 25, 2781. 16 R. C. Scarrow, J. W. Pyrz and L. Que, jun., J. Am.Chem. Soc., 1990, 112, 657. 17 A. E. True, R. C. Scarrow, C. R. Randall, R. C. Holz and L. Que, jun., J. Am. Chem. Soc., 1993, 115, 4246. 18 N. Strater, T. Klabunde, P. Tucker, H. Witzel and B. Krebs, Science, 1995, 268, 1489. 19 T. Klabunde, N. Strater, R. Frohlich, H. Witzel and B. Krebs, J. Mol. Biol., 1996, 259, 737. 20 K. Schepers, B. Bremer, B. Krebs, G. Henkel, E. Althaus, B. Mosel and W. Muller-Warmuth, Angew. Chem., Int. Ed. Engl., 1990, 29, 531. 21 B. Krebs, K. Schepers, B.Bremer, G. Henkel, E. Althaus, B. Mosel, W. Muller-Warmuth, K. Griesar and W. Hasse, Inorg. Chem., 1994, 33, 1907. 22 S. Drueke, K. Wieghardt, B. Nuber, J. Weiss, H. P. Fleischhauer, S. Gehring and W. Hasse, J. Am. Chem. Soc., 1989, 111, 8622. 23 W. H. Armstrong and S. J. Lippard, J. Am. Chem. Soc., 1985, 107, 3730. 24 P. N. Turowski, W. H. Armstrong, M. E. Roth and S. J. Lippard, J. Am. Chem. Soc., 1990, 112, 681. 25 S. Yan, D. D. Cox, L. L. Pearce, C. Juarez-Garcia, L. Que, jun., J. H. Zhang and C. J. O’Connor, Inorg. Chem., 1989, 28, 2507. 26 R. E. Norman, S. Yan, L. Que, jun., G. Backes, J. Ling, J. Sanders- Loehr, J. H. Zhang and C. J. O’Connor, J. Am. Chem. Soc., 1991554. 27 P. N. Turowski, W. H. Armstrong, S. Liu, S. N. Brown and S. J. Lippard, Inorg. Chem., 1994, 33, 636. 28 B. Bremer, K. Schepers, P. Fleischhauer, W. Haase, G. Henkel and B. Krebs, J. Chem. Soc., Chem. Commun., 1991, 510. 29 Y. Nishida and K. Takahashi, J. Chem. Soc., Dalton Trans., 1988, 691. 30 E. A. Boudreaux and L. N. Mulay, Theory and Application of Molecular Paramagnetism, Wiley, New York, 1976, p. 491. 31 SDP-PLUS, B. A. Frenz & Associates, Inc., College Station, TX and Enraf-Nonius, Delft, 1985. 32 N. Walker and D. Stuart, Acta Crystallogr., Sect. A, 1983, 39, 158. 33 C. K. Johnson, ORTEP, a Fortran thermal-ellipsoid plot program for crystal structure illustrations, Report ORNL-5138 (third revision), Oak Ridge Natonal Laboratory, Oak Ridge, TN, 1976. 34 S. Gehring, P. Fleischhauer, W. Haase, M. Dietrich and H. Witzell, Biol. Chem. Hoppe-Seyler, 1990, 371, 786. Received 10th December 1996; Paper 6/08298J

ISSN:1477-9226    

DOI:10.1039/a608298j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2113–2117 2113 Synthesis and reactivity of [Ru{HB(pz)3}{P(C6H11)3}Cl(OCH2R)] (pz = pyrazolyl, R = H or Me)† Christian Gemel, Guido Kickelbick, Roland Schmid and Karl Kirchner * Institute of Inorganic Chemistry, Technical University of Vienna, Getreidemarkt 9, A-1060 Vienna, Austria The complex [Ru{HB(pz)3}(cod)Cl] 1 (cod = cycloocta-1,5-diene) reacted with P(C6H11)3 (>1 equivalent) in boiling dimethylformamide (dmf) to give the highly air-sensitive intermediate [Ru{HB(pz)3}{P(C6H11)3}Cl(dmf)] which, on exposure to air in either ethanol or methanol as the solvent, was converted to the ruthenium(III) complexes [Ru{HB(pz)3}{P(C6H11)3}Cl(OCH2R)] (R = Me 2a or H 2b) in good yields.Complex 2b has been characterized by X-ray crystallography. Treatment of 2a or 2b with L = MeCN, pyridine, CO, P(OMe)3, or PMe3 in CH2Cl2 afforded the (diamagnetic) ruthenium(II) compounds [Ru{HB(pz)3}{P(C6H11)3}(Cl)L] 3–7. Most remarkably, 2a or 2b reacted also with terminal alkynes HC]] ] CR (R = Ph, CO2Et, Bun or SiMe3) giving the neutral vinylidene complexes [Ru{HB(pz)3}{P(C6H11)3}Cl (]] C]] CHR)] 8–11.Preliminary results of a study of the catalytic activity of 2 are also presented. Thus, 2a and 2b catalysed the dimerization of some terminal alkynes HC]] ] CR (R = Ph, CO2Et or SiMe3). In our continuing systematic studies of the chemistry of ruthenium tris(pyrazolylborate) complexes 1–5 we have recently shown that [Ru{HB(pz)3}(PPh3)Cl(dmf )] (pz = pyrazolyl, dmf = dimethylformamide) is a very usable precursor for the easy production of a variety of complexes of the types [Ru{HB- (pz)3}(PPh3)(Cl)L] and [Ru{HB(pz)3}(PPh3)Cl(]] C]] CHR)] (R = CO2Et, Bun or SiMe3).1 The method fails, however, when bulkier phosphines such as P(C6H11)3 or PPri 3 are used instead of PPh3.The reason is that the corresponding complex [Ru- {HB(pz)3}{P(C6H11)3}Cl(dmf)] is extremely air-sensitive and, in addition, dmf is highly labilized obviously due to both the greater steric demand as well as the higher basicity of P(C6H11)3 relative to PPh3.When [Ru{HB(pz)3}{P(C6H11)3}Cl(dmf)] was used in situ in the presence of an alcohol (MeOH or EtOH) the novel complexes [Ru{HB(pz)3}{P(C6H11)3}Cl(OCH2R)] (R = H or Me) were formed. In making a virtue of necessity, the complexes appear to be useful precursors for new complexes of the types [Ru{HB(pz)3}{P(C6H11)3}(Cl)L] [L = MeCN, pyridine, CO, P(OMe)3 or PMe3] and [Ru{HB(pz)3}{P(C6H11)3}- Cl(]] C]] CHR)] (R = Ph, CO2Et, SiMe3 or Bun).Results and Discussion Synthesis of [Ru{HB(pz)3}{P(C6H11)3}Cl(OCH2R)] (R = Me or H) The complexes [Ru{HB(pz)3}{P(C6H11)3Cl(OCH2R)] (R = Me 2a or H 2b) were synthesized in a one-pot reaction with [Ru{HB(pz)3}(cod)Cl] 1 (cod = cycloocta-1,5-diene) used as the starting material. This reaction appears to proceed via the highly reactive intermediate [Ru{HB(pz)3}{P(C6H11)3}- Cl(dmf)].Though the latter complex could not be isolated in pure form, the PPh3 analogue [Ru{HB(pz)3}(PPh3)Cl(dmf )] has recently been isolated and crystallographically characterized.2 When 1 is refluxed in dmf in the presence of P(C6H11)3 (>1 equivalent) and the resulting solid residue is exposed to air in ethanol or methanol as the solvent, complexes 2a and 2b are, on work-up, obtained in 65 and 49% yields (Scheme 1). It should be noted that even in the presence of P(C6H11)3 in excess † Ruthenium tris(pyrazolyl)borate complexes. Part 5.1 Non-SI unit employed: mB ª 9.27 × 10224 J T21.there was no evidence of the formation of [Ru{HB(pz)3}{P- (C6H11)3}2Cl], apparently for steric reasons. A similar observation has been made in the case of Ru(h5-C5Me5) complexes.6 Complexes 2a and 2b are thermally robust red solids which are stable to air both in the solid state and in solution. Characterization was by elemental analysis. The NMR spectra exhibited severe line broadening due to the paramagnetic nature of the complexes.The measured magnetic moment of 2b is meff = 1.83mB at 295 K, consistent with a d5 (RuIII) low-spin configuration with one unpaired electron. The molecular structure of 2b is depicted in Fig. 1 with important bond distances. The co-ordination geometry is approximately octahedral with all angles at ruthenium being between 88 and 96 Scheme 1 (i) P(C6H11)3, dmf, reflux; (ii) RCH2OH, O22114 J. Chem.Soc., Dalton Trans., 1997, Pages 2113–2117 and 175 and 1778. The three Ru–N (pz) bond lengths show only small deviations from the average distance of 2.108(2) Å, which is within the range of related ruthenium complexes.1–5,7 The Ru-O distance and the Ru-O-C(28) angle is 1.943(1) Å and 123.8(2)8, respectively. This means that there are no structural features implying unusual deviations or distortions. It should be noted that the Ru-Cl distance is only 2.370(1) Å, which is somewhat shorter than those found in many other HB(pz)3 complexes of RuII, e.g. 2.409(3) Å in [Ru{HB(pz)3}(PPh3)2Cl],8 2.401(1) Å in [Ru{HB(pz)3}(PPh3)Cl(]] C]] CHPh]1 and 2.418(2) Å in [Ru{HB(pz)3}(PPh3)Cl(CO)].9 Complexes 2a and 2b turned out to be useful reagents for the preparation of compounds of the types [Ru{HB(pz)3}- {P(C6H11)3}(Cl)L] and [Ru{HB(pz)3}{P(C6H11)3}Cl(]] C]] CHR)] as will be outlined in the following paragraphs. Reaction of [Ru{HB(pz)3}{P(C6H11)3}Cl(OCH2R)] with MeCN, pyridine, CO, P(OPh)3, PMe3 and HC]] ] CR9 (R9 = Ph, CO2Et, Bun or SiMe3) Treatment of complex 2a or 2b with L = MeCN, pyridine, CO, P(OMe)3 and PMe3 in CH2Cl2 affords the diamagnetic ruthenium(II) compounds [Ru{HB(pz)3}{P(C6H11)3}(Cl)L] 3–7 each in high yields (Scheme 2).All these compounds are thermally robust solids which are stable to air both in the solid state and in solution. Characterization was by elemental analysis, 1H and 31P-{1H} NMR spectroscopy, and in the case of 4–6 also by 13C-{1H} NMR spectroscopy, noting no unusual features. The reaction of complex 2a with L = MeCN, py, CO, P(OMe)3 and PMe3 has been monitored by 1H NMR spectroscopy showing the formation 3–7 together with 0.5 equivalent of acetaldehyde and 0.5 equivalent of ethanol according to equation (1).In the absence of kinetic data it should just 2[Ru{HB(pz)3}{P(C6H11)3}Cl(OEt)] 1 2 L æÆ 2a 2[Ru{HB(pz)3}{P(C6H11)3}(Cl)L] 1 MeCHO 1 EtOH (1) 3–7 be noted that the reaction rate seems to increase with the basicity of L.In the same way the reaction of 2b is found to release 0.5 equivalent of each formaldehyde and methanol. Overall, reaction (1) represents the recombination of two alkoxy radicals. In order to see whether a free-radical pathway operates, we treated 2a in CDCl3 with a five-fold excess of P(OMe)3 in the presence of an eight-fold excess of PriOH. Since in the 1H NMR spectrum no acetone could be detected (but a Fig. 1 Structural view of [Ru{HB(pz)3}{P(C6H11)3}Cl(OMe)] 2b.Selected bond lengths (Å) and angles (8): Ru]O 1.943(1), Ru]N(2) 2.133(2), Ru]N(4) 2.084(2), Ru]N(6) 2.109(2), Ru]Cl 2.370(1), Ru]P 2.394(1) and O]C(28) 1.370(4); C(28)]O]Ru 123.8(2), Cl]Ru]N(4) 174.7(1), N(6)]Ru]O 175.4(1) and N(2)]Ru]P 177.3(1) small amount of acetaldehyde) homolytic Ru]O bond cleavage can be ruled out. An alternative, although speculative, pathway could be initial b elimination in 2a with the ruthenium(III) hydride complex formed reacting with another molecule of 2a.Most remarkably, complex 2a (2b) reacts also with terminal alkynes HC]] ] CR9 (R9 = Ph, CO2Et, Bun or SiMe3) in CH2Cl2 giving the neutral vinylidene complexes [Ru{HB(pz)3}{P(C6- H11)3}Cl(]] C]] CHR9)] 8–11 according to equation (1) (Scheme 2) in high yields, except for 8. All of these solids are pale red, air stable in the solid state, but decompose slowly in aerobic solutions to the carbonyl complex [Ru{HB(pz)3}{P(C6H11)3}- Cl(CO)] 5, adding to the known cases of the oxidation of ruthenium(II) vinylidene complexes by dioxygen.10 In another type of conversion, complex 11 reacts with MeOH as the solvent at room temperature to give the alkoxycarbene complex [Ru{HB(pz)3}{P(C6H11)3}Cl{]] C(OMe)Me}] 12 in almost quantitative yield.All other vinylidene complexes are stable in this solvent. All the vinylidene complexes have been characterized by 1H and 31P-{1H} NMR and, in the case of sufficient stability as for 10 and 11, 13C-{1H} NMR spectra.In the latter there are characteristic low-field resonances at d 361.0 and 340.2 assignable to the a-carbon of the vinylidene moiety. The Cb hydrogen atom gives rise to a resonance in the range from d 4.06 to 3.71 (1 H). Finally, the resonances of the HB(pz)3 and P(C6H11)3 ligands are in the expected ranges. Catalytic dimerization of terminal acetylenes Reaction of complex 2b with an excess of HC]] ] CPh in toluene at reflux for 20 h results in the formation (about 50% conversion) of the head-to-head dimers (E)-1,4-diphenylbut-1-en-3- yne (I) and the Z isomer (II) in 67 and 33% yields, respectively (Table 1).The selectivity is found to vary with the alkyne substituent as follows. For R = CO2Et the reaction is selective giving predominantly the head-to-head dimer I and only small amounts of the 1,3,5-tricarboxylic acid ester III, while for R = SiMe3 the regioselectivity is reversed with no I but 100% of II.For R = Bun, no coupling reaction took place at all. Scheme 2 (i) L; (ii) HC]] ] CR9J. Chem. Soc., Dalton Trans., 1997, Pages 2113–2117 2115 The mechanism of the catalytic dimerization of terminal alkynes can only be speculated upon at present. From our preceding paper it is reasonable to suggest that the reaction is initiated by the neutral vinylidene complex [Ru{HB(pz)3}- {P(C6H11)3}Cl(]] C]] CHR)] formed as an intermediate with subsequent HCl elimination affording a 16e alkynyl catalyst.2 Neutral vinylidene complexes have been shown recently to undergo 1,3-HCl eliminations upon treatment with base to give 16e alkynyl intermediates which could be trapped in the presence of potential ligands such as CO, pyridine or MeCN.11 Similar intermediates have been suggested to be involved in the coupling reaction of terminal acetylenes catalysed by [Ru{HB- (pz)3}(PPh3)2Cl] and [Ru(h5-C5Me5)(PR3)H3] (R = Ph, Me or C6H11).2,12 Experimental General information All reactions were performed under an inert atmosphere of purified argon using Schlenk techniques.All chemicals were standard reagent grade used without further purification. The solvents were purified according to standard procedures. The deuteriated solvents (Aldrich) were dried over 4 Å molecular sieves. The complex [Ru{HB(pz)3}(cod)Cl] was prepared according to the literature.5 Proton, 13C-{1H} and 31P-{1H} NMR spectra were recorded on a Bruker AC-250 spectrometer operating at 250.13, 62.86 and 101.26 MHz, respectively, and were referenced to SiMe4 and to H3PO4 (85%).Microanalyses were by Microanalytical Laboratories, University of Vienna. Syntheses [Ru{HB(pz)3}{P(C6H11)3}Cl(OEt)] 2a. A solution of complex 1 (465 mg, 1.02 mmol) in dmf (8 cm3) was treated with P(C6H11)3 (285 mg, 1.02 mmol) and the mixture heated under reflux for 2 h. After removal of the solvent, ethanol was added and air was admitted to the solution, whereupon an immediate change from yellow to dark red occurred.After 15 min a red precipitate was formed, which was collected on a glass frit, washed with diethyl ether, and dried under vacuum. Yield: 445 mg (65%) (Found: C, 51.25; H, 7.3; N, 12.25. C29H48BClN6- OPRu requires C, 51.6; H, 7.15; N, 12.45%). [Ru{HB(pz)3}{P(C6H11)3}Cl(OMe)] 2b. This complex was synthesized analogously to 2a using methanol instead of ethanol as the solvent. Yield: 49% (Found: C, 50.75; H, 7.1; N, Table 1 Conversion and product distribution of the catalytic dimerization of terminal alkynes Product (%) % Catalyst R I II III Conversion 2b 2a 2b 2a Ph CO2Et SiMe3 Bun 67 91 33 100 9 50 44 47 0 12.6.C28H46BClN6OPRu requires C, 50.9; H, 7.0; N, 12.7%). meff = 1.83mB (295 K). [Ru{HB(pz)3}{P(C6H11)3}Cl(MeCN)] 3. A solution of complex 2a (70 mg, 0.104 mmol) in benzene (5 cm3) was treated with MeCN (0.1 cm3, 1.91 mmol) and the mixture stirred at 70 8C for 5 h. After removal of the solvent the residue was redissolved in acetone and the product precipitated by addition of diethyl ether and light petroleum (b.p. 40–70 8C). It was collected on a glass frit, washed with light petroleum and dried under vacuum. Yield: 51 mg (73%) (Found: C, 52.1; H, 7.05; N, 14.25. C29H46BClN7PRu requires C, 51.9; H, 6.9; N, 14.6%). NMR (C6D6, 20 8C): dH 8.30 (m, 2 H), 7.71 (d, 2 H, J = 2.5), 7.63 (d, 1 H, J = 1.6), 7.57 (d, 1 H, J = 2.5 Hz), 6.15–6.00 (m, 3 H), 2.57 (m, 3 H), 2.10–1.60 (m, 30 H) and 1.53 (s, 3 H, CH3CN); dP 38.5.[Ru{HB(pz)3}{P(C6H11)3}Cl(py)] 4. A solution of complex 2a (70 mg, 0.104 mmol) in CH2Cl2 (5 cm3) was treated with pyridine (py) (0.1 cm3, 1.24 mmol) and stirred at room temperature for 12 h. After removal of the solvent the residue was redissolved in CH2Cl2 and the product precipitated by addition of diethyl ether and light petroleum. It was collected on a glass frit, washed with light petroleum and dried under vacuum. Yield: 60 mg (81%) (Found: C, 54.05; H, 7.05; N, 13.6.C32H48BClN7PRu requires C, 54.2; H, 6.8; N, 13.85%). NMR (CDCl3, 20 8C): dH 9.7 (br s, 2 H, py), 8.07 (s, 1 H), 7.85 (s, 1 H), 7.52 (s, 1 H), 7.49 (m, 1 H, py), 7.21 (s, 1 H), 6.98 (s, 1 H), 6.90 (br s, 2 H, py), 6.24 (s, 1 H), 6.19 (s, 1 H), 6.04 (s, 1 H) and 2.23–1.05 (m, 33 H); dC 148.4, 146.8, 142.3, 137.3, 136.2, 134.5, 134.4, 128.9, 128.5, 128.1, 123.4, 36.4 (br s), 30.0 (br s), 28.9 and 27.08; dP 34.5. [Ru{HB(pz)3}{P(C6H11)3}Cl(CO)] 5.A solution of complex 2a (70 mg, 0.104 mmol) in CH2Cl2 (5 cm3) was purged with CO for 5 min and then stirred for 48 h. After removal of the solvent the residue was redissolved in CH2Cl2 and the product precipitated by addition of diethyl ether and light petroleum. It was collected on a glass-frit, washed with light petroleum and dried under vacuum. Yield: 52 mg (76%) (Found: C, 50.95; H, 6.65; N, 12.55. C28H43BClN6OPRu requires C, 51.1; H, 6.6; N, 12.75%). NMR (CDCl3, 20 8C): dH 8.11 (s, 1 H), 7.89 (s, 1 H), 7.77 (s, 1 H), 7.72 (s, 1 H), 7.49 (s, 1 H), 7.42 (s, 1 H), 7.26 (s, 1 H), 6.27 (s, 1 H), 6.19 (s, 1 H), 6.13 (s, 1 H), 2.45–2.10 (m, 3 H), 1.93–1.45 (m, 21 H) and 1.42–1.0 (m, 9 H); dC 205.9 (d, J = 14.5), 146.4, 144.8, 143.1, 137.1, 136.6, 134.5, 106.9, 106.0, 105.7, 34.8 (d, J = 19.3), 29.6, 29.4 and 28.1 (d, J = 9.6 Hz); dP 35.3.[Ru{HB(pz)3}{P(C6H11)3}Cl{P(OMe)3}] 6. This complex was prepared analogously to 4 using P(OMe)3 instead of pyridine.Yield: 84% (Found: C, 47.6; H, 7.1; N, 10.85. C30H52BClN6- O3P2Ru requires C, 47.8; H, 6.95; N, 11.15%). NMR (CDCl3, 20 8C): dH 8.14 (d, 1 H, J = 1.7), 7.92 (d, 1 H, J = 2.1), 7.84 (d, 1 H, J = 2.1), 7.71 (d, 1 H, J = 2.44), 7.68 (s, 1 H), 7.49 (d, 1 H, J = 2.44), 6.21 (m, 1 H), 6.05 (m, 2 H), 3.39 (d, 9 H, J = 10.1), 2.46 (m, 3 H) and 1.93–1.05 (m, 30 H); dC 150.1, 145.5 (d, J = 3.8), 145.2, 137.8, 135.4 (d, J = 2.9), 134.7, 106.3 (d, J = 3.8), 105.7 (d, J = 1.9), 104.9, 52.3 (d, J = 7.2), 38.0 (m), 29.6 (br s), 29.1 (d, J = 8.6) and 27.3; dP 146.9 (d, J = 50.9) and 28.7 (d, J = 50.9 Hz).[Ru{HB(pz)3}{P(C6H11)3}Cl(PMe3)] 7. This complex was prepared analogously to 4 using PMe3 instead of pyridine. Yield: 59% (Found: C, 52.85; H, 7.55; N, 11.75. C30H52- BClN6P2Ru requires C, 51.05; H, 7.4; N, 11.9%). NMR (CDCl3, 20 8C): dH 8.02 (d, 1 H, J = 1.9), 7.81 (d, 1 H, J = 1.9), 7.68 (br s, 1 H), 7.65 (d, 1 H, J = 2.6), 7.50 (d, 1 H, J = 2.2), 7.19 (s, 1 H), 6.17 (m, 1 H), 6.05 (m, 2 H), 2.28 (m, 3 H), 2.0–1.0 (m, 30 H) and2116 J.Chem. Soc., Dalton Trans., 1997, Pages 2113–2117 1.33 (d, 9 H, J = 6.3); dP 33.4 (d, J = 31.1) and 6.2 (d, J = 31.1 Hz). [Ru{HB(pz)3}{P(C6H11)3}Cl(]] C]] CHPh)] 8. A 5 mm NMR tube was charged with a solution of complex 2a (20 mg, 0.0296 mmol) in CDCl3 (0.5 cm3) and was capped with a septum. The compound HC]] ] CPh (10 ml, 0.089 mmol) was added by syringe and the sample was transferred to a NMR probe.Proton and 31P-{1H} NMR spectra were immediately recorded showing the slow but quantitative formation of 8. All attempts to isolate this complex failed. NMR (CDCl3, 20 8C): dH 8.25 (d, 1 H, J = 2.2), 7.83 (d, 2 H, J = 2.2), 7.78 (d, 1 H, J = 2.6), 7.41 (d, 1 H, J = 1.7), 7.3 (d, 1 H, J = 1.7), 7.14 (m, 3 H), 6.94 (m, 2 H), 6.35 (m, 1 H), 6.23 (m, 1 H), 6.02 (m, 1 H), 5.01 (d, 1 H, J = 3.5 Hz), 2.37 (m, 3 H) and 2.0–0.7 (m, 30 H); dP 30.3. [Ru{HB(pz)3}{P(C6H11)3}Cl(]] C]] CHCO2Et)] 9.This complex was prepared analogously to 4 using HC]] ] CCO2Et instead of pyridine. Yield: 79% (Found: C, 52.6; H, 7.0; N, 11.35. C32H49BClN6O2PRu requires C, 52.8; H, 6.8; N, 11.55%). NMR (C6D6, 20 8C): dH 8.48 (d, 1 H, J = 2.2), 8.18 (d, 1 H, J = 2.2), 8.04 (d, 1 H, J = 2.2), 7.62 (d, 1 H, J = 2.2), 7.50 (d, 1 H, J = 2.5), 7.27 (s, 1 H), 6.10 (m, 1 H), 5.95 (m, 1 H), 5.81 (m, 1 H), 5.18 (d, 1 H, J = 3.6), 4.07 (q, 1 H, J = 7.1), 4.06 (q, 1 H, J = 7.0), 2.62 (m, 3 H), 2.1–1.1 (m, 30 H) and 1.0 (t, 3 H, J = 7.1 Hz); dP 29.5.[Ru{HB(pz)3}{P(C6H11)3}Cl(]] C]] CHBun)] 10. This complex was prepared analogously to 4 using hex-1-yne instead of pyridine. Yield: 87% (Found: C, 55.45; H, 7.2; N, 12.15. C33H53- BClN6PRu requires C, 55.65; H, 7.5; N, 11.8%). NMR (CDCl3, 20 8C): dH 8.14 (d, 1 H, J = 2.1), 7.79 (d, 1 H, J = 2.5), 7.76 (d, 1 H, J = 2.9), 7.69 (d, 1 H, J = 2.9), 7.43 (d, 1 H, J = 2.9), 7.41 (d, 1 H, J = 2.9), 6.27 (m, 1 H), 6.15 (m, 1 H), 6.06 (m, 1 H), 4.06 (dt, 1 H, J = 3.6, 8.0), 2.37 (dt, 1 H, J = 13.8, J = 8.0), 2.25–2.05 (m, 3 H), 2.0–1.4 (m, 21 H), 1.4–1.0 (m, 14 H) and 0.95–0.65 (m, 4 H); dC 361.0 (d, J = 16.9), 146.4, 145.1, 143.3, 137.5, 136.6, 134.5, 108.6, 106.6, 106.2, 105.8, 35.7, 35.4, 35.0, 29.8 (d, J = 7.2), 28.5 (d, J = 8.8 Hz), 27.0, 22.7, 18.4 and 14.4; dP 33.9.[Ru{HB(pz)3}{P(C6H11)3}Cl(]] C]] CHSiMe3)] 11. This complex was prepared analogously to 4 using HC]] ] CSiMe3 instead of pyridine.Yield: 76% (Found: C, 52.65; H, 7.4; N, 11.4. C32H53BClN6PRuSi requires C, 52.8; H, 7.35; N, 11.5%). NMR (CDCl3, 20 8C): dH 8.10 (d, 1 H, J = 2.0), 8.0 (d, 1 H, J = 2.0), 7.72 (d, 1 H, J = 2.0), 7.70 (d, 1 H, J = 2.8), 7.67 (d, 1 H, J = 2.4), 7.43 (d, 1 H, J = 2.4), 6.22 (m, 1 H), 6.18 (m, 1 H), 6.08 (m, 1 H), 3.71 (d, 1 H, J = 3.6), 2.0–1.0 (m, 33 H) and 20.27 (s, 9 H); dC 340.2 (d, J = 15.3), 146.6, 144.6, 143.4, 137.3, 136.7, 134.7, 106.6, 106.0, 105.9, 94.9, 35.5 (d, J = 19.5), 29.9, 28.5 (d, J = 10.2 Hz), 27.1 and 1.2; dP 33.9.[Ru{HB(pz)3}{P(C6H11)3}Cl{]] C(OMe)Me}] 12. A solution of complex 11 (68 mg, 0.093 mmol) in MeOH (5 cm3) was stirred at room temperature for 15 h. The product was obtained on addition of diethyl ether and light petroleum. Yield: 53 mg (83%) (Found: C, 52.25; H, 7.3; N, 12.05. C30H49BClN6OPRu requires C, 52.35; H, 7.2; N, 12.2%). NMR (CDCl3, 20 8C): dH 8.21 (d, 1 H, J = 2.1), 7.73 (d, 1 H, J = 2.4), 7.71 (d, 1 H, J = 2.4), 7.53 (d, 1 H, J = 2.7), 7.25 (d, 1 H, J = 1.7), 6.88 (d, 1 H, J = 2.4), 6.25 (m, 1 H), 6.10 (m, 1 H), 6.03 (m, 1 H), 4.07 (s, 3 H), 2.51 (s, 3 H) and 2.1–0.7 (m, 33 H); dC 318.2 (d, J = 13.7), 146.3, 145.9, 142.7, 137.0, 135.4, 134.4, 106.4, 106.1, 105.8, 59.7, 40.2, 35.4 (d, J = 14.5), 29.8, 28.8 (d, J = 7.2 Hz) and 27.7; dP 40.1.Catalytic dimerization of HC]] ] CR (R = Ph, CO2Et, Bun or SiMe3) In a typical procedure, the alkyne (0.3 mmol) was added to a suspension of either complex 2a or 2b (2 mol %) in toluene (5 cm3) and the sealed Schlenk tube was heated in an oil-bath for 20 h at 111 8C.After that time the reaction mixture was evaporated to dryness under vacuum and the coupling products were extracted with hexane. The solvent was again removed under vacuum affording isomeric mixtures of coupling products. The product distribution was determined by 1H NMR spectroscopy. Crystallography Crystal data and experimental details are given in Table 2.X-Ray data for complex 2b were collected on a Siemens Smart CCD area-detector diffractometer, with graphite-monochromated Mo-Ka radiation, (l 0.710 73 Å), a nominal crystalto- detector distance of 3.85 cm, and 0.38 w-scan frames were used. Corrections for Lorentz-polarization effects, crystal decay, and absorption (SADABS)13 were applied. The structures were solved by direct methods.14 All non-hydrogen atoms were refined anisotropically, and hydrogen atoms were included in idealized positions.15 The structures were refined against F2.Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/504. Acknowledgements Financial support by the Fonds zur Förderung der wissenschaftlichen Forschung is gratefully acknowledged (Project No. 11896). Thanks are due to Professor Scot Wherland and Dr. John Coddington (Washington State University, USA) for performing the magnetic susceptibility measurements. References 1 Part 4, C. Slugovc, K. Mereiter, E. Zobetz, R. Schmid and K. Kirchner, Organometallics, 1996, 15, 5275. 2 C. Slugovc, V. N. Sapunov, P. Wiede, K. Mereiter, R. Schmid and K. Kirchner, unpublished work. Table 2 Crystallographic data for [Ru{HB(pz)3}{P(C6H11)3}Cl(OMe)] 2b Formula M Crystal size/mm Space group Crystal system a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 F(000) Z Dc/g cm23 T/K m(Mo-Ka)/mm21 qmax/8 hkl Index ranges No.reflections measured No. unique reflections No. reflections F > 4s(F) No. parameters R(F)[F > 4s(F)] (all data) wR(F2) (all data) Minimum, maximum Fourier-difference peaks/e Å23 C28H46BClN6OPRu 661.01 0.32 × 0.25 × 0.21 P1� Triclinic 9.638(1) 10.715(1) 16.335(1) 108.17(1) 92.37(1) 103.83(1) 1 544.1(1) 690 2 1.422 297 0.678 30.5 213 to 11, 210 to 15, 223 to 23 13 407 9290 9289 350 0.038 0.063 0.105 20.69, 0.53 R(F) = S Fo| 2 |Fc /S|Fo|, wR(F2) = [Sw(Fo 2 2 Fc 2)2/Sw(Fo 2)2]� �� , w = 1/ [s2(Fo 2) 1 (0.0464P)2 1 0.27P] where P = (Fo 2 1 2Fc 2)/3.J. Chem.Soc., Dalton Trans., 1997, Pages 2113–2117 2117 3 G. Trimmel, C. Slugovc, P. Wiede, K. Mereiter, V. N. Sapunov, R. Schmid and K. Kirchner, Inorg. Chem., 1997, 36, 1076. 4 C. Gemel, P. Wiede, K. Mereiter, V. N. Sapunov, R. Schmid and K. Kirchner, J. Chem. Soc., Dalton Trans., 1996, 4071. 5 G. Gemel, G. Trimmel, C. Slugovc, K. Mereiter, S. Kremel, R. Schmid and K. Kirchner, Organometallics, 1996, 15, 3998. 6 B. K. Campion, R. H. Heyn and T. D. Tilley, J. Chem. Soc., Chem. Commun., 1988, 278. 7 N. W. Alcock, A. F. Hill and R. B. Melling, Organometallics, 1991, 10, 3898; A. F. Hill, J. Organomet. Chem., 1990, 395, C35; M. M. deV. Steyn, E. S. Singleton and D. C. Liles, J. Chem. Soc., Dalton Trans., 1990, 2991; A. M. McNair, D. C. Boyd and K. R. Mann, Organometallics, 1986, 5, 303. 8 N. W. Alcock, I. D. Burns, K. S. Claire and A. F. Hill, Inorg. Chem., 1992, 31, 2906. 9 N.-Y. Sun and S. J. Simpson, J. Organomet. Chem., 1992, 434, 341. 10 C. Bianchini, P. Innocenti, M. Peruzzini, A. Romerosa and F. Zanobini, Organometallics, 1996, 15, 272. 11 M. I. Bruce, B. C. Hall, N. N. Zaitseva, B. W. Skelton and A. H. White, J. Organomet. Chem., 1996, 522, 307. 12 C. S. Yi and N. Liu, Organometallics, 1996, 15, 3968. 13 G. M. Sheldrick, SADABS, Program for empirical absorption correction of Siemens SMART CCD detector data, University of Göttingen, 1996. 14 G. M. Sheldrick, SHELXS 86, Program for the Solution of Crystal Structures, University of Göttingen, 1986. 15 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. Received 27th January 1997; Paper

