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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2001–2006 2001 Mono-, di- and tri-dentate binding modes of a substituted isocytosine derivative in complexes of palladium and zinc Clayton Price,a Nicholas H. Rees,a Mark R. J. Elsegood,b William Clegg b and Andrew Houlton *,†,a a Department of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne, UK NE1 7RU b Crystallography Laboratory, Department of Chemistry, University of Newcastle upon Tyne, Newcastle upon Tyne, UK NE1 7RU The crystal and molecular structures of three metal complexes of the pyrimidine derivative, 1-(2-hydroxyethyl)- (2-aminoethyl-N2)-5-methylisocytosine reveal that, as a ligand, this heterocyclic base exhibited a diverse range of co-ordination modes.With zinc(II), monodentate co-ordination via the carbonyl oxygen of the pyrimidine base was observed. In the case of palladium(II), both a didentate mode, via endo- and exo-cyclic nitrogen donors, and a tridentate mode, involving exocyclic nitrogens and the alcohol oxygen donors, was observed.In the latter case the pyrimidine exists in the rare iminooxo tautomeric form. Studies on the interactions of metal ions with purine and pyrimidine bases are central to bioinorganic chemistry.1,2 While the predominant binding sites are now well established, an increasing number of reports indicate that metal binding may occur at relatively unreactive sites in both biological and model systems with significant consequences.1,3–10 For example, such binding has been shown to stabilize rare tautomeric forms,7,8 and this may be an important factor in the general toxic eVect of metal ions, since base-pair mismatching can result.1,7,8 We have recently begun to explore the co-ordination chemistry of modified nucleobase derivatives which feature tethered chelating groups.9,10 For the purines adenine and guanine, the eVect of such a tether is profound with the result that nucleobase –metal binding occurs at typically unreactive sites, such as N3 or C8.9,10 Having extended these ideas to pyrimidines, we report here on the reaction of 1-(2-chloroethyl)thymine with ethylenediamine, which results in a rearrangement to form a substituted isocytosine derivative.Some aspects of the coordination chemistry of this substituted pyrimidine have been explored and we present the crystal and molecular structures of complexes containing zinc(II) and palladium(II).Results and Discussion Synthesis Reaction of 1-(2-chloroethyl)thymine11 with excess ethylenediamine yields 1-(2-hydroxyethyl)-(2-aminoethyl-N2)-5-methylisocytosine, L, as a hydrochloride salt. A proposed mechanistic scheme for the reaction is shown in Scheme 1. On the basis of NMR experiments alone an unequivocal assignment of structure L rather than 1-{2-[(2-aminoethyl)amino]ethyl}thymine, L1, is diYcult. The expected sets of four triplets of the two ethyl chains are apparent, as is the C5]CH3 group.The through-space interaction between the C6 proton and the N1-bonded methylene group, seen in the ROESY spectrum, confirm alkylation at N1, but none of these allows discrimination between L and L1. The absence of a broad resonance at d ª 11.0, typically seen for the imide proton at N3, and the reduction in intensity of the carbonyl stretching vibrations in the infrared spectra compared to 1-(2-chloroethyl)thymine are however suggestive of some † E-Mail: andrew.houlton@newcastle.ac.uk modification of the pyrimidine moiety.Conclusive proof for the structure of L was obtained from X-ray crystallography (see below). Co-ordination chemistry of L. Zinc(II). Reaction of [LH]1Cl2 with ZnCl2 in water (1 : 1 molar ratio) followed by concentration and the addition of ethanol produced, on standing, colourless crystals of 1, [ZnCl3(LH)], suitable for X-ray analysis. Owing to the acidic nature of the reaction media (pH 0.8) the pH-dependence of the species present in solution was investigated.From electrospray MS, an aqueous solution of the complex at pH 7.1 contained peaks at m/z 213 (M1, LH) and 171 Scheme 1 Proposed mechanism for the formation of L from 1-(2- chloroethyl)thymine HN N O O Cl Me N N O O Cl Me N N O O Me H2N NH2 H2N NH2 N N O HN Me HO H2N L – HN N O CH3 O NH NH2 L12002 J. Chem. Soc., Dalton Trans., 1998, Pages 2001–2006 (M2, [ZnCl3]2), while at pH 0.8 the positive-ion spectrum also contained peaks at 279 [M1, Zn(LH)], and a higher molecular weight ion at 491 [M1, Zn(LH)2].Proton NMR spectra of aqueous solutions of the isolated product were measured over a similar pH range (0.8–7.1). The spectra show only one set of signals for the ligand, indicating that if multiple complexes are present they are in fast exchange. Furthermore, no significant changes in the spectral features were observed over the pH range. Palladium(II). From 1H NMR spectroscopic and ES-MS studies it is evident that the reaction of Pd21 with LH1 does not yield a single species in solution. Indeed, two diVerent products were isolated from the reactions with LH1 (see below).Monitoring the reaction of K2PdCl4 and LH1 with 1H NMR spectroscopy revealed that the reaction yields a complex mixture of species over time. Monitoring the signals from the C(5)]Me group, initially one major (C) and two minor species (D and E) were formed. After 15 min all the ligand had reacted and a new major species (A) was detected in addition to the previous signals. Over a period of 2 h the concentration of A reduced and a new minor species B was detected along with an increase in D and E.Over the next 18 h no additional species were detected, though the relative concentrations of B, D and E gradually increased as A decreased. Electrospray MS of the reaction media indicated the presence of ions at m/z 355 [M1, PdCl(L)], 317 [M1, Pd(L)]. The negative ionization for this reaction mixture was very poor and peaks corresponding to [PdCl4]22 or [Pd2Cl6]22 were not easily discerned.From a preparative scale reaction, following work-up, these conditions yielded unreacted K2PdCl4, [PdCl2L] 2, and a third material, [PdClL]2[Pd2Cl6] 3 (all three species were identified by their unit cell parameters). Compound 2 was also isolated as the major product from the reaction with PdCl2(MeCN)2. Electrospray MS data of the reaction media containing PdCl2(MeCN)2 and LH1 revealed the presence of the following complex ions: m/z 443 {M2, [PdCl3(L)H2O]1}, 440 [M1, PdCl(LH)(MeCN)2 1 2H], 425 {M2, [PdCl3(L)]}, 396 [M1, PdCl(LH)MeCN], 355 [M1, PdCl(L)], 317 [M1, Pd(L) 2 H].These data reveal that a mixture of products is formed in solution, of which two (compounds 2 and 3) were isolated and studied by single-crystal X-ray structure analyses. Crystal and molecular structures of 1, 2 and 3 Table 1 presents selected structural parameters for compounds 1–3.In compound 1, [ZnCl3LH], the zinc ion adopts a distorted tetrahedral geometry with a {3Cl, 1O} donor set involving the Table 1 Selected bond lengths (Å) and angles (8) for compounds 1–3 N(1)]C(2) C(2)]N(2) C(2)]N(3) N(3)]C(4) C(4)]O(4) C(4)]C(5) C(5)]C(6) C(6)]N(1) M]O(4) M]N(2) M]N(3) M]N(12) M]Cl(1) M]Cl(2) M]Cl(3) M]O(1) C(2)]N(3)]C(4) 1 1.362(5) 1.343(5) 1.332(5) 1.349(5) 1.273(5) 1.437(5) 1.343(6) 1.399(5) 2.014(3) 2.2835(12) 2.3125(12) 2.2677(14) 119.6(4) 2 1.360(6) 1.332(7) 1.351(6) 1.391(6) 1.237(6) 1.446(7) 1.343(7) 1.370(7) 2.044(4) 2.039(4) 2.2970(12) 2.3185(12) 121.6(4) 3 * 1.361(11) 1.323(10) 1.364(11) 1.387(10) 1.242(10) 1.432(13) 1.358(12) 1.376(10) 2.040(7) 1.987(7) 2.303(2) 2.045(6) 126.1(7) * Average values of independent molecules A and B of compound 3.carbonyl oxygen O(4) of the pyrimidine (see Fig. 1). Bond lengths to the metal ion are Zn(1)]Cl(1) 2.2835(12), Zn(1)]Cl(2) 2.3125(12), Zn(1)]Cl(3) 2.2677(14) [Zn(1)]Clave = 2.288 Å] and Zn(1)]O(4) 2.014(3) Å.The zinc-bound O(4) is also involved in intermolecular hydrogen-bonding interactions with the alcohol proton O(1)H [O(4) ? ? ? O(1A) 2.90 Å] generating an R2 2(18) motif with dimers formed through an inversion centre (Fig. 2). Within a dimer the two aromatic rings are slipped with respect to one another; the vertical distance between the ring planes is 3.458 Å. Further hydrogen bonding exists, involving both the N(12)H3 1 and the N(2)H group protons with metal-bound chloride ions [N(2) ? ? ? Cl(1) 3.200, N(12) ? ? ? Cl(2) 3.209, N(12) ? ? ? Cl(3) 3.166 Å].The two pendant ethyl chains of the molecules, although interacting with neither the metal nor with one another, lie on the same face of the aromatic ring. The geometry of N(2) is essentially trigonal [C(2)]N(2)]C(10) 122.0(4)8] indicating delocalization of the lone pair into the aromatic ring [H(20) was clearly located in the planar bisecting position in the diVerence map, then included in a constrained position for refinement].A few structural reports have been made on alkylaminopyrimidines, though to the best of our knowledge none of their metal complexes.12 The carbonyl bond lengths in 2-(5-bromo-3- methyl-2-pyridyl)butylaminopyrimid-4-one,13 1-methylcytosine 14 and isocytosine 15 are 1.249, 1.234 and 1.248 Å, respect- Fig. 1 Molecular structure of compound 1 showing the co-ordination geometry around zinc and the ligation by the carbonyl oxygen O(4) Fig. 2 Hydrogen-bonded dimers of compound 1 related through inversion centres generating an R2 2(18) motifJ. Chem. Soc., Dalton Trans., 1998, Pages 2001–2006 2003 ively. By comparison the equivalent C(4)]] O(4) in 1 is longer at 1.273 Å, as may be expected due to metal co-ordination and is also longer than that seen in Zn(L2)2(H2O)2 (HL2 = 6-carboxyuracil) (1.244 Å) despite the fact that the metal is chelated through O4 and the oxygen of the C6-bound acid group.16 If comparison with nucleobases is to be made it is most appropriate for cytosine, as here both a carbonyl and amino function are present, although these are in the 2- and 4-positions, respectively.Crystallographically characterized ZnII complexes of cytosine reveal that N3 is a general binding site,17,18 though in the trinuclear [Zn3(OH)2(1-MeCyt)8][NO3]4 either of N3 or O2 acts as donor atom.19 The Zn]O2 bond lengths range from 2.010–2.046 Å.The C]] O bond lengths are longer, at ª1.24 Å, compared with the 1.234 Å of 1-methylcytosine,15 though again this is less than observed in 1. Fig. 3 shows the molecular structure of [PdCl2L] 2. The palladium adopts a distorted square planar co-ordination geometry comprising a {2Cl, 2N} donor set, which involves the formation of a seven-membered chelate ring resulting from the endocyclic N(3) and exocyclic N(12) donor atoms binding to the metal. The bond lengths to palladium are Pd]N(3) 2.044(4), Pd]N(12) 2.039(4), Pd]Cl(1) 2.2970(12) and Pd] Cl(2) 2.3185(12) Å. The Pd]N bond length is typical for N3-palladated pyrimidines.20 The angle between the coordination plane and the pyrimidine ring is 1158.The mode of ligation in 2 is analogous to that seen in [Zn(H2O)2L3] (H2L3 = 2-hydrazino-4-hydroxy-6-methylpyrimidine) where the pyrimidine also acts to chelate the metal via N3 and the terminal NH2 group of the hydrazino function, here forming a five-membered ring.21 Extensive intermolecular hydrogen bonding is observed within the crystal structure of 2.Among these are the interactions between carbonyl oxygen O(4) with an N(2)H proton of the adjacent molecule [N(2) ? ? ? O(4) 2.901 Å] and several involving the co-ordinated chloride ions [e.g. Cl(2) ? ? ? O(1) 3.255, Cl(2) ? ? ? N(12) 3.440 Å]. Fig. 4 shows the infinite chains generated through the first two such interactions. Compound 3, isolated as a minor component of the reaction of [LH]1Cl2 with K2PdCl4, comprises [PdClL]2[Pd2Cl6] and contains two crystallographically independent, though chemically equivalent, [PdClL]1 cations.The distorted square planar metal ion in the cation comprises a {1Cl, 2N, 1O} donor set (Fig. 5). The ligand L adopts a tridentate binding mode utilising N(2), N(12) and the alcohol oxygen O(1) as donors. Bond lengths to Pd, averaged over the two independent molecules A and B are Pd]Cl 2.303(2), Pd]N(2) 2.040(7), Pd]O(1) 2.045(6), Pd]N(12) 1.987(7) Å.The angles between the co-ordination Fig. 3 Molecular structure of compound 2 showing the distorted square planar co-ordination geometry and the seven-membered chelate ring formed by N(12) and N(3) binding to palladium planes and the pyrimidine ring are 36 and 398 for molecules A and B respectively. The [Pd2Cl6]22 anions have typical Pd]Cl distances.12 Intermolecular hydrogen-bonding interactions in the crystal lattice involving the pyrimidine ring are distinct for the two independent molecules.For molecule A, N(3)H interacts with occluded water [N(3A) ? ? ? O(100) 2.929 Å], while for molecule B, a chain motif is formed through interactions between N(3B) ? ? ? Cl(1B) and O(4) ? ? ? O(1)H [N(3) ? ? ? Cl(1) 3.399, O(4) ? ? ? O(1) 2.573 Å]. Fig. 4 Hydrogen-bonding interactions in the crystal structure of 2. Intermolecular interactions involving C(4)]] O? ? ?H2N(2) and OH? ? ? Cl]Pd generating a chain motif Fig. 5 Molecular structure of one of the cations in 3 highlighting the tridentate binding mode involving five- and seven-membered chelate rings2004 J. Chem. Soc., Dalton Trans., 1998, Pages 2001–2006 A search of the Cambridge Structural Database 12 reveals that complexes of 1-alkylcytosine generally prefer N3 as the binding site.20 However, other modes of co-ordination involving N4 are known.22 Bond lengths for the exocyclic amino group of cytosine binding to PdII as an anionic donor group lie in the range 1.973–2.014 Å and compare with a Pd]N(2) distance of 2.040(7) Å in 3.22 A significant diVerence in 3 compared to 1 and 2 is that the pyrimidine ring exists in a diVerent tautomeric form.Two principal resonance structures, I and II, may be written for the pyrimidine (Fig. 6). Evidence suggestive of the iminooxo tautomer in 3 was obtained by consideration of the bond lengths within the pyrimidine ring (refer to Table 1). The C(2)]N(3) bond in 3 is longer [1.364(11) Å] than that observed in 1 and 2 [1.332(5) and 1.351(6) Å, respectively]. The greater bond length in 3 is indicative of single bond character, and conversely in both 1 and 2 greater double bond character is apparent. It should be noted that due to the eVect of N(3) metallation the bond length is greater in 2 than in 1.The C(2)]N(2) bond length in 3 [1.323(10) Å] is shorter than that observed in 1 [1.343(5) Å] and 2 [1.332(7) Å]. Again these bond length data are consistent with the pyrimidine existing as the iminooxo tautomer in 3 and the aminooxo tautomer in both 1 and 2.Further support for the existence of L as the iminooxo tautomer in 3 is gained from the bond angle data of the three complexes. The large value of the angle at N(3) [126.1(7)8] in 3 agrees with a proton being bonded to this nitrogen. Generally the angle is significantly smaller in cases where the N(3) site carries no proton, as in isocytosine (119.78) for example.In 1 the angle is 119.6(4)8, again as expected for form I. Finally, an analysis of diVerence electron density maps gave a clear indication as to the location of indicative protons in the three structures: N(2) in 1 with no peak near N(3), a single proton on N(2) in 2 and a single proton on N(3) for both molecules in the structure of 3. Lippert and co-workers have reported on various metalstabilized rare tautomers of the nucleobases adenine 7 and cyto- Fig. 6 Aminooxo (I) and iminooxo (II) tautomeric forms of L N N O Me OH HN NH2 HN N O Me OH N NH2 I II Fig. 7 Incompatible hydrogen-bonding interactions for the G]C pair (top) containing the iminooxo tautomer, and mismatched base pair between A]C (bottom) N NH HNH O N N N N N N HNH HN N HN O HN N HN O sine.8 These latter examples are highly comparable to the case of 3, particularly the complexes trans,trans,trans-[Pt(NH3)2- (OH)2(1-MeCyt-N4)2]21 and trans-[Pt(NH3)2(1-MeCyt-N4)2]21 (1-MeCyt = 1-methylcytosine).8 The authors have discussed the biological implications of these metal-stabilized tautomers with respect to DNA base-pair mismatching, and it is of interest to consider such eVects here.Stabilization of the iminooxo form should preclude base-pairing with guanine but allow for mismatching with adenine or thymine for example (Fig. 7). The data presented here further indicate that PdII binding at the exocyclic nitrogen donors can stabilize the iminooxo form.8 Conclusion The substituted pyrimidine, 1-(2-hydroxyethyl)-(2-aminoethyl- N2)-5-methylisocytosine, has been shown to bind metal ions as a mono-, di- and tri-dentate ligand, the last two examples being observed for PdII.In addition to exhibiting diVerent modes of co-ordination, the pyrimidine moiety in the two PdII complexes exists in diVerent tautomeric forms, with the iminooxo form associated with the tridentate binding mode involving coordination to the N(2) amino group. This result further indicates that metal-ion binding at the exocyclic nitrogen atoms of nucleobases may induce nucleobase tautomerism and is thus implicated as a mechanism for metal-based mutagenicity.Experimental The NMR data were measured on a JEOL Lambda 500 instrument with either D2O or (CD3)2SO as solvent. Syntheses 1-(2-Hydroxyethyl)-(2-aminoethyl-N2)-5-methylisocytosine hydrochloride [LH]1Cl2. 1-(2-Chloroethyl)thymine11 (1.00 g, 5.79 mmol) was stirred with an excess of ethylenediamine (5 ml, 75 mmol) at room temperature under an atmosphere of nitrogen for 24 h.Excess ethylenediamine was removed under reduced pressure, the resultant yellow viscous liquid was taken up in ethanol (10 ml). The mixture was warmed gently, after a short time a white solid precipitated. The resultant crude product was recrystallized from ethanol (25 ml). The white solid (0.89 g, 62%) was collected by filtration, washed with cold ethanol and air dried. 1H NMR [(CD3)2SO]: d 1.73 (s, 3 H, pyrimidine CH3), 2.99 (t, 2 H, CH2NH3 1), 3.50 (t, 2 H, NHCH2CH2), 3.62 (t, 2 H, CH2OH), 3.79 (t, 2 H, CH2CH2OH), 7.13 (s, br, 1 H, pyrimidine NH), 7.27 (s, 1 H, C6H); 13C NMR [(CD3)2SO]: d 13.18 (pyrimidine CH3), 38.55 (NHCH2CH2), 38.68 (CH2NH3), 51.89 (CH2CH2OH), 58.74 (CH2OH), 140.55 (C6), 112.61, 153.29, 170.36 (C2, C5, C4) (Found: C, 40.69; H, 6.26; N, 20.68.Calc. for C9H19ClN4O3: C, 40.53; H, 7.18; N, 21.01%). Infrared; n (cm21) 3352, 3280 (N]H) and 1660 (C]] O).[ZnCl3(LH)] 1. To a solution of zinc chloride (0.14 g, 1.00 mmol) in H2O (15 ml) was added with stirring an aqueous solution (15 ml) of 1-(2-hydroxyethyl)-(2-aminoethyl-N2)-5-methylisocytosine hydrochloride (0.25 g, 1.00 mmol), the mixture was allowed to stir overnight. The colourless solution was concentrated to a minimum volume on a rotary evaporator, ethanol (60 ml) was added and the mixture was allowed to stand undisturbed overnight. Complex 1 crystallized as colourless crystals which were found to be suitable for a single-crystal X-ray structure analysis (Found: C, 27.35; H, 4.45; N, 14.14.Calc. for C9H17Cl3N4O2Zn: C, 28.23; H, 3.95; N, 14.63%). Infrared; n (cm21) 3471, 3293 (N]H) and 1654 (C]] O). [PdCl2L] 2. To a refluxing solution of PdCl2 (0.18 g, 1.0 mmol) in acetonitrile (25 ml) was added dropwise an aqueous (25 ml) solution of 1-(2-hydroxyethyl)-(2-aminoethyl-N2)-5- methylisocytosine hydrochloride (0.25 g, 1.0 mmol). The mixture was allowed to remain at reflux for 24 h.The cooled solu-J. Chem. Soc., Dalton Trans., 1998, Pages 2001–2006 2005 Table 2 Summary of crystal data and structure determination for compounds 1–3 Compound Formula MT /K 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/mm21 F(000) Reflections for cell refinement q Range/8 2q Range for data collection/8 Maximum indices: h, k, l Reflections measured Unique reflections Reflections with F2 > 2s(F2) Transmission Rint Weighting parameters a a, b Extinction coeYcient xb R [F2 > 2s(F2)]c wR2 [all data] d Number of refined parameters Goodness of fit e Maximum, minimum electron density/ e Å23 1 C9H17Cl3N4O2Zn 384.99 160 0.70 × 0.20 × 0.16 Monoclinic P21/n 7.539(3) 14.800(4) 13.169(4) 93.74(4) 1466.2(8) 4 1.744 2.224 784 28 10.16–12.52 5.5–50.0 28 to 8, 217 to 17, 215 to 15 6998 2574 2256 0.530 to 0.649 0.0393 0.0703, 3.8892 — 0.0430 0.1259 175 1.070 1.146, 20.735 2 C9H16Cl2N4O2Pd 389.56 160 0.44 × 0.29 × 0.09 Monoclinic Cc 12.6211(14) 17.1181(19) 6.2311(7) 90.939(3) 1346.0(3) 4 1.922 1.775 776 4002 2.00–28.44 4.0–50.0 214 to 15, 220 to 11, 27 to 7 3513 2215 2152 0.694 to 0.862 0.0248 0.0384, 1.3244 0.0012(3) 0.0274 0.0697 166 1.071 0.662, 20.784 3 C9H16Cl4N4O2Pd2?0.5H2O 575.87 160 0.26 × 0.10 × 0.01 Triclinic P1� 8.4069(10) 9.8060(12) 21.805(3) 90.973(3) 90.010(3) 105.406(3) 1732.7(4) 4 2.208 2.702 1116 8135 1.87–28.26 4.3–56.8 210 to 11, 212 to 12, 228 to 26 11 943 7538 5476 0.498 to 0.927 0.0407 0.0978, 0 — 0.0619 0.1700 396 1.006 2.141, 23.001 a w21 = s(Fo 2) 1 (aP)2 1 bP, where P = (Fo 2 1 2Fc 2)/3.b Fc = Fc(1 1 0.001xFc 2l3/sin 2q)2� �4 . c R = S||Fo| 2 |Fc||/S|Fo|. d wR2 = [Sw(Fo 2 2 Fc 2)2/ Sw(Fo 2)2]� �� . e S = [Sw(Fo 2 2 Fc 2)2/(no. of unique reflections 2 no. of variables)]� �� . tion was concentrated under reduced pressure, the addition of ethanol precipitated the crude product which was collected by filtration, washed with ethanol and vacuum dried (0.21 g, 54%).Crystallization from water–ethanol (1 : 1) produced orange platelets suitable for X-ray analysis. 1H NMR (D2O): d 1.78 (s, 1 H, pyrimidine CH3), 3.14 (t, 2 H, CH2NH3), 3.62 (t, 2 H, NHCH2CH2), 3.77 (t, 2 H, CH2OH), 3.87 (t, 2 H, CH2CH2OH), 7.37 (s, 1 H, C6H); 13C NMR (D2O): d 10.90 (pyrimidine CH3), 40.00 (CH2NH3), 41.00 (NHCH2CH2), 50.00 (CH2CH2OH), 59.09 (CH2OH), 145.45 (C6) (Found: C, 27.25; H, 3.91; N, 13.84.Calc. for C9H16Cl2N4O2Pd: C, 27.75; H, 4.14; N, 14.38%). [PdClL]2[Pd2Cl6] 3. To K2PdCl4 (0.26 g, 0.80 mmol) in aqueous solution (30 ml) was added with stirring a solution of 1-(2-hydroxyethyl)-(2-aminoethyl-N2)-5-methylisocytosine hydrochloride (0.20 g, 0.80 mmol) in water (20 ml). The mixture was allowed to stir at room temperature for 18 h. The solvent was removed in vacuo. The resultant brown-red solid was dissolved in a small volume of water, ethanol (20 ml) was added and the mixture was left to stand undisturbed overnight.This resulted in the formation of a variety of crystalline material, which was mechanically separated and analysed by singlecrystal X-ray structure analyses (crystals of unreacted K2PdCl4 and compounds 2 and 3 were formed and identified by their unit cell parameters). Crystallography Details of crystal data, structure solution and refinement for compounds 1–3 are given in Table 2. For 1 data were collected on a Stöe-Siemens four-circle diVractometer using graphitemonochromated Mo-Ka radiation (l = 0.710 73 Å).Cell parameters were refined from 2q values measured at ±w to minimize systematic errors. Intensities were measured with w–q scans and on-line profile fitting.23 Data were corrected semiempirically for absorption using y scans. For 2 and 3 all diVraction measurements were made on a Bruker AXS SMART CCD area-detector diVractometer using graphite-monochromated Mo-Ka radiation. Cell parameters were refined from observed setting angles of all strong reflections in the complete data set.Intensities were integrated from several series of exposures, each taken over 0.38 w rotation, covering more than a hemisphere of reciprocal space. Data were corrected semiempirically for absorption based on equivalent and repeated reflections. There was no significant intensity decay during the experiments. For all three structures all non-H atoms were refined anisotropically.Hydrogen atoms were located in diVerence maps and then included using a riding model with isotropic U values set to be 150% of those of the carrier atoms for methyl and hydroxyl hydrogens and 120% for all others, except for H(1A) and H(1B) in 3 for which the coordinates were refined freely. Programs used were SHELXTL24 for structure solution, graphics and tables, and SHELXL 9725 for structure refinement. CCDC reference number 186/980. Acknowledgements The University of Newcastle Research Development Fund is thanked for a studentship (C.P.), the NuYeld foundation for a gron Matthey plc for the generous loan of metal salts, the EPSRC for funding for a diVractometer (W. C.) and the MS Service Centre, University of Wales, Swansea.2006 J. Chem. Soc., Dalton Trans., 1998, Pages 2001–2006 References 1 Metal Ions in Biological Systems, eds. A. Sigel and H. Sigel, Marcel Dekker, New York, Basel, Hong Kong, 1996, vol. 32, pp. 1–814; ibid., 1996, vol. 33, pp. 1–678. 2 B. Lippert, Prog. Inorg. Chem., 1989, 37, 1; B. Lippert, Coord. Chem. Rev., 1997, 156, 275. 3 S. S. Massoud and H. Sigel, Eur. J. Biochem., 1989, 179, 451. 4 J. W. Suggs, M. J. Dube and N. Nichols, J. Chem. Soc., Chem. Commun., 1993, 307. 5 C. A. Blindauer, A. H. Emwas, A. Holy, H. Dvorakova, E. Sletten and H. Sigel, Chem. Eur. J., 1997, 3, 1526. 6 C. Mesier, B. Song, E. Freisinger, M. Peilert, H. Sigel and B. Lippert, Chem. Eur. J., 1997, 3, 388. 7 F. Zamora, M. Kunsman, M. Sabat and B. Lippert, Inorg. Chem., 1997, 36, 1583. 8 F. Pichierri, D. Holthenrich, E. Zangrando, B. Lippert and L. Randaccio, J. Biol. Inorg. Chem., 1996, 1, 439. 9 C. Price, M. R. J. Elsegood, W. Clegg and A. Houlton, J. Chem. Soc., Chem. Commun., 1995, 2285. 10 C. Price, M. R. J. Elsegood, W. Clegg, N. H. Rees and A. Houlton, Angew. Chem., Int. Ed. Engl., 1997, 36, 1762; unpublished work. 11 O. F. Schall and G. W. Gokel, J. Am. Chem. Soc., 1994, 116, 6089. 12 F. H. Allen and O. Kennard, Chem. Design Automation News, 1993, 8, 31. 13 C. Bannister, K. Burns, K. Prout, D. J. Watkin, D. G. Cooper, G. J. Durant, C. R. Ganellin, R. J. Ife and G. S. Sach, Acta Crystallogr., Sect. B, 1994, 50, 221. 14 M. Rossi and T. J. Kistenmacher, Acta Crystallogr., Sect. B, 1977, 33, 3962. 15 B. D. Sharma and J. F. McConnell, Acta Crystallogr., 1965, 19, 797. 16 J. H.-U. M. N. Moreno-Carretero, M. A. Romero-Molina, J. M. Salas-Peregrin, M. P. Sanchez-Sanchez, G. A. de Cienfuegos-Lopez and R. Faure, J. Inorg. Biochem., 1993, 51, 613. 17 A. L. Beauchamp, Inorg. Chim. Acta, 1984, 91, 33. 18 S. K. Miller, L. G. Marzilli, S. Dörre, P. Kollat, R.-D. Stilger and J. J. Stezowski, Inorg. Chem., 1986, 25, 4272. 19 E. C. Fusch and B. Lippert, J. Am. Chem. Soc., 1994, 116, 7204. 20 E. Sinn, C. M. Flynn and R. B. Martin, Inorg. Chem., 1977, 16, 2403; M. Krumm, I. Mutikainen and B. Lippert, Inorg. Chem., 1991, 30, 884; M. Wienken, E. Zangrando, L. Randaccio, S. Menzer and B. Lippert, J. Chem. Soc., Dalton Trans., 1993, 3349; J. E. Kickham, S. J. Loeb and S. L. Murphy, J. Am. Chem. Soc., 1993, 115, 7031; J. E. Kickham and S. J. Loeb, Inorg. Chem., 1994, 33, 4351. 21 H. Sakaguchi, H. Anzai, K. Furuhata, H. Ogura and Y. Iitaka, Chem. Pharm. Bull., 1977, 25, 2267. 22 M. Krumm, E. Zangrando, L. Randaccio, S. Menzer and B. Lippert, Inorg. Chem., 1993, 32, 700; M. Krumm, B. Lippert, L. Randaccio and E. Zangrando, J. Am. Chem. Soc., 1991, 113, 5129. 23 W. Clegg, Acta Crystallogr., Sect. A, 1981, 37, 22. 24 G. M. Sheldrick, SHELXTL user manual, Bruker AXS, Madison, WI, 1994. 25 G. M. Sheldrick, SHELXL 97, program for crystal structure refinement, University of Göttingen, 1997. Received 9th January 1998; Paper 8/00271A

ISSN:1477-9226    

DOI:10.1039/a800271a

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1997, Pages 2003–2004 2003 Intramolecular thioacyl hydroboration: synthesis of [W(Á2-S2CR)- (CO)2{Á3-HB(pz)2(SCH2R)}] (pz = pyrazol-1-yl, R = C6H4Me-4) Anthony F. Hill *,† and John M. Malget Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London SW7 2AY, UK The sequential treatment of [W(]] ] CR)Br(CO)4] (R = C6H4- Me-4) with sulfur and K[HnB(pz)4 2 n] (n = 1 or 2; pz = pyrazol- 1-yl) provided [W(h2-S2CR)(CO)2{HB(pz)3}] or [W(h2-S2CR)- (CO)2{h3-HB(pz)2(SCH2R)}], the latter via an unusual reduction of the alkylidyne–tungsten linkage.The addition of elemental sulfur to alkylidyne complexes provides either thioacyl (A, Scheme 1, Group 8 metals) 1 or dithiocarboxylate (B, Group 6 metals) 2 complexes depending on the metal centre involved (Scheme 1). Within Group 6, only dithiocarboxylate complexes have been isolated, with no evidence, to date, for the intermediacy of thioacyls, however plausible these might be.The hydroboration of metal–carbon triple bonds has been demonstrated using external boranes,3 and the results obtained (C, D) reflect the analogy with carbon–carbon multiple bonds. Furthermore, the interaction of alkylidyne ligands with carbaborane co-ligands is itself a field enjoying intense study,4 although in many cases, it is clear that the intramolecular hydroboration processes often follow initial protoninduced alkylidene formation.Herein we report the unexpected combination of these two aspects of alkylidyne chemistry, viz. the sulfur-induced coupling of alkylidyne and dihydrobis- (pyrazolyl)borate ligands to provide a co-ordinated bis(pyrazolyl) thiolatoborate (E). The reaction of [W(]] ] CR)Br(CO)4] (hereafter R = C6H4- Me-4)‡ with elemental sulfur at low temperature provides a thermolabile complex which, although not yet isolated, is assumed to be either ‘[W(h2-S2CR)Br(CO)4]’ 1a or ‘[W(h2- SCR)Br(CO)4]’ 1b.This assumption is supported by (i) the analogy with the compound [W(h2-S2CR)(CO)2(h-C5H5)] which results from the reaction of [W(]] ] CR)(CO)2(h-C5H5)] with sulfur 2 and (ii) the formation of the thermally stable dithiocarboxylate complex [W(h2-S2CR)(CO)2{HB(pz)3}]§ 2 (pz = pyrazol-1-yl) on treatment with K[HB(pz)3] (Scheme 2). Two processes are plausible. (i) The formation of a thioacyl species (1b) which reacts slowly with K[HB(pz)3] to provide [W(h2-SCR)(CO)2{HB(pz)3}] and then rapidly with the excess sulfur present to provide 2. (ii) Alternatively, the dithiocarboxylate (1b) may be formed directly, and then react with K[HB- (pz)3] to provide 2.Unfortunately, attempts to isolate either 1a or 1b by varying conditions or reagent stoichiometry have so far met with failure. This intermediacy of the thioacyl species (1b) is, however, supported by the unusual results obtained from treating [W(]] ] CR)Br(CO)4] sequentially with sulfur and K[H2B- (pz)2]: rather than the anticipated complex [W(h2-S2CR)(CO)3- {H2B(pz)2}],¶ a deep purple complex was isolated which is formulated as the bis(pyrazolyl)thiolatoborate complex [W(h2- S2CR)(CO)2{h3-HB(pz)2(SCH2R)}] 3 on the basis of spectro- † E-Mail: a.hill@ic.ac.uk ‡ Prepared in situ from the successive treatment of [W(CO)6] with LiR?LiBr and (CF3CO)2O.scopic data.§ Fast atom bombardment (FAB) mass spectral data confirm the gross formulation: in addition to a clear molecular ion, fragmentations are observed due to sequential decarbonylation.In contrast to a structured infrared absorbance, typical of the ‘H2B(pz)2’ ligand, a single sharp n(BH) stretch is observed at 2507 cm21. Both the intensity profile and position of the carbonyl absorbances for 3 are very similar to those for 2. The 1H NMR data indicate two chemically distinct pyrazolyl and tolyl environments in addition to an AB system arising from the diastereotopic methylene group of the SCH2R substituent.Finally, the 13C-{1H} NMR spectrum reveals Scheme 1 Cp = h5-C5H5, R = C6H4Me-4 (Ph3P)2(OC)ClOs C S R Cp(OC)2W S C S R B Cp(OC)2W W(CO)2Cp C R RH2C H H B W(CO)2Cp MLn N N N N H-B S R A B C D E § Data for 2: [W(]] ] CR)Br(CO)4] (0.50 g)‡ and sulfur (0.05 g) in thf (50 cm3) were stirred for 10 h at 210 8C. K[HB(pz)3] (0.21 g) was added and the mixture stirred for 12 h. The solvent was removed, the residue chromatographed (silica gel, hexane–diethyl ether, 5 : 1) and the purple eluate crystallised from pentane (278 8C).Yield 0.47 g (90%). IR (Nujol)/cm21: 2496 [n(BH)], 1925, 1835 [n(CO)]. NMR (CDCl3, 25 8C): 1H, d 2.38 [s, 3 H, CH3], 6.24 [t, 3 H, H4 (pz), J(HH) = 2 ], 7.19, 7.77 [(AB)2, 4 H, C6H4, J(AB) 8], 7.22, 8.26 [d × 2, 6 H, H3,5 (pz), J(HH) 2 Hz]; 13C-{1H}, d 243.9 [WCO], 215.8 [S2C], 146.4–106.6 [C6H4 and pz], 21.6 [CH3] (Found: C, 36.2; H, 2.8; N, 12.5. C19H17BN6O2S2W?0.25 CH2Cl2 requires C, 36.1; H, 2.8; N, 13.1%). 3: Similar treatment of [W(]] ] CR)Br(CO)4] (0.50 g) as above, replacing K[HB(pz)3] with K[H2B(pz)2] (0.16 g) provided 3. Yield 0.08 g (28% based on R). IR (Nujol)/cm21: 2507 [n(BH)], 1930, 1836 [n(CO)]. NMR (CDCl3, 25 8C): 1H, d 2.24, 2.28 [s × 2, 6 H, CH3], 2.61, 3.39 [AB, 2 H, SCH2, J(HH) 13], 6.08, 6.22 [t × 2, 2 H, H4 (pz), J(HH) 2], 6.95, 7.02 [(AB)2, 4 H, C6H4, J(AB) 8], 7.11, 7.73 [(AB)2, 4 H, C6H4, J(AB) 8], 7.52, 7.73, 7.82, 8.07 [d × 4, 4 H, H3,5 (pz), J(HH) 2 Hz]; 13C-{1H}, d 245.8 [WCO, J(WC) 124], 241.8 [WCO, J(WC) 127 Hz], 226.8 [S2C], 145.3–107.3 [C6H4 and pz], 39.5 [SCH2], 21.7, 21.2 [CH3].FAB mass spectrum (m-nitrobenzyl alcohol): m/z 690 (43, [M]1), 664 (6, [M 2 CO]1), 634 (41, [M 2 2CO]1), 558 (82%, [M 2 2CO 2 C7H7]1) (Found: C, 41.5; H, 3.4; N, 7.9. C24H23BN4O2S3W requires C, 41.8; H, 3.4; N, 8.1%). ¶ This complex has been reported to result from the reaction of [W(]] ] CR)(CO)3{H2B(pz)2}] with sulfur.52004 J.Chem. Soc., Dalton Trans., 1997, Pages 2003–2004 signals for two carbonyl ligands [d 245.8, J(WC) 124; 241.8, J(WC) 127 Hz], the dithiocarboxylate carbon [d 226.8] and a singlet resonance [d 39.5] showing no coupling to tungsten thereby indicating that it is remote from the tungsten coordination sphere. The mechanism which we favour (Scheme 2) for the formation of 3 remains equivocal, however we note that Carmona et Scheme 2 Tetrahydrofuran, 210 8C, R = C6H4Me-4. (i) LiR?LiBr, (CF3CO)2O; (ii) 1– 4 S8; (iii) K[H2B(pz)2]; (iv) K[HB(pz)3]; (v) RCS2H.* Indicates proposed intermediate, not isolated W OC N CO N N N B N N H Br(OC)4W S C S R Br(OC)4W C S R S C S R W OC N CO N N N B H H C O S C R W OC N CO N N N B H C O S C R H W OC N CO N N N B H S C S R S CH2R [W(ºCR)Br(CO)4] [W(CO)6] + ( i ) ( ii ) ( iii ) (iii ) (iv ) ( v ) 1a 1b 2 3 * * * * ( ii ) al.6 have recently discussed the intramolecular hydroboration of an acyl ligand by a H2B(pz)2 co-ligand.Should a thioacyl complex [W(h2-SCR)(CO)3{h2-H2B(pz)2}] be formed it is therefore plausible that intramolecular hydroboration of the thioacyl ligand provides [W{h2-SCH(R)BH(pz)2}(CO)3]. The reaction of this species with RCS2H (formed by hydrolysis of 1a) could then produce the final product 3. Further support for the intermediacy of a thioacyl complex is provided by our very recent isolation of a range of such complexes based on tungsten and molybdenum.7 The co-ordination chemistry of one pre-formed mixed thiolate –pyrazolyl borate has been mentioned once before 8 when it was suggested that the complex [Cu(SR){h3-HB(Me2pz)2(SR)}] could serve as a model for the tetrahedral ‘CuS2N2’ site in some copper proteins.In principle this otherwise neglected class of scorpionate ligand should show a rich co-ordination chemistry, a direction we are currently investigating. Acknowledgements We gratefully acknowledge the financial support of the Engineering and Physical Sciences Research Council (UK), and the Royal Society. References 1 G. R. Clark, K. Marsden, W. R. Roper and L. J. Wright, J. Am. Chem. Soc., 1980, 102, 6570. 2 D. S. Gill, M. Green, K. Marsden, I. Moore, G. Orpen, F. G. A. Stone, I. D. Williams and P. Woodward, J. Chem. Soc., Dalton Trans., 1984, 1343. 3 D. Barratt, S. J. Davies, G. P. Elliott, J. A. K. Howard, D. B. Lewis and F. G. A. Stone, J. Organomet. Chem., 1987, 325, 185. 4 S. A. Brew and F. G. A. Stone, Adv. Organomet. Chem., 1993, 35, 135. 5 M. D. Bermudez, F. P. E. Brown and F. G. A. Stone, J. Chem. Soc., Dalton Trans., 1988, 1139. 6 E. Carmona, E. Gutiérrez, A. Monge, A. Pizzano and L. Sanchéz, Organometallics, 1995, 14, 14. 7 D. J. Cook and A. F. Hill, Chem. Commun., 1997, 955. 8 J. S. Thompson, J. L. Zitzmann, T. J. Marks and J. A. Ibers, Inorg. Chim. Acta, 1980, 46, L101. Received 13th February 1997; Communication 7/01040K