ISSN:1477-9226    

DOI:10.1039/a700588a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2119–2123 2119 Synthesis and structural characterisation of silver(I) compounds with nitrogen ligands Elizabeth C. Plappert, D. Michael P. Mingos,* Simon E. Lawrence and David J. Williams Chemistry Department, Imperial College of Science, Technology and Medicine, South Kensington, London, UK SW7 2AY Some silver(I) complexes of acyclic tri- and tetra-dentate nitrogen-containing ligands have been prepared and structurally characterised.In those complexes containing only the silver ion and the ligand a polymeric structure was observed in the solid state. However, the addition of another co-ordinating ligand, e.g. trimethylphosphine, inhibited polymer formation, leading to a dimeric structure. There is an increasing interest in the use of silver(I) compounds as drugs and diagnostic agents. For example, Sadler and coworkers 1 reported that silver(I) compounds with bidentate phosphine ligands exhibit antimicrobial and anticancer activity.Macrocyclic silver(I) complexes have also been widely studied because such compounds undergo very slow acid-dependent decomplexation and therefore may be useful for 111Ag-based radioimmunotherapy.2 Most of these macrocyclic compounds and a great number of silver(I) compounds with acyclic multidentate ligands are mono- or di-nuclear complexes. The coordination number of silver in these complexes varies from four to six.3 Polymeric silver(I) complexes with inorganic 4–7 and organic 8–12 ligands have been reported, but the synthesis and characterisation of many of these compounds is incomplete because of their insolubilities.10,11 Richmond and co-workers have shown that AgO3SCF3 with 1,4-di-tert-butyl-1,4-diazabuta- 1,3-diene gives a polymeric derivative,11 but a reversible polymerisation reaction results when the related phenyl derivatives XC6H4CHNC2H4NCHC6H4X (X = Cl or Br) are added in a 1 : 2 molar ratio.12 The study of silver(I) with simple acyclic nitrogen-donor ligands has, however, been relatively neglected.In this paper we describe the synthesis and structural characterisation of some novel silver(I) complexes of diethylenetriamine (dien), tris- (2-aminoethyl)amine (tren) and N,N9-bis(aminoethyl)propane- 1,3-diamine (tetraen) as ligands. To our knowledge this work represents the first structural characterisation of silver(I) polymers with simple acyclic aliphatic tri- and tetra-dentate nitrogen ligands.Results and Discussion Synthesis and characterisation Silver hexafluorophosphate dissolved in ethanol reacts at room temperature with dien in a 1 : 1 ratio to give an insoluble compound which could not be fully characterised. However, AgPF6 reacts under similar conditions with dien in a 1 : 2 ratio to yield a compound which remains soluble in ethanol. The resulting solution was stirred for 30 min and the colourless product was precipitated in 85% yield, based on silver, on addition of a large volume of pentane.These and all subsequent reactions of silver(I) salts described in this paper were done in reaction vessels where direct light was excluded. The resulting complex, [Ag(dien)][PF6] 1 is slightly light-sensitive, but may be stored indefinitely under nitrogen at 230 8C in the dark. It is very soluble in organic solvents such as methanol, ethanol and acetonitrile but not in pentane and toluene. Single crystals suitable for X-ray crystallography were grown by recrystallising the compound from ethanol at room temperature.The compounds [Ag(tren)][PF6] 2 and [Ag(tetraen)][PF6] 3 were synthesised in a similar manner, acetonitrile being used as solvent since both these compounds are insoluble in ethanol. The infrared spectra of 1–3 show N]H stretching vibrations in the range 3386–3324 cm21, d(NH2) bending vibrations between 1606–1660 cm21 and n(Ag]N) bands in the range 559–550 cm21. The 1H and 13C NMR spectral data for these compounds are summarised in the Experimental section.Since the crystallographic determinations which are described below have shown that compounds 1 and 2 adopt polymeric structures it was of interest to establish whether the chains could be broken up by the addition of monodentate ligands. Therefore, PMe3, PPh3 and ButNC were added to silver(I)–dien solutions. Silver hexafluorophosphate reacts with 1 equivalent of PMe3 and 2 equivalents of dien in ethanol at 23 8C to give [Ag2(dien)2(PMe3)2][PF6]2 4 in 88% yield, based on silver.The complex is slightly light-sensitive, but may be stored under nitrogen at 230 8C in the dark without decomposition. The complex is soluble in organic solvents such as methanol, ethanol and acetonitrile, but not in pentane or toluene. Single crystals of 4 suitable for X-ray crystallography were grown by crystallising the compound from ethanol and pentane at 225 8C. The compounds [Ag(dien)(PPh3)]n[PF6]n 5 and [Ag(dien)(ButNC)]n[PF6]n 6 were synthesised in an analogous manner, but acetonitrile was used as solvent since these last two are less soluble in ethanol.The infrared spectra of 4–6 show N]H stretching vibrations in the range 3390–3310 cm21, d(NH2) bending vibrations between 1600 and 1590 cm21 and n(Ag]N) bands in the range 563–547 cm21. The n(NC) band for [Ag(dien)(ButNC)]n[PF6]n appears at 2194 cm21 and the d(CMe3) band at 1376 cm21. The 1H and 13C NMR data of these compounds are summarised in the Experimental section.In the 31P NMR spectra the signals of the phosphines are shifted to low field on complexation, for [Ag2(dien)2(PMe3)2][PF6]2 from d 262.0 (free PMe3) to 238.0 (complex) and for [Ag(dien)(PPh3)]n[PF6]n from d 26.0 (free PPh3) to 14.3 (complex), the PF6 resonance is observed at d 2143.9 as a septet for both complexes. Crystal structures The crystal data, data collection and refinement parameters for compounds 1, 2 and 4 are summarised in Table 1 and selected bond lengths and angles are given in Table 2.Unfortunately single crystals of compound 3 suitable for X-ray crystallographic analysis could not be obtained. The X-ray analysis of 1 shows it to have a catena structure comprising two crystallographically independent silver atoms and two non-equivalent dien ligands which link adjacent silver centres to form the polymeric chain shown in Fig. 1. The silver co-ordination2120 J. Chem.Soc., Dalton Trans., 1997, Pages 2119–2123 Table 1 Details of the crystallographic data collection and refinement for compounds 1, 2 and 4 a Compound 1 2 4 Empirical formula M Colour, habit Crystal size/mm Crystal system Space group a/Å b/Å c/Å b/8 U/Å3 Z Dc/Mg m23 Radiation (l/Å) m/mm21 Maximum, minimum transmission 2q range/8 F(000) Independent reflections (Rint) Observed reflections [F > 4s(F)] No. of parameters refined Weighting factors a,b d Final R1, wR2 e Goodness of fit Largest, mean D/s Largest difference peak, hole/e Å23 Extinction [C4H13AgN3?PF6]n 356.02 Colourless, platy needles 0.27 × 0.20 × 0.07 Monoclinic P21/c 10.048(1) 14.776(3) 14.931(1) 93.59(1) 2212.5(5) 8 b 2.138 Cu-Ka (1.541 78) 16.616 0.1319, 0.0322 8–120 1392 3274 (0.075) 2184 356 0.100, 5.000 0.066, 0.169 1.08 0.000, 0.000 0.734, 21.227 0.0016 [C6H18AgN4?PF6]n 399.08 Colourless, needles 0.60 × 0.30 × 0.30 Orthorhombic P212121 10.577(1) 13.940(1) 18.088(3) — 2667.0(6) 8 b 1.988 Mo-Ka (0.710 73) 1.691 0.5341, 0.4891 3.6–60 1584 4331 (0.00) 3475 326 0.040, 1.900 0.041, 0.097 1.08 20.003, 0.001 0.786, 20.416 0.0023 C14H44Ag2N6?2PF6 864.17 Colourless, needles 0.23 × 0.16 × 0.10 Monoclinic P21/n 9.998(3) 9.555(2) 17.924(2) 104.66(2) 1656.6(6) 2 c 1.732 Cu-Ka (1.541 78) 12.100 0.8412, 0.3403 9.2–120 864 2462 (0.054) 1711 172 0.100, 2.750 0.066, 0.163 1.04 20.001, 0.000 0.691, 20.931 — a Details in common: graphite-monochromated radiation, w scans, Siemens P4 diffractometer, refinement based on F 2, 293 K, semiempirical absorption corrections from y scans.b There are two crystallographically independent molecules in the asymmetric unit. c The molecule has crystallographic Ci symmetry. d w21 = s2(Fo 2) 1 (aP)2 1 bP. e R1 = S |Fo| 2 |Fc| /S|Fo|; wR2 = {S[w(Fo 2 2 Fc 2)]/S[w(Fo 2)2]}� �� . geometry in the chain is approximately T-shaped. The terminal atoms of the dien ligands generate angles at Ag(1) and Ag(9) of 159.0(4) [N(2)]Ag(1)]N(16A)] and 159.7(5)8 [N(10)] Ag(9)] N(8)].The associated Ag]N distances are 2.23(1) and 2.17(1) Å at Ag(1) for N(2) and N(16A), and 2.22(1) and 2.17(1) Å at Ag(9) for N(10) and N(8) respectively. These silver–nitrogen bond lengths are relatively long compared with those found in polymeric compounds where the silver is Table 2 Selected bond lengths (Å) and angles (8) for compounds 1, 2 and 4 Compound 1 Ag(1)]N(16A) Ag(1)]N(2) Ag(1)]N(5) 2.17(1) 2.23(1) 2.46(1) Ag(9)]N(8) Ag(9)]N(10) Ag(9)]N(13) 2.17(1) 2.22(1) 2.47(1) N(16A)]Ag(1)]N(2) N(16A)]Ag(1)]N(5) N(2)]Ag(1)]N(5) 159.0(4) 123.7(4) 77.0(4) N(8)]Ag(9)]N(10) N(8)]Ag(9)]N(13) N(10)]Ag(9)]N(13) 159.7(5) 122.8(4) 77.4(4) Compound 2 Ag(1)]N(2) Ag(1)]N(5) Ag(1)]N(8) Ag(1)]N(22A) 2.384(6) 2.478(5) 2.326(5) 2.246(6) Ag(12)]N(1) Ag(12)]N(13) Ag(12)]N(16) Ag(12)]N(19) 2.254(5) 2.442(6) 2.545(5) 2.285(5) N(2)]Ag(1)]N(5) N(2)]Ag(1)]N(8) N(5)]Ag(1)]N(8) N(2)]Ag(1)]N(22A) N(5)]Ag(1)]N(22A) N(8)]Ag(1)]N(22A) 76.0(2) 109.7(2) 75.3(2) 118.2(2) 126.9(2) 130.5(2) N(11)]Ag(12)]N(13) N(11)]Ag(12)]N(16) N(11)]Ag(12)]N(19) N(13)]Ag(12)]N(16) N(13)]Ag(12)]N(19) N(16)]Ag(12)]N(19) 104.7(2) 133.6(2) 140.8(2) 73.7(2) 109.6(2) 75.3(2) Compound 4 Ag(1)]P(1) Ag(1)]N(5) 2.372(3) 2.368(9) Ag(1)]N(8) Ag(1)]N(11A) 2.516(9) 2.343(8) P(1)]Ag(1)]N(5) P(1)]Ag(1)]N(8) P(2)]Ag(1)]N(11A) 124.2(3) 116.7(2) 134.9(2) N(5)]Ag(1)]N(8) N(5)]Ag(1)]N(11A) N(8)]Ag(1)]N(11A) 74.9(3) 94.3(3) 93.7(3) two-co-ordinate, e.g.[Ag(XC6H4CHNC2H4NCHC6H4X)]O3- SCF3 : 2.13(1), 2.16(4) Å; 12 [Ag(NCS)2AsF6]n : 2.11(7) Å 5 or [AgN(CN)2] : 2.11(1) Å.7 The Ag(1)]N(2) and Ag(9)]N(10) bond distances in compound 1 are approximately equal to the average Ag]N bond lengths in compounds with higher coordination numbers.4,8,9 The T-shaped co-ordination geometry in 1 is completed by a secondary weaker ‘side-on’ interaction to the central nitrogen atom of each dien chain [2.46(1)Å to N(5) and 2.47(1) Å to N(13)], resulting in pairs of five-membered chelate rings.The bond angles 77.0(4)8 for N(2)]Ag(1)]N(5) and 77.4(4)8 for N(10)]Ag(9)]N(13) are comparable with those reported for other related five-membered chelate rings Fig. 1 Structure of the polymeric cation in compound 1J. Chem. Soc., Dalton Trans., 1997, Pages 2119–2123 2121 [73.9(3)8, 76.8(1)8 in related silver(I)-nitrogen compounds].10,13 It is noticeable that the ‘in-chain’ Ag]N distances within the five-membered chelate rings are slightly longer than those that are outside.Each AgN3 unit is essentially planar, with maximum deviations from planarity of 0.05 Å for Ag(1) and 0.03 Å for Ag(9). The two ligand conformations are virtually identical; the principal difference being that adjacent ligands within any one chain are enantiomeric giving rise to alternating d and l conformations for the five-membered chelate rings. The polymeric chains, which extend in the crystallographic a direction, are approximately sinusoidal in nature and pack such that the peaks of one chain lie in the troughs of the next (Fig. 2). There are no short inter-chain contacts. The ‘in-chain’ Ag? ? ?Ag separations of 5.9 and 6.1 Å are shorter than those between Ag atoms in adjacent chains (shortest distance 7.5 Å). The PF6 anions lie in interstices between the polymer chains. In the analogous gold complex [{Au2(dien)2}21]n the dien ligand is bidentate and an infinite linear polymer based on weak gold–gold contacts is formed.14 The only copper(I)–dien complexes with supporting co-ligands which have been structurally characterised are monomeric, i.e.[Cu(dien)(CO)]115 and [Cu- (dien)R]1 (R = hex-1-ene).16 The structure of compound 2 is also based on a polymeric arrangement comprising of two crystallographically independent silver–tris(2-aminoethyl)amine units which are illustrated in Figs. 3 and 4. The amine tren acts as a tetradentate ligand in this complex.The co-ordination geometries at the two silver centres may be described as distorted tetrahedral and exhibit significant differences. The geometry at Ag(1) is less distorted and the trigonal base is formed from N(2), N(8) and N(22A) (the silver atom only lies 0.17 Å out of the plane of the three nitrogen atoms), the ‘in-plane’ Ag]N distances being 2.384(6), 2.326(5) and 2.246(6) Å to N(2), N(8) and N(22A) respectively. These bond distances are comparable with those reported for other tetrahedral silver(I) complexes with nitrogen ligands.9–11 There are angled ‘apical’ approaches of both bridgehead nitrogen atoms N(5), N(16) at slightly longer Ag]N distances of 2.478(5) and 2.545(5) Å respectively, the N(5)]Ag(1) linkage being inclined by 578 to the N(2), N(8), N(22A) plane, the N(16)]Ag(12) vector by 518 to Fig. 2 Packing of the polymeric chains in compound 1 the N(11), N(13), N(19) plane. The N]Ag]N angles [73.7(2)– 76.0(2), 109.6(2) and 109.7(2)8] and the longer silver– bridgehead nitrogen bonding are comparable with the values reported for the macrobicyclic hexamine cryptate [Ag2- {N[(CH2)2N]] CH(p-C6H4)CH]] N(CH2)2]3N}]21.17 It is interesting that at both silver centres it is the bond from the terminal nitrogen atom which is the shortest.As in 1 the chains have a sinusoidal nature and pack with the peaks at one chain lying approximately in the troughs of the next. The ‘in-chain’ Ag ? ? ? Ag separations are 6.5 and 7.7 Å and the shortest interchain Ag ? ? ? Ag distance is 6.7 Å.The PF6 anions also lie in the interstices between the polymer chains. The X-ray structural analysis of compound 4 reveals the formation of a Ci symmetric bimetallic macrocyclic complex Fig. 3 Structure of the polymeric cation in compound 2 Fig. 4 Packing of the polymeric chains in compound 22122 J. Chem. Soc., Dalton Trans., 1997, Pages 2119–2123 comprising two silver atoms and two bridging diens (Fig. 5). The co-ordination geometries at the silver atoms are probably best described as severely distorted tetrahedral.The atoms N(5), N(11A) and P(1) are at 2.368(9), 2.343(8) and 2.372(3) Å from Ag which lies 0.34 Å out of the plane formed by these three atoms. The Ag]P bond length of 2.372(3) Å is slightly shorter than silver–phosphorus bonds reported in the literature [2.39–2.63 Å].18 The Ag]N distances with 2.368(9) Å [Ag(1)]N(5)] and 2.343(8) Å [Ag(1)]N(11A)] are in good agreement with the average values of 2.31–2.44 Å found for four-coordinated silver.10,11,13,17 As observed in the 1 : 1 Ag: dien complex 1 there is a longer approach [2.516(9) Å] of the central nitrogen atom, N(8), to the silver centre, the N(8)]Ag vector being inclined by 668 to the P(1), N(5), N(11A) plane. The transannular Ag ? ? ? Ag separation is 4.71 Å, and the shortest intermacrocycle Ag ? ? ? Ag contact is 6.4 Å, there being no notable intercomplex interactions. The formation of this macrocyclic complex is directly analogous to the cyclic compound formed between AuBF4 and dien 14 which is propagated via weak Au ? ? ?Au interactions to give a polymeric structure.Polymer formation in compound 4, however, is inhibited by the presence of the co-ordinated trimethylphosphine. Although in both the Au and Ag macrocyclic complexes the dien ligand has consistent anti and gauche geometries about the C]N and C]C bonds respectively, in the ‘chain’ polymers a mixture of anti and gauche geometries is observed for both the C]N and the C]C bonds.Conclusion Silver(I) forms an interesting range of polymeric chain compounds with polydentate nitrogen acyclic ligands, two of which have been structurally characterised. The addition of monodentate ligands such as phosphines or isocyanides to these compounds leads to the formation of simpler binuclear species. Experimental All manipulations were carried out under an atmosphere of nitrogen usingard Schlenk techniques and in vessels from which light was excluded.Organic solvents were of reagent grade and were dried by published procedures and distilled under N2 and vacuum degassed before use. All chemicals were purchased from Aldrich and used without further purification. The infrared spectra of the compounds were recorded on Nujol Fig. 5 Structure of the cationic macrocycle in compound 4 mulls using a Perkin-Elmer 1720 Infrared Fourier-transform Spectrometer.The NMR spectra were recorded on a JEOL JNM-EX270 FT-NMR spectrometer; 1H and 13C chemical shifts were referenced to tetramethylsilane and those of 31P to H3PO4. Syntheses [Ag(dien)][PF6] 1. To AgPF6 (0.2 g, 0.70 mmol) in ethanol (20 cm3), dien (0.17 cm3, 1.58 mmol) was added at room temperature. The resulting colourless solution was stirred for 30 min and the product was crystallised by the addition of a large volume of pentane affording colourless microcrystalline [Ag(dien)][PF6]. Yield: 85%, based on silver.IR (Nujol, cm21): 3386, 3324 (n N]H), 2922, 2873 (n C]H), 830 (n PF6), 559 (n Ag]N). 1H NMR (CD3CN): d 2.84 (4 H, CH2), 2.69 (4 H, CH2), 2.10 (5 H, NH2/NH). 13C NMR (CD3CN): d 51.00, 41.70. Fast atom bombardment (FAB) mass spectrum: m/z 567 [M]21[PF6], 422 [Ag2(dien)2]1 (Found: C, 13.10; H, 3.60; N, 11.31. C4H13AgF6N3P requires: C, 13.51; H, 3.65; N, 11.80%). [Ag(tren)][PF6] 2. The amine tren (0.28 cm3, 1.87 mmol) was added slowly to a solution of AgPF6 (0.22 g, 0.87 mmol) in acetonitrile (30 cm3) at room temperature.After stirring for 35 min the colourless product was crystallised by the addition of a large volume of ethanol affording colourless, analytically pure [Ag(tren)][PF6]. Yield: 87%, based on silver. IR (Nujol, cm21): 3386, 3325 (n N]H), 2920, 2875 (n C]H), 834 (n PF6), 558 (n Ag]N). 1H NMR (CD3CN): d 2.81 (6 H, CH2), 2.56 (6 H, CH2), 2.14 (6 H, NH2/NH). 13C NMR (CD3CN): d 55.79, 40.57. FAB mass spectrum: m/z 413 [Ag(tren)(NH2)]21[PF6], 397 [Ag(tren)]21[PF6] (Found: C, 18.25; H, 4.17; N, 13.79.C6H18AgF6N4P requires: C, 18.05; H, 4.51; N, 14.00%). [Ag(tetraen)][PF6] 3. The complex was synthesised as described for [Ag(tren)][PF6]. Yield: 79%, based on silver. IR (Nujol, cm21): 3386 (n N]H), 2923, 2858 (n C]H), 820 (n PF6), 559 (n Ag]N). 1H NMR (CD3CN): d 2.74–2.58 (12 H, CH2), 1.63 (2 H, CH2), 2.12 (6 H, NH2/NH). 13C NMR (CD3CN): d 51.53, 48.80, 41.11, 29.47. FAB mass spectrum: m/z 267 [Ag(tetraen)]1, 167 [Ag(H2NC2H4NH)]1 (Found: C, 20.96; H, 4.56; N, 13.39.C7H20AgF6N4P requires: C, 20.84; H, 4.34; N, 13.56%). [Ag2(dien)2(PMe3)2][PF6]2 4. The phosphine PMe3 [0.87 cm3 of 1.0 mol dm23 solution in tetrahydrofuran (thf), 0.87 mmol] was added dropwise to a solution of AgPF6 (0.22 g, 0.87 mmol) in ethanol (25 cm3) at room temperature. After stirring for 10 min dien (0.18 cm3, 1.74 mmol) was added. The colourless solution was stirred for 30 min and the product was crystallised by the addition of pentane to give colourless, analytically pure [Ag2(dien)2(PMe3)2][PF6]. Yield: 88% based on silver.IR (Nujol, cm21): 3390 (n N]H), 2923, 2857 (n C]H), 835 (n PF6), 547 (n Ag]N). 1H NMR (CD3CN): d 2.71 (8 H, CH2), 2.60 (8 H, CH2), 1.97 (10 H, NH2/NH), 1.29, 1.27 (18 H, PCH3). 13C NMR (CD3CN): d 49.41, 40.81 (CH2), 15.97, 15.67 (PCH3). 31P NMR (CD3CN): d 238. (FAB) mass spectrum m/z: 285 [Ag- (dien)(PMe) 2 2H]1, 260 [M 2 C2H4]1, 210 [Ag(dien)]1. (Found: C, 19.58; H, 4.22; N, 9.81.C14H44Ag2F12N6P4 requires: C, 19.44; H, 5.32; N, 9.72%). [Ag(dien)(PPh3)]n[PF6]n 5. To AgPF6 (0.25 g, 0.98 mmol) in acetonitrile (40 cm3) the phosphine PPh3 (0.26 g, 0.98 mmol) was added at room temperature. The solution was stirred for 15 min and dien (0.22 cm3, 1.97 mmol) was added. After stirring for 40 min the product was crystallised by the addition of pentane to give colourless microcrystalline [Ag(dien)(PPh3)]n[PF6]n.Yield: 82%, based on silver. IR (Nujol, cm21): 3379, 3323 (n N]H), 2923, 2856 (n C]H), 823 (n PF6), 557 (n Ag]N). 1HJ. Chem. Soc., Dalton Trans., 1997, Pages 2119–2123 2123 NMR (CD3CN): d 7.42 (15 H, Ph3), 2.70 (4 H, CH2), 2.66 (4 H, CH2), 1.90 (5 H, NH2/NH). 13C NMR (CD3CN): d 133.60– 128.89 (Ph3), 48.23, 40.11 (CH2). 31P NMR (CD3CN): d 14.30. FAB mass spectrum: m/z 472 [Ag(dien)(PPh3)]1, 369 [Ag- (PPh3)]1, 210 [Ag(dien)]1 (Found: C, 42.76; H, 4.31; N, 6.74. C22H28AgF6N3P requires: C, 42.77; H, 4.53; N,6.80%).[Ag(dien)(ButNC)]n[PF6]n 6. The complex was synthesised as described for [Ag(dien)(PPh3)]n[PF6]n. Yield: 78%, based on silver. IR (Nujol, cm21): 3384, 3310 [n N]H], 2915, 2852 [n C]H], 2194 [n NC], 838 [n PF6], 563 [n Ag]N]. 1H NMR (CD3CN): d 2.73 (4 H, CH2), 2.62 (4 H, CH2), 1.99 (5 H, NH2/NH), 1.58 (9 H, But). 13C NMR (CD3CN): 151.43 (NC), 57.03, 29.00 (But), 48.26, 39.94 (CH2). FAB mass spectrum: m/z 293 [Ag(dien)(ButNC)]1, 210 [Ag(dien)]1 (Found: C, 24.44; H, 4.48; N, 11.87.C9H22AgF6N4P requires: C, 24.64; H, 5.02; N, 11.77%). Crystallography Compound 1 was solved using the heavy-atom method, 2 and 4 by direct methods. All three structures were refined by fullmatrix least-squares based on F 2. The non-hydrogen atoms were refined anisotropically. In 2, there was disorder in both of the PF6 anions, which was resolved into alternate partial occupancy orientations, the major occupancies of which were refined anisotropically.For all three structures the N]H hydrogen atoms were located from a difference map and idealised, the C]H hydrogen atom positions were calculated. All hydrogen atoms were assigned isotropic thermal parameters U(H) = 1.2 Ueq (C/N) and allowed to ride on their parent atoms. The absolute structure for 2 was determined by both an R-factor test and a Flack parameter test. Computations were carried out using the SHELXTL PC program system 6.19 Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/512. Acknowledgements This research was supported by the Swiss National Science Foundation (E. C. P.) and the EPSRC (S. E. L.). B.P. plc is thanked for endowing D. M.P. M.s Chair. References 1 S. J. Berners-Price and P. J. Sadler, Coord. Chem. Res., 1990, 15, 1; S. J. Berners-Price and P. J. Sadler, Struct. Bonding (Berlin), 1988, 70, 27; S. J. Berners-Price, P. J. Sadler and C. Brevard, Magn. Reson. Chem., 1990, 28, 145; S. J. Berners-Price, D. C. Collier, M. A. Mazid, P. J. Sadler, R. E. Sue and D. Wilkie, Met. Based Drugs, 1995, 2, 111; S. J. Berners-Price, R. K. Johnson, A. J. Giovenella, L. F. Faucette, C. K. Mirabelli and P. J. Sadler, J. Inorg.Biochem., 1988, 33, 285. 2 A. S. Craig, R. Kataky, D. Parker, H. Adams, N. Bailey and H. Schneider, J. Chem. Soc., Chem. Commun., 1989, 1870; A. S. Craig, R. Kataky, R. C. Matthews, D. Parker, G. Ferguson, A. Lough, H. Adams, N. Bailey and H. Schneider, J. Chem. Soc., Perkin Trans. 2, 1990, 1523. 3 B. de Groot and S. J. Loeb, Inorg. Chem., 1991, 30, 3103; K. Saito, S. Murakami and A. Muromatsu, Polyhedron, 1993, 12, 1587; A. J. Blake, R. O. Gould, A. J. Holder, T.I. Hyde and M. Schröeder, Polyhedron, 1989, 8, 513; M. G. B. Drew, C. Cairns, S. G. McFall and S. M. Nelson, J. Chem. Soc., Dalton Trans., 1980, 2020; H. Adams, N. A. Bailey, W. D. Carlisle, D. E. Fenton and G. Rossi, J. Chem. Soc., Dalton Trans., 1990, 127; E. C. Constable, M. G. B. Drew, G. Forsyth and M. D. Ward, J. Chem. Soc., Chem. Commun., 1988, 1450; G. C. van Stein, G. van Koten, A. L. Spek, A. J. M. Duisenberg and E. A. Klop, Inorg. Chim. Acta, 1983, 78, L61; G. C.van Stein, G. van Koten, K. Vrieze, A. L. Spek, E. A. Klop and C. Brevard, Inorg. Chem., 1985, 24, 1367. 4 H. W. Roesky, T. Gries, J. Schimkowiak and P. G. Jones, Angew. Chem., Int. Ed. Engl., 1986, 25, 84. 5 H. W. Roesky, J. Schimkowiak and K. Meyer-Baese, Angew. Chem., Int. Ed. Engl., 1986, 25, 1006. 6 H. W. Roesky, H. Hofmann, J. Schimkowiak, P. G. Jones, K. Meyer- Baese and G. M. Sheldrick, Angew. Chem., Int. Ed. Engl., 1985, 24, 417. 7 D. Britton and Y. M. Chow, Acta Crystallogr., Sect.B, 1977, 33, 697. 8 T. J. Kistenmacher, M. Rossi and L. G. Marizilli, Inorg. Chem., 1979, 18, 240. 9 J. F. Modder, G. van Koten, K. Vrieze and A. L. Spek, Angew. Chem., Int. Ed. Engl., 1989, 28, 1698. 10 T. G. Richmond, E. P. Kelson, A. M. Arif and G. B. Carpenter, J. Am. Chem. Soc., 1988, 110, 2334. 11 A. M. Arif and T. G. Richmond, J. Chem. Soc., Chem. Commun., 1990, 871. 12 T. G. Richmond, E. P. Kelson and A. T. Patton, J. Chem. Soc., Chem. Commun., 1988, 96. 13 C. Stockheim, K. Wieghardt, B. Nuber, J. Weiss, U. Floerke and H. J. Haupt, J. Chem. Soc., Dalton Trans., 1991, 1487. 14 J. Yau, D. M. P. Mingos, S. Menzer and D. J. Williams, J. Chem. Soc., Dalton Trans., 1995, 2575. 15 M. Pasquali, F. Marchetti and C. Floriani, Inorg. Chem., 1978, 17, 1684. 16 M. Pasquani, C. Floriani, A. Gaetami-Manfredotti and A. Chiesi- Villa, Inorg. Chem., 1979, 18, 3535. 17 M. G. B. Drew, D. McDowell and J. Nelson, Polyhedron, 1988, 7, 2229. 18 P. Karagannidis, P. Aslanidis, S. Kokkon and C. J. Cheer, Inorg. Chim. Acta, 1990, 172, 247; D. M. Ho and R. Bau, Inorg. Chem., 1983, 22, 4073; M. Camalli and F. Caruso, Inorg. Chim. Acta, 1990, 169, 189; A. Baiada, F. H. Jardine and R. D. Willet, Inorg. Chem., 1990, 29, 3042; C. M. Che, H. K. Yip, D. Li, S. M. Peng, G. H. Lee, Y. M. Wang and S. T. Lin, J. Chem. Soc., Chem. Commun., 1991, 1615; E. W. Ainscough, A. M. Brodie, S. L. Ingham and J. M. Waters, J. Chem. Soc., Dalton Trans., 1994, 215; M. Coucouvanis, N. C. Baenziger and S. M. Johnson, Inorg. Chem., 1974, 13, 1191; E. C. Alyea, G. Ferguson and A. Somogyvari, Inorg. Chem., 1982, 21, 1369. 19 G. M. Sheldrick, SHELXTL PC, version 5.03, Siemens Analytical X-Ray Instruments, Madison, WI, 1994. Received 20th March 1997; Paper 7/01970J

ISSN:1477-9226    

DOI:10.1039/a701970j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2125–2130 2125 Equilibrium and solution structural study of the proton, copper(II), nickel(II) and zinc(II) complexes of 1-(2-aminoethylamino)-1-deoxy-Dgalactitol Béla Gyurcsik,*,†,a Tamás Gajda,b Attila Jancsó,b René Lammersc and László Nagy b a Bioco-ordination Chemistry Research Group of the Hungarian Academy of Sciences, A. József University, H-6701 Szeged, PO Box 440, Hungary b Department of Inorganic and Analytical Chemistry, A.József University, H-6701 Szeged, PO Box 440, Hungary c Laboratory of Organic Chemistry and Catalysis, Delft University of Technology, Julianalaan 136, BL-2628 Delft, The Netherlands Protonation and copper(II), nickel(II) and zinc(II) complex-formation equilibria of 1-(2-aminoethylamino)-1- deoxy-D-galactitol and the solution co-ordination structure of the complexes were investigated by potentiometric titrations, UV/VIS absorption, CD, EPR and 13C NMR spectroscopies in aqueous solution (I = 0.1 mol dm23, NaClO4; T = 298 K).In acidic media the ethane-1,2-diamine (en) residue dominates the co-ordination for all the metal ions studied, but the spectroscopic results are consistent with weak co-ordination of alcoholic hydroxy group(s). In equimolar solution and at neutral pH, dialkoxide-bridged dimeric species were formed with nickel(II) and copper(II). In case of an excess of galactitol bis- and tris-complexes were also detected. In the latter system metal-promoted deprotonation occured above pH 9 and in this way the second ligand is successively displaced from the co-ordination sphere of copper(II).In the finally formed MLH22 species the ligand is co-ordinated by two amino and two deprotonated alcoholic hydroxy groups. Nickel(II) formed a ML2H22 complex in the alkaline pH region. The deprotonation processes of the ZnL2 complex leading also to ML2H22 took place at almost the same pH as for NiL2. Evidence of the deprotonation of the alcoholic hydroxy groups is available only above pH ª 11 in the zinc(II)-containing system. The complex formation of amino alcohols is of increasing interest from both chemical and biological aspects.1–4 The presence of anchoring amino group(s) may promote the deprotonation of strongly basic donor groups, such as the amide group in peptides 5 or the alcoholic hydroxy group in aldosamines,6 by the formation of a stable chelate ring.In the case of cyclic amino alcohols it was established that the conformation of the compound determines the number and quality of the coordinating donor groups.7 Still several questions remained concerning the behaviour of open-chain-type carbohydrate derivatives such as: (i ) the co-ordination of still protonated alcoholic hydroxy groups to the metal ions, (ii ) the assignment of the deprotonated alcoholic hydroxy groups and (iii ) the number of such groups.To answer these questions we started a systematic study on the metal-ion complexation of polyalcohol type ligands obtained from simple sugars by varying the anchoring groups in the molecule.8 The present compound is 1-(2-aminoethylamino)- 1-deoxy-D-galactitol (aegaln), prepared from Dgalactose and ethane-1,2-diamine.Potentiometric, UV/VIS, CD, EPR and NMR spectroscopic methods were utilised to obtain the stability constants and the solution co-ordination structure of its copper(II), nickel(II) and zinc(II) complexes formed in aqueous media.Experimental Materials The galactitol was obtained as described previously.2 Its purity was checked by elemental analysis, 1H and 13C NMR spectroscopy and by potentiometric titration. Copper(II), nickel(II) and † E-Mail: gyurcsik@chem.u-szeged.hu zinc(II) perchlorate (Fluka) solutions were standardised complexometrically. pH-Metric titrations were performed using Titrisol standard NaOH solution (Merck). All other reagents were Reanal products of analytical grade.pH-Metric measurements The co-ordination equilibria were investigated by potentiometric titrations in aqueous solution (I = 0.1 mol dm23, made up using NaClO4 and T = 298 ± 0.1 K) in an automatic titration set including a Dosimat 665 (Metrohm) autoburette, a Radelkis OP-201/8 precision digital pH-meter and an IBM compatible personal computer. The Orion 9103BN type semimicro combined pH electrode was calibrated 8 using the modified Nernst equation (1), where JH and JOH are fitting E = E0 1 K?log[H1] 1 JH[H1] 1 JOHKW[H1]21 (1) parameters in acidic and alkaline media for the correction of experimental errors, mainly due to the liquid junction and to the alkaline and acidic errors of the glass electrode; KW = 10213.75 mol2 dm26 is the autoprotolysis constant of water.9 The parameters were calculated by a non-linear least-squares method.The species formed in the systems were characterised by the C H OH CH2 C NH CH2 CH2 NH2 C OH H C H HO HO H CH2 OH 1 1¢ 2¢ 6 2 S 4 S 5 R 3 R aegaln2126 J.Chem. Soc., Dalton Trans., 1997, Pages 2125–2130 equilibrium process (2) or (3) while the formation constants for pM 1 qL bMpLqH2r MpLqH2r 1 rH (2) pM 1 qL 1 rOH bMpLq(OH)r MpLq(OH)r (3) these generalised species are given by equation (4) and were bMpLqH2r = [MpLqH2r][H]r [M]p[L]q = [MpLq(OH)r](KW)r [M]p[L]q[OH]r = bMpLq(OH)r(KW)r (4) calculated by the computer program PSEQUAD.10 Here M denotes the metal ion and L the non-protonated ligand molecule.In the following, charges are omitted and the water molecules (necessary to ensure six-co-ordination) are not shown. The protonation constants were determined from five titrations (80–110 data points per titration and the galactitol concentration was varied from 2 × 1023 to 2 × 1022 mol dm23). The complex stability constants were also determined from five independent titrations (80–110 data points per titration) for all metal-to-galactitol ratios in each system.The copper(II)-togalactitol ratio was varied from 1: 1 to 1 : 10, while the nickel(II)- and zinc(II)-to-galactitol ratio was varied from 1: 2 to 1 : 10; in all systems studied the metal-ion concentration ranged from 2 × 1023 to 1022 mol dm23. Electronic absorption and CD measurements The UV/VIS spectra were recorded on a Hewlett-Packard 8452A diode-array spectrophotometer. The individual spectra of the copper(II) complexes formed were calculated by PSEQUAD. The CD spectra were recorded on a Jobin Yvon CD6 spectropolarimeter in the wavelength interval from 230 to 800 nm.The metal-ion concentration was 5 × 1023 mol dm23 in cells with 0.1 and 1 cm optical pathlengths in the UV and VIS spectral regions, respectively. The CD data are given as the differences in molar absorption coefficients between left and right circularly polarised light, normalised to the metal-ion concentration in dm3 mol21 cm21 units. EPR measurements The EPR spectra were recorded on a JEOL-JES-FE 3X spectrometer in the X band at 298 K with 100 KHz field modulation.Manganese(II)-doped MgO powder served as the field standard. The copper(II) concentration was 5 × 1023 mol dm23. The EPR parameters were calculated by a recently developed computer program11 able to treat the spectra of several (but preferably two) coexisting species. NMR measurements The 13C NMR measurements were performed on a Bruker AM- 400 at 100.12 MHz operating at room temperature.The pH readings in a mixture of 10% D2O–90% water were uncorrected for the isotopic effect. The chemical shifts are given as relative shifts from the sodium salt of 4,4-dimethyl-4-silapentane-1- sulfonate using 1,4-dioxane as internal reference (d 67.4 from this sodium salt). Results and Discussion The galactitol undergoes two deprotonation processes during the potentiometric titration (Table 1) from pH 2 to 11 which can be assigned to the two ammonium groups, on the basis of 13C NMR titrations,2 the larger protonation constant to the primary, the smaller to the secondary ammonium group having two electron-attracting substituents.The protonation constants are in very good agreement with those reported previously 2 (see Table 1). Comparison with the protonation constants of en 12,13 and N-(2-hydroxyethyl)ethane-1,2-diamine (hen),14 shown in Table 1, reflects the negative inductive effect of the polyhydroxyalkyl chain present in aegaln. The first alcoholic hydroxy group has the largest effect, while that of the further hydroxy groups is much smaller.The alcoholic hydroxy groups do not deprotonate in the pH interval studied. Copper(II) complexes In the course of the potentiometric titrations no precipitation of the metal hydroxide was observed at any metal to galactitol ratios and concentrations applied in the region pH 2–11.5. The stability constants for the set of complex species giving the best fit to the experimental data are presented in Table 2.Complexes between pH 2 and 5. In the acidic pH region Cu(HL) and CuL species were formed at any metal-togalactitol ratio studied (Fig. 1). The formation constants for these species on the basis of equation (5) are 4.13(2) and M 1 HrL M(HrL), where r = 1 or 0 (5) 10.08(1), respectively, reflecting an extra stabilisation in species CuL caused by the chelate ring formation. The basicity-adjusted stability constants log K = log bML 2 log bH2L relating to equation (6) for the CuL species of en, hen M 1 H2L ML 1 2H (6) and aegaln [26.57;13 26.10 14 and 25.85(1) in logarithmic units, respectively] reveal some extra stabilisation in complexes of hydroxyamines compared to en.The UV/VIS (Table 2) and EPR spectra of the CuL complex (Table 3, Fig. 2) are entirely compatible with a 2N,2O donor set in the equatorial plane of copper(II). The above-mentioned extra stabilisation and the existence of a relatively low intensity CD spectrum for this complex (Fig. 3) suggest the weak, additional co-ordination of at least one of the oxygen-donor atoms of the polyhydroxyalkyl chain located on carbon atom(s) having S configuration, taking Table 1 Protonation constants of aegaln and related diamine compounds (I = 0.1 mol dm23, NaClO4; T = 298 K) aegaln en hen pKd H2L pKd HL 6.43(1) 6.39 c 9.50(1) 9.48 c 7.10 a 7.12 d 9.70 a 9.96 d 6.60 b 9.59 b a From ref. 12 (I = 0.1 mol dm23, NaClO4). b From ref. 14 (I = 0.1 mol dm23, KNO3).c From ref. 2 (I = 0.1 mol dm23, NaCl). d From ref. 13 (I = 0.1 mol dm23, KNO3). Table 2 Overall stability constants and the visible absorption properties of the complex species formed in the copper(II)–aegaln system, calculated by the PSEQUAD computer program (I = 0.1 mol dm23, NaClO4; T = 298 K) Species log b lmax/nm emax/dm3 mol21 cm21 Cu(HL) CuL Cu2L2H22 Cu2L2H23 CuLH22 CuL(HL) CuL2 CuL2H21 13.63(2) 10.08(1) 10.67(1) 0.77(2) 26.28(1) 22.25(3) 17.21(1) 7.45(1) — 671 597 647 638 — 580 662 — 48 128 133 67 — 92 93J.Chem. Soc., Dalton Trans., 1997, Pages 2125–2130 2127 into account the shape of the spectrum 6,8 because of the lack of any optical activity in the en part of the ligand. Complexes between pH 5 and 8. The species distribution diagrams for the L :M = 1 : 1 and 3 : 1 systems at physiological pH (Fig. 1) show an equilibrium between two species depending on the metal-to-galactitol ratio. The species formed in equimolar solution could be characterised as CuLH21 or its oligomer (CuLH21)n.The process leading to this species can be explained in two ways: either by deprotonation (i ) of an alcoholic hydroxy group from the polyhydroxyalkyl chain or (ii ) of Fig. 1 Species distribution curves for the copper(II)–aegaln 1 : 1 (a) and 1:3 (b) systems calculated on the basis of the copper(II) contents of the individual species ([Cu21] = 0.01 mol dm23) a co-ordinated water molecule. The pKd value for an alcoholic hydroxy group is higher even in the presence of copper(II) ions when only this type of donor group is present in the ligand molecule,15 and copper(II) hydroxide precipitation is also expected.If an anchoring donor group is present in the molecule, and the ligand conformation allows the co-ordination of the alcoholic OH group, its deprotonation occurs in the region pH 5–7.6,8 However, the co-ordinated water molecule deprotonates in the same pH region (pKd ª 5–6) in the aqueous copper(II) solutions.16 Since pH-metric measurements alone cannot distinguish between these processes, spectroscopic Fig. 3 Circular dichroism curves detected in copper(II)–aegaln 1 : 1 (a) and 1 : 2 (b) systems as a function of pH: ([Cu21] = 0.005 mol dm23) Fig. 2 The EPR curves for copper(II)–aegaln 1 : 1.25 (a) and 1 : 2.5 systems (b) ([Cu21] = 0.005 mol dm23) systems as a function of pH2128 J. Chem. Soc., Dalton Trans., 1997, Pages 2125–2130 measurements are required to obtain additional information on the structure of the above complex.The dramatic decrease in the intensity of EPR spectra [Fig. 2(a)] between pH 5 and 7 indicates the formation of oligomeric copper(II) complex(es) having strong antiferromagnetic interactions between the adjacent copper(II) centres. The strong coupling suggests the formation of a dihydroxide- (or dialkoxide)-bridged dimer complex. The increase in the CD intensity associated with the d–d transition [see Fig. 3(a)] between pH 5 and 9 in equimolar solution is evidence in support of the deprotonation of alcoholic hydroxy group(s) in the oligomeric species. Thus the anchoring en residue effectively promotes deprotonation of an alcoholic OH group. In this complex the vicinal dissymmetry of the C(2) carbon atom determines the sign and the intensity of the Cotton effect observed. The presence of a charge-transfer (c.t.) absorption band at about 380 nm (Fig. 4), strongly indicates a dibridged dimeric structure in (CuLH21)n.This c.t. band disappears when the galactitol excess is increased to L :M = 2.4 : 1. It is characteristic for dibridged copper(II) complexes, when alkoxide, phenoxide, carboxylate or hydroxide oxygen-donor atoms serve as bridges,1,17–19 and was assigned to a copper(II)–oxygen– copper(II) charge-transfer transition.18,19 It is associated with CD bands of low intensity 18 when an optically active ligand coordinates [Fig. 3(a)]. Experimental results showed20 that the intensity of the above-mentioned charge transfer band is affected by the Cu]O]Cu angle, which also depends on the number of the chelate ring atoms containing the bridging oxygen.From literature data,20 we suggest the deprotonated C(2)]OH groups to be the bridges, in accord with the CD spectroscopic results (see Scheme 1). A number of di- and oligo-meric copper(II) complexes with similar ligands (short-chain diamines and mono- and di-aminoalcohols) were prepared and characterised by X-ray diffraction, 3,17 revealing copper(II) dimers with either hydroxide or alcoholic hydroxy oxygen bridging atoms.The formation of dimeric species has also been suggested with some related ligands in solution.1,18 Replacement of the monomeric species with dimeric Cu2L2H22 complexes in the computation of the pH-metric titration curves significantly improved the fit of the experimental data. The stability constant log Ko = log bM2L2(OH)2 2 2log bML 2 2log KW = 18.01(1) for the olation reaction (7) is higher than analogous constants for complexes 2ML 1 2OH M2L2(OH)2 (7) of N-alkyl-substituted en derivatives (log Ko ª 15), where hydroxo-bridged dimers definitely exist.21 This also suggests that the bridging donor groups are the alcoholic hydroxy groups rather than hydroxide ions (Scheme 1).In the systems containing an excess of galactitol a monomeric bis complex is formed instead of the dimer in the same Table 3 The EPR parametersa calculated for the individual complex species in the copper(II)–aegaln systems sM/mT Species g0 A0/mT A0(N)/mT nN 2��� 2��� ��� ��� CuL CuLH22 CuL2 CuL2H21 CuLH22 b 2.141 2.119 2.112 2.123 2.119 6.59 7.94 7.88 6.32 7.93 1.0 0.9 1.0 1.0 0.8 22432 4.9 4.1 8.9 4.2 4.4 3.4 2.8 4.8 2.9 3.0 2.4 1.9 2.8 2.0 2.1 1.6 1.3 1.5 1.4 1.5 a The g0 values are assumed to be accurate to 0.001, A0 values for copper(II) to 0.01 mT, A0 values for nitrogens to 0.05 mT, and the linewidth values to a maximum of 0.3 mT in the low magnetic field region; 1G = 1024 T.b Determined from the spectra of the solutions containing an excess of galactitol. pH region. If we compare the basicity-adjusted stability constantbH2L [28.80(2)] for reaction (8) ML 1 H2L ML2 1 2H (8) with that for the en complex (28.04),12 in contrast to the CuL species, the CuL2 complex of aegaln is less stable, due to the steric effect of the large polyhydroxyalkyl side chains.Such a steric effect has also been found in copper(II) complexes of Nalkyl- substituted en derivatives.13 The wavelength of the absorption maximum for the CuL2 complex formed in the presence of an excess of galactitol between pH 5 and 9 (580 nm, Table 2) is similar to that of the en bis complex (560 nm22), indicating the presence of four amino nitrogen-donor groups in the equatorial positions of the copper(II) ions. The small red shift suggests weak axial coordination of alcoholic hydroxy groups, but the large CD intensity [Fig. 3(b)], compared to that of the CuL complex, requires us to take into account the conformational contribution of the chelate rings, enforced by the steric interaction of the two ligands.23 The EPR parameters determined from the spectra recorded the presence of an excess of galactitol in solution at physiological pH are similar to those for copper(II) complexes with four amino nitrogen-donor atoms in equatorial co-ordination sites.24,25 The increased linewidths (Table 3), especially at lower magnetic fields, reflect the increased radius of the complex molecule compared to that formed in solutions with equimolar metal : ligand composition.Complexes above pH 8. In equimolar solution, first the Cu2L2H23 complex forms (Fig. 1) at increasing pH, still with antiferromagnetic coupling between the two metal ions. However, the charge-transfer band discussed above disappears, while an important red shift of the d–d transition can be observed (see Table 2), indicating that this further deprotonation process changes the geometrical arrangement around the copper(II) chromophores in the Cu2L2H23 complex.In case of an excess of galactitol deprotonation of the bis complex CuL2 give the CuL2H21 species was detected with a pKd value of 9.76(2). Increase of pH up to 10 causes a large red shift, approximately 90 nm, of the absorption maximum (Table 2) for this complex, which cannot be explained 22 only by axial co-ordination of a deprotonated alcoholic hydroxy group.Scheme 1 Structure proposed for the dimeric complex M2L2H22 H2N HN Cu O– O– Cu NH NH2 R R Fig. 4 Visible absorption spectra of the copper(II)–aegaln system as a function of the galactitol excess ([Cu21] = 0.01 mol dm23)J. Chem. Soc., Dalton Trans., 1997, Pages 2125–2130 2129 Rather it suggests a rearrangement of donor groups around copper(II) as seen later. The best fit to the experimental EPR spectrum recorded at pH 10.35 [Fig. 2(b)] was obtained by taking into account two coexisting major species. One is dominant at pH 7 and was assigned as the CuL2 species. The second can therefore be attributed to the CuL2H21 complex. The EPR parameters of the latter species (Table 3) indicated three nitrogen donor atoms in the equatorial plane of the copper(II) ion and a strong tetragonal distortion of the co-ordination sphere, which could also explain the red shift of the visible absorption maximum.Thus, in agreement with previous results, we suggest the rearrangement of the co-ordination sphere as follows: one of the ligands is co-ordinated by two amino and one deprotonated alcoholic hydroxy groups in equatorial positions, while one of the amino groups of the second ligand is displaced from an equatorial to axial position. The CD intensity at pH ª 10.3 is decreased in comparison with that of the CuL2 complex [Fig. 3(b)], suggesting that the vicinal dissymmetric effect through a deprotonated alcoholic hydroxy group became again the main contribution to the optical activity. On increasing the pH to 11.5 further deprotonation processes were detected and the spectroscopic results suggest the formation of the same CuLH22 species at any metal-to-ligand ratio studied.In this way, the displacement of the second ligand from the co-ordination sphere of copper(II), starting with the formation of CuL2H21, was found to be complete at this pH.The absorption maximum for the complex CuLH22 (638 nm, Table 2), formed either from Cu2L2H23 or CuL2H21, is consistent with values for copper(II) complexes with two amino and two deprotonated hydroxy groups in the equatorial plane (lmax,calc = 629 nm22). The EPR parameters of the CuLH22 species suggest a ligand-field energy increase, g0 is decreased and A0 is increased, compared to that of CuL. The formation of mixed hydroxo complexes results in a significant decrease in hyperfine coupling constants 25b (A0).Therefore our results suggest a metal-promoted deprotonation and co-ordination of the second alcoholic hydroxy group too, in the equatorial positions of the copper(II) in CuLH22. The patterns of the CD spectra further indicate deprotonation of the second alcoholic hydroxy group, which could be the C(4)]OH for steric reasons. Nickel(II) and zinc(II) complexes The potentiometric titration curves of the nickel(II)–aegaln 1 : 1 system can be fitted with the same set of species as that for the copper(II)-containing system, though there is no independent evidence for the presence of dinuclear species. Zinc(II) forms a hydroxide precipitate in equimolar solution.Apart from the shift of the complex-formation processes toward higher pH as compared to the copper(II) complexes, one can only observe differences in the behaviour of these metal ions when an excess of galactitol is applied: (i ) nickel(II) and zinc(II) formed ML3 besides the mono and bis complexes, while this complex was not detected with copper(II) even at a ten-fold galactitol excess; (ii ) in alkaline solutions ML2H22 species were also detected, in contrast to the copper(II)-containing systems.The stability constants calculated for the complexes formed with nickel(II) and zinc(II) are given in Table 4. The stability of the parent complexes follows the Irving–Williams order for the transitionmetal complexes.The log(KML/KML2) values, however, are significantly lower than the same value for the copper(II) complexes due to the relatively strong, supplementary axial coordination of the alcoholic hydroxy groups in ML2 species too, which is not favoured in the case of copper(II). The stability increase for both ML and ML2 compared to the complexes of diamine ligands containing no polyhydroxyalkyl chain is also shown by the basicity-adjusted stability constants. According to equations (6) and (8) these are 210.26, 29.37, 29.12(1) and 211.14, 210.57, 210.17(2) for the nickel(II) complexes of en,14 hen14 and aegaln, respectively. The same values for the zinc(II) complexes are 211.99,14 210.91,26 210.80(1) from equation (6) and 212.98,14 211.40,26 211.15(2) from equation (8).The existence of CD spectra provides evidence for alcoholic hydroxy group co-ordination in the nickel(II) complexes. The wavelengths of the absorption maxima are very similar to those predicted by Jörgensen’s rule of average environment.27 Both the UV/VIS and the CD spectra of the equimolar and the galactitol excess systems are different above pH 6 and they remain different until the end of the titration (pH 11.5) as a consequence of the formation of NiL2H22 species.Circular dichroism spectra of similar shape and intensity were observed by Yano and coworkers 28 for the ternary nickel(II) complexes with en and glycosylamine ligands (the latter derived from ketoses and ethanediamines), and crystal structure determination demonstrated the co-ordination of two alcoholic hydroxy groups.Carbon-13 NMR titration have been performed for the zinc- (II)–aegaln system as a function of pH at 3 : 1 galactitol to metal ratio. The results are shown in Fig. 5 together with the 13C NMR chemical shifts of the galactitol itself as a function of pH. In the presence of zinc(II) ions one set of eight signals was observed over the whole pH region, indicating that the com- Fig. 5 The 13C NMR chemical shifts of the aegaln carbon atoms in the absence (dotted line) and in the presence (full line) of zinc(II) ions as a function of pH ([Zn21] = 0.1 mol dm23, [aegaln] = 0.3 mol dm23) Table 4 Overall stability constants of the complex species formed in the nickel(II)– and zinc(II)–aegaln systems (I = 0.1 mol dm23, NaClO4; T = 298 K) log b Species M21 = Ni21 Zn21 MHL ML M2L2H22 M2L2H23 MLH22 ML2 ML3 ML2H21 ML2H22 11.79(1) 6.81(1) 21.37(1) 211.03(2) 212.31(1) 12.57(1) 14.77(2) 2.97(1) 28.40(2) 11.01(2) 5.13(1) 22.72(1) 211.91(2) 212.06(1) 9.91(1) 12.14(3) 0.86(1) 210.25(3)2130 J.Chem. Soc., Dalton Trans., 1997, Pages 2125.2130 plexes formed are in fast exchange with each other on the 13C NMR time-scale. The first significant shifts occurred in the region pH 6.8. The signals of C(19), C(29) and C(2) are most affected by the complex-formation processes (Fig. 5). According to the b effect,29 co-ordination of the primary and secondary amino groups is suggested in this pH region for the ZnL and ZnL2 parent complexes.This is in good agreement with the species distribution in this system (Fig. 6). Further increase of pH did not result in changes of the chemical shifts of the carbon signals of the en residue. Above pH 9 small but significant shifts can be observed in the C(2) and C(3) signals due to deprotonation processes (Fig. 5). This shows that one of the alcoholic hydroxy groups takes part in co-ordination either directly or through hydrogen bonding with a co-ordinated hydroxide ion.While the signals are sharp in this spectrum, above pH 11 severe broadening of the 13C NMR lines occurs which affects mostly the C(2) carbon. Owing to this the chemical shift cannot be determined with accuracy, but it suggests that deprotonation of the alcoholic hydroxy groups takes place only at strongly alkaline pH. Conclusion The compound aegaln proved to be an effective complexforming agent for copper(II) ions.The en-type chelate ring serves as an anchor for metal-promoted deprotonation of the alcoholic hydroxy groups in aegaln which results in the formation of a dialkoxide-bridged dimeric species in the equimolar systems. In the presence of an excess of galactitol, the bis-en type of co-ordination is favoured near pH 7. With increasing pH, however, metal-promoted deprotonation of alcoholic hydroxy group(s) also occurs in this system near pH 9.During this process the second ligand is successively displaced from the co-ordination sphere of copper(II). The formation of CuL2H21 and CuLH22 species in the alkaline pH region reflects that the polyhydroxyalkyl side chain effectively competes with the entype co-ordination even in the presence of an excess of galactitol. In nickel(II)- and zinc(II)-containing systems complexes of composition ML3 and ML2H22 have also been observed. The CD spectra showed that the nickel(II) complexes are optically active, indicating participation of the alcoholic hydroxy groups in the co-ordination; NMR spectroscopy revealed that these groups take part in co-ordination at pH �£ 9 for the zinc(II) complexes but their deprotonation occurs only above pH 11.Acknowledgements The authors gratefully acknowledge Dr. Robert Rajko for assistance in programming automatic potentiometric titration apparatus and Dr. Antal Rockenbauer and Dr. Laszlo Korecz for the EPR measurements.This work has been financially sup- Fig. 6 Species distribution curves for the zinc(II).aegaln 1 : 3 system calculated on the basis of the zinc(II) contents of the individual species ([Zn21] = 0.01 mol dm23) ported by the Hungarian National Science Foundation (OTKA F14439, OTKA T014867). References 1 M. Jezowska-Bojczuk, H. Kozlowski, S. Lamotte, P. Decock, A. Temeriusz, I. Zajaczkowski and J. Stepinski, J. Chem. Soc., Dalton Trans., 1995, 2657 and refs.therein. 2 H. Lammers, H. van Bekkum and J. A. Peters, Carbohydr. Res., 1996, 284, 159; H. Lammers, J. A. Peters and H. van Bekkum, Tetrahedron, 1994, 50, 8103. 3 W. F. Zeng, Ch. P. Cheng, S. M Wang, M.-Ch. Cheng, G.-H. Lee and Y. Wang, Inorg. Chem., 1995, 34, 728; T. Lindgren, R. Sillanpaa, K. Rissanen, L. K. Thompson, C. J. O¡�Connor, G. A. van Albada and J. Reedijk, Inorg. Chin. Acta, 1990, 171, 95. 4 T. Kiss, in Handbook on Metal.Ligand Interactions in Biological Fluids, ed.G. Berthon, Marcell Dekker, New York, 1990, vol. 1, p. 666. 5 I. Sovago, in Biocoordination Chemistry, ed. K. Burger, Ellis Horwood, London, 1990. 6 H. Kozlowski, P. Decock, I. Olivier, G. Micera, A. Pusino and L. D. Pettit, Carbohydr. Res., 1990, 197, 109 and refs. therein. 7 Th. Kradolfer and K. Hegetschweiler, Helv. Chim. Acta, 1992, 75, 2243; K. Hegetschweiler, V. Gramlich, M. Ghisletta and H. Samaras, Inorg. Chem., 1992, 31, 2341. 8 K. Burger, L. Nagy and B.Gyurcsik, J. Mol. Liq., 1995, 65/66, 213 and refs. therein. 9 E. Hogfeldt, in Stability Constants of Metal.Ion Complexes, Part A. Inorganic Ligands, Pergamon, New York, 1982, p. 32. 10 L. Zekany and I. Nagypal, in Computational Methods for the Determination of Formation Constants, ed. D. J. Leggett, Plenum, New York, 1991. 11 A. Rockenbauer and L. Korecz, Appl. Magn. Reson., 1996, 10, 29. 12 J. Maslowska and J. Szmich, Pol. J. Chem., 1984, 58, 675. 13 A. Avdeef, J. Zabronski and H.H. Stuting, Anal. Chem. (USA), 1983, 55, 298. 14 R. M. Smith and A. E. Martell, in Critical Stability Constants, Plenum, New York, 1975, vol. 2, p. 95. 15 S. J. Angyal, Carbohydr. Res., 1990, 200, 181. 16 Ch. F. Bates and R. E. Mesmer, in The Hydrolysis of Cations, Wiley, New York, 1976. 17 J. A. Bertrand, E. Fujita and D. G. VanDerveer, Inorg. Chem., 1980, 19, 2022; B. P. Murphy, Coord. Chem. Rev., 1993, 124, 63; S. P. Perlepes, J. C. Huffman, G. Christou and S. Paschalidou, Polyhedron, 1995, 14, 1073. 18 P. R. Bontchev, H. Kadum, B. Evtimova, Ch. Nachev, E. Yhecheva, D. Mehandjiev and D. Ivanov, J. Inorg. Biochem., 1992, 48, 153; T. Kiss, Cs. Simon and Zs. Vachter, J. Coord. Chem., 1987, 16, 225; I. Murase, M. Tanaka, Sh. Ueno, H. Okawa and S. Kida, Bull. Chem. Soc. Jpn., 1982, 55, 2404. 19 J. R. Watson, C. I. Shyr and C. Trapp, Inorg. Chem., 1968, 7, 469; K. D. Karlin, A. Farooq, J. C. Hayes, B. I. Cohen, T. M. Rowe, E. Sinn and J. Zubieta, Inorg. Chem., 1987, 26, 1271. 20 D. E. Lewis, W. E. Hatfield and D. J. Hodgson, Inorg. Chem., 1972, 11, 2216; S. J. Loeb, J. W. L. Martin and Ch. J. Willis, Inorg. Chem., 1979, 18, 3160. 21 R. Barbucci, L. Fabrizzi, P. Paoletti and A. Vacca, J. Chem. Soc., Dalton Trans., 1972, 740; C. Arcus, K. P. Fivizzani and S. F. Pavkovic, J. Inorg. Nucl. Chem., 1977, 39, 285. 22 E. J. Billo, Inorg. Nucl. Chem. Lett., 1974, 10, 613. 23 F. S. Richardson, Chem. Rev., 1979, 79, 17. 24 B. A. Goodman, D. B. McPhail and H. K. J. Powell, J. Chem. Soc., Dalton Trans., 1981, 822 and refs. therein. 25 (a) W. S. Kittl and B. M. Rode, J. Chem. Soc., Dalton Trans., 1983, 409; (b) T. Szabo-Planka, G. Peintler, A. Rockenbauer, M. Gyo¢©r, M. Varga-Faian, L. Institorisz and L. Balazspiri, J. Chem. Soc., Dalton Trans., 1989, 1925. 26 V. J. Thom, M. S. Shaikjee and R. D. Hancock, Inorg. Chem., 1986, 25, 2992. 27 C. K. Jorgensen, Acta Chem. Scand., 1956, 10, 887. 28 T. Tsubomura, S. Yano, K. Toriumi, T. Ito and S. Yoshikawa, Inorg. Chem., 1985, 24, 3218. 29 J. G. Batchelor, J. Feeny and G. C. K. Roberts, J. Magn. Reson., 1975, 20, 19. Received 30th January 1997; Paper 7/00