ISSN:1477-9226    

DOI:10.1039/a701040k

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2005–2008 2005 Synthesis and structures of carboxylate-bridged polynuclear copper(II)–lanthanide(III) complexes [CuLn(C5H5N1CH2- CO2 2)5(H2O)5][ClO4]5?2H2O (Ln 5 La or Nd) and [Cu3Nd2(C5H5N1CH2CO2 2)10(NO3)2(H2O)8][ClO4]10?4H2O Yang-Yi Yang,a Yu-Luan Wu,a La-Sheng Long a,b and Xiao-Ming Chen *a a School of Chemistry and Chemical Engineering, Zhongshan University, Guangzhou 510275, P.R. China. E-mail: cescxm@zsu.edu.cn b State Key Laboratory of Structural Chemistry, Chinese Academy of Sciences, Fuzhou 350002, P. R. China Received 25th January 1999, Accepted 23rd April 1999 Two types of carboxylate-bridged copper(II)–lanthanide(III) complexes, [CuLn(C5H5N1CH2CO2 2)5(H2O)5][ClO4]5? 2H2O 1 (LnIII = LaIII a or NdIII b) and [Cu3Nd2(C5H5N1CH2CO2 2)10(NO3)2(H2O)8][ClO4]10?4H2O 2, have been synthesized and characterized by X-ray structural analysis.Complexes 1a and 1b are isomorphous. In both, a CuII atom is quadruply bridged to a LnIII atom by four m-carboxylate groups at the basal positions, and co-ordinated by an aqua ligand at the apical position to form a square-pyramidal CuO4(OH2) geometry, while the LnIII atom is coordinated in a monocapped square antiprism by five carboxy oxygen atoms and four aqua ligands.In 2, a pair of CuII atoms in two centrosymmetrically related tetrakis(m-carboxylate)-bridged dinuclear CuIINdIII subunits is each linked to the central CuII atom by a single syn-anti m-carboxylate bridge, resulting in a pentanuclear cation. The central CuII atom is co-ordinated by two carboxy oxygen atoms and two aqua ligands in a distorted square-planar fashion; the other two CuII atoms adopt the same square-pyramidal geometry, each being ligated by the four oxygen atoms from the quadruple carboxylate bridges at the basal plane and by one oxygen atom of the syn-anti m-carboxylate group at the apical position.The NdIII atom is co-ordinated in a distorted monocapped square antiprism by the four carboxy oxygen atoms, three aqua ligands and a chelate nitrate group.We have recently found that the stable [Cu(betaine)4]21 core found in the monomeric copper(II) tetracarboxylates (betaine = trimethylammonioacetate, Me3N1CH2CO2 2) 1 can be used as a “metallo-ligand” to bind other hard metal ions such as CaII and LiI to form heterometallic complexes,2 thus providing a new synthetic route for heterometallic complexes in metal carboxylate chemistry.Since lanthanide(III) ions (designated as LnIII hereafter) are very similar to hard calcium ions in co-ordination chemistry, the above-mentioned interesting strategy can also be applied to the preparations of carboxylate-bridged heterometallic tetranuclear CuII 2LnIII 2 compounds.3 Heterometallic compounds consolidated by carboxylate groups have not been well documented;4 only a few examples of heteronuclear CuII– LnIII compounds have very recently been uncovered.3,5,6 This may be attributed to the fact that CuII and LnIII are very diVerent in co-ordination ability.Therefore heteronuclear CuII–LnIII compounds have commonly been synthesized with heterodonor ligands comprising two types of ligating atoms (such as N and O) co-ordinated each to Cu and Ln atoms, respectively, which are currently of interest because of the magnetic interaction between transition and rare-earth metal ions in bridged systems, and their possible application in production of high temperature superconductors.7–9 We have recently reported a series of polynuclear CuII–LnIII complexes containing chloroacetate, betaine and its derivatives, including tetranuclear CuII 2LnIII 2,3 pentanuclear CuII 3LnIII 2,5 octadecanuclear CuII 12LnIII 6 clusters.10,11 At high pH hydroxide participates in co-ordination, resulting in the formation of the octadecanuclear CuII 12LnIII 6 clusters.10,11 We expect that at low pH the [Cu(carboxylate)4] core can bind a LnIII to form a stable dimeric [CuLn(carboxylate)4] compound, although the tetranuclear compounds have been isolated in the cases of betaine.3 In this paper we document the synthesis and structures of the first tetrakis(m-carboxylate)-bridged dinuclear CuIILnIII compounds of pyridinioacetate (C5H5N1CH2CO2 2, designated as pyb hereafter) and a pentanuclear compound consisting of two [CuLn(carboxylate)4] cores, namely [CuLn(pyb)5(H2O)5]- [ClO4]5?2H2O 1 (LnIII = LaIII a or NdIII b) and [Cu3Nd2(pyb)10- (NO3)2(H2O)8][ClO4]10?4H2O 2.Experimental Pyridinioacetate was synthesized by the literature method.12 Other reagents were commercially available and used as received. The C, H and N microanalyses were carried out with a Perkin-Elmer 240Q elemental analyzer.FT-IR spectra were recorded from KBr pellets in the range 4000–400 cm21 on a Nicolet 5DX spectrometer. CAUTION. Metal perchlorates containing organic ligands are potentially explosive. Only a small amount of material should be prepared and handled with great care. Preparation of compounds [CuLa(pyb)5(H2O)5][ClO4]5?2H2O 1a. A mixture of pyb (3.0 mmol) and Cu(NO3)2 (0.5 mmol) was dissolved in distilled water (5 cm3) and heated at 60 8C for 10 min, La(NO3)3 (1.0 mmol) was then added followed by an aqueous solution (2 cm3) of NaClO4 (5 mmol) upon stirring for 10 min.The resulting blue solution was adjusted to pH 2.5 and allowed to stand in air at room temperature for about 10, yielding blue prismatic crystals (ca. 20% yield) (Calc. for C35H49Cl5CuLaN5O37: C, 27.81; H, 3.27; N, 4.63.Found: C, 28.04; H, 3.02; N, 4.83%). IR data for the carboxylate groups (n& /cm21): 1688 (sh), 1637s and 1405vs.2006 J. Chem. Soc., Dalton Trans., 1999, 2005–2008 Table 1 Crystallographic data for complexes 1a, 1b and 2 1a 1b 2 Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z m/cm21 R1/wR2 (I > 2s) (all data) C35H49Cl5CuLaN5O37 1511.49 Monoclinic C2/c (no. 15) 37.950(8) 11.286(2) 27.859(6) 104.70(3) 11542(4) 8 14.35 0.0539/0.1506 0.0964/0.1773 C35H49Cl5CuN5NdO37 1516.82 Monoclinic C2/c (no. 15) 37.51(2) 11.172(2) 27.557(14) 104.810(10) 11166(9) 8 16.48 0.0657/0.1566 0.1157/0.1850 C70H94Cl10Cu3N12Nd2O78 3185.17 Triclinic P1� (no. 2) 11.410(4) 14.992(6) 18.447(7) 73.380(10) 72.140(10) 88.900(10) 2869.8(19) 1 17.89 0.0497/0.1187 0.0728/0.1317 [CuNd(pyb)5(H2O)5][ClO4]5?2H2O 1b.This was prepared as for complex 1a (Calc. for C35H49Cl5CuN5NdO37: C, 28.19; H, 3.10; N, 4.81. Found: C, 28.39; H, 3.06; N, 4.73%). IR data for the carboxylate groups (n& /cm21): 1688 (sh), 1630vs and 1405vs. [Cu3Nd2(pyb)10(NO3)2(H2O)8][ClO4]10?4H2O 2. This was prepared similarly to complex 1a, but the blue solution was adjusted to pH 3.0, yielding deep blue polyhedral crystals after two weeks (Calc.for C70H94Cl10Cu3N12Nd2O78: C, 26.40; H, 2.97; N, 5.28. Found: C, 26.25; H, 3.05; N, 5.31%). IR data for the carboxylate groups (n& /cm21): 1686s, 1637s and 1405s. X-Ray crystallography A summary of selected crystallographic data for the three compounds is given in Table 1.The data collections were carried out on a Siemens R3m diVractometer using graphitemonochromated Mo-Ka (l = 0.71073 Å) radiation at 293(2) K. For each complex, determination of the crystal class, orientation matrix, and cell dimensions were performed according to the established procedures. The intensity data were collected using the w-scan mode. Two standard reflections were monitored after every 120 data measurements, showing only small random variations (<1.0%). Absorption corrections were applied by fitting a pseudoellipsoid to the y-scan data of selected strong reflections over a range of 2q angles.13 Most of the non-hydrogen atoms in each crystal structure were located with the direct methods and subsequent Fourier syntheses were used to derive the remaining non-hydrogen atoms.14 All the non-hydrogen atoms were refined anisotropically.All the hydrogen atoms were held stationary and included in the final stage of full-matrix least-squares refinement based on F2 using the SHELXL 97 program package.15 Analytical expressions of the neutral-atom scattering factors were employed, and anomalous dispersion corrections were incorporated.16 Selected bond lengt and bond angles are listed in Tables 2 and 3.CCDC reference number 186/1436. See http://www.rsc.org/suppdata/dt/1999/2005/ for crystallographic files in .cif format. Results and discussion Crystal structures [CuLa(pyb)5(H2O)5][ClO4]5?2H2O 1a. The crystal structure of complex 1a consists of discrete dinuclear [CuLa(pyb)5- (H2O)5]51 cation, perchlorate anions and lattice water molecules. An ORTEP17 view of the dimeric cation is shown in Fig. 1. The CuII atom is co-ordinated by four carboxylate oxygen atoms at the basal plane [Cu(1)–O 1.929(4)–1.998(4) Å] (Table 2) and completed by an aqua ligand at the apical position [Cu(1)–O(5w) 2.232(4) Å] to form a square-pyramidal geometry. The LaIII atom is quadruply bridged to the CuII atom by four m-carboxylate bridges of pyb ligands [La(1)–O 2.525(4)– 2.549(4) Å], giving rise to a dinuclear cation with the intramolecular CuII ? ? ? LaIII distance of 3.764(2) Å.This dinuclear structure is similar to that found for the tetranuclear [CuII 2- LnII 2(betaine)10(H2O)8][ClO4]10?2H2O (Ln = La, Ce or Gd),3 and somewhat similar to those of the well known [Cu2(m-carboxylate) 4] complexes.18 Except for the four m-carboxylate oxygen atoms, the LaIII atom is further co-ordinated by one monodentate carboxylate oxygen atom [La(1)–O(51) 2.487(4) Å] and four aqua ligands [La(1)–O = 2.556(5)–2.630(4) Å] to form nine-co-ordination.The co-ordination polyhedron about the LaIII ion can be best described as a distorted monocapped square antiprism; one square face consists of one oxygen atom [O(51)] of the monodentate carboxylate group and three aqua oxygen atoms [O(1w), O(2w) and O(4w)], whereas the other face is defined by four carboxylate oxygen atoms [O(12), O(22), O(32) and O(42)] from the quadruple m-carboxylate bridges between the pair of CuII and LaIII atoms.The dihedral angle between the square faces is ca. 58.[CuNd(pyb)5(H2O)5][ClO4]5?2H2O 1b. The crystal structure of complex 1b is isomorphous to that of 1b, only very small metric diVerences having been observed for the two complexes. Owing to the slightly smaller radius of NdIII than that of LaIII,19 all the metal–ligand bonds in 1b are slightly shorter than the corresponding bonds in 1a, as compared in Table 2, however the bond angles in both are almost the same.It is noteworthy that only one dinuclear CuIILnIII compound has recently been reported so far,20 in which a pair of CuII and LaIII atoms are chelated by a polydentate SchiV base containing m-phenoxy bridges. Therefore, 1a and 1b are novel dinuclear CuIILnIII compounds with the pair of metal atoms bridged uniquely by carboxylate groups. Fig. 1 An ORTEP view showing the dinuclear cation in complex 1a.J.Chem. Soc., Dalton Trans., 1999, 2005–2008 2007 Table 2 Selected bond lengths (Å) and angles (8) for complexes 1a and 1b Ln(1)–O(51) Ln(1)–O(12) Ln(1)–O(22) Ln(1)–O(4w) Ln(1)–O(2w) Cu(1)–O(31) Cu(1)–O(41) O(51)–Ln(1)–O(42) O(42)–Ln(1)–O(12) O(42)–Ln(1)–O(32) O(51)–Ln(1)–O(22) O(12)–Ln(1)–O(22) O(51)–Ln(1)–O(1w) O(12)–Ln(1)–O(1w) O(22)–Ln(1)–O(1w) O(42)–Ln(1)–O(4w) O(32)–Ln(1)–O(4w) O(1w)–Ln(1)–O(4w) O(42)–Ln(1)–O(3w) O(32)–Ln(1)–O(3w) O(1w)–Ln(1)–O(3w) O(51)–Ln(1)–O(2w) O(12)–Ln(1)–O(2w) O(22)–Ln(1)–O(2w) O(4w)–Ln(1)–O(2w) O(21)–Cu(1)–O(31) O(31)–Cu(1)–O(11) O(31)–Cu(1)–O(41) O(21)–Cu(1)–O(5w) O(11)–Cu(1)–O(5w) C(11)–O(12)–Ln(1) C(21)–O(21)–Cu(1) C(31)–O(31)–Cu(1) C(41)–O(41)–Cu(1) C(51)–O(51)–Ln(1) 1a 2.487(4) 2.526(4) 2.549(4) 2.606(4) 2.630(4) 1.968(4) 1.998(4) 79.77(13) 72.07(13) 108.89(12) 71.68(13) 106.79(12) 90.97(16) 69.04(15) 136.26(16) 140.17(13) 70.04(12) 138.88(14) 124.55(15) 126.23(14) 66.27(15) 134.94(13) 67.52(13) 136.24(14) 81.28(14) 91.52(17) 89.42(16) 174.51(14) 93.84(15) 88.94(15) 160.5(4) 126.9(3) 122.8(3) 118.2(3) 139.6(4) 1b 2.418(5) 2.459(5) 2.478(5) 2.506(5) 2.542(6) 1.939(5) 1.965(5) 78.47(17) 72.36(17) 110.10(16) 71.38(17) 107.89(16) 89.8(2) 68.9(2) 136.6(2) 140.87(18) 70.32(17) 137.76(18) 124.5(2) 125.15(19) 66.7(2) 134.97(18) 67.73(18) 136.84(19) 80.65(19) 91.4(2) 89.6(2) 173.83(19) 94.1(2) 88.9(2) 160.5(5) 126.4(5) 122.7(5) 118.3(4) 139.5(5) Ln(1)–O(42) Ln(1)–O(32) Ln(1)–O(1w) Ln(1)–O(3w) Cu(1)–O(21) Cu(1)–O(11) Cu(1)–O(5w) O(51)–Ln(1)–O(12) O(51)–Ln(1)–O(32) O(12)–Ln(1)–O(32) O(42)–Ln(1)–O(22) O(32)–Ln(1)–O(22) O(42)–Ln(1)–O(1w) O(32)–Ln(1)–O(1w) O(51)–Ln(1)–O(4w) O(12)–Ln(1)–O(4w) O(22)–Ln(1)–O(4w) O(51)–Ln(1)–O(3w) O(12)–Ln(1)–O(3w) O(22)–Ln(1)–O(3w) O(4w)–Ln(1)–O(3w) O(42)–Ln(1)–O(2w) O(32)–Ln(1)–O(2w) O(1w)–Ln(1)–O(2w) O(3w)–Ln(1)–O(2w) O(21)–Cu(1)–O(11) O(21)–Cu(1)–O(41) O(11)–Cu(1)–O(41) O(31)–Cu(1)–O(5w) O(41)–Cu(1)–O(5w) C(11)–O(11)–Cu(1) C(21)–O(22)–Ln(1) C(31)–O(32)–Ln(1) C(41)–O(42)–Ln(1) 1a 2.525(4) 2.535(4) 2.556(5) 2.608(4) 1.929(4) 1.983(4) 2.232(4) 149.78(14) 130.16(13) 71.15(13) 68.62(13) 67.15(13) 68.92(15) 138.57(15) 73.37(13) 136.41(13) 75.23(12) 70.18(14) 117.70(14) 135.51(13) 72.64(14) 137.37(14) 70.31(14) 84.23(18) 66.92(14) 176.98(15) 89.19(16) 89.60(16) 95.09(15) 90.29(14) 111.7(3) 141.1(3) 146.3(3) 150.8(4) 1b 2.454(5) 2.469(5) 2.459(6) 2.543(5) 1.920(5) 1.962(5) 2.229(5) 148.51(18) 131.61(18) 71.32(17) 69.21(17) 68.38(17) 68.8(2) 138.3(2) 74.60(18) 136.63(17) 75.54(17) 69.91(19) 118.10(18) 134.01(17) 71.06(19) 137.63(18) 69.89(18) 83.9(2) 66.67(19) 176.8(2) 89.2(2) 89.5(2) 95.6(2) 90.5(2) 110.5(4) 140.8(5) 146.3(5) 150.5(5) [Cu3Nd2(pyb)10(NO3)2(H2O)8][ClO4]10?4H2O 2.The crystal structure of complex 2 consists of a centrosymmetrical pentanuclear [Cu3Nd2(pyb)10(NO3)2(H2O)8]101 cation, perchlorate anions and lattice water molecules. As shown in Fig. 2, each NdIII atom is quadruply bridged to a CuII atom by four syn-syn m-carboxylate bridges of pyb ligands with an intramolecular CuII ? ? ?NdIII separation of 3.650(2) Å, resulting in a dinuclear CuIINdIII subunit, which is similar to those found in 1.Besides the four carboxy oxygen atoms [Nd(1)–O 2.394(3)–2.440(3) Å] (Table 3), the co-ordination sphere of the NdIII atom is completed by a bidentate nitrate group [Nd(1)–O 2.539(4) or 2.636(3) Å] and three aqua ligands [Nd(1)–O 2.449(3)– 2.499(4) Å] to form a monocapped square-antiprism nine-coordination geometry.The Cu(1) atom in the subunit is ligated in a distorted square pyramid with the four oxygen atoms [Cu(1)–O 1.945(3)–1.981(3) Å] from the quadruple m-carboxylate bridges at the basal plane and one oxygen atom from another carboxylate bridge at the apical position [Cu–O Fig. 2 An ORTEP view showing the pentanucler cation in complex 2. Symmetry code: a 2x, 1 2 y, 2z. 2.154(3) Å]. A pair of CuII atoms in two centrosymmetrically related dinuclear CuIINdIII subunits are each linked to the central Cu(2) atom by a single syn-anti m-carboxylate bridge, resulting in a centrosymmetrical pentanuclear cation. The Cu(2) atom, being located at the crystallographic inversion centre, is co-ordinated by two oxygen atoms of the carboxylate groups and two aqua oxygen atoms in a slightly distorted square-planar fashion with the O(4w)–Cu(2)–O(52) angle at 89.34(16)8 and Cu(2)–O bonds at 1.912(3)–1.918(3) Å; the trans-related O(21) and O(21a) atoms are in close contact with the Cu(2) atom [Cu(2) ? ? ? O(21) 2.828(3) Å], indicative of some weak interaction.2 It is noteworthy that the central Cu(2) atom is linked to the Cu(1) atoms of both CuIINdIII subunits with the Cu(1) ? ? ? Cu(2) distance of 3.837(2) Å, diVerent from that of a pentanuclear CuII 3GdIII 2 cluster bridged by chloroacetate groups.5 In the chloroacetate compound the central CuII atom is linked to the GdIII atoms in both of tetrakis(m-carboxylate)-bridged CuIIGdIII subunits by two syn-anti m-carboxylate bridges, and the co-ordination sphere of this central CuII atom is completed by two monodentate carboxylate groups to form a distorted square-planar geometry.Synthesis Acidity of the reaction solution is critically important. Although it is diYcult to explain, a subtle change in acidity of the reaction mixture can cause a drastic change in the structures of the products. Both complexes 1 and 2 are synthesized under similar conditions with a slight diVerence in pH values of the solutions; at low pH (pH < 3) the [Cu- (pyb)4]21 core can bind a LnIII to form a dinuclear [CuLn- (pyb)4]51 core as found in 1, which can be connected to construct larger clusters as found in 2.At higher pH (�3.5) hydroxide anions may participate in co-ordination to form2008 J. Chem. Soc., Dalton Trans., 1999, 2005–2008 larger clusters, and the formation of octadecanuclear clusters 10 may be promoted.Acknowledgements This work was supported by the National Natural Science Foundation of China (29625102) and Science Foundation of Guangdong. We are also indebted to the Chemistry Department of the Chinese University of Hong Kong for donation of the diVractometer. Table 3 Selected bond lengths (Å) and bond angles (8) for complex 2 Nd(1)–O(22) Nd(1)–O(32) Nd(1)–O(42) Nd(1)–O(12) Nd(1)–O(1w) Nd(1)–O(2w) Nd(1)–O(3w) Nd(1)–O(61) O(22)–Nd(1)–O(32) O(22)–Nd(1)–O(42) O(32)–Nd(1)–O(42) O(22)–Nd(1)–O(12) O(32)–Nd(1)–O(12) O(42)–Nd(1)–O(12) O(22)–Nd(1)–O(1w) O(32)–Nd(1)–O(1w) O(42)–Nd(1)–O(1w) O(12)–Nd(1)–O(1w) O(22)–Nd(1)–O(2w) O(32)–Nd(1)–O(2w) O(42)–Nd(1)–O(2w) O(12)–Nd(1)–O(2w) O(1w)–Nd(1)–O(2w) O(22)–Nd(1)–O(3w) O(32)–Nd(1)–O(3w) O(42)–Nd(1)–O(3w) O(12)–Nd(1)–O(3w) O(1w)–Nd(1)–O(3w) O(2w)–Nd(1)–O(3w) O(22)–Nd(1)–O(61) O(32)–Nd(1)–O(61) O(3w)–Nd(1)–O(61) O(42)–Nd(1)–O(61) N(6)–O(61)–Nd(1) N(6)–O(62)–Nd(1) C(11)–O(12)–Nd(1) C(21)–O(22)–Nd(1) C(31)–O(32)–Nd(1) C(41)–O(42)–Nd(1) 2.394(3) 2.402(3) 2.411(3) 2.440(3) 2.449(3) 2.470(4) 2.499(4) 2.539(4) 73.74(13) 110.40(11) 70.60(13) 70.31(12) 113.67(11) 72.57(12) 134.09(13) 142.90(13) 75.60(13) 68.63(11) 149.21(13) 81.67(12) 77.41(12) 138.31(12) 76.41(13) 76.31(13) 69.93(12) 135.84(14) 143.09(13) 132.02(11) 78.06(13) 71.27(11) 137.75(12) 79.35(13) 144.79(13) 99.0(3) 94.1(2) 140.2(3) 157.0(3) 150.9(3) 142.8(3) Cu(1)–O(41) Cu(1)–O(11) Cu(1)–O(31) Cu(1)–O(21) Cu(1)–O(51) Cu(2)–O(4w) Cu(2)–O(52) Nd(1)–O(62) O(41)–Cu(1)–O(11) O(41)–Cu(1)–O(31) O(11)–Cu(1)–O(31) O(41)–Cu(1)–O(21) O(11)–Cu(1)–O(21) O(31)–Cu(1)–O(21) O(41)–Cu(1)–O(51) O(11)–Cu(1)–O(51) O(31)–Cu(1)–O(51) O(21)–Cu(1)–O(51) O(4w)–Cu(2)–O(52) O(22)–Nd(1)–O(62) O(32)–Nd(1)–O(62) O(42)–Nd(1)–O(62) O(12)–Nd(1)–O(62) O(1w)–Nd(1)–O(62) O(2w)–Nd(1)–O(62) O(3w)–Nd(1)–O(62) O(61)–Nd(1)–O(62) O(12)–Nd(1)–O(61) O(1w)–Nd(1)–O(61) O(2w)–Nd(1)–O(61) C(11)–O(11)–Cu(1) C(21)–O(21)–Cu(1) C(21)–O(21)–Cu(2) Cu(1)–O(21)–Cu(2) C(31)–O(31)–Cu(1) C(41)–O(41)–Cu(1) C(51)–O(51)–Cu(1) C(51)–O(52)–Cu(2) 1.945(3) 1.954(4) 1.969(4) 1.981(3) 2.154(3) 1.913(4) 1.918(3) 2.636(3) 90.96(16) 89.00(17) 172.67(13) 174.65(13) 88.65(15) 90.71(15) 92.52(13) 90.79(13) 96.53(14) 92.82(12) 89.34(16) 112.35(11) 131.83(12) 136.01(11) 113.03(11) 67.61(12) 71.34(12) 65.97(12) 48.72(11) 75.47(11) 79.34(13) 120.04(11) 124.9(3) 113.1(3) 139.9(3) 104.50(12) 117.7(3) 124.5(3) 133.9(3) 123.8(3) References 1 X.-M.Chen and T. C. W. Mak, Polyhedron, 1991, 10, 273; S. W. Ng, X.-M. Chen and G. Yang, Acta Crystallogr., Sect. C, 1998, 54, 1389. 2 X.-M. Chen and T. C. W. Mak, Inorg. Chem., 1994, 33, 2444; Polyhedron, 1994, 13, 1087. 3 X.-M. Chen, Y.-L. Wu and Y.-Y. Yang, Inorg. Chem., 1998, 37, 6186. 4 C. Mehrotra and R. C. Bohra, Metal Carboxylates, Academic Press, New York, 1983; C. Oldham, in Comprehensive Coordination Chemistry, eds. G. Wilkinson, R. Gillard and J. A. McCleverty, Pergamon, Oxford, 1987, vol. 2, pp. 435–460; A. Ouchi, Y. Suzuki, Y. Ohki and Y. Koizumi, Coord.Chem. Rev., 1988, 92, 29. 5 X.-M. Chen, M.-L. Tong, Y.-L. Wu and Y.-J. Luo, J. Chem. Soc., Dalton Trans., 1996, 2181; M.-L. Tong, Y.-L. Wu, X.-M. Chen, Z. Sun and D. N. Hendrickson, Chem. Res. Chin. Univ., 1998, 14, 230. 6 Y. Cui, J.-T. Chen, D.-L. Long, F.-K. Zheng, W.-D. Cheng and J.-S. Huang, J. Chem. Soc., Dalton Trans., 1998, 2955. 7 M. Andruh, I. Ramade, E. Codjovi, O. Guillou, O.Kahn and J. C. Trombe, J. Am. Chem. Soc., 1993, 115, 1822; C. Benelli, A. Caneschi, D. Gatteschi, O. Guillou and L. Pardi, Inorg. Chem., 1990, 29, 1750; M. Andruh, O. Kahn, J. Sainto, Y. Dromzee and S. Jeannin, Inorg. Chem., 1993, 32, 1623. 8 R. Georges, O. Kahn and O. Guillou, Phys. Rev. B, 1994, 49, 3235; L. L. Sanz, R. Ruiz, F. Lloret, J. Faus, M. Juvle, J. J. Borrás- Almemar and Y.Journaux, Inorg. Chem., 1996, 35, 7393. 9 S. Wang, Z. Pang and D. L. Smith, Inorg. Chem., 1993, 32, 4992; E. K. Brechin, S. G. Harris, S. Parson and R. E. Winpenny, J. Chem. Soc., Dalton Trans., 1997, 1665 and refs. therein. 10 X.-M. Chen, S. M. J. Aubin, Y.-L. Wu, Y.-S. Yang, T. C. W. Mak and D. N. Hendrickson, J. Am. Chem. Soc., 1995, 117, 9600; X.-M. Chen, Y.-L. Wu and R.-J. Wang, Sci. China, Ser. B, 1996, 39, 536. 11 X.-M. Chen, Y.-L. Wu, Y.-X. Tong and X.-Y. Huang, J. Chem. Soc., Dalton Trans., 1996, 2443. 12 X.-M. Chen and T. C. W. Mak, J. Chem. Soc., Dalton Trans., 1991, 3253. 13 A. C. T. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr., Sect. A, 1968, 24, 351. 14 G. M. Sheldrick, SHELXTL PLUS, Siemens Analytical X-Ray Instruments Inc., Madison, WI, 1990. 15 G. M. Sheldrick, SHELXL 97, Program for X-Ray Crystal Structure Refinement, Göttingen University, 1997. 16 International Tables for X-Ray Crystallography, Kluwer, Dordrecht, 1992, vol. C, Tables 4.2.6.8 and 6.1.1.4. 17 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 18 X.-M. Chen and T. C. W. Mak, Struct. Chem., 1993, 4, 247; X.-M. Chen, X.-L. Feng, Z.-T. Xu, X.-H. Zhang, F. Xue and T. C. W. Mak, Polyhedron, 1998, 17, 2639 and refs. therein. 19 R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751. 20 J.-P. Costes, F. Dahan, A. Dupuis and J.-P. Laurent, Inorg. Chem., 1996, 35, 2400. Paper 9/0064

ISSN:1477-9226    

DOI:10.1039/a900647h

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 2007 Reactivity of electrophilic palladium alkyl cations stabilized by electron-rich chelating diphosphine ligands. Evidence for dinuclear intermediates and the formation of a dinuclear mixed-valence methyl cation ‡ Michael D. Fryzuk,* Guy K. B. Clentsmith and Steven J. Rettig † Department of Chemistry, University of British Columbia, 2036 Main Mall, Vancouver, BC, Canada V6T 1Z1 The reactivity of the electron-rich palladium alkyl cation, [Pd(dippe)R]1BAr4 2 (dippe = 1,2-bis(diisopropylphosphino) ethane; R = h3-CH2Ph or CH3; BAr4 = {B[3,5-(F3C)2C6H3]4}) with a variety of small molecules is reported.Although the benzyl cation is unreactive towards carbon monoxide and dihydrogen, the corresponding methyl cation, [Pd(dippe)Me(s)]1 (s = Et2O, THF or o-dichlorobenzene) reacts rapidly with H2 to produce the dihydride-bridged dimer {[(dippe)Pd]2(m-H)2}21, and with CO to produce the dinuclear mixed-valence, cationic complex [Pd(dippe)(m-CO)Pd(dippe)Me][BAr4]. In addition, the methyl cation can abstract alkyl groups from neutral dialkyl complexes; thus, the addition of [Pd(dippe)Me(s)]1 to Pd(dippe)(CH2Ph)2 results in the formation of the methyl benzyl derivative Pd(dippe)Me(CH2Ph) and the cationic benzyl cation [Pd(dippe)(h3-CH2Ph)]1.Methyl group interchange is also observed for the reaction of the methyl cation with the neutral dimethyl; when [Pd(dippe)Me(s)]1 is mixed with Pd(dippe)(13CH3)2, the carbon-13 label is immediately scrambled to the cation.These exchange reactions are suggested to occur via dinuclear intermediates. The mixed-valence dinuclear species mentioned above has been investigated in some detail; mechanistic studies have indicated that the addition of CO to [Pd(dippe)Me(s)]1 probably proceeds via simple substitution of the solvent by CO to generate the expected mononuclear methyl carbonyl cation [Pd(dippe)Me(CO)]1, followed by migratory insertion to give the acetyl carbonyl derivative [Pd(dippe)(COMe)(CO)]1.The final product is the dinuclear mixed-valence species [Pd(dippe)(m-CO)Pd(dippe)Me][BAr4], which is accompanied by the formation of acetone (Me2CO) and the dicarbonyl dication [Pd(dippe)(CO)2]21. Presumably, methyl transfer occurs at some stage from the methyl cation to generate the methyl–acetyl complex, Pd(dippe)Me(COMe); reductive elimination of acetone under CO from the methyl–acetyl complex produces the Pd0 complex Pd(dippe)CO which then reacts with the starting methyl cation to generate the dinuclear mixed-valence species.Addition of CO to the mixed-valence species does not result in formation of mononuclear complexes, rather 1 equivalent of CO adds to form a new dinuclear complex with two bridging COs. Soluble palladium complexes are widely used as catalysts for many organic transformations.1,2 Recently, cationic PdII derivatives have come under intense scrutiny as catalysts for the copolymerization of carbon monoxide and olefins, and for the polymerization of functionalized olefins.3–19 In both of these processes, one of the propagating species is believed to consist of a cationic square-planar derivative (A) stabilized by a bidentate chelating ligand, usually a diphosphine or a diimine, with the other two sites occupied by monomer and growing polymer.20 From a design point of view, such a configuration would appear ideal since the chelating ancillary ligand restricts the two reactive sites to be cis disposed, exactly as required for the migratory insertion type reaction.21 In addition, the steric and electronic properties of the ancillary ligand can be varied to influence the stereochemistry and molecular weight of the resulting polymers.5 In this paper we report the stoichiometric reactivity of electrophilic palladium(II) alkyl cations with small molecules D Pd L P D D D diphosphine or diimine P polymer; L co-ordinated monomer A + † Professional OYcer: UBC Structural Chemistry Laboratory.‡ Non-SI units employed: atm = 101 325 Pa; mmHg = 133.322 Pa. such as H2 and CO and make comparisons with the neutral dialkyl analogues. What we find is that the reactivity of these cations is generally enhanced as compared with their neutral counterparts, and that dinuclear products and intermediates play an important role in the chemistry of these species. Results and Discussion Preparation of cationic alkyls and hydrides of PdII We have previously reported the preparation of dinuclear hydrides of palladium(I) 22 and catalytically active palladium( 0) 23 complexes that incorporate electron-rich chelating ligands bearing isopropyl substituents, i.e. 1,2-bis(diisopropylphosphino) ethane (dippe) and 1,3-bis(diisopropylphosphino)- propane (dippp). To prepare cationic alkyl complexes, we chose the method developed by Brookhart et al. involving protonation of neutral dialkyl complexes using HBAr4 (HBAr4 = [H(OEt2)2]1{B[3,5-(F3C)2C6H3]4}2).7 The starting dialkyl derivatives, Pd(dippe)R2 and Pd(dippp)R2 (where R = Me or CH2Ph) are prepared via standard preparative routes as described in the Experimental section.Protonation of the dibenzyl complex Pd(dippe)(CH2Ph)2 leads to the formation of the h3-benzyl derivative [Pd(dippe)(h3-CH2C6H5)]1BAr4 2 [equation (1)]. The 31P-{1H} NMR spectrum of 1 shows the required AX pattern due to inequivalent phosphorus nuclei, i.e.a pair of doublets at d 88.7 and 75.2 (JPP9 = 32.1 Hz), and the 1H and 1H-{31P} NMR spectra are representative of an unsymmetrical complex. Of particular note are the four isopropyl methyl2008 J. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 signals between d 1.07 and 0.75 and the two isopropyl methine resonances at d 2.37 and 1.98; the 1H-{31P} NMR spectrum again shows the inequivalence of the methylene backbone of the ligand with the two triplets required for the A2X2 spinsystem of the CH2CH92 linkage.Significantly, signals due to the ortho protons of the benzyl group are observed at d 6.41.24 This upfield value indicates h3-co-ordination and the assignment is further evidenced by an NOE experiment: irradiation of the benzylic protons results in signal enhancement of the peak at d 6.41, due to the ortho protons, and a negative NOE with the meta protons at d 7.3. The ortho and benzylic protons each appear as single multiplets in the 1H NMR spectrum and their equivalence is maintained even at 290 8C, as is the inequivalence of the phosphorus nuclei in the 31P-{1H} NMR spectrum.This dynamic behaviour is consistent with a fast h1– h3 suprafacial shift of the palladium nucleus, which interchanges both syn and anti benzyl protons, and ortho-phenyl protons but maintains the non-equivalence of the phosphine donors.25 The preparation of the same benzyl cation 1 could also be eVected by benzyl abstraction from the starting neutral derivative Pd(dippe)(CH2C6H5)2 by B(C6F5)3, one of the Lewis acids that has been used in the synthesis of single-site olefin polymerization catalysts.26 Although a 1 : 1 mixture of the two reagents generated an oil, the solution spectra of the product were equivalent to that of 1, except for the benzylic signals due to [B(C6F5)3CH2C6H5]2 observed in the 1H NMR spectrum.The labeled derivative, 1-d7, was also prepared by protonation with HBAr4 on Pd(dippe)(CD2C6D5)2 [prepared in turn from Pd(dippe)Cl2 and 2 equivalents of KCD2C6D5], and a doublet was observed at d 2.30 (JHD = 2.5 Hz) in the 2H NMR spectrum of the reaction mixture due to extruded HD2CC6D5.Although cationic, the reactivity of [Pd(dippe)(h3-CH2- C6H5)]1 is unremarkable. Cation 1 is inert to both CO and H2, and is in fact air-stable. This is not too surprising as examples of stable h3-allyl palladium cations are legion, and their chemistry is mature.27 We therefore chose to examine protonation reactions of Pd(dippe)Me2 and Pd(dippp)Me2.To an ethereal solution of either palladium dimethyl complex, the addition of 1 equivalent of HBAr4 causes a rapid eVervescence, undoubtedly of methane, and the methyl cations [Pd(dippe)- Me(OEt2)]1 2 and [Pd(dippp)Me(OEt2)]1 3 are obtained as shown for 2[BAr4] in equation (2). Because the remaining methyl group bound to the Pd centre cannot oVer additional p interaction as can an allyl or benzyl group, the metal nucleus is now highly electrophilic and is loosely stabilized by whatever solvent molecules are available.In diVerent NMR solvents, or even an ethereal solution of the cation to which diVerent solvents are successively added, this gives rise to a series of solution spectra which indicates the progressive filling of the vacant co-ordination site by the P Pd P CH2Ph CH2Ph + HBAr4 P Pd P H H BAr4 – Et2O (–PhCH3) (1) 1 [BAr4] + P Pd P Me + s BAr4 – (2) P Pd P Me Me + HBAr4 Et2O (–MeH) 2[BAr4] (s = Et2O) stronger donor.The 31P-{1H} NMR spectrum of 2 thus consists of an AX pattern and in diVerent NMR solvents the chemical shift of the two doublets change noticeably. From a starting solution of Pd(dippe)Me2 plus HBAr4 in Et2O–C6D6 the following 31P-{1H} NMR parameters can be generated: an AX pattern at d 84.2 and 63.1 (JAX = 17.4 Hz) due to [Pd(dippe)- Me(OEt2)]1 2a; following addition of a few drops of THF, an AX pattern at d 86.0 and 69.0 (JAX = 17.0 Hz), due to [Pd- (dippe)Me(THF)]1 2b; and following addition of excess PPh3, an AMX pattern at d 78.3, 70.0 and 29.8 (JAX = 368.0, JAM = 21.9, JMX = 29.5 Hz) due to [Pd(dippe)Me(PPh3)]1 2c.These data are in accord with a square-planar palladium cation whose fourth co-ordination site is filled by a labile solvent molecule. For this reason, we will refer to 2 as the cation [Pd(dippe)Me(s)]1 where s is the reaction- or NMR-solvent.Additional information can be obtained by examination of the 13C-{1H} and 31P-{1H} NMR spectra of the carbon-13 labelled species [Pd(dippe)13Me(s)]1 (2-13C1). The 31P-{1H} NMR spectrum of 2-13C1 is an ABX pattern with two nonequivalent phosphorus nuclei (JPP9 = 16.7 Hz) coupled to a single 13C nucleus (JCP = 86.1, JCP9 = 2.8 Hz). The two values of 2JCP are again consistent with a trans and cis coupling respectively across a square-planar centre. The corresponding 13C- {1H} NMR spectrum exhibits an apparent doublet of doublets for the enriched methyl resonance due to the strong trans coupling and the cis coupling of much smaller magnitude (this splitting is not well resolved in the 31P-{1H} NMR spectrum).The non-ambiguous coupling constants and chemical shifts detailed above for the [Pd(dippe)Me]1 system prove useful in monitoring the reactivity of this complex. As a sidebar, elemental analyses of the methyl cations 2 and 3 do not show evidence for the presence of co-ordinated solvent; presumably, in the solid state, the anion weakly co-ordinates enough so that the solvent can be removed by pumping under vacuum.Attempts to obtain X-ray quality crystals of these cations have failed thus far. In the reactions with small molecules, the electrophilic methyl cation 2 shows enhanced reactivity as compared to the neutral precursor. For example, Pd(dippe)Me2, the parent complex of 2, is completely inert to dihydrogen. In contrast, a THF solution of 2, placed under 1–4 atm of H2, rapidly develops a red colour, the 31P-{1H} NMR spectroscopy reveals a singlet at d 92.0, due to equivalent phosphorus donors.The corresponding 1H NMR spectrum reveals a binomial quintet in the hydride region at d 25.75 (JPH = 55.0 Hz) indicative of rapid fluxional exchange similar to that found for the related neutral hydride dimers.22 Solution spectroscopy therefore indicates that a dinuclear Pd species, {[(dippe)Pd]2(m-H)2}[BAr4]2 4[BAr4]2, results from the activation of dihydrogen by 2. As shown by the corresponding reaction between H2 and [Pd(dippe)13Me(s)]1 (2-13C1) and the observation of 13CH4 in solution, the methyl residue of 2 is lost as methane as shown in equation (3).The orientation of the bridging hydrides of 4, shown to be planar in equation (3), is speculation at this point and is based on the propensity for four-co-ordinate, PdII systems to be square planar; however, other geometries 22 are certainly possible and cannot be ruled out. With regards to the enhanced reactivity of the methyl cation 2 with H2, it is interesting to note that the cationic nature of 2 is not a suYcient condition to augment reactivity since, as already mentioned, the 16-e benzyl cation 1 is also inert to H2.Thus it P Pd P Me s P Pd P H Pd H P P + 2 (s = THF) 2+ (3) 1/2 4 atm H2 THF (–MeH) 4J. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 2009 would appear that the reactivity is a result of both co-ordinative unsaturation at the palladium centre and the positive charge, although it is diYcult to rank the relative merit of either eVect since they are intimately connected in these systems; neutral PdII systems with labile ligands would be the obvious targets to try to compare to these cationic systems.The electrophilicity of the palladium nucleus in 2 can also be demonstrated by the reaction of 2 with Pd(dippe)(CH2C6H5)2. The stoichiometric solution of methyl cation 2 and Pd(dippe)- (CH2C6H5)2 in Et2O–C6D6 leads to the formation of two products, of diVerent solubility, both of which give rise to AX patterns in the 31P-{1H} NMR spectrum.The identity of the benzene insoluble but ether soluble product is the h3-benzyl cation 1, whereas the other product, which is soluble in benzene and displays both methyl and benzylic resonances in its 1H NMR spectrum, was identified as Pd(dippe)(Me)(CH2C6H5) 5. Complex 5 was unequivocally characterized by independent synthesis from Pd(dippe)MeCl and benzyl potassium.Evidently, the acidic palladium centre of 2 abstracts a benzyl group from Pd(dippe)(CH2C6H5)2 to give quantitative yields of the neutral, mixed hydrocarbyl complex, 5, and the stabilized h3- benzyl cation 1 [equation (4)]. A potentially more interesting result occurs when an ethereal solution of 2 is mixed with 1 equivalent of its labelled parent molecule, Pd(dippe)(13CH3)2. Hydrocarbyl transfer is again observed with the decrease in intensity of the second order [AX]2 multiplet due to Pd(dippe)(13CH3)2 in the 31P-{1H} or 13C-{1H} NMR spectra and the observation of simpler ABX patterns due to isotopomeric [Pd(dippe)Me]1/[Pd(dippe)Me*]1 and Pd(dippe)Me2/Pd(dippe)MeMe* [equation (5)].It is clear that there is no thermodynamic driving force in this last reaction in that a more stable species such as the h3-benzyl P Pd P Me s P Pd P H H 1 + P Pd P CH2C6H5 CH2C6H5 + + 2 (s = Et2O) Et2O–C6D6 r.t.(4) P Pd P CH2C6H5 Me 5 + P Pd P Me s + P Pd P s Me* + P Pd P Me* Me* + P Pd P Me Me* + 2 (s = Et2O) Et2O–C6D6 r.t. 2–13 C (5) cation is not generated. It must simply be that the Lewis acidity of the palladium nucleus of 2 renders the complex exceptionally kinetically labile. Hydrocarbyl transfer was also observed in the reaction between [Cp*2ZrCH3]1 and Cp*2Zr(13CH3)2, where the Zr nucleus was similarly Lewis-acidic, and the anion [B(C6F5)3Me]2, similarly poorly co-ordinating.26 In both reactions shown in equations (4) and (5) an intermediate cannot be observed in the 31P-{1H} NMR spectrum, and yet a hydrocarbyl residue has been demonstrably transferred from one PdII nucleus to another.In order to account for this process a dinuclear species, as an intermediate or transition state, must be invoked. One possibility is shown in B, in which the hydrocarbyl residues bridge both metal centres. Reaction with carbon monoxide As part of our interest in the reactivity of the electron-rich PdII methyl cation 2, we examined its reaction with CO.Based on many model studies for palladium alkyl phosphine and diimine complexes,11,28–32 one would predict that the sequence of reactions would involve CO first displacing the solvent molecule, then migratory insertion would occur to yield a Pd–acyl species, which would be trapped either by solvent or by CO. These acyl species are regarded as important intermediates in the copolymerization of CO and ethylene.5,33 Moreover, this is simply an example of migratory insertion, which has long been recognized as a fundamental organometallic reaction pathway. 21 However, when a solution of 2 in [2H8]THF is placed under 1–4 atm of CO, instead of observing a new doublet of doublets in the 31P-{1H} NMR spectrum, as would be generated by the AX spin system of a [Pd(dippe)(COMe)s]1 species (s = solvent molecule or CO), the major feature observed was a singlet at d 58.7, indicating equivalence of the phosphorus donors of the dippe ligand, accompanied by the appearance of a deep orange colour for the solution. In addition, it was observed that this product remained stable under added pressure of CO (i.e.ca. 5 atm), and signals attributable to acyl groups could not be identified in the 1H NMR spectrum. Under an atmosphere of 13CO the 31P-{1H} NMR signal at d 58.7 splits into a doublet of doublets (JPC = 28.1; JPC9 = 25.5 Hz) and quintet absorptions with the same coupling constants were observed at low field in the 13C-{1H} NMR spectrum (d 236.4 and 228.1 respectively). When the corresponding experiment was performed using 2-13C1 under CO, the 31P-{1H} NMR spectrum revealed a doublet at d 58.7 (JPC = 14.4 Hz), and in the 13C-{1H} NMR spectrum a binomial quintet was observed at d 47.3 (JCP = 14.6 Hz). These results indicate the formation of some dinuclear palladium species that is bridged by two chemically diVerent carbonyl groups and in which the four phosphorus donors are equivalent.However, as will be seen in the next section, the solid-state molecular structure required modification of this conclusion. Solid-state and solution structure of [Pd(dippe)(Ï-CO)Pd(dippe)- Me][BAr4] 6[BAr4] Amber crystals from the reaction of 2 with CO were obtained from Et2O–toluene. The structure is shown in Fig. 1; crystal data and selected bond lengths and angles are listed in Tables 1 and 2 respectively.Each palladium nucleus of 6 resides in a distinct co-ordination environment. The dipalladium core of 6 is monocationic, and the structure depicted is associated with a BAr4 anion that is isolated from both palladium nuclei though P Pd P CH2 Pd P P C6H5 Me CH2C6H5 + B2010 J. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 closer in space to Pd(1). In the cation, Pd(2) interacts with the carbonyl group with a Pd]C separation of 1.873(10) Å, meanwhile its interaction with C(30) of the methyl group is minimal; here the separation is 2.94(1) Å.On the other hand, Pd(1) is separated from C(29) by 2.32(1) Å, yet its distance of 2.172(7) Å from the methyl carbon, C(30), clearly indicates that the methyl group is covalently bound to this centre.34 Given this non-symmetric bridging of the carbonyl group across the palladium centres, and the disposition of the methyl group, it is reasonable to formulate 6 as a mixed-valence species of Pd, that is, as an adduct of a basic Pd0 complex, Pd(dippe)CO, and a Lewis-acidic PdII species, [Pd(dippe)Me]1.Indeed, 6 could be reformulated as a conventional square-planar palladium coordination complex, with Pd(1) as the central metal atom and the Pd(dippe)CO moiety as the fourth ligand, if the relevant bond angles are considered. The angles P(2)]Pd(1)]C(30) and P(1)]Pd(1)]Pd(2) are tolerably close to 1808 [177.7(2) and 170.32(6)8 respectively], and the angles Pd(2)]Pd(1)]C(30) and P(1)]Pd(1)]C(30) [78.5(2) and 91.9(2)8] are reasonably close to 908.In this respect, of possible significance is the separation between the palladium nuclei; its exceptionally short value of 2.6886(8) Å {cf. approx. 2.81 Å for the [(dippp)Pd]2(m-H)2 series} 22 may represent an electrostatic interaction between the electron-rich Pd0 centre and the cationic PdII, or, more likely a co-ordinate bond 35 from Pd(2) to cationic Pd(1). This bond is bridged by the CO group, which may be designated as semibridging 36 on the basis of its unequal span across the two nonequivalent palladium centres and the bent Pd(2)]C(29)]O(1) angle of 160.1(2)8.The P(2)]Pd(1)]C(30) angle of 177.7(2)8 also seems to preclude an agostic interaction between Pd(2) and the methyl group; if such an agostic interaction were operating a more acute angle might be expected. Also of interest is the unusual disposition of the co-ordination planes: the plane defined by P(1)]Pd(1)]P(2) is tilted to that defined by P(3)]Pd(2)]P(4) by an angle of 92.108, i.e.the co-ordination planes of the palladium nuclei are normal to each other; as discussed below, this structural feature complicated the solution behaviour. Fig. 1 Molecular structure and numbering scheme for the cation [Pd(dippe)(m-CO)Pd(dippe)Me]1 6 We have yet to reconcile the solid-state structure of 6 with that observed in solution, and in fact under 13CO the species in solution is certainly not 6 but an allied dinuclear palladium complex to whose core two distinct carbonyl units are coordinated (viz.the 31P-{1H} NMR spectrum exhibits a doublet of doublets with two values of JPC observed). Nevertheless, an analytically pure, crystalline sample of 6 dissolved in [2H8]THF does give a singlet at d 58.6 in its 31P-{1H} NMR spectrum, and if 13CO is introduced the doublet of doublet pattern is observed centred at d 58.8. It appears that the 31P-{1H} NMR chemical shifts of the two species are more or less coincident, and that the species giving rise to the ABX pattern is the dicarbonyl, [Pd(dippe)(m-13CO)2Pd(dippe)Me][BAr4] 6a[BAr4], the carbonyl adduct of 6;37 the structure of the dicarbonyl is unknown, but must be similar to the isolated monocarbonyl 6 with the added proviso that the two bridging carbonyls are inequivalent.All attempts to isolate dicarbonyl 6a simply result in isolation of 6 as the extra CO group is lost upon crystallization.It is worthwhile adding in passing that zerovalent palladium species such as Pd(dippp)CO (see below) and Pd(dippp)(CO)2 have been characterized in solution, and the CO ligand is quite labile.38 Admittedly, the low-field carbonyl absorptions in the 13C-{1H} NMR spectrum observed for 6a, at d 236.4 and 228.1, could be consistent with acyl carbons, but since both carbonyls bridge two palladium centres (as witnessed by their appearance as binomial quintets), the low-field chemical shifts are quite appropriate for bridging ligands.39,40 Table 1 Crystallographic data for [(dippe)Pd(m-CO)(dippe)PdMe]- {B[3,5-(CF3)2C6H3]4}?0.5C7H8 * Formula M Colour, habit Crystal size/mm Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z rcalc/g cm23 F(000) m(Mo-Ka)/cm21 Transmission factors Scan type Scan range/8 in w Scan speed/8 min21 Data collected 2qmax/8 Crystal decay (%) Total reflections Unique reflections Rmerge Reflections with I > 3s(I) No.of variables RR 9 S Max. D/s (last cycle) Residual density/e Å23 C62H79BF24OP4Pd2?0.5C7H8 1689.84 Yellow, plate 0.15 × 0.35 × 0.40 Triclinic P1� (no. 2) 17.134(2) 18.454(2) 12.932(2) 93.22(1) 94.98(1) 70.366(7) 3835.1(8) 2 1.463 1714 6.49 0.82–1.00 w–2q 1.26 1 0.35 tan q 16 (up to 8 rescans) 1h, ±k, ±l 50 22.5 13 984 13 489 0.054 5769 927 0.044 0.039 2.05 0.14 20.51, 10.48 * T 294 K, Rigaku AFC6S diVractometer, Mo-Ka radiation (l = 0.710 69 Å), graphite monochromator, takeoV angle 6.08, aperture 6.0 × 6.0 mm at a distance of 285 mm from the crystal, stationary background counts at each end of the scan (scan/background time ratio 2 : 1), s2(F2) = [S2(C 1 4B)]/Lp2 (S = scan rate, C = scan count, B = normalized background count), function minimized Sw(|Fo| 2 |Fc|)2 where w = 4Fo 2/s2(Fo 2), R = S||Fo| 2 |Fc||/S|Fo|, R9 = (Sw(|Fo| 2 |Fc|)2/ Sw|Fo|2)� �� and S = [Sw(|Fo| 2 |Fc|)2/(m 2 n)]� �� .Values given for R, R9 and S are based on those reflections with I > 3s(I).J.Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 2011 As regards the apparent equivalence of the phosphorus nuclei in the 31P-{1H} NMR spectrum, clearly an exchange process must be operating which serves to equate the phosphorus nuclei. Such a process must not only interchange the phosphorus nuclei on each one of the dippe ligands, it must also equate the donor nuclei on alternate ligands. Lability of the CO group would partially satisfy the first requirement, however since 6 is a 30-e dinuclear species, it is likely that the CO remains tightly bound to theternatively, the equivalence of the phosphorus donors may be explained by an intermediate with both a bridging methyl and a bridging carbonyl group, and with the co-ordination planes coplanar. Transfer of the methyl or carbonyl group may occur in either a stepwise or concerted fashion, and rapid equilibration results in the observation of a singlet in the 31P-{1H} NMR spectrum. A proposal for this fluxional process is shown in Scheme 1.We suggest that one end of the dinuclear unit rotates to generate two coplanar units which then undergo a symmetrization process through a species such as C with equivalent palladium nuclei; such a rearrangement allows for methyl group and CO transfer between the two palladium centres and exchange of the phosphorus donors by virtue of the sense of the rotation to form C. At low temperature (<270 8C), the singlet at d 58.6 splits into four broad signals, i.e.four phosphorus environments, and is therefore consistent with the solid-state structure. Such fluxionality was also observed in the related cation, {[(dippp)Pd]2- (m-H)(m-CO)}1,39,40 but in this case the limiting spectrum was not reached. Mechanistic experiments The mechanism of formation of dinuclear 6 from the mononuclear methyl cation 2 and CO is not obvious. As shown as a reminder in equation (6), the initial reactants were [Pd(dippe)- Table 2 Selected intramolecular bond distances (Å) and angles (8) observed in [Pd(dippe)(m-CO)Pd(dippe)Me][BAr4] 6[BAr4] Pd(1)]Pd(2) Pd(1)]P(1) Pd(1)]P(2) Pd(1)]C(29) Pd(1)]C(30) Pd(2)]P(3) Pd(2)]P(4) Pd(2)]C(29) P(1)]C(1) P(1)]C(3) P(1)]C(4) P(2)]C(2) Pd(2)]Pd(1)]P(1) Pd(2)]Pd(1)]P(2) Pd(2)]Pd(1)]C(29) Pd(2)]Pd(1)]C(30) P(1)]Pd(1)]P(2) P(1)]Pd(1)]C(29) P(1)]Pd(1)]C(30) P(2)]Pd(1)]C(29) P(2)]Pd(1)]C(30) C(29)]Pd(1)]C(30) Pd(1)]Pd(2)]P(3) Pd(1)]Pd(2)]P(4) Pd(1)]Pd(2)]C(29) P(3)]Pd(2)]P(4) P(3)]Pd(2)]C(29) P(4)]Pd(2)]C(29) Pd(1)]P(1)]C(1) Pd(1)]P(1)]C(3) Pd(1)]P(1)]C(4) C(1)]P(1)]C(3) C(1)]P(1)]C(4) C(3)]P(1)]C(4) 2.6886(8) 2.302(2) 2.332(2) 2.32(1) 2.172(7) 2.325(2) 2.340(2) 1.87(1) 1.831(7) 1.822(8) 1.84(1) 1.849(7) 170.32(6) 102.94(5) 43.1(2) 78.5(2) 86.74(7) 135.4(2) 91.9(2) 100.9(3) 177.7(2) 81.4(3) 170.32(6) 102.94(5) 43.1(2) 86.74(7) 135.4(2) 100.9(3) 106.6(3) 114.7(3) 120.0(3) 103.7(4) 106.7(5) 103.7(5) P(2)]C(5) P(2)]C(6) P(3)]C(15) P(3)]C(17) P(3)]C(18) P(4)]C(16) P(4)]C(19) P(4)]C(20) O(1)]C(29) C(2)]C(2) C(15)]C(16) Pd(1)]P(2)]C(2) Pd(1)]P(2)]C(5) Pd(1)]P(2)]C(6) C(2)]P(2)]C(5) C(2)]P(2)]C(6) C(5)]P(2)]C(6) Pd(2)]P(3)]C(15) Pd(2)]P(3)]C(17) Pd(2)]P(3)]C(18) C(15)]P(3)]C(17) C(15)]P(3)]C(18) C(15)]P(3)]C(18) Pd(2)]P(4)]C(16) Pd(2)]P(4)]C(19) Pd(2)]P(4)]C(20) C(16)]P(4)]C(19) C(16)]P(4)]C(20) C(16)]P(4)]C(20) Pd(1)]C(29)]Pd(2) Pd(1)]C(29)]O(1) Pd(2)]C(29)]O(1) 1.829(8) 1.852(7) 1.85(1) 1.82(1) 1.844(9) 1.837(8) 1.835(9) 1.841(8) 1.130(9) 1.51(1) 1.41(1) 107.2(2) 117.0(3) 119.0(3) 103.3(3) 103.4(3) 105.1(4) 106.1(3) 120.7(3) 114.6(3) 105.4(6) 104.4(5) 104.1(5) 105.9(3) 120.4(3) 118.5(3) 104.3(4) 102.7(4) 102.8(4) 79.0(4) 120.8(8) 160.1(2) Me(s)]1 2, formally a PdII species, and carbon monoxide in THF.The product isolated is a PdII/Pd0 dimer. Thus, somewhere along the reaction pathway a divalent palladium nucleus undergoes a formal two-electron reduction to Pd0.When the CO reaction was performed in Et2O–C6D6 with 2-13C1, the 31P-{1H} NMR spectrum revealed two sets of doublet of doublets at d 73.7 and 70.7 (JPP9 = 40.6 Hz), and in the 13C-{1H} NMR spectrum a doublet of doublets at d 47.3 was observed (JCP = 38.7, JCP9 = 17.3 Hz). This species is formulated as the square-planar, acyl–carbonyl complex, [Pd(dippe)- (CO13CH3)CO]1 7 with the two phosphorus–carbon coupling constants of the 3JCP type corresponding to a trans and cis coupling respectively.When the reaction of 2-13C1 was performed in the poorly co-ordinating solvent o-dichlorobenzene under a deficiency of CO, the carbonyl adduct of the labelled methyl cation, [Pd(dippe)(13CH3)CO]1 8, was observed (Scheme 2), as indicated by a new ABX pattern in the 31P-{1H} NMR at d 84.2 and 83.8 (JPP9 = 21.2 Hz), and the corresponding spectrum in the 13C-{1H} NMR centred at d 24.9 [JCP (trans) = 105, JCP9 (cis) = 28.5 Hz], whose upfield value indicates a Pd]Me group rather than a Pd–acyl.41 These results are summarized in Scheme 2.From these latter experiments one can obtain spectroscopic parameters for acyl–carbonyl 7 and methyl–carbonyl 8 to use in subsequent experiments described below; the change in solvents shown in Scheme 2 provided the best conditions to prepare the putative intermediates 7 and 8. As mentioned above, at moderate pressures of CO (1–4 atm), signals due to a putative Pd–acyl species were conspicuously absent from a solution of 2 in [2H8]THF.However, when an NMR sample of the labelled precursor 2-13C1 was prepared under lower pressures of CO (300 mmHg pressure), signals attributable to both [Pd(dippe)(CO13CH3)CO]1 7 and [Pd- (dippe)(13CH3)CO]1 8 could be observed in the 31P-{1H} NMR spectrum, which diminished in intensity relative to the peak due to 6 on standing. Also a peak at d 81.0 was observed that grows Scheme 1 P PdA P OC PdB H3C P P + P PdA P OC PdB H3C P P + P PdA P OC PdB CH 3 P P + C P PdA P OC PdB CH3 P S + P PdA P OC PdB P P CH3 + P Pd P OC Pd H3C P P P Pd P CH3 s + + CO 2 (s = THF) THF + (6) 6 31P-{1H} NMR: d 58.6 (s) IR nCO (KBr disc): 1830 cm–12012 J.Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 in with the peak at d 58.7 but then diminishes in intensity on standing with several new absorptions above d 100 observed. The observation of 7 and 8 seems to indicate that these species are intermediates in the formation of 6/6a, and not the converse.When the volatiles were distilled away from an NMR sample of 6 prepared using 13CO, a peak at d 204.0 was observed in the 13C-{1H} NMR spectrum of the distillate, and a doublet resonance was observed at d 2.03 (JHC = 6.0 Hz) in the 1H NMR spectrum, i.e. chemical shifts consistent with acetone.42,43 The identity of this coproduct was confirmed by GC-MS, which, along with peaks for Et2O and [2H8]THF, gave a molecular ion at m/z 59, i.e.corresponding to H3C(13CO)CH3. For the experiment performed with 2-13C1 under 12CO, H3 13C(CO)- 13CH3 was identified by GC-MS. The origin of acetone is thus due to the methyl group of the starting material 2. In order to account for the coupling of two methyl units and the one carbonyl we must invoke hydrocarbyl transfer, presumably between 7 and 8 or 2, of a methyl group to a palladium acyl species (or conversely, an acyl group to a palladium methyl species), of the kind represented in equation (7).Under CO, such a process would produce two new compounds: a neutral PdII complex, Pd(dippe)(COMe)Me, which reductively eliminates to give acetone and a zerovalent palladium species, presumably Pd(dippe)CO [equation (8)]; and a PdII species, [Pd(dippe)]21 or one of its carbonyl adducts. It is this dicationic species that therefore gives rise to the peak at d 81.9 in the Scheme 2 P Pd P 13CH3 s + 2–13 C1 CO Et2O CO o-dichlorobenzene P Pd P C CO 13CH3 O + 7 P Pd P 13CH3 CO + 8 31P-{1H} NMR: d 73.7 (dd), 70.7 (dd) 13C-{1H} NMR: d 47.3 (dd) 31P-{1H} NMR: d 84.2 (m), 83.8 (m) 13C-{1H} NMR: d –4.90 (m) P Pd P C CH3 CO O P Pd P CH3 s + + + 7 s = solvent or CO CO THF P Pd P C CH3 CH3 O P Pd P CO CO 2+ + 9 (7) 31P-{1H} NMR spectrum.The identity of this species is probably [Pd(dippe)(CO)2](BAr4)2 9 since under 13CO, the peak at d 81.0 appears as a second-order multiplet due to the [AX]2 spin system of the square-planar [Pd(dippe)(13CO)2]21 dication.In a separate experiment we tried to access these Pd21 complexes by the addition of 2 equivalents of HBAr4 to a solution of Pd(dippe)Me2 in THF. The evolution of a gas was indeed observed, but unfortunately the species so produced, presumably [Pd(dippe)(THF)2][BAr4]2 10b[BAr4]2, rapidly polymerizes the THF solvent which makes characterization impossible. In CD3CN spectroscopic parameters for the dication [Pd(dippe)- (N]] ] CCD3)2][BAr4]2 10a[BAr4]2 can be obtained and its 31P-{1H} NMR spectrum exhibits a singlet at d 118.9.However, CO is too poorly co-ordinating to displace the strongly bound acetonitrile molecules from the palladium centre, and 9 was therefore inaccessible by this route. However, when Pd(dippe)- Me2 is treated with 2 equivalents of HBAr4 in THF, but under stringent temperature control (i.e. a temperature of 278 8C was not exceeded) evidence for 9 could be obtained. Thus, after the reaction mixture was warmed to 220 8C and the volatiles were removed, a solution of the residue in CD2Cl2 under 12CO exhibited a singlet at d 83.8 in the 31P-{1H} NMR spectrum.When the solution was warmed to room temperature, the singlet at d 83.8 diminished in intensity and a new singlet was observed at d 115.6. From the original mixture, crystals of the bis(THF) dication 10b were indeed isolated, after recrystallization from methylene chloride at low temperature (<220 8C). In CD2Cl2 10a briefly gives a singlet in the 31P-{1H} NMR spectrum at d 118.9, to be replaced by a singlet due to the decomposition product at d 115.6.Thus, one can conclude that the singlet at d 81.9 in the original reaction between 2 and CO was in fact [Pd(dippe)(CO)2]21. The slight discrepancy in chemical shift may be explained by the diVerent NMR solvent used in each case. To summarize, the mononuclear acyl 7 combines with a Pd]Me complex, whose methyl group is exchanged for the carbonyl of 7 (possibly via the intermediacy of a dinuclear intermediate).The complex Pd(dippe)(COMe)Me is thereby formed, which, in the presence of CO, reductively eliminates acetone to generate the zerovalent palladium complex, Pd- (dippe)CO [equations (7) and (8)]. Meanwhile, the other product arising from the reaction of 7 and 8, the dication [Pd(dippe)(CO)2]21 9, eventually decomposes by reacting with the solvent. This decomposition side reaction does not complicate isolation of the dinuclear final product 6.The extrusion of acetone thus produces one of the elements required for formation of 6/6a, the zerovalent Pd(dippe)CO unit. It is proposed that this electron-rich moiety acts as a donor towards [Pd(dippe)Me]1 2, which is present in the mixture, in a type of Lewis acid–metal base interaction. Therefore we can finally balance the reaction of CO and 2 to give 6 as shown in equation (9). As further confirmation of the mixed-valence nature of dinuclear 6, we prepared an analogue using independently prepared Pd(dippp)CO, and authentic [Pd(dippe)Me(OEt2)]1 2.The use of the three-carbon backbone ligand dippp for the starting Pd0 portion represents a negligible chemical change, but a dramatic change in magnetic resonance results, and this provides excellent handles for 31P-{1H} NMR spectroscopy. As shown in equation (10), if Pd(dippp)CO is generated in situ {i.e. by placing a THF solution of [Pd(dippp)]2 under CO}, and 1 equivalent of [Pd(dippe)Me(OEt2)]1 2 is added, a pair of triplets are observed in the 31P-{1H} NMR spectrum of the solution at d 53.8 and 23.8 (JPP9 = 28.5 Hz).This result is precisely P Pd P C CH3 CH3 O P Pd P CO + H3C C CH3 O (8) CO THFJ. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 2013 what is expected if adduct formation between Pd(dippp)CO and 2 occurs, and the formation of {[Pd(dippp)(m-CO)Pd(dippe)- Me]} 11, the dippp analogue of 6, is indicated. It should be noted that only one of the two limiting, instantaneous structures of 11 is shown in equation (10); as before, an exchange process serves to equilibrate the phosphorus nuclei of each ligand (cf.Scheme 1). Conclusion From this work, one major conclusion emerges and that is that dinuclearity figures prominently in these cationic palladium methyl complexes stabilized with electron-rich diphosphine ligands. It is useful to review the occurrences of dinuclear systems in this study. The reaction of the methyl cation 2 with H2 generates a dinuclear palladium hydride species; the interchange of alkyl groups between neutral dialkyl derivatives and cationic alkyl complexes is proposed to involve a dinuclear intermediate; and the formation of a dinuclear mixed-valence complex is observed upon carbonylation of the methyl cation 2 in THF.This is hardly coincidence but not easily rationalized. If one examines the literature on Pd chemistry, dinuclearity is not particularly common;15 it would appear that electron-rich diphosphine ancillary ligands tend to promote this kind of behaviour.Nitrogen-based ligands such as diimines, bipyridine or phenanthroline apparently do not promote formation of dinuclear Pd complexes; nevertheless, it should be emphasized that beyond these observations we have no explanation. The copolymerization of carbon monoxide with olefins is typically carried out in MeOH or CH2Cl2.4,5,8,11,16,32 To our knowledge no one has reported the use of THF for this reaction although there is one brief report 44 that mentions that no polymerization was observed in THF.It stands to reason that any strongly co-ordinating solvent will compete for substrate binding (i.e. co-ordination of ethylene or carbon monoxide) and reduce the tendency for the propagation step. However, P Pd P OC Pd H3C P P P Pd P CH3 s + + 3 2 3 CO THF C H3C CH3 O – + + P Pd P CO CO 2+ 9 6 (9) P Pd P OC Pd H3C P P P Pd P CH3 s + 2 + (10) THF 11 P Pd P CO + from this work, we have shown that there is a further point to consider and that is the formation of catalytically inactive species due to the presence of strongly co-ordinating solvents such as THF.In the case reported here, catalyst poisoning occurs by formation of an inactive dinuclear complex. In this report we have described some reactivity patterns for [Pd(dippe)Me(s)]1 2. The fact that this cationic system shows enhanced reactivity towards small molecules as compared to the inertness of its parent complex, Pd(dippe)Me2, is apparent from its reaction with dihydrogen.Late metals can activate small molecules by oxidative addition pathways, and the reaction of 2 to give {[Pd(dippe)]2(m-H)2}1 4 could be accounted for by an oxidative addition of 2 to give a PdIV species, followed by a reductive elimination of methane to give 4. Such a mechanism is in marked contrast to the inability of both neutral PdII and Pd0 to add dihydrogen.45 The rapid reaction of 2 with H2 could even be said to resemble hydrogenolysis (i.e.s-bond metathesis 46), a process that is normally associated with the alkyls of the early transition metals. This apparent reversal of the normal trends of reactivity of the Periodic Table has been noted in a similar system, viz. {Cp*Ir(PMe3)Me(CH2Cl2)}BAr4,47,48 a cationic complex of IrIII which will induce selective C]H activation in alkanes. Experimental The GC-MS analysis was performed by the Mass Spectrometry Service of the University of British Columbia upon a KRATOS MS80 RFA instrument.Other procedures are identical to that reported previously.22,23 The salt HBAr4 was prepared by a literature method,7 as was B(C6F5)3.49 Methyllithium (Aldrich, halide content <0.05 mol L21) was used as supplied as a 1.4 mol L21 solution in Et2O; PhCH2MgCl (Aldrich) was used as supplied as a 1.0 mol L21 solution in Et2O; Mg(13CH3)2 was prepared by a literature method and used as either a 0.05 mol L21 solution in Et2O, or recrystallized from benzene–pentane as Mg(13CH3)2?diox (diox = 1,4-dioxane).50 The metal precursor Pd(COD)MeCl was prepared according to the literature,51 as were Pd(dippe)Cl2 and Pd(dippp)I2.22,23 Methylene chloride was distilled from CaH2 under N2.Acetonitrile was dried over activated 4 Å molecular sieves, distilled from trap to trap, and stored over molecular sieves. The solvents CD2Cl2 and CD3CN were distilled from CaH2 after a prolonged period at reflux under N2; [2H8]THF was distilled from sodium benzophenone under N2; C6D4Cl2-o was distilled from CaH2 under N2.All deuteriated solvents were subjected to four freeze–pump–thaw cycles. Preparations Pd(dippe)Me2. To a slurry of Pd(dippe)Cl2 (1.54 g; 3.50 mmol) in THF (30 mL) at 278 8C was added a solution of MeLi (5.0 mL; 7.0 mmol) dropwise over 5 min. The cooling bath was then removed, and as the mixture attained room temperature a reaction ensued evidenced by the disappearance of the Pd(dippe)Cl2 and the formation of a clear, dark brown solution.The solution was stirred for 1 h after which time the solvent was removed in vacuo. The brown residue was extracted with toluene (25 mL), passed through a frit lined with Celite to remove LiCl, and concentrated to a small volume (ca. 3 mL). The brown solution was layered with pentane (10 mL) and cooled to 240 8C to give colourless crystals of Pd(dippe)Me2 after 12 h (1.25 g; 89% yield). 1H NMR ([2H8]toluene, 500.13 MHz): d 1.88 (spt, 4 H, CHMeMe9, JHMe = 7.1), 1.14 (m, 4 H, PCH2CH2P), 1.06 (dd, 12 H, CHMeMe9, JHMe = 7.1, JMeP = 15.4), 0.84 (dd, 12 H, CHMeMe9, JHMe = 7.1, JMeP = 12.4), 0.72 [dd, 6 H, PdMe2, JMeP (trans) = 6.6, JMeP (cis) = 1.0 Hz]. 31P-{1H} NMR ([2H8]toluene): d 61.0 (Found: C, 47.69; H, 9.42. Calc. for C16H38P2Pd: C, 48.19; H, 9.60%). Following the preparation of Pd(dippe)Me2, Pd(dippe)-2014 J. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 (13CH3)2 was similarly prepared, with Pd(dippe)Cl2 (0.509 g; 1.16 × 1023 mol) and Mg(13CH3)2(C4H8O)2 (0.165 g; 1.16 × 1023 mol).Recrystallization from toluene (1 mL) layered with hexanes gave colourless crystals (0.371 g; 80% yield). 1H NMR (C6D6, 500.13 MHz): d 1.88 (spt, 4 H, CHMeMe9, JHMe = 7.1), 1.14 (m, 4 H, PCH2CH2P), 1.09 (dd, 12 H, CHMeMe9, JHMe = 7.1, JMeP = 15.4), 0.83 (dd, 12 H, CHMeMe9, JHMe = 7.1, JMeP = 12.4), 0.87 [ddd, 6 H, Pd*Me2, JHC = 124.0, JMeP (trans) = 6.6, JMeP (cis) = 1.0 Hz]. 31P-{1H} (C6D6, 81.015 MHz): d 65.4 [m, JPC (trans) = 108.5, JPC (cis) = 210.5, JPP9 = 8.1 Hz]. 13C-{1H} (C6D6, 50.32 MHz): d 0.0 [m, JCP (trans) = 108.5, JCP (cis) = 210.5, JCC9 = 0.5 Hz]. Microanalysis was not obtained. Pd(dippp)Me2. The complex Pd(dippp)Me2 was synthesized as for Pd(dippe)Me2, with Pd(dippp)I2 (0.565 g; 8.88 × 1024 mol) and MeLi (1.3 mL; 1.80 × 1023 mol). Successive recrystallizations from toluene (3 mL) layered with hexanes (6 mL) gave Pd(dippp)Me2 as colourless crystals (0.179 g; 49% yield). 1H NMR (C6D6, 299.99 MHz): d 2.45 (m, 2 H, PCH2CH2CH2P), 1.92 (m, 4 H, CHMeMe9, JHMe = 7.2), 1.58 (m, 4 H, PCH2CH2- CH2P), 1.14 and 0.91 (dd, 24 H, CHMeMe9, JMeH = 7.2, JMeP = 15.0), 0.59 [dd, 6 H, PdMe2, JMeP (trans) = 5.0, JMeP (cis) = 1.0 Hz]. 31P-{1H} NMR (C6D6, 121.41 MHz): d 16.4 (Found: C, 49.15; H, 9.95. Calc. for C17H40P2Pd: C, 49.46; H, 9.77%). Pd(dippe)(CH2Ph)2. As for Pd(dippe)Me2 with Pd(dippe)Cl2 (1.09 g; 2.48 × 1023 mol) and PhCH2MgCl (5 mL; 5.0 × 1023 mol). Recrystallization from toluene (2 mL) layered with hexanes (10 mL) aVorded Pd(dippe)(CH2Ph)2 as clear brown needles (1.00 g; 73% yield). 1H NMR (C6D6, 500.13 MHz): d 7.43 (m, 4 H, o-H of Ph), 7.21 (m, 4 H, m-H of Ph), 6.96 (m, 2 H, p-H of Ph), 3.11 (dd, 4 H, CH2Ph, JHP = 9.0, JHP9 = 7.5), 1.75 (spt, 4 H, CHMeMe9, JHMe = 7.0), 1.00 (m, 4 H, PCH2- CH2P), 0.91 and 0.82 (dd, 24 H, CHMeMe9, JMeP = 16.0, JMeH = 7.0 Hz). 31P-{1H} NMR (C6D6, 202.47 MHz): d 62.0 (Found: C, 60.75; H, 7.94. Calc. for C28H46P2Pd: C, 61.03; H, 8.01%). [Pd(dippe)(Á3-CH2Ph)]{B(C6F5)3CH2Ph}. To a solution of Pd(dippe)(CH2Ph)2 (0.100 g; 1.82 × 1024 mol) in Et2O (2 mL) was added solid B(C6F5)3 (0.093 g; 1.82 × 1024 mol) with stirring. The initial brown colour discharged to give a colourless solution. The solvent was removed in vacuo to give a slimy brown oil which resisted crystallization. The product was characterized in solution. 1H NMR (CD3CN, 200.12 MHz): d 7.75, 7.70, 7.58, 7.10 and 6.59 (m, 10 H, CH2Ph and BCH2Ph), 3.09 (d, 2 H, CH2Ph, JHP = 9.4 Hz), 2.54 (s, 2 H, PhCH2B), 2.40 and 2.10 (m, 4 H, CHMeMe9), 2.04 and 1.81 (m, 4 H, PCH2CH29P), 1.17, 1.06, 0.95 and 0.92 (m, 24 H, CHMeMe9). 31P-{1H} NMR (CD2Cl2, 121.42 MHz): d 89.3 (d, 1 P, JPP9 = 30.6), 76.9 (d, 1 P, JPP9 = 30.6 Hz). [Pd(dippe)(Á3-CH2C6H5)][BAr4] 1[BAr4]. To a solution of Pd(dippe)(CH2Ph2)2 (0.072 g; 1.28 × 1024 mol) in THF (10 mL) at 210 8C was added a solution of HBAr4 (0.130 g; 1.28 × 1024 mol) in THF (1 mL).The original dark colour became clear. After the solvent was removed, the residue was dissolved in Et2O (2.5 mL), and the solution placed in the freezer. Colourless crystals appeared after 24 h (0.127 g; 76%). 1H NMR (CD2Cl2, 500.13 MHz): d 7.75 (br s, 8 H, o-H of Ar4), 7.68 (m, 1 H, p-H of h3-CH2Ph), 7.55 (br s, 4 H, p-H of Ar4), 7.30 (m, 2 H, m-H of h3-CH2Ph), 6.41 (m, 2 H, o-H of h3-CH2Ph), 3.06 (d, 2 H, h3-CH2Ph, JHP = 7.8), 2.37 and 1.98 (dspt, 4 H, CHMeMe9, JHP = 1.8, JHMe = 7.2), 2.04 and 1.76 (dt, 4 H, PCH2CH29P, JHP = 19.7, JHH9 = 7.0), 1.07, 1.10, 0.92 and 0.75 (dd, 24 H, CHMeMe9, JMeP = 14.7, JMeH = 7.2 Hz). 31P-{1H} NMR (CD2Cl2, 121.42 MHz): d 88.7 (d, 1 P, JPP9 = 32.1), 75.2 (d, 1 P, JPP9 = 32.1 Hz) (Found: C, 48.16; H, 3.96. Calc. for C53H51BF24P2Pd: C, 48.11; H, 3.89%). [Pd(dippe)(s)Me][BAr4] 2[BAr4]. To a solution of Pd(dippe)- Me2 (0.126 g; 3.16 × 1024 mol) in Et2O (5 mL) was added a solution of HBAr4 (0.320 g; 3.16 × 1024 mol) in Et2O (5 mL) at 210 8C.The solution vigorously eVervesced and lightened in intensity. The volatiles were removed in vacuo and the residue was recrystallized from Et2O (3 mL) and placed in the freezer. Colourless crystals appeared after 24 h (0.323 g; 82% yield). 1H NMR ([2H8]THF, 500.13 MHz): d 7.79 (br s, 8 H, o-H of Ar4), 7.58 (br s, 4 H, p-H of Ar4), 3.35 (q, 4 H, free OCH2CH3, JHH9 = 7.0), 2.43 and 2.31 (spt, 4 H, CHMeMe9, JHMe = 7.2), 2.15 and 2.11 (dt, 4 H, PCH2CH92P, JHP = 13.3, JHH9 = 6.1), 1.31, 1.26, 1.24 and 1.21 (dd, 24 H, CHMeMe9, JMeP = 16.0, JMeH = 7.2), 1.07 (t, 6 H, free OCH2CH3, JHH9 = 7.0), 0.63 [dd, 3 H, Pd]Me, JMeP (trans) = 6.3, JMeP (cis) = 0.9 Hz]. 31P-{1H} NMR ([2H8]THF, 202.42 MHz): d 86.0 (d, 1 P, JPP9 = 17.0), 69.0 (d, 1 P, JPP9 = 17.0 Hz) (Found: C, 45.37; H, 4.00. Calc. for C47H47BF24P2Pd: C, 45.27; H, 3.80%). Labelled 2-13C1 was prepared likewise from Pd(dippe)(13CH3)2 and HBAr4. 31P-{1H} NMR (C6D6–Et2O, 81.015 MHz): d 87.9 [dd, 1 P, JPP9 = 16.7, JPC (cis) = 2.8], 67.3 [dd, 1 P, JP9P = 16.7, JPC (trans) = 86.1 Hz]. 13C-{1H} NMR (C6D6–Et2O, 50.32 MHz): d 4.49 [dd, JCP (trans) = 86.1, JCP (cis) = 2.8 Hz]. [Pd(dippp)(s)Me][BAr4] 3[BAr4]. As for 2 with Pd(dippp)Me2 (0.086 g; 2.08 × 1024 mol) and HBAr4 (0.211 g; 2.08 × 1024 mol). Recrystallization from Et2O (2 mL) gave clear crystals which darkened on standing (0.100 g; 38% yield). 1H NMR (CD2Cl2, 200.13 MHz): d 7.63 (br s, 8 H, m-H of Ar4), 7.50 (br s, 4 H, p-H of Ar4), 3.67 (q, 4 H, OCH2CH3, JHH9 = 7.0), 2.39 (m, 2 H, PCH2CH2CH92P), 2.10 (m, 4 H, CHMeMe9), 1.59 and 1.43 (m, 4 H, PCH2CH2CH92P), 1.15 (t, 6 H, OCH2CH3, JHH9 = 7.0), 1.10 (m, 24 H, CHMeMe9), 0.60 [dd, 3 H, Pd]Me, JMeP (trans) = 5.0, JMeP (cis) = 1.0 Hz]. 31P-{1H} NMR (CD2Cl2, 81.015 MHz): d 49.6 (d, 1 P, JPP9 = 39.2), 16.2 (d, 1 P, JPP9 = 39.2 Hz) (Found: C, 46.01; H, 3.59. Calc. for C48H49BF24P2Pd: C, 45.72; H, 3.92%).{[Pd(dippe)]2(Ï-H)2}[BAr4]2 4[BAr4]. Complex cation 2 (0.250 g; 1.89 × 1024 mol) was dissolved in THF (10 mL), and the solution was subjected to four freeze–pump–thaw cycles. The solution was cooled to 2196 8C and placed under 4 atm of dihydrogen. Upon warming to 278 8C the solution developed a deep red colour. The solution was warmed with stirring to 0 8C and the THF was removed in vacuo. The red residue remaining was dissolved in THF (2 mL) and cooled to 240 8C.Deep red needles deposited after 12 h (0.120 g; 51%). 1H NMR ([2H8]THF, 500.13 MHz): d 7.79 (br s, 16 H, o-H of Ar4), 7.56 (br s, 8 H, p-H of Ar4), 2.20 (spt, 8 H, CHMeMe9, JHMe = 7.0), 2.08 (m, 8 H, PCH2CH92P), 1.20 and 1.14 (dd, 48 H, CHMeMe9, JMeP = 16.5, JMeH = 7.0), 25.75 [qnt, 2 H, (m-H)2, JPH = 55.0 Hz]. 31P-{1H} NMR ([2H8]THF, 202.42 MHz): d 92.0 (Found: C, 45.01; H, 3.71. Calc. for C92H90B2F48P4Pd2: C, 44.81; H, 3.68%). Methyl transfer between cation 2 and Pd(dippe)(13CH3)2.To a solution of 2 (0.035 g; 2.81 × 1025 mol) in Et2O (0.20 mL) was added a solution of Pd(dippe)(13CH3)2 (0.12 g; 2.82 × 1025 mol) in C6D6 (0.20 mL). The products were characterized in solution. 31P-{1H} NMR (C6D6–Et2O, 81.015 MHz): d 71.0 (br s). 13C- {1H} NMR (C6D6–Et2O, 50.32 MHz): d 23.8 (br s). Pd(dippe)(Me)CH2Ph 5. To a solution of Pd(COD)MeCl (0.344 g; 1.26 × 1023 mol) in THF (20 mL) was added a solution of dippe (0.330 g; 1.26 × 1023 mol) in toluene (2 mL) to produce a white precipitate.The reaction vessel was then cooled to 278 8C in a dry-ice–acetone bath and a solution of KCH2Ph (0.166 g; 1.26 × 1023 mol) in THF (5 mL) was added by cannulation. The reaction mixture was allowed to warm to room temperature with stirring, and the solvent was removed in vacuo to give an orange residue. The residue was taken up in tolueneJ. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 2015 (20 mL), and this solution was passed through Celite. The filtrate was concentrated to 2 mL and then layered with hexanes (5 mL). After 24 h at 240 8C orange crystals deposited (0.453 g; 76% yield). 1H NMR (C6D6, 500.13 MHz): d 7.51 (m, 2 H, m-H of Ph), 7.26 (m, 2 H, o-H of Ph), 6.96 (m, 1 H, p-H of Ph), 3.18 [dd, 2 H, CH2Ph, JHP (trans) = 10.0, JHP (cis) = 8.0], 1.81 and 1.83 (spt, 4 H, CHMeMe9, JHMe = 7.5), 1.06 and 1.04 (m, 4 H, PCH2CH29P), 1.00, 0.96, 0.82 and 0.75 (dd, 24 H, CHMeMe9, JHP = 12.0, JMeH = 7.5), 0.67 [dd, 3 H, Pd]Me, JMeP (trans) = 7.0, JMeP (cis) = 6.0 Hz]. 31P-{1H} NMR (C6D6, 202.42 MHz): d 68.6 (d, 1 P, JPP9 = 10.0), 60.4 (d, 1 P, JPP9 = 10.0 Hz) (Found: C, 55.62; H, 8.88. Calc. for C22H42P2Pd: C, 55.64; H, 8.91%). [Pd(dippe)(Ï-CO)Pd(dippe)Me][BAr4] 6[BAr4] and [Pd- (dippe)(Ï-13CO)2Pd(dippe)Me][BAr4] 6a[BAr4]. In a thickwalled reactor vessel a solution of 2 (0.480 g; 3.62 × 1024 mol) in THF (10 mL) was subjected to several freeze–pump–thaw cycles. At room temperature, the reactor was charged with 4 atm CO gas and stirred for 1 h.The solution developed a red– amber colour during this time. The volatiles were removed in vacuo and the orange residue was recrystallized from Et2O (2 mL) under CO and a few drops of toluene to give deep amber plates of 6[BAr4] (0.200 g; 33% yield). 1H NMR ([2H8]THF, 500.13 MHz): d 7.79 (br s, 8 H, o-H of Ar4), 7.51 (br s, 4 H, p-H of Ar4), 2.38–2.25 (m, 8 H, CHMeMe9), 1.97 (m, 8 H, PCH2- CH2P), 1.49, 1.39, 1.25 and 1.19 (m, 48 H, CHMeMe9), 0.55 (m, 3 H, Pd]Me). 31P-{1H} NMR ([2H8]THF, 202.42 MHz): d 58.6; at 270 8C, 68.5, 64.5, 59.0, 58.0 (Found: C, 48.05; H, 4.95.Calc. for C69H86BF24OP4Pd2 i.e. {[Pd(dippe)CO][Pd- (dippe)Me]}[BAr4]?C7H8: C, 47.74; H, 5.05%). Similarly was prepared 6-13C1 with 2-13C1 (0.050 g; 4.01 × 1025 mol) in [2H8]THF (0.4 mL). The product was characterized in solution. 31P-{1H} NMR ([2H8]THF, 81.015 MHz): d 58.6 (d, JPC = 14.6 Hz). 13C-{1H} NMR ([2H8]THF, 50.32 MHz): d 47.3 (qnt, Pd]Me, JCP = 14.6 Hz); 13C NMR (q of qnt, Pd]Me, JHC = 127.6, JCP = 14.6 Hz).Similarly was prepared 6a with 2 (0.050 g; 4.01 × 1025 mol) in [2H8]THF (0.4 mL). The product was characterized in solution under 13CO. 31P-{1H} NMR ([2H8]THF, 202.42 MHz): d 58.7 (dd, JPC = 28.2, JPC9 = 25.6 Hz). 13C-{1H} NMR ([2H8]THF, 50.32 MHz): d 236.4 (qnt, CO, JCP = 28.2), 228.1 (qnt, CO, JC9P = 25.6 Hz). [Pd(dippe)(CO13CH3)CO][BAr4] 7[BAr4]. In a 5 mm NMR tube, 2-13C1 (0.030 g; 2.27 × 1025 mol) was dissolved in Et2O (0.4 mL) and a few drops of C6D6 were added.The solution was freeze–pump–thawed, sealed under ca. 2 equivalents of carbon monoxide, and its 31P-{1H} and 13C-{1H} NMR spectra were recorded. 31P-{1H} NMR (C6D6–Et2O, 81.015 MHz): d 73.7 (dd, 1 P, JPP9 = 40.6, JCP = 38.7), 70.7 (dd, 1 P, JPP9 = 40.6, JCP = 17.3 Hz). 13C-{1H} NMR (C6D6–Et2O, 50.32 MHz): d 47.3 [dd, CO13CH3, JCP (trans) = 38.7 Hz, JCP9 (cis) = 17.3 Hz]. [Pd(dippe)(13CH3)CO][BAr4] 8[BAr4].In a 5 mm NMR tube, 2 (0.030 g; 2.27 × 1025 mol) was dissolved in C6D4Cl2-o (0.35 mL). The solution was freeze–pump–thawed, sealed under ca. 2 equivalents of carbon monoxide, and its 31P-{1H} and 13C- {1H} NMR spectra were recorded. 31P-{1H} NMR (C6D4Cl2-o, 81.015 MHz): d 84.2 (dd, 1 P, JPP9 = 21.2, JCP = 105), 83.8 (dd, 1 P, JPP9 = 21.2, JCP = 28.5 Hz). 13C-{1H} NMR (C6D4Cl2-o, 50.32 MHz): d 24.9 [dd, Pd]CH3, JCP (trans) = 105, JCP9 (cis) = 28.5 Hz]. [Pd(dippe)(CO)2][BAr4]2 9[BAr4]2, [Pd(dippe)(N]] ] CCH3)2]- [BAr4]2 10a[BAr4]2 and [Pd(dippe)(THF)2][BAr4]2 10b[BAr4]2.To a solid mixture of HBAr4 (0.416 g; 4.11 × 1024 mol) and Pd(dippe)Me2 (0.133 g; 2.06 × 1024 mol) under vacuum at 2196 8C, was added THF (2.0 mL) by trap to trap distillation. The reaction vessel was backfilled with CO (ca. 20 equivalents) and allowed to warm to 278 8C, at which temperature a clear yellow solution was observed. The solvent was removed in vacuo at 220 8C and [Pd(dippe)(CO)2][BAr4]2 9[BAr4]2 was characterized in solution. 31P-{1H} NMR (CD2Cl2, 121.42 MHz): d 83.8. The residue of the reaction mixture was recrystallized from methylene chloride (2 mL) and cooled to 240 8C. Yellow crystals of [Pd(dippe)(THF)2][BAr4]2 10b appeared after 12 h (0.220 g; 25%). 1H NMR (CD2Cl2, 500.13 MHz): d 7.64 (br s, 16 H, o-H of Ar4), 7.49 (br s, 8 H, p-H of Ar4), 3.86 (m, 8 H, OCH2CH2), 2.32 (spt, 4 H, CHMeMe9, JHMe = 7.3), 2.17 (m, 4 H, PCH2CH92P), 1.97 (m, 8 H, OCH2CH2), 1.36 and 1.28 (dd, 24 H, CHMeMe9, JMeP = 18.5, JMeH = 7.3 Hz). 31P-{1H} NMR (CD2Cl2, 202.42 MHz): d 118.9 {Found: C, 45.48; H, 2.97. Calc. for C82H64B2F48OP2Pd i.e. [Pd(dippe)(THF)][BAr4]2: C, 45.44; H, 2.98%}. [Pd(dippe)- (N]] ] CCH3)2][BAr4]2 10a[BAr4]2 was prepared by adding CD3CN (1 mL) to a mixture of HBAr4 (0.102 g; 5.01 × 1025 mol) and Pd(dippe)Me2 (0.020 g; 2.50 × 1025 mol), and characterized in solution. 1H NMR (CD3CN, 200.13 MHz): d 7.71 (br s, 16 H, o-H of Ar4), 7.66 (br s, 8 H, p-H of Ar4), 2.57 (spt, 4 H, CHMeMe9, JHMe = 7.3), 2.31 (m, 4 H, PCH2CH92P), 1.38 and 1.30 (dd, 24 H, CHMeMe9, JMeP = 15.0, JMeH = 7.3 Hz). 31P-{1H} NMR (CD3CN, 81.015): d 118.9. [Pd(dippp)(Ï-CO)Pd(dippe)Me][BAr4] 11[BAr4]. To a solution of Pd(dippp)CO {prepared from [Pd(dippp)]2 (0.015 g; 2.00 × 1025 mol) under CO in 5 mL Et2O} was added 2 (0.050 g; 4.01 × 1025 mol). The product was characterized in solution. 31P-{1H} NMR (C6D6, 81.015 MHz): d 53.8 (t, 1 P, JPP9 = 28.5), 23.8 (t, 1 P, JP9P = 28.5 Hz).X-Ray crystallographic analysis of [(dippe)Pd(Ï-CO)Pd(dippe)- Me]{B[3,5-(CF3)2C6H3]4}?0.5C7H8 6 Crystallographic data appear in Table 1. The final unit-cell parameters were obtained by least-squares on the setting angles for 25 reflections with 2q = 20.0–22.98. The intensities of three standard reflections, measured every 200 reflections throughout the data collections, decayed linearly by 22.5%. The data were processed 52 and corrected for Lorentz and polarization eVects, decay and absorption (empirical, based on azimuthal scans).The structure was solved by direct methods. The structure analysis was initiated in the centrosymmetric space group P1� , this choice being confirmed by subsequent calculations. The C(53) trifluoromethyl group was modelled as 1 : 1 disordered. Several more CF3 groups and the Pd(2) chelate ring show signs of minor disordering, but the quality of the data set was not suYcient to permit full modelling of this disorder.The toluene solvent is disordered in a complex fashion about a centre of symmetry; no models having reasonable geometry could be refined successfully. The seven largest peaks in the toluene region were refined as carbon atoms with occupancy factors constrained to total 3.5 and thermal parameters constrained to be approximately equal. All non-hydrogen atoms except C(63) and C(69) (which had non-positive definite thermal parameters when refined anisotropically) were refined with anisotropic thermal parameters.The hydrogen atoms associated with the cation and the anion were fixed in calculated positions with C]H = 0.98 Å and BH = 1.2 Bbonded atom while those associated with the toluene molecule were not included in the model. No secondary extinction correction was necessary. Neutral atom scattering factors and anomalous dispersion corrections were taken from ref. 53. CCDC reference number 186/968.Acknowledgements Financial support for this research was generously provided by the Donors of the Petroleum Research Fund, administered by the American Chemical Society. We also thank Johnson Matthey for e loan of palladium salts.2016 J. Chem. Soc., Dalton Trans., 1998, Pages 2007–2016 References 1 P. M. Maitlis, The Organic Chemistry of Palladium, Academic Press, New York, London, 1971. 2 G. W. Parshall and S. D. Ittel, Homogeneous Catalysis, John Wiley and Sons, New York, 1992. 3 A. Sen and T. W. Lai, J. Am. Chem. Soc., 1982, 104, 3520. 4 A. Sen, Acc. Chem. Res., 1993, 26, 303. 5 E. Drent, J. A. M. v. Broekhoven and M. J. Doyle, J. Organomet. Chem., 1991, 417, 235. 6 E. Drent, Pure Appl. Chem., 1990, 62, 661. 7 M. Brookhart, M. Grant and A. F. Volpe, jun., Organometallics, 1992, 11, 3920. 8 M. Brookhart, F. C. Rix, J. M. DeSimone and J. C. Barborak, J. Am. Chem. Soc., 1992, 114, 5894. 9 M. Brookhart, M. I. Wagner, G. G. Balavoine and H. A. Haddou, J.Am. Chem. Soc., 1994, 114, 3641. 10 F. C. Rix and M. Brookhart, J. Am. Chem. Soc., 1995, 117, 1137. 11 F. C. Rix, M. Brookhart and P. S. White, J. Am. Chem. Soc., 1996, 118, 4746. 12 L. K. Johnson, S. Mecking and M. Brookhart, J. Am. Chem. Soc., 1996, 118, 267. 13 L. K. Johnson, C. M. Killian and M. Brookhart, J. Am. Chem. Soc., 1995, 117, 6414. 14 Z. Jiang and A. Sen, J. Am. Chem. Soc., 1995, 117, 4455. 15 C. Pisano, G. Consiglio, A. Sironi and M. Moret, J. Chem. Soc., Chem.Commun., 1991, 421. 16 A. Batistini and G. Consiglio, Organometallics, 1992, 11, 1766. 17 C. Pisano, S. C. A. Nefkens and G. Consiglio, Organometallics, 1992, 11, 1975. 18 M. Barsacchi, G. Consiglio, L. Medici, G. Petrucci and U. W. Suter, Angew. Chem., Int. Ed. Engl., 1991, 30, 989. 19 A. Batistini, G. Consiglio and U. W. Suter, Angew. Chem., Int. Ed. Engl., 1992, 31, 303. 20 S. Bronco, G. Consiglio, S. D. Benedetto, M. Fehr, F. Spindler and A. Togni, Helv. Chim. Acta, 1995, 78, 883. 21 For specific accounts of carbonylation reactions of metal alkyls, see: F. Calderazzo, Angew. Chem., Int. Ed. Engl., 1977, 16, 299; E. J. Kuhlmann and J. J. Alexander, Coord. Chem. Rev., 1980, 33, 195; G. K. Anderson and R. J. Cross, Acc. Chem. Res., 1984, 17, 67. 22 M. D. Fryzuk, B. R. Lloyd, G. K. B. Clentsmith and S. R. Rettig, J. Am. Chem. Soc., 1994, 116, 3804. 23 M. D. Fryzuk, G. K. B. Clentsmith, G. Hägele and S. J. Rettig, Organometallics, 1996, 15, 2083. 24 M.D. Fryzuk, D. H. McConville and S. J. Rettig, J. Organomet. Chem., 1993, 445, 245. 25 F. A. Cotton and T. J. Marks, J. Am. Chem. Soc., 1969, 91, 1339. 26 X. Yang, C. L. Stern and T. J. Marks, J. Am. Chem. Soc., 1994, 116, 10 015. 27 P. W. Jolly, Angew. Chem., Int. Ed. Engl., 1985, 24, 283. 28 F. Ozawa, T. Hayashi, H. Koide and A. Yamamoto, J. Chem. Soc., Chem. Commun., 1991, 1469. 29 G. P. C. M. Dekker, C. J. Elsevier, K. Vrieze and P. W. N. M. van Leeuwen, Organometallics, 1992, 11, 1598. 30 G. P. C. M. Dekker, C. J. Elsevier, K. Vrieze, P. W. N. M. van Leeuwen and C. F. Roobeek, J. Organomet. Chem., 1992, 430, 357. 31 I. Tóth and C. J. Elsevier, J. Chem. Soc., Chem. Commun., 1993, 529. 32 P. W. N. M. van Leeuwen, C. F. Roobeck and H. v. d. Heijden, J. Am. Chem. Soc., 1994, 116, 12 117. 33 For reviews on CO/alkene polymerization, see: A. Sen, Adv. Polym. Sci., 1986, 73/74, 125; E. Drent, Chem. Rev., 1996, 96, 663. 34 A. L. Seligson and W. C. Trogler, J. Am. Chem. Soc., 1991, 113, 2520. 35 H. B. Davis, F. W. B. Einstein, P. G. Glavina, T. Jones, R. K. Pomeroy and P. Rushman, Organometallics, 1989, 8, 1030. 36 F. A. Cotton, Prog. Inorg. Chem., 1976, 21, 1. 37 An alternative formulation of 6a, as [Pd(dippe)(m-13CO)Pd(dippe)- (13COMe)]1, i.e. a dinuclear system bridged by CO, and having an acetyl group, is untenable due to the observed 13C-{1H} NMR spectrum of 2-13C1 under 13CO: JCC9 values of 4–10 Hz are measured; therefore the scalar coupling is not of the 1JCC9 type [cf. 1JCC = 40.6 Hz for the AX2 pattern of 13CH3(13CO)CH3, which is observed in the same spectrum] and a formulation of [Pd(dippe)- (m-13CO)2Pd(dippe)Me]1 is justified. 38 M. Portnoy and D. Milstein, Organometallics, 1993, 12, 1655. 39 M. Portnoy, F. Frolow and D. Milstein, Organometallics, 1991, 10, 3960. 40 M. Portnoy and D. Milstein, Organometallics, 1994, 13, 600. 41 I. Tóth and C. J. Elsevier, J. Am. Chem. Soc., 1993, 115, 10 388. 42 T. Yamamoto, T. Kohara and A. Yamamoto, Chem. Lett., 1976, 1217. 43 B. A. Markies, P. Wijkens, A. Dedieu, J. Boersma, A. L. Spek and G. van Koten, Organometallics, 1995, 14, 5628. 44 A. Sen, CHEMTECH, 1986, 48. 45 J. P. Collman, L. S. Hegedus, J. R. Norton and R. G. Finke, Principles and Applications of Organotransition Metal Chemistry, University Science Books, Mill Valley, CA, 1987. 46 M. E. Thompson, S. M. Baxter, A. R. Bulls, B. J. Burger, M. C. Nolan, B. D. Santarsiero, W. P. Schaefer and J. E. Bercaw, J. Am. Chem. Soc., 1987, 109, 203. 47 P. Burger and R. G. Bergman, J. Am. Chem. Soc., 1993, 115, 10 462. 48 B. A. Arndtsen and R. G. Bergman, Science, 1995, 270, 1970. 49 A. G. Massey and A. Park, J. Organomet. Chem., 1966, 5, 218. 50 N. H. Dryden, P. Legzdins, J. Trotter and V. C. Yee, Organometallics, 1991, 10, 2857. 51 R. E. Rülke, J. M. Ernsting, A. L. Spek, C. J. Elsevier, P. W. N. M. van Leeuwen and K. Vrieze, Inorg. Chem., 1993, 32, 5769. 52 TEXSAN, Structure Analysis Package, Molecular Structure Corporation, The Woodlands, TX, 1995. 53 International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974, vol. 4, pp. 99–102 (present distributor Kluwer Academic Publishers, Boston, MA); International Tables for Crystallography, Kluwer Academic Publishers, Boston, MA, 1992, vol. C, pp. 200–206. Received 29th December 1997; Paper 8/00152I