ISSN:1477-9226    

DOI:10.1039/a700701i

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2131–2137 2131 Pentanuclear copper(II) complexes with the novel 6-(phenylethynyl)-2- pyridonate ligand: synthesis, structures and magnetic properties Allan A. Doyle, Simon Parsons, Gregory A. Solan and Richard E. P. Winpenny* Department of Chemistry, The University of Edinburgh, West Mains Road, Edinburgh, UK EH9 3JJ Three pentanuclear copper(II) complexes, [Cu5(OMe)2(CF3CO2)(pehp)6(Cl)] 1, [Cu5(OMe)2(CF3CO2)(pehp)6- (NO3)] 2 and [Cu5(OH)(CF3CO2)3(pehp)6] 3, have been prepared via the solid-state reaction of hydrated copper(II) nitrate with the sodium salt of the novel ligand, 6-(phenylethynyl)-2-pyridone (Hpehp) in the presence of sodium trifluoroacetate. Crystal structural analysis at 220 K of 1–3 reveals capped-butterfly arrangements of the five copper atoms with the two shortest Cu ? ? ? Cu vectors in 1 and 2 [3.024(6)–3.050(3) Å] occurring between the caps and the wingtips while in 3 the wingtip–cap distances are more asymmetric with one short [3.042(7) Å] and one long [3.638(7) Å] Cu ? ? ? Cu vector.Mass spectroscopic studies of 1–3 show fragmentation patterns consistent with the observed structures, while magnetic studies of the complexes indicate antiferromagnetic exchange coupling within the Cu5 cores and S = ��� ground states for all compounds. The trifluoroacetate adduct of Hpehp, Hpehp?0.5CF3CO2H was synthesised in three steps from 2-bromo-6-benzyloxypyridine via 2-benzyloxy-6- (phenylethynyl)pyridine and the single crystal X-ray structure of Hpehp was also determined.The controlled synthesis of polymetallic complexes with specific magnetic properties continues to provide a motivation for research. The nature of the ligand is crucial in governing the nuclearity and arrangement of the resulting species,1–4 while substituents on a given ligand may play a more subtle but as significant a role in the way the cluster assembles.5–9 The 2-pyridonate family of ligands has been widely employed in recent years in co-ordination chemistry due in part to the variety of bonding modes possible.5 In particular, a range of polynuclear complexes are accessible by shrewd choice of 6- substituted-2-pyridonate. For example, the solid-state reactions of copper(II) nitrate with either 6-chloro-2-pyridonate (chp), 6-fluoro-2-pyridonate (fhp) or 6-methyl-2-pyridonate (mhp) gave respectively homoleptic dinuclear,6 tetranuclear7 or hexanuclear8 copper(II) species.In contrast, the combination of carboxylate and the 6-substituted-2-pyridonate [6-bromo-2- pyridonate (bhp), chp or mhp] ligands gave exclusively octanuclear copper(II) complexes.9 To investigate the factors that contribute to the nature of the polynuclear assembly we have sought to extend the range of substituents located at the six position on the pyridonate ring. Here we report the synthesis of the protonated phenylethynyl derivative, 6-(phenylethynyl)-2- pyridone (Hpehp), and the reaction of the sodium salt of its anion with hydrated copper(II) nitrate.Experimental Hydrated copper(II) nitrate, 2,6-dibromopyridine, 1,4,7,10,13, 16-hexaoxacyclooctadecane (18-crown-6), bis(triphenylphosphine) palladium dichloride, copper(I) iodide, phenylacetylene, diethylamine, trifluoroacetic acid and lanthanum nitrate hexahydrate were obtained from Aldrich. Solvents were used as obtained from suppliers. Hydrogen and 13C NMR spectra were recorded in CDCl3 at room temperature on a Bruker AM-250 MHz spectrometer.Mass spectra were obtained by fast-atom bombardment (FAB) of samples in a 3-nitrobenzyl alcohol matrix on a Kratos MS50 spectrometer. Infrared spectra were recorded on a Perkin-Elmer Paragon 1000 FT-IR spectrometer as Nujol mulls (KBr or NaCl plates) or as KBr discs. The EPR measurements were made at Q-band (ca. 34.2 GHz) using a Bruker ESP300E spectrometer fitted with an ER4118CF cryostat.Analytical data were obtained on a Perkin-Elmer 2400 elemental analyser by the University of Edinburgh microanalytical service. Preparation of compounds 6-(Phenylethynyl)-2-pyridone (Hpehp). The three-step synthesis of Hpehp from 1 was based on that reported for dipyridonylacetylene [(C5H4NO)CC(ONC5H4)] (see Scheme 1).10 (i) 2-Bromo-6-benzyloxypyridine. A mixture of 2,6- dibromopyridine (5.03 g, 21.2 mmol), benzyl alcohol (2.64 g, 24.4 mmol), potassium hydroxide (2.60 g, 46.4 mmol) and 18- crown-6 (0.24 g, 0.91 mmol, 4 mol%) in toluene (70 cm3) was heated under reflux, with a Dean–Stark apparatus, for 1 h.Scheme 1 Synthetic route for the formation of Hpehp?0.5CF3CO2H from 2,6-dibromopyridine N Br Br N Br PhCH2O N PhCH2O N O H 1 PhCH2OH KOH 18-crown-6 Toluene PhC CH CuI [PdCl2(PPh3)2] Et2NH CF3CO2H Hpehp •0.5CF3CO2H2132 J. Chem. Soc., Dalton Trans., 1997, Pages 2131–2137 After this time TLC [silica, cyclohexane–ethyl acetate (2 : 1)] indicated complete consumption of starting material.The reaction mixture was cooled and quenched by the addition of ice/ water (50 cm3). The layers were separated and the aqueous layer extracted into toluene (2 × 50 cm3). The combined organic layers were dried over Na2SO4, filtered and evaporated to dryness to give 2-bromo-6-benzyloxypyridine as an orange liquid (5.59 g, 99.9%). IR (KBr, thin film, cm21) 1587, 1554, 1496 and 1437. NMR: 1H, d 7.54–7.25 (m, 6 H), 7.08 (dd, JHH 7.5, JHH 0.6, 1 H), 6.75 (dd, JHH 8.2, JHH 0.6 Hz, 1 H), 5.37 (s, 2 H, PhCH2); 13C-{1H}, d 162.9 (s, C), 140.4 (s, CH), 138.3 (s, C), 136.4 (s, C), 128.3 (s, 2CH, Ph), 128.2 (s, 2CH, Ph), 127.9 (s, CH, Ph), 120.3 (s, CH), 109.6 (s, CH) and 68.3 (s, PhCH2). (ii) 2-Benzyloxy-6-phenylethynylpyridine.Copper(I) iodide (0.22 g, 1.16 mmol, 3 mol%) was added to a mixture of 2- bromo-6-benzyloxypyridine (10.08 g, 38.18 mmol), [PdCl2- (PPh3)2] (0.18 g, 1.15 mmol, 3 mol%) and phenylacetylene (4.29 g, 42.1 mmol, 1.1 equivalents) in diethylamine (120 cm3) under argon. The reaction mixture was allowed to stir at room temperature for 20 h after which time TLC [silica, hexane–ether (95:5)] indicated the absence of any starting material.The solvent was removed under reduced pressure and water (400 cm3) added to the residue. The mixture was extracted into toluene (3 × 400 cm3) and the combined organic layers dried over MgSO4, filtered and the solvent removed to afford a brown sticky solid.The crude product was subjected to flash chromatography [silica, hexane–ether (100 : 1–95 : 5)] to give 2-benzyloxy- 6-phenylethynylpyridine as a pale yellow solid. The solid was recrystallised from hexane to give pale yellow crystals (7.69 g, 70%). IR (KBr, cm21) 2208 [n(C]] ] C)], 1582, 1489, 1440. M.p. 70.4–72.4 8C. NMR: 1H, d 7.63–7.48 (m, 5 H), 7.48–7.33 (m, 6 H), 7.17 (d, JHH 7.1, 1 H), 6.78 [dd, JHH 8.6, JHH 0.8, Hz, 1 H], 5.44 (s, 2 H, PhCH2); 13C-{1H} (62.9 MHz), d 163.3 (s, C), 140.1 (s, C), 138.6 (s, CH), 136.9 (s, C), 131.9 (s, C), 128.7 (s, 2CH), 128.3 (s, CH), 128.2 (s, 2CH), 128.1 (s, 2CH), 127.8 (s, CH), 122.3 (s, C), 120.9 (s, CH), 111.2 (s, CH), 88.7 (s, C]] ] C), 88.5 (s, C]] ] C) and 67.8 (s, PhCH2).(iii) 6-(Phenylethynyl )-2-pyridone (Hpehp). A solution of 2- benzyloxy-6-phenylethynylpyridine (8.17 g, 28.7 mmol) in tri- fluoroacetic acid (120 cm3) was stirred at room temperature for 4 d. The trifluoroacetic acid was stripped off under reduced pressure and the residue treated with benzene (50 cm3) then re-evaporated.The residue was partitioned between 1 M sodium hydroxide solution (200 cm3) and ethyl acetate (200 cm3) and the layers separated. The aqueous layer was acidified to pH 1 by the addition of 6 M hydrochloride acid, then extracted into ethyl acetate (2 × 200 cm3). The combined organic layers were dried over MgSO4, filtered and the solvent removed to give a sticky brown solid.The crude product was then triturated with ether to give Hpehp?0.5CF3CO2H as an off-white solid (5.98 g, 83%). In general, Hpehp?0.5CF3CO2H was used in further reactions, but pure Hpehp could be obtained by recrystallisation from ethyl acetate (Found: C, 66.85; H, 3.75; N, 5.35. C13H9NO?0.5CF3CO2H requires C, 66.65; H, 3.75; N, 5.55%). IR (KBr disc, cm21) n(N]H)], 2213 [n(C]] ] O)], 1687 [n(C]] O)], 1654, 1600. M.p. 173–175 8C. NMR: 1H, d 12.35 (s, 1 H, NH), 7.58–7.51 (m, 2 H), 7.41–7.20 (m, 4 H), 6.62 [dd, JHH 9.2, JHH 0.8, 1 H], 6.48 [dd, JHH 6.8, JHH 0.6 Hz, 1 H]; 13C-{1H} (62.9 MHz), d 164.3 (s, C]] O), 140.1 (s, CH), 131.9 (s, 2CH, Ph), 129.5 (s, CH, Ph), 129.3 (s, C), 128.3 (s, 2CH, Ph), 121.0 (s, C, Ph), 120.7 (s, CH), 111.7 (s, CH), 94.6 (s, C]] ] C) and 81.9 (s, C]] ] C). [Cu5(OMe)2(CF3CO2)(pehp)6(Cl)] 1.Hydrated copper(II) nitrate (0.21 g, 0.87 mmol) and the sodium salt of Hpehp? 0.5CF3CO2H (0.50 g, 1.75 mmol, prepared by deprotonation of the adduct with 1.5 equivalents of NaOH in MeOH, followed by evaporation to dryness) were mixed intimately together as solids.The dark green paste formed was extracted into CH2Cl2 (100 cm3) and the resulting dark green solution was filtered. The filtrate was concentrated to 10 cm3 and methanol (10 cm3) was added to give green crystals of 1 (0.81 g, 55%) after 2–3 d (Found: C, 54.95: H, 3.35; N, 4.35. C82H54ClCu5F3- N6O10?1.5CH2Cl2?CH3OH requires C, 54.80; H, 3.25; N, 4.55%).IR (KBr disc, cm21) 2216 [n(C]] ] C)], 1676, 1589, 1560, 1492, 1261, 1203, 1027, 809, 754, 726 and 688. FAB-MS: significant peaks (m/z), possible assignments: 1625, [Cu5(OMe)(CF3CO2)- (pehp)6]; 1513, [Cu5(OMe)(pehp)6]; 1450, [Cu4(OMe)(pehp)6]; 1256, [Cu4(OMe)(pehp)5]; 1224, [Cu4(pehp)5]; 1030, [Cu4- (pehp)4]; 967, [Cu3(pehp)4]; 772, [Cu3(pehp)3]; 708, [Cu2(pehp)3]; 514, [Cu2(pehp)2]. [Cu5(OMe)2(CF3CO2)(pehp)6(NO3)] 2. Complex 2 was made using the procedure outlined for 1 but, after concentration of the filtrate, MeOH (10 cm3) containing an excess of La(NO3)3?6H2O was added to give green crystals of 2 (0.60 g, 40%) after 2–3 d (Found: C, 56.65; H, 2.95; N, 5.65.C82H54Cu5F3N7O13?1.5CH3OH requires C, 56.70; H, 3.40; N, 5.55%). IR (KBr disc, cm21) 2213 [n(C]] ] C)], 1671, 1589, 1546, 1289 [n(O2N]O)], 1202, 1022, 804, 760 and 717. FAB-MS: significant peaks (m/z) possible assignments: 1625, [Cu5- (OMe)(CF3CO2)(pehp)6]; 1593, [Cu5(pehp)6(CF3CO2)]; 1512, [Cu5(OMe)(pehp)6]; 1480, [Cu5(pehp)6]; 1339, [Cu4(pehp)5- (CF3CO2)]; 1256, [Cu4(OMe)(pehp)5]; 1224, [Cu4(pehp)5]; 1143, [Cu4(pehp)4(CF3CO2)]; 1030, [Cu4(pehp)4]; 967, [Cu3(pehp)4]; 772, [Cu3(pehp)4]; 708, [Cu2(pehp)3].[Cu5(OH)(CF3CO2)3(pehp)6] 3. The same procedure as used for 1 was followed, except that after concentration of the filtrate to 10 cm3 it was allowed to stand at room temperature for 3 w to give green plates of 3 (0.16 g, 10%) (Found: C, 59.90; H, 3.75; N, 4.55.C82H49Cu5F9N6O13?2.4Hpehp requires C, 59.80; H, 3.05; N, 5.10%). IR (KBr, cm21) 3250 [n(O]H)], 2217 [n(C]] ] C)], 1666, 1603, 1534, 1492, 1358, 1294, 1261, 1205, 1158, 802, 757, 690 and 557. FAB-MS: significant peaks (m/z), possible assignments: 1513, [Cu5(CF3CO2)2(pehp)5]; 1400, [Cu5- (CF3CO2)(pehp)5]; 1287, [Cu5(pehp)5]; 1224, [Cu4(pehp)5]; 1030, [Cu4(pehp)4]; 967, [Cu3(pehp)4]; 772, [Cu3(pehp)3]; 708, [Cu2(pehp)3]; 515, [Cu2(pehp)2]. Crystallography Crystal data and data collection and refinement parameters for Hpehp and 1–3 are given in Table 1; selected bond distances and angles in Tables 2–4.The structure of 1 Hpehp was performed on the free ligand, and not on the trifluoroacetate adduct. Data collection and processing. Data were collected using w–q scans on a Stoë Stadi-4 four-circle diffractometer equipped with an Oxford Cryosystems low-temperature device11 operating at 220.0(2) K, using Cu-Ka radiation for Hpehp, 1 and 3 and graphite-monochromated Mo-Ka radiation for 2.All data were corrected for Lorentz and polarisation effects.Data for 1–3 were corrected for absorption using y-scans. For 2 a lamina correction was used, based on 238 data, which gave Tmin and Tmax of 0.506 and 0.814 respectively. For 3 an ellipsoidal correction was used, based on 345 data, which gave Tmin and Tmax of 0.287 and 0.622 respectively. Structure analysis and refinement. Following data reduction all structures were solved by direct methods (SIR 9212 for Hpehp or SHELXS 8613 for 1–3) and refined by full-matrix least squares against F for Hpehp (CRYSTALS)14 and F2 for 1–3 (SHELXL).15 In Hpehp and 3 all non-hydrogen atoms were refined anisotropically, whereas in 1 and 2 only the full-weight atoms constituting the complex were so refined, the solvent of crystallisation being modelled isotropically. Hydrogen atoms were placed in calculated positions in all structures. In 3 there is a two-fold rotational disorder in two of the three CF3 groups;J. Chem.Soc., Dalton Trans., 1997, Pages 2131–2137 2133 Table 1 Experimental data for the X-ray diffraction studies of Hpehp and complexes 1–3 Compound Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 Crystal size/mm Crystal shape and colour Radiation m/mm21 Unique data Observed data Parameters Restraints Max. D/s ratio R1, wR2a (wR for Hpehp) Weighting scheme, w21 b Goodness of fit Largest residuals/e Å23 Hpehp C13H9NO 195.2 Monoclinic P21/n 5.887(4) 16.047(4) 10.697(3) 90 92.27(4) 90 1010 4 1.280 0.54 × 0.27 × 0.16 Colourless slab Cu-Ka 0.62 1314 1135 137 0 0.007 0.0468, 0.0602 Chebychev three-term polynomial 0.821 10.15, 20.16 1 C82H54ClCu5F3N6O10? CH4O?2CH2Cl2 1895.4 Monoclinic P21/n 19.317(14) 19.133(14) 24.03(2) 90 108.82(6) 90 8410 4 1.497 0.51 × 0.31 × 0.04 Green plate Cu-Ka 3.43 9561 4876 1046 113 20.048 0.0744, 0.1995 [s2(Fo 2) 1 (0.0871P)2] 1.006 10.621, 20.576 2 C82H54Cu5F3N7O13? 1.91CH4O?0.13H2O 1783.4 Triclinic P1� 12.021(8) 16.822(8) 23.058(17) 92.05(5) 94.95(7) 110.59(4) 4338 2 1.365 0.35 × 0.23 × 0.19 Green block Mo-Ka 1.28 11 950 7751 1032 72 20.019 0.0821, 0.2754 [s2(Fo 2) 1 (0.1215P)2 1 29.5P] 1.055 11.187, 20.857 3 C82H49Cu5F9N6O13? 3.7CH2Cl2 2153.2 Triclinic P1 13.299(4) 16.292(5) 22.808(7) 86.74(3) 89.85(2) 68.60(2) 4529 2 1.579 0.31 × 0.27 × 0.12 Green tablet Cu-Ka 4.02 13 287 7431 1126 66 0.028 0.0966, 0.2586 [s2(Fo 2) 1 (0.1599P)2] 0.953 11.242, 21.776 a R1 based on observed data, wR2 on all unique data.Refinement on F for Hpehp and F2 for 1–3. b P = ��� [max(Fo 2, 0) 1 2Fc 2]. these were refined with similarity restraints on the C]F distances and FCF angles, while the anisotropic displacement parameters of pairs of fluorine atoms either opposite one another or very close to one another were constrained to be equal. In addition to two molecules of ordered CH2Cl2 in the structure of 3 it was clear from DF maps that there were two more regions containing disordered CH2Cl2 molecules.These (amounting to 1.4 CH2Cl2 per formula unit) were treated in the manner described in reference 16. In 1 phenyl groups 1 and 3 are rotationally disordered about a common pivot atom [C(91) and C(93) respectively]. In ring 1 the geometry of the ring was restrained explicitly, with common isotropic thermal parameters for chemically equivalent atoms; ring 3 was restrained to have two-fold symmetry and independent isotropic thermal parameters refined for each atom.The CF3 groups in 1 and 2 were rotationally disordered and treated as described above for 3. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/492.Magnetic measurements Variable-temperature magnetic measurements on complexes 1– 3 in the region 1.8–300 K were made using a SQUID magnetometer (Quantum Design) with samples sealed in capsules. In all cases diamagnetic corrections for the sample holders were applied to the data. Diamagnetic corrections for the samples were determined from Pascal’s constants17 and literature values.18 Results and Discussion Synthesis and characterisation of 6-(phenylethynyl)-2-pyridone (Hpehp) The ligand, 6-(phenylethynyl)-2-pyridone (Hpehp) was synthesised in a three-step procedure (see Scheme 1).Firstly, treatment of 2,6-dibromopyridine with benzyl alcohol and potydroxide in toluene using 18-crown-6 as a phase-transfer catalyst19 gave the pyridine benzyl ether, 2-bromo-6- benzyloxypyridine in quantitative yield. Secondly, coupling of 2-bromo-6-benzyloxypyridine with phenylacetylene to give 2- benzyloxy-6-phenylethynylpyridine was achieved in high yield (70%) upon treatment with a catalytic amount of bis(triphenylphosphine) palladium dichloride–copper(I) iodide in diethylamine. 20 Thirdly, the benzyl protecting group was removed by treatment with trifluoroacetic acid using the procedure outlined by Marsh and Goodman,21 to give Hpehp?0.5CF3CO2H (83%). Pure Hpehp could be obtained by recrystallisation from ethyl acetate. A single crystal of Hpehp was the subject of an X-ray diffraction study at 220 K.Selected bond distances and angles are given in Table 2. Fig. 1 shows a view of four Hpehp molecules, two of which have self associated into dimers by hydrogen bonding through the NH hydrogens and the oxygen functionalities. The C(6)]O(6) bond length [1.252(2) Å] is consistent Table 2 Selected bond distances (Å) and angles (8) for Hpehp N(1)]C(2) N(1)]C(6) C(2)]C(3) C(2)]C(7) C(3)]C(4) C(4)]C(5) C(5)]C(6) C(6)]O(6) 1.367(3) 1.378(2) 1.362(3) 1.427(3) 1.412(3) 1.350(3) 1.427(3) 1.252(2) C(7)]C(8) C(8)]C(9) C(9)]C(10) C(9)]C(14) C(10)]C(11) C(11)]C(12) C(12)]C(13) C(13)]C(14) 1.199(3) 1.431(3) 1.395(3) 1.396(3) 1.380(3) 1.382(3) 1.367(3) 1.381(3) C(2)]N(1)]C(6) N(1)]C(2)]C(3) N(1)]C(2)]C(7) C(3)]C(2)]C(7) C(2)]C(3)]C(4) C(3)]C(4)]C(5) C(4)]C(5)]C(6) N(1)]C(6)]C(5) N(1)]C(6)]O(6) C(5)]C(6)]O(6) 123.7(2) 120.4(2) 115.1(2) 124.5(2) 117.9(2) 121.6(2) 120.8(2) 115.6(2) 119.6(2) 124.9(2) C(2)]C(7)]C(8) C(7)]C(8)]C(9) C(8)]C(9)]C(10) C(8)]C(9)]C(14) C(10)]C(9)]C(14) C(9)]C(10)]C(11) C(10)]C(11)]C(12) C(11)]C(12)]C(13) C(12)]C(13)]C(14) C(9)]C(14)]C(13) 175.3(2) 178.4(2) 120.8(2) 119.9(2) 119.3(2) 119.5(2) 120.9(2) 119.6(2) 120.9(6) 119.8(2)2134 J.Chem. Soc., Dalton Trans., 1997, Pages 2131–2137 with a double bond supporting the preference for the 2- pyridone over the 2-pyridinol tautomer. A similar tautomeric preference is observed in the solid-state structure of 5-chloro-2- pyridone22 while in the 6-halogeno-substituted derivatives, Hchp and Hbhp, the pyridinol tautomer is preferred.23 Fig. 1 also shows possible but very weak C–H ? ? ?C]] ] C hydrogen bonds between p-phenyl hydrogens of one molecule and the alkyne moiety of another [H(13b) ? ? ? C(8a) 3.094(3), H(13b) ? ? ? C(7a) 3.247(3) Å] which may be compared with the recently reported C]H? ? ?C]] ] C intermolecular contacts of 2.54 Å in DL-prop-2-ynylglycine.24 The packing of molecules within the crystal of Hpehp also resembles that in DL-prop-2- ynylglycine with co-operative C–H ? ? ?p interactions resulting in a zigzag arrangement of the dimeric 2-pyridone units.The infrared data supports the preference for the pyridone over pyridinol tautomer with a well defined n(NH) stretch occurring at 2932 cm21. In addition, IR reveals a n(C]] ] C) band at 2213 cm21 while the NH proton can be detected as a singlet at d 12.35 in the room temperature 1H NMR spectrum suggesting a strong hydrogen bond also exists in CDCl3 solution.Although pure Hpehp could be obtained from recrystallisation from ethyl acetate and was the subject of structural studies, reactions involving the trifluoroacetic acid adduct are reported below. Fig. 1 Association of four molecules of Hpehp in the crystal, also showing the numbering scheme adopted Fig. 2 Structure of 1 in the crystal showing the numbering scheme adopted Synthesis and characterisation of complexes 1–3 The sodium salt of the Hpehp?0.5CF3CO2H adduct was prepared by deprotonation with NaOH then mixed in a 2 : 1 ratio with hydrated copper(II) nitrate, and the two powders were ground together in a pestle and mortar.The resulting olive green paste was extracted with dichloromethane to give a dark green solution which was filtered to remove unreacted starting materials. The pentanuclear copper complexes 1–3 were crystallised as follows. The yields reported are for the crystalline material obtained. Selected bond distances and angles for all three structures are given in Tables 3 and 4.(i ) Addition of methanol to the dichloromethane solution: concentration of the dichloromethane solution and addition of an equal volume of methanol gave green plates in 55% yield after 2–3 d. A single crystal X-ray diffraction study at 220 K, showed a pentanuclear copper(II) complex of composition [Cu5(OMe)2(CF3CO2)(pehp)6(Cl)] 1, a view of which is shown in Fig. 2. (ii ) Addition of La(NO3)3?6H2O in methanol to the dichloromethane solution: concentration of the dichloromethane solution and addition of an equal volume of methanol containing an excess of La(NO3)3?6H2O gave green blocks after 2–3 d (40%).A single crystal X-ray diffraction study at 220 K, revealed a closely related pentanuclear copper(II) complex with composition [Cu5(OMe)2(CF3CO2)(pehp)6(NO3)] 2, a view of which is shown in Fig. 3. (iii ) Prolonged standing of a dichloromethane solution: concentration of the dichloromethane solution and prolonged standing (ca. 3 w) at room temperature gave green plates in 10% yield. A single crystal X-ray diffraction study at 220 K revealed a less symmetric pentanuclear copper(II) complex of composition [Cu5(OH)(CF3CO2)3(pehp)6] 3, which is shown in Fig. 4. The structures of 1–3 (Figs. 2–4) are related with each containing five copper atoms held together by a variety of bridging ligands in a capped butterfly arrangement (Fig. 5). In 1 and 2 this array has pseudo-two-fold symmetry with a noncrystallographic axis passing through Cu(4) and the mid-point of the Cu(1) ? ? ? Cu(5) vector.Complex 3 is less symmetric due to inequivalent cap–wingtip bridging ligands. The coordination numbers within the Cu5 cores are the same with two four-co-ordinate copper atoms occupying the wingtip sites [Cu(2), Cu(3)] and three five-co-ordinate copper atoms occupying the body and cap sites [Cu(1), Cu(5), Cu(4)]. The four-coordinate sites have a distorted-square-planar geometry, while the five-co-ordinate sites can be described as distorted trigonal Fig. 3 Structure of 2 in the crystal showing the numbering scheme adoptedJ. Chem. Soc., Dalton Trans., 1997, Pages 2131–2137 2135 bipyramidal with the axial sites being defined at Cu(1), by O(61) and O(62) [O(61)]Cu(1)]O(62) ca. 1678] and at Cu(5), by O(63) and O(65) [O(63)]Cu(5)]O(65) ca. 1698] and at the capping Cu(4), by O(1M) and O(2M) in 1 and 2 [O(1M)] Cu(4)]O(2M): 159.2(3) 1, 164.3(3)8 2] while at Cu(4) for 3 by O(1) and O(2B) [O(1)]Cu(4)]O(2B): 170.4(3)8].The co-ordination spheres of the copper centres in 1–3 are similar with each complex containing six deprotonated Hpehp molecules which bridge within the Cu5 core through the exocyclic oxygen and ring nitrogen atoms in three different ways: (i) 1,3-bridging one site on the body and a wingtip [Cu(5) ? ? ? Cu(3) and Cu(1) ? ? ? Cu(2)]; (ii ) 1,19,3-bridging across the body and to a wingtip [Cu(1) ? ? ? Cu(5) ? ? ? Cu(3) and Cu(1) ? ? ? Cu(5) ? ? ? Cu(2)]; (iii) 1,19,3-bridging the cap, a wingtip and one site on the body [Cu(4) ? ? ? Cu(3) ? ? ? Cu(1) and Cu(4) ? ? ? Cu(3) ? ? ? Cu(5)].To complete the co-ordination spheres in 1–3 a further four monoanionic ligands are required. In 1 and 2 there are two bridging methoxide groups [wingtip–cap; Cu(2) ? ? ? Cu(4), Cu(3) ? ? ? Cu(4)], one body-bridging trifluoroacetate [Cu(1) ? ? ? Cu(5)] and a terminally bound anion [Cl2 1 or NO3 2 2 on Cu(4)].The source of the terminal chloride anion for 1 is presumably the CH2Cl2 solvent as the moderate, and reproducible, yield of 1 indicates this cannot be due to an impurity. In 3 there is one bridging hydroxide group [Cu(3)]O(H)]Cu(4)] and three trifluoroacetate groups, which are body bridging [Cu(1) ? ? ? Cu(5)], one wingtip–cap bridging [Cu(2) ? ? ? Cu(4)] and one terminal [Cu(4)]. The Cu ? ? ? Cu distances within the complexes vary in a similar manner for both 1 and 2.The shortest Cu ? ? ? Cu contacts, 3.050(3) and 3.058(3) Å in 1 and 3.024(6) and 3.049(6) Å in 2, occur between the capping Cu site [Cu(4)] and the wingtip Cu atoms [Cu(2) and Cu(3)]. One pair of body–wingtip contacts [Cu(1) ? ? ? Cu(2) and Cu(3) ? ? ? Cu(5)] are intermediate, 3.178(3) and 3.148(3) in 1 and 3.148(6) and 3.197(6) Å in 2, and slightly shorter than the Cu(1) ? ? ? Cu(5) contacts of 3.194(3) and 3.235(6) Å in 1 and 2 respectively. The second pair of body– wingtip contacts [Cu(1) ? ? ? Cu(3) and Cu(2) ? ? ? Cu(5)] are longer in both complexes; in 1 the contacts are 4.461(4) and 4.400(4) Å respectively, and in 2 4.437(4) and 4.445(4) Å.This difference between the two pairs of body–wingtip contacts is a large distortion from an ideal tetrahedron, capped or otherwise. Within such a distorted metal array the description chosen is somewhat arbitary, however alternative descriptions of the polyhedron, e.g. as a pentagon, are much less satisfactory than the description based on a capped butterfly.For a regular pentagon the Cu ? ? ? Cu contacts should all be consistent, where here they vary from 3.050(3) to 3.194(3) Å in 1, and from Fig. 4 Structure of 3 in the crystal showing the numbering scheme adopted 3.024(4) to 3.235(6) Å in 2. More seriously, four of the five internal angles of the ‘pentagon’ are in the range 88–928 for structures 1 and 2, rather than close to 1088 as required for a pentagon.Finally in both structures the ‘pentagon’ is far from planar, with the Cu(1) ? ? ? Cu(5) vector at an angle of 368 to the mean plane of the other three Cu atoms within the cage. In 3 the capping site [Cu(4)] is bridged to the two wingtip sites in dissimilar ways. The Cu(3) ? ? ? Cu(4) vector is bridged by an hydroxide ligand and a m-O from pehp, and this distance is similar [3.042(7) Å] to the equivalent contacts in 1 and 2. The Cu(2) ? ? ? Cu(4) vector is bridged by a trifluoroacetate group and a m-O from pehp, and the contact of 3.638(7) Å is much longer.The remaining Cu ? ? ? Cu distances in 3 are very similar to equivalent contacts in 1 and 2. It is also noteworthy that the bridging hydroxide in 3 and the methoxide groups in 1 and 2 appear to exert the same structural requirements as exemplified both by the similar Cu(3) ? ? ? Cu(4) distances and the Cu(4)]O(R)]Cu(3) angles [R = Me, 106.9(3) 1 vs. R = Me, 106.4(3) 2 vs. R = H, 107.7(3)8 3].Intramolecular hydrogen-bond interactions also play roles in the structures of 1–3 which seem to be of two types namely, C]H? ? ? O and C]H? ? ?C]] ] C. In 3 a conventional hydrogenbond interaction exists between H(1) of the bridging hydroxide and O(2C) of the terminal trifluoroacetate on Cu(4) [H(1) ? ? ? O(2C) 1.969(4) Å] while more unusually there exist some short C]H? ? ?C]] ] C contacts between pehp groups in all the structures. In 3 the o-phenyl hydrogen H(141) has a contact with an alkyne moiety [H(141) ? ? ? C(85) 2.68; H(141) ? ? ? C(75) 2.61 Å] which is significantly shorter than the C]H? ? ?C]] ] C intermolecular distance in Hpehp [H(13b) ? ? ? C(8a) 3.09, H(13b) ? ? ? C(7a) 3.25 Å] but compares well with the reported value of 2.54 Å in DL-prop-2-ynylglycine.24 Therefore comparison of the structures of Hpehp and 3 suggests that the shortness of the contact in 3 is imposed by other structurally directing interactions, and is in itself unlikely to be of significance. Complexes 1–3 were, in addition, characterised by infrared and mass spectrometry and by elemental analysis.It has previously been observed that the pyridonate-bridged species, [Cu6Na(mhp)12][NO3] and [Cu8(O)2(O2CR)4(xhp)8] (where R = CH3, C6H5 or CF3 and xhp = 6-chloro-, 6-bromo- or 6- methyl-pyridonate) give clear FAB-MS results so it was hoped similar good quality mass spectroscopic data would be observed for the pentanuclear complexes. Indeed, the FAB mass spectra for 1–3 gave sensible fragmentation peaks although the parent-ion peaks themselves were not seen.For example, in 2 peaks are seen for both [Cu5(OMe)(CF3CO2)(pehp)6] (M1 2 OMe 2 NO3) and [Cu5(CF3CO2)(pehp)6] (M122 OMe 2 NO3), and a large number of polycopper fragments down to [Cu2(pehp)2]. A general observation for all the spectra is that the methoxide, trifluoroacetate and nitrate/chloride ligands tend to be lost first during the fragmentation to leave units of the general formula [Cux(pehp)y].The IR spectra of 1–3 were Fig. 5 ‘Capped-butterfly’ metal polyhedron in 1. The numbering of metal sites is common to 2 and 32136 J. Chem. Soc., Dalton Trans., 1997, Pages 2131–2137 Table 3 Selected bond distances (Å) for compounds 1–3 Compound 1 2 3 Compound 1 2 3 Cu(1) ? ? ? Cu(2) Cu(1) ? ? ? Cu(5) Cu(2) ? ? ? Cu(4) Cu(3) ? ? ? Cu(4) Cu(3) ? ? ? Cu(5) Cu(1)]O(61) Cu(1)]O(62) Cu(1)]O(63) Cu(1)]O(2A) Cu(1)]N(16) Cu(2)]N(12) Cu(2)]N(13) Cu(2)]O(66) Cu(2)]O(1B) Cu(2)]O(2M) Cu(3)]N(11) Cu(3)]N(15) 3.178(3) 3.194(3) 3.058(3) 3.050(3) 3.148(3) 1.924(7) 1.908(7) 2.271(8) 2.048(8) 2.000(9) 1.975(9) 1.971(9) 1.969(7) 1.890(7) 1.976(9) 1.971(9) 3.148(6) 3.235(6) 3.024(6) 3.049(6) 3.197(6) 1.937(6) 1.903(6) 2.351(7) 2.020(7) 2.031(8) 1.984(8) 1.996(8) 1.970(6) 1.895(7) 1.995(8) 1.958(8) 3.156(7) 3.259(7) 3.638(7) 3.042(7) 3.206(7) 1.932(6) 1.922(6) 2.370(6) 2.038(6) 1.999(7) 1.979(8) 1.979(7) 1.910(6) 2.007(7) 1.976(8) 1.960(8) Cu(3)]O(64) Cu(3)]O(1) Cu(3)]O(1M) Cu(4)]O(64) Cu(4)]O(66) Cu(4)]O(1) Cu(4)]O(1M) Cu(4)]O(2B) Cu(4)]O(2M) Cu(4)]O(1C) Cu(4)]Cl Cu(4)]O(1T) Cu(5)]O(61) Cu(5)]O(63) Cu(5)]O(65) Cu(5)]O(1A) Cu(5)]N(14) 1.971(7) 1.902(8) 2.131(7) 2.195(70 1.894(8) 1.920(8) 2.243(7) 2.263(7) 1.946(7) 1.911(8) 2.072(8) 2.016(8) 1.978(7) 1.900(7) 2.183(7) 2.067(7) 1.907(7) 1.929(6) 2.087(11) 2.337(6) 1.944(6) 1.902(6) 2.031(7) 2,017(8) 2.000(6) 1.879(6) 2.010(6) 2.249(6) 1.889(6) 1.949(6) 1.968(6) 2.418(6) 1.942(6) 1.875(7) 2.015(6) 2.020(8) Table 4 Selected bond angles (8) for compounds 1–3 Compound 1 2 3 Compound 1 2 3 O(62)]Cu(1)]O(61) O(62)]Cu(1)]N(16) O(61)]Cu(1)]N(16) O(62)]Cu(1)]O(2A) O(61)]Cu(1)]O(2A) N(16)]Cu(1)]O(2A) O(62)]Cu(1)]O(63) O(61)]Cu(1)]O(63) N(16)]Cu(1)]O(63) O(2A)]Cu(1)]O(63) O(2M)]Cu(2)]O(66) O(2M)]Cu(2)]N(13) O(66)]Cu(2)]N(13) O(2M)]Cu(2)]N(12) O(66)]Cu(2)]N(12) O(66)]Cu(2)]O(1B) N(12)]Cu(2)]O(1B) N(13)]Cu(2)]O(1B) N(13)]Cu(2)]N(12) O(1M)]Cu(3)]O(64) O(1M)]Cu(3)]N(15) O(64)]Cu(3)]N(15) O(1M)]Cu(3)]N(11) O(64)]Cu(3)]N(11) N(15)]Cu(3)]N(11) O(1)]Cu(3)]N(15) O(1)]Cu(3)]N(11) O(1)]Cu(3)]O(64) O(1M)]Cu(4)]O(2M) O(1M)]Cu(4)]O(64) O(2M)]Cu(4)]O(64) O(1M)]Cu(4)]O(66) O(2M)]Cu(4)]O(66) O(64)]Cu(4)]O(66) 166.7(3) 94.9(3) 94.8(3) 86.9(3) 92.2(3) 137.4(3) 90.4(3) 76.3(3) 129.7(3) 92.8(3) 80.9(3) 98.7(4) 147.3(4) 156.2(4) 93.5(3) 98.4(4) 78.6(3) 157.7(4) 96.2(3) 97.2(4) 146.7(3) 98.7(4) 159.2(3) 74.9(3) 94.2(3) 93.8(3) 74.6(3) 115.3(3) 165.8(3) 95.8(3) 94.1(3) 86.8(3) 92.5(3) 138.6(3) 89.9(3) 75.9(2) 128.3(3) 93.0(3) 79.0(3) 99.0(3) 145.8(3) 156.6(3) 95.9(3) 97.8(3) 79.4(3) 157.0(3) 96.5(3) 98.2(3) 147.9(3) 97.0(3) 164.3(3) 74.2(3) 96.6(3) 96.8(3) 75.8(3) 117.3(3) 168.9(3) 93.0(3) 94.9(3) 85.9(2) 91.1(2) 149.5(3) 89.4(2) 79.9(2) 122.1(2) 88.4(2) 154.5(3) 95.1(3) 93.6(3) 146.5(3) 91.6(3) 94.1(3) 93.5(3) 150.4(3) 98.7(3) 156.2(3) 100.0(3) 77.0(3) 99.5(2) O(1M)]Cu(4)]Cl O(2M)]Cu(4)]Cl O(64)]Cu(4)]Cl O(66)]Cu(4)]Cl O(1M)]Cu(4)]O(1T) O(2M)]Cu(4)]O(1T) O(66)]Cu(4)]O(1T) O(1T)]Cu(4)]O(64) O(1)]Cu(4)]O(2B) O(1)]Cu(4)]O(1C) O(2B)]Cu(4)]O(1C) O(1)]Cu(4)]O(64) O(2B)]Cu(4)]O(64) O(1C)]Cu(4)]O(64) O(1)]Cu(4)]O(66) O(2B)]Cu(4)]O(66) O(1C)]Cu(4)]O(66) O(65)]Cu(5)]O(63) O(65)]Cu(5)]N(14) O(63)]Cu(5)]N(14) O(65)]Cu(5)]O(1A) O(63)]Cu(5)]O(1A) N(14)–Cu(5)–O(1A) O(65)]Cu(5)]O(61) O(63)]Cu(5)]O(61) N(14)]Cu(5)]O(61) O(1A)]Cu(5)]O(61) Cu(4)]O(1M)]Cu(3) Cu(3)]O(1)]Cu(4) Cu(2)]O(2M)]Cu(4) Cu(1)]O(61)]Cu(5) Cu(5)]O(63)]Cu(1) Cu(3)]O(64)]Cu(4) Cu(2)]O(66)]Cu(4) 99.6(3) 100.9(3) 129.9(2) 114.7(2) 169.5(3) 94.3(3) 93.6(3) 85.3(3) 93.0(3) 140.4(3) 93.5(3) 76.1(3) 130.0(3) 89.4(3) 106.9(3) 106.8(4) 99.1(3) 98.1(3) 96.0(3) 94.4(3) 101.9(4) 91.7(3) 144.5(4) 96.8(4) 166.2(3) 96.1(3) 93.5(3) 86.5(3) 92.3(3) 140.7(3) 90.2(3) 76.1(2) 127.2(3) 91.9(3) 106.4(3) 104.5(3) 98.0(3) 97.3(3) 94.1(3) 97.0(3) 170.4(3) 98.1(3) 88.2(3) 76.6(3) 95.0(3) 159.9(3) 94.8(3) 91.1(2) 100.3(2) 172.2(3) 93.8(3) 92.0(3) 84.6(3) 92.8(3) 152.4(3) 94.1(3) 78.4(2) 121.1(2) 86.5(2) 107.7(3) 96.4(2) 97.7(3) 98.7(3) 121.8(3) also useful in identification with a number of clearly observable absorption bands.In addition to the alkyne stretch in the region 2113–2117 cm21 seen for all the complexes, the intramolecular H-bond in 3 results in a n(O]H) band at 3250 cm21 while in 2 a n(O2N]O) band occurs at 1289 cm21. While there are many structurally characterised pentanuclear CuI and mixed-valence CuII–CuI complexes in the literature25 there are fewer examples of discrete pentameric CuII species.26 Apart from [Cu5(bta)6(acac)4] (Hacac = pentane-2,4-dione, Hbta = benzotriazole)26b the structural motifs of the remaining CuII 5 are based on a square-planar tetrameric unit with the fifth CuII ion sitting in or above the plane.In [Cu5(bta)6(acac)4] a distorted-tetrahedral arrangement of four copper atoms has its fifth copper centre sitting in the centre of the tetrahedron. Therefore complexes 1–3 have a quite different metal polyhedron to any reported previously for CuII.Magnetic studies of complexes 1–3 The magnetic properties of complexes 1–3 were studied over the temperature range 1.8–300 K in an applied field of 1000 G (0.1 T) (Fig. 6). All three complexes behave in an essentially identical manner. At room temperature the value for the product cmT (where cm is the molar magnetic susceptibility) is between 1.6 and 2.0 cm3 K mol21, depending on sample.This value is consistent with, if slightly below, that calculated for five noninteracting copper(II) centres (for g = 2.1 a calculated value of cmT = 2.1 cm3 K mol21). As the temperature is lowered the value falls steadily, and for each sample reaches a low temper-J. Chem. Soc., Dalton Trans., 1997, Pages 2131–2137 2137 ature value consistent with an S = ��� ground state. The exchange coupling is therefore predominantly antiferromagnetic, and comparatively weak as the room temperature value for cmT indicates occupation of all possible spin levels.The low symmetry of the structures would require at least three exchange integrals to model the data properly. As such a model would inevitably involve correlation of the values for the various exchange terms we do not feel it is worth pursuing, especially as the spin of the ground state is low. The S = ��� ground state was confirmed by EPR measurements at 3.6–10 K and Q-band.These show for each sample a broad resonance near g = 2.15. For 2 this signal could be interpreted as due to an axial system with g values of 2.22 and 2.08. Warming the sample to 80 K rendered this signal broader and isotropic. For 3 EPR studies also indicated presence of an uncoupled monomeric impurity which gave a typical spectrum for an isolated CuII centre. Conclusion By introduction of the phenylethynyl group to the sixth position of the pyridonate ring the reactivity towards copper salts has been varied. While octanuclear species are generated on reaction of copper(II) nitrate with xhp (x = Br, Cl or Me) and carboxylates, the corresponding reaction with pehp results in exclusively pentanuclear complexes.This structural variation is probably due to the bulky phenylethynyl substituent in the 6- position of the pyridone. The formation of compound 1 by abstraction of chloride from CH2Cl2 was unexpected, and this reaction can be prevented by addition of a source of nitrate anions, to give 2.What is interesting is that the pentanuclear core is preserved, suggesting that the metal cage is formed in solution prior to crystallisation, and that substitution reactions might be possible at the terminal co-ordination site on Cu(4). Acknowledgements We thank the EPSRC for funding for a diffractometer, and the Leverhulme Trust for funding a post-doctoral fellowship (A. A. D.). We also thank the Royal Society of Edinburgh for Fig. 6 Plots of cm and cmT against T for 1.Similar behaviour is observed for 2 and 3. cm is shown as full squares; cmT is shown as open diamonds support (G. A. S.), and Drs. F. E. Mabbs and E. J. L. McInnes of the EPSRC c.w.e.p.r. centre at the University of Manchester for the Q-band spectra of 1–3. References 1 S. J. Lippard, Angew. Chem., Int. Ed. Engl., 1988, 27, 344. 2 A. Caneschi, A. Cornia, A. C. Fabretti and D. Gatteschi, Angew. Chem., Int. Ed.Engl., 1995, 34, 2862 and refs. therein. 3 A. K. Powell, S. L. Heath, D. Gatteschi, L. Pardi, R. Sessoli, R. Spina, F. Del Giallo and F. Pieralli, J. Am. Chem. Soc., 1995, 117, 2491. 4 E. Rentschler, D. Gatteschi, A. Cornia, A. C. Fabretti, A.-L. Barra, O. I. Shchegolikhina and A. A. Zhdanov, Inorg. Chem., 1996, 35, 4427 and refs. therein. 5 J. M. Rawson and R. E. P. Winpenny, Coord. Chem. Rev., 1995, 139, 313. 6 A. J. Blake, C. M. Grant, E. J. L. McInnes, F. E. Mabbs, P. E.Y. Milne, S. Parsons, J. M. Rawson and R. E. P. Winpenny, J. Chem. Soc., Dalton Trans., 1996, 4077. 7 A. J. Blake, C. M. Grant, S. Parsons and R. E. P. Winpenny, J. Chem. Soc., Dalton Trans., 1995, 1765. 8 A. J. Blake, R. O. Gould, P. E. Y. Milne and R. E. P. Winpenny, J. Chem. Soc., Chem. Commun., 1991, 1453. 9 A. J. Blake, C. M. Grant, S. Parsons, J. M. Rawson, D. Reed and R. E. P. Winpenny, J. Chem. Soc., Dalton Trans., 1995, 163. 10 Y. Ducharme and J. D. Wuest, J. Org. Chem., 1988, 53, 5788. 11 J. Cosier and A. M. Glazier, J. Appl. Crystallogr., 1986, 19, 105. 12 A. Altomare, M. C. Burla, M. Camelli, G. Cascarano, C. Giacovazzo, A. Guagliardi and G. Polidori, J. Appl. Crystallogr., 1994, 27, 435. 13 G. M. Sheldrick, SHELXS 86, program for crystal structure solution, Acta Crystallogr., Sect. A, 1990, 46, 467. 14 D. J. Watkin, J. R. Curruthers, C. K. Prout and P. W. Betteridge, CRYSTALS, ISSUE 10, Chemical Crystallography Laboratory, University of Oxford, 1996. 15 G. M. Sheldrick, SHELXL 93, program for crystal structure refinement, University of Göttingen, 1993. 16 P. van der Sluis and A. L. Spek, Acta Crystallogr., Sect. A., 1990, 46, 194. 17 C. J. O’Connor, Prog. Inorg. Chem., 1982, 29, 203. 18 Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Boca Raton, FL, 70th edn., 1990, p. E134. 19 A. J. Serio Duggan, E. J. J. Grabowski and W. K. Russ, Synthesis, 1980, 573. 20 K. Sonogasira, Y. Tohda and N. Hagihara, Tetrahedron Lett., 1975, 4467. 21 J. P. Marsh and L. Goodman, J. Org. Chem., 1965, 30, 2491. 22 A. Kvick, Acta Crystallogr., Sect. B, 1976, 32, 220. 23 A. Kvick and I. Olovsson, Ark. Khim., 1968, 30, 71; A. Kvick and S. S. Booles, Acta Crystallogr., Sect. B, 1972, 28, 3405. 24 T. Steiner, J. Chem. Soc., Chem. Commun., 1995, 95. 25 See for example, L. P. Wu, M. Yamamoto, T. Kuroda-Sowa, M. Maekawa, Y. Suenaga and M. Munakata, J. Chem. Soc., Dalton Trans., 1996, 2031; G. M. Kapteijn, I. C. M. Wehman-Ooyevaar, D. M. Grove, W. J. J. Smeets, A. L. Spek and G. van Koten, Angew. Chem., 1993, 32, 72; A. Eichhöfer, D. Fenske and W. Holstein, Angew. Chem., 1993, 32, 242. 26 (a) B. R. Gibney, D. P. Kesissoglou, J. W. Kampf and V. L. Pecoraro, Inorg. Chem., 1994, 33, 4840; (b) J. Handley, D. Collison, C. D. Garner, M. Helliwell, R. Docherty, J. R. Lawson and P. A. Tasker, Angew. Chem., 1993, 32, 1036; (c) S. Meenakumari and A. R. Chakravarty, J. Chem. Soc., Dalton Trans., 1992, 2305; (d ) B. Kurzak, E. Farkas, T. Glowiak and H. Kozlowski, J. Chem. Soc., Dalton Trans., 1991, 163; (e) E. Gojon, J. Gaillard, J.-M. Latour and J. Laugier, Inorg. Chem., 1987, 26, 2046. Received 6th January 1997; Pa

ISSN:1477-9226    

DOI:10.1039/a700107j

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 2139 Structural and bonding trends in osmium carbonyl cluster chemistry: metal–metal bond lengths and calculated strengths in the anions [Osx(CO)y]22, hydrides [Osx(CO)yHz] and hydride anions [Osx(CO)yHz]c2 * Andrew K. Hughes, Karen L. Peat and Ken Wade Department of Chemistry, University Science Laboratories, South Road, Durham, UK DH1 3LE The metal–metal bond distances [d(M]M)] in the known structurally characterised osmium carbonyl anions, [Osx(CO)y]22, neutral carbonyl hydrides, [Osx(CO)yHz] and carbonyl hydride anions, [Osx(CO)yHz]c2, have been used to calculate bond enthalpy terms E(Os]Os) using the relationship E(Os]Os) = 1.928 × 1013 [d(Os]Os)]24.6, itself derived from published structural and enthalpy data.Summation of the metal–metal bond enthalpy terms, to give the total metal–metal bond enthalpy, SE(Os]Os), has revealed the varying efficiency with which these compounds use their electrons for metal–metal bonding.There is a strong correlation between the total metal– metal bond enthalpy per metal atom, SE(Os]Os)/x, and the number of ligand electrons per metal atom, the data falling on a curve which includes bulk osmium metal and [Os(CO)5] at the extremes. Correlations are also noted between SE(Os]Os) and the number of skeletal electron pairs (polyhedral skeletal electron pair theory) or number of formal two-centre two-electron (2c2e) bonds (18-electron rule).These correlations show that the electrons are used more efficiently for metal–metal bonding in larger clusters with fewer ligands. Thus, the metal–metal bond enthalpy per electron pair available (using the 18-electron rule) increases as the cluster becomes larger, indicating the error in models based on assigning fixed energies to notional 2c2e Os]Os bonds. Trends in SE(Os]Os) were explored as Os(CO)4, Os(CO)3 or Os(CO)2 fragments are added to clusters in cluster build-up processes, as CO ligands are replaced by H2, and on oxidative addition of H2 to clusters, the latter leading to a prediction of limiting values of Os]H bond enthalpy terms. Trends in SE(Os]Os) were examined for series of closely related clusters, including those derivable from [Os4(CO)14] by replacing CO by H2 or H2, and a series of clusters derived from [Os6(CO)18].The sum SE(Os]Os) is shown to be a single parameter which quantifies the overall effect of small changes in metal–metal distances in osmium carbonyl clusters.In a recent paper 1 we showed how one could assess the relative stabilities of neutral osmium carbonyl clusters, Osx(CO)y, from their structures. Our approach assigned bond enthalpies, E(Os]Os), to the individual pairwise (though not necessarily electron pairwise) metal–metal bonding interactions they contained. These bond enthalpies were calculated from the respective bond lengths, d(Os]Os), using the relationship (1) where E(Os]Os) = 1.928 × 1013 [d(Os]Os)]24.6 (1) E(Os]Os) is measured in kJ mol21 when d(Os]Os) is measured in picometres.This relationship, and related ones of the same type (E = Ad24.6) for other metals, had been derived earlier 2 from published structural and thermochemical data on metals of the iron and cobalt sub-groups and had been shown to allow realistic estimates to be made of the strength of attachment, E(M]CO), of the carbonyl ligands to clusters Mx(CO)y of these elements.We found that E(M]CO) increased slightly, but consistently, as the cluster nuclearity x increased, and as the proportion of ligand molecules to metal atoms, y/x, decreased. Here, we explore the value of using equation (1) to probe stability relationships within a wider series of osmium carbonyl clusters, including carbonyl anions, [Osx(CO)y]c2, neutral osmium carbonyl hydrides, [Osx(CO)yHz], and osmium carbonyl hydride anions, [Osx(CO)yHz]c2. By focusing on the total metal– metal bond enthalpy, SE(Os]Os), we show how efficiently such clusters make use of the electrons that are in principle available for metal–metal bonding in these systems.They fall on a con- * Supplementary data available (No. SUP 57248, 12 pp.): Os]Os bond lengths and bond enthalpies. See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. tinuum extending from the mononuclear complex [Os(CO)5] at one extreme (no metal–metal bonding) to the bulk metal at the other extreme (only metal–metal bonding).We also show the relative efficiencies with which Os(CO)4, Os(CO)3 and Os(CO)2 units use for metal–metal bonding purposes the electrons and orbitals available to them for cluster formation, estimate the strength of attachment to these clusters of hydride ligands, and note their influence on metal–metal bonding. It should be stressed that the basis of our approach is that the metal–metal bonds in osmium carbonyl clusters resemble those in the bulk metal sufficiently to permit use of the same bond length–bond enthalpy relationship [equation (1)].The metal– metal bonds in question are relatively weak, much weaker than the metal–ligand bonds, which is why adsorption of ligands such as carbon monoxide molecules on metal surfaces can cause drastic rearrangement of the metal surface atoms.3 Being weak, the metal–metal bonds may be influenced by the bonding requirements of the ligands, and we illustrate that here.However, despite the relative softness of the metal–metal bonding potential-energy well, we consider the use of the bond length– bond enthalpy relationship (1) to be justified, particularly because we focus on the total bond enthalpy, SE(Os]Os), rather than attempt to interpret in detail the lengths and strengths of individual bonds. We are encouraged to use this approach because of the reliability of such relationships elsewhere in chemistry,†,4 and in particular because of their evident superiority in cluster chemistry over energies assigned to notional single (two centre two electron, 2c2e), double (2c4e) or triple (2c6e) † We are aware of at least one case where longer bonds are associated with greater metal–ligand binding energies, although these energies were determined in a co-ordinating solvent.52140 J.Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 Fig. 1 Structures of the osmium carbonyl clusters discussed in this work. The following symbols are used: j = Os(CO)4; m = Os(CO)3; y = Os(CO)2; d = Os(CO).Hydride and bridging carbonyl ligands are drawn explicitly n n s s s s s s z s s z s s z z CO OC s s s s s s z z z s s n H H n s n H H s s H H H H s s s n H H s s s s s s H H n s s n H CO s s H s s OC s s H H H s s s s s H s s s s s s s s H s s s s s s z z z H n n n n n n n s s s s s s n s n s n n s n n s s s n CO s n n n n s s s n s s s s H s z n n H s s s s n H H s z s s s H s s n H s s s s H H s s s z z s z s z z OC z s CO s z z z s z s z z z z z z z z l l l l s s H H s s s s s s z z z l l l [Os2(CO)8]2– [Os17(CO)36]2– [Os20(CO)40]2– [Os3H(m-H)(CO)11] [Os4(m-H)4(CO)12] [Os5(m-H)2(CO)16] [Os6(m-H)2(CO)18] [Os8(CO)22]2– s l l s [[Os3(m-H)2(CO)10] [Os9(CO)24]2– [Os4(m-H)2(CO)13] [Os6(CO)18]2– [Os10(CO)26]2– [Os6H(m-H)(CO)19] [Os7(m3-H)2(CO)20] [Os7(m-H)2(CO)21] [Os7(m-H)2(CO)22] [Os3(m-H)(CO)11]– [Os4(m-H)(CO)13]– s z z z s z z [Os10(m-H)4(CO)24]2– [Os9(m3-H)(CO)24]– [Os4(m-H)3(CO)12]– [Os4(m-H)2(CO)12]2– H H H H s z s [Os8(m-H)(CO)22]– [Os6(m3-H)(CO)18]– [Os5(m-H)(CO)15]– [Os4(CO)14] s s l [Os5(CO)19] s s s s n H z zH [Os5(CO)18] s s s s z s z s H [Os4(CO)16] [Os6(CO)18] n s s n s n [Os3(CO)12] [Os7(CO)21] [Os4(CO)15] [Os5(CO)16] s s s s s s s [Os6(CO)17{P(OMe)3}4] '[Os6(CO)21]' bonds, which still have some value elsewhere, e.g.for simple organic systems. Attempts have been made in the past to rationalise the bonding in metal clusters in terms of 2c2e metal– metal bonds of defined energy,6 even though such electron-pairbased bond enthalpy terms are of negligible value for dealing with bulk metals (where bonding contacts greatly exceed the numbers of bond pairs available) and of very limited value for describing the bonding in metal clusters, as we shall show.Our approach allows us to show how variable is the metal–metal bond enthalpy per metal–metal bond pair [which in turn has to be calculated using the 18-electron rule or the polyhedral skeletal electron pair theory (PSEPT)], and so by implication how unreliable are bond-energy approaches that assume the enthalpy per bond pair to be constant.Results and Discussion Before embarking on a discussion of the likely strengths of the metal–metal bonds in these clusters, it is worthwhile noting the patterns to which their shapes conform. Although the shapes themselves have been documented in recent structural compilations, 7 and reviews of osmium8 and cluster chemistry,9 and the patterns defined by sets of osmium carbonyl clusters, e.g.those based on an octahedral Os6 unit or fragment thereof, are now familiar figures in textbooks,10 we are not aware of any recent surveys that explore all of the structural relationships that underpin the skeletal shapes in Fig. 1. Three main ways of predicting or rationalising the shapes of metal clusters in general, and osmium carbonyl clusters in particular, have been explored.One, the treatment of metal clusters as fragments of the bulk metal,11 has evident merit for several of the clusters illustrated in Fig. 1, e.g. most of the carbonyl anions, [Osx(CO)y]22, and several of the carbonyl hydrides, [Osx(CO)yHz]c2, can be seen as fragments of a close-packed metal lattice, although it is exceedingly difficult to estimate the ligand-bonding capacity of the metal atoms on the fragment surfaces. A second approach is to assume that each metal atom obeys the 18-electron rule, i.e.that it uses all nine valence-shell orbitals either to bond ligands, to accommodate lone-pair electrons, or to participate in two-centre two-electron metal–metal bonds. This approach works well for small clusters such as [Os2(CO)8]22, [Os3(CO)12], [Os4(CO)14], [Os4(CO)15] and [Os4- (CO)16], indeed for rationalising the metal networks in most of the neutral carbonyls in Fig. 1, but has limited use for certain important species such as [Os6(CO)18]22, for which there is an electron pair too many to explain the 12 edges of the octahedron as 2c2e bonds.Drawing a localised bond structure in the case of even relatively simple clusters, such as [Os4(CO)14], requires the use of dative bonds. Several resonance structures are possible and these dative bonds do not correlate well with the longer bond lengths in such clusters. The 18-electron rule approach to cluster-electron counting is not readily able to predict cluster geometries, in contrast to the third method described below.Nevertheless, we indicate the numbers of 2c2e Os]Os bonds required by the 18-electron rule approach in Tables 1–4 below. The third method of treating the bonding in osmium carbonyl and similar metal clusters, PSEPT,12 exploits the analogy with borane clusters.13 This too assumes that each metal atom uses all nine valence-shell atomic orbitals, six for bonding to carbonyl ligands or accommodating lone-pair electrons, the remaining three orbitals being available for metal– metal bonding use.This approach allows many structures to be rationalised or even predicted, including some important systems that appear anomalous in localised bond terms, like the octahedral [Os6(CO)18]22 (and related clusters) referred to above. However PSEPT classifies as skeletal electron pairs some electrons that contribute little or not at all to the actual metal– metal bonding, even though the presence of these (lone-pair) electrons does influence the molecular shape.In our discussion of metal–metal bond energies below we draw attention to some of these features, and analyse the effectiveness with which the available electrons, counted by each of these latter two schemes, are used for metal–metal bonding. Since the important parameters we wish to consider in this discussion, apart from the metal–metal bond distances, are the polyhedral shapes of these metal carbonyl clusters, the numbersJ.Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 2141 Table 1 Neutral binary osmium carbonyls, [Osx(CO)y], studied, with electron numbers, structural types and metal–metal bond energies a Formula [Os4(CO)16] [Os3(CO)12] [Os5(CO)19] [Os4(CO)15] [Os5(CO)18] ‘Os6(CO)21’ b [Os4(CO)14] [Os5(CO)16] [Os6(CO)18] [Os7(CO)21] 2y/x 8.0 8.0 7.6 7.5 7.2 7.0 7.0 6.4 6.0 6.0 PSEPT type (Sp) hypho (8) arachno (6) hypho (9) arachno (7) arachno (8) arachno (9) nido (6) closo (6) capped closo (6) capped closo (7) S1b 4 3 6 5 7 9 6 9 12 14 c SE(Os]Os) 349 283 543 464 690 860 608 955 1290 1526 SE(Os]Os)/x 87 94 109 116 138 143 152 191 215 218 SE(Os]Os)/S1b 87 94 91 93 99 96 101 106 108 109 SE(Os]Os)/Sp 44 47 60 66 86 96 101 159 215 218 a All thermodynamic data in kJ mol21. b Structurally characterised as the phosphite-substituted cluster, [Os6(CO)17{P(OMe)3}4]. c This compound has 15 polyhedron edges, but only 14 electron pairs in the localised-bond model.Table 2 Osmium carbonyl anions [Osx(CO)y] c2 studied, with electron numbers, structural types and metal–metal bond energies a Formula [Os2(CO)8]22 [Os6(CO)18]22 [Os8(CO)22]22 [Os9(CO)24]22 [Os10(CO)26]22 [Os17(CO)36]22 [Os20(CO)40]22 (2y 1 c)/x 9 6.33 5.75 5.56 5.4 4.35 4.1 PSEPT type (Sp) arachno (5) closo (7) Bicapped closo (7) Tricapped closo (7) Capped tricapped closo (7) c c S1b 1 11 17 20 23 48 59 SE(Os]Os) 78 1205b 1943 2314 2603 6011 7108 SE(Os]Os)/x 39.3 201 243 257 260 354 355 SE(Os]Os)/S1b 78 110 114 116 113 125 120 SE(Os]Os)/Sp 16 172 278 331 372 a All thermodynamic data in kJ mol21.b For the 2[Mo4(h-C5H4Pri)4S4]1 salt form 1. For the 2[PMePh3]1 salt, SE(Os]Os) = 1217 kJ mol21. For the 2[Mo4(h-C5H4Pri)4S4]1 salt form 2, SE(Os]Os) = 1201 kJ mol21. c Contains some metal atoms that clearly use more than three AOs for skeletal bonding so are beyond the scope of simple PSEPT. Table 3 Neutral osmium carbonyl hydrides [Osx(CO)yHz] studied, with electron numbers, structural types and metal–metal bond energies a Formula [Os3H(m-H)(CO)11] [Os3(m-H)2(CO)10] [Os4(m-H)4(CO)12] [Os4(m-H)2(CO)13] [Os5(m-H)2(CO)16] [Os6H(m-H)(CO)19] [Os7(m-H)2(CO)22] [Os6(m-H)2(CO)18] [Os7(m-H)2(CO)21] [Os7(m3-H)2(CO)20] (2y 1 z)/x 8 7.33 7 7 6.8 6.67 6.57 6.33 6.29 6 PSEPT type (Sp) arachno (6) nido (5) nido (6) nido (6) Edge-bridged tetrahedron (7) Spiked TBPY (8) d Spiked TBPY (9) Capped nido (7) Edge-bridged capped nido (8) Edge-bridged capped closo (7) S1b 3 4 6 6 8 10 12 11 13 14 SE(Os]Os) 266 339b 536 596 c 763 1005 1179 1114 1300 1430 SE(Os]Os)/x 89 113 134 149 153 167.5 168 186 186 204 SE(Os]Os)/S1b 89 85 89 99 95 100.5 98 101 100 102 SE(Os]Os)/Sp 44 68 89 99 109 126 131 159 162.5 204 a All thermodynamic data in kJ mol21.b For the structure of the pure cluster; SE(Os]Os) = 344 kJ mol21 for 0.5 molecule of this cluster cocrystallised with [Os3Ni(CO)9(h-C5H5)H3]. c For one molecule in the asymmetric unit; the other has SE(Os]Os) = 591 kJ mol21.d TBPY = Trigonal bipyramid. of bonding contacts (polyhedron edge lengths) therein, and the numbers and distribution of the carbonyl ligands, it is helpful to illustrate their structures in a manner that shows where the ligands are. Fig. 1 shows the structures of the osmium carbonyl clusters discussed here in a way that draws attention to the polyhedral shape defined by the metal atoms, the number of terminal carbonyl ligands attached to each, and the locations of bridging carbonyl ligands and hydrides.The clusters are arranged within Fig. 1 according to cluster type (binary carbonyl, carbonyl anion, carbonyl hydride, carbonyl hydride anion) and by increasing cluster nuclearity. Although the neutral carbonyls were the subject of our previous paper,1 for completeness, and to allow a wider range of comparisons to be made, we include them in the discussion in the current paper. Additionally, the parent binary carbonyl, [Os(CO)5], and the raft-cluster [Os6(CO)21] are included in several aspects of the discussion in this paper, although the former has not been characterised by diffraction methods in the solid state,14 and clearly contains no Os]Os bonding, and the Os6 raft has only been structurally characterised as the phosphite derivative, [Os6- (CO)17{P(OMe)3}4].15 Details of the steric and electronic influence of phosphite, phosphine and other ligands on the metal–metal bond enthalpy will be discussed subsequently.16 All of these clusters have been structurally characterised by diffraction techniques, the majority using X-ray diffraction, so that the hydrogen atoms have only rarely been located directly.Their positions have generally been determined by potential-energy calculations,17,18 often using NMR evidence to confirm these positions. As an example, in the initial publication of the structure of [Os6H2(CO)18] it was suggested (mainly on the basis of NMR evidence) that there was one m-H ligand and one m3- or m4-H ligand,19,20 whilst potential-energy calculations17 suggested that both ligands are in the m-H sites shown in Fig. 1. The structural differences between [Os6(CO)18]22 and [Os6H2(CO)18], and the electronic origin of these differences, are discussed below. We indicate in tabular form (Tables 1–4) the total metal– metal bond enthalpies, SE(Os]Os), calculated for these clusters using equation (1), including as before, all first-co-ordinationsphere contacts and cross-polyhedral distances <421 pm.The limit of 421 pm was chosen, as before,1 in order to include cross-octahedron distances as in [Os6(CO)18]22, and equivalent distances in fragments of octahedra, e.g. across the square face of [Os6H2(CO)18], whilst excluding longer cross-polyhedra distances, such as the apex–apex distance in the trigonal bipyramid [Os5(CO)15H]2. Cross-octahedron distances are included since these are equivalent to the next-nearest neighbour distances of2142 J.Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 Table 4 Osmium carbonyl hydride anions, [Osx(CO)yHz]c2, studied, with electron numbers, structural types and metal–metal bond energies a Formula [Os3(m-H)(CO)11]2 [Os4(m-H)3(CO)12]2 [Os4(m-H)2(CO)12]22 [Os4(m-H)(CO)13]2 [Os5(m-H)(CO)15]2 [Os6(m3-H)(CO)18]2 [Os8(m-H)(CO)22]2 [Os9(m3-H)(CO)24]2 [Os10(m-H)4(CO)24]22 (2y1z1c)/x 8 7 7 7 6.4 6.33 5.75 5.56 5.4 PSEPT type (Sp) arachno (6) nido (6) nido (6) nido (6) closo (6) closo (7) (7) Tricapped closo (7) Tetracapped closo (7) S1b 3 6 6 6 9 11 17 20 23 SE(Os]Os) 299 575b 600 614 935 1161 c 1864d 2178 2513 SE(Os]Os)/x 100 144 150 153.5 187 193.5 233 242 251 SE(Os]Os)/S1b 100 96 100 102 104 105 110 109 109 SE(Os]Os)/Sp 50 96 100 102 156 166 266 311 359 a All thermodynamic data in kJ mol21.b For [NMe4]1 salt; SE(Os]Os) = 567 kJ mol21 for [Ph2PNPPh2]1 salt. c For [Ph2PNPPh2]1 salt; SE(Os]Os) = 1158 kJ mol21 for [NBu4]1 salt.d For [PMePh3]1 salt; SE(Os]Os) = 1871 kJ mol21 for [Ph2PNPPh2]1 salt. The structure consists of a tetrahedron sharing an edge of the monocapped closo six-vertex structure. the body-centred cubic lattice, which were included in deriving equation (1). In order clearly to illustrate some of the trends which this paper explores, the clusters are listed in each table in order of increasing number of ligand electrons per metal atom {the fraction (2y 1 z 1 c)/x for the general formula [Osx- (CO)yHz]c2}; for clusters with the same number of ligand electrons per metal atom the total metal–metal bond enthalpy per metal atom is used to decide the order in which they are listed.The tables also show PSEPT structural type and number of skeletal electron pairs (Sp), and also the number of electronpair bonds according to a localised [18-electron or effective atomic number (EAN)] bond model (S1b), and show the total metal–metal bond enthalpy per osmium, per localised electronpair bond and per PSEPT electron pair.Tables 1–4 indicate, by footnotes, several cases where the same cluster has been crystallographically characterised more than once, either with differing cations or a second molecule such as a solvent cocrystallised. There are also clusters with more than one molecule in the asymmetric unit or the same molecular formula crystallises in more than one polymorph. The range of SE(Os]Os) values for the same cluster is a representation of the potential error in SE(Os]Os) and derived thermodynamic quantities.21 The SE(Os]Os) data included in the tables as footnotes differ from the values in the main body of the tables by between 0.25 and 1.5% or 3 to 12 kJ mol21, suggesting that 2% can be taken as a likely crystallographic contribution to the error limit for the data in Tables 5–12.Tables 1–4 also contain cases where multiple structural determinations have been published of the same compound.These entries appear only once, the data being taken from the most recent or most accurate determination as referenced in the Experimental section. In our previous publication we used our calculations of the metal–metal bond enthalpies for neutral binary osmium carbonyl clusters, together with the experimentally determined enthalpy of formation of [Os3(CO)12], to determine the Os–CO bond enthalpy of these neutral clusters, and hence the enthalpies of disruption [to Os(g) and CO(g)] and gas-phase standard enthalpies of formation (from the elements in their standard states) of all the known crystallographically characterised binary osmium carbonyls, Osx(CO)y.Such data are clearly of relevance to cluster-interconversion reactions, and we have previously explored some examples. The calculation of enthalpies of disruption and formation of the wider range of osmium clusters discussed in this work would require knowledge of bond enthalpy terms for terminal, m- and m3-Os]H bonds, as well as the electron affinities of osmium carbonyl clusters.Reliable data are not available for these terms, and so we have chosen to investigate the usefulness of the total metal–metal bond enthalpy, SE(Os]Os), in exploring trends within these osmium carbonyl clusters, the thermodynamics of cluster interconversion reactions, and the implication of SE(Os]Os) for possible values of Os]H bond enthalpy terms. The thermodynamics of reactions involving CO and H2 at metal clusters and on metal surfaces are of fundamental importance in catalysis,22 and there is a need for consistent values for bond enthalpies and bond-dissociation enthalpies of M]CO and M]H bonds,23 as well as for other important moieties including surface and core carbide (MC), methylene (M]] CH2) and formyl [M]C(O)H] for a range of metals.Trends in ”E(Os]Os) as a function of the number of metal atoms and ligand electrons In our earlier publication on the neutral binary osmium carbonyls, [Osx(CO)y], we demonstrated that there is a relationship between the metal–metal bond enthalpy per metal atom, SE(Os]Os)/x, and the number of carbonyl ligands per metal atom, y/x.In considering the wider range of clusters in Fig. 1 we similarly examine the relationship (Fig. 2) between the total metal–metal bond enthalpy per metal atom, SE(Os]Os)/x, and the number of ligand electrons per metal atom, counting two electrons for each CO ligand and one electron for each H ligand or anionic charge.Fig. 2 shows the same overall trend as was observed for the smaller range of data available for the neutral binary carbonyls, namely an upward trend in the curve towards larger cluster species (with fewer ligands per metal atom). The figure shows that there are a number of isoelectronic series of clusters, and the trends in metal–metal bond enthalpy as CO ligands are replaced by H2 or H2 are discussed below.As before, the data fit a second-order polynomial (see Experimental section for details) which, given the wider range of data made possible by considering the large cluster anions, predicts a value of the metal–metal bond enthalpy for zero ligand electrons per metal of 785 kJ mol21, satisfyingly close to the value for bulk osmium metal (790 kJ mol21). Given that the total number of electrons which can be accommodated per metal atom is limited by the 18-electron rule, we can expect that as the number of electrons involved in metal–ligand bonding decreases the number of electrons available for metal–metal bonding will increase.The observation that the data plotted in Fig. 2 follow a curve, rather than a straight line, indicates that as more electrons become available for metal–metal bonding so these electrons are used more effi- ciently in metal–metal bonding. The metal–metal distances in small clusters are typically 10–15% longer than those in bulk metal; those in the larger clusters are nearer to those in the bulk metal.Trends in ”E(Os]Os) as a function of the number of PSEPT skeletal electron pairs, Sp Metal carbonyl clusters can be viewed as analogues of borane clusters, and their bonding considered in terms of the number of skeletal electron pairs, Sp, formally available for cluster bonding.13 One way of viewing the trends in metal–metal bond enthalpy is to chart the metal–metal bond enthalpy per skeletal electron pair, SE(Os]Os)/Sp, against the number of skeletalJ.Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 2143 Table 5 The efficiency, SE(Os]Os)/Sp (kJ mol21), with which the Sp skeletal electron pairs are used in metal–metal bonding in the osmium carbonyl clusters, classified by their cluster type. Clusters marked with an asterisk have structures which are more open than required on the basis of their electron counts Skeletal electron pairs Cluster type Tetracapped closo Tricapped closo Bicapped closo Monocapped closo closo nido arachno hypho 5 [Os3H2(CO)10] [Os2(CO)8]22 68 16 6 [Os6(CO)18] [Os5(CO)16] [Os5H(CO)15]2 [Os4H(CO)13]2 [Os4(CO)14] [Os4H2(CO)12]22 [Os4H2(CO)13] [Os4H3(CO)12]2 [Os4H4(CO)12] [Os3H(CO)11]2 [Os3(CO)12] [Os3H2(CO)11] [Os2(CO)10] 215 159 156 102 101 100 99 96 89 50 47 44 0 7 [Os10(CO)26]22* [Os10H4(CO)24]22 [Os9(CO)24]22 [Os9H(CO)24]2 [Os8(CO)22]22 [Os8H(CO)22]2* [Os7(CO)21] [Os7H2(CO)20]* [Os6(CO)18]22 [Os6H(CO)18]2 [Os6H2(CO)18]* [Os5H2(CO)16]* [Os4(CO)15] 372 359 331 311 278 266 218 204 172 166 159 109 66 8 [Os7H2(CO)21]* [Os6H2(CO)19]* [Os5(CO)18] [Os4(CO)16] 162 126 86 44 9 [Os7H2(CO)22]* [Os6(CO)17- {P(OMe)3}4]* [Os5(CO)19]* 131 96 60 electron pairs and the resulting predicted cluster geometry, as shown in Table 5.It should be noted that some clusters 24,25 show isomeric geometries less symmetrical than the simplest corresponding to the electron count, e.g. capped-nido instead of closo, etc.Such clusters are classified in Table 5 according to the simplest formal type, and are indicated by an asterisk. The reasons for their less symmetrical actual shapes are not always clear, and may arise from both steric and electronic factors, thus [Os6H2(CO)18] needs to accommodate 20 ligands rather than the 18 of [Os6(CO)18]22, equally a comparison of [Os6(CO)18]22 (closo, octahedral) with [Os6H2(CO)18] (capped-nido) may suggest that the need by bridging hydride ligands for regions of relatively high electron density may favour the less spherically symmetrical skeleton of the latter, as indicated by calculations on [B6H6]22, [B6H7]2 and B6H8 as models.26 Indeed most of the ‘anomalous’ systems marked by an asterisk in Table 5 contain bridging hydride ligands.It may also be worth noting that where less symmetrical, more open, capped-nido or similar structures are found, these generally have the numbers of metal–metal contacts (polyhedron edges) that are compatible with the 18-electron rule and 2c2e metal–metal bonds.27,28 These Fig. 2 Plot of metal–metal bond enthalpy per osmium as a function of the number of ligand electrons per osmium perturbations in the overall structural pattern do not appear to affect very greatly the efficiency with which the skeletal electron pairs are used. Table 5 illustrates the same trends in cluster stability as we noted when discussing the binary carbonyls. The data illustrate that the available skeletal electrons are used more efficiently for metal–metal bonding as the clusters become less open, or as the number of metal atoms increases.In the open series of clusters (arachno and hypho) some of the skeletal electrons are not involved in metal–metal bonding but are effectively lone pairs (and thus are important in determining the cluster geometry). The most extensive trend of data is within the series of clusters with seven skeletal electron pairs, whose structures are based on the octahedron, either with vertices removed, or with up to four of the eight faces capped; these clusters show a steady, and regular, progression in the value of SE(Os]Os)/Sp, the difference between successive rows in the table being around 50 kJ mol21.The trends in total metal–metal bond enthalpy within the series of clusters isoelectronic with [Os4(CO)14] will be discussed below. The Os17 and Os20 cluster anions cannot be accounted for simply in terms of the PSEPT rules, because they contain metal atoms that evidently use more than three atomic orbitals (AOs) for cluster bonding.They have structures closely related to the bulk metal, a fact which is also borne out by the multiple redox behaviour of these clusters. Trends in ”E(Os]Os) as a function of the number of polyhedron edges and metal–metal bonds As indicated above, the bonding in many of the clusters in Fig. 1 can be accounted for in terms of a localised 18-electron bonding model.The number of metal–metal bonds in a structure can be determined by application of the 18-electron rule, and a localised bonding model can be appropriate when the number of metal–metal bonds equals the number of cluster edges. In clusters such as [Os6(CO)18]22, which has only 11 metal–metal bonding electron pairs for the 12 edges of the octahedron, it is either necessary to invoke resonance of the 11 bonds around the polyhedron, or to accept that delocalised bonding models such as PSEPT are preferable for such clusters.Tables 1–4 list for each cluster the number (S1b) of localised Os]Os bonds2144 J. Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 required to satisfy the EAN rule, and the total metal–metal bond enthalpy per localised bond, SE(Os]Os)/S1b. In the majority of cases the number of Os]Os bonds equals the number of polyhedron edges, and it is possible to draw electronprecise structures, with a metal–metal bond along each polyhedron edge, using dative bonds and resonance structures where necessary.We have included the number of localised bonds for all the clusters, including those with fewer metal– metal bond pairs than polyhedron edges. The data in each of Tables 1–4 show a trend to increasing SE(Os]Os)/S1b as the cluster nuclearity increases, again indicating that metal–metal bonding electron pairs are used more efficiently in bonding in larger clusters, but also showing the error of any approach to cluster thermodynamics which assumes that all 2c2e Os]Os bonds have the same strength. Trends in ”E(Os]Os) for cluster interconversions The total metal–metal bond enthalpy, SE(Os]Os), provides a parameter which can be used to explore the influence of adding osmium carbonyl fragments to clusters leading to larger clusters. We note that SE(Os]Os) data, when presented in the format of Table 5, illustrate trends in the total metal–metal bond enthalpy per skeletal electron pair, SE(Os]Os)/Sp, both vertically and horizontally, and an investigation of these data illustrates important trends in cluster geometry and bonding.Columns in Table 5 contain clusters which are formally related by the addition or removal of an Os(CO)2 fragment. Rows in Table 5 contain clusters related by addition or removal of Os(CO)3 units. We have chosen to investigate changes in SE(Os]Os) accompanying the formal reactions of adding Os(CO)2, Os(CO)3 and Os(CO)4 fragments to clusters and also the more practical reactions of oxidative addition of H2, and addition or removal of H1 or H2 to osmium carbonyl clusters.Table 6 lists all the pairs of osmium carbonyl clusters described in this work which are related by the addition of an Os(CO)2 fragment to the smaller cluster. The Os(CO)2 fragment provides three orbitals but no electrons to the cluster, and so addition of an Os(CO)2 fragment will convert a cluster into the next example along the sequence: hypho, arachno, nido, closo, capped-closo, retaining the same number of skel- Table 6 Pairs of osmium carbonyl clusters related by the addition or removal of Os(CO)2 fragments, with total metal–metal bond enthalpies, SE(Os]Os)/kJ mol21, and the change in SE(Os]Os).Clusters labelled with an asterisk have structures which are more open than required for their electron counts Cluster pair With six skeletal electron pairs [Os3(CO)12] æÆ [Os4(CO)14] [Os4(CO)14] æÆ [Os5(CO)16] [Os5(CO)16] æÆ [Os6(CO)18] [Os3H2(CO)11] æÆ [Os4H2(CO)13] [Os3H(CO)11]2 æÆ [Os4H(CO)13]2 [Os4H(CO)13]2 æÆ [Os5H(CO)15]2 With seven skeletal electron pairs [Os4(CO)15] æÆ [Os7(CO)21] [Os5H2(CO)16]* æÆ [Os6H2(CO)18]* [Os6H2(CO)18]* æÆ [Os7H2(CO)20]* [Os6(CO)18]22 æÆ [Os8(CO)22]22 [Os8(CO)22]22 æÆ [Os9(CO)24]22 [Os9(CO)24]22 æÆ [Os10(CO)26]22 [Os8H(CO)22]2* æÆ [Os9H(CO)24]2 With eight skeletal electron pairs [Os4(CO)16] æÆ [Os5(CO)18] [Os6H2(CO)19]* æÆ [Os7H2(CO)21]* SE(Os]Os) 283 æÆ 608 608 æÆ 955 955 æÆ 1290 266 æÆ 596 299 æÆ 614 614 æÆ 935 464 æÆ 1526 763 æÆ 1114 1114 æÆ 1430 1205 æÆ 1943 1943 æÆ 2314 2314 æÆ 2603 1864 æÆ 2178 349 æÆ 690 1005 æÆ 1300 D[SE(Os] Os)] 1325 1347 1335 1330 1315 1321 11062 (÷3 = 354) 1351 1316 1738 (÷2 = 369) 1371 1289 1314 1341 1295 etal electron pairs as the cluster becomes less ‘open’. Table 6 shows that the increase in SE(Os]Os) on addition of an Os(CO)2 fragment is remarkably insensitive both to the number of skeletal electron pairs and to the presence of hydride ligands or negative charges.An Os(CO)3 fragment provides three orbitals and two electrons to the cluster and so its addition will convert a cluster into another of the same class (hypho, arachno, nido, closo or capped-closo) with an additional vertex, and hence an additional pair of skeletal electrons. Table 7 shows that the increase in metal–metal bonding, as quantified by SE(Os]Os), is remarkably similar for the addition of Os(CO)3 to a wide range of clusters, of different classes and with differing numbers of skeletal electron pairs.An Os(CO)4 unit can be considered as providing three AOs and four electrons or two AOs and two electrons to a cluster {as if derived from [Os(CO)4Cl2] by removal of two Cl atoms}. Addition of an Os(CO)4 unit to a cluster will therefore generate a more ‘open’ cluster, with two additional pairs of skeletal electrons. Alternatively Os(CO)4 can offer one vacant orbital to a cluster, when viewed as derived from Os(CO)5 by removal of a CO ligand.As Table 8 shows, there are fewer examples of this formal addition of an Os(CO)4 unit, but again the additional metal–metal bonding when an Os(CO)4 fragment is added to a cluster is remarkably similar for these examples. The addition of an Os(CO)2 unit increases the value of SE(Os]Os) by an average of 326 kJ mol21 for each of the single Os(CO)2 additions listed. Similarly, the addition of Os(CO)3 Table 7 Pairs of osmium carbonyl clusters related by the addition or removal of Os(CO)3 fragments, with total metal–metal bond enthalpies, SE(Os]Os)/kJ mol21, and the change in SE(Os]Os).Clusters labelled with an asterisk have structures which are more open than required for their electron counts Cluster pair Capped-closo [Os6(CO)18] æÆ [Os7(CO)21] closo [Os6H2(CO)18]* æÆ [Os7H2(CO)21]* [Os5H(CO)15]2 æÆ [Os6H(CO)18]2 nido [Os3H2(CO)10] æÆ [Os4H2(CO)13] [Os4H2(CO)13] æÆ [Os5H2(CO)16] [Os5H2(CO)16]* æÆ [Os6H2(CO)19]* [Os6H2(CO)19]* æÆ [Os7H2(CO)22]* arachno [Os3(CO)12] æÆ [Os4(CO)15] [Os4(CO)15] æÆ [Os5(CO)18] [Os3(CO)12] æÆ [Os5(CO)18] hypho [Os4(CO)16] æÆ [Os5(CO)19]* SE(Os]Os) 1290 æÆ 1526 1114 æÆ 1300 935 æÆ 1161 339 æÆ 596 596 æÆ 763 763 æÆ 1005 1005 æÆ 1179 283 æÆ 464 464 æÆ 690 283 æÆ 690 349 æÆ 543 D[SE(Os] Os)] 1236 1186 1226 1257 1167 1242 1174 1181 1226 1407 (÷2 = 203) 1194 Table 8 Pairs of osmium carbonyl clusters related by the addition or removal of Os(CO)4 fragments, with total metal–metal bond enthalpies, SE(Os]Os)/kJ mol21, and the change in SE(Os]Os).Clusters labelled with an asterisk have structures which are more open than required for their electron counts Cluster pair [Os3(CO)12] æÆ [Os4(CO)16] [Os4(CO)14] æÆ [Os5(CO)18] [Os4(CO)15] æÆ [Os5(CO)19]* [Os6H2(CO)18] æÆ [Os7H2(CO)22] SE(Os]Os) 283 æÆ 349 608 æÆ 690 464 æÆ 543 1114 æÆ 1179 D[SE(Os] Os)] 166 182 179 165J. Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 2145 units increases the total metal–metal bond enthalpy by an average of 209 kJ mol21, and the addition of an Os(CO)4 unit increases the metal–metal bonding by an average of 73 kJ mol21.Many experimentally accessible cluster-interconversion reactions involve either spontaneous loss, or gain under pressure, of CO ligands. Table 9 illustrates the change in metal–metal bond enthalpy, SE(Os]Os), associated with the addition of a CO ligand for a number of examples. Increasing the number of CO ligands will increase the ratio of y/x in Osx(CO)y, or in the more general case of [Osx(CO)yHz]c2 will increase the number of ligand electrons per metal atom, and will have an influence on SE(Os]Os) which can be predicted from the fit to the data in Fig. 2. The ligand addition will also have a small influence on the osmium–carbon monoxide bond enthalpy, E(Os]CO), for the ligands already present, since we have previously argued that E(Os]CO) is a function of the ratio y/x.The reactions shown in Table 9 will be exothermic left to right (addition of CO) provided that the gain in osmium–carbon monoxide bond enthalpy, E(Os]CO), exceeds significantly the losses in metal– metal bond enthalpy, SE(Os]Os), which will be the case since E(Os]CO) is ca. 200 kJ mol21. The exact thermodynamic viability of the CO addition reactions will be influenced by entropic factors, since one of the reactants, CO, is a gas. Table 10 lists three pairs of clusters which are related by the formal oxidative addition of H2 to one of the clusters.The total metal–metal bond enthalpies, SE(Os]Os), are also listed, along with the change in SE(Os]Os) plus the H2 bond enthalpy term. The significance of [DSE(Os]Os) 1 E(H2)] is that the oxidativeaddition reactions listed in Table 10 would be thermoneutral (DH = 0) if the total Os]H bond enthalpy were equal to [DSE(Os]Os) 1 E(H2)]. It seems reasonable to suppose that the enthalpy difference between [Os5(CO)16] 1 H2 and [Os5- H2(CO)16] does not exceed say 50 kJ mol21.There must also be an entropy difference, which we have neglected, which can be estimated 29 at about 14 J K21 mol21, giving a TDS term less than 5 kJ mol21. We can predict a mean value for the Os]H bond enthalpy in [Os5H2(CO)16] of (612 ± 50)/2 = 306 ± 25 kJ mol21. Similar arguments provide estimates of mean Os]H bond enthalpy terms for [Os6H2(CO)18] (314 ± 25 kJ mol21) and [Os7H2(CO)21] (332 ± 25 kJ mol21), although [Os7H2(CO)21] Table 9 Pairs of osmium carbonyl clusters related by addition of CO, with total metal–metal bond enthalpies, SE(Os]Os)/kJ mol21, and the change in SE(Os]Os).Clusters labelled with an asterisk have structures which are more open than required for their electron counts Cluster pair [Os4(CO)14] æÆ [Os4(CO)15] [Os4(CO)15] æÆ [Os4(CO)16] [Os5(CO)16] æÆ [Os5(CO)18] [Os5(CO)18] æÆ [Os5(CO)19]* [Os6H2(CO)18]* æÆ [Os6H2(CO)19]* [Os7H2(CO)21]* æÆ [Os7H2(CO)22]* SE(Os]Os) 608 æÆ 464 464 æÆ 349 955 æÆ 690 690 æÆ 543 1114 æÆ 1005 1300 æÆ 1179 D[SE(Os] Os)] 2144 2115 2265 (÷2 =2133) 2147 2109 2121 Table 10 Pairs of osmium carbonyl clusters related by the oxidative addition of H2, with total metal–metal bond enthalpies, SE(Os]Os)/kJ mol21, and the change in [SE(Os]Os) 1 E(H2)].All the hydride clusters have structures which are more open than required for their electron counts and are labelled with an asterisk Cluster pair [Os5(CO)16] æÆ [Os5H2(CO)16]* [Os6(CO)18] æÆ [Os6H2(CO)18]* [Os7(CO)21] æÆ [Os7H2(CO)21]* SE(Os]Os) 955 æÆ 763 1290 æÆ 1114 1526 æÆ 1300 D{[SE(Os]Os)] 1 E(H2)} 2176 2 436 = 2612 2192 2 436 = 2628 2228 2 436 = 2664 does contain a slightly different distribution of carbonyl ligands from the parent binary carbonyl cluster.In all three of these dihydride clusters the two hydride ligands have been placed by potential-energy calculations in doubly bridging sites, and it seems reasonable to suggest that the bond enthalpy terms for terminal Os]H or triply bridging, m3-H, hydride ligands will differ from these estimates. There are experimental data which also allow an estimation of the Os]H bond enthalpy terms in osmium carbonyl hydride clusters.From a study of the kinetics of the interconversion of [Os3(CO)12], [Os3(m-H)2(CO)10] and [Os3H(m-H)(CO)11] Poë et al.30 were able to determine that the enthalpy of formation of [Os3H(m-H)(CO)11] was 35 kcal mol21 (146 kJ mol21) more positive than that of [Os3(CO)12], whilst that of [Os3(m-H)2(CO)10] was 72 kcal mol21 more positive than that of [Os3(CO)12].However, ref. 30 appears to contain an error for the enthalpy of formation, DHf, of [Os3(CO)12](g), which is given as 637 kcal mol21, quoting a review by Connor,31 which in fact contains the value 21644 ± 28 kJ mol21. The enthalpy of formation of gaseous [Os3(CO)12] is quoted as 2393 kcal mol21 (21644 kJ mol21) in the original publication by Connor et al.32 Close examination of the data in ref. 30 indicates to us that Poë et al. have correctly calculated the difference in the enthalpies of formation of the three Os3 clusters, but have used an incorrect value (in sign and magnitude) for the enthalpy of formation of [Os3(CO)12] as their base point. Using the correct value, we suggest that the experimentally determined enthalpy of formation is 2393 1 35 = 2358 kcal mol21 (21498 ± 28 kJ mol21) for gaseous [Os3H(m-H)(CO)11] and 2393 1 72 = 2321 kcal mol21 (21343 ± 28 kJ mol21) for gaseous [Os3(m-H)2(CO)10]. Using the SE(Os]Os) bond enthalpy terms for the Os3 hydride clusters, [Os3H(m-H)(CO)11] and [Os3(m-H)2(CO)10], together with the SE(Os]CO) enthalpy terms [calculated using E(Os]CO) of 201 kJ mol21 for each CO in Os(CO)4 units and 209 kJ mol21 in Os(CO)3 units, as described in ref. 1] and the experimental enthalpies of formation of these two clusters, the only unknown terms are the Os]H and Os(m-H)Os bond enthalpy terms which are derived as in equations (2) and (3) for DHdisrupt = SE(Os]Os) 1 SE(Os]CO) 1 2E(Os]H]Os) = 338.7 1 (4 × 201 1 6 × 209) 1 2x = 2396.7 1 2x (2) DHf = 21343 kJ mol21 = 3DHf[Os(g)] 1 10DHf[CO(g)] 1 2DHf[H(g)] 2 DHdisrupt (3) [Os3(m-H)2(CO)10].Hence E(Os]H]Os) = 324 kJ mol21. The largest contribution to the error bar on this number is the 2.5 kJ mol21 per CO ligand error which we estimate for the Os]CO bond enthalpy term. From equations (4) and (5) for [Os3H(m-H)(CO)11], E(Os]H) = 264 kJ mol21.DHdisrupt = SE(Os]Os) 1 SE(Os]CO) 1 E(Os]H]Os) 1 E(Os]H) = 265.6 1 (8 × 201 1 3 × 209) 1 324 1 y = 2824.6 1 y (4) DHf = 21498 kJ mol21 = 3DHf[Os(g)] 1 11DHf[CO(g)] 1 2DHf[H(g)] 2 DHdisrupt (5) These calculations suggest experimentally derived Os]H bond enthalpies of 264 (Os]H) and 324 kJ mol21 (Os2]m-H). We note that the enthalpy required to convert the bridging hydride in [Os3H(m-H)(CO)11] into the terminal form has been estimated 33 at 46 kJ mol21, the values which we have derived are consistent and would suggest a value of 60 kJ mol21.Our values are also consistent with other data for M]H bond strengths for third-row transition metals.23 The replacement of a CO ligand by H2 leads to no net change in cluster electron count, and Table 11 lists the four examples, together with the SE(Os]Os) change accompanying2146 J. Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 this substitution.These data do not cover a wide range, but there are clearly two cases where this substitution leads to an increase in metal–metal bonding, SE(Os]Os), and two cases where the metal–metal bonding is reduced. Conversion of [Os3(CO)12] (all COs terminal) into [Os3(m-H)(m-CO)(CO)10]2 gives a cluster where one Os]Os bond is bridged by both a hydride ligand and a carbonyl ligand. There are a number of possible rationalisations for this structural change. Replacement of a p-acceptor ligand (CO) by a strong s donor (H) and an anionic charge results in an increased ‘p-electron density’ within the Os3 core, which can be accommodated by the introduction of a m-CO ligand, which is a better p acceptor than a terminal CO ligand.Alternatively, the bond enthalpy term for a bridging hydride, m-H, is larger than for a terminal hydride ligand, so there is a thermodynamic preference for H to occupy a bridging site. Equally the bond enthalpy term which we have associated1 with a bridging CO ligand (205 kJ mol21) is slightly greater than that for a CO ligand in an Os(CO)4 group (201 kJ mol21), so that there is a small enthalpic preference for a CO group in [Os3(m-H)(CO)11]2 to occupy a bridging position.The shorter Os]Os bond needed to accommodate both the bridging hydride and carbonyl ligands will also make enhance SE(Os]Os). Similarly, replacement of one CO ligand in [Os4(CO)14] by m-H2 gives a cluster, [Os4(m-H)(CO)13]2, which in the, hypothetical, all terminal-CO form contains one Os(CO)4 vertex, whilst the observed structure is [Os4(m-H)(m-CO)(CO)12]2.The observed cluster has a thermodynamically preferred m-CO ligand rather than an Os(CO)4 vertex, and [Os4(m-H)(m-CO)(CO)12]2again has stronger metal–metal bonding, SE(Os]Os), than in neutral [Os4(CO)14], although here it appears likely that the m-H and m-CO functions do not bridge the same Os]Os bond, but are on opposite edges of the tetrahedron. In contrast, replacement of one CO ligand in [Os5(CO)16] by (m-H)2 gives [Os5(m-H)(CO)15]2, which contains only Os(CO)3 fragments, and there is no thermodynamic driving force for a CO ligand to occupy a bridging site.Similarly there are no Os(CO)4 fragments in the product when [Os4H2(CO)13] is converted into [Os4H3(CO)12]2, and both of these conversions are accompanied by a reduction in SE(Os]Os). In addition to [Os4H(CO)13]2, there are four further Os4 clusters which are formally derived from [Os4(CO)14]; in order of decreasing SE(Os]Os) these are [Os4(m-H)2(CO)12]22, [Os4- (m-H)2(CO)13], [Os4(m-H)3(CO)12]2 and [Os4(m-H)4(CO)12], all containing tetrahedral Os4 cores.The trend within this series is for the Os]Os bonds to become longer, and hence for SE(Os]Os) to become smaller, as the number of hydride ligands increases. With one exception, these four clusters all contain only Os(CO)3 fragments, and effectively the hydride ligands {which can be thought of as protonating a hypothetical tetrahedral anion [Os4(CO)12]42, which formally contains six skeletal electron pairs, i.e. a 2c2e bond along each edge} convert into metal–hydrogen–metal (3c2e) bonding electrons which would otherwise be exclusively metal–metal bonding.Protonation of a cluster does not affect the number of skeletal electron pairs available for bonding, but since it does require electrons which were previously involved in metal–metal bonding to adopt a metal–hydrogen–metal bonding role it reduces SE(Os]Os) as observed for these Os4 clusters, and illustrated in Table 12 for all Table 11 Pairs of osmium carbonyl clusters related by the isoelectronic replacement of a CO ligand by H2, with total metal–metal bond enthalpies, SE(Os]Os)/kJ mol21, and the change in SE(Os]Os) Cluster pair [Os3(CO)12] æÆ [Os3H(CO)11]2 [Os4(CO)14] æÆ [Os4H(CO)13]2 [Os4H(CO)13]2 æÆ [Os4H2(CO)12]22 [Os5(CO)16] æÆ [Os5H(CO)15]2 SE(Os]Os) 283 æÆ 299 608 æÆ 614 614 æÆ 598 955 æÆ 935 D[SE(Os] Os)] 116 16 216 220 the pairs of clusters which are related by protonation. The data suggest that the absolute loss of metal–metal bonding is greater for the larger clusters, although the reduction in metal–metal bonding is comparable in percentage terms.However, the large reduction in metal–metal bonding energy on protonation of [Os9(CO)24]22 implies that this cluster is a weak base, or that [Os9H2(CO)24] and [Os9H(CO)24]2 are strong acids, as borne out by the chemistry exhibited by these three clusters.34 The delocalisation of charge in metal carbonyl cluster anions also means that (de)protonation reactions are accompanied by changes in bond length throughout the cluster, and the reorganisation associated with this results in carbonyl clusters, in common with many organometallic acids, having low kinetic acidities.35 The series of hexaosmium clusters also displays an interesting trend in total metal–metal bond enthalpy.The most effi- ciently bonded Os6 cluster is [Os6(CO)18], which has 12 metal– metal bonding electron pairs in a localised bond treatment, and has SE(Os]Os) = 1290 kJ mol21. This cluster can be converted into [Os6(CO)18]22 by the addition of two electrons, considered as metal–metal antibonding in a localised bond description, resulting in a reduced total metal–metal bond enthalpy, SE(Os]Os) = 1209 kJ mol21. Addition of protons to the dianionic cluster requires electrons which are involved in 2c2e Os]Os bonds to be used for 3c2e Os]H]Os bonds, and so the total metal–metal bond enthalpies for [Os6H(CO)18]2 and [Os6H2(CO)18] are 1158 and 1114 kJ mol21 respectively.Conclusion We have shown that the use of a bond length–bond enthalpy relationship for the Os]Os contacts in osmium carbonyl clusters leads to a single parameter, the total metal–metal bond enthalpy, SE(Os]Os), which reflects and quantifies energetically the structural changes which occur in series of such clusters.Use of this parameter has allowed us to investigate the electronic factors which determine such structural changes, using either localised-bond (18-electron rule) or delocalised (PSEPT) electron-counting methods. Knowledge of the changes in metal–metal bond enthalpy which accompany cluster interconversion reactions has allowed estimates to be made of limiting values of the Os]H and Os]H]Os bond enthalpies, and it is expected that extension of these ideas could lead to estimates of other metal–ligand bond enthalpies, and of the electron affinities of metal carbonyl clusters.Experimental Fractional atomic coordinates for the osmium carbonyl clusters [Os2(CO)8]22,36 [Mo(h-C5H4Pri)4S4]2[Os6(CO)18] (two forms),37 [Os8(CO)22]22,38 [Os9(CO)24]22,34 [Os10(CO)26]22,39 [Os17- (CO)36]22,40 [Os20(CO)40]22,41 [Os3H2(CO)10],42 [Os3H2(CO)11],43 [Os4H4(CO)12],44 [Os4H2(CO)13],45 [Os5H2(CO)16],46 [Os7H2- (CO)22],47 [Os3H(CO)11]2,45 [Os4H(CO)13]2,48 [Os4H3(CO)12]2,49 Table 12 Pairs of osmium carbonyl clusters related by protonation, with total metal–metal bond enthalpies, SE(Os]Os)/kJ mol21, and the change in SE(Os]Os).Hydride clusters labelled with an asterisk have structures which are more open than required for their electron counts Cluster pair [Os3H(CO)11]2 æÆ [Os3H2(CO)11] [Os4H(CO)13]2 æÆ [Os4H2(CO)13] [Os4H2(CO)12]22 æÆ [Os4H3(CO)12]2 [Os4H3(CO)12]2 æÆ [Os4H4(CO)12] [Os6(CO)18]22 æÆ [Os6H(CO)18]2 [Os6H(CO)18]2 æÆ [Os6H2(CO)18]* [Os8(CO)22]22 æÆ [Os8H(CO)22]2* [Os9(CO)24]22 æÆ [Os9H(CO)24]2 SE(Os]Os) 299 æÆ 266 614 æÆ 593 598 æÆ 570 570 æÆ 536 1205 æÆ 1161 1161 æÆ 1114 1943 æÆ 1871 2314 æÆ 2178 D[SE(Os] Os)] 233 221 228 234 244 247 272 2136J.Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 2147 [Os5H(CO)15]2,50 [NBu4][Os6H(CO)18],51 [PMePh3][Os8H- (CO)22],28 [Ph2PNPPh2][Os8H(CO)22],28 [Os9H(CO)24]234 and [Os10H4(CO)24]2252 were retrieved from the Cambridge Structural Database (CSD April 1996 release, version 5.11 on the University of Durham UNIX network) 53 using QUEST and Os]Os distances were evaluated using BABEL.54 Fractional atomic coordinates for the clusters [Os6H2(CO)19] 55 and [Os7H2(CO)21] 47 have not been deposited in the CSD and were retrieved from the Inorganic Crystal Structure Datafile (ICSD) at Daresbury Laboratory; the resulting CSSR files were analysed with BABEL or directly with the Daresbury program CRAD.Fractional atomic coordinates for [PMePh3]2[Os6- (CO)18],20 [ Os7H2(CO)20],27 [ Os4H2(CO)12]2256 and [Ph2PNPPh2]- [Os6H(CO)18] 20 are not available in either of the databases or in the original publications, and metal–metal distances were retrieved directly from figures or tables in the publications, in some of these cases it was necessary to estimate next-nearest neighbour distances. Tables of Os]Os distances from BABEL or CRAD were pasted directly into a spreadsheet for bond enthalpy calculations.Given the large number of clusters discussed in this work, and the number of Os]Os interatomic distances in some of the larger clusters, tables listing all of the Os]Os interatomic distances, d(Os]Os), used in deriving the E(Os]Os) and SE(Os]Os) data in this paper are available separately as SUP 57248. The data in Fig. 2 relate Os]Os bond enthalpy per metal atom, SE(Os]Os)/x, to ligand electron: Os ratio in [Osx(CO)y- Hz]c2. Given the trends in SE(Os]Os) as CO is replaced by H2 or H2, the curve is fitted only for the neutral binary carbonyls, Osx(CO)y, and the carbonyl anions, [Osx(CO)y]c2.It is described by SE(Os]Os)/x = 785.5 2 117.4ec 1 3.84(ec)2 [where ec = number of ligand electrons per osmium = (2y 1 z 1 c)/x] with a correlation coefficient of 0.9968. A Kaleidagraph running on a Mac LCII computer was used to draw Fig. 2 and to fit the data. The Os]Os distances used in this work are without estimated standard deviations (e.s.d.s) since they were derived from fractional atomic coordinate data available from the Cambridge Structural Database which does not contain e.s.d.s, and in many cases complete lists of Os]Os distances (especially next-nearest neighbour) are not available in the original publication, so we are unable to extract e.s.d.s from that source; as indicated previously, 1 we feel that the crystallographic contribution to the errors in SE(Os]Os) is less than 1 kJ mol21.In contrast the e.s.d.s on M]C and C]O distances are typically larger, reflecting the lighter atomic masses of these elements and libration of carbonyl ligands,57 and mean that any attempt to estimate Os]C and C]O bond enthalpies from current crystallographic data will result in large estimated errors.Acknowledgements We wish to acknowledge the use of the EPSRC’s Chemical Database Service at Daresbury,58 and thank Professor A. J. 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Bruce, in Comprehensive Organometallic Chemistry II, eds.E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995, vol. 13, pp. 687–724. 8 J. Lewis and P. R. Raithby, J. Organomet. Chem., 1995, 500, 227; R. K. Pomeroy, in Comprehensive Organometallic Chemistry II, eds. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995, vol. 7, ch. 15; M. P. Cifuentes and M. G. Humphrey, in Comprehensive Organometallic Chemistry II, eds. E. W. Abel, F. G. A. Stone and G. Wilkinson, Pergamon, Oxford, 1995, vol. 7, ch. 16. 9 M. D. Vargas and J. N. Nicholls, Adv. Inorg. Chem. Radiochem., 1986, 30, 123. 10 F. A. Cotton and G. Wilkinson, Advanced Organometallic Chemistry 5th edn., Wiley, Chichester, 1988, p. 1052; C. E. Housecroft, Metal– Metal Bonded Carbonyl Dimers and Clusters, Oxford University Press, Oxford, 1996; D. M. P. Mingos and D. J. Wales, Introduction to Cluster Chemistry, Prentice-Hall, Englewood Cliffs, NJ, 1990. 11 E. L. Muetterties, T. N. Rhodin, E. Band, C. F. Brucker and W.R. Pretzer, Chem. Rev., 1979, 79, 91; M. R. Albert and J. T. Yates, The Surface Scientist’s Guide to Organometallic Chemistry, American Chemical Society, Washington, 1987. 12 K. Wade, Adv. Inorg. Chem. Radiochem., 1976, 18, 1. 13 C. E. Housecroft and K. Wade, Gazz. Chim. Ital., 1980, 110, 87. 14 J. Huang, K. Hedberg and R. K. Pomeroy, Organometallics, 1988, 7, 2049. 15 R. J. Goudsmit, B. F. G. Johnson, J. Lewis, P. R. Raithby and K. H. Whitmire, J. Chem. Soc., Chem. Commun., 1982, 640. 16 A. K. Hughes, K. L. Peat, L. C. Rabbitt and K. Wade, unpublished work. 17 A. G. Orpen, J. Chem. Soc., Dalton Trans., 1980, 2509. 18 G. Ciani, D. Gusto, M. Manassero and A. Albinati, J. Chem. Soc., Dalton Trans., 1976, 1943. 19 C. R. Eady, B. F. G. Johnson and J. Lewis, J. Chem. Soc., Chem. Commun., 1976, 302. 20 M. McPartlin, C. R. Eady, B. F. G. Johnson and J. Lewis, J. Chem. Soc., Chem. Commun., 1976, 883. 21 A. Martin and A. G. Orpen, J. Am. Chem. Soc., 1996, 118, 1464. 22 P. M. Maitlis, H. C. Long, R. Quyoum, M. L. Turner and Z. Q. Wang, Chem. Commun., 1996, 1; G. Süss-Fink and G. Meister, Adv. Organomet. Chem., 1993, 35, 41; E. L. Muetterties and M. J. Krause, Angew. Chem., Int. Ed. Engl., 1983, 22, 135; C. Masters, Homeogeneous Transition Metal Catalysis – a Gentle Art, Chapman and Hall, London, 1981. 23 D. Wang and R. J. Angelici, J. Am. Chem. Soc., 1996, 118, 935; ACS Symp. Ser., 1990, 428; J. A. Martinho Simoes and J. L. Beauchamp, Chem.Rev., 1990, 90, 629. 24 M. McPartlin, Polyhedron, 1984, 3, 1279; M. McPartlin and D. M. P. Mingos, Polyhedron, 1984, 3, 1321. 25 D. G. Evans and D. M. P. Mingos, Organometallics, 1983, 2, 435. 26 M. A. Cavanaugh, T. P. Fehlner, R. Stramel, M. E. O’Neill and K. Wade, Polyhedron, 1985, 4, 687. 27 E. J. Ditzel, H. D. Holden, B. F. G. Johnson, J. Lewis, A. Saunders and M. J. Taylor, J. Chem. Soc., Chem. Commun., 1982, 1373. 28 D. Braga, K. Henrick, B. F. G. Johnson, J. Lewis, M.McPartlin, W. J. H. Nelson and M. D. Vargas, J. 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Commun., 1980, 60. 39 A. J. Amoroso, B. F. G. Johnson, J. Lewis, P. R. Raithby and W. T. Wong, Angew. Chem., Int. Ed. Engl., 1991, 30, 1505.2148 J. Chem. Soc., Dalton Trans., 1997, Pages 2139–2148 40 E. Charalambous, L. H. Gade, B. F. G. Johnson, J. Lewis, M. McPartlin and H. R. Powell, J. Chem. Soc., Chem. Commun., 1990, 688. 41 A. J. Amoroso, L. H. Gade, B. F. G. Johnson, J. Lewis, P. R. Raithby and W. T. Wong, Angew. Chem., Int. Ed. Engl., 1991, 30, 107. 42 M. R. Churchill, F. J. Hollander and J. P. Hutchinson, Inorg. Chem., 1977, 16, 2697; G. Lavigne, F. Papageorgiou, C. Bergounhou and J.-J. Bonnet, Inorg. Chem., 1983, 22, 2485. 43 M. R. Churchill and B. G. DeBoer, Inorg. Chem., 1977, 16, 878. 44 B. F. G. Johnson, J. Lewis, P. R. Raithby and C. Zuccaro, Acta Crystallogr., Sect. B, 1981, 37, 1728. 45 J. A. Krause, U. Siriwardane, T. A. Salupo, J. R. Wermer, D. W. Knoeppel and S. G. Shore, J. Organomet. Chem., 1993, 454, 263. 46 J. J. Guy and G. M. Sheldrick, Acta Crystallogr., Sect. B, 1978, 34, 1725. 47 B. F. G. Johnson, J. Lewis, M. McPartlin, J. Morris, G. L. Powell, P. R. Raithby and M. D. Vargas, J. Chem. Soc., Chem. Commun., 1986, 429. 48 P. A. Dawson, B. F. G. Johnson, J. Lewis, D. A. Kaner and P. R. Raithby, J. Chem. Soc., Chem. Commun., 1980, 961. 49 B. F. G. Johnson, J. Lewis, P. R. Raithby and C. Zuccaro, Acta Crystallogr., Sect. B, 1981, 34, 3765; M. McPartlin and W. J. H. Nelson, J. Chem. Soc., Dalton Trans., 1986, 1557. 50 J. J. Guy and G. M. Sheldrick, Acta Crystallogr., Sect. B, 1978, 34, 1722. 51 A. G. Orpen and T. F. Koetzle, Acta Crystallogr., Sect. C, 1987, 43, 2084. 52 D. Braga, J. Lewis, B. F. G. Johnson, M. McPartlin, W. J. H. Nelson and M. D. Vargas, J. Chem. Soc., Chem. Commun., 1983, 241; A. Bashall, L. H. Gade, J. Lewis, B. F. G. Johnson, G. J. McIntyre and M. McPartlin, Angew. Chem., Int. Ed. Engl., 1991, 30, 1164. 53 F. H. Allen and O. Kennard, Chem. Des. Autom. News, 1993, 8, 1; 31. 54 BABEL, P. Walters and M. Stahl, Department of Chemistry, University of Arizona, 1994. 55 B. F. G. Johnson, R. Khattar, J. Lewis, M. McPartlin, J. Morris and G. L. Powell, J. Chem. Soc., Chem. Commun., 1986, 507. 56 B. F. G. Johnson, J. Lewis, P. R. Raithby, G. M. Sheldrick and G. Suss, J. Organomet. Chem., 1978, 162, 179. 57 D. Braga and T. F. Koetzle, J. Chem. Soc., Chem. Commun., 1987, 144. 58 D. A. Fletcher, R. F. McMeeking and D. Parkin, J. Chem. Inf. Comput. Sci., 1996, 36, 746. Received 19th February 1997; Paper 7/01174A