ISSN:1477-9226    

DOI:10.1039/a800152i

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2009–2014 2009 Stable mononuclear rhodium(II) polypyridyl complexes: synthesis, spectroscopic and structural characterisation Parimal Paul,* Beena Tyagi, Anvarhusen K. Bilakhiya, Mohan M. Bhadbhade and E. Suresh Discipline of Silicates and Catalysis, Central Salt and Marine Chemicals Research Institute, Bhavnagar 364 002, India. E-mail: salt@cscsmcri.ren.nic.in Received 28th January 1999, Accepted 13th March 1999 The reaction of RhCl3?3H2O and 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) in refluxing ethanol–water (1 : 1) resulted in the hydrolysis of tptz to bis(2-pyridylcarbonyl)amide anion (bpca) and aVorded a mixture of RhIII and RhII complexes which were separated and characterised as [RhIII(bpca)2][PF6] and [RhII(bpca)2]?3H2O 1.Similarly the reaction of tptz and Rh(tpy)Cl3 (tpy = 2,29:69,20-terpyridyl) yielded mixed ligand complexes [RhIII(bpca)(tpy)]21 and [RhIi(bpca)(tpy)]Cl?8H2O 2. The molecular structures of complexes 1 and 2 have been established by single-crystal X-ray analysis.In complex 1 two bpca moieties are co-ordinated to RhII with nitrogen as donor atoms in a mutually perpendicular fashion. In complex 2 bpca and tpy are bound to the metal ion in a similar fashion to that found in 1. The axial Rh–N bond distances in 1 and 2 are significantly shorter compared to equatorial Rh–N bond distances, indicating an axially compressed octahedral geometry of the metal ion.Complexes 1 and 2 exhibit absorption bands in the 545–600 nm region whereas their RhIII analogues do not show any band in this region. Electrochemical studies of 1 and 2 revealed a metal based reduction (RhIIÆRhI) at 21.13 and 20.72 V, respectively, followed by two ligandbased redox couples. EPR studies of 1 and 2 in acetonitrile at 77 K show g|| > g^ ª ge indicating a dx2 2 y2 ground state and a compressed octahedral geometry for the metal ion, consistent with the crystal structures. Introduction The co-ordination chemistry of rhodium is dominated by its 11 and 13 oxidation states.Among known Rh(II) complexes diamagnetic dimers with an Rh–Rh bond are the most common.1–5 Only a limited number of reports have addressed mononuclear paramagnetic Rh(II) complexes.6,7 The stability of the mononuclear complexes depends mainly on the structural and electronic properties of the ligands. Many of those complexes were stabilised using sterically crowded ligands such as tertiary phosphine, porphyrins, crown thioethers, SchiV bases, arynes and hydrotris(pyrazolyl) borate.6–8 Molecular geometries of only a few of these complexes have been established by single-crystal X-ray studies.8–16 However, using poly(pyridyl) ligands a few dimeric Rh(II) complexes have been isolated 5,17 but no stable monomer has been reported with the exception [Rh(bipy)2][NO3].18 However, short-lived RhII mononuclear complexes were generated by one-electron reduction of the corresponding RhIII complexes either photochemically19–21 or electrochemically 22,23 and their properties were studied in solution.Generally, when mononuclear octahedral RhIII complexes are reduced to RhII they undergo ligand labilization, which results in the loss of one ligand and either dimerization or disproportionation to RhIII and RhI species.19–23 Recently we studied the reaction of RhCl3 with 2,4,6-tris- (2-pyridyl)-1,3,5-triazine (tptz), which in ethanol–water resulted in the hydrolysis of tptz to the bis(2-pyridylcarbonyl)- amide anion (bpca) and aVorded a mixture of RhIII and RhII complexes, the RhIII complex was characterised as [Rh- (bpca)2][PF6].24 The reaction of Rh(tpy)Cl3(tpy = 2,29:69,20- terpyridine) with tptz also promoted the hydrolysis of tptz to bpca and yielded a mixture of mixed ligand complexes of RhIII and RhII.The RhIII complex, [Rh(bpca)(tpy)][PF6]2 has also been reported.25 The RhII complexes (minor products) were separated successfully from their RhIII analogues.Herein, we report the synthesis, purification, spectroscopic and structural characterisation of these two rare examples of mononuclear RhII complexes. Experimental Materials Sephadex SP C-25 and the ligand 2,29:69,20-terpyridine and tetrabutylammonium tetrafluoroborate were obtained from Aldrich. Hydrated rhodium trichloride was obtained from Arora Matthey. Solvents were purified by standard methods before use.Physical measurements Elemental analyses (C, H, N) were performed on a model 2400 Perkin-Elmer Elemental Analyser. UV/VIS spectra were recorded on a model 8452A Hewlett-Packard Diode Array spectrophotometer. EPR studies were performed on a Bruker ESP 300 X-band spectrometer attached to an ESP 1600 data system. Electrochemical measurements were carried out with a model 273A EG & G Princeton Applied Research Potentiostat. All electrochemical experiments were conducted in an argon atmosphere with a glassy carbon working electrode.A saturated calomel electrode (SCE) was used as reference with 0.1 mol dm23 [NBun 4][BF4] as the supporting electrolyte. Syntheses [Rh(bpca)2]?3H2O 1. A mixture of tptz (624 mg, 2 mmol) and RhCl3?3H2O (264 mg, 1 mmol) in ethanol–water (1 : 1, 60 cm3) was refluxed under an argon atmosphere for 45 h. The volume of the reaction mixture was reduced to ca. 20 cm3 by rotary evaporation and an aqueous solution (5 cm3) of NH4PF6 (326 mg, 2 mmol) was added.The resulting precipitate ([RhIII- (bpca)2][PF6]) was filtered oV and washed with water (5 cm3, three times). The filtrate and washing were collected and evaporated to dryness by rotary evaporation. The crude solid was chromatographed on deactivated alumina (5% H2O) in acetonitrile–water (9 : 1). After removal of a minor first fraction the desired compound was separated as a greenish brown solution which was kept at room temperature allowing slow evaporation.After ten days a crystalline compound suitable for single2010 J. Chem. Soc., Dalton Trans., 1999, 2009–2014 crystal X-ray study was obtained. Yield: 20% (Found: C, 47.04; H, 3.81; N, 13.52. Calc. for C24H22N6O7Rh: C, 47.30; H, 3.64; N, 13.79%). Molar conductance (LM/W21 cm2 mol21): 16 (nonelectrolyte). lmax/nm (e/dm3 mol21 cm21) (acetonitrile): 270 (20400), 335sh (4700), 400sh (1300), 545sh (235) and 592 (310). [Rh(bpca)(tpy)]Cl?8H2O 2. [Rh(tpy)Cl3] 25 (442 mg, 1 mmol) and tptz (312 mg, 1 mmol) were refluxed in ethanol–water (1 : 1, 60 cm3) under an argon atmosphere for 40 h.The solution was then concentrated to ca. 20 cm3 and chromatographed on a Sephadex SP C-25 column with an aqueous 0.05 mol dm23 solution of sodium chloride as eluent. After separation of a small first fraction complex 2 was separated and finally the RhIII complex was eluted using a 0.2 mol dm23 solution of sodium chloride. Solvent was removed from the desired fraction in a rotary evaporator and the residue was extracted with dry ethanol (5 cm3), the process was repeated three times, the solid mass was then dissolved in acetonitrile–water (1 : 1, 10 cm3) and allowed slowly to evaporate at room temperature.After 15 days a crystalline compound suitable for X-ray study was separated. Yield: 14% (Found: C, 43.46; H, 4.92; N, 11.08. Calc. for C27H35N6O10ClRh: C, 43.71; H, 4.75; N, 11.33%). Molar conductance (LM/W21 cm2 mol21): 148 (1 : 1 electrolyte).lmax/nm (e/dm3 mol21 cm21) (acetonitrile): 280 (22800), 326 (11800), 338 (10500), 356 (7000), 410sh (550), 552 (375) and 600 (170). Crystal structure determination Preliminary data on the space group and unit cell dimensions as well as intensity data were collected on an Enraf-Nonius CAD4 X-ray diVractometer using graphite-monochromatised Mo-Ka radiation (l = 0.7107 Å) in the range q 2–238. Accurate cell dimensions were obtained using 25 high angle reflections (10 < q < 14).The crystal orientation, refinement of cell parameters and intensity measurements were carried out using the program CAD-4 PC.26 Intensities were corrected for Lorentz-polarisation eVects but not for absorption. The Lorentz-polarisation correction and data reduction were carried out using the NRCVAX program.27 The structure was solved by the heavy-atom method using the program SHELXL 97.28 Intermolecular calculations were carried out using the program CSU.29 All computations were performed on a Pentium-Pro PC.Crystallographic data for complexes 1 and 2 are summarised in Table 1. Table 1 Summary of crystallographic data and parameters for complexes 1 and 2 Empirical Formula M Crystal system Space group Crystal dimensions/mm a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 Z Dc/g cm23 F(000) m(Mo-Ka)/mm21 Total reflections Observed reflections [I > 2s(I)] Parameters refined Final R1 (on F) a Final wR2 (on F2) b 1 C24H23.6N6O7.8Rh 623.80 Monoclinic C2/c 0.14 × 0.10 × 0.08 23.410(4) 16.013(7) 15.006(8) 108.23(3) 5343.0(4) 8 1.551 2536 0.697 4679 3686 360 0.059 0.187 2 C27H35N6O10ClRh 741.97 Triclinic P1� 0.22 × 0.09 × 0.05 9.072(4) 11.749(3) 16.605(5) 75.09(2) 77.14(3) 89.52(3) 1665.1(10) 2 1.480 762 0.654 5843 5292 406 0.044 0.141 a R1 = S Fo| 2 |Fc /S|Fo|.b wR2 = [Sw(Fo 2 2 Fc 2)2]/S[w(Fo 2)2]1/2. For complex 1, the diVerence Fourier map after the anisotropic refinement of non-hydrogen atoms of [Rh(bpca)2] contained one peak of height 9.2 e Å23 and eleven other peaks of height varying from 4.9 to 1.19 e Å23.These peaks were assigned to water molecules, the first one with full occupancy and others with partial occupancies according to peak height. The occupancies of oxygen atoms were refined using SHELXL 97. For complex 2, after the anisotropic refinement of nonhydrogen atoms of [Rh(bpca)(tpy)]Cl the diVerence map revealed seven peaks of height 7.6 to 6 e Å23 followed by two peaks of height 3.5 and 3.3 e Å23.As in complex 1, the first seven peaks were assigned to seven water molecules with full occupancies and refined anisotropically and the last two were assigned to a two component disordered water molecule and refined by using the FVAR facility in SHELXL 97. The H-atoms of the bpca and tpy moieties were fixed stereochemically and refined using a riding model. The H-atoms of the water molecules with full occupancies were modelled taking into account their H-bonding interactions using the program CSU.29 CCDC reference number 186/1424.See http://www.rsc.org/suppdata/dt/1999/2009/ for crystallographic files in .cif format. Results and discussion Synthesis of the complexes The reaction of rhodium trichloride and tptz in refluxing ethanol–water resulted in the hydrolysis of tptz to the bis(2- pyridylcarbonyl)amide anion (bpca) and aVorded RhIII and RhII complexes of composition [Rh(bpca)2]n1 (n = 0 and 1). Similarly, the reaction of [Rh(tpy)Cl3] and tptz yielded complexes of composition [Rh(bpca)(tpy)]n1 (n = 1 and 2).In both cases the RhIi complexes were the minor products. The addition of NH4PF6 to the [Rh(bpca)2]n1 mixture allowed the isolation of RhIII complex as its PF6 2 salt, [Rh(bpca)2][PF6]. The RhII complex is a neutral species (n = 0) and it remained in solution from which it was isolated and purified by column chromatography on deactivated alumina. In the [Rh(bpca)(tpy)]n1 mixture both the complexes are cations and the separation was carried out by ion-exchange chromatography on Sephadex.From the eluent the desired complex can be isolated as its PF6 2 anion but the Cl2 salt gave better quality crystals for X-ray study. The RhIII complexes were pale yellow and those of RhII were greenish brown. The ligand (tptz) and complexes 1 and 2 are shown in Scheme 1. The reduction of RhIII to RhII, induced by ligand or solvent has been known for many years. It is common in the reactions between hydrated rhodium(III) chloride and phosphines in ethanol 7 but is also found in the presence of other ligands such as lithium aryl (2,4,6-triisopropylphenyl), C6Me6, 5,59-thiodisalicylic acid and NO.7,13 It has also been reported that the reaction between rhodium trichloride hydrate and bulky phosphine resulted in a mixture of rhodium(III) and rhodium(II) complexes. 12,30 Our observations, therefore, are similar to some earlier reports with diVerent types of ligands.12,30 Crystal structures ORTEP31 views of complexes 1 and 2 along with their atom numbering schemes are shown in Figs. 1 and 2, respectively. Selected bond distances and angles of both the complexes are presented in Table 2. The tridentate bpca ligands in 1 and tridentate bpca and tpy in 2 are bound to the metal ion almost in a mutually perpendicular fashion forming a distorted octahedral geometry around the rhodium(II) centre. In both complexes 1 and 2 the middle nitrogen atoms [N(2) and N(5)] of the ligands are at the axial positions and the nitrogen atoms of the wing pyridyl rings [N(1), N(3), N(4) and N(6)] formed the equatorialJ.Chem. Soc., Dalton Trans., 1999, 2009–2014 2011 Table 2 Selected bond distances (Å) and angles (8) for complexes 1 and 2 Rh–N(1) Rh–N(2) Rh–N(3) Rh–N(4) Rh–N(5) N(1)–Rh–N(4) N(1)–Rh–N(6) N(3)–Rh–N(4) N(3)–Rh–N(6) N(1)–Rh–N(3) N(4)–Rh–N(6) 1 2.059(5) 1.990(5) 2.036(5) 2.043(5) 1.997(5) 93.18(19) 89.55(19) 91.0(2) 91.4(2) 163.22(17) 162.38(18) 2 2.024(3) 1.990(3) 2.023(3) 2.049(4) 1.963(3) 92.80(14) 89.47(14) 90.65(14) 92.66(14) 163.22(14) 160.76(14) Rh–N(6) C(6)–O(1) C(7)–O(2) C(18)–O(3) C(19)–O(4) N(2)–Rh–N(5) N(2)–C(6)–C(5) N(2)–C(7)–C(8) N(5)–C(18)–C(17) N(5)–C(19)–C(20) N(5)–C(22)–C(23) 1 2.022(5) 1.198(7) 1.165(7) 1.207(7) 1.219(7) 178.5(2) 111.6(2) 110.9(5) 111.9(5) 111.8(5) — 2 2.046(3) 1.202(6) 1.205(6) —— 179.33(13) 110.9(4) 111.0(4) 112.8(3) — 112.9(4) base.The trans angles of the axial nitrogens [N(2)–Rh–N(5) 178.5(2) in 1 and 179.33(13)8 in 2] are very close to the ideal value of 1808.The same angles for the equatorial nitrogens Fig. 1 An ORTEP (50% probability) view of complex 1 with the atom labelling scheme shown; water molecules and hydrogen atoms are omitted for clarity. Scheme 1 N N N O O Rh N N N O O n+ N N N O O Rh N N N n+ n = 1, Rh(III) n = 2, Rh(II) 1 n = 2, Rh(III) n = 1, Rh(II) 2 N N N N N N tptz RhCl3•3H2O ethanol–water Rh(tpy)Cl3 ethanol–water deviate significantly [160.76(14)–163.22(17)8] from the ideal value indicating a tetrahedral distortion in the equatorial base, which may be due to constraints imposed by the five-membered chelate ring. The axial Rh–N distances in both complex 1 and 2 are significantly shorter compared to the equatorial Rh–N distances (Table 2) indicating an axially compressed octahedral geometry of the rhodium ion.The wing pyridyl rings of the bpca and tpy ligands in both complexes show slight deviations from their mean plane.In complex 1 the amido oxygen atoms of both bpca moieties make strong intermolecular C–H ? ? ? O interactions 32 essentially along the ab-plane, forming a polymeric network as illustrated in Fig. 3. It is interesting to note that the C–H ? ? ?O interaction from both the bpca moieties is diVerent, O(1) and O(2) make a bifurcated H-bond with the pyridyl carbon C(12); whereas O(3) and O(4) each make a single interaction with C(1) and C(24), respectively (Table 3).The disordered water molecules are distributed within the cavity created by the molecule along the ab-plane. In complex 2 the molecular cations in the unit cell can be described as H-bonded dimers via bifurcated C–H ? ? ? O interactions 32 between the oxygen atoms of the bpca moiety [O(1) and O(2)] and the C(13) of the tpy as illustrated in Fig. 4(a). The Cl2 also shows a short C–H ? ? ? Cl contact with C(24) of tpy.The water molecules are distributed around the dimers as shown in Fig. 4(b) and show strong H-bonding among themselves. Electronic spectra The electronic spectra of complexes 1 and 2 were recorded in Fig. 2 An ORTEP (50% probability) view of the cation of complex 2 with the atom labelling scheme; hydrogen atoms are omitted for clarity.2012 J. Chem. Soc., Dalton Trans., 1999, 2009–2014 Table 3 Hydrogen bonding parameters (excluding water molecules) in compxes 1 and 2 Complex 1 2 Da C(12) C(12) C(1) C(24) C(13) C(13) C(24) Hb H(12) H(12) H(1) H(24) H(13) H(13) H(24) Ac O(1) O(2) O(3) O(4) O(1) O(2) Cl D? ? ? A/Å 3.152(1) 2.958(1) 3.06(8) 3.205(5) 3.154(1) 3.066(3) 3.678(3) H? ? ? A/Å 2.55(7) 2.165(8) 2.483(4) 2.542(2) 2.49(2) 2.32(1) 2.79(3) D–H? ? ? A/8 122(5) 144(6) 121(1) 128(3) 128(3) 136(3) 159(3) Symmetry code x, 1 2 y, 21/2 1 z x, 1 2 y, 21/2 1 z 1/2 2 x, 1/2 2 y, 2z x, 1 2 y, 1/2 1 z 1 2 x, 1 2 y, 2z 1 2 x, 1 2 y, 2z x, 1 2 y, 1/2 1 z a D = Donor.b H = Hydrogen. c A = Acceptor. acetonitrile. The spectra of complex 1 and its RhIII analogue are illustrated in Fig. 5. In the visible region complex 1 exhibits a band at 592 nm and a shoulder at 545 nm, complex 2 also shows absorption maxima at 600 and 552 nm whereas their RhIII analogues did not show any band above the 400 nm region (Fig. 5). In the low-spin Rh(II) (d7) mononuclear complexes a close similarity was noted between the electronic spectra of six-coordinate, five-co-ordinate square pyramidal and four-coordinate square-planar complexes.6 Most of these complexes exhibit two or more absorption bands in the 530–600 nm region,6,30,33,34 similar to that found in complexes 1 and 2 and those bands can be assigned to d–d transitions.6,10 The bands in the UV region of complexes 1 and 2 are similar to those of their RhIII analogues except for a small shift of the absorption maxima around 270 nm and a significant decrease in the e value of the band at ª330 nm in complex 1.Electrochemistry The cyclic voltammograms of complexes 1 and 2 were recorded in acetonitrile. Complex 1 shows reductions at 21.13 (DE 70), 21.44 (122 mV) and 21.84 V vs. SCE, the reduction waves of complex 2 appear at 20.72, 21.48 (DE 94 mV) and 21.80 V. In both complexes the last peak is poorly resolved in the cyclic voltammograms but well resolved in the square wave. The peak potentials of the complexes are similar to those of their RhIII analogues but the cathodic current for the first reduction peak of the RhII complexes is almost half that of their RhIII analogues (Ic RhII/Ic RhIII = 0.54 for 1 and 0.56 for 2), as shown in Fig. 6. The first reduction peak is metal-centred, for RhIII complexes it is in fact a composite wave corresponding to a two-electron process 22–25,35 (RhIIIÆRhI). For RhII complexes it is a one-electron process (RhIIÆRhI), which is consistent with the observed diVerence in cathodic current for the first peak.The other two reductions are ligand based. The similarity in the Fig. 3 A view showing the C–H ? ? ? O interactions involving amido oxygen atoms of the bpca moieties of complex 1. peak potentials of the RhII and RhIII complexes is probably due to their similar ligand environments. Metal-based two oneelectron reduction processes (RhIIIÆRhII and RhIIÆRhI) at the same potential were found by us 24,25 and others 10,22,23,35 in many RhIII systems. EPR spectroscopy The X-band EPR spectra of complexes 1 and 2 were recorded in acetonitrile at 77 K.The spectrum of 1 is shown in Fig. 7, the g values are g|| = 2.392 and g^ = 2.075 with hyperfine coupling (doublet) to 103Rh (I = 1/2) in the g|| region (A|| = 155 G). The g values are reversed from those found in most of the RhII systems (g^ > g||) but are similar to those found in complexes such as [RhCl2(PPh3)2],9,36 [Rh(NO)Cl3(PPh3)2],37 [RhCl4?2H2O]22 (studied by X-ray crystallography),38 [RhH6]42 trapped in LiH lattice 39 and in a number of RhII species in zeolite cavities.40 The g|| > g^ ª ge relationship suggests a dx2 2 y2 ground state if the unpaired electron is located on a rhodium(II) ion as a result of a compressed octahedral geometry.38–40 The X-ray data for 1 show an axially compressed octahedral geometry of the rhodium which is consistent with Fig. 4 (a) A view showing the dimeric nature of complex 2 via C–H? ? ? O interactions; (b) packing diagram of complex 2 showing the water molecules in the channels around the dimers.J.Chem. Soc., Dalton Trans., 1999, 2009–2014 2013 the EPR data. The large A|| value (155 G), also found in many other systems, suggests a large amount of spin density at the rhodium nucleus.6,41 Complex 2, however, shows three g values g1 = 2.349, g2 = 2.070 and g3 = 1.956. The g1 value is close to that of g|| of complex 1 and is split into a doublet (A1 = 216 G) due to hyperfine interaction with 103Rh.The observed diVerence in the spectra of 1 and 2 is probably due to the lowering of symmetry which occurs in the mixed ligand complex. Stability aspects Six co-ordinate mononuclear rhodium(II) complexes generally possess structural and electronic features that make them susceptible to ligand substitution. Strong interaction of a s-donor ligand along the z axis destabilises the unpaired electron in the Fig. 5 Electronic absorption spectra of complex 1 (——) and its RhIII analogue, [Rh(bpca)2][PF6] (· · · · ·) in acetonitrile; (a) UV region and (b) visible region.Fig. 6 Cyclic voltammograms of complex 1 and its RhIII analogue, [Rh(bpca)2][PF6], recorded in acetonitrile; scan rate 100 mV s21. dz2 orbital resulting in ligand labilisation. This eVect causes either a disproportionation reaction [Rh(III) and Rh(I)] or dimerisation with the Rh–Rh bond utilising the dz2 orbital.6,7 However, it is evident that the steric and electronic eVects of the ligands influence the stability of the mononuclear rhodium(II) complexes.Factors which can stabilise the mononuclear rhodium(II) complexes are: bulky ligands which protect the metal ion from external attack, the s-donor and p-donor– acceptor capabilities of the ligand and the presence of a delocalized p-system in the ligand backbone.7 In complexes 1 and 2 the X-ray (axial Rh–N < equatorial Rh–N distances) and EPR data (g|| > g^) suggest a compressed octahedral geometry about the rhodium centre, indicating the unpaired electron to be in the dx2 2 y2 orbital.Since the unpaired electron is no longer in the dz2 orbital, ligand labilisation due to destabilisation of the dz2 orbital did not occur. The strong tridentate chelate eVect of the bpca and tpy moieties also protected the periphery of the complex from external attack. The presence of a delocalised p-system (pyridyl ring) in the ligand backbone also contributed to the stabilisation of the rhodium(II).The formation of stable Rh(II) as well as Rh(III) complexes with the same or similar ligands has been reported earlier.10,12 Conclusions The metal-promoted hydrolysis of tptz aVorded a class of complexes containing the ligand bis(2-pyridylcarbonyl)amide anion which provides the necessary structural and electronic requirement to stabilise mononuclear paramagnetic RhII complexes. To our knowledge these are the first examples of structurally characterised mononuclear RhII complexes containing poly- (pyridyl) ligands.Therefore, it is a significant contribution in the area of mononuclear rhodium(II) chemistry. Acknowledgements We are grateful to the Department of Science and Technology (DST), Government of India, for financial support. Our sincere thanks go to Dr S. D. Gomkale, Dr R. V. Jasra and Professor P. Natarajan for their keen interest, encouragement and valuable suggestions in this work. Dr D. Srinivas and Mr Paresh C. Dave are thanked for recording the EPR spectra.We also thank Dr Parthasarathi Dastidar for assistance with the crystallographic study. References 1 T. R. Felthouse, Prog. Inorg. Chem., 1982, 29, 73. 2 E. B. Boyar and S. D. Robinson, Coord. Chem. Rev., 1983, 50, 109. 3 F. P. Pruchnik, Pure Appl. Chem., 1989, 61, 795. Fig. 7 X-Band EPR spectrum of complex 1 recorded in acetonitrile at 77 K.2014 J. Chem. Soc., Dalton Trans., 1999, 2009–2014 4 L. Natkaniec and F. P. Pruchnik, J.Chem. Soc., Dalton Trans., 1994, 3261. 5 F. P. Pruchnik, F. Robert, Y. Jeannin and S. Jeannin, Inorg. Chem., 1996, 35, 4261. 6 K. K. Pandey, Coord. Chem. Rev., 1992, 121, 1. 7 D. G. DeWit, Coord. Chem. Rev., 1996, 147, 209. 8 N. G. Connelly, D. J. H. Emslie, B. Metz, A. G. Orpen and M. J. Quayle, Chem. Commun., 1996, 2289. 9 C. A. Ogle, T. C. Masterman and J. L. Hubbard, J. Chem. Soc., Chem. Commun., 1990, 1733. 10 S. C. Haefner, K. R. Dunbar and C. Bender, J. Am. Chem. Soc., 1991, 113, 9540. 11 K. R. Dunbar and S. C. Haefner, Organometallics, 1992, 11, 1431. 12 R. L. Harlow, D. L. Thorn, R. T. Baker and N. L. Jones, Inorg. Chem., 1992, 31, 993. 13 R. S. Hay-Motherwell, S. U. Koschmieder, G. Wilkinson, B. Hussain-Bates and M. B. Hursthouse, J. Chem. Soc., Dalton Trans., 1991, 2821. 14 M. P. Garcia, M. V. Jimenez, L. A. Oro, F. J. Lahoz, J. M. Casas and P. J. Alonso, Organometallics, 1993, 12, 3257. 15 S. Peng, Inorg. Chim. Acta, 1985, 101, L35. 16 K. R.Dunbar and S. C. Haefner, Inorg. Chem., 1992, 31, 3676. 17 T. Glowiak, H. Pasternak and F. Pruchnik, Acta Crystallogr., Sect. C, 1987, 43, 1036. 18 B. Martin, W. R. McWhinnie and G. M. Waind, J. Inorg. Nucl. Chem., 1961, 23, 207. 19 G. M. Brown, S. F. Chan, C. Creutz, H. A. Schwartz and N. Sutin, J. Am. Chem. Soc., 1979, 101, 7638. 20 Q. G. Mulazzani, S. Emmi, M. Z. HoVman and M. Venturi, J. Am. Chem. Soc., 1981, 103, 3362. 21 H. A. Schwarz and C. Creutz, Inorg. Chem., 1983, 22, 707. 22 G. Kew, K. DeArmond and K. Hanck, J. Phys. Chem., 1974, 78, 727. 23 G. Kew, K. Hanck and K. DeArmond, J. Phys. Chem, 1975, 79, 1828. 24 P. Paul, B. Tyagi, M. M. Bhadbhade and E. Suresh, J. Chem. Soc., Dalton Trans., 1997, 2273. 25 P. Paul, B. Tyagi, A. K. Bilakhiya, M. M. Bhadbhade, E. Suresh and G. Ramachandraiah, Inorg. Chem., 1998, 37, 5733. 26 E. I. Gabe, Y. LePage, I. P. Charland, F. L. Lee and P. S. White, J. Appl. Crystallogr., 1989, 22, 384. 27 G. M. Sheldrick, Acta. Crystallogr., Sect. A, 1990, 46, 467. 28 G. M. Sheldrick, SHELXL 97, Program for refinement of crystal structures, University of Göttingen, 1997. 29 I. Vickovic, Crystal Structure Utility (CSU), a highly automated program for the calculation of geometrical parameters in the crystal structure analysis, Faculty of Science, University of Zagreb, Yugoslavia, 1988. 30 B. R. James and D. V. Stynes, J. Am. Chem. Soc., 1972, 94, 6225. 31 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge National Laboratory, TN, 1976. 32 G. R. Desiraju, Acc. Chem. Res., 1991, 24, 290; Angew. Chem., Int. Ed. Engl., 1995, 34, 2311. 33 S. M. Peng, K. Peters, E. M. Peters and A. Simon, Inorg. Chim Acta, 1985, 101, L35. 34 G. P. Kakis and P. Saroulis, Inorg. Chim. Acta, 1980, 46, 97. 35 S. C. Rasmussen, M. M Richter, E. Yi, H. Place and K. J. Brewer, Inorg. Chem., 1990, 29, 3926. 36 J. A. Osborn, F. J. Jardine, J. F. Young and G. Wilkinson, J. Chem. Soc. A, 1966, 1711. 37 M. C. Baird, Inorg. Chim Acta, 1971, 5, 46. 38 M. D. Sastry, K. Savitri and B. D. Joshi, J. Chem. Phys., 1980, 73, 5568. 39 G. C. Abell and R. C. Bowman, Jr., J. Chem. Phys., 1979, 70, 2611. 40 D. Goldfarb and L. Kevan, J. Phys. Chem., 1986, 90, 264, 2137 and 5787. 41 C. Bianchini, P. Frediani, F. Laschi, A. Meli, F. Vizza and P. Zonello, Inorg. Chem., 1990, 29, 3402. Paper 9/00757A