ISSN:1477-9226    

DOI:10.1039/a701174a

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2149–2153 2149 Pyridine-2-carboxamide complexes of arylimidorhenium(VI) derived from 2-pyridylmethyleneamine complexes of arylimidorhenium(V) via oxygen-atom transfer† Sangeeta Banerjee, Bimal Kumar Dirghangi, Mahua Menon, Amitava Pramanik and Animesh Chakravorty* Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, Calcutta 700 032, India Complexes of type [ReVL(NC6H4Y-p)Cl3] (Y = H or Cl) have been synthesized where L is the Schiff base formed from pyridine-2-carbaldehyde and the aniline p-XC6H4NH2 (X = Me or Cl).Treatment with aqueous nitric acid in acetonitrile converts them into [ReVIL9(NC6H4Y-p)Cl3], where L9 is a monoanionic pyridine-2-carboxamide. The latter complexes display hyperfine-split six-line solution EPR spectra at room temperature. The crystal structures of [ReL(NC6H4Cl)Cl3] and [ReL9(NC6H4Cl)Cl3] (X = Me in both cases) revealed the presence of severely distorted and meridionally configured ReCl3N3 co-ordination spheres.The effective metal radius decreases only marginally upon metal oxidation and the imide fragment is approximately linear and triple bonded, Re]] ] N]C, in both cases. The rhenium(VI)–rhenium(V) reduction potentials in the two types of complex are ª1.0 and ª0.2 V respectively. Rhenium-promoted oxygen-atom-transfer reactions1 have received significant recent attention.2–5 The usual type of transfer is from an oxo complex ‘ReiO’ (i = metal valence) to an oxophilic substrate E, equation (1), where ‘Rei 2 2’ is the reduced ReiO 1 E æÆ Rei 2 2 1 EO (1) rhenium product.We have shown that rhenium(III) complexes of 2-pyridylmethyleneamines 1 undergo an unusual oxygenatom- transfer reaction in oxidizing aqueous environments affording rhenium(IV) pyridine-2-carboxamide species of type 2.6 The synthetic scope of this transformation is being further explored. Herein we report its utilization for making stable pyridine-2-carboxamide complexes incorporating the very rare arylimide motif of hexavalent rhenium.The precursors are the 2-pyridylmethyleneamine chelates of arylimidorhenium(V). The structure and properties of these arylimidorhenium-(V) and -(VI) families are described. Results and Discussion Synthesis The aldimine complexes [ReL(NC6H4Y)Cl3] 3 were synthesized in excellent yields by treating the phosphine oxide species6 of type 1 with an excess of arylamine, p-YC6H4NH2, in boiling toluene, equation (2).The reaction involves a redistri- [ReIIIL(OPVPh3)Cl3] 1 p-YC6H4NH2 æÆ [ReVL(NC6H4Y-p)Cl3] 1 PIIIPh3 1 H2O (2) bution of the oxidation states of the metal and the phosphorus atom. Violet solutions of [ReL(NC6H4Y)Cl3] treated with aqueous 0.5 mol dm23 nitric acid in acetonitrile solution at room temperature rapidly change to brown and from the reaction mixture the carboxamide complexes [ReL9(NC6H4Y)Cl3] 4 incorporating arylimidorhenium(VI) can be isolated in high yields.Authentic complexes of ReVI(NR) (R = alkyl or aryl) are very rare7–10 and no complex with R = aryl has so far been † Dedicated to the memory of Professor Sir Geoffrey Wilkinson. Non-SI units employed: mB ª 9.27 × 10224 J T21, G = 1024 T. structurally characterized. The type 4 complexes are of special interest in this context. Rate studies on 1 æÆ 2 and related aldimine æÆ amide conversions in oxidizing aqueous environments have revealed that the rate-determining step is the addition of a molecule of water to the aldimine function polarized by one-electron metal oxidation.6b,11,12 The water adduct undergoes induced electron transfer13 associated with proton dissociation.It is logical to assume that a similar mechanism is applicable for the conversion 3 æÆ 4, the initial steps being the one-electron oxidation (by nitric acid) of 3 to [ReVIL(NC6H4Y)Cl3]1 (also accessible electrochemically, see below) and formation of its water adduct, 5.The net transformation is as in equation (3). The three [ReVL(NC6H4Y)Cl3] 1 H2O æÆ [ReVIL9(NC6H4Y)Cl3] 1 3e2 1 3H1 (3) N H N ReIII Cl OPPh3 Cl Cl X N O N ReIV Cl OPPh3 Cl Cl X 1 2 N H N ReV Cl Cl Cl X 3a [ReL1(NPh)Cl3] (X = Me, Y = H) 3b [ReL1(NC6H4Cl)Cl3] (X = Me, Y = Cl) 3c [ReL2(NC6H4Cl)Cl3] (X = Cl, Y = Cl) N Y2150 J. Chem. Soc., Dalton Trans., 1997, Pages 2149–2153 Table 1 Electronic spectral a and IRb data at 298 K Compound UV/VIS lmax/nm (e/dm23 mol21 cm21) IR n& /cm21 3a [ReL1(NPh)Cl3] 3b [ReL1(NC6H4Cl)Cl3] 3c [ReL2(NC6H4Cl)Cl3] 4a [ReL19(NPh)Cl3] 4b [ReL19(NC6H4Cl)Cl3] 4c [ReL29(NC6H4Cl)Cl3] 740 (1530), 540 (7310), 315 (10 500) 740 (1460), 540 (7180), 325 (13 285) 740 (1150), 545 (6125), 330 (10 210) 530 (1930), 345 (14 605) 530 (2030), 360 (17 650) 530 (2050), 360 (18 600) 330, 1600 325, 1595 320, 1600 325, 1595, 1635 310, 330, 1600, 1635 320, 330, 1600, 1640 a The solvent is dichloromethane.b In KBr disc; n(Re]Cl) 310–330, n(C]] N) 1595–1600, n(C]] O) 1595–1640 cm21.electrons are consumed by the external oxidant, nitric acid. The aldimine and amide complexes show one or two Re]Cl stretch(es) around 330 cm21, Table 1. The two strong amide bands of [ReL9(C6H4Y)Cl3] and the C]] N stretch of [ReL- (C6H4Y)Cl3] occur in the region 1590–1640 cm21. Characteristic electronic bands in the visible region are listed in Table 1. Structures The crystal structures of [ReL1(NC6H4Cl)Cl3] 3b and [ReL19- (NC6H4Cl)Cl3] 4b have been determined.Views of the molecules are shown in Figs. 1 and 2 and selected bond parameters are listed in Table 2. In both compounds the co-ordination geometry is distorted octahedral and the ReCl3 fragment is meridionally spanning. The five-membered chelate ring along with the pyridine ring constitute an excellent plane in each case with mean deviation of ª0.01 Å. The Cl(1), Cl(2), Cl(3) and Fig. 1 An ORTEP14 plot and atom labelling scheme for [ReL1- (NC6H4Cl-p)Cl3] 3b.All atoms are represented by their 30% thermal probability ellipsoids; H atoms are omitted for clarity N O N ReVI Cl Cl Cl X 4a [ReL1¢(NPh)Cl3] (X = Me, Y = H) 4b [ReL1¢(NC6H4Cl)Cl3] (X = Me, Y = Cl) 4c [ReL2¢(NC6H4Cl)Cl3] (X = Cl, Y = Cl) N Y N HO N ReVI Cl Cl Cl X N Y 5 H H + N(2) atoms define virtually perfect planes from which the metal atom is displaced towards the imide nitrogen N(3) by 0.30 Å in 3b and 0.28 Å in 4b. The amide group C(1)C(6)ON(2) in complex 4b is planar with a mean deviation of 0.01 Å, the C(6)]O distance being 1.227(9) Å.The average Re]Cl length in 4b is shorter than that in 3b by ª0.02 Å probably reflecting a small radial contraction between rhenium-(V) and -(VI). The Re–N(1) length in each complex is longer than the corresponding Re]N(2) length by ª0.2 Å due to the trans influence of the imide nitrogen. The imide fragment Re]N(3)]C(14) is roughly linear in both complexes and the Re]N distance corresponds to triple bonding (ideal length ReV]] ] NR ª 1.69 Å).15 Fig. 2 An ORTEP plot and atom labelling scheme for [ReL19- (NC6H4Cl-p)Cl3] 4b. Details as in Fig. 1 Table 2 Selected bond lengths (Å) and angles (8) for complexes 3b and 4b 3b 4b Re]Cl(1) Re]Cl(2) Re]Cl(3) Re]N(1) Re]N(2) Re]N(3) N(2)]C(6) C(6)]O 2.357(4) 2.392(4) 2.359(3) 2.224(8) 2.033(8) 1.697(8) 1.302(13) — 2.343(3) 2.347(3) 2.327(3) 2.208(6) 2.058(6) 1.722(6) 1.353(9) 1.227(9) Cl(1)]Re]Cl(2) Cl(1)]Re]Cl(3) Cl(2)]Re]Cl(3) Cl(1)]Re]N(1) Cl(2)]Re]N(1) Cl(3)]Re]N(1) Cl(1)]Re]N(2) Cl(2)]Re]N(2) Cl(3)]Re]N(2) N(1)]Re]N(2) Cl(1)]Re]N(3) Cl(2)]Re]N(3) Cl(3)]Re]N(3) N(1)]Re]N(3) N(2)]Re]N(3) Re]N(3)]C(14) 88.1(1) 87.8(1) 165.5(1) 90.0(2) 81.4(2) 84.7(2) 164.1(2) 92.0(2) 88.2(2) 74.3(3) 103.0(3) 96.0(3) 98.4(3) 166.7(4) 92.9(4) 168.4(7) 88.7(1) 87.6(1) 166.1(1) 89.7(2) 81.8(2) 84.8(2) 165.0(2) 90.9(2) 89.3(2) 75.4(2) 102.1(2) 92.0(2) 101.9(2) 166.6(2) 92.9(3) 166.8(5)J.Chem.Soc., Dalton Trans., 1997, Pages 2149–2153 2151 Only one other six-co-ordinated complex of ReVI(NR), viz. [Re(NC2Cl5)Cl4(POCl3)] having a perhalogenated R group, has been structurally characterized.9 The structures of two tetrahedral ReVI(NR) species with a bulky R group (But) are also known.10 Complex 4b represents the first structurally characterized pseudo-octahedral ReVI(NR) species in which a simple aryl function devoid of special electronic/steric features constitutes the R group.In the case of ReV(NR) a few six-co-ordinated structures are known.7,15–21 EPR spectra of [ReL9(NC6H4Y)Cl3] The [ReVL(NC6H4Y)Cl3] complexes are diamagnetic (5dxy 2). The bulk magnetic moments of [ReVIL9(NC6H4Y)Cl3] (5dxy 1) are however significantly lower (1.4–1.5 mB, 298 K) than the spin-only value due to orbital coupling.22,23 The amide complexes display well resolved EPR lines in fluid solutions at room temperature which is relatively unusual for rhenium(VI) species.18,23 The hyperfine structure consists of six lines (I = 5– 2 for 185Re, 37.07% and 187Re, 62.93%).The lines are Fig. 3 (a) X-Band EPR spectrum of [ReL19(NC6H4Cl-p)Cl3] in dichloromethane–toluene (1 : 1). Instrument settings: power 28 dB; modulation, 100 kHz; sweep centre, 3000 G; sweep time, 250 s, at 298 K; dpph = diphenylpicrylhydrazyl. (b) Cyclic voltammogram of a ª1023 mol dm23 solution of [ReL19(NC6H4Cl-p)Cl3] in acetonitrile (0.1 mol dm23 NEt4ClO4) at a platinum electrode (scan rate, 50 mV s21) Table 3 Cyclic voltammetric formal potentials a and EPR spectral data b at 298 K Compound E2� 1 /V (DEp/mV) g c A/Gd 3a 3b 3c 4a 4b 4c 0.96 (80) 1.04 (80) 1.08 (60) 0.14 (80), 1.50 (80) 0.16 (80), 1.52 (80) 0.23 (80), 1.63 (80) 1.906 1.923 1.917 484 488 492 a Solvent, acetonitrile; scan rate, 50 mV s21; E2� 1 = ��� (Epa 1 Epc) where Epa and Epc are the anodic and cathodic peak potentials respectively; DEp = Epc 2 Epa.Reference electrode, SCE.The concerned couples are 31–3 (ReVI–ReV), 4–42 (ReVI–ReV), 41–4 (ReVII–ReVI). b Solvent, dichloromethane –toluene (1 : 1). c At centre field. d Average values of hyperfine splitting. unequally spaced reflecting second-order effects.24 Centre-field g values and average hyperfine splittings are collected in Table 3 and a representative spectrum is shown in Fig. 3(a). Reduction potentials The aldimine and amide complexes display quasi-reversible one-electron voltammetric responses with peak-to-peak separations of ª80 mV in acetonitrile solutions at a platinum electrode.Reduction potentials are listed in Table 3 and a representative voltammogram is shown in Fig. 3(b). A single response occurs for [ReVL(NC6H4Y)Cl3] corresponding to the couple in equation (4). The reduction potential [ReVIL(NC6H4Y)Cl3]1 1 e2 [ReVL(NC6H4Y)Cl3] (4) is ª1.0 V vs. SCE and thus the one-electron oxidized complex which is crucial for the aldimine æÆ amide conversion (see above) is accessible via nitric acid oxidation as well.The amide complexes [ReVIL9(NC6H4Y)Cl3] show two successive redox processes, equations (5) and (6). [ReVIIL9(NC6H4Y)Cl3]1 1 e2 [ReVIL9(NC6H4Y)Cl3] (5) [ReVIL9(NC6H4Y)Cl3] 1 e2 [ReVL9(NC6H4Y)Cl3]2 (6) The reduction potentials are subject to the usual Hammett effect (Table 3) of the X and Y substituents. The most remarkable feature is the depression of the rhenium(VI)–rhenium(V) couple by ª0.8 V on going from [ReVL(NC6H4Y)Cl3] [equation (4)] to [ReVIL9(NC6H4Y)Cl3] [equation (6)].In the redox sense the deprotonated amide function stabilizes the rhenium(VI) state to a great extent and this forms the basis of the stabilization of the arylimidorhenium(VI) motif upon co-ordination to pyridine-2-carboxamide. The stabilization is sufficient to make the rhenium(VII)–rhenium(VI) couple, equation (5), observable near 1.5 V. Conclusion It is demonstrated that the 2-pyridylmethyleneamine complexes [ReVL(NC6H4Y-p)Cl3] undergo facile oxygen-atom transfer in aqueous nitric acid affording the pyridine-2- carboxamide species [ReVIL9(NC6H4Y-p)Cl3] in excellent yields.Structural characterization of [ReVL1(NC6H4Cl)Cl3] and [ReVIL19(NC6H4Cl)Cl3] has revealed the presence of nearly linear and triple bonded Re]] ] N]C fragments. The metal radius contracts only slightly upon metal oxidation. The amide ligand imparts remarkable redox stability to the rhenium(VI) state shifting the rhenium(VI)–rhenium(V) reduction potential to lower values by ª0.8 V on going from the aldimine to the amide species.The latter display well resolved solution EPR spectra at room temperature. Experimental Materials Complexes of type 16 were prepared by reported methods. The purification and drying of dichloromethane and acetonitrile for synthesis as well as for electrochemical and spectral work were done as described.25 Toluene was distilled over sodium before use. All other chemicals and solvents were of reagent grade and used as received.Physical measurements Spectra were recorded with the following equipment: electronic spectra, Hitachi 330 spectrophotometer; infrared spectra (KBr disc, 4000–300 cm21), Perkin-Elmer 783 spectrophotometer; X-band EPR spectra, Varian E-109C spectrometer (calibrant2152 J. Chem. Soc., Dalton Trans., 1997, Pages 2149–2153 dpph, g = 2.0037). Electrochemical measurements were done by using a PAR model 370-4 electrochemistry system as described.26 All experiments were performed at a platinum working electrode under a dinitrogen atmosphere, the supporting electrolyte being tetraethylammonium perchlorate.The potentials are referred to the saturated calomel electrode (SCE) and are uncorrected for the junction contribution. Magnetic susceptibilities were measured on a PAR-155 vibrating-sample magnetometer. Microanalyses were done using a Perkin-Elmer 240C elemental analyser. All compounds afforded satisfactory elemental analysis and only some representative instances will be cited.Syntheses [ReVL(NC6H4Y-p)Cl3] 3. The complexes were prepared by the same general method. Details are given for 3b. Yields were in the range 70–75%. The complex [ReL(OPPh3)Cl3] (100 mg, 0.13 mmol) was suspended in toluene (10 cm3) and warmed to 60 8C. p- Chloroaniline (150 mg, 1.18 mmol) was added and the mixture refluxed for 2 h. The violet solution obtained was evaporated to dryness under reduced pressure and the resulting solid product dissolved in dichloromethane (5 cm3) and subjected to chromatography on a silica gel column (20 × 1 cm; 60–120 mesh, BDH).The small yellow band which separated upon elution with benzene was rejected. The violet band that followed was eluted with benzene–acetonitrile (10 : 1). The required complex was obtained from the eluate as shiny dark microcrystals, by slow evaporation. Yield: 59 mg, 74% (Found: C, 39.2; H, 3.0; N, 7.2. Calc.for C19H17Cl3N3Re 3a: C, 39.35; H, 2.95; N, 7.25. Found: C, 37.25; H, 2.55; N, 6.90. Calc. for C19H16Cl4N3Re 3b: C, 37.15; H, 2.6; N, 6.85. Found: C, 35.15; H, 2.15; N, 6.55. Calc. for C18H13Cl5N3Re 3c: C, 34.05; H, 2.05; N, 6.6%). [ReVIL9(NC6H4Y-p)Cl3] 4. The same general method was used to synthesize complexes 4 from 3. Details are given for 4b. Yields varied in the range 80–85%. The complex [ReL1(NC6H4Cl)Cl3] (100 mg, 0.16 mmol) was dissolved in acetonitrile (20 cm3) and 0.5 mol dm23 aqueous nitric acid (0.2 cm3) was added.The solution was stirred for 1 h during which time it turned brown. Solvent evaporation afforded a dark product which was repeatedly washed with water and dried in vacuo over P4O10. Yield: 84 mg, 82% (Found: C, 38.2; H, 2.75; N, 7.1. Calc. for C19H16Cl3N3ORe 4a: C, 38.35; H, 2.7; N, 7.05. Found: C, 36.3; H, 2.3; N, 6.6. Calc. for C19H15Cl4N3ORe 4b: C, 36.25; H, 2.4; N, 6.7. Found: C, 33.2; H, 2.0; N, 6.4. Calc. for C18H12Cl5N3ORe 4c: C, 33.25; H, 1.85; N, 6.45%).Crystallography Single crystals of complexes 3b and 4b were grown by slow diffusion of hexane into dichloromethane solutions of the respective complexes. Both crystals were dark coloured and similar procedures were used for both. Cell parameters were determined by a least-squares fit of 30 machine-centred reflections (2q = 15–308). Data were collected at 22 8C by the w-scan technique in the range 3 < 2q < 508 on a Siemens R3m/V four-circle diffractometer with graphitemonochromated Mo-Ka radiation (l 0.710 73 &A check reflections after every 198 showed no intensity reduction. All data were corrected for Lorentz-polarization and absorption.27 A total of 3885 (complex 3b) and 4096 (4b) reflections were collected of which 3611 and 3716 were respectively unique; of these 2715 and 2685 were respectively taken as observed [I > 3s(I)] for structure solution and refinement. The metal atoms were located from Patterson maps, and the rest of the non-hydrogen atoms emerged from successive Fourier syntheses. The structures were then refined by full-matrix least-squares procedures. All hydrogen atoms were included in calculated positions with fixed U = 0.08 Å2.All calculations were done on a Micro VAX II computer using the SHELXTL PLUS program package28 and crystal structure plots were drawn using ORTEP.14 Significant crystal data are listed in Table 4. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Instructions for Authors, J. Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the reference number 186/478. Acknowledgements We thank the Department of Science and Technology, Indian National Science Academy, and the Council of Scientific and Industrial Research, New Delhi for financial support.Affiliation with the Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore is acknowledged. References 1 G. Rouschias and G. Wilkinson, J. Chem. Soc. A, 1967, 993; J. F. Rowbottom and G. Wilkinson, J. Chem. Soc., Dalton Trans., 1972, 826. 2 M. M. Abu-Omar and J. H. Espenson, J. Am. Chem. Soc., 1995, 117, 272; W. A. Herrmann, F. E. Kühn, F. E. Rauch, J. D. G. Carreia and G. Artus, Inorg. Chem., 1995, 34, 2914; D. D. du Mez and J. M. Mayer, Inorg.Chem., 1995, 34, 6396; Z. Zhu, A. M. Al-Ajlouni and J. H. Espenson, Inorg. Chem., 1996, 35, 1408. 3 X. L. R. Fontaine, E. H. Fowles, T. P. Layzell, B. L. Shaw and M. Thornton-Pett, J. Chem. Soc., Dalton Trans., 1991, 1519. 4 J. M. Mayer and T. H. Tulip, J. Am. Chem. Soc., 1984, 106, 3878; J. C. Bryan, R. E. Stenkamp, T. H. Tulip and J. M. Mayer, Inorg. Chem., 1987, 26, 2283. 5 R. H. Holm, Chem. Rev., 1987, 87, 1401 and refs. therein. Table 4 Crystal data for [ReVL1(NC6H4Cl)Cl3] 3b and [ReVIL19(NC6- H4Cl)Cl3] 4b Complex Formula M Crystal size/mm Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 m(Mo-Ka)/cm21 F(000) Transmission coefficient Total reflections Number unique reflections Number observed reflections g in w = 1/[s2(|F|) 1 g|F|2] Number refined parameters Ra R9 b Goodness of fit Maximum and mean D/s Data-to-parameter ratio Maximum, minimum difference peaks/e Å23 3b C19H16Cl4N3Re 614.3 0.16 × 0.14 × 0.08 Triclinic P1� 7.176(5) 11.929(6) 12.919(10) 105.69(5) 97.85(6) 90.73(5) 1054(1) 2 1.937 62.86 588 0.6728/1.0000 3885 3611 2715 0.0003 244 0.044 0.051 1.73 0.001, 0.000 11.1 : 1 1.38, 22.16 4b C19H15Cl4N3ORe 629.3 0.20 × 0.26 × 0.48 Monoclinic P21/c 13.286(7) 11.286(7) 13.500(7) — 98.79(4) — 2100(2) 4 1.991 63.11 1204 0.5923/1.0000 4096 3716 2685 0.0002 253 0.033 0.036 1.39 0.000, 0.000 10.6 : 1 1.05, 21.01 a R = S|Fo| 2 |Fc|/S|Fo|.b R9 = [Sw(|Fo| 2 |Fc|)2/Sw|Fo|2]� �� .J. Chem. Soc., Dalton Trans., 1997, Pages 2149–2153 2153 6 (a) M.Menon, S. Choudhury, A. Pramanik, A. K. Deb, S. K. Chandra, N. Bag, S. Goswami and A. Chakravorty, J. Chem. Soc., Chem. Commun., 1994, 57; (b) M. Menon, A. Pramanik, N. Bag and A. Chakravorty, Inorg. Chem., 1994, 33, 403. 7 G. R. Clark, A. J. Nielson and C. E. F. Rickard, Polyhedron, 1988, 7, 117. 8 G. La Monica and S. Cenini, J. Chem. Soc., Dalton Trans., 1980, 1145. 9 U. Weiher, K. Dehnicke and D. Fenske, Z. Anorg. Allg.Chem., 1979, 457, 115. 10 A. A. Danopoulos, C. J. Longley, G. Wilkinson, B. Hussain and M. B. Hursthouse, Polyhedron, 1989, 8, 2657; A. A. Danopoulos, G. Wilkinson, T. K. N. Sweet and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1996, 2995. 11 B. K. Dirghangi, M. Menon, S. Banerjee and A. Chakravorty, unpublished work. 12 M. Menon, A. Pramanik and A. Chakravorty, Inorg. Chem., 1995, 34, 3310. 13 H. L. Chum and P. Krumholtz, Inorg. Chem., 1974, 13, 519; H. Taube, Electron Transfer Reactions of Complex Ions in Solution, Academic Press, New York, 1973, p. 73. 14 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 15 G. V. Goeden and B. L. Haymore, Inorg. Chem., 1983, 22, 157; W. A. Nugent and B. L. Haymore, Coord. Chem. Rev., 1980, 31, 123. 16 M. Bakir, S. Paulson, P. Goodson and B. P. Sullivan, Inorg. Chem., 1992, 31, 1127; M. A. Masood and D. J. Hodgson, Inorg. Chem., 1994, 33, 2488; M. A. Masood, B. P. Sullivan and D. J. Hodgson, Inorg. Chem., 1994, 33, 5360; M. Bakir and B. P. Sullivan, J. Chem. Soc., Dalton Trans., 1995, 2189. 17 W. P. Wang, C. M. Che, K. Y. Wong and S. M. Peng, Inorg. Chem., 1993, 32, 5827; C. M. Che, Polyhedron, 1995, 14, 1791; U. W. W. Yan, K. K. Tam and K. K. Cheung, J. Chem. Soc., Dalton Trans., 1995, 2779. 18 G. K. Lahiri, S. Goswami, L. R. Falvello and A. Chakravorty, Inorg. Chem., 1987, 26, 3365. 19 R. Rossi, A. Marchi, A. Marvelli, L. Magon, M. Peruzzini, U. Casellato and R. Graziani, J. Chem. Soc., Dalton Trans., 1993, 723. 20 R. S. Shandles, R. K. Murmann and E. O. Schlemper, Inorg. Chem., 1974, 13, 1373. 21 D. Bright and J. A. Ibers, Inorg. Chem., 1969, 8, 703. 22 J. K. Gardner, N. Paryadath, J. L. Corbin and E. I. Stiefel, Inorg. Chem., 1978, 17, 897. 23 L. A. de Learie, R. C. Haltiwanger and C. G. Pierpont, Inorg. Chem., 1987, 26, 817. 24 A. Abragam and B. Bleaney, Electron Paramagnetic Resonance of Transition Ions, Clarendon, Oxford, 1970, p. 163. 25 P. Basu, S. Bhanja Choudhury and A. Chakravorty, Inorg. Chem., 1989, 28, 2680. 26 A. Pramanik, N. Bag, G. K. Lahiri and A. Chakravorty, Inorg. Chem., 1991, 30, 410. 27 A. C. T. North, D. C. Philips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. 28 G. M. Sheldrick, SHELXTL PLUS 88, Structure Determination Software Programs, Siemens Analytical X-Ray Instruments, Madison, WI, 1990. Received 23rd January 1997; Paper