ISSN:1477-9226    

DOI:10.1039/a900757a

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2015–2020 2015 Synthesis and structure of uranium(III) complexes with dihydrobis(pyrazolyl)borates Leonor Maria,a Maria Paula Campello,a Ângela Domingos,a Isabel Santos *a and Richard Andersen b a Departamento de Química, Instituto Tecnológico e Nuclear (ITN), 2686 Sacavém Codex, Portugal. E-mail: isantos@itn1.itn.pt b Chemistry Department and the Chemical Sciences Division of Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720, USA Received 27th January 1999, Accepted 14th April 1999 The synthesis of the novel uranium(III) complexes [UI2{H2B(3tBu,5Me-pz)2}(THF)2] 1, [UI2{H2B(3tBu,5Me-pz)2}- (OPPh3)2] 2 (3tBu,5Me-pz = 3-tert-butyl-5-methylpyrazolyl) and [U{Ph2B(pz)2}3] 3 are reported. The molecular structures have been determined by single crystal X-ray diVraction. In monomeric complexes 1 and 2 the UIII is seven-co-ordinated by the two pyrazolyl nitrogens, the two iodides and two oxygen atoms of the neutral ligands and by an agostic B–H ? ? ? U interaction.In monomeric 3 the uranium is six-co-ordinated by the nitrogen atoms of the chelating Ph2B(pz)2 ligands which are arranged in a trigonal prismatic geometry around the uranium. Introduction Poly(pyrazolyl)borates are very interesting supporting ligands for d- and f-metal centers as their steric and electronic properties can easily be modified by changing the number of pyrazolyl rings co-ordinated to the boron atom and by introducing various sterically bulky pyrazolyl ring substituents.1–3 For actinides the fine tuning of the co-ordination environment has been dominated by the hydrotris(pyrazolyl)borate ligands [HB(pz*)3, pz* = pyrazolyl or substituted pyrazolyl].3–6 Previously, we 7 and Takats and co-workers 8 have used dihydrobis(pyrazolyl)borates in trivalent uranium chemistry and the complexes [U{H(m-H)- B(3,5Me2-pz)2}3] (3,5Me2-pz = 3,5-dimethylpyrazolyl) and [U{H(m-H)B(pz)2}3(THF)] were structurally characterized.Steric eVects play a dominant role in determining the coordination number and geometry around the metal center and it was of interest to determine what eVect replacing the BH2 group with a BPh2 group would have on the nature of the complexes. In addition, the eVect of functionalization of the 3 and 5 positions of the pyrazolyl rings with bulky groups, tBu and Me, respectively, in the ligand with BH2 groups was examined.Here we report the synthesis and structural characterization of the monosubstituted complexes [UI2{H(m-H)B(3tBu,5Mepz) 2}(L)2] (L = THF 1 or OPPh3 2) and of the tris-chelate [U{Ph2B(pz)2}3] 3 which have been obtained by treating [UI3(THF)4] with K[H2B(3tBu,5Me-pz)2] and Na[Ph2B(pz)2], respectively. Experimental General procedures All reactions were carried out under nitrogen, using standard Schlenk and vacuum-line techniques or in an nitrogen-filled glove-box. Solvents were dried and deoxygenated by standard methods and distilled immediately prior to use.Benzene-d6 and toluene-d8 were dried over sodium–benzophenone. Triphenylphosphine oxide was recrystallized from ethyl acetate and vacuum dried. The salts Na[Ph2B(pz)2] and K[H2B(3tBu,5Mepz) 2] and the complex [UI3(THF)4] were prepared according to published methods.9–11 The 1H NMR spectra were recorded on a Varian 300 MHz multinuclear spectrometer, using the chemical shift of the solvent as the internal standard, IR spectra as Nujol mulls on a Perkin-Elmer 577 spectrophotometer and absorption electronic spectra as solutions on a Cary 2390 Varian spectrometer.Carbon, hydrogen and nitrogen analyses were performed on a Perkin-Elmer automatic analyser. Syntheses [UI2{H(Ï-H)B(3tBu,5Me-pz)2}(THF)2] 1. To a slurry of [UI3(THF)4] (1.8 g, 2 mmol) in THF (20 mL) was slowly added a solution of K[H2B(3tBu,5Me-pz)2] (653 mg, 2 mmol) in THF. After stirring overnight at room temperature the reaction mixture was centrifuged and the black solution separated.Slow diVusion of n-hexane into this black THF solution, during several days, led to the formation of black prismatic crystals, which were separated, washed with n-hexane and vacuum dried (1.1 g, 1.2 mmol, 61% yield) (Found: C, 31.1; H, 4.8; N, 5.8. Calc. for C24H44BI2N4O2U: C, 31.2; H, 4.8; N, 6.1%). IR (cm21): 2420s, 2280w, 2240w, 2200m, all n(B–H); 1525s, 1260w, 1240w, 1210w, 1160s, 1120w, 1110w, 1060w, 1010s, nasym(C–O–C), 980w, 910w, 890m, 880s, 850s, nsym(C–O–C), 790s, 735s, 730s, 720m, 650m, 630s, 605s, 520m, 465m, 390w, 320w and 300w. 1H NMR: (benzene-d6, 27 8C) d 12.6 (8 H, br, THF), 9.5 (2 H, br, H(4)), 7.58 (8 H, br, THF), 1.4 (18 H, br, 3-tBu,), 23.3 (6 H, br, 5-Me) and 215.7 (2 H, vbr, B–H); (toluene-d8, 27 8C) d 11.2 (8 H, br, THF), 9.6 (2 H, br, H(4)), 6.8 (8 H, br, THF), 1.5 (18 H, br, 3-tBu,), 23.3 (6 H, br, 5-Me) and 215.7 (2 H, vbr, B–H); (toluene-d8, 250 8C) d 30.3 (vbr, THF), 23.8 (vbr, THF), 18.1 (vbr, THF), 15.8 (vbr, THF), 14.3 (1 H, H(4)), 7.5 (9 H, 3-tBu,), 2.8 (1 H, H(4)), 21.8 (9 H, 3-tBu,), 28.1 (3 H, 5-Me), 210.8 (3 H, 5-Me), 236.6 (1 H, br, B–H) and 266.5 (1 H, vbr, B–H).UV-vis (THF) (lmax/nm): 754w, 904s, 1000s, 1020w, 1040vs, 1070vw, 1170w, 1200s, 1220m and 1240m. [UI2{H(Ï-H)B(3tBu,5Me-pz)2}(OPPh3)2] 2. Addition of OPPh3 (121 mg, 0.43 mmol) to a suspension of complex 1 (200 mg, 0.22 mmol) in toluene (10 cm3) gave a dark red insoluble solid.The supernatant was removed and the solid washed with n-hexane and dried. The dark red solid obtained (200 mg, 0.15 mmol, 70% yield) was formulated as 2. Dark red crystals suitable for X-ray analysis were obtained by layering hexane on a toluene solution of OPPh3 (42 mg, 0.15 mmol) and layering this on a toluene solution of 1 (70 mg, 0.076 mmol) (Found: C, 47.5; H, 4.5; N, 4.1. Calc. for C52H58BI2N4O2P2U: C,2016 J. Chem. Soc., Dalton Trans., 1999, 2015–2020 47.2; H, 4.3; N, 4.2%).IR (Nujol, cm21): 2440s, 2280m, 2250w, 2240w, all n(B–H); 1585s, 1530s, 1480s, 1370s, 1355m, 1135s, 1305w, 1255s, 1235m, 1200m, 1170m, 1155m, 1145s, 1115s, 1095m, 1080m, 1070s, 1020s, 1010m, 990s, 970w, 920w, 890s, 790w, 780s, 750s, 720s, 690s, 550s and 460w. UV-vis (THF) (lmax/nm): 752w, 904s, 1010m, 1070m, 1200m and 1210m. [U{Ph2B(pz)2}3] 3. To a slurry of [UI3(THF)4] (328 mg, 0.36 mmol) in THF (20 mL) was slowly added a solution of Na[Ph2- B(pz)2] (350 mg, 1.09 mmol) in THF.After stirring overnight at room temperature the reaction mixture was vacuum dried. The solid was extracted with toluene and after centrifugation a dark red solution and a white precipitate of NaI was obtained. Slow diVusion of hexane into the saturated solution of toluene led to prismatic red crystals, which were separated, washed with n-hexane and vacuum dried (200 mg, 0.18 mmol, 49% yield) (Found: C, 56.6; H, 4.39; N, 14.4. Calc. for C54H48B3N12U: C, 57.1; H, 4.22; N, 14.8%). IR (Nujol, cm21): 1491m,1480 (sh), 1270s, 1250 (sh), 1180 (sh), 1170s, 1135m, 1100w, 1050s, 1025 (sh), 970m, 910w, 890w, 880s, 825m, 800m, 770w, 740s, 720s, 700s, 640s, 620s and 330m.UV-vis. (THF, lmax/nm): 920s, 1030w, 1080w, 1180 (sh) and 1230s. 1H NMR (toluene-d8, 27 8C): d 13.2 (6 H, pz), 6.5 (6 H, pz), 3.2 (6 H, pz), 8.2 (6 H, d, J = 6.6, o-H, Ph), 8.1 (6 H, br, Ph), 7.6 (6 H, t, J = 6.9, m-H, Ph), 7.5 (6 H, t, J = 7.0, m-H, Ph) and 6.9 (6 H, t, J = 6 Hz, p-H, Ph).X-Ray crystallographic analysis X-Ray data were collected from black crystals of complex 1 (0.20 × 0.10 × 0.09 mm), dark red crystals of 2 (0.49 × 0.43 × 0.27 mm) and from a pink crystal of 3 (0.25 × 0.16 × 0.14 mm). All the crystals were mounted in thin-walled glass capillaries within a nitrogen filled glove-box. Owing to decomposition problems, the crystal of 2 was mounted in Nujol and with solvent of crystallization. Data were collected at room temperature on an Enraf- Nonius CAD-4 diVractometer with graphite-monochromatized Mo-Ka radiation, using an w–2q scan mode.Unit cell dimensions were obtained by least-squares refinement of the setting angles of 25 reflections with 15.4 < 2q < 29.18 for 1, 15.3 < 2q < 26.98 for 2 and 14.9 < 2q < 27.78 for 3. The crystal data are summarized in Table 1. The data were corrected 12 for Lorentzpolarization eVects, for linear decay (no decay was observed for 1) and empirically for absorption (y scans).The crystal of 2 did not provide a good quality data set (variable half-width of the reflections, and a large decay, 61%, during data collection) but the structure was determined unambiguously, although with less accuracy. The heavy atom positions were located by Patterson methods using SHELXS 86.13 The remaining atoms were located in successive Fourier-diVerence maps and refined by least squares on F2 using SHELXL 93.14 For all three compounds, solvent of crystallization was located in the lattice, severely disordered: one THF molecule in 1, and in 2 and 3 two and one and a half toluene molecules per asymmetric unit.All the non-hydrogen atoms were refined with anisotropic thermal motion parameters, except for the phenyl carbon atoms in 2 and the atoms of the solvent molecules. When attempting to refine anisotropically the phenyl carbon atoms in 2 some gave negative thermal parameters and others split positions.The contributions of the hydrogen atoms were included in calculated positions, constrained to ride on their carbon and boron atoms (a fixed B–H bond length of 1.01 Å was used) with group Uiso values assigned (for 2 and 3 no hydrogen atoms of the solvent molecules were introduced). The final Fourierdi Verence syntheses revealed electron densities between 10.98 and 21.16 e Å23 for 1, 1.96 and 22.14 e Å23 for 2 and 2.13 and 21.01 e Å23 for 3, near the uranium atom.Atomic scattering factors and anomalous dispersion terms were as in SHELXL 93.14 The drawings were made with ORTEP II15 and all the calculations were performed on a 3000 Dec a computer. CCDC reference number 186/1425. See http://www.rsc.org/suppdata/dt/1999/2015/ for crystallographic files in .cif format. Results and discussion The reaction between [UI3(THF)4] 11 and one equivalent of K[H2B(3tBu,5Me-pz)2] in tetrahydrofuran proceeds readily and gives a very dark solution.The KI formed was separated from this suspension by centrifugation and n-hexane added to the supernatant solution leading to black crystals of [UI2- {H(m-H)B(3tBu,5Me-pz)2}(THF)2] 1. Addition of OPPh3 to a solution of complex 1 in toluene, in the molar ratio 2 : 1, gives an insoluble dark red solid formulated as [UI2{H(m-H)- B(3tBu,5Me-pz)2}(OPPh3)2] 2. Complex 3 is obtained from [UI3(THF)4] with Na[Ph2B(pz)2] in tetrahydrofuran in the molar ratio 1 : 3. Removal of the solvent, extraction with toluene and addition of n-hexane leads to dark red crystals of [U{Ph2B(pz)2}3] 3.Complexes 1 and 3 are soluble in toluene, benzene and tetrahydrofuran and sparingly soluble in hexane, but 2 is only soluble in tetrahydrofuran in which it decomposes, partially regenerating 1. Complexes 1 and 3 have been characterized in the solid state and in solution, but 2 cannot be characterized in solution, due to its low solubility in nonco- ordinating solvents. The IR spectra of complexes 1 and 2 show the absorption bands due to the poly(pyrazolyl)borate, namely one sharp and medium B–H stretching band centered at 2420 and 2440 cm21, respectively, and a complex group of weak bands between 2280 and 2200 cm21. The higher frequency bands are most certainly due to normal terminal B–H stretches, while the bands at lower frequency are due to the bridging n(B–H) ? ? ? U interaction.7,8,16 This deduction was confirmed in the solid state by X-ray crystallography.The presence of the co-ordinated THF is also clear in the IR of 1 due to the presence of two broad and intense absorption bands at 1010 and 850 cm21.11 In the IR spectrum of 2 the presence of one very strong absorption band at 550 cm21, two strong bands at 690 and at 720 cm21 and a weak band at 1585 cm21 [n(C]] C)] confirms the presence of the triphenylphosphine oxide ligands.17 In the IR spectrum of 2 also appears a complex group of absorption bands between 1000 and 1170 cm21, with a profile and intensity much higher than observed in the same region for complex 1.However, the complexity of the spectrum in this region makes an accurate assignment of the n(P]] O) stretch diYcult. The 1H NMR spectrum of complex 1 in toluene-d8 presents at 27 8C one set of resonances for the dihydrobis(pyrazolyl)- borate and two resonances of equal intensity for the two THF molecules at d 1.5 (tBu), 23.3 (Me), 9.6 (H(4)), 215.7 (B–H), 11.2 (THF) and 6.8 (THF) in an area ratio of 18:6:2:2:8:8.Addition of THF to this solution shifts the two resonances observed at d 11.2 (THF) and 6.8 (THF) towards the frequencies for free THF, confirming the assignment and indicative of THF exchange. The pattern observed in the spectrum of 1 indicates magnetic equivalence of the pyrazolyl rings, of the two B– H protons and of the THF molecules co-ordinated to the metal center, which is not in agreement with the C1 symmetry found in the solid state.This indicates that some dynamic process is occurring in solution, which is common in complexes of felements with poly(pyrazoly)borates.3,4,18 By lowering the temperature, it was possible to slow down the dynamic process and the spectrum obtained at 250 8C is consistent with the solid state structure, presenting four resonances for the protons of the THF molecules, two distinct sets of resonances for the two magnetically diVerent pyrazolyl rings and two resonances of equal intensity for the protons co-ordinated to the boron atom (see Experimental section).The assignment of the resonances due to the pyrazolyl protons was based on their intensities andJ. Chem. Soc., Dalton Trans., 1999, 2015–2020 2017 the resonances due to the B–H protons were assigned based on their form. The two signals observed at 250 8C at d 266.5 and 236.6 were assigned to B–H ? ? ? U bridge and B–H terminal units, respectively, since the former is much broadened, certainly because of the influence of the paramagnetic uranium(III) center.The 1H NMR spectrum of complex 3 has one set of three broad resonances at d 13.2 (6 H), 6.5 (6 H) and 3.2 (6 H) for the protons of the pyrazolyl rings. The protons of the phenyl groups appear as five resonances integrating for six protons each at d 8.2, 8.1, 7.6, 7.5 and 6.9 (see Experimental section). The pattern indicates the magnetic equivalence of the pyrazolyl rings and the non-equivalence of the two individual phenyl groups on each boron atom.The observation of only five resonances, instead of six, for the phenyl groups is because the p-H protons of the two phenyl groups are accidentally degenerate. The pattern obtained is consistent with the structure found in the solid state and indicates therefore a rigid behaviour for the molecule at room temperature in solution. Molecular structures of [UI2{H(Ï-H)B(3tBu,5Me-pz)2}(THF)2] 1 and [UI2{H(Ï-H)B(3tBu,5Me-pz)2}(OPPh3)2] 2 The ORTEP drawings of [UI2{H(m-H)B(3tBu,5Me-pz)2}- (THF)2] 1 and [UI2{H(m-H)B(3tBu,5Me-pz)2}(OPPh3)2] 2 are shown in Figs. 1 and 2. Selected bond distances and angles are Fig. 1 An ORTEP drawing of complex 1 with atom numbering scheme. Thermal ellipsoids are drawn at the 40% probability level. Fig. 2 An ORTEP drawing of complex 2. Details as in Fig. 1. presented in Tables 2 and 3, respectively. In 1 and 2 the uranium atom is seven-co-ordinated by the two pyrazolyl nitrogens, by an agostic B–H ? ? ? U interaction, by two iodides and by two oxygen atoms of the neutral ligands.Not surprisingly, due to the diVerent nature of the ligands and also due to the tridentate bonding of the dihydrobis(pyrazolyl)borate ligand, the coordination geometry is not regular and assignment to one of the common seven-co-ordinate polyhedra (capped octahedron, monocapped trigonal prism and pentagonal bipyramid) is diYcult. Related seven-co-ordinated uranium(III) complexes are [UI2{HB(3,5Me2-pz)3}(THF)2], [UI{HB(3,5Me2-pz)3}2], [U{HB(3,5Me2-pz)3}2(THF)]1 and [UI3(THF)4].4,5,11,19 The complexes stabilized by the hydrotris(pyrazolyl)borate ligand display distorted capped octahedral geometries, but the triiodide displays a pentagonal bipyramidal geometry.Capped octahedral is also the co-ordination geometry that better describes the environment around the UIV in the sevenco- ordinated complexes [UCl3{HB(3,5Me2-pz)3}(THF)], [UCl3{HB(3,5Me2-pz)3}{OP(OEt)3}] and [UCl(OC6H5)2- {HB(3,5Me2-pz)3}(THF)].20–22 Apparently, the face capping nature of the h3-hydrotris(pyrazolyl)borate ligand and the presence of the methyl groups on the 3 position seems to impose a more or less distorted capped octahedral geometry.Another common feature of all the seven-co-ordinated complexes of UIII and UIV with one hydrotris(pyrazoly)borate is that the (pyrazolyl)borate is tridentate and the nitrogen atoms define one triangular face which is trans to the capped site.By analogy with other uranium complexes with one poly(pyrazolyl)borate ligand, specifically [UI2{HB(3,5Me2- pz)3}(THF)2], [UCl3{HB(3,5Me2-pz)3}(THF)], [UCl3{HB- (3,5Me2-pz)3}{OP(OEt)3}] and [UCl(OC6H5)2{HB(3,5Me2- pz)3}(THF)],4,20–22 the co-ordination geometry around the metal in 1 and 2 is tentatively defined as capped octahedral. In 1 the two staggered triangular faces are defined by N(1)–N(2)–I(1) and I(2)–O(1)–H(1A), respectively. The N(1)–N(2)–I(1) face is capped by the O(2) atom of one tetrahydrofuran (Figs. 1 and 3). In 2 the staggered triangular faces are defined by N(1)–N(2)– Fig. 3 View of complex 1 emphasizing the conformation of the UN4B chelate ring and the B–H ? ? ? U agostic interaction; all the carbon atoms are omitted for clarity. Fig. 4 View of complex 2 as in Fig. 3.2018 J. Chem. Soc., Dalton Trans., 1999, 2015–2020 Table 1 Crystal data for [UI2{H(m-H)B(3tBu,5Me-pz)2}(THF)2]?THF 1, [UI2{H(m-H)B(3tBu,5Me-pz)2}(OPPh3)2]?2C6H5Me 2 and [U{Ph2- B(pz)2}3]?1.5C6H5Me 3 Formula M Crystal system Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 T/K Z Dc/g cm23 l(Mo-Ka)/Å m/mm21 No.reflections measured No. unique reflections R1 [I > 2s(I)] wR2 [I > 2s(I)] 1 C24H44BI2N4O2U?C4H8O 995.38 Orthorhombic P212121 10.386(1) 13.115(1) 26.556(2) 3617.3(5) 293 4 1.828 0.71073 6.225 5512 5247 0.0724 0.1003 2 C52H58BI2N4O2P2U?2C7H8 1519.87 Monoclinic P21/n 17.950(3) 19.866(3) 18.793(2) 96.894(12) 6653(2) 293 4 1.517 0.71073 3.459 9576 9070 0.1004 0.1902 3 C54H48B3N12U?1.5C7H8 1273.71 Triclinic P1� 13.565(1) 15.715(2) 15.929(2) 118.957(9) 92.650(11) 97.36(2) 2923.7(6) 293 2 1.447 0.71073 2.828 9397 8202 0.0501 0.1161 O(1) and I(1)–O(2)–H(1A), with the first face capped by the I(2) atom (Figs. 2 and 4). In both complexes the capped and uncapped triangular faces are not parallel and are inclined by 18.5 and 7.78 for 1 and 2, respectively. The stereochemistry of a homoleptic ML7 complex with capped octahedral geometry can be defined by the two spherical angles formed by the metal– ligand vectors and the capping ligand.23 The calculated parameters are 74.6 and 130.38.23 For 1 these parameters are the angles O(2)–U–N(1), O(2)–U–N(2), O(2)–U–I(1), O(2)–U–O(1), O(2)– U–I(2) and O(2)–U–H(1A) which are respectively, 74.1(5), 74.3(6), 83.6(4), 134.6(5), 148.2(3) and 110.98.For 2 the angles I(2)–U–N(1), I(2)–U–N(2), I(2)–U–O(1), I(2)–U–O(2), I(2)–U– I(1) and I(2)–U–H(1A) are 84.8(4), 83.9(5), 79.5(4), 139.5(3), 129.31(6) and 132.38, respectively. These angles average to 77.3 and 131.28 for 1 and 82.7 and 133.78 for 2.Compound 2 experiences the greatest distortion from the regular capped octahedral geometry, and the values found for 2 can only be compared to the values found for the uranium(III) complex [UI2{HB(3,5Me2- pz)3}(THF)2] (82.1 and 134.88), also described as capped octahedral. 19 In terms of these parameters, compound 1 is more comparable to the CO geometry in the uranium(IV) complexes [UCl3{HB(3,5Me2-pz)3}(THF)] (74.6, 134.9), [UCl3{HB- (3,5Me2-pz)3}{OP(OEt)3}] (75.8, 135.4) and [UCl(OC6- H5)2{HB(3,5Me2-pz)3}(THF)] (74.2, 135.3).20–22 Distortions from the ideal capped octhaedral geometry in 1 and 2 are also manifested in both interatomic angles and distances (Tables 2 and 3).In complex 1 the U–N bond distances are comparable, U–N(1) 2.55(2) and U–N(2) 2.50(2) Å, with a mean value of Table 2 Selected bond lengths (Å) and angles (8) for [UI2{H(m-H)- B(3tBu,5Me-pz)2}(THF)2]?THF 1 U–I(1) U–I(2) U–N(1) U? ? ?B I(1)–U–I(2) I(1)–U–N(1) I(1)–U–N(2) I(2)–U–N(1) I(2)–U–N(2) I(1)–U–O(1) I(1)–U–O(2) I(2)–U–O(1) O(2)–U–H(1A) 3.104(2) 3.132(2) 2.55(2) 3.19 91.59(6) 126.7(4) 128.2(4) 130.8(4) 84.6(5) 89.7(4) 83.6(4) 76.5(3) 110.9 U–N(2) U–O(1) U–O(2) U? ? ? H(1A) I(2)–U–O(2) N(1)–U–N(2) O(1)–U–O(2) N(1)–U–O(1) N(1)–U–O(2) N(2)–U–O(1) N(2)–U–O(2) N(11)–B–N(21) 2.50(2) 2.51(2) 2.584(12) 2.79 a 148.2(3) 91.4(6) 134.6(5) 74.6(6) 74.1(5) 138.2(6) 74.3(6) 113(2) a This parameter was calculated using a B–H bond distance of 1.01 Å. 2.53(2) Å and the N(1)–U–N(2) bond angle is 91.4(6)8. In complex 2 the average U–N [U–N(1) 2.61(2) and U–N(2) 2.58(2) Å] bond distance and the N(1)–U–N(2) bond angle are 2.60(2) Å and 85.1(6)8, respectively. Comparing these values we can say that in 2 they are, respectively, larger and smaller than in complex 1. The short B ? ? ? U distances of 3.19 and 3.11 Å in 1 and 2 indicate a B–H ? ? ? U interaction, stronger in complex 2 than in 1 (Figs. 3 and 4).This stronger B–H ? ? ? U and the presence of two bulky OPPh3 ligands in 2 are presumably responsible for the increase in the U–N bond distances and for the decrease in the N–U–N bond angle found in 2. The agostic interaction observed in both complexes is manifest in a short U ? ? ? B separation and also in the folding of the six-membered UN4B ring into a “twisted-boat” conformation (Figs. 3 and 4). The folding of the rings is quite pronounced, with dihedral angles between the UN(1)N(2) and the N(11)BN(21) planes of 86.1 and 74.18, in 1 and 2, respectively. The smaller dihedral angle in 2 indicates a greater bending of the ring which enables the B–H bond to approach closer the U atom than in 1. The distorted nature of the UN4B rings is also shown in the U–N–N–B torsional angles U–N(1)–N(11)–B, U–N(2)–N(21)–B: 1, 214 and 22; 2, 7 and 168. Agostic interactions involving dihydrobis- (pyrazolyl)borates and UIII have also been previously observed.For [U{H2B(pz)2}3(THF)] (ten-co-ordinated) and [U{H2B- (3,5Me2-pz)2}3] (nine-co-ordinated) the solid state structures indicated three-center agostic U ? ? ? H–B bonding interactions and U ? ? ? B separations that average to 3.42 and 3.20 Å, respectively.7,8 It is diYcult to compare these values with the Table 3 Selected bond lengths (Å) and angles (8) for [UI2{H(m-H)- B(3tBu,5Me-pz)2}(OPPh3)2]?2C6H5Me 2 U–I(1) U–I(2) U–N(1) P(1)–O(1) U? ? ?B I(1)–U–I(2) N(1)–U–N(2) O(1)–U–O(2) I(1)–U–N(1) I(1)–U–N(2) I(1)–U–O(1) I(1)–U–O(2) I(2)–U–N(1) I(2)–U–N(2) 3.164(2) 3.199(2) 2.61(2) 1.50(2) 3.11 129.31(6) 85.1(6) 79.6(5) 80.7(4) 141.8(5) 85.8(4) 83.0(3) 84.8(4) 83.9(5) U–N(2) U–O(1) U–O(2) P(2)–O(2) U? ? ? H(1A) I(2)–U–O(2) N(1)–U–O(1) N(1)–U–O(2) N(2)–U–O(1) N(2)–U–O(2) U–O(1)–P(1) U–O(2)–P(2) O(1)–U–H(1A) I(2)–U–O(1) 2.58(2) 2.36(2) 2.351(14) 1.52(2) 2.62 a 139.5(3) 145.6(6) 129.3(6) 123.0(6) 79.0(5) 159.8(10) 168.7(9) 146.2 79.5(4) a This parameter was calculated using a B–H bond distance of 1.01 Å.J.Chem. Soc., Dalton Trans., 1999, 2015–2020 2019 ones fnd for 1 and 2 and to discuss steric or electronic eVects, since the complexes have diVerent co-ordination numbers. In complex 1 one iodide ligand occupies an axial coordination site with a U–I(1) bond distance 3.104(2) Å, while the other iodide lies in the equatorial plane with U–I(2) 3.132(2) Å. In 2 there are also two types of U–I bonds: one occupies the capping position [U–I(2) 3.199(2) Å] and the other lies in the equatorial plane [U–I(1) 3.164(2) Å].These relatively diVerent bond lengths may be compared to those found in 1, where a weak B–H ? ? ? U interaction exists and where the less bulky tetrahydrofuran ligands are co-ordinated. Although the diVerence between the U–I distances in 1, 2 and [UI3(THF)4] 11 makes the averaging somewhat artificial, some trends in U–I distances can be detected by comparing the average values: 3.13(3) ([UI3(THF)4]) ª 3.118(2) (1) <3.182(2) Å (2).This can be interpreted as showing that a h3-{H2B(3tBu,5Me-pz)2} ligand occupies somewhat the same space as one iodide and two THF ligands. As referred to above it is clear that replacing two THF molecules by two OPPh3 ligands in 2 causes more congestion around the metal center, resulting in longer U–I and U–N bond distances. The two THF ligands in complex 1 occupy diVerent positions: one lies in the equatorial position [U–O(1) 2.51(2) Å] and the other is capping the triangular face defined by N(1)–N(2)– I(1) [U–O(2) 2.584(12) Å].The shorter U–O bond distance compares with the average of 2.52(1) Å found in [UI3(THF)4],11 but the oxygen atom of the THF in the capping site is at a longer distance from the metal. The two co-ordinated THF ligands are in their normal twisted conformation. In complex 2 the two U–O bond distances are comparable with a mean value of 2.36(2) Å, but are shorter than the U–O [2.389(6) Å] distance found in [U{MeC5H4}3(OPPh3)].24 This diVerence is reasonable considering the larger co-ordination number (10) of the cyclopentadienyl complex.The U–O–P bond angles in 2 are relatively diVerent, U–O(1)–P(1) 159.8(10) and U–O(2)–P(2) 168.7(9)8. These values compare with the almost linear angle observed in [U{MeC5H4}3(OPPh3)] (162.8(4)8).24 The diVerence of 8.98 observed for the U–O–P angle in the two phosphine oxides in 2 is certainly related to steric reasons.The O(2)PPh3 ligand occupies an equatorial position, as well as the two pyrazolyl rings (Fig. 4). In this complex, as discussed above, there is a strong B–H ? ? ?U interaction, which results in a buckling of the six-membered UN4B ring. This buckling causes the 3tBu group of the pyrazolyl ring to move towards the phosphine ligand and certainly forces the linearization of the U–O(2)–P(2) bond (Fig. 4). To compare the structural data of complexes 1 and 2 with those of other compounds stabilized by pyrazolylborates of this type is diYcult, as these are the only examples known of uranium complexes stabilized by one dihydrobis(pyrazolyl)- borate ligand that have been structurally characterized. Solid state structures are only known for complexes of uranium-(IV) and -(III) with one hydrotris(pyrazolyl)borates.3–5,19 Molecular structure of [U{Ph2B(pz)2}3] 3 Compound 3 in the solid state is composed of discrete [U{Ph2- B(pz)2}3] molecules.An ORTEP drawing is shown in Fig. 5. Selected bond distances and angles are presented in Table 4. The uranium atom is co-ordinated to a pair of nitrogens from each of the three bidentate {Ph2B(pz)2} ligands. The six nitrogen donors of the poly(pyrazolyl)borates define a trigonal prismatic co-ordination geometry around the metal center, with the bidentate ligands spanning the three vertical edges between the two triangular faces.The two triangular faces of the prism are defined by N6–N2–N3 and by N1–N4–N5, respectively. These faces are almost parallel and the angle between the planes is 0.48. The distortion of the trigonal prism is not signifi- cant compared to the regular polyhedron of rigorous D3h symmetry. In the related complex [U{H2B(3,5Me2-pz)2}3] 7 the solid state structure has approximate C3h molecular symmetry with the bidentate ligands also spanning the three vertical edges between triangular faces of the trigonal prism.However, for [U{H2B(3,5Me2-pz)2}3] the angles between the two triangular faces are 2.83 and 2.958 for molecules 1 and 2. These values are larger than the value 0.48 found in 3, a diVerence that is certainly due to the presence of U ? ? ? H–B agostic interactions in [U{H2B(3,5Me2-pz)2}3] as well as the methyl groups in the 3 and 5 positions of the pyrazolyl rings. In complex 3 there is no interaction between the uranium and the nearest phenyl group, evident from the long bond distances U? ? ? B(1), U ? ? ? B(2), U ? ? ? B(3) of 3.763, 3.841 and 3.848 Å, respectively.The dihedral angles between the two phenyl groups of each ligand are 72.1, 74.8, and 75.58, respectively. The U–N bond distances are comparable, with a mean value of 2.53(3) Å. This value is shorter than the average values 2.59(2) and 2.58(3) Å found in the previously characterized analogous [U{H2B(pz)2}3(THF)] (ten-co-ordinated) and [U{H2B(3,5Me2- pz)2}3] (nine-co-ordinated), respectively.7,8 Complex 3 is sixco- ordinated and this must be the reason why its U–N bond distances are shorter.Concluding remarks The use of a bulky dihydrobis(pyrazolyl)borate has allowed the preparation of the first mono-dihydrobis(pyrazolyl)borate uranium(III) complexes, [UI2{H(m-H)B(3tBu,5Me-pz)2}- (THF)2] 1 and [UI2{H(m-H)B(3tBu,5Me-pz)2}(OPPh3)2] 2. The infrared spectra of 1 and 2, the 1H NMR static spectra of 1 and the crystal structures of 1 and 2 (short U ? ? ? B distances and Fig. 5 An ORTEP drawing of complex 3 with atom numbering scheme. Thermal ellipsoids are drawn at the 50% probability level. Table 4 Selected bond lengths (Å) and angles (8) for [U{Ph2B- (pz)2}3]?1.5C6H5Me 3 U–N(1) U–N(2) U–N(3) N(1)–U–N(2) N(3)–U–N(4) N(5)–U–N(6) N(1)–U–N(3) N(1)–U–N(4) N(1)–U–N(5) N(1)–U–N(6) N(2)–U–N(3) N(2)–U–N(4) 2.518(7) 2.531(6) 2.487(7) 73.6(2) 73.6(2) 73.2(2) 132.3(2) 84.4(2) 91.0(2) 134.3(2) 95.1(2) 137.9(2) U–N(4) U–N(5) U–N(6) N(2)–U–N(6) N(3)–U–N(5) N(3)–U–N(6) N(4)–U–N(5) N(4)–U–N(6) N(5)–U–N(6) av.N–B–N av. N–B–C N(2)–U–N(5) 2.569(7) 2.497(7) 2.558(7) 83.0(2) 128.2(2) 87.7(2) 86.7(2) 135.1(2) 73.2(2) 108.3(7) 108(1) 128.2(2)2020 J. Chem. Soc., Dalton Trans., 1999, 2015–2020 buckling of the six-membered UN4B chelate ring) are consistent with an agostic B–H ? ? ? U interaction and indicate a tridentate co-ordination mode of the {H2B(3tBu,5Me-pz)2} ligand in these complexes.A large distortion of the coordination geometry is observed due to the symmetry of the ligand and the diVerent nature of the atoms around the metal. This is perhaps the reason why in 1 and 2 the capped face in the capped octahedral geometry is adjacent to the face defined by the h3-{H2B(3tBu,5Me-pz)2} ligand, and is not trans, as observed in the complexes of UIII or UIV of the h3-{HB(3,5Me2- pz)3} ligand. By using the diphenylbis(pyrazolyl)borate ligand it was possible to avoid agostic interactions and the sixco- ordinated trigonal prismatic complex [U{Ph2B(pz)2}3] was isolated.Acknowledgements The work at ITN was partially supported by PRAXIS XXI (2/2.1/QUI/454/94) and the work at Berkeley was supported by the Director, OYce of Energy Research, OYce of Basic Energy Sciences, Chemical Sciences Division of the U. S. Department of Energy under Contract No. DE-ACO3-765F00098. I. S. and R. A. thank FLAD for travelling financial support.L. M. and M. P. C. thank PRAXIS XXI for BIC and Ph.D. research grants, respectively. References 1 S. Trofimenko, Chem. Rev., 1993, 93, 943; G. Parkin, Adv. Inorg. Chem., 1995, 42, 291. 2 N. Kitajima and W. B. Tolman, Prog. Inorg. Chem., 1995, 43, 419; D. L. Reger, Coord. Chem. Rev., 1996, 147, 571. 3 I. Santos and N. Marques, New J. Chem., 1995, 19, 551; M. Etienne, Coord. Chem. Rev., 1997, 156, 201. 4 Y. Sun, R. McDonald, J. Takats, V. W. Day and T. A. Eberspacher, Inorg.Chem., 1994, 33, 4433. 5 Y. Sun, R. McDonald, J. Takats, V. W. Day and T. A. Eberspacher, J. Alloys Compd., 1994, 213. 6 A. J. Amoroso, J. C. JeVery, P. L. Jones, J. A. McCleverty, L. Rees, A. L. Rheingold, Y. Sun, J. Takats, S. Trofimenko, M. D. Ward and G. P. A. Yap, J. Chem. Soc., Chem. Commun., 1995, 1881. 7 A. Carvalho, A. Domingos, P. Gaspar, N. Marques, A. Pires de Matos and I. Santos, Polyhedron, 1992, 11, 1481. 8 Y. Sun, J. Takats, V. W. Day and T. A. Eberspacher, Inorg. Chim. Acta, 1995, 229, 315. 9 S. Trofimenko, J. Am. Chem. Soc., 1967, 88, 6288. 10 S. Trofimenko, J. Calabrese and J. S. Thompson, Inorg. Chem., 1987, 26, 1507. 11 D. L. Clark, A. P. Sattelberger, S. G. Bott and R. N. Vrtis, Inorg. Chem., 1989, 28, 1771; L. R. Avens, S. G. Bott, D. L. Clark, A. P. Sattelberger, J. G. Watkin and B. D. Zwick, Inorg. Chem., 1994, 33, 2248. 12 C. K. Fair, MOLEN, Enraf-Nonius, Delft, 1990. 13 G. M. Sheldrick, SHELXS 86, Program for Solution of Crystal Structure, University of Göttingen, 1986. 14 G. M. Sheldrick, SHELXL 93, Program for Crystal Structure Refinement, University of Göttingen, 1993. 15 C. K. Johnson, ORTEP II, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 16 D. L. Reger, J. A. Lindeman and L. Lebioda, Inorg. Chem., 1988, 27, 1890. 17 D. Dalphin and A. E. Wick, Tabulation of Infrared Spectral Data, Wiley, New York, 1977. 18 X. Zhang, R. McDonald and J. Takats, New J. Chem., 1995, 19, 573. 19 Y. Sun, Ph.D. Thesis, University of Alberta, 1995. 20 R. G. Ball, F. Edelmann, J. G. Matisons, J. Takats, N. Marques, J. Marçalo, A. Pires de Matos and K. W. Bagnall, Inorg. Chim. Acta, 1987, 132, 137. 21 R. Maier, J. Müller, B. Kanellakopulos, C. Apostolides, A. Domingos, N. Marques and A. Pires de Matos, Polyhedron, 1993, 12, 2801. 22 A. Domingos, J. Marçalo, N. Marques, A. Pires de Matos, J. Takats and K. W. Bagnall, J. Less Common Met., 1989, 149, 271. 23 D. L Kepert, Inorganic Stereochemistry, Springer, Berlin, Heidelberg, 1982, vol. 6, p. 117. 24 J. G. Brennan, R. A. Andersen and A. Zalkin, Inorg. Chem., 1986, 25, 1761. Paper 9/00744J

ISSN:1477-9226    

DOI:10.1039/a900744j

出版商:RSC    

年代:1999

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2017–2021 2017 Synthetic and electrochemical studies of some metal complexes of 1,3,5-triethynylbenzene Nicholas J. Long,*,a Angela J. Martin,a Fabrizia Fabrizi de Biani b and Piero Zanello b a Department of Chemistry, Imperial College of Science, Technology and Medicine, South Kensington, London, UK SW7 2AY b Dipartimento di Chimica dell’ Università di Siena, Pian dei Mantellini 44, I-53100, Siena, Italy A series of compounds featuring metallic fragments around the periphery of a 1,3,5-triethynylbenzene core have been synthesized.By using several synthetic methods, metallic units such as cis-[RuCl2(dppm)2], cis-[OsCl2- (dppm)2] and [RuCl(h-C5H5)(PPh3)2] have been treated with the aromatic acetylide ligand to introduce one, two or three metallic centres. Electrochemical studies showed that the bimetallic trans-[HC]] ] CC6H3{C]] ] CRuCl(dppm)2}2] and trans-[HC]] ] CC6H3{C]] ] COsCl(dppm)2}2] species undergo two separated one-electron oxidations thus indicating that the central triethynylbenzene unit allows communication between the two peripheral metal subunits.The compounds [(HC]] ] C)2C6H3C]] ] CRu(h-C5H5)(PPh3)2], [HC]] ] CC6H3{C]] ] CRu(h-C5H5)(PPh3)2}2] and [C6H3{C]] ] CRu(h-C5H5)(PPh3)2}3] each show separated one-electron oxidations (though these are less reversible than for the previous compounds mentioned) again demonstrating the electronic communication amongst the peripheral metal centres through the organic linkage.Chemical oxidation has been carried out on the [Ru(h-C5H5)(PPh3)2]-containing species aVording mixed-valence species consistent with those produced by successive electrochemical oxidation. Carbon-rich organometallics containing rigid p-conjugated chains are of increasing interest due to their uses in the syntheses of unsaturated organic species,1 organometallic polymers2 and p-conjugated bi- or multi-metallic systems.3 A central triethynylbenzene core is of particular interest due to its geometry and its active co-ordination sites.This enables simple dehydrohalogenation reactions to be used in order to extend the core in three directions thus building up a first generation dendrimer.4 Other recent examples featuring this core unit have involved the incorporation of [Fe(h-C5Me5)(dppe)],5 [IrCl(PPh3)2(CO)(MeCN)],6 [Cr(h-C6H6)(CO)3],7 [Ru(bpy)2- (phen)]21,8 [Au(PR3)] 9 and [PtCl(XBun 3)2] (X = P or As)3h around the periphery of the organic ligand, in order to probe the ability of the metal to participate in p delocalisation, as well as the potential for interaction of the metal d orbitals with the conjugated p orbitals of the organic moiety.In particular, metal acetylide complexes have attracted interest as precursors to molecules containing delocalised p systems and additionally allow communication between co-ordinated metal centres.10 These studies aim to exploit the electronic- and photonic-based co-operation between individual transition metal subunits of a molecular assembly having a delocalised p backbone and the complexes are predicted to find applications in the areas of molecular devices,11 organometallic polymers,2,12 non-linear optics 13 and molecular electronics.11,14,15 Utilisation here of the reaction of terminal alkynes with halide-bearing metal complexes via several synthetic routes has resulted in the isolation and characterisation of seven new compounds.The complexes discussed herein form a series of novel precursors for the production of metal–aromatic polyyne networks. Results and Discussion Synthesis The multinuclear s-acetylide complexes synthesized were of the type (XC]] ] C)3C6H3 {X = H, trans-[RuCl(dppm)2], trans-[OsCl- (dppm)2] or [Ru(h-C5H5)(PPh3)2]} using the versatile starting material 1,3,5-triethynylbenzene and the relevant metal fragments (Scheme 1). A high level of purity of the starting materials ensured that the yellow, microcrystalline products were isolated in reasonable to good yields, depending on the synthetic method employed.All eVorts to produce X-ray quality crystals failed due to the instability of the products in solution over prolonged periods. For the trans-[MCl(dppm)2] complexes the preferred synthetic method was one elucidated by Dixneuf and co-workers,10j modified in the Experimental section. Importantly, the dichlorides used oVer two reactive sites and therefore have potential to form oligomeric and polymeric structures 10b based around a trisubstituted benzene unit.The monosubstituted species, trans-[(HC]] ] C)2C6H3C]] ] CRu(dppm)2Cl] 1 and trans-[(HC]] ] C)2- C6H3C]] ] COs(dppm)2Cl] 3 were formed in good yields of 63% and 50% respectively with the 1 : 1 stoichiometry of reactants reducing the number of possible by-products and side reactions. The reaction times of 4 (Ru) and 8 h (Os) were relatively Scheme 1 Synthesis of complexes 1–7.(a) CH2Cl2, cis-[RuCl2- (dppm)2], NaPF6, 1,8-diazabicyclo[5.4.0]undec-7-ene (dbu); (b) CH2Cl2, cis-[OsCl2(dppm)2], NaPF6, dbu; (c) method (i) CH2Cl2, NH4PF6, [RuCl(h-C5H5)(PPh3)2], dbu; (d) method (ii) MeOH, [RuCl- (h-C5H5)(PPh3)2], reflux, Na X X X Ph2P PPh2 PPh2 Ph2P Cl X = 3 x H X = 1 x Ru¢, 2 x H (1) X = 2 x Ru¢, 1 x H (2) X = 1 x Os¢, 2 x H (3) X = 2 x Os¢, 1 x H (4) X = 1 x Ru(C5H5)(PPh3)2 , 2 x H (5) X = 2 x Ru(C5H5)(PPh3)2 , 1 x H (6) X = 3 x Ru(C5H5)(PPh3)2 (7) (c) Method (i) (d) Method (ii) (a) (b) M¢ = M2018 J.Chem. Soc., Dalton Trans., 1998, Pages 2017–2021 short in comparison to those for the disubstituted species trans- [HC]] ] CC6H3{C]] ] CRu(dppm)2Cl}2] 2 and trans-[HC]] ] CC6H3- {C]] ] COs(dppm)2Cl}2] 4 which featured reaction times of ca. 24 h and lower yields of 20 (Ru) and 30% (Os). This may be accounted for by cross-coupling reactions of the starting materials (facilitated by longer reaction times) or by the instability of intermediates or products in solution.Surprisingly, all attempts to form the trisubstituted metal acetylide species were unsuccessful using these methods and instead resulted in the isolation of the disubstituted species with reduced yields and purity. The mono-, di- and tri-substituted species, [(HC]] ] C)2- C6H3C]] ] CRu(h-C5H5)(PPh3)2] 5, [HC]] ] CC6H3{C]] ] CRu(h-C5H5)- (PPh3)2}2] 6 and [C6H3{C]] ] CRu(h-C5H5)(PPh3)2}3] 7, respectively, were formed in good yields (60–66%) by the reaction of [RuCl(h-C5H5)(PPh3)2] with 1,3,5-triethynylbenzene in refluxing methanol followed by the addition of sodium metal.This methodology, adapted from that of Field et al.,3p was preferred over the method illustrated above, as the latter only produced the mono- (5) and di-substituted (6) forms in low yields of 20 and 17% respectively. However, the method using sodium metal could not be employed to form complexes 1–4 as both chlorides would be activated encouraging the formation of species such as [(HC]] ] C)2C6H3(C]] ] C)M(dppm)2(C]] ] C)C6H3(C]] ] CH)2] and higher nuclearity materials instead of the desired products. Chemical oxidation of 6 and 7 using ferrocenium hexafluorophosphate as oxidising agent in dry dichloromethane resulted in the isolation of [HC]] ] CC6H3{C]] ] CRu(h-C5H5)(PPh3)2}2][PF6] 8 (after single oxidation of 6), [C6H3{C]] ] CRu(h-C5H5)- (PPh3)2}3][PF6] 9 and [C6H3{C]] ] CRu(h-C5H5)(PPh3)2}3][PF6]2 10 (after single and double oxidations of 7 respectively).During the reactions an associated colour change was observed of yellow to dark green for all the mixed-valence species formed. The complexes were characterised by IR and NMR spectroscopies. The IR spectra show a typical absorption for the carbon–carbon triple bond in the range 2063–2071 cm21 for 1–7 which represents a useful monitoring tool as there is a signifi- cant shift in frequency from the free alkyne [n(C]] ] C) 2114 cm21].The C]] ] C stretching values are consistent with those observed for similar metal acetylide complexes 4,5 and furthermore formation of the trinuclear species 7 could be followed to completion by disappearance of the C]] ] C]H band (3302 cm21). The IR spectra for the mixed-valence compounds 8–10 illustrated both the stretching frequencies for the oxidised [n(]] C]] C]] ) 1970–1980 cm21] and non-oxidised [n(C]] ] C)] sites within the molecules.16 The 1H NMR spectra (CDCl3) of complexes 1–7 exhibit resonances characteristic of the CH2 group in the bridging phosphine (d 4.9), the acetylenic proton (when present) (d 2.9) as well as a complicated series of multiplets for the aromatic protons of the phenyls present (d 7.0–7.6).The 31P-{1H} NMR of all the complexes showed a singlet indicative of equivalent phosphine environments and this is consistent with the trans geometry of the dppm ligands in 1–4 and of the equivalence of the PPh3 ligands for 5–7.The 1H NMR spectra of 8–10 showed a significant broadening of the resonances detailed above, but the 31P-{1H} NMR of each species showed two singlets indicative of the oxidised and non-oxidised sites at ca. d 42.5 and 51.1 respectively as well as a septet centred at d 2143.6 characteristic of the counter anion PF6 2. Electrochemistry Fig. 1 shows the redox behaviour of complexes 1 and 2 in CH2Cl2 solution. In contrast to the precursor cis-[RuCl2- (dppm)2], which exhibits an oxidation process followed by chemical complications,17 the oxidation of 1 involves a chemically and electrochemically reversible one-electron transfer.In fact, controlled potential coulometry (Ew = 10.7 V) consumes one electron per molecule and the resulting solution displays a cyclic voltammetric profile quite complementary to the original one; in addition, analysis 18 of the cyclic voltammetric responses with scan rate varying from 0.02 to 1.00 V s21 shows that: (i) the ipc : ipa ratio is equal to 1 : 1 throughout; (ii) the current function ipa/n� �� remains virtually constant, decreasing by less than 10% for a ten-fold increase in scan rate; (iii) the peak-to-peak separation slightly increases from 70 to 90 mV.Upon exhaustive oxidation the original yellow solution turns green, and in the visible region displays a band at lmax = 597 nm (absorption coeYcient e = 3.9 × 103 M21 cm21) and a broad band at lmax = 820 nm (too broad to obtain the absorption coeYcient), attributable to metal to ligand charge transfer. Complex 2 displays two sequential one-electron oxidations, which are chemically and electrochemically reversible.Both the first exhaustive one-electron oxidation (Ew = 10.35 V) and the subsequent one (Ew = 10.7 V) turn the original yellow solution green. In both cases, similar bands to those cited above, at lmax = 596 nm (e = 4.7 × 103 M21 cm21) and 825 nm, are displayed.Owing to our spectrophotometric upper limit of 1100 nm we were unable to detect the likely presence of the charge transfer band of the mixed valent monocation [2]1. It must be taken into account that the larger the Kcom (comproportionation constant = 16.9DE2� 1 ) value the higher is the wavelength of the intervalence charge transfer.15 The formal electrode potentials of all these redox changes are listed in Table 1. It is clear that replacing the one electron-withdrawing chlorine atom of cis-[RuCl2(dppm)2] with the triethynylbenzene fragment not only facilitates the RuII–RuIII oxidation, indicating that it acts Fig. 1 Cyclic voltammetric responses recorded at a platinum electrode on a CH2Cl2 solution containing [NBu4][PF6] (0.2 M) and complexes 1 (6 × 1024) (–––) and 2 (6 × 1024 M) (——). Scan rate 0.2 V s21 Table 1 Formal electrode potentials (in V, vs. SCE) and peak-to-peak separations (in mV) exhibited by the triethynylbenzene complexes of RuII and OsII and related species in CH2Cl2 solution Complex cis-[RuCl2(dppm)2] 12 1A 2A cis-[OsCl2(dppm)2] 34[ Ru(h-C5H5)(PPh3)2Cl] 567 f E890/1 10.75 10.79 10.41 10.26 10.49 10.15 10.60 10.64 10.19 10.05 10.52 10.60 10.48 10.32 10.22 DEp a 74 — 81 76 90 c 80 c 64 — 84 59 109 — 261 d ee E890/21 10.46 10.51 10.23 10.48 10.35 DEp a 76 80 c 67 ee Ref.b 17 bb 10( g) 10( g) b 17 bbb 19 bbb a Measured at 0.2 V s21, in mV. b Present work. c Measured at 0.1 V s21. d Quasi-reversible process followed by irreversible chemical reactions.e Peak-to-peak separation not well defined. f E890/31 1 0.50 V, see footnote e.J. Chem. Soc., Dalton Trans., 1998, Pages 2017–2021 2019 as an electron donating group, but also results in a more stable ruthenium(III) species than that resulting from the oxidation of cis-[RuCl2(dppm)2]. Similar behaviour was observed for the related 1,4-diethynylbenzene complexes [HC]] ] CC6H4C]] ] CRu(dppe)2Cl] 1A and [Cl(dppe)2RuC]] ] CC6H4C]] ] CRu(dppe)2- Cl] 2A.10g The fact that the diruthenium complex 2 exhibits two separated one-electron oxidations shows that the central triethynylbenzene units allow communication between the two peripheral ruthenium subunits.The separation between the two oxidation processes (DE89 = 0.20 V) allows a Kcom of 2.4 × 103 to be calculated, which testifies that the mixed-valence RuII–RuIII monocation belongs to the slightly delocalised Robin-Day’s Class II. It should be noted that the electronic communication between the two ruthenium centres through the triethynylbenzene unit is perhaps surprising in that we have recently found that complexes 1-bromo-3,5-bis(ethynylferrocenyl) benzene and 1,3,5-tris(ethynylferrocenyl)benzene undergo single-stepped two- and three-electron oxidations, respectively. 4 This datum, however, is consistent with for example Dixneuf’s observation that the communication between metal centres through a bridging unit is aVected by the nature of either the bridge or the terminal metal fragments.10g The osmium analogues cis-[OsCl2(dppm)2] 3 and 4 show similar electrochemical responses to those discussed above for the ruthenium species except that, as previously reported,17 cis-[OsIICl2(dppm)2] undergoes a chemically reversible oneelectron oxidation. Exhaustive oxidation of cis-[OsIICl2- (dppm)2] to cis-[OsIIICl2(dppm)2]1 turns the original yellow dichloromethane solution violet and displays a broad absorption band in the range from 510 to 750 nm.The electrochemical characteristics of the osmium complexes are included in Table 1. In agreement with previous findings on related species,17,20,21 the OsII–OsIII redox change is easier than the RuII–RuIII one. As far as the oxidation of complexes 3 and 4 is concerned, the green solutions of [3]1 and [4]1 exhibit absorption bands at lmax = 700 and 710 nm respectively. In agreement with a brief, preliminary report,19 [RuCl- (h-C5H5)(PPh3)2] undergoes a chemically reversible oneelectron oxidation. The change from orange to pale orange which accompanies the electron removal causes a shoulder at 550 nm to appear in the original broad absorption located between 330 and 510 nm.The RuII–RuIII oxidation appears electrochemically quasi-reversible and suggests that some Fig. 2 Cyclic (a) and diVferential pulse (b) voltammetric responses recorded at a platinum electrode on a CH2Cl2 solution containing complex 7 (5 × 1024 M) and [NBu4][PF6] (0.2 M).Scan rates: (a) 0.2, (b) 0.004 V s21 significant structural reorganisation accompanies the electron removal. Progressive attachment of {Ru(C5H5)(PPh3)2} fragments results in decreasing stability of the cations. In fact, 5 undergoes a one-electron oxidation followed by fast chemical complications. On the other hand, 6 and 7 undergo separated two- and three-electron oxidations respectively, which in cyclic voltammetry have features of chemical reversibility but in the longer times of controlled potential coulometry are followed by complete decomposition of the electrogenerated cations.As an example, Fig. 2 shows the electrochemical profile exhibited by 7. This behaviour is rather reminiscent of that exhibited by the related tris-{Fe(C5H5)(dppe)} derivative,5 even if the latter exhibits fairly reversible FeII–FeIII oxidations, at least, on the cyclic voltammetric timescale. Despite the instability of complexes [6]21 and [7]31, as discussed above the appearance of separated one-electron oxidations is significant from the viewpoint of the electronic communication amongst the peripheral metal centres, when one considers that the tri(ethynylferrocene)- benzene anal not show communication between ferrocenyl subunits.4 Experimental General All preparations were carried out using standard Schlenk techniques. 22 All solvents were distilled over standard drying agents under nitrogen directly before use and all reactions were carried out under an atmosphere of nitrogen. All NMR spectra were recorded using a Delta upgrade on a JEOL 270 MHz spectrometer. Chemical shifts are reported in d using CDCl3 (1H d 7.25) as reference. Infrared spectra were recorded using NaCl solution cells (CH2Cl2) on a Mattson Polaris Fourier transform IR spectrometer, FAB (positive ion) mass spectra using an AutoSpec-Q mass spectrometer, 35 keV Cs1 primary ion beam and 3-nitrobenzyl alcohol as matrix (eV ª 1.60 × 10219 J).Microanalyses were carried out in the Department of Chemistry, Imperial College of Science, Technology and Medicine. Electrochemistry Anhydrous dichloromethane (packaged under nitrogen, 100 cm3 bottles, Aldrich) for electrochemistry and tetrabutylammonium hexafluorophosphate supporting electrolyte (dried and stored in a vacuum oven at 40 8C, Fluka) were commercial products. The cyclic voltammetric measurements were performed with a BAS 100A electrochemical analyser.23 A threeelectrode cell was designed to allow the tip of the saturated calomel electrode (SCE) to approach closely, via a Luggin capillary, the platinum disc working electrode, which in turn was surrounded by a platinum spiral counter electrode.Controlled potential coulometry was carried out by using a AMEL model 552 potentiostat, connected to a model 558 integrator. A threecompartment cell was designed with a central unit bearing a platinum gauze working macroelectrode.The lateral compartments contained the reference (SCE) and the auxiliary (mercury pool) electrodes, respectively. The compartments containing the working and the auxiliary electrodes were separated by a sintered-glass disc. In situ visible spectra of products electrogenerated by macroelectrolysis were recorded with a Lambda 2 Fibre Optic System UV/VIS spectrometer (Perkin-Elmer). Deoxygenation of the solutions was achieved by bubbling ultrapure nitrogen for at least 10 min.All the potential values are referred to the SCE and under the present experimental conditions the one-electron oxidation of ferrocene occurs at 10.35 V, displaying a peak-to-peak separation of 82 mV at 0.2 V s21. Synthesis The complexes cis-[RuCl2(dppm)2], cis-[OsCl2(dppm)2] and [RuCl(h-C5H5)(PPh3)2] were prepared by literature methods,242020 J. Chem. Soc., Dalton Trans., 1998, Pages 2017–2021 as was 1,3,5-triethynylbenzene 25 and ferrocenium hexafluorophosphate. 26 The complexes 1–7 were formed from the aforementioned species using the following general methods adapted from literature procedures.3p,10j Representative reaction to synthesize complexes 1–4. The ratio of the reagents and metal used varies, along with the reaction times, see Results and Discussion section. Freshly sublimed 1,3,5-triethynylbenzene (17.9 mg, 0.12 mmol) and cis-[RuCl2- (dppm)2] (112 mg, 0.12 mmol) were dissolved in CH2Cl2 (15 cm3). Sodium hexafluorophosphate (20 mg, 0.24 mmol) was then added and the mixture stirred for 4 h, during which time a yellow to red-orange change was observed.The solution was filtered to remove any excess of NaPF6 and NaCl by-product and dbu (2 drops) was added to the vinylidene solution and stirring continued for 2 h. The resulting yellow solution was filtered and the solvent removed in vacuo. The residue was redissolved in CH2Cl2–hexane and following slow solvent evaporation complex 1 was isolated as a fine yellow powder which was washed with cold hexane. This powder could be further purified by reprecipitation from a CH2Cl2–hexane two-layered system.Yield 78.8 mg (63%) (Found: C, 68.4; H, 4.5. C62H49ClP4Ru?CH2Cl2 requires C, 66.4; H, 4.5%); n& /cm21 (CH2Cl2) 2071 (C]] ] C) and 3300 (C]] ] C]H); dH(CDCl3) 8.0–7.0 (40 H, m, C6H5, C6H3), 4.93 (4 H, m, PCH2P) and 3.07 (2 H, s, C]] ] CH); dP(CDCl3) 25.9; m/z 1054 (M1), 1019, 905 and 869. trans-[HC]] ] CC6H3{C]] ] CRu(dppm)2Cl}2] 2.Yield 20 mg (20%) (Found: C, 66.8; H, 4.3. C112H92Cl2P8Ru2?CH2Cl2 requires C, 66.4; H, 4.7%); n& /cm21 (CH2Cl2) 2068 (C]] ] C) and 3304 (C]] ] C]H); dH(CDCl3) 8.0–7.0 (80 H, m, C6H5, C6H3), 4.93 (8 H, m, PCH2P) and 2.94 (1 H, s, C]] ] CH); dP(CDCl3) 25.7; m/z 1959 (M1), 1054, 905 and 869. trans-[(HC]] ] C)2C6H3C]] ] COs(dppm)2Cl] 3. Yield 93.0 mg (50%) (Found: C, 62.2; H, 3.9. C62H49ClOsP4?CH2Cl2 requires C, 61.6; H, 4.2%); n& /cm21 (CH2Cl2) 2066 (C]] ] C) and 3302 (C]] ] C]H); dH(CDCl3) 8.0–7.0 (40 H, m, C6H5, C6H3), 4.92 (4 H, m, PCH2P) and 3.05 (2 H, s, C]] ] CH); dP(CDCl3) 248.4; m/z 1145 (M1), 995, 959, 759, 573, 495, 417 and 375.trans-[HC]] ] CC6H3{C]] ] COs(dppm)2Cl}2] 4. Yield 53.0 mg (30%) (Found: C, 61.1; H, 4.3. C112H92Cl2Os2P8?CH2Cl2 requires C, 61.3; H, 4.2%); n& /cm21 (CH2Cl2) 2064 (C]] ] C) and 3304 (C]] ] C]H); dH(CDCl3) 8.0–7.0 (80 H, m, C6H5, C6H3), 4.90 (8 H, m, PCH2P) and 3.02 (1 H, s, C]] ] CH); dP(CDCl3) 247.0; m/z 2138 (M1), 2102, 1145, 1070 and 1023.Complexes 5–7. These were prepared using two methods adapted from literature procedures.3p,10a The first was similar to that described for complexes 1–4 but resulted in low yields of products (5, 20; 6, 17%) so the second method was preferred for 5–7. The complex [RuCl(h-C5H5)(PPh3)2] (121 mg, 0.17 mmol) was heated to reflux in methanol (20 cm3) for 15–20 min to give an orange-red suspension to which 1,3,5-triethynylbenzene (25 mg, 0.17 mmol) was then added.The mixture was stirred and heated to reflux for 20 min and then cooled to room temperature. Addition of 2–3 equivalents of sodium resulted in rapid precipitation of a yellow powder. The mixture was stirred for 1 h, filtered and the yellow solid washed with cold methanol. The product could be further purified by reprecipitation from a CH2Cl2–hexane two-layered system (84 mg, 60%) (Found: C, 70.2; H, 4.8. C53H40P2Ru?CH2Cl2 requires C, 70.1; H, 4.6%); n& /cm21 (CH2Cl2) 2063 (C]] ] C) and 3301 (C]] ] C]H); dH(CDCl3) 7.7– 6.9 (33 H, m, C6H5, C6H3), 4.36 (5 H, s, C5H5), 3.01 (1 H, s, C]] ] C]H) and 2.97 (1 H, s, C]] ] C]H); dP(CDCl3) 50.9; m/z 840 (M1), 691, 579, 501, 429 and 350.[HC]] ] CC6H3{C]] ] CRu(h-C5H5)(PPh3)2}2] 6. Yield 182 mg (60%) (Found: C, 70.9; H, 4.7. C93H74P4Ru2?CH2Cl2 requires C, 70.7; H, 4.7%); n& /cm21 (CH2Cl2) 2064 (C]] ] C) and 3302 (C]] ] C]H); dH(CDCl3) 7.7–6.9 (63 H, m, C6H5, C6H3), 4.34 (10 H, s, C5H5) and 3.01 (1 H, s, C]] ] C]H); dP(CDCl3) 51.0; m/z 1530 (M1) and 1267.[C6H3{C]] ] CRu(h-C5H5)(PPh3)2}3] 7. Yield 243 mg (66%) (Found: C, 71.0; H, 5.0. C135H108P6Ru3?CH2Cl2 requires C, 70.8; H, 4.8%); n& /cm21 (CH2Cl2) 2065 (C]] ] C); dH(CDCl3) 7.7–6.9 (93 H, m, C6H5, C6H3) and 4.34 (15 H, s, C5H5); dP(CDCl3) 51.3; m/z 2219 (M1), 1958, 1696, 1530 and 1171. Complexes 8–10. These were prepared by following a literature procedure 16 and the formation of complex 10 is detailed as a representative example. The complex [C6H3{C]] ] CRu- (h-C5H5)(PPh3)2}3] (40 mg, 0.018 mmol) was dissolved in dry CH2Cl2 (10 cm3) and the solution cooled to 278 8C.Ferrocenium hexafluorophosphate (10 mg, 0.036 mmol) was then added and on warming to room temperature a colour change was noted. The mixture was stirred at room temperature for 2 h and then reduced to dryness in vacuo. After washing with hexane (2 × 10 cm3) the product was isolated as a dark brown microcrystalline solid (27 mg, 60%).n& /cm21 (Nujol) 2059 (C]] ] C, non-oxidised site) and 1978 (]] C]] C]] , oxidised site); dP(CDCl3) 51.6, 42.5 (spt) and 2143.6. [HC]] ] CC6H3{C]] ] CRu(h-C5H5)(PPh3)2}2][PF6] 8. Yield 15 mg (60%); n& /cm21 (Nujol) 2060 (C]] ] C, non-oxidised site) and 1973 (]] C]] C]] , oxidised site); dP(CDCl3) 51.0, 42.3 (spt) and 2143.6. [C6H3{C]] ] CRu(h-C5H5)(PPh3)3}2][PF6] 9. Yield 18 mg (64%); n& /cm21 (Nujol) 2060 (C]] ] C, non-oxidised site) and 1972 (]] C]] C]] , oxidised site); dP(CDCl3) 51.3, 42.5 (spt) and 2143.6.Acknowledgements We thank the EPSRC for a studentship (to A. J. M.) and P. Z. gratefully acknowledges the financial support of Ministero dell’ Università e della Ricerca Scientifica e Tecnologica of Italy (quota 60%) and the technical support of Mrs. G. Montomoli. References 1 U. H. F. Bunz, Angew. Chem., 1994, 106, 1127; Angew. Chem., Int. Ed. Engl., 1994, 33, 1073; F. Diederich and Y.Rubin, Angew. Chem., 1992, 104, 1123; Angew. Chem., Int. Ed. Engl., 1992, 31, 1101; F. Diederich, Molecular Chemistry, NATO ASI Series, ed. J. Michl, Kluwer, Dordrecht, 1996; Modern Acetylene Chemistry, eds. P. J. 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Enkelmann, Organometallics, 1994, 13, 3823; (r) U. H. F. Bunz and J. E. C. Wiegelmann-Kreiter, Chem.J. Chem. Soc., Dalton Trans., 1998, Pages 2017–2021 2021 Ber., 1996, 129, 785 and refs. therein; (s) E.Viola, C. Lo Sterzo and F. Trezzi, Organometallics, 1996, 21, 4352; (t) M. I. Bruce, P. Hinterding, P. J. Low, B. W. Skelton and A. H. White, Chem. Commun., 1996, 1009. 4 H. Fink, N. J. Long, A. J. Martin, G. Opromolla, A. J. P. White, D. J. Williams and P. Zanello, Organometallics, 1997, 16, 2646. 5 T. Weyland, C. Lapinte, G. Frapper, M. J. Calhorda, J.-F. Halet and L. Toupet, Organometallics, 1997, 16, 2024. 6 R. R. Tykwinski and P. J. Stang, Organometallics, 1994, 13, 3203. 7 T. J. J. Müller and H. J. Lindner, Chem. Ber., 1996, 129, 607. 8 D. Tzalis and Y. Tor, Chem. Commun., 1996, 1043. 9 M. J. Irwin, L. Manojlovic-Muir, K. W. Muir, R. J. Puddephatt and D. S. Yufit, Chem. Commun., 1997, 219. 10 (a) M. Sato, H. Shintate, Y. Kawata and M. 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Pirio, D. Touchard, L. Toupet and P. H. Dixneuf, J. Chem. Soc., Chem. Commun., 1993, 163; (j ) D. Touchard, P. Haquette, N. Pirio, L. Toupet and P. H. Dixneuf, Organometallics, 1993, 12, 3132; (k) N. Pirio, D. Touchard and P. H. Dixneuf, J. Organomet. Chem., 1993, 462, C18; (l) S. Guesmi, D. Touchard and P. H. Dixneuf, Chem. Commun., 1996, 2773. 11 A. Harriman and R. Ziessel, Chem. Commun., 1996, 1707. 12 W. Beck, B. Niemer and M. Wieser, Angew. Chem., 1993, 105, 969; Angew. Chem., Int. Ed. Engl., 1993, 32, 923. 13 N. J. Long, Angew. Chem., 1995, 107, 37; Angew. Chem., Int. Ed. Engl., 1995, 34, 21. 14 R. Chukwu, A. D. Hunter and B. D. Santarsiero, Organometallics, 1992, 11, 589. 15 M. D. Ward, Chem. Soc. Rev., 1995, 121. 16 M. C. B. Colbert, J. Lewis, N. J. Long, P. R. Raithby, A. J. P. White and D. J. Williams, J. Chem. Soc., Dalton Trans., 1997, 99. 17 P. Sullivan and T. J. Meyer, Inorg. Chem., 1982, 21, 1037. 18 E. R. Brown and J. Sandifer, Physical Methods of Chemistry. Electrochemical Methods, eds. B. W. Rossiter and J. F. Hamilton, Wiley, New York, 1986, vol. 2, ch. 4. 19 J. Amarasekera and T. B. Rauchfuss, Inorg. Chem., 1989, 28, 3875. 20 A. J. Blake, N. R. Champness, R. J. Forder, C. S. Frampton, C. A. Frost, G. Reid and R. H. Simpson, J. Chem. Soc., Dalton Trans., 1994, 3377. 21 R. J. Forder and G. Reid, Polyhedron, 1996, 15, 3249. 22 D. F. Shriver, Manipulation of Air-sensitive Compounds, McGraw- Hill, New York, 1969. 23 A. Togni, M. Hobi, G. Rihs, G. Rist, A. Albinati, P. Zanello, D. Zech and H. Keller, Organometallics, 1994, 13, 1224. 24 J. Chatt and R. G. Hayter, J. Chem. Soc., 1961, 896; M. I. Bruce and N. J. Windsor, Aust. J. Chem., 1977, 30, 1601; M. I. Bruce, C. Hameister, A. G. Swincer and R. C. Wallis, Inorg. Synth., 1982, 21, 79. 25 E. Weber, M. Hedur, E. Koepp, W. Orlia and M. Czugler, J. Chem. Soc., Perkin Trans. 2, 1988, 1251. 26 N. G. Connelly and W. E. Geiger, Chem. Rev., 1996, 96, 877. Received 2nd January 1998; Paper 8/00039E