ISSN:1477-9226    

DOI:10.1039/a700529f

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 2155 New SchiV bases derived from trans-pyrazolylcyclohexanol: synthesis, co-ordination chemistry and structural features‡ Michael Barz, Monika U. Rauch and Werner R. Thiel*,† Anorganisch-chemisches Institut der Technischen Universität München, Lichtenbergstrasse 4, D-85747 Garching, Germany Transformation of the OH function of trans-2-(pyrazol-1-yl)cyclohexan-1-ol into an amino group was achieved by various methods with inversion of the reaction centre and provided access to new polydentate Schiff bases bearing phenol, pyridine and furan donors.The co-ordination chemistry of these bases was investigated for PdII, ReI and ReV. It was shown by means of NMR spectroscopy that the special stereochemical situation of the 1,2-cisconfigurated cyclohexane backbone allows a flexible adaptation to different co-ordination conditions. On the other hand, the rigid asymmetrically substituted cyclohexane ring is responsible for an asymmetric arrangement of the donor fragments at the metal centre, which is required for applications of these compounds in enantioselective catalysis.During the last 25 years the development of new chiral compounds has led to rapid progress in the area of enantioselective catalysis. Especially the introduction of C2-symmetric phosphanes gave rise to a multitude of new catalytic and enantioselective reactions, like hydrogenations, isomerisations or hydroformylations.2 Besides these new chiral phosphanes, chiral nitrogen-containing compounds play an increasingly important role in enantioselective catalysis.An outstanding example is the enantioselective cis hydroxylation of olefins, catalysed by osmium complexes in the presence of cinchona alkaloids.3 Additionally, compounds bearing nitrogen atoms as donor centres have been applied for enantioselective hydrogenations (Co, Rh), hydrosilylations (Rh), the synthesis of chiral cyclopropanes (Co, Cu, Rh), stereoselective Diels–Alder reactions (Al, Mg, Fe), alkylation of ketones with dialkylzinc compounds, coupling reactions [MgR(X) and Pd], oxidations (Mo, V, Mn) and olefin metathesis (Mo).4 In our group the ring-opening reaction of prochiral, cyclic epoxides with various nucleophiles is used for the synthesis of new cycloalkanol ligands bearing two stereocentres at a rigid cyclic backbone. Pyrazoles and imidazoles, for example, give exclusively the corresponding trans-substituted 2-(diazol-1-yl)- cycloalkan-1-ols.We previously demonstrated for the corresponding phosphanes1 that the cyclic backbone forces the (bulky) substituents at the donor moieties into a pseudo-C2- symmetrical arrangement around the metal centre, as is known for complexes of C2-symmetric diphosphanes.2c Obviously, racemic mixtures are obtained in the ring-opening reaction, which have to be separated. We therefore recently worked out a procedure for the separation of the enantiomers of 2-(pyrazol- 1-yl)cyclohexan-1-ol I by an enzymatic kinetic resolution,5 which gives access to a multitude of enantiomerically pure 1,3- diaminoalcohols.Besides the co-ordination chemistry of these aminoalcohols, which turned out to be ideal ligands for the complexation of first-row transition metals,6 we are interested in these compounds as starting materials for the synthesis of other chiral chelates like Schiff bases, diamines or phosphorus donors.In all these cases the molecular geometry of the resulting transition-metal complexes depends on the absolute configurations of the stereocentres and on the particular conformation † E-Mail: thiel@arthur.anorg.chemie.tu-muenchen.de ‡ Cycloalkanes as ligand backbones. Part 3.1 of the cycloalkane ring. Additionally, if several donor centres can compete for a co-ordination site, fluxional behaviour may be observed. In the present paper we report the synthesis of Schiff bases derived from racemic I and their co-ordination chemistry with high- and low-valent transition-metal fragments with special regard to the conformational behaviour of the cyclohexane ring system.Results and Discussion Ligands For the synthesis of new Schiff bases, compounds known to be excellent donors for transition and main-group elements,7 the OH functionality of I had to be transformed into an amino group. Since the second stereocentre at the cyclohexane ring will not be affected during the synthetic procedure, the stereoselectivity of the appropriate transformations can easily be determined by NMR spectroscopy.The conversion of the alcohol I into the corresponding amine IV was realised by two different routes (Scheme 1): via a classical nucleophilic substitution reaction or a Mitsunobu amination. The tosylate II, accessible in good yields by reaction of I with toluene-psulfonyl chloride,8 is converted in a SN2 type reaction with sodium azide in dmf solution at 160 8C into the cis- Scheme 1 (i) p-MeC6H4SO2Cl (RCl), pyridine, room temperature (r.t.), 48 h; (ii) NaN3, dimethylformamide (dmf), 160 8C, 3 h; (iii) LiAlH4, diethyl ether, reflux, 3 h; (iv) (a) EtO2CN]] NCO2Et, PPh3, tetrahydrofuran (thf), 24 h, r.t.; (b) N2H4, methanol, HCl, reflux, 14 h OH N N OR N N N3 N N NH2 N N I IV ( i ) ( iv ) ( iii ) II III ( ii )2156 J.Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 configurated azide III.9 Irrespective of the high reaction temperatures, III is formed in more than 99% diastereomeric excess (inversion at the reaction centre).It can be used as a chelate for complexation of transition metals, and its stereochemistry (1,2- cis substitution) was demonstrated by a X-ray analysis of the corresponding CuCl2 complex.6 Reduction of III with LiAlH4 in thf solution leads to the desired amine IV.10 In an alternative reaction sequence, the alcohol I is converted into the amine IV by the so-called Mitsunobu reaction, which also proceeds with more than 99% diastereomeric excess under inversion at the reaction centre.11 Starting from diastereomerically pure compound IV, the Schiff bases Va–Vd are obtained in almost quantitative yields (Scheme 2).12 In the case of free Va and Vb, 1H NMR spectroscopy revealed an interaction between the phenolic hydrogen atoms and the imine nitrogen as the resonances of these protons are shifted to lower field (d 13.57 and 14.69).As previously shown by means of NMR spectroscopy and X-ray analysis,5 the 1,2-trans-disubstituted cyclohexane ring of I occupies the energetically favourable chair conformation with both the pyrazolyl and the hydroxy substituent orientated in equatorial positions, minimising axial–axial interactions. The same situation is found for the corresponding tosylate II.During the formation of the amine IV, described above, inversion at the reaction centre takes place. This results in a 1,2-cisconfigurated cyclohexane ring, a common structural feature for III, IV, the imines V and the corresponding transition-metal complexes discussed later on.These compounds can now exist as a mixture of two conformers, which should be in equilibrium in solution. In these conformers the pyrazolyl group either occupies an equatorial or an axial position (opposite orientation of the second substituent X, Scheme 3). Proton NMR spectroscopy allows one to distinguish between these conformers, as in each case only one of the protons in 1 or 2 position will show one strong trans coupling of about 12 Hz, while the other proton–proton couplings are weak (ca. 2–3 Hz) due to dihedral angles (H]C]C]H) of about 608. Molecular mechanics (MM) calculations, using the MM2 force field implemented in CHEM3D,13 showed that the equatorial orientation of the pyrazolyl moiety should be favoured by about 6–8 kJ mol21, depending on the second substituent, and a barrier of about 30 kJ mol21 should hinder the interconversion of the conformers.While the latter value corresponds to reported Scheme 2 NH2 N N N N N R¢ OH OH Cl Cl O N + IV R¢ = d b a c R¢CHO V Scheme 3 The equilibrium between the two conformers of compounds III, IV and Va, Vb H N H H X H H H X H H H H N N N data,14 the calculated energy differences between the conformers should be underestimated by some kJ mol21. In the case of the pure organic compounds III–V, we only observed one conformer (>98%), bearing an equatorial pyrazolyl group, by NMR spectroscopy. Depending on the metal fragment, the imines V can coordinate in a mono- (excluded for reasons of complex stability), bi- or tri-dentate mode.Additionally, the geometry of the cyclohexane backbone of the ligands will be determined by the specific co-ordination pattern, as the barriers to ring interconversion and the energy differences between the conformers described above are low. Metal complexes Substitution of the labile benzonitrile ligands of [PdCl2- (PhCN)2] by compound Va in the presence of NEt3 results in tridentate co-ordination of the ligand.While one chloro ligand is displaced by the deprotonated phenol fragment, the second chloride occupies the fourth co-ordination site of the squareplanar palladium centre (complex 1a, Scheme 4). If palladium acetate is used as the starting material, the corresponding acetato complex 1b is obtained even in the absence of a base by simple elimination of acetic acid.Proton NMR spectroscopy reveals the stereochemistry of the cyclohexane ring in 1a, 1b: in both cases, a large coupling constant is observed for the ring proton geminal to the imine nitrogen, indicating an equatorial orientation of the imine fragment and an axial orientation of the pyrazole moiety, which is opposite to the geometry of the free imine. There is no special influence of the chloro or the acetato ligand on the geometry of the ligand backbone.One single C]] O absorption at 1716 cm21 in the infrared spectrum of 1b is characteristic for a h1-co-ordinated acetato ligand. By slowly cooling a saturated acetonitrile solution of the palladium complex 1a orange plates are obtained. The complex crystallizes in the monoclinic, centric space group P21/c with one additional solvent molecule per formula unit, which does not co-ordinate to the palladium centre. Fig. 1 presents the molecular structure, characteristic bond lengths and angles are given in Table 1, and further crystallographic and experimental details in Table 2.The distances between the square-planar palladium centre and the four ligands are comparable to those of analogous compounds.17 Five different ring systems are responsible for the molecular structure of 1a. Three (pyrazole, cyclohexane, phenol) originate from the chelate Va, while the two new rings are formed by co-ordination of the metal atom by three donor centres of the chelate.The first three ring systems show normal conformations after co-ordination. While the pyrazole and the phenol ring are almost planar, the cyclohexane ring is in the energetically favourable chair conformation. In that conformation the pyrazole moiety is orientated in an axial, and the nitrogen atom of the imine in an equatorial, Scheme 4 (i) [PdCl2(PhCN)2], NEt3; (ii) Pd(O2CMe)2 O N Cl Pd N N O N O Pd O Me N N 1a Va 1b ( i ) ( ii ) – NEt3HCl – MeCO2HJ. Chem.Soc., Dalton Trans., 1997, Pages 2155–2161 2157 position as observed in solution. The pyrazole ring is twisted about 218 around the axis Pd]N(2), which leads to a remarkable asymmetry in the co-ordination sphere of palladium. Owing to the cis arrangement of the substituents at the cyclohexane ring, the six-membered ring formed by co-ordination of N(2) and N(3) to palladium is found in a skewed-boat conformation. The least-squares planes of the cyclohexane ring and the pyrazole are orientated almost perpendicular (ca. 838) to each other. Obviously, cis substitution of cyclohexane ring systems is an ideal tool for generation of asymmetric ligand spheres at catalytically active metal centres. We are now looking for derivatives of our compounds, bearing bulky substituents at C(1) (pyrazole) or C(15) (phenol), which should lead to a further increase in steric demand at the metal atom. Fig. 1 A PLATON plot15 of complex 1a (the additional acetonitrile molecule is omitted).Thermal ellipsoids are at the 50% probability level Table 1 Selected bond lengths (Å) and angles (8) for complex 1a Pd]Cl Pd]O Pd]N(2) Pd]N(3) 2.3181(7) 1.977(2) 2.010(2) 1.988(2) O]C(16) N(3)]C(9) N(3)]C(10) 1.313(3) 1.483(3) 1.298(3) Cl]Pd]O Cl]Pd]N(2) Cl]Pd]N(3) Pd]N(3)]C(9) Pd]O]C(16) 84.32(5) 90.54(6) 177.16(6) 121.9(2) 125.4(2) O]Pd]N(3) N(2)]Pd]N(3) O]Pd]N(2) Pd]N(3)]C(10) C(9)]N(3)]C(10) 93.24(8) 91.92(8) 174.83(8) 123.4(2) 114.7(2) Table 2 Crystallographic data for complex 1a Formula Mr Crystal system Crystal dimensions/mm Space group a/Å b/Å c/Å b/8 U/Å3 Dc/g cm23 ZF (000) m/cm21 q Range/8 T/8C Absorption correction Data measured Unique data Reflections used [I > 2s(I)] No.parameters Residual electron density/e Å23 Ra wR2b Goodness of fit C16H18ClN3OPd?CH3CN 451.224 Monoclinic 0.40 × 0.16 × 0.08 P21/c (no. 14) 9.120(1) 19.626(2) 10.903(1) 108.19(1) 1854.0(3) 1.617 4 912 11.6 2.2–25.06 280 Ref. 16(a) 14 240 3232 2949 310 10.36, 20.63 0.0282 0.0776 1.09 a S Fo| 2 |Fc /S|Fo|.b wR2 = [Sw(Fo 2 2 Fc 2)2/SwFo 2]� �� , w = 1/[s2Fo 2 1 (0.0555P)2 1 0.68P] where P = [max(Fo 2, 0) 1 2Fc 2]/3.16b Reaction of the pyridine-substituted compound Vc with [PdCl2(PhCN)2] leads, by displacement of one chloro ligand, to the square-planar complex 2a (Scheme 5). The cationic nature of this species, bearing a tridentate ligand, is revealed by conductivity measurements (Lm = 62 S cm2 mol21, 25 8C, 0.001 mol dm23 in dmf).Additionally, mass spectrometric investigations [fast atom bombardment (FAB)] only showed the isotope pattern of the cationic species PdL(Cl)1. In the 1H NMR spectrum all resonances are shifted to lower field, with respect to 1a and Vc, which is in accordance with the cationic nature of the palladium complex. At room temperature broad signals are observed, indicating a dynamic process in the ligand sphere. For a detailed investigation of this process we carried out NMR experiments in the temperature range between 120 and 280 8C. At low temperatures (<240 8C) the resonances of two cationic palladium complexes, observed in a 1 : 1 ratio, can be identified.Two-dimensional NMR experiments allowed a complete assignment of the signals and, in combination with data from experiments at various temperatures, the calculation of the energy of activation for this dynamic process (DG‡ = 57 ± 2 kJ mol21). Since NMR spectroscopy clearly demonstrates a tridentate co-ordination for both species, the only explanation possible for the nature of this process is an inversion of the cyclohexane ring, as shown in Scheme 6.Replacing the pyridine fragment of compound Vc by the weaker donating furan group of Vd generates a new system, which could co-ordinate either in a bidentate mode or as a tridentate chelate with a labile donor site.18 The composition of the corresponding dichloropalladium complex 2b, obtained by reaction of Vd with [PdCl2(PhCN)2], is verified by elemental analysis; NMR spectroscopic investigations were impossible as the compound is completely insoluble in most organic solvents, with the exception of hot dimethylformamide and hot dimethyl sulfoxide, wherein decomposition occurs. Refluxing [ReBr(CO)5], synthesized from [Re2(CO)10] and bromine,19 with 1 equivalent of compound Va in thf solution, yields the octahedral rhenium(I) complex 3.Even in its depro- Scheme 5 2a + Cl – [PdCl2(PhCN)2] + Vc N N N Pd N Cl Scheme 6 Fluxional process equilibrating the two isomers of the cation of complex 2a N N N CO Re CO CO Br H O H N N N Cl Pd Cl H O 2b 32158 J.Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 tonated form Va is not able to replace the bromo ligand at the low-valent rhenium centre. From NMR and IR investigations it is clear that the carbonyl ligands are co-ordinated facially, as is known for other complexes of the type [ReBr(CO)3(L]L)] (L]L = bidentate chelate ligand).20 If the donor sites of the chelate ligand are inequivalent, as they are in our case, the metal becomes a centre of chirality.In combination with the racemic ligand Va, the introduction of a new chiral centre should result in the formation of two diastereomeric speciesh are not observed in the NMR spectra of 3. At the moment we do not know why only one of the diastereomers is formed selectively. Since the resonance of the OH proton is observed fairly deshielded at d 10.87, a weak hydrogen interaction of the OH group and the bromo ligand may be the reason for this behaviour.If this is true, the imine fragment must be orientated almost perpendicular to the phenol group. This would minimise p interactions between these fragments and lead to a low-field shift of the resonance of the imine proton, which is indeed observed at d 9.80. For steric reasons, the imine group should be configurated, as shown in Scheme 6, to prevent interaction of the bulky phenol group with the equatorial carbonyl ligand in the cis position, a fact which also may be responsible for the deshielding of the imine proton.Switching to the more Lewis-acidic rhenium(V) precursor [NEt4][ReOCl4] results in a tridentate co-ordination mode of the chelates Vc, Vb with oxygen as well as both nitrogen atoms binding to rhenium. The octahedral complexes 4a, 4b are obtained in high yields. For steric reasons, the three donor centres of the ligand co-ordinate meridionally.This mode allows the formation of three isomers, one (C) with the oxo ligand trans to the imine nitrogen. In the other isomers one chloro ligand is trans to the imine nitrogen and the oxo ligand is in the cis position, which results in the generation of a new chiral centre, the metal atom. As we use racemic mixtures of Va, Vb these isomers are diastereomers (A and B). All three isomers can be observed by NMR spectroscopy.While the resonances of the diastereomeric complexes A and B can be assigned without problems (see Experimental section), the minor (ca. 10% of intensity) product C can be clearly identified by a characteristic resonance for the imine proton at about d 9.27, indicating the strong trans influence of the oxo ligand. In contrast to the square-planar palladium(II) complexes 1a, 1b, the geometry of the cyclohexane backbone in 4a, 4b switches back to that of the free Schiff bases: pyrazole in equatorial, imine in axial orientation. As described in this paper, the 1,2-cis-substituted cycloalkane ring system allows detailed investigations into stereochemical N N N Re O X X Cl Cl O N N N Re O X X Cl O Cl N N N Re O X X O Cl Cl Isomer A and B Isomer C 4a X = H 4b X = Cl features of the ligands and transition-metal complexes.Its conformational flexibility, in combination with the rigidity of the six-membered ring, can readily be compared with the structural characteristics of e.g.C2-symmetric phosphanes like the well known 2,29-bis(diphenylphosphino)-1,19-binaphthyl system.2c We therefore are now looking out for catalytic applications of the enantiomerically pure Schiff bases. Experimental The compounds rac-trans-2-(pyrazol-1-yl)cyclohexan-1-ol I,5 [PdCl2(PhCN)2],21 [ReBr(CO)5] 19 and [NEt4][ReOCl4] 22 were synthesized according to published procedures. All other starting materials were from Aldrich and used without further puri- fication.The NMR (Bruker DPX 400), infrared (Perkin-Elmer 1600 Series FTIR) and mass spectra (Hewlett-Packard HP 5890 gas chromatograph and mass-selective detector HP 5970, Finnigan MAT 90) and all elemental analyses were carried out at the Anorganisch-chemisches Institut der TU München. The assignments of the NMR spectra of the 2-(pyrazol-1-yl)- cyclohexyl moiety were made according to Fig. 1, those of the imine residues according to Scheme 7. Syntheses rac-trans-2-(Pyrazol-1-yl)cyclohexyl toluene-p-sulfonate II.Compound I (20.0 g, 120 mmol) and toluene-p-sulfonyl chloride (22.9 g, 120 mmol) were dissolved in CHCl3 (150 cm3) at 0 8C. Pyridine (40 cm3) was added dropwise and the reaction mixture stirred for 2 d at room temperature. The solution was extracted three times with water (30 cm3), the organic layer separated, dried over MgSO4 and the solvent removed in vacuo. After washing the colourless residue with diethyl ether (50 cm3) and pentane it was recrystallised from ethyl acetate.Colourless crystals, m.p. 154–156 8C, yield 17.1 g (45%) (Found: C, 59.95; H, 6.2; N, 8.75; S, 10.6. C16H20N2O3S requires C, 60.0; H, 6.3; N, 8.75; S, 10.0%); n& max/cm21 (KBr) 1192s, 1177vs (SO2); dH(250.13 MHz, 25 8C, CDCl3) 7.35 [d, 3J(HoHm) 8.0, Ho], 7.23 [d, 3J(H1H2) 1.5, H1], 7.15 [d, 3J(H2H3) 2.5, H3], 7.12 (d, Hm), 5.99 (dd, H2), 4.69 [dt, 3J(H8 eqH9) 5.1, 3J(H4H9) 10.2, 3J(H8 axH9) 10.2, H9], 3.99 [dt, 3J(H4H5 eq) 7.0, 3J(H4H5 ax) 10.2 Hz, H4], 2.36 (3 H, s, CH3) and 2.44–1.34 (8 H, 5m, CH2); dC(100.62 MHz, 25 8C, CDCl3) 144.0 (ipso-C), 139.2 (C1), 133.3 (Cp), 129.5 (Co), 129.2 (C3), 127.5 (Cm), 104.7 (C2), 82.5 (C9), 63.7 (C4), 32.7 (C8), 31.8 (C5), 24.3 (C6), 23.8 (C7) and 21.5 (CH3); m/z (electron impact, EI) 320 (1, M1), 256 (6, M 2 SO2), 228 (6, M 2 C7H8), 171 (53, C7H7O3S), 165 (27, M 2 C7H7O2S), 155 (10, C7H8O2S), 148 (74, M 2 C7H8O3S), 121 (8, C3H3N2]C4H6), 120 (14, C3H3N2]C4H5), 119 (12, C3H3N2]C4H4), 107 (30, C3H3N2]C3H4), 91 (63, C7H7), 81 (37, C3H3N2]CH2), 77 (9, C6H5), 69 (100, C3H5N2), 55 (8, C4H7), 51 (6, C4H3) and 41 (36%, C3H5).rac-cis-1-(2-Azidocyclohexyl)pyrazole III. A mixture of compound II (4.00 g, 12.5 mmol) and sodium azide (6.50 g, 100 mmol) in dry dmf (50 cm3) was heated to reflux for 3 h. After completion of the reaction, water (50 cm3) was added and the Scheme 7 N OH N Cl Cl OH N N 10 14 15 11 12 13 N 11 13 16 12 14 11 O 16 10 15 12 10 14 15 13 11 12 10 14 13J. Chem.Soc., Dalton Trans., 1997, Pages 2155–2161 2159 resulting orange solution extracted three times with diethyl ether (30 cm3). The combined organic layers were extracted three times with water (30 cm3), dried over MgSO4 and the solvent removed in vacuo. The product was obtained as a pale yellow oil, which solidifies at 234 8C. Yield 1.80 g (75%) (Found: C, 56.4; H, 6.8; N, 36.75. C9H13N5 requires C, 56.55; H, 6.85; N, 36.6%); n& max/cm21 (KBr) 2110vs (N3); dH(400.13 MHz, 25 8C, CDCl3) 7.51 [d, 3J(H1H2) 1.5, H1], 7.45 [d, 3J(H2H3) 2.5, H3], 6.25 (dd, H2), 4.32 [dt, 3J(H4H9) 3.4, 3J(H4H5 eq) 3.4, 3J(H4H5 ax) 12.6, H4], 4.20 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.12–1.37 (8 H, 6m, CH2); dC(100.62 MHz, 25 8C, CDCl3) 139.2 (C1), 127.0 (C3), 105.2 (C2), 62.5, 62.2 (C4, C9), 29.3 (C5), 25.5, 24.7 (C8, C6) and 19.5 (C7); m/z (EI) 191 (1, M1), 163 (3, M 2 N2), 149 (1, M 2 N3), 121 (3, C3H3N2]C4H6), 120 (4, C3H3N2]C4H5), 119 (6, C3H3N2]C4H4), 107 (4, C3H3N2] C3H4), 95 (8, C3H3N2]C2H4), 81 (16, C3H3N2]CH2), 69 (24, C3H5N2), 68 (15, C3H4N2), 67 (10, C3H3N2) and 41 (26%, C3H5).rac-cis-1-(2-Aminocyclohexyl)pyrazole IV. Method A, reduction of III. A solution of compound III (6.9 g, 36 mmol) in diethyl ether (50 cm3) was added dropwise to a suspension of LiAlH4 (2.1 g, 55 mmol) in diethyl ether (250 cm3) and the resulting mixture refluxed for 3 h. The reaction was quenched by the addition of water (1 cm3), the resulting precipitate was filtered off, the filtrate dried over Na2SO4 and the solvent removed in vacuo.The product was obtained as a colourless oil. Yield 3.2 g (53%). Method B, from compound I. A solution of compound I (6.7 g, 40 mmol) in dry thf (50 cm3) and EtO2CN2CO2Et (6.3 cm3, 40 mmol) were added dropwise and simultaneously to a solution of phthalimide (5.9 g, 40 mmol) and PPh3 (10.5 g, 40 mmol) in dry thf (200 cm3) under a nitrogen atmosphere.The reaction mixture was stirred at 20 8C for 1 d and the solvent removed in vacuo. After dissolution of the residue in methanol (200 cm3), hydrazine hydrate (80%, 4.9 cm3, 80 mmol) was added and the mixture refluxed for 7 h. Concentrated hydrochloric acid (6 cm3) was added and the mixture refluxed for 7 h. A colourless precipitate formed, which was filtered off and rinsed with dilute hydrochloric acid. The combined aqueous solutions were extracted with CHCl3 (7 × 30 cm3) and Et2O (4 × 30 cm3) and then treated with saturated NaOH until pH > 13.A brownish oil separated, which was extracted with diethyl ether (4 × 30 cm3). The combined organic layers were washed with brine (4 × 30 cm3) and dried over MgSO4. The solvent was removed in vacuo to yield a yellow oil. Kugelrohr distillation gave the pure amine IV as a colourless oil. Yield 3.70 g (56%). n& max/cm21 (CHCl3) 3372m and 3300m (NH2); dH(400.13 MHz, 25 8C, CDCl3) 7.43 [d, 3J(H1H2) 1.5, H1], 7.38 [d, 3J(H2H3) 2.0, H3], 6.15 (dd, H2), 4.17 [ddd, 3J(H4H9) 3.5, 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.0, H4], 3.41 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.15–1.24 (10 H, 6m, CH2, NH2); dC(100.62 MHz, 25 8C, CDCl3) 138.6 (C1), 127.2 (C3), 104.4 (C2), 63.4 (C4), 50.1 (C9), 31.5 (C5), 24.7, 24.6 (C8, C6) and 18.9 (C7); m/z (EI) 165 (1, M1), 81 (34, C3H3N2]CH2), 69 (61, C3H5N2), 55 (9, C4H7), 41 (35, C3H5), 30 (33, CH2NH2), 28 (100, N2) and 27 (28%, C2H3). Schiff bases V (general procedure).An equimolar solution of compound IV and of the appropriate aromatic aldehyde in ethanol (200 cm3) was refluxed for 2 h. The solvent was removed and pentane added to the resulting yellow oil. With the exception of Vc, the Schiff bases crystallised after 24 h at 228 8C. Yields 70–90%. rac-cis-2-[2-(Pyrazol-1-yl)cyclohexyliminomethyl]phenol Va. (Found: C, 70.95; H, 7.0; N, 15.55; O, 6.45. C16H19N3O requires C, 71.35; H, 7.1; N, 15.6; O, 5.95%); n& max/cm21 (KBr) 3428vs (OH), 1626vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 13.57 (s, OH), 7.66 (s, H10), 7.45 [d, 3J(H1H2) 1.8, H1], 7.26 [ddd, 3J(H14H15) 8.2, 3J(H13H14) 7.4, 4J(H12H14) 1.7, H14], 7.19 [d, 3J(H2H3) 2.4, H3], 7.00 [dd, 3J(H12H13) 7.6, H12], 6.91 [dd, 4J(H13H15) 0.5, H15], 6.78 (dt, H13), 6.03 (dd, H2), 4.54 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.9, H4], 3.95 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9] and 2.25–1.50 (8 H, 6m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 165.4 (C10), 161.1 (C16), 139.0 (C1), 132.4 (C12), 131.5 (C14), 127.0 (C3), 118.7, 118.6 (C11, C15), 116.8 (C13), 104.7 (C2), 68.4 (C4), 63.8 (C9), 32.1 (C5), 26.1, 25.5 (C8, C6) and 20.2 (C7); m/z (EI) 269 (3, M1), 201 (3, M 2 C3H4N2), 120 (9, C7H6NO), 81 (11, C3H3N2]CH2), 69 (100, C3H5N2) and 41 (19%, C3H5).rac-2,4-Dichloro-6-[cis-(2-pyrazol-1-yl)cyclohexyliminomethyl] phenol Vb. (Found: C, 56.25; H, 5.15; Cl, 20.8; N, 12.45. C16H17Cl2N3O requires C, 56.8; H, 5.05; Cl, 20.95; N, 12.4%); n& max/cm21 (KBr) 3406 (br) (OH), 1628vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 14.69 (s, OH), 7.48 (s, H10), 7.47 [d, 4J(H12H14) 2.5, H12], 7.35 [d, 3J(H1H2) 2.5, H1], 7.19 [d, 3J(H2H3) 2.0, H3], 6.87 (d, H14), 6.06 (dd, H2), 4.53 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.6, H4], 4.08 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.25–1.50 (8 H, 6m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 163.9 (C10), 157.3 (C16), 139.4 (C1), 132.4 (C14), 129.0 (C12), 127.0 (C3), 122.9, 122.4 (C11, C15), 119.1 (C13), 104.7 (C2), 67.7 (C4), 63.3 (C9), 31.4 (C5), 25.7, 25.5 (C8, C6) and 20.1 (C7); m/z [chemical ionisation (CI), 35Cl] 338 (100, M 1 H), 337 (50, M1) and 269 (3%, M 2 C3H4N2).rac-cis-2-[2-(Pyrazol-1-yl)cyclohexyliminomethyl]pyridine Vc. n& max/cm21 (KBr) 1647vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 8.43 [d, 3J(H14H15) 5.0, H15], 7.88 [d, 3J(H12H13) 7.5, H12], 7.67 (s, H10), 7.66 [d, 3J(H2H3) 2.0, H3], 7.58 [t, 3J(H13H14) 7.5, H13], 7.31 [s, 3J(H1H2) < 1.0, H1], 7.13 (dd, H14), 5.91 (br, H2), 4.45 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.5, H4], 3.85 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9] and 2.25–1.30 (8 H, 4m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 161.6 (C10), 154.3 (C11), 148.9 (C15), 138.7 (C1), 136.1 (C12), 126.7 (C3), 124.3, 120.6 (C13, C14), 104.5 (C2), 68.6 (C4), 64.3 (C9), 29.9 (C5), 26.8, 25.6 (C8, C6) and 19.8 (C7); m/z (EI) 254 (3, M1), 186 (42, M 2 C3H4N2), 176 (63, M 2 C5H4N), 157 (9, C5H4N]CHNC4H4), 145 (52, C5H4N]CHNC3H4), 131 (52, C5H4N]CHNC2H2), 119 (32, C5H4N]CHNCH2), 118 (35, C5H4N]CHNCH), 107 (13, C5H4N]CHNH2), 105 (26, C5H4N]CNH), 92 (58, C5H4N] CH2), 81 (30, C3H3N2]CH2), 80 (26, C5H6N), 79 (41, C5H5N), 78 (35, C5H4N), 69 (100, C3H5N2), 68 (30, C3H4N2), 67 (23, C3H3N2), 65 (36, C4H3N) and 41 (44%, C3H5).rac-cis-2-[2-(Pyrazol-1-yl)cyclohexyliminomethyl]furan Vd. (Found: C, 67.65; H, 7.35; N, 16.95. C14H17N3O requires C, 69.1; H, 7.05; N, 17.25%); n& max/cm21 (KBr) 1642vs (C]] N); dH(400.13 MHz, 25 8C, CDCl3) 7.46 [dd, 3J(H13H14) 1.2, 4J(H12H14) 0.6, H14], 7.43 [d, 3J(H1H2) 1.8, H1], 7.41 (s, H10), 7.28 [d, 3J(H2H3) 2.3, H3], 6.55 [dd, 3J(H12H13) 3.4, H12], 6.40 (dd, H13), 6.05 (dd, H2), 4.52 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 12.9, H4], 3.95 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9] and 2.46–1.50 (8 H, 3m, CH2); dC(100.25 MHz, 25 8C, CDCl3) 151.7 (C11), 149.8 (C10), 144.7 (C14), 138.5 (C1), 127.4 (C3), 114.2 (C12), 111.4 (C13), 104.4 (C2), 69.9 (C4), 64.8 (C9), 32.9 (C5), 26.4, 25.9 (C8, C6) and 20.1 (C7); m/z (EI) 243 (4, M1), 175 (10, M 2 C3H4N2), 150 (42, M 2 C4H3O 2 CN), 146 (32, M 2 C3H4N2 2 C2H5), 134 (8, M 2 C3H4N2 2 C3H5), 107 (21, C4H3O]CHNCH), 94 (57, C4H3O]CHN), 81 (49, C5H5O), 80 (32, C4H4N2), 79 (19, C4H3N2), 69 (100, C3H5N2), 68 (34, C3H4N2), 67 (29, C3H3N2) and 52 (56%, C4H4).Chloro{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- phenolato}palladium(II) 1a.Bis(benzonitrile)dichloropalladium( II) (1.42 g, 3.70 mmol) and triethylamine (0.50 cm3) were added to a solution of compound Va (1.00 g, 3.70 mmol) in dry CH2Cl2 (30 cm3) and the mixture stirred for 48 h at room temperature. The product, which precipitated as a yellow2160 J. Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 microcrystalline solid, was contaminated with a small amount of triethylammonium chloride and traces of elemental palladium. It can be recrystallised from methanol or concentrated acetonitrile solution at 50 8C, resulting in formation of the acetonitrile adduct 1a?MeCN as deep orange plates (m.p. 288 8C). Yield 1.27 g (76%) (Found: C, 47.75; H, 4.65; Cl, 7.75; N, 12.35; Pd, 24.0. C16H18ClN3OPd?CH3CN requires C, 47.9; H, 4.7; Cl, 7.85; N, 12.4; Pd, 23.6%); n& max/cm21 (KBr) 1611vs (C]] N); dH(400.13 MHz, 25 8C, [2H7]dmf) 8.40 [d, 3J(H1H2) 2.0, H1], 8.38 [d, 3J(H2H3) 3.0, H3], 8.28 (s, H10), 7.42 [dd, 3J(H12H13) 8.0, 4J(H12H14) 1.8, H12], 7.31 [ddd, 3J(H14H15) 8.5, 3J(H13H14) 6.8, H14], 6.83 (d, H15), 6.49 (m, H2, H13), 4.92 [br, 3J(H4H9) = 3J(H4H5 eq) = 3J(H4H5 ax) 2–3, H4], 4.10 [dt, 3J(H4H9) = 3J(H8 eqH9) 2.0, 3J(H8 axH9) 11.6 Hz, H9] and 2.16–1.22 (8 H, 4m, CH2); dC(100.25 MHz, 25 8C, [2H7]dmf) 164.1, 162.0 (C10, C16), 145.4 (C1), 136.0, 135.4, 134.7 (C3, C12, C14), 120.1 (C15), 118.2 (C11), 115.6 (C13), 107.0 (C2), 69.0 (C4), 60.5 (C9), 28.4, 28.4, 24.4 (C5, C6, C8) and 20.0 (C7). Acetato{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- phenolato}palladium(II) 1b.Compound Va (0.20 g, 0.74 mmol) in dry CH2Cl2 (5 cm3) was added dropwise via a syringe to a solution of palladium acetate (0.17 g, 0.74 mmol) in dry CH2Cl2 (5 cm3). After 48 h of stirring at room temperature the solvent was removed in vacuo. The residue was washed with diethyl ether (20 cm3) and dried in vacuo. Yield 0.27 g (85%), yellow microcrystalline solid (Found: C, 48.55; H, 5.3; N, 10.05.C18H21N3O3Pd requires C, 49.85; H, 4.85; N, 9.7%); n& max/cm21 (KBr) 1610vs (C]] N); dH(400.13 MHz, 25 8C, CD2Cl2) 7.70 [d, 3J(H1H2) 2.4, H1], 7.69 (s, H10), 7.65 [d, 3J(H2H3) 2.8, H3], 7.31 [ddd, 3J(H14H15) 8.8, 3J(H13H14) 6.8, 4J(H12H14) 1.8, H14], 7.18 [dd, 3J(H12H13) 7.9, H12], 6.93 (d, H15), 6.57 [ddd, 4J(H13H15) 1.0, H13], 6.42 (dd, H2), 4.75 [br, 3J(H4H9) = 3J(H4H5 eq) = 3J(H4H5 ax) 2–3, H4], 3.71 [dt, 3J(H4H9) = 3J(H8 eqH9) 2.6, 3J(H8 axH9) 12.1 Hz, H9], 2.12 (s, O2CCH3) and 2.54–1.26 (8 H, 4m, CH2); dC(100.25 MHz, 25 8C, CD2Cl2) 177.7 (C]] O), 164.8 (C16), 162.2 (C10), 142.4 (C1), 136.0, 134.8 (C12, C14), 132.0 (C3), 120.2 (C15), 119.6 (C11), 115.6 (C13), 107.2 (C2), 70.6 (C4), 60.1 (C9), 30.1 (CH3), 28.7 (C5), 24.7, 24.0 (C6, C8) and 19.3 (C7).Chloro{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- pyridine}palladium(II) chloride 2a. The compound [PdCl2- (PhCN)2] (1.11 g, 2.90 mmol) was added to a solution of compound Vc (0.74 g, 2.90 mmol) in dry CH2Cl2 (30 cm3). The mixture was stirred for 5 h at room temperature.The solvent was removed in vacuo and the brown oily residue recrystallised from CH2Cl2–diethyl ether to give bright yellow crystals containing about 2.5 equivalents of CH2Cl2 per molecule of complex 2a. Yield 0.99 g (53%) (Found: C, 32.2; H, 3.4; N, 9.1. C15H18Cl2N4Pd?2.5CH2Cl2 requires C, 32.65; H, 3.6; N, 8.7%); n& max/cm21 (KBr) 1624vs (C]] N); dH(400.13 MHz, 260 8C, CD2Cl2), isomer A, 10.37 (s, H10), 9.11 [d, 3J(H14H15) 4.5, H15], 9.02 [d, 3J(H12H13) 7.5, H12], 8.31 [d, 3J(H1H2) 2.6, H1], 8.24 [dd, 3J(H13H14) 8.0, H13], 7.96 [d, 3J(H2H3) 3.5, H3], 7.70 (m, H14), 6.55 (dd, H2), 4.87 [dt, 3J(H8 axH9) 12.0, 3J(H4H9) = 3J(H8 eqH9) 3.5, H9], 4.74 [br, 3J(H4H5 eq) = 3J(H4H5 ax) 2–3, H4) and 2.55– 1.30 (8 H, m, CH2); isomer B, 10.52 [d, 3J(H9H10) 2.0, H10], 9.10 [d, 3J(H14H15) 4.5, H15], 8.65 [d, 3J(H12H13) 7.0, H12], 8.22 [dd, 3J(H13H14) 8.0, H13], 8.15 [d, 3J(H1H2) 2.0, H1], 7.95 [d, 3J(H2H3) 2.0, H3], 7.70 (m, H14), 6.44 (t, H2), 5.00 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.5, 3J(H4H5 ax) 13.0, H4], 4.45 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.55–1.30 (8 H, m, CH2); isomer ratio A:B 1.00); m/z (FAB, 35Cl, 106Pd) 395 (13, PdLCl) and 359 (2%, C15H17N4Pd). Dichloro{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl]- furan}palladium(II) 2b. The compound [PdCl2(PhCN)2] (1.57 g, 4.1 mmol) was added to a solution of compound Vd (1.0 g, 4.1 mmol) in dry CH2Cl2 (30 cm3).The mixture was stirred for 48 h at room temperature. A brown precipitate formed which was washed three times with CH2Cl2 (10 cm3) and dried in vacuo. Yield 1.66 g (96%), orange-brown microcrystalline powder (Found: C, 39.55; H, 3.9; Cl, 17.05; N, 9.85; O, 3.85; Pd, 25.0. C14H17Cl2N3OPd requires C, 40.0; H, 4.05; Cl, 16.85; N, 10.0; O, 3.8; Pd, 25.3%); n& max/cm21 (KBr) 1608vs (C]] N). Bromotricarbonyl{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl] phenol}rhenium(I) 3.A solution of [ReBr(CO)5] (0.3 g, 0.74 mmol) and compound Va (0.20 g, 0.74 mmol) in thf (20 cm3) was heated under reflux for 48 h, changing from yellow to orange. After evaporation of the solvent in vacuo, the solid residue was washed three times with diethyl ether (10 cm3) and dried in vacuo. Yield: 0.18 g (41%), yellow microcrystalline powder (Found: C, 35.25; H, 3.2; Br, 13.3; N, 6.5; O, 11.25; Re, 31.0. C19H19BrN3O4Re requires C, 36.85; H, 3.1; Br, 12.9; N, 6.8; O, 10.35; Re, 30.05%); n& max/cm21 (KBr) 2019vs, 1902vs (CO), 1609vs (C]] N); (thf) 2020vs, 1914vs, 1888s (CO); dH(400.13 MHz, 25 8C, CD2Cl2) 10.87 (s, OH), 9.80 (s, H10), 7.88 [d, 3J(H1H2) 2.5, H1], 7.64 [d, 3J(H2H3) 2.0, H3], 7.60 [dd, 3J(H12H13) 7.5, 4J(H12H14) 1.5, H12], 7.55 [dd, 3J(H14H15) 8.8, 3J(H13H14) 7.5, H14], 7.04 [ddd, 4J(H13H15) 1.1, H13], 6.98 (dd, H15), 6.45 (dd, H2), 4.62 [dt, 3J(H4H9) = 3J(H4H5 eq) 3.0, 3J(H4H5 ax) 10.0, H4], 3.80 [br, 3J(H8 axH9) = 3J(H8 eqH9) 2–3 Hz, H9) and 2.25–1.80 (8 H, 6m, CH2); dC(100.25 MHz, 25 8C, CD2Cl2) 196.9 (2COeq), 194.8 (COax), not observed (C10, C16), 146.5 (C1), 137.0 (C3), 133.8 (C12), 133.2 (C14), 119.9 (C15), 117.4, 117.4 (C11, C13), 107.8 (C2), 63.0 (C4, C9), 33.1 (C5), 28.7, 23.2 (C8, C6) and 20.0 (C7).Dichlorooxo{rac-cis-2-[2-(pyrazol-1-yl)cyclohexyliminomethyl] phenolato}rhenium(V) 4a and dichloro{rac-cis-2,4-dichloro- 6-[2-(pyrazol-1-yl)cyclohexyliminomethyl]phenolato}oxorhenium( V) 4b.The appropriate compound Va or Vb (1 mmol) was added to a solution of [NBu4][ReOCl4] (293 mg, 0.5 mmol) in ethanol (20 cm3). The resulting brown reaction mixture was heated to reflux for 3 h during which a green precipitate formed, which was filtered off, washed with ethanol and pentane and dried in vacuo. Yield 0.20 (73%) of 4a and 0.20 g (65%) of 4b, green microcrystalline solids, poorly soluble in organic solvents. Complex 4a (Found: C, 35.6; H, 3.65; N, 7.3.C16H18Cl2- N3O2Re requires C, 35.5; H, 3.35; N, 7.75%); n& max/cm21 (KBr) 1614vs (C]] N); dH[400.13 MHz, 25 8C, (CD3)2SO], isomer A, 8.92 (s, H10), 8.91 [d, 3J(H1H2) 2.5, H1], 8.76 [d, 3J(H2H3) 2.5, H3], 7.69 [ddd, 3J(H14H15) 8.5, 3J(H13H14) 7.0, 4J(H12H14) 1.5, H14], 7.63 [dd, 3J(H12H13) 8.0, H12], 7.15 (d, H15), 7.07 (t, H2), 7.00 (dd, H13), 5.20 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 12.5, H4], 5.01 [br, 3J(H4H9) = 3J(H8 eqH9) = 3J(H8 axH9) ca. 2–3, H9] and 2.90–1.35 (8 H, 5m, CH2); isomer B, 9.16 (s, H10), 8.98 [d, 3J(H1H2) 2.5, H1], 8.87 [d, 3J(H2H3) 2.5, H3], 7.79 [td, 3J(H14H15) = 3J(H13H14) 7.8, 4J(H12H14) 1.5, H14], 7.75 [dd, 3J(H12H13) 8.0, H12], 7.25 (d, H15), 7.13 (t, H2), 7.10 (dd, H13), 5.17 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 14.0, H4], 4.77 [br, 3J(H4H9) = 3J(H8 eqH9) = 3J(H8 axH9) ca. 2–3 Hz, H9] and 2.90–1.35 (8 H, 5m, CH2), isomer ratio A:B 1.56; dC[100.15 MHz, 25 8C, (CD3)2SO], isomer A, 174.7, 174.1 (C10, C16), 147.8 (C1), 138.5, 138.0, 137.7 (C3, C12, C14), 121.2, 120.8, 118.8 (C11, C13, C15), 108.7 (C2), 76.8 (C4), 60.8 (C9), 29.7, 28.7, 24.2 (C5, C6, C8), 18.7 (C7); isomer B, 175.8 (C10), 172.0 (C16), 149.2 (C1), 139.7, 139.0, 138.5 (C3, C12, C14), 121.5, 120.6 (C11, C15), 120.6 (C13), 109.5 (C2), 75.4 (C4), 56.2 (C9), 29.0, 28.8, 23.9 (C5, C6, C8) and 18.6 (C7).Complex 4b (Found: C, 31.7; H, 2.7; Cl, 22.6; N, 6.95; O, 5.55; Re, 30.1. C16H16Cl4N3O2Re requires C, 31.5; H, 2.65; Cl, 23.25; N, 6.9; O, 5.25; Re, 30.5%); n& max/cm21 (KBr) 1619vs (C]] N); dH[400.13 MHz, 25 8C, (CD3)2SO], isomer A, 8.93 [d, 3J(H1H2) 2.5, H1], 8.88 (s, H10), 8.81 [d, 3J(H2H3) 2.5, H3], 8.00 [d, 4J(H12H14) 2.5, H12], 7.70 (d, H14), 7.10 (t, H2), 5.15 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 12.0, H4], 5.01 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3, H9] and 2.90–1.35 (8 H, 5m, CH2); isomer B, 9.11 (s, H10), 8.99 [d, 3J(H1H2) 2.5, H1], 8.91 [d,J.Chem. Soc., Dalton Trans., 1997, Pages 2155–2161 2161 3J(H2H3) 2.5, H3], 8.13 [d, 4J(H12H14) 2.5, H12], 7.84 (d, H14), 7.15 (t, H2), 5.12 [br d, 3J(H4H9) = 3J(H4H5 eq) ca. 2–3, 3J(H4H5 ax) 17.6, H4], 4.78 [br, 3J(H8 axH9) = 3J(H8 eqH9) ca. 2–3 Hz, H9] and 2.90–1.35 (8 H, 5m, CH2); isomer ratio A:B 1.35. Crystallography Intensity data for complex 1a were collected on a STOE-IPDS diffractometer using graphite-monochromated Mo-Ka radiation (l 0.710 73 Å). The structure was solved by the Patterson method with SHELXS 8623 and refined (based on F 2) by fullmatrix least-squares analysis with SHELXL 93.24 All non-H atoms were refined with anisotropic thermal parameters.The positions of all H atoms were obtained from the least-squares refinement and were refined with isotropic thermal parameters. Atomic coordinates, thermal parameters, and bond lengths and angles have been deposited at the Cambridge Crystallographic Data Centre (CCDC). See Instructions for Authors, J.Chem. Soc., Dalton Trans., 1997, Issue 1. Any request to the CCDC should quote the full literature citation and the reference number 186/496. Acknowledgements The authors thank Professor Dr. W. A. Herrmann, the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie for support of this work and Dr. E. Herdtweck for X-ray data collection. References 1 Part 2, C. Thurner, M. Barz, M. Spiegler and W. R. Thiel, J. Organomet. 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ISSN:1477-9226    

DOI:10.1039/a608031f

出版商:RSC    

年代:1997

数据来源: RSC