ISSN:1477-9226    

DOI:10.1039/a800039e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

DALTON J. Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 2019 Dominant cation–cation supramolecular motifs in crystals. Hexagonal arrays of sextuple phenyl embraces in halometalate salts of MePh3P1 Catrin Hasselgren,a Philip A. W. Dean,*,b Marcia L. Scudder,*,c Don C. Craig c and Ian G. Dance *,†,c a Institute of Chemistry, Uppsala University, Uppsala S751 21, Sweden b Department of Chemistry, University of Western Ontario, London, Ontario N6A 5B7, Canada c School of Chemistry, University of New South Wales, Sydney 2052, Australia The crystal structures of five compounds with phosphonium cations and bromocadmate anions have been determined, and analysed in terms of the supramolecular interactions which determine the lattice types.The salts [MePh3P]2[CdBr4] and [MePh3P]2[CdBr4]?CH2Cl2 crystallise in a large rhombohedral lattice in which dimers of cations in sextuple phenyl embraces (SPE) form a pseudo-diamondoid array, with the anions (and CH2Cl2) contained in cavities surrounded by 12 cations.The same hexagonal array of sextuply embracing cations occurs also in [MePh3P]2[CdI4] and [MePh3P]2[Cu4I6], with the dimensions of the array of cations quite variable according to the size and shape of the anion. This newly recognised lattice type (HASPE, hexagonal array of sextuple phenyl embraces) is maintained principally by the strongly attractive SPEs and by attraction between the anion and surrounding cations. The HASPE is a crystal structure type with general occurrence.The cations in the crystal structures of [Ph4P]2[CdBr4] and [Ph4P]2[Cd2Br6] occur as zigzag infinite sextuple phenyl embraces (ZZISPEs), chains of cations which are orthogonal and parallel respectively. Determination of the crystal structure of [HPh3P]2[CdBr4] reveals an absence of specific cation–cation interactions. In the field of inorganic crystal supramolecularity we identify two general uncertainties and one fundamental challenge.1 The uncertainties are (1) whether a crystallised compound represents the most abundant species of a dynamic equilibrium mixture in solution, and (2) the extent to which the molecular structure and stereochemistry in solution is distorted by the crystal environment.The basic challenge is to be able to understand supramolecular interactions in crystals to the extent that crystal packing can be predicted and engineered. These uncertainties are amplified for anionic metal halide (X) complexes, [MmXx]z2, which normally are involved in multicomponent equilibria in solution.There is now a large accumulation of data on the crystal structures of anionic metal complexes with halide ligands. The structures for Cu and Ag have been reviewed by Jagner and Helgesson,2 and Hg structures reviewed by House et al.,3 with the general conclusion that the cation with which the anionic complex is crystallised can have a profound influence on the composition and structure of the anion.The previous reviewers were unable to interpret clearly the influence of the cation, and little correlation between anion structure and cation properties was evident. Rohl and Mingos4–7 have analysed the packing of neutral molecules and ions in crystals. In previous papers we have described the multiple phenyl embraces between the Ph4P1 cations in a wide variety of crystalline compounds.8–10 The most prominent of these embraces is the sextuple phenyl embrace (SPE), in which three phenyl groups on one molecule face three phenyl groups on an adjacent molecule, and interleave them such that the partially positive H atoms of any ring are directed towards the negative p density of a ring on the other cation (see Fig. 1). These local attractions are the established edge-to-face (ef) local supramolecular motifs of phenyl rings, and there is a concerted cycle of six such ef interactions in the SPE. The net attractive energy between two Ph4P1 cations embracing in this motif is calculated † E-Mail: I.Dance@unsw.edu.au to be in the range 50–80 kJ mol21,9 which is stronger than most hydrogen bonds.In further investigations we have shown that extended networks of multiple phenyl embraces between Ph4P1 cations are also a general feature of crystal supramolecularity. 10,11 In particular, the zigzag infinite sextuple phenyl embrace (ZZISPE) is a general chain motif of Ph4P1 cations, often arranged in crystals as parallel chains between which there are stacks of anions.10 An SPE requires three phenyl groups per molecule, and therefore triphenylphosphonium cations RPh3P1 are also able to participate in SPEs.Accordingly we are investigating the crystal supramolecularity of such cations, and particularly MePh3P1 and HPh3P1 which are able to retain three-fold symmetry. In this paper we describe the structures of new crystals containing the cations MePh3P1, HPh3P1 or Ph4P1, with anions [CdBr4]22 or [Cd2Br6]22. We have discovered that MePh3P1 with [CdBr4]22 forms a large rhombohedral lattice in which the SPEs lie along threefold axes and dominate the lattice packing, causing the anions to be partially disordered in order to maintain the lattice symmetry.This rhombohedral lattice of embracing cations occurs in the crystal structures of [MePh3P]2[CdI4] and [MePh3P]2- Fig. 1 The sextuple phenyl embrace adopted by pairs of Ph4P1 cations in crystals: the arrows identify the six concerted edge-to-face phenyl– phenyl interactions2020 J.Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 [Cu4I6], which also have cation-enforced orientational disorder of the anions. This lattice of cations is able to undergo large dimensional changes to accommodate anions of different sizes. Experimental Preparations and crystallisations [MePh3P]2[CdBr4]. The salt MePh3PBr (1.79 g, 5.00 mmol) dissolved in boiling absolute ethanol (10 cm3) was added dropwise to a solution of CdBr2?4H2O (0.868 g, 2.50 mmol) in boiling absolute ethanol (35 cm3) with constant stirring.The product formed immediately as a white precipitate which was collected and washed with cold absolute ethanol [Found (Calc.): C, 45.54 (46.26); H, 3.99 (3.67%)]. The crystals used in the diffraction analysis were obtained from a solution in hot ethanol layered with cyclohexane. [MePh3P]2[CdBr4]?CH2Cl2. The salt MePh3PBr (0.38 g, 1.00 mmol) and CdBr2?4H2O (0.344 g, 1.00 mmol) were dissolved in a hot solution of methylene chloride (100 cm3) plus absolute ethanol (35 cm3).This solution was warmed to effect slow evaporation, forming well shaped clear crystals during one week [Found (Calc.): C, 44.29 (43.71); H, 3.98 (3.57%)]. These crystals were stable at room temperature and were used for the diffraction analysis. On heating these crystals effervesced at 130 8C, and then melted at 130–132 8C, which is also the m.p. of [MePh3P]2[CdBr4].[HPh3P]2[CdBr4]. To CdBr2?4H2O (0.172 g, 0.50 mmol) suspended in MeCN (ca. 2 cm3) was added HBr (48%, aq, ca. 0.5 cm3) to cause dissolution. This solution was added to a solution of Ph3P (0.261 g, 1.0 mmol) in MeCN (ca. 15 cm3) containing ca. 1 cm3 of 48% aqueous HBr. There was no immediate precipitation, and the mixture was allowed to evaporate very slowly. After 20 d, the flat rectangular plates which formed were removed and washed twice with ca. 0.1 cm3 of 10 : 1 (v : v) 48% HBr–MeCN.This preparation was based on the methods of Taylor and Tuck.12 [Ph4P]2[CdBr4]. The salt CdBr2?4H2O (0.344 g, 1.00 mmol) and Ph4PBr (0.838 g, 2.00 mmol) were dissolved together in methylene chloride (100 cm3) and absolute ethanol (35 cm3) with heating. Crystals of the product formed during evaporation of this solution during several days, and were characterised by X-ray diffraction. [Ph4P]2[Cd2Br6]. The salt CdBr2?4H2O (0.688 g, 2.00 mmol) and Ph4PBr (0.838 g, 2.00 mmol) were dissolved together in methylene chloride (100 cm3) and absolute ethanol (35 cm3) with heating.Crystals of the product formed during evaporation of this solution during several days, and were characterised by X-ray diffraction. [Ph4P]2[HgBr4]. The salt Ph4PBr (2.10 g, 5 mmol) dissolved in boiling absolute ethanol (5 cm3) was added dropwise to a solution of HgBr2 (0.901 g, 2.5 mmol) in boiling absolute ethanol (5 cm3) with constant stirring. The product formed as a white precipitate immediately and was collected on a glass filter and washed with cold absolute ethanol.These crystals were isomorphous with [Ph4P]2[CdBr4]. X-Ray crystallography Reflection data were measured at 21(1) 8C using an Enraf- Nonius CAD-4 diffractometer in q–2q scan mode with graphite-monochromated molybdenum radiation (l 0.7107 Å). Data were measured to 2qmax of 508 (458 for [HPh3P]2- [CdBr4]) with an w scan angle of (0.50 1 0.35 tan q). Corrections were made for absorption using the analytical method of de Meulenaer and Tompa13 and for any decomposition.Reflections with I > 3s(I) were considered observed. The structures were determined by direct phasing using the program SIR 92.14 Hydrogen atoms of the cations were included in calculated positions and were assigned thermal parameters equal to those of the atom to which they were bonded. Positional and anisotropic thermal parameters for the non-hydrogen atoms of [HPh3P]2[CdBr4], [Ph4P]2[CdBr4] and [Ph4P]2[Cd2Br6] were refined on F using full-matrix least squares.The anion in [MePh3P]2[CdBr4] lies on a 32 site, and therefore must be disordered. Initially, the Cd and one Br (Brax) were situated on the three-fold axis while the remaining Br atoms (Breq) which are related by the three-fold axis were positioned on the two-fold axes which are perpendicular to the three-fold axis. There are two possible sites for the Cd atom, corresponding to application of the two-fold axes, and these were assumed to be equally occupied.The structure was refined anisotropically, using RAELS.15 In the final refinement, the [CdBr4]22 ion was modelled as a rigid group of C3 symmetry. The Cd and Brax atoms were fixed on the three-fold axis (but allowed to move along it) while Breq was allowed to move off the two-fold axis: the displacement of Breq from the two-fold axis was 0.17 Å, causing small variation in the Brax]Cd]Breq angles. The thermal motion of the anion was described using a 15 parameter TLX rigid body parameterisation,16 while the cation was refined anisotropically (T is the translation tensor, L the libration tensor and X the origin of libration).The composition of [MePh3P]2[CdBr4]?CH2Cl2 was unknown when attempts were made to solve its structure. The structure appeared to be very similar to that of [Me- Ph3P]2[CdBr4], but there had been an increase in the c cell dimension of the otherwise isomorphous cell.Since CH2Cl2 had been used as a solvent, it was thought that the cavity could contain one [CdBr4]22 ion and one CH2Cl2 molecule disordered over two possible sites for [CdBr4]22 ions in the previous structure. The CH2Cl2 molecule was incorporated into the structure at positions indicated from a Fourierdifference map. The Cl atoms were located around the threefold axis such that each position would be ��� occupied. The C atom was positioned on the three-fold axis. Rigid group refinement of the [CdBr4]22 anion was as described above for the non-solvated species, with the Breq atom 0.12 Å from the two-fold axis.The CH2Cl2 was also refined as a rigid group. In the final refinement the C atom was held on the three-fold axis and the rigid group was allowed rotational freedom. Thermal motions for the rigid groups were described using 15 parameter TLX rigid body parameterisations.16 The cation was refined anisotropically.15 Reflection weights used for all structures were 1/s2(Fo), with s(Fo) being derived from s(Io) = [s2(Io)1(0.04Io)2]� �� .The weighted residual is defined as R9 = (SwD2/SwFo 2)� �� . Atomic scattering factors and anomalous dispersion parameters were taken from ref. 17. A DEC Alpha-AXP workstation was used for calculations. Crystallographic details for the crystal structures of [MePh3P]2[CdBr4], [MePh3P]2[CdBr4]?CH2Cl2, [HPh3P]2[CdBr4], [Ph4P]2[CdBr4] and [Ph4P]2[Cd2Br6] are provided in Table 1. 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 186/483. Energy calculations Through-space interaction energies were calculated with an atom–atom model, as described previously.1,9 For the dispersion energy the relevant van der Waals parameters ra (Å) and ea (kJ mol21) respectively were: H 1.50, 0.17; C 2.00, 0.65; P 2.10, 0.87; Cd 2.05, 0.87; Br 2.3, 0.90.For evaluation of the coulombic energy contributions atomic partial charges were obtainedJ. Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 2021 Table 1 Crystallographic details Formula M Crystal description Crystal symmetry Space group a/Å b/Å c/Å a/8 b/8 g/8 U/Å3 ZF (000) Dc/g cm23 m/cm21 Crystal dimensions No. of intensity measurements No.of independent observed relections No. of reflections (m) and variable (n) in final refinement R = Sm|DF|/Sm|Fo| R9 = [Smw|DF|2/Smw|Fo|2]� �� s = [Smw|DF|2/(m 2 n)]� �� Crystal decay Maximum, minimum transmission coefficients R for (p) multiple measurements [MePh3P]2[CdBr4] C38H36Br4CdP2 986.7 {001}(2102) (10–2)(2107) (0–14)(01–4) (211–2)(1–12) Rhombohedral R3� c 10.865(3) 10.865(3) 59.23(3) 120 6055(3) 6 2892 1.62 45.6 0.13 × 0.13 × 0.09 2588 600 600, 71 0.043 0.056 2.37 None 0.67, 0.49 979, 0.018 [MePh3P]2[CdBr4]? CH2Cl2 C39H38Br4CdCl2P2 1258.9 Irregular fragment Rhombohedral R3� c 10.821(2) 10.821(2) 62.39(1) 120 6327(2) 6 3144 1.69 45.0 ª0.14 × 0.14 × 0.13 2715 682 682, 80 0.030 0.033 1.43 None 0.61, 0.45 1112, 0.016 [HPh3P]2[CdBr4] C36H32Br4CdP2 958.6 {010}{001}{111} (2110) (21–10) (311) Orthorhombic Pbca 17.825(7) 21.84(1) 19.188(7) 7471(6) 8 3728 1.70 49.3 0.10 × 0.14 × 0.16 5410 1884 1884, 388 0.049 0.052 1.60 1Æ0.94 0.58, 0.53 — [Ph4P]2[CdBr4] C48H40Br4CdP2 1110.8 {021}{001}{112} (0–10){01–1} Monoclinic C2/c 11.325(4) 19.751(6) 20.705(7) 92.58(2) 4627(3) 4 2184 1.59 39.9 ª0.08 × 0.10 × 0.27 4326 2665 2665, 249 0.032 0.041 1.34 1Æ0.96 0.69, 0.51 152, 0.021 [Ph4P]2[Cd2Br6] C48H40Br6Cd2P2 1383.0 {100}{010} {2111}{11–1} Triclinic P1� 9.98(1) 10.11(1) 13.13(1) 108.53(5) 94.15(6) 100.34(5) 1224(2) 1 664 1.88 58.1 0.14 × 0.08 × 0.13 4560 3263 3263, 262 0.027 0.035 1.23 None 0.60, 0.50 416, 0.013 by fitting them to the electrostatic potentials of these and related molecules: the electrostatic potentials were evaluated from the total electron density by non-local density functional methods.The atomic charges calculated in this way are intermediate between those calculated using the conventional Mulliken and Hirshfeld methods: the intermolecular coulombic energies are not sensitive to variations of atomic charge in this range. The charges used here were [(C20.06H10.07 3)- (C20.1 6H10.15 5)3P10.4] and [Cd10.4(Br20.6)4]: the permittivity e was set as dij.1 Results and Discussion The geometries of the individual cations and anions in these compounds are normal and need no comment.The main significance of these compounds derives from their crystal packing. Crystal structure of [MePh3P]2[CdBr4] All MePh3P1 cations occur as SPE dimers, with a P ? ? ? P separation of 6.38 Å and the two methyl groups linearly opposed, as shown in Fig. 2. The P ? ? ? P vectors of the SPE interactions are aligned with three-fold axes of the lattice, and there is an inversion centre at the centroid of the SPE, so each SPE has 3� symmetry.The unit cell is hexagonal, 10.86 × 59.23 Å, with space group R3� c. The array of the cation P atoms and anion locations in this unit cell is shown in Fig. 3. In addition to the prominent P ? ? ? P vectors of the SPE (coloured pink in Fig. 3), there are puckered hexagonal nets of P atoms (coloured blue in Fig. 3), within which all P ? ? ? P distances are 7.18 Å, and all P ? ? ?P? ? ? P angles 988. The hexagonal net of P atoms is comprisetween the hexagonal nets are the P ? ? ? P vectors of the SPEs, which are directed alternately up and down from contiguous P atoms in one hexagonal net, and thus the three-dimensional array of P atoms is prolate diamondoid, elongated along the hexagonal axis. The centroids of the SPEs, which lie on 3� sites (special positions b in space group R3� c), form layers of triangular grids within which the centroid–centroid distances are 10.9 Å.This lattice of cations in tight SPEs is named the hexagonal array of sextuple phenyl embraces (HASPE). The [CdBr4]22 anions are located at the centroids of the P6 chairs as shown in Fig. 3. These anion sites have 32 (D3) crystallographic symmetry, and therefore the tetrahedral anions are necessarily disordered, as shown in Fig. 4. As three Br atoms of each anion lie on the two-fold axes at these sites, the two orientations of the [CdBr4]22 anion at each site are effectively mirrored by a plane perpendicular to the three-fold axis.In the Fig. 2 The tight sextuple phenyl embrace (SPE) adopted by a pair of MePh3P1 cations in crystalline [MePh3P]2[CdBr4]. This SPE has exact 3� symmetry2022 J. Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 following the three Br atoms off the three-fold axis are labelled equatorial, Breq, and the two on-axis positions for the fourth Br atom are labelled Brax.‡ In addition to the SPEs which link the puckered hexagonal nets of cations, there are cation–cation interactions within these nets.Fig. 5 shows axial and lateral views of a net. As the cations are directed alternately up and down from the hexagonal net, each CH3 group (shown in yellow) of one cation lies between three Ph groups (of these the two Ph groups included in Fig. 5 Fig. 3 Contents of the unit cell (white box, hexagonal, 10.9 × 59.2 Å) of crystalline [MePh3P]2[CdBr4].The white spheres show the location of the anions, and the pink and blue rods connect the P atoms of the cations, in a pseudo-diamondoid array. Carbon atoms (green) for eight cations are shown. The pink rods signify the SPE interactions of cation dimers Fig. 4 The disordered positions of the [CdBr4]22 anion at a 32 site in crystalline [MePh3P]2[CdBr4] ‡ In the final refinement (see Experimental section), the Breq atoms were allowed to move slightly off the two-fold axis, but rigid group C3 symmetry for the [CdBr4]22 ion was maintained.In this general discussion we assume that the Breq lies on the two-fold axis, but any dimensions quoted refer to the actual refined positions. are coloured blue) from the three adjacent cations in the net. Around the hexagonal net there are also ef interactions between Ph groups of 1–3 related cations: the two blue Ph rings in Fig. 5 show this.Each anion is surrounded by six cations in the immediate chair-hexagon. In addition to these six cations, there is another triangle of cations either side (along the three-fold axis) of the chair-hexagon, so that there are 12 cations surrounding the anion sites. Although the 32 site illustrated in Fig. 3 is at the centre of the chair-hexagon, the actual location of each anion is displaced along the three-fold axis (see Fig. 4), and so any one anion is within contact of 3 1 6 cations.These contacts are shown in Fig. 6. Each Breq atom of an anion is near H(2) (2.84 Å), H(2) (2.90 Å) and H(3) (2.93 Å) atoms of Ph groups of three surrounding cations, and Brax also makes contact (3.08 Å) with each H(4) atom on three surrounding cations. The slight rotation of the three-fold axis of the [CdBr4]22 ion from the three-fold axis of the unit cell ‡ allows the Breq ? ? ?H distances to be equalised. Fig. 7 is a space-filling picture of the cations and anions in one hexagonal net of the lattice.In summary, the essential features of ion locations in this lattice are (1) a prolate diamondoid array of MePh3P1 cations, connected by SPEs along the c-axis of the hexagonal lattice, and by CH3 ? ? ? Ph and Ph ? ? ? Ph interactions within the puckered hexagonal net of cations normal to this axis, and (2) [CdBr4]22 anions located at the centres of the hexagons in the puckered net of cations, and constrained by Br ? ? ? H interactions. However, there is a more subtle feature which derives from the rotational conformations of ions around the three-fold axes.A diamond lattice repeats after three puckered hexagonal nets, whereas the crystal structure of [MePh3P]2[CdBr4] has six hexagonal nets along the c axis of 59.23 Å. Hexagonal nets separated by c/2 (i.e. 1,4 sequenced in the stack of nets) in [MePh3P]2[CdBr4] differ in their rotational conformation about the three-fold axes. The symmetry element which relates ions separated by c/2 is a c glide plane.The reason for the doubling of the repeat along c derives from the interactions between the anion and cation shown in Fig. 6, specifically the H ? ? ? Breq interactions in Fig. 6(a) prevent rotation of the anion about its three-fold axis. Thus the rotational conformation of the anion is locked into the rotational conformations of the cations in its puckered net. The SPEs which link cations in contiguous nets are centrosymmetric, and consequently the cations in one net are rotated by 1808 relative to those in adjacent nets.Therefore the anions in successive layers of anions are also rotated by 1808. Then, after the diamondoid repeat of three hexagonal nets there is rotation of anions (and their surrounding cations) by 3 × 1808, and thus identity requires 3 × 2 layers. What attractive energies maintain this lattice? We have calculated the through-space energies for the relevant components: all of the energies quoted here are attractive. The SPE has an attractive energy of 83.8 kJ mol21 for the Ph3–Ph3 set, and a total attractive energy for MePh3P1–MePh3P1 of 69.3 kJ mol21.In the chair-hexagon of cations, the 1–3 related cations have a net attraction of 4.4 kJ mol21 mainly due to two Ph rings, while the 1–2 related cations have Me]Ph attraction of 2.6 kJ mol21, and total Ph3]Ph3 attraction of 11.7 kJ mol21 (of which one pair of Ph rings contributes 7.2 kJ mol21). There are substantial attractive energies, mostly coulombic, between [CdBr4]22 and its surrounding cations: between [CdBr4]22 and cations in the chair-hexagon (taking into account the actual disorder) there are three independent energies for anion–cation pairs, namely 73.7, 74.8 and 90.4 kJ mol21: between [CdBr4]22 and one of the three cations nearer to Brax the anion–cation energy is 45.1 kJ mol21.Crystal structure of [MePh3P]2[CdBr4]?CH2Cl2 This compound was crystallised from a mixture with a Br2–J.Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 2023 Fig. 5 Three-fold (a) and approx two-fold (b) views of six MePh3P1 cations which comprise a hexagon in chair conformation in the hexagonal net of cations in crystalline [MePh3P]2[CdBr4]. The P atoms are pink, and the carbon atoms of the methyl groups are coloured yellow: the alternation of pink and yellow in (a) shows the up–down alternation of cation methyl vectors around the hexagon. Three SPE (not shown) occur on either side of the hexagon, and the trigonal array of canted phenyl groups Ph3 which form an SPE is evident around each pink P atom in (a).Two of the phenyl groups in 1–3 cations around the hexagon are coloured blue, to emphasise the ef interaction between them, and to show how the CH3 group of the intervening cation nestles between these two Ph groups (and a third not shown) with C]H? ? ? Ph interactions Fig. 6 (a) A [CdBr4]22 anion near the centre of a [MePh3P1]6 chair-hexagon, showing the H atoms which most closely approach Breq, at the distances marked: the view direction is along the three-fold axis of the unit cell, and the very slight rotation of the three-fold [CdBr4]22 anion from this axis can be discerned.(b) The three MePh3P1 cations which are near Brax of an anion, with the shortest H ? ? ? Brax distance marked. The Cd atom is black, Br bubbled, C grey, H white and P black Cd21 ratio of 3 : 1, and which was intended to crystallise the [Cd2Br6]22 ion with MePh3us, in the presence of MePh3P1 the bromocadmate anion which crystallises does not match the stoichiometry of the crystallisation solution (in contrast to crystallisation with Ph4P1: see below).The crystal structure of [MePh3P]2[CdBr4]?CH2Cl2 is similar to that of [MePh3P]2[CdBr4], in that the space group is the same, the general array of ions is the same, and the unit cell is slightly larger. The location of the cations was unequivocal and showed that the two structures had dimensional differences.The P ? ? ? P separation of the SPE in [MePh3P]2[Cd- Br4]?CH2Cl2 is 6.74 Å, 0.36 Å longer, while the P ? ? ? P separation within the hexagonal net is virtually unchanged at 7.24 Å. The location of the additional CH2Cl2 is inside the cavity which contains the [CdBr4]22 anion: this cavity, which has an ellipsoidal shape elongated along the three-fold axis, accommodates both species simultaneously along the ellipsoid axis, resulting in the expansion of the c dimension of the lattice by 3.2 Å.The CH2Cl2 molecule is centred on the three-fold axis in the cavity, with one C]H bond collinear with the three-fold axis and directed towards the centre of the cavity and between the (Breq)3 set of the partner [CdBr4]22. This attractive relationship between the CH2Cl2 and [CdBr4]22 is shown in Fig. 8. There is three-fold rotational disorder of the other C]H and (C]Cl)2 bonds, and adherence to the 32 crystallographic site symmetry of the cavity requires the locations of the [CdBr4]22 and CH2Cl2 to be disordered.The shortest contacts between the CH2Cl2 and surrounding cations are Cl ? ? ? C 3.2 Å (which is comparable to the shortest contacts of this type present in the Cambridge2024 J. Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 Table 2 Comparative dimensions of the lattices and anions in four crystals with comparable hexagonal arrays of MePh3P1 cations (distances in Å, angles in 8) Space Cell dimensions SPE length Dimensions of hexagonal net Anion ? ? ?P radical, Anion Anion cross- Compound {refcode} [MePh3P1]2[CdBr4]22 [MePh3P1]2[CdBr4]22? CH2Cl2 [MePh3P1]2[CdI4]22 {MTPHCI} [MePh3P1]2[Cu4I6]22 {MPPICU} group R3� c R3� c R3� c R3� c a, c 10.9, 59.2 10.8, 62.4 11.0, 64.0 14.0, 40.1 P ? ? ?P 6.38 6.74 6.74 6.22 P ? ? ?P 7.18 7.24 7.45 8.07 P ? ? ?P? ? ?P 98.4 96.7 94.9 119.7 axial 6.5, 11.6 6.5, 12.2 6.6, 12.6 8.1, 6.9 length a 6.6 7.3 7.5 4.5 section b Triangular, 7.8 Triangular, 7.8 Triangular, 9.1 Circular, 20.0 a Atom–atom length of the anion along the three-fold axis, including disorderd positions.b Cross-sectional shape and area (Å2, calculated to atom centres) of the anion, perpendicular to the three-fold axis. Structural Data Base 18) and Cl ? ? ? H 2.7 Å.§ The hexagonal lattice in [MePh3P]2[CdBr4] could be considered to be an inclusion host, with CH2Cl2 as guest. We are exploring this concept further, with evidence that other molecules can occupy the cavity in place of CH2Cl2.Related crystal structures of [MePh3P]2[CdI4] and [MePh3P]2[Cu4I6] Interrogation of the Cambridge Structural Database reveals two other compounds which have similar crystal structures, namely [MePh3P]2[CdI4] 19 and [MePh3P]2[Cu4I6].20 The cell Fig. 7 Space-filling view of cations and anions in one hexagonal net of [MePh3P]2[CdBr4]. All anions are shown oriented in the same direction along the three-fold axes, but can be disordered by reflection through the plane of the Breq atoms Fig. 8 The [CdBr4]22–CH2Cl2 embrace within the cavity of crystalline [MePh3P]2[CdBr4]?CH2Cl2 § As in the case of [MePh3P]2[CdBr4], the Breq of the anion were allowed to refine away from the two-fold axis. Similarly, in the final refinement, the CH2Cl2 molecule was allowed to refine away from the ideal location described here. The C atom was held on the three-fold axis. dimensions vary, as do the lattice dimensions, defined by the SPE P ? ? ? P distance, the P ? ? ? P distance around the hexagonal net, and the P ? ? ?P? ? ? P angle which defines the extent of ring puckering: these dimensions are in provided in Table 2.However all of these compounds have the same general array of cations, SPE motifs, and of anions within this network of cations, and the same symmetry. Of the four compounds listed, [MePh3P]2[Cu4I6] differs from the other three in that its hexagonal net is nearly planar, as shown by the P ? ? ?P? ? ? P angle (119.78), with the c axis consequently ca. 20 Å shorter and the a axis ca. 3 Å longer. The variation in the dimensions and puckering of the net are related to the overall dimensions of the anions as portrayed in their disordered state. Fig. 9 shows the lattice array for [MePh3- P]2[Cu4I6] in the same style as Fig. 3, and Fig. 10 shows the collection of atoms for the disordered [Cu4I6]22 ions. Only the Cu atoms need be disordered for [Cu4I6]22 to adopt the 32 site symmetry.It is clear from comparison of Figs. 4 and 10 that disordered [CdBr4]22 is prolate while disordered [Cu4I6]22 is oblate, and from comparison of Figs. 3 and 9 that the hexagonal net of cations in the [CdBr4]22 crystal can undergo substantial concertina compression in order to accommodate [Cu4I6]22. It is remarkable that the lattice is able to adjust with the degree of geometrical variation presented in Table 2: the variation is however consistent with the energy calculations because the (blue) interactions within the hexagonal net are less energetic than the (pink) SPE and the attraction between the anion with surrounding cations.We comment that the isostructural relationship between [MePh3P]2[Cu4I6] and the other compounds could not have been detected via the usual test for isomorphous lattices. Finally, we note (Table 2) that the lattice of [MePh3P]2- [CdI4] accommodates [CdI4]22 which is larger than [CdBr4]22 by weakening (elongating) the SPE, increasing the dimensions of the hexagonal net, and slightly flattening the hexagonal net, changes which also account for the difference between [MePh3P]2[CdBr4]?CH2Cl2 and [MePh3P]2[CdBr4].Table 2 also contains the dimensions of the disordered objects included in each lattice. These are the atom–atom length along the c axis and the approximate cross-sectional areas. There is a direct correlation between the anion length and the c cell dimension, and in addition, the cross-sectional area is correlated to the a (b) cell dimension.There remains the question as to why [MePh3P]2[Cd2Br6] did not crystallise from the solution which has this composition. We have computer modelled the structure of the crystal which has [Cd2Br6]22 in the cavity. Although this anion does not conform to 32 symmetry, it is possible that it, like [CdBr4]22, would be accommodated if it were disordered. However, it was not possible to locate [Cd2Br6]22 within the ellipsoidal cavity of [MePh3P]2[CdBr4]?CH2Cl2 without introducing unacceptablyJ.Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 2025 short anion/cation contacts. It is possible, however, that some rearrangement of the host lattice could allow inclusion of [Cd2Br6]22. The dimensions of a disordered [Cd2Br6]22 are approximately 6.3 Å in length with a roughly circular cross sectional area of 12.9 Å2. By comparison of the corresponding dimensions for the other disordered anions/solvent molecules incorporated into this lattice (Table 2) it seems likely that [Cd2Br6]22 could be accommodated if a (and b) increased while c decreased.Perhaps it remains to optimise the preparative conditions in order to crystallise [MePh3P]2[Cd2Br6]. Fig. 9 Contents of the unit cell (white box) of crystalline [MePh3P]2- [Cu4I6]. The components are represented in the same manner as for Fig. 3, except that the centres of the disordered [Cu4I6]22 ions are shown as buff spheres Fig. 10 Atom positions for the disordered [Cu4I6]22 anion at a 32 site in crystalline [MePh3P]2[Cu4I6]: three-fold axis vertical. The I positions are not disordered, but there are two sets of Cu positions, shown as dark and light Crystal structures of [Ph4P]2[CdBr4] and [Ph4P]2[Cd2Br6] These two compounds were crystallised from mixtures containing Br2–Cd21 ratios of 4 and 3 respe and the composition of the crystallised anion matches the stoichiometry of the solution. Unlike MePh3P1, Ph4P1 can engage two SPEs and frequently does so with the zigzag infinite sextuple phenyl embrace (ZZISPE) which we have previously described.10 Crystalline [Ph4P]2[CdBr4] and crystalline [Ph4P]2[Cd2Br6] both contain ZZISPEs, but with different inter-ZZISPE motifs.The salt [Ph4P]2[CdBr4] contains orthogonal ZZISPE chains where the P ? ? ? P distances are alternately 6.41 and 6.65 Å, as shown in Fig. 11. Where the orthogonal chains abut, the P ? ? ? P distance of 7.41 Å represents an unusual quadruple phenyl embrace which incorporates two face-to-face interactions, shown in Fig. 12. The anions in [Ph4P]2[CdBr4] are positioned in the cavities created between the cation chains (see Fig. 11). Two other tetrahalometalate structures are isomorphous Fig. 11 Crystal structure of [Ph4P]2[CdBr4] showing the two orthogonal ZZISPE chains of cations (pink rods) which separate the [CdBr4]22 ions Fig. 12 Orthogonal views of the unusual quadruple phenyl embrace which occurs between ZZISPE chains in crystalline [Ph4P]2[CdBr4]2026 J.Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 with [Ph4P]2[CdBr4], namely [Ph4P]2[HgBr4] and [Ph4P]2- [NiCl4] {TADGAG},¶ but in addition there are other structures with chemically diverse anions which adopt the same cation packing with orthogonal ZZISPEs. These include [Ph4P]2- [MoSe4] {GEPFIQ}, [Ph4P]2[WSe4] {GEPFOW}, [Ph4P]2- [NbS3(SH)] {YUBDUU}, [Ph4P]2[S2Mo(m-S)2Cu(CN)] {BECPII10}, [Ph4P]2[Se2Mo(m-Se)2Cu(CN)] {POPCEC}, [Ph4P]2[CoCl(N3)3] {FURHEF} and three cubane type Fe]S clusters, [Ph4P]2[{Fe(Br)}4S4] {DEXXIN}, [Ph4P]2[{Fe- (SH)}4S4] {FAGREK} and [Ph4P]2[{Fe(Cl)}2{Fe(S2CNEt2)}2S4] {DAMNUA}.In crystalline [Ph4P]2[Cd2Br6] the ZZISPEs are parallel and coplanar, with P ? ? ? P SPE distances alternately 6.63 and 6.59 Å in each chain (see Fig. 13). Where the chains come closest together, the P ? ? ? P distance is 8.44 Å and the arrangement is that of a parallel quadruple phenyl embrace (PQPE).There is a centre of symmetry at the centroid of each SPE and the centroid of the PQPE. Consequently there is a pseudohexagonal planar array of cations, a motif which occurs frequently in compounds containing Ph4P1 and will be reported separately.11 The anions, which themselves contain a centre of symmetry, form layers between the cation layers, as shown in Fig. 13. Other [Ph4X]2[M2Y6] crystal structures fall into two crystal classes, triclinic P1� and monoclinic P21/c (or equivalent).In both cases, the structures are layered, but in the monoclinic case, the SPEs can be longer and the layer undulates. These structures are: (a) triclinic [Ph4P]2[Hg2I6] {CUGFIT}, [Ph4P]2- [Mn2Br6] {GAYWIM}, [Ph4P]2[Zn2Cl6] {KAVHEU}, [Ph4P]2[Cd2Cl6] {KAVHIY}, [Ph4As]2[Hg2Cl6] {KASTED}; (b) monoclinic [Ph4P]2[Cu2Cl6] {JADNOR, TPHCLC}, [Ph4As]2- [Cu2Cl6] {TPHASC01}, [Ph4Sb]2[Cu2Cl6] {DADZUD}; [Ph4P]2[Cd2Br6] is in the triclinic class.Crystal structure of [HPh3P]2[CdBr4] Salts containing the triphenylphosphonium cation HPh3P1 form a large rhombohedral lattice similar to that of [MePh3P]2- [CdBr4], and dominated by cation interactions.21 Therefore we prepared [HPh3P]2[CdBr4] and examined its crystal structure. The structure is a three-dimensional array of cations containing cavities where the anions are located, but unlike the other structures reported in this paper the crystal structure of [HPh3P]2[CdBr4] does not exhibit any SPE interactions.One of the features of halometalate complexes with the cation HPh3P1 is the occurrence of hydrogen bonds between the cation P]H and the halogen atoms of the anions. In [HPh3P]2[CdBr4] each H]P is directed towards an anion giving rise to H ? ? ? Br interactions of 2.61 and 2.80 Å, well within the Fig. 13 Crystal structure of [Ph4P]2[Cd2Br6] showing two coplanar but opposed ZZISPE chains of cations (pink rods). The centrosymmetric [Cd2Br6]22 ions form layers between the cation layers ¶ The identifiers in braces are the reference codes of the Cambridge Structural Database.range of 2.5–3.1 Å found for similar contacts in other structures. In addition there are other H ? ? ? Br contacts for aromatic H atoms of comparable length to those found for [MePh3P]2- [CdBr4]. This structure seems to have rather inefficient packing, as indicated by the high thermal motion of the ring carbon atoms.It is reasonable to question why this cation does not give HASPE crystalline packing (which indeed does occur for some other halometalates, e.g. [HPh3P]2[Ga2Cl6] {FUPSEO}). We surmise that the empty space resulting from the substitution of H for Me is too large to allow this to form and that the required variation in the host lattice would be too great. Conclusion We have identified a new structure type for structurally molecular salts involving the three-fold cation MePh3P1, which dimerises to form strong sextuple phenyl embraces as a dominant supramolecular motif.Secondary phenyl embraces generate a diamondoid network of cations, forming cavities which contain a dianion which is orientationally disordered as necessary to adhere to the symmetry dictated by the cation array. The anion cavity can also contain the small molecule CH2Cl2 in a host– guest relationship. This structure type is named the hexagonal array of sextuple phenyl embraces (HASPE).This matrix of embracing cations is dimensionally adjustable, and undergoes concertina compression to accommodate the more oblate anion [Cu4I6]22, or concertina expansion to accommodate CH2Cl2 with the anion. The main contributions to the favourable lattice energy are the strongly attractive SPEs (69 kJ per mol of [MePh3P1]2), and the attractions between an anion and the 12 cations which surround its cavity. Corresponding compounds with Ph4P1 and the anions [CdBr4]22 or [Cd2Br6]22 form the previously described ZZISPEs as the key supramolecular motif for the cations.Returning to the questions raised at the outset, about the integrity of composition and structure for halometalate anions, we note that a solution with the stoichiometry of [Cd2Br6]22 crystallised this anion with Ph4P1 but crystallised [CdBr4]22 with MePh3P1. The stable lattice of embracing MePh3P1 cations has changed the identity of the anion crystallising from solution.Acknowledgements C. H. acknowledges funding as an exchange student at the University of New South Wales from Uppsala University. P. A. W. D., an Honorary Visiting Professor at UNSW in 1996, acknowledges a leave of absence from the University of Western Ontario and partial travel funding from the Natural Sciences and Engineering Research Council of Canada. This research is funded by the Australian Research Council. References 1 I. G. Dance, in The Crystal as a Supramolecular Entity, ed. G. R. Desiraju, John Wiley, New York, 1996, pp. 137–233. 2 S. Jagner and G. Helgesson, Adv. Inorg. Chem., 1991, 37, 1. 3 D. A. House, W. T. Robinson and V. McKee, Coord. Chem. Rev., 1994, 135/136, 533. 4 D. M. P. Mingos and A. L. Rohl, Inorg. Chem., 1991, 30, 3769. 5 A. L. Rohl and D. M. P. Mingos, J. Chem. Soc., Dalton Trans., 1992, 3541. 6 D. M. P. Mingos, A. L. Rohl and J. Burgess, J. Chem. Soc., Dalton Trans., 1993, 423. 7 A. L. Rohl and D. M. P. Mingos, Inorg. Chim. Acta, 1993, 212, 5. 8 I. G. Dance and M. L. Scudder, J. Chem. Soc., Chem. Commun., 1995, 1039. 9 I. G. Dance and M. L. Scudder, Chem. Eur. J., 1996, 2, 481. 10 I. G. Dance and M. L. Scudder, J. Chem. Soc., Dalton Trans., 1996, 3755. 11 I. G. Dance and M. L. Scudder, unpublished work. 12 M. J. Taylor and D. G. Tuck, Inorg. Synth., 1983, 22, 135.J. Chem. Soc., Dalton Trans., 1997, Pages 2019–2027 2027 13 J. de Meulenaer and M. Tompa, Acta Crystallogr., 1965, 19, 1014. 14 A. Altomare, M. C. Burla, M. Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi and G. Polidori, J. Appl. Crystallogr., 1994, 27, 435. 15 A. D. Rae, RAELS 92, a Comprehensive Constrained Least Squares Refinement Program, Australian National University, 1992. 16 A. D. Rae, Acta Crystallogr., Sect. A, 1975, 31, 560. 17 J. A. Ibers and W. C. Hamilton, International Tables for X-RaCrystallography, Kynoch Press, Birmingham, 1974. 18 F. H. Allen, J. E. Davies, J. J. Galloy, O. Johnson, O. Kennard, C. F. Macrae and D. G. Watson, J. Chem. Inf. Comput. Sci., 1991, 31, 204. 19 C. Couldwell and K. Prout, Acta Crystallogr., Sect. B, 1978, 34, 2312. 20 G. A. Bowmaker, R. J. H. Clark and D. K. P. Yuen, J. Chem. Soc., Dalton Trans., 1976, 2329. 21 I. G. Dance and M. L. Scudder, unpublished work. Received 2nd January 1997; Paper 7/00004I

ISSN:1477-9226    

DOI:10.1039/a700004i

出版商:RSC    

年代:1997

数据来源: RSC

摘要:

DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1999, 2021–2029 2021 Disruption of the �-perpendicular component of a 4-electron donor alkyne ligand in a high-valent complex of tungsten by introduction of an organoimido ligand Alastair J. Nielson *a and Clifton E. F. Rickard b a Chemistry, Institute of Fundamental Sciences, Massey University at Albany, Private Bag 102904, North Shore Mail Centre, Auckland, New Zealand b Department of Chemistry, The University of Auckland, Private Bag 92019, Auckland, New Zealand Received 24th November 1998, Accepted 28th April 1999 Addition of Me3SiNHCMe3 to the 4-electron donor alkyne complex [{WCl4(PhC2Ph)}2] gave [{WCl2(NCMe3)(PhC2Ph)(NH2CMe3)}x] 1 for which the acetylenic carbon resonance position, d 156.23, in the 13C-{1H} NMR spectrum indicated a 2-electron donor alkyne.Small changes in d for derivatives [NEt4][WCl3- (NCMe3)(PhC2Ph)(NH2CMe3)] 2 (161.28), trans-dichloro complexes [WCl2(NCMe3)(PhC2Ph)(bipy)] 3 (bipy = 2,29- bipyridyl, d 163.60) and [WCl2(NCMe3)(PhC2Ph)(dmbipy)] 4 (dmbipy = 4, 49-dimethyl-2,29-bipyridyl, d 162.93) as well as cis-dichloro complexes [WCl2(NCMe3)(PhC2Ph)(py)2] 5 (py = pyridine, d 155.78), [WCl2(NCMe3)(PhC2Ph)- (PMe3)2] 6 (d 151.15) and [WCl2(NCMe3)(PhC2Ph)(PMe2Ph)2] 7 (d 153.37) indicate small electronic diVerences in the alkyne–metal bonding. A crystal structure determination of 6 showed trans-phosphines, cis-chloro ligands and a cis arrangement of a 4-electron donor imido ligand [W–N 1.763(6) Å] and a 2-electron donor alkyne [W–C 2.131(6) and 2.111(7) Å].The compound Me3SiNHCHMe2 added to [{WCl4(PhC2Ph)}2] followed by dmbipy gave [WCl2(NCHMe2)- (PhC2Ph)(dmbipy)] 8 (d 163.16), Me3SiNHCH2Me and dmbipy formed cis- and trans-dichloro complexes [WCl2(NCH2Me)(PhC2Ph)(dmbipy)] 9 (d 152.76 and 159.03) and 10 (d 163.31) respectively. A crystal structure of determination 10 showed W–C bond lengths [2.085(8) Å] somewhat shorter than in 6, consistent with the increase in alkyne p^ donation for 10 indicated by d.The compound Me3SiNHC6H3Pri 2-2,6 and [{WCl4(PhC2Ph)}2] gave [{WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(NH2C6H3Pri 2-2,6)}x] 11 (d 166.51) which with dmbipy gave cis-dichloro [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(dmbipy)] 12 (d 167.50). Other complexes prepared were [WCl2(NC6H3Me2-2,6)- (PhC2Ph)(dmbipy)] 13 (d 167.26), [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(py)2] 14 (d 158.78) and [WCl2(NC6H3Pri 2-2,6)- (PhC2Ph)(PMe3)2] 15 (d 154.40).The compound Me3SiNHC6H3Pri 2 22,6 and [NEt4][WCl5(PhC2Ph)] gave [NEt4][WCl4(NHC6H3Pri 2-2,6)(PhC2Ph)] 16 where d (167.40) indicates an amido ligand allows conversion of the alkyne into a 2-electron donor. We have reported that the complex [{WCl4(PhC2Ph)}2], which contains 4-electron donor alkyne ligands, may be regarded as a d0 complex of tungsten as it exhibits chemistry similar to that of d0 organoimido tungsten complexes.1–3 This work arose from previous suggestions that alkynes could stabilise high oxidation states,4 a concept which now has more acceptance.5 We have also shown that a 2-electron donor alkyne is present in complexes of the type [WCl2(NR)(R9C2R0)(PR3)2] (R = Ph or CHMe2; R9, R0 = Ph or H; PR3 = PMe3 or PMe2Ph) where there is a d2 electron configuration.6 An alkyne ligand can be regarded as a 2-electron donor if donation to the metal is from the p|| (acetylene p-parallel) frontier orbital only, and a 4-electron donor if there is also donation from the p^ (acetylene p-perpendicular) frontier orbital.7 These two electronic types can be distinguished on the basis of the acetylenic carbon resonance position in 13C-{1H} NMR spectra {for example d 270.7 for [NEt4][WCl5(PhC2Ph)],1 d 155.77 for [WCl2(NPh)(PhC2Ph)- (PMe3)2]6}. In view of the reaction between [{WCl4(NPh)}2] and the silylamines Me3SiNHR (R = Ph, C6H4Me-4, CMe3, CHMe2 or CH2Me) which provides the means of introducing a second imido function,8 it was of interest to establish if an imido ligand could be added to [{WCl4(PhC2Ph)}2)] in a similar manner.We report here the results of these studies using 13C- {1H} NMR spectroscopy in particular to probe the C]] ] C electronic environment. A preliminary account of some of this work has appeared.9 Results and discussion Addition of Me3SiNHCMe3 to a suspension of [{WCl4(PhC2- Ph)}2] in benzene gives rise to a red-brown solution which pales after several hours giving the colourless complex 1, eqn.(1). After isolation the complex is not particularly soluble in [{WCl4(PhC2Ph)}2] 1 4Me3SiNHCMe3 æÆ [{WCl2(NCMe3)(PhC2Ph)(NH2CMe3)}x] 1 4Me3SiCl (1) 1 benzene and decomposes slowly in chlorinated hydrocarbons. A 13C-{1H} NMR spectrum accumulated rapidly in CDCl3 showed quaternary carbon resonances in the vicinity of d 70 and d 54 which are characteristic of tert-butylimido and -butylamine ligands respectively which shows the complex is not the alternative bis-tert-butylamido complex [{WCl2(NHCMe3)2- (PhC2Ph)}x].The IR spectrum shows a W–Cl stretch at 305 cm21 and there is a weaker peak at 208 cm21 (Table 1) which coupled with the insolubility of the complex suggests a chlorobridged dimer or polymeric species. The 13C-{1H} NMR spectrum shows the acetylenic carbon resonance at d 156.23 and in the IR spectrum n(C]] ] C) occurs at 1762 cm21. These features are similar to those found for the d2 tungsten complex [WCl2- (NPh)(PhC2Ph)(PMe3)2] and compare with values of d 244–283 and n(C]] C) 1590–1638 cm21 found for complexes of the type2022 J.Chem. Soc., Dalton Trans., 1999, 2021–2029 Table 1 Physical data Analysis a (%) IR (cm21) Complex Colour C H N n(C]] ] C) n(W–Cl) 1 [WCl2(NCMe3)(PhC2Ph)(NH2CMe3)] b,c 3 [WCl2(NCMe3)(PhC2Ph)(bipy)] c,d 6 [WCl2(NCMe3)(PhC2Ph)(PMe3)2] c,e 7 [WCl2(NCMe3)(PhC2Ph)(PMe2Ph)2] 8 [WCl2(NCHMe2)(PhC2Ph)(dmbipy)] 9 cis-[WCl2(NCH2Me)(PhC2Ph)(dmbipy)] 10 trans-[WCl2(NCH2Me)(PhC2Ph)(dmbipy)] c,f 11 [WCl2(NC6Pri 2-2,6)(PhC2Ph)(NH2C6H3Pri 2-2,6)] 12 [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(dmbipy)] 16 [NEt4][WCl4(NHC6H3Pri 2-2,6)(PhC2Ph)] c,h Colourless Yellow Colourless Colourless Yellow Yellow Yellow Orange Yellow Colourless 47.2 (46.8) 53.3 (53.2) 44.5 (44.4) 52.0 (52.3) 51.7 (51.7) 49.6 (50.9) 55.1 (55.3) 57.0 (58.1) 56.7 (57.6) 49.4 (49.2) 5.8 (5.3) 4.9 (4.3) 5.3 (5.7) 5.4 (5.3) 4.6 (4.3) 4.8 (4.1) 4.7 (4.5) 5.9 (5.9) 5.0 (4.9) 6.0 (5.8) 5.2 (4.8) 6.3 (6.0) 2.0 (2.1) 1.9 (1.8) 6.3 (6.2) 6.9 (6.4) 5.7 (5.7) (3.3) (3.6) 5.1 (5.3) 3.3 (3.3) 1762 1740 1770 1755 1765 1785 1770 g 1790 1765 305, 208 298 265, 215 265, 235 295 305, 212 300 g 300 g a Calculated values given in parentheses.b Calculated analytical data include 1– 6C6H6. c Solvent supported by NMR spectra. d Calculated analytical data include 0.5C6JH6. e Calculated analytical data include 1 –– 12C6H6. f Calculated analytical data include C6H6. g Complex did not mull well in Nujol giving poorly resolved spectrum. h Calculated analytical data include 1– 3CH2Cl2.[{WCl4(RC2R)}2] 10 which are regarded as d0 systems. Thus addition of the strongly p-donating imido ligand appears to convert the alkyne ligand from a 4- into a 2-electron donor. To obtain further information on this process, the reaction between Me3SiNHCMe3 and [{WCl4(PhC2Ph)}2] was carried out in an NMR tube in CDCl3 and the acetylenic carbon position monitored by 13C-{1H} NMR spectroscopy.A 10 min accumulation after mixing showed a spectrum consistent with the formation of [WCl4(PhC2Ph)(Me3SiNHCMe3)] A as indicated by a shift in the silylamine CMe3 group quaternary carbon compared with that of the free amine. The acetylenic carbon resonance appeared at d 254.43 consistent with a 4-electron donor alkyne ligand. After a further 15 min accumulation the characteristics of A had disappeared but new features were present attributable to an amido species B (CMe3 group quaternary carbon d 56.20,11 acetylenic carbon resonance d 188) and an imido species C (CMe3 group quaternary carbon d 71.74,11 acetylenic carbon resonances d 161.62 and 161.77).After 50 min from mixing a 10 min accumulation showed essentially only C was present. The spectra thus show transformation of the diphenylacetylene ligand from a 4-electron donor in to a 2-electron donor in C. This apparently occurs as the imido group is the stronger p donor and competes more successfully for the available tungsten d orbitals.Species B is of interest as the acetylenic carbon resonance at d 188 may represent an intermediate competitive situation. A crystal structure determination of the molybdenum complex [Mo(NC6H4Me-4)- (MeO2CC2CO2Me)(S2CNEt2)2] 12 suggests that the alkyne donates p-electron density to the molybdenum atom in competition with the imido ligand but 13C-{1H} NMR data are not available for this compound. However for [{WCl2(PhC2Ph)- (MeOCH2CH2OMe)}2(m-N2)],13 where the crystal structure shows similar features, the acetylenic carbon resonance occurs at d 184.4.In comparison, the complex [WCl2(PhC2Ph)2- (PMe3)2] 14 containing two alkyne ligands donating to the same metal orbital shows the resonance for the acetylenic carbons at d 185.5. A complex that is more stable after isolation than complex 1 can be formed if [Et4N]Cl in CH2Cl2 is added to the reaction mixture after the solution has lightened in colour.In this case the characteristics of an imido complex with a 2-electron donor diphenylacetylene ligand are present (CMe3 quaternary carbon d 69.7,11 acetylenic carbon d 150.89). This complex can also be formed if two equivalents of Me3SiNHCMe3 are added to [NEt4][WCl5(PhC2Ph)] 2 generated in CH2Cl2. However we have not been able to obtain an analytically pure sample of this complex or grow crystals suitable for X-ray crystallography. The NMR spectra suggest the complex is [NEt4][WCl3(NCMe3)- (PhC2Ph)(NH2CMe3] 2.The 1H NMR spectrum shows a 1:1:1 ratio of diphenylacetylene, tert-butylimido and -butylamine ligands with the NH2 protons at d 3.96 while in the 13C-{1H} NMR spectrum the tert-butylimido and -butylamine ligand quaternary carbons appear at d 69.84 and 52.46 respectively and the acetylenic carbons at d 161.28. Derivatives of complex 1 can be prepared with nitrogen donor ligands (Scheme 1). Refluxing the light coloured solution obtained after treating Me3SiNHCMe3 and [{WCl4(PhC2Ph)}2] with 2,29-bipyridyl (bipy) gave [WCl2(NCMe3)(PhC2Ph)(bipy)] 3. The 13C-{1H} NMR spectrum showed a single resonance for the tert-butyl methyl groups and resonances in the aromatic region which at 400 MHz were separated suYciently to allow first-order analysis.For the diphenylacetylene ligand the ortho protons appear as a doublet (d 7.83) and the meta and para protons as triplets (d 7.44 and 7.25 respectively) indicating that the two phenyl groups are symmetrical.However there are 8 separate resonances for the bipy ligand indicating asymmetry for this part of the complex. The two C6 protons (for the bipy numbering scheme see Table 2) appear at greater separation (d 9.41 and 8.27) than the other proton pairs indicative of different environments. Similarly, the 13C-{1H} NMR spectrum Scheme 1 (i) bipy or dmbipy in benzene, reflux 2–4 h; (ii) neat pyridine, stir 3 h; (iii) neat PMe3, stir 3 h; neat PMe2Ph, reflux 2 h.[WCl2(NCMe3)(PhC2Ph)(L2)] 3 L2 = bipy 4 L2 = dmbipy (i) [{WCl2(NCMe3)(PhC2Ph)(NH2CMe3)}x] (iii) (ii) [WCl2(NCMe3)(PhC2Ph)(PR3)2] [WCl2(NCMe3)(PhC2Ph)(py)2] 6 PR3 = PMe3 7 PR3 = PMe2Ph 5J. Chem. Soc., Dalton Trans., 1999, 2021–2029 2023 Table 2 NMR Spectroscopic data (d, J/Hz) a Complex 1Hb 13C-{1H}b,c 2 0.99[t, 3J(HH) 6.9, 12 H, Me]; 1.15 (s, 9 H, CMe3); 1.58 (br, 9 H, CMe3); 2.92 [q, 3J(HH) 7.1, 8 H, CH2], 3.96 (br, 2 H, NH2); 7.11 [t, 3J(HH) 7.3, 2 H, p-H, PhC2Ph]; 7.31, [t, 3J(HH) 7.6, 4 H, m-H, PhC2Ph]; 7.71 [d, 3J(HH) 7.5, 4 H, o-H, PhC2Ph] 7.63 (Me, NEt4); 29.44 (Me, NCMe3); 31.33 (br, Me, NH2CMe3); 52.15 (CH2); 52.46 (br, C, NH2CMe3); 69.84 (C, NCMe3); 125.78 (p-C, PhC2Ph); 127.25 (m-C, PhC2Ph); 130.46 (o-C, PhC2Ph); 142.30 (ipso-C, PhC2Ph); 161.28 (C]] ] C) 3 1.32 (2, 9 H, Me); 7.21 (prt, 1 H, H5, bipy); 7.25 [t, 3J(HH) 7.4, 2 H, p-H, PhC2Ph]; 7.28 (s, benzene); 7.44 [t, 3J(HH) 7.7, 4 H, m-H, PhC2Ph]; 7.65 [t, 3J(HH) 6.5, 1 H, H5, bipy]; 7.76 [t, 3J(HH) 7.9, 4J(HH), 1.4, 1 H, H4, bipy]; 7.83 [d, 3J(HH) 8.2, 4J(HH) 1.2, 4 H, o-H, PhC2Ph]; 7.93 [d, 3J(HH) 8.1, 1 H, H3, bipy], 8.00 [t, 3J(HH) 7.8, 4J(HH) 1.5, 1 H, H4, bipy]; 8.08 [d, 3J(HH) 8.0, 1 H, H3, bipy]; 8.27 [d, 3J(HH) 4.5, 1 H, H6, bipy]; 9.41 [d, 3J(HH) 5.2, 1 H, H6, bipy] 29.76 (Me); 70.14 (C); 122.36 and 123.25 (C3, bipy); 125.85 and 127.04 (C5, bipy); 127.34 (p-C, PhC2Ph); 128.08 (m-C, PhC2Ph); 128.34 (benzene); 130.48 (o-C, PhC2Ph); 139.41 and 139.46 (C4, bipy); 139.74 (ipso-C, PhC2Ph); 149.36 (C6, bipy); 151.72 and 152.67 (C2, bipy); 153.39 (C6, bipy); 163.60 [t, 1J(CW) 30.2, C]] ] C] 4 1.22 (s, 9 H, Me); 2.18 and 2.36 (2s, 6 H, Me); 6.90 [d, 3J(HH) 4.8, 1 H, H5, dmbipy]; 7.15 [t, 3J(HH) 7.4, 2 H, p-H, PhC2Ph]; 7.28 (s, benzene); 7.35 [t, 3J(HH) 7.6, 5 H, m-H, PhC2Ph and H5, dmbipy (obscured)]; 7.73 [d, 3J(HH) 7.6, 5 H, o-H, PhC2Ph and H3, dmbipy]; 7.83 (b, 1 H, H3, dmbipy); 8.16 [d, 3J(HH) 5.0, 1 H, H6, dmbipy]; 9.42 [d, 3J(HH) 5.0, 1 H, H6, dmbipy] 21.28 and 21.44 (Me, dmbipy); 29.35 (Me, CMe3); 69.52 (C, CMe3); 123.32 and 123.93 (C5, dmbipy); 125.94; (C3, dmbipy); 126.74 (p-C, PhC2Ph); 127.49 (C3, dmbipy); 127.57 (m-C, PhC2- Ph); 127.98 (benzene); 129.98 (o-C, PhC2Ph); 139.61 (ipso-C, PhC2Ph); 148.41 (C6, dmbipy); 151.03 (C2 or C4, dmbipy); 151.13 (C6, dmbipy); 151.24 (C4 or C2, dmbipy); 162.93 [t, 1J(CW) 31.4, C]] ] C] 5 1.28 (s, 9 H, Me); 6.89 [d, 3J(HH) 7.6, 4 H, o-H, PhC2Ph]; 6.99 [t, 3J(HH) 7.1, 2 H, H4, py]; 7.08 (m, 6 H, m and p-H, PhC2Ph); 7.63 [t, 3J(HH) 7.2, 4 H, H3 and H5 py]; 9.25 [d, 3J(HH) 5.5, 4 H, H2 and H6, py] 29.50 (Me); 69.44 (C); 123.64 (C3 and C5, py); 126.35 (p-C, PhC2Ph); 127.76 (o-C, PhC2Ph); 128.12 (m-C, PhC2Ph); 137.85 (C4, py); 139.49 (ipso-C, PhC2Ph); 155.24 (C]] ] C); 155.78 (C2 and C6, py) 6 1.26 (s, 9 H, Me); 1.58 [t, 2J(HP)d 9.3, 18 H, PMe3]; 7.12 [t, 3J(HH) 7.3, 2 H, p-H, PhC2Ph]; 7.21 [d, 3J(HH) 7.3, 4 H, o-H, PhC2Ph]; 7.29 [t, 3J(HH) 7.3, 4 H, m-H, PhC2Ph] 16.23 [t, 1J(CP) 30.4, PMe3]; 31.15 (Me); 69.38 (C); 126.09 (p-C, PhC2Ph); 127.04 (o-C, PhC2Ph); 128.10 (m-C, PhC2Ph); 128.33 (benzene); 144.57 (ipso-C, PhC2Ph); 151.15 [t, 2J(CP) 24.0, C]] ] C] 7 0.74 (s, 9 H, CMe3); 1.62 and 3.14 (prt, 12 H, PMe2); 7.13 (m, 6 H, aromatic H); 7.26 (m, 4 H, aromatic H); 7.36 (br, 6 H, aromatic H); 7.79 (br, 4 H, o-H, PMe2Ph) 12.77 [t, 2J(HP) 31.9, PMe2]; 17.38 [t, 2J(HP) 35.4, PMe2]; 29.81 (s, Me); 69.70 (C); 126.28 (p-C, PhC2Ph); 128.0 (m- and o-C, PhC2Ph); 128.11 (m-C, PMe2Ph); 129.70 (p-C, PMe2Ph); 131.36 (o-C, PMe2Ph); 137.19 [t, 1J(CP) 36.2, ipso-C, PMe2Ph]; 143.56 (ipso-C, PhC2Ph); 153.37 [t, 2J(CP) 24.1, C]] ] C] 8 1.26 [d, 3J(HH) 6.4, 6 H, Me2]; 2.16 and 2.36 (2s, 6 H, Me); 4.36 [sept, 3J(HH) 6.4, 1 H, CH]; 6.95 [d, 3J(HH) 5.4, 1 H, H5, dmbipy]; 7.22 [t, 3J(HH) 7.4, 2 H, p-H, PhC2Ph]; 7.38 (prd, 1 H, H5, dmbipy); 7.42 [t, 3J(HH) 7.7, 4 H, m-H, PhC2Ph]; 7.77 (s, 1 H, H3, dmbipy); 7.80 [d, 3J(HH) 7.9, 4 H, o-H, PhC2Ph]; 7.89 (s, 1 H, H3, dmbipy); 8.09 [d, 3J(HH) 5.5, 1 H, H6, dmbipy], 9.35 [d, 3J(HH) 5.6, 1 H, H6, dmbipy] 20.79 and 21.13 (Me, dmbipy); 23.11 (Me, CHMe2); 64.63 (CH, CHMe2); 123.17 and 123.83 (C5, dmbipy); 128.33 (C3, dmbipy); 127.02 (p-C, PhC2Ph); 127.61 (C3, dmbipy); 127.83 (m-C, PhC2Ph); 130.26 (o-C, PhC2Ph); 139.99 (ipso-C, PhC2Ph); 148.56 (C6, dmbipy); 151.34, 151.40 and 151.55 (C2 and C4, dmbipy); 151.99 (C6, dmbipy); 152.39 (C2 or C4, dmbipy); 163.16 [t, 1J(CW) 30.2, C]] ] C] 9 1.30 [t, 3J(HH) 7.1, 3 H, Me]; 2.40 and 2.42 (2s, 6 H, Me, dmbipy); 4.21 (obsq, 2 H, CH2); 6.27 [d, 3J(HH) 7.6, 2 H, o-H, PhC2Ph]; 6.87 [t, 3J(HH) 7.2, 1 H, p-H, PhC2Ph]; 6.93 [t, 3J(HH) 7.5, 2 H, m-H, PhC2Ph]; 7.13 [d, 3J(HH) 5.5, 1 H, H5, dmbipy]; 7.26 [prt, 3J(HH) 7.2, p-H, PhC2Ph]; 7.27 [prd, 3J(HH) 5.4, 1 H, H5, dmbipy]; 7.39 (m, 2 H, m-H, PhC2Ph); 7.68 (s, 1 H, H3, dmbipy); 7.39 (s, 1 H, H3, dmbipy); 7.80 [d, 3J(HH) 8.2, 2 H, o-H, PhC2Ph]; 8.72 [d, 3J(HH) 5.6, 1 H, H6, dmbipy]; 8.85 [d, 3J(HH) 5.9, 1 H, H6, dmbipy] 15.55 (Me, CH2Me); 21.27 and 21.54 (Me, dmbipy); 58.33 (CH2); 122.26 and 123.95 (C5, dmbipy); 126.04 (C3, dmbipy); 126.31 (o-C, PhC2Ph); 126.92 (p-C, PhC2Ph); 127.39 (C3, dmbipy); 127.49 (m- C, PhC2Ph); 128.01 (m-C, PhC2Ph); 130.45 (p-C, PhC2Ph); 131.06 (o-C, PhC2Ph); 138.76 and 140.84 (ipso-C, PhC2Ph); 148.59 (C6, dmbipy); 150.45 and 150.88 (C2 or C4, dmbipy); 151.77 (C6, dmbipy); 152.19 and 152.76 (C4 or C2, dmbipy); 159.02 (C]] ] C) 10 1.23 [t, 3J(HH) 7.1, 3 H, Me]; 2.27 and 2.47 (2s, 6 H, Me, dmbipy]; 4.19 [q, 3J(HH) 7.1, 2 H, CH2]; 7.03 [d, 3J(HH) 5.5, 1 H, H5, dmbipy]; 7.23 [t, 3J(HH) 7.4, 2 H, p-H, PhC2Ph]; 7.28 (s, benzene); 7.43 [t, 3J(HH) 7.7, 5 H, m-H, PhC2Ph and H5, dmbipy (obscured)]; 7.54 [d, 3J(HH) 7.5, 5 H, o-H, PhC2Ph and H3, dmbipy (obscured)]; 7.92 (s, 1 H, H3, dmbipy); 8.13 [d, 3J(HH) 5.6, 1 H, H6, dmbipy]; 9.26 [d, 3J(HH) 5.7, 1 H, H6, dmbipy] 15.55 (Me, CH2Me); 21.37 and 21.62 (Me, dmbipy); 58.70 (CH2); 123.15 and 123.83 (C5, dmbipy); 126.61 (C3, dmbipy); 127.20 (p-C, PhC2Ph); 127.89 (C3, dmbipy); 127.98 (m-C, PhC2Ph); 128.32 (benzene); 130.43 (o-C, PhC2Ph); 140.03 (ipso-C, PhC2Ph); 149.04 (C6, dmbipy); 151.46, 151.54 and 151.64 (C2 and C4, dmbipy); 151.89 (C6, dmbipy); 152.58 (C2 or C4, dmbipy); 163.31 [t, 1J(CW) 29.8, C]] ] C] 12 1.07 [d, 3J(HH) 6.8, 12 H, Me]; 2.40 and 2.56 (2s, 6 H, Me); 4.16 [sept, 3J(HH) 6.8, 2 H, CH]; 7.02 [d, 3J(HH) 6.8, 1 H, H5, dmbipy]; 7.10 [d, 3J(HH) 7.9, 2 H, m-H, imido]; 7.25 [t, 3J(HH), 6.8, 1 H, p-H, imido]; 7.26 [t, 3J(HH) 6.3, 2 H, p-H, PhC2Ph]; 7.36 (prd, 1 H, H5, dmbipy); 7.40 [t, 3J(HH) 7.9, 4 H, m-H, PhC2Ph]; 7.86 (s, 1 H, H3, dmbipy); 7.89 [d, J(HH) 7.6, 4 H, o-H, PhC2Ph]; 7.98 (s, 1 H, H3, dmbipy); 8.17 [d, 3J(HH) 5.7, 1 H, H6, dmbipy]; 9.15 [d, 3J(HH) 5.7, 1 H, H6, dmbipy] 21.47 and 21.67 (Me, dmbipy); 24.68 (Me, CHMe2); 27.24 (CH); 122.77 (m-C, imido); 123.14 and 123.88 (C5, dmbipy); 125.38 (p-C, imido); 126.91 (C3, dmbipy); 127.47 (p-C, PhC2Ph); 127.55 (C3, dmbipy); 127.90 (m-C, PhC2Ph); 130.66 (o-C, PhC2Ph); 140.05 (ipso-C, PhC2Ph); 146.47 (C6, dmbipy); 149.21 (C6, dmbipy); 151.24, 151.54, 151.61 and 151.67 (C2, C4, dmbipy and o-C, imido); 151.80 (ipso-C, imido); 167.50 (C]] ] C) 13 2.21 and 2.35 (2s, 6 H, Me, dmbipy); 2.43 (s, 6 H, Me, imido); 6.73 [t, 3J(HH) 7.1, 1 H, p-H, imido]; 6.89 [d, 3J(HH), 2 H, m-H, imido]; 6.94 [d, 3J(HH) 5.4, 1 H, H5, dmbipy]; 7.15 [t, 3J(HH) 7.4, 2 H, p-H, PhC2Ph]; 7.23 [d, 3J(HH) 5.2, 1 H, H5, dmbipy]; 7.33 [t, 3J(HH) 7.6, 4 H, m-H, PhC2Ph]; 7.74 [d, 3J(HH) 7.4, 5 H, o-H, PhC2Ph and H3, dmbipy (obscured)]; 7.86 (s, 1 H, H3, dmbipy); 8.05 [d, 3J(HH) 5.4, 1 H, H6, dmbipy]; 9.09 [d, 3J(HH) 5.5, 1 H, H6, dmbipy] 19.70 (Me, imido); 21.36 and 21.51 (Me, dmbipy); 121.36 (m-C, imido); 124.05 and 125.05 (C5, dmbipy); 126.64 (C3, dmbipy); 127.28 (p-C, imido); 127.36 (p-C, PhC2Ph); 127.59 (C3, dmbipy); 127.88 (m-C, PhC2Ph); 130.19 (o-C, PhC2Ph); 135.75 (o-C, imido); 139.86 (ipso-C, PhC2Ph); 148.67 and 150.69 (C6, dmbipy); 151.49 (C4, dmbipy); 151.54 and 152.33 (C2, dmbipy); 153.29 (ipso-C, imido); 167.27 (C]] ] C) 14 0.85 and 0.95 (br, 12 H, Me); 3.81 and 4.09 (br, 2 H, CH); 6.81 [d, 3J(HH) 7.5, 4 H, o-H, PhC2Ph]; 6.98–7.07 (m, 7 H, H4, py, p-H, PhC2Ph, m- and p-H, imido); 7.13 [t, 3J(HH) 6.4, 4 H, m-H, PhC2Ph]; 7.67 [t, 3J(HH) 7.0, 4 H, H3, py]; 9.10 (br, 4 H, H2, py) 24.74 (Me); 26.84 (CH); 124.80 (C3 and C5, py); 126.73 (p-C, PhC2Ph); 127.83 (o-C, PhC2Ph); 127.92 (m-C, imido); 128.06 (p-C, imido); 128.24 (m-C, PhC2Ph); 138.01 (C4, py); 139.07 (ipso-C, PhC2Ph); 147.73 (ipso-C, imido); 149.87 (o-C, imido); 154.42 (C2 and C6, py); 158.78 (C]] ] C)2024 J.Chem. Soc., Dalton Trans., 1999, 2021–2029 Table 2 (Contd.) Complex 1Hb 13C-{1H}b,c 16 1.06 (prt, 12 H, Me, NEt4); 1.38 (prd, 12 H, Me); 2.90 (prq, 8 H, CH2, NEt4); 3.55 (br, 2 H, CH); 5.28 (CH2Cl2); 6.95–7.45 (m, aromatic H); 7.45–7.95 (m, aromatic H); 9.82 (br, 1 H, NH) 8.78 (Me, NEt4); 23.37 and 23.89 (CHMe2); 26.69 and 27.24 (CH); 55.30 (CH2); 88.77 (CH2Cl2); 123.63, 127.26, 127.79, 130.40 and 130.97 (aromatic C); 141.88 (ipso-C, PhC2Ph); 150.52 (o-C, imido); 151.23 (ipso-C, imido); 167.40 (C]] ] C) a Spectra obtained in CDCl3 solution.b t = Triplet s = singlet, br = broad, q = quartet, d = doublet, pr = partially resolved, m = multiplet; sept = septet, obs = obscured.c Aromatic ring resonance assignments: ortho-carbons shift from d 128.5, meta-carbons based on d 128.5, para-carbons from relative peak height. d For virtual HP spin coupling 2J(HP) quoted as 1– 2[2J(HP) 1 6J(HP9)] where 6J(HP9) is very small. N N N 6 5 4 3 2 6 5 4 3 2 4 3 2 6 5 shows one set of resonances for each of the diphenylacetylene ligand ortho, meta and para carbons and 10 resonances for the bipy carbons with the two C6 carbons showing the greatest separation (d 153.39 and 149.36).The tert-butylimido quaternary carbon appears at d 70.14 and the acetylenic carbons at d 163.60 which is further downfield than the parent complex 1 (d 156.23) and may represent a small electronic change. From the symmetry of the diphenylacetylene ligand and asymmetry of the bipy ligand in the NMR spectra and also a single W–Cl stretch in the IR spectrum, complex 3 has trans-chloro ligands and the bipy nitrogen atoms lying trans to the imido and diphenylacetylene ligands (structure I).Evidence for the complex being a d2 tungsten species comes from a preliminary X-ray photoelectron spectral (XPS) study where the tungsten(4f7/2) binding energy (33.84 eV) is well below that found for [{WCl4(PhC2Ph)}2] (35.1 eV)1 and falls in the range considered to be of tungsten(IV).15 A fuller XPS study of imido and h2-acetylene complexes of tungsten will be reported in the future.That the diphenylacetylene ligand in 3 is a 2-electron donor is verified by the position of n(C]] ] C) (1740 cm21) 6 in the IR spectrum and the position of the acetylenic carbon resonance (d 163.60) in the 13C-{1H} NMR spectrum. We have also prepared the 4,49-dimethylbipyridyl (dmbipy) analogue to increase solubility and decrease the complexity of the NMR spectra. With the C4 protons of bipy replaced by methyl groups in [WCl2(NCMe3)(PhC2Ph)(dmbipy)] 4 the 1H NMR spectrum shows two methyl group resonances, two singlets for the C3 protons [4J(HH) coupling was not resolved at 400 MHz] and two doublets each for the C5 and C6 protons.The doublets have 3J(HH) coupling constants of about 5 Hz which distinguishes them from the diphenylacetylene protons where 3J(HH) is 7–8 Hz.† The 13C-{1H} NMR spectrum now contains two dmbipy methyl group resonances and shows C4 tertiary carbon resonances which simplifies the diphenylacetylene ipso- N N C Me Me Me Cl C C N W Cl Structure I † NMR Spectra were run as concentrated CDCl3 solutions to facilitate 13C-{1H} NMR spectra accumulation times.As a result 3J(HH9) and 3J(H9H) coupling constants reported in Table 2 are not always exactly equal. carbon region (d 139.61). The acetylenic carbon resonance is at d 162.93. Addition of pyridine (py) to a solution of complex 1 gave [WCl2(NCMe3)(PhC2Ph)(Py)2] 5 which was characterised by NMR spectroscopy. Both the 1H and 13C-{1H} NMR spectra show a single resonance for the diphenylacetylene ligand ortho, meta and para positions as well as the pyridine a and b positions indicating that the pyridines are symmetrically ligated.The complex thus has a trans-(bis)pyridine, cis-dichloro structure (structure II). For this complex the acetylenic carbon resonance occurs at d 155.78 in the 13C- {1H} NMR spectrum which is upfield to that of dmbipy complex 4 (d 162.93) but similar to that of the parent complex 1 (d 156.23).Phosphine derivatives of complex 1 can also be prepared. Addition of PMe3 gave [WCl2(NCMe3)(PhC2Ph)(PMe3)2] 6 which has a trans-phosphine cis-dichloro structure based on an apparent triplet for the PMe3 ligand in both the 1H and 13C- {1H} NMR spectra and W–Cl stretches at 265 and 215 cm21 in the IR spectrum. The 13C-{1H} NMR spectrum shows the tertbutylimido quaternary carbon at d 69.38 and the acetylenic carbons as a 31P-coupled triplet at d 151.15. This resonance is further upfield than for pyridine complex 5 (d 155.78) which has a similar molecular geometry and considerably upfield of that of the dmbipy complex 4 (d 162.93) where the geometry is diVerent.The trans-(bis)phosphine cis-dichloro structure for complex 6 was confirmed by a crystal structure determination. The molecular structure is shown in Fig. 1, and selected bond lengths and angles are contained in Table 3. The structure is essentially the same as that found for [WCl2(NPh)(PhC2Ph)- (PMe3)2] 5 with similar W–N bond lengths [1.763(6) and 1.770(14) Å respectively], no lengthening of the W–Cl bond trans to the imido function [W–Cl(1) and W–Cl(2) 2.520(2) and 2.519(2) Å compared with 2.503(8) and 2.515(8) Å], similar W– C(1) [2.131(6) and 2.128(20) Å respectively] and W–C(2) [2.111(7) and 2.123(21) Å respectively] as well as similar C(1)– C(2) bond lengths [1.267(9) and 1.26(2) Å respectively].Data for the acetylene part of the molecule are consistent with this ligand being a 2-electron donor to tungsten.The major Cl N C Me Me Me N C C Cl W N Structure IIJ. Chem. Soc., Dalton Trans., 1999, 2021–2029 2025 structural diVerence between the two molecules is that in complex 6 a small twist of the diphenylacetylene ligand about the tungsten–acetylene axis [N–W–C(1) and N–W–C(2) bond angles 99.4(2) and 96.0(3)8] allows the phenyl rings to sit above the plane of the two PMe3 ligands whereas in [WCl2(NPh)- (PhC2Ph)(PMe3)2] a larger twist occurs [N–W–C(1) and N–W– C(2) bond angles 104.6(7) and 94.9(7)8 respectively] with the phenyl rings sitting above and below the two phosphines.The reason for this is not clear but may be related to the p-donor strength of the two diVerent imido ligands. While the PMe3 ligands bend away from the diphenylacetylene ligand in 6 and [WCl2(NPh)(PhC2Ph)(PMe3)2] to similar extents [P(1)–W–P(2) angles 151.15(7) and 151.9(2)8 respectively] the P–W–P pushback angle from the imido ligand is greater for the more electron donating tert-butylimido ligand [relevant angles 200.3(2) and 186.9(5)8 respectively].We have also investigated the eVect of increasing phosphine ligand size in complexes similar to 6. Reaction of PMe2Ph with complex 1 gives [WCl2(NCMe3)(PhC2Ph)(PMe2Ph)2] 7 which also has the trans-(bis)phosphine cis-dichloro structure based on a pair of triplets for the PMe2Ph methyl groups in the 1H and 13C-{1H} NMR spectra, a triplet for the aromatic ring ipso carbon of the phosphine and W–Cl stretches at 265 and 235 cm21 in the IR spectrum.The 13C-{1H} NMR spectrum shows the tert-butylimido ligand quaternary carbon at a similar position to that of the PMe3 complex (d 69.70 for 7 compared to Fig. 1 Molecular structure of complex 6; atoms are represented at 50% probability surfaces. Table 3 Selected bond lengths (Å) and angles (8) for complex 6 W–N(1) W–Cl(1) W–Cl(2) W–C(1) W–C(2) W–P(1) N(1)–W–C(1) N(1)–W–C(2) N(1)–W–Cl(1) N(1)–W–Cl(2) N(1)–W–P(1) N(1)–W–P(2) C(1)–W–Cl(1) C(1)–W–Cl(2) C(1)–W–P(1) C(1)–W–P(2) C(2)–W–Cl(1) C(2)–W–Cl(2) C(2)–W–P(1) 1.763(6) 2.520(2) 2.519(2) 2.131(6) 2.111(7) 2.574(2) 99.4(3) 96.0(3) 169.4(2) 86.0(2) 102.9(2) 97.3(2) 90.2(2) 163.9(2) 114.2(2) 82.2(2) 94.4(2) 160.4(2) 81.6(2) W–P(2) N(1)–C(3) C(1)–C(2) C(1)–C(31) C(2)–C(21) C(2)–W–P(2) Cl(1)–W–P(1) Cl(1)–W–P(2) Cl(2)–W–P(1) Cl(2)–W–P(2) Cl(2)–W–Cl(1) C(2)–W–C(1) P(2)–W–P(1) C(3)–N(1)–W C(1)–C(2)–C(21) C(2)–C(1)–C(31) C(1)–C(2)–W C(2)–C(1)–W 2.562(2) 1.400(1) 1.267(9) 1.460(9) 1.471(10) 116.9(2) 76.98(7) 79.46(8) 78.95(7) 82.10(8) 83.58(8) 34.7(2) 151.15(7) 173.7(6) 136.3(6) 136.7(7) 73.5(4) 71.8(4) d 69.38 for 6), whereas there is a small downfield shift of the acetylenic carbon triplet (d 153.37 for 7 compared with d 151.15 for 6).Attempts to form a similar complex with PMePh2 were not successful. Additions of the silylamines Me3SiNHR containing less sterically demanding R groups (R = CHMe2 or Et) to [{WCl4- (PhC2Ph)}2] also give light coloured solutions.We have not characterised the complexes (expected to be of the form [{WCl2- (NR)(PhC2Ph)(NH2R)}x]) directly, other than to check the position of the acetylenic carbon resonance in the 13C-{1H} NMR spectra (for example [{WCl2(NCHMe2)(PhC2Ph)- (NH2CH2Me2)}x] d 151.99). Instead the light coloured solutions were treated directly with dmbipy. The NMR spectra of [WCl2(NCHMe2)(PhC2Ph)(dmbipy)] 8 are similar to those of [WCl2(NCMe3)(PhC2Ph)(dmbipy)] except for the characteristic isopropylimido group resonances (1H NMR septet at d 4.36, 13C-{1H} NMR, CH resonance d 64.63).On crystallising the ethylimido complex [WCl2(NCH2Me)(PhC2Ph)(dmbipy)] a small quantity of a less soluble form 9 was obtained which had diVerent spectral characteristics to those of the remaining sample 10. The IR spectrum showed cis-chloro ligands for 9 [n(W–Cl) 305 and 212 cm21] and exhibited n(C]] ] C) at 1785 cm21 while for 10 trans-chloro ligands were apparent [n(W–Cl) 300 cm21] and n(C]] ] C) was at 1770 cm21.The two dmbipy methyl group resonances in the 1H NMR of 9 are closer together than in 10 (d 2.40 and 2.42 compared with d 2.27 and 2.47) as are the dmbipy C6 protons (d 8.72, 8.85 and d 8.13, 9.26 respectively) while there are two sets of diphenylacetylene phenyl ring resonances for 9 and only one for 10. In the 13C-{1H} NMR spectra complex 9 showed two sets of resonances for the diphenylacetylene ligand phenyl groups and two acetylenic carbon resonances (d 152.76 and 159.03) while complex 10 has only a single set for the respective carbons (d 163.31).The asymmetry in 9 can be explained by two cis-chloro structures, 9a and 9b, but 9a is preferred on the basis of similarities of the dmbipy resonances in the NMR spectra to those of [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)- (dmbipy)]3 prepared by reduction of [WCl3(NC6H3Pri 2-2,6)- (dmbipy)] by Na/Hg amalgam in the presence of diphenylacetylene where steric factors do not favour the type b isomer.NMR spectra show that 9 does not turn into 10 on refluxing in benzene and similarly 10 does not turn into 9. Crystals of complex 9 suitable for X-ray crystallography have not been obtained but a structural determination of 10 has been carried out. The complex (Fig. 2) has a distorted octahedral geometry with trans-orientated chloro ligands and mutually cis ethylimido and diphenylacetylene ligands which are both trans to the dmbipy nitrogen ligand atoms.The geometry is that predicted on the basis of the spectral data for complex 10 as well as the other dmbipy complexes. The structure shows that the dmbipy C6 protons will have diVerent environments with one pointing towards the equatorial C(1)–C(2) multiple bond of diphenylacetylene and the other towards the longitudinally orientated W–N multiple bond, which will result in diVerent eVects in relation to the 1H NMR spectrum, as is observed.Selected bond lengths and angles for complex 10 are contained in Table 4. The W–N(1) bond length [1.733(6) Å] is not significantly diVerent to that found for [WCl2(NCMe3)- (PhC2Ph)(PMe3)2] 6 [1.763(6) Å]. For the dmbipy ligand the Cl N C Me H H Cl C C N W N 9a N N C Me H H Cl C C Cl W N 9b2026 J. Chem. Soc., Dalton Trans., 1999, 2021–2029 W–N(3) bond length [2.331(6) Å] is significantly longer than the W–N(2) bond length [2.233(7) Å] apparently to remove interaction of the C11 proton with the diphenylacetylene C(1)– C(2) multiple bond.The W–Cl bond lengths [2.447(2) and 2.448(2) Å] are considerably shorter than the two cis-orientated W–Cl bonds in complex 6 [2.519(2) and 2.520(2) Å] where imido and diphenylacetylene ligands are the trans ligands. The W–C bond lengths in complex 10 [2.086(8) and 2.085(8) Å] are outside the 3s limit for the W–C(1) bond length [2.131(6) Å] in complex 6 and just inside the 3s limit for the WC(2) bond length [2.111(7) Å] indicating that these bonds in the dmbipy complex are becoming shorter.This may involve the acetylene p^ orbitals donating to the same metal orbital as one of the imido donors, resulting in a competitive p-donor situation which is reflected in the 13C-{1H} NMR spectrum where there is an 11.8 ppm shift to lower field for the acetylenic carbon of complex 10 (d 163.31) compared to that of 6 (d 151.15). However this eVect is small and the diphenylacetylene ligand can still be regarded as a nett 2-electron donor.The chloro ligands in complex 10 push further away from the diphenylacetylene ligand than the imido ligand [relevant angles 215.8(4) and 192.2(4)8] while there is only a very small twist of the C]] ] C bond about the tungsten–acetylene axis [N–W–C(1) and N–W–C(2) bond angles 99.9(3) and 102.7(3)8 respectively]. We have also investigated the reaction of Me3SiNHC6H3Pri 2- 2,6 with [{WCl4(PhC2Ph)}2] as a route to complexes of the type [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(L)2].16 This reaction is best carried out in diethyl ether and requires refluxing to give Fig. 2 Molecular structure of complex 10; atoms are represented as 50% probability surfaces. Table 4 Selected bond lengths (Å) and angles (8) for complex 10 W–N(1) W–N(2) W–N(3) W–Cl(1) W–Cl(2) W–C(1) N(1)–W–C(1) N(1)–W–C(2) N(1)–W–Cl(1) N(1)–W–Cl(2) N(1)–W–N(2) N(1)–W–N(3) C(1)–W–Cl(1) C(1)–W–Cl(2) C(1)–W–N(2) C(1)–W–N(3) C(2)–W–Cl(1) C(2)–W–Cl(2) C(2)–W–N(2) 1.733(6) 2.233(7) 2.331(6) 2.447(2) 2.448(2) 2.086(8) 99.9(3) 102.7(3) 94.3(3) 97.9(3) 96.0(3) 166.2(3) 118.8(2) 82.3(2) 156.2(3) 93.7(3) 83.4(2) 116.5(2) 153.9(3) W–C(2) N(1)–C(3) C(1)–C(2) C(1)–C(17) C(2)–C(23) C(2)–W–N(3) Cl(2)–W–Cl(1) N(2)–W–Cl(1) N(2)–W–Cl(2) N(3)–W–Cl(1) N(3)–W–Cl(2) N(3)–W–N(2) C(3)–N(1)–W C(23)–C(2)–C(1) C(17)–C(1)–C(2) C(1)–C(2)–W C(2)–C(1)–W C(2)–W–C(1) 2.085(8) 1.420(10) 1.271(11) 1.461(12) 1.463(11) 89.8(3) 153.32(8) 77.2(2) 78.0(2) 81.3(2) 81.3(2) 70.3(2) 178.1(7) 139.6(8) 141.6(8) 72.3(5) 72.2(5) 35.5(3) [{WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(NH2C6H3Pri 2-2,6)}x] 11.The NMR spectra are complex and individual assignments have not been attempted other than again to note the position of the acetylenic carbon resonance in the 13C-{1H} NMR spectrum at d 166.51 which compares with the alkylimido complexes at ca. d 155.00. Reaction of complex 11 with dmbipy gave [WCl2- (NC6H3Pri 2-2,6)(PhC2Ph)(dmbipy)] 12 which has IR and NMR spectral characteristics for the dmbipy and diphenylacetylene ligands similar to those of dmbipy complexes 4 and 8.The complex thus has a trans-dichloro structure and not the cisdichloro structure (similar to complex 9) found for [WCl2- (NC6H3Pri 2-2,6)(PhC2Ph)(dmbipy)] produced by the reduction of [WCl3(NC6H3Pri 2-2,6)(dmbipy)] in the presence of diphenylacetylene. 3 The 13C-{1H} NMR spectrum of complex 12 shows the acetylenic carbon resonance at d 167.50 which is higher than those of all the other complexes and may represent some acetylene ligand p^ orbital donation in a competitive manner to the tungsten orbital involved in the imido p-donor system.An XPS spectrum shows the tungsten(4f7/2) binding energy at 33.97 eV which is slightly higher than that found for [WCl2(NCMe3)- (PhC2Ph)(bipy)] 3 (33.84 eV) where the acetylenic carbon resonance in the 13C-{1H} NMR spectrum occurs at d 163.60. For a further comparison of this resonance position, [WCl2- (NC6H3Me2-2,6)(PhC2Ph)(dmbipy)] 13 prepared by reaction of Me3SiNHC6H3Me2-2,6 with [{WCl4(PhC2Ph)}2] and characterised by NMR spectroscopy, has the acetylenic carbons at d 167.26 which is not significantly diVerent to those of complex 12 (d 167.50).The complexes [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(py)2] 14 and [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(PMe3)2] 15 were also prepared from [{WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(NH2C6H3Pri 2-2,6)}x] 11 with characterisation made by NMR spectroscopy.The 1H and 13C-{1H} spectral characteristics of the py and diphenylacetylene ligands for complex 14 are similar to those found for [WCl2(NCMe3)(PhC2Ph)(py)2] 5 with the respective acetylenic carbon resonances in the 13C-{1H} NMR spectra at d 158.78 and 155.78. Phosphine complex 15 has identical NMR spectra to those of [WCl2(NC6H3Pri-2,6)(PhC2Ph)(PMe3)2] 16 prepared by the reaction of [WCl2(NC6H3Pri 2-2,6)(PMe3)3] and diphenylacetylene [13C-{1H} NMR spectrum, dC]] ] C 154.40].3 Finally, we have found that addition of one equivalent of Me3SiNHC6H3Pri 2-2,6 to [NEt4][WCl5(PhC2Ph)] generated in CH2Cl2 gives the amido complex [NEt4][WCl4(NHC6H3Pri 2- 2,6)(PhC2Ph)] 16 but it is not particularly stable.The 1H NMR spectrum shows the NH proton at d 9.82 with poorly resolved peaks for the isopropyl methyl groups and those of the NEt4 cation. The 13C-{1H} NMR spectrum accumulated over a longer period shows resonances consistent with this formulation although some decomposition is evident.However the main feature is the acetylenic carbon resonance at d 167.40 and in the IR spectrum n(C]] ] C) occurs at 1765 cm21 indicating that a single amido ligand (1s and 1p donor interactions) is suYcient to convert the acetylene ligand into a 2-electron donor. The crystal structure of the 2,6-diisopropylphenylimido analogue, [NH3C6H3Pri 2-2,6][WCl4(NC6H3Pri 2-2,6)(NHC6H3Pri 2-2,6)], has been described.17 Conclusion The results of these studies show that the 4-electron donor alkyne ligands in [{WCl4(PhC2Ph)}2] are converted into 2- electron donors when an imido ligand is added to the complex.This occurs as the imido ligand is a stronger p donor (2p donor interactions) compared with the alkyne (1p donor interaction). This complex exhibits properties and chemistry consistent with it being a d0 tungsten complex whereas the imido complexes are d2 so that in formal terms a change in oxidation state has occurred.The position of the acetylenic carbon resonance in the 13C-{1H} NMR spectra is an important indicator of this change with the downfield shifts observed for some ofJ. Chem. Soc., Dalton Trans., 1999, 2021–2029 2027 the imido complexes suggesting increasing involvement of the alkyne p^ component (p-donor interaction). Our initial studies aimed at converting the alkyne back into a 4-electron donor via such species as a five-co-ordinate cation, [WCl(NR)(PhC2Ph)- (L)2]1, or neutral five-co-ordinate complex [WCl2(NR)- (PhC2Ph)(L)] where L is a bulky ligand, have so far been unsuccessful. This approach has been taken in view of the 4-electron donor nature of the alkyne ligand in the tantalum complex [TaCl2(NC6H3Pri 2-2,6)(PhC2Ph)(py)2] (dC]] ] C 195.9).18 Such reactions are important as the alkyne ligand has the potential to act as an electron sink so that cycling through the d0/d2 system would provide a reversible redox system.The synthetic strategy outlined in this work also allows the preparation of a variety of d2 imido-alkyne complexes which we have otherwise found diYcult to prepare.3 Experimental General procedures and instrumentation have been described. The IR spectra were obtained as Nujol mulls and 1H and 13C- {1H} NMR spectra were recorded at 400 and 100 MHz respectively. Analytical data were obtained by Dr A. Cunningham and associates, University of Otago, New Zealand.The trimethylsilylalkylamines (Me3SiNHR, R = CMe3 or CHMe2) were prepared by reaction of the alkylamine with Me3SiCl and the substituted trimethylsilylanilines by reaction of the lithium amide with Me3SiCl. The complex [{WCl4(PhC2Ph)}2] was prepared by treating WCl6 with PhC2Ph in the presence of tetrachloroethylene. 19 Trimethylphosphine was prepared by reaction of MgMeI with P(OPh)3 in di-n-butyl ether 20 and PMe2Ph by reaction of MgMeI on PCl2Ph. Pyridine was dried over and distilled from freshly ground calcium hydride and [Et4N]Cl was dried at 100 8C under vacuum for 2 h prior to use.The bipy and dmbipy were obtained from Aldrich and used without further purification. Benzene, light petroleum (bp range 40–60 8C) and diethyl ether were distilled over sodium wire, tetrahydrofuran from sodium–benzophenone and dichloromethane from freshly ground calcium hydride. Syntheses [{WCl2(NCMe3)(PhC2Ph)(NH2CMe3)}x] 1. A solution of Me3SiNHCMe3 (1.1 cm3, 5.7 mmol) in benzene (30 cm3) was added to a suspension of [{WCl4(PhC2Ph)}2] (1.30 g, 1.6 mmol) in benzene and the mixture stirred for 18 h.The solution was filtered and the solvent removed to small volume (ca. 5 cm3) and allowed to stand. The colourless solid was filtered oV, washed with cold benzene (10 cm3, 5 8C), and dried under vacuum. Yield 0.95 g (63%). IR spectrum: 3254w, 3252w, 2752w, 2605w, 2502w, 1762w, 1590w, 1562m, 1515w, 1396w, 1340w, 1302m, 1250s, 1210m, 1185m, 1158w, 1075w, 1028w, 925w, 770m, 695m, 600w, 535w, 455w, 350w, 305w and 208w cm21.[NEt4][WCl3(NCMe3)(PhC2Ph)(NH2CMe3)] 2. The salt [Et4N]Cl (0.33 g, 2.0 mmol) in CH2Cl2 (20 cm3) was added to [{WCl4(PhC2Ph)}2] (1.0 g, 0.95 mmol) suspended in CH2Cl2 (40 cm3) and the mixture stirred for 10 min giving a red-brown solution which was filtered from a small amount of solid. A solution of Me3SiNHCMe3 (0.8 cm3, 4.1 mmol) in CH2Cl2 was added and the mixture stirred for 2.5 h. The solution was filtered and the solvent removed to give a colourless solid.Yield 1.23 g. The complex could not be obtained analytically pure by recrystallisation and was characterised tentatively on the basis of NMR spectra. [WCl2(NCMe3)(PhC2Ph)(bipy)] 3. A solution of Me3SiNHCMe3 (0.5 cm3, 2.6 mmol) in benzene (30 cm3) was added to a suspension of [{WCl4(PhC2Ph)}2] (0.6 g, 0.6 mmol) in benzene (50 cm3) and the mixture stirred for 16 h and filtered. A solution of 2,29-bipyridyl (0.2 g, 1.3 mmol) in benzene (20 cm3) was added and the mixture refluxed for 2 h and then filtered while hot.The volume was reduced while keeping the solution hot and on standing yellow crystals of the complex formed. Yield: 0.6 g (72%). IR spectrum: 1740w, 1600m, 1575w, 1515w, 1405w, 1360m, 1310m, 1275s, 1220m, 1175m, 1158m, 1108w, 1076w, 1045w, 1030m, 1020m, 970w, 920w, 905w, 848w, 808w, 770s, 738m, 700s, 680s, 655w, 640w, 595w, 560w, 540w, 505w, 455w, 355w and 298m cm21.[WCl2(NCMe3)(PhC2Ph)(dmbipy)] 4. A solution of Me3Si- NHCMe3 (2.0 cm3, 10.3 mmol) in benzene (35 cm3) was added to [{WCl4(PhC2Ph)}2] (2.4 g, 2.4 mmol) suspended in benzene (40 cm3). The solution was stirred for 16 h, filtered, 4,49- dimethyl-2,29-bipyridyl (0.90 g, 4.9 mmol) in benzene (25 cm3) added and the mixture refluxed for 4 h. The solution was filtered and the product cropped successively by reducing the amount of solvent. Yield: 2.67 g (81%). The complex was characterised by NMR spectroscopy.[WCl2(NCMe3)(PhC2Ph)(py)2] 5. A solution of Me3SiNHCMe3 (0.8 cm3, 4.1 mmol) in benzene (10 cm3) was added to [{WCl4(PhC2Ph)}2] (1.0 g, 1.0 mmol) suspended in benzene. The mixture was stirred for 18 h, neat pyridine added (1 cm3) and the solution stirred for 3 h. The yellow solid obtained on removing the solvent and washing the residue with light petroleum (100 cm3) was characterised by NMR spectroscopy. [WCl2(NCMe3)(PhC2Ph)(PMe3)2] 6. A solution of Me3Si- NHCMe3 (0.7 cm, 3.6 mmol) in benzene (15 cm3) was added to a suspension of [{WCl4(PhC2Ph)}2] (0.9 g, 0.9 mmol) in benzene (50 cm3) and the mixture stirred for 20 h.The solution was filtered, PMe3 (0.5 cm3, 4.6 mmol) added, and the mixture stirred for 3 h. After filtering and removal of the volatiles the complex was obtained as a colourless crystalline solid. Yield 0.8 g (67%). IR spectrum: 1770w, 1685w, 1415m, 1305w, 1280m, 1255s, 1212w, 1065w, 1020w, 940s, 850w, 780w, 730w, 700w, 580w, 560w, 500w, 265w and 215w cm21.[WCl2(NCMe3)(PhC2Ph)(PMe2Ph)2] 7. A solution of Me3Si- NHCMe3 (0.7 cm3, 4.8 mmol) in benzene (30 cm3) and [{WCl4(PhC2Ph)}2] (0.9 g, 1.8 mmol) suspended in benzene (20 cm3) were treated in the usual manner. After filtering, PMe2Ph (0.5 cm3, 4.1 mmol) was added and the mixture refluxed for 2 h. The volatiles were removed from the filtered solution giving a gum which solidified on standing under light petroleum for several hours. Crude yield 1.1 g (79%).Recrystallisation of the solid from toluene at 220 8C gave colourless crystals. Yield: 0.8 g (57%). IR spectrum: 1755m, 1590m, 1565w, 1460s, 1415s, 1450s, 1290w, 1245s, 1210w, 1108w, 1075w, 1012w, 1000w, 945m, 905s, 845m, 778m, 740s, 695s, 585w, 555w, 490s, 410m, 350w, 318w, 265m and 235w cm21. [WCl2(NCHMe2)(PhC2Ph)(dmbipy)] 8. A solution of Me3Si- NHCHMe2 (0.75 cm3, 4.2 mmol) in benzene (10 cm3) was added to a suspension of [{WCl4(PhC2Ph)}2] (1.0 g, 1.0 mmol) in benzene (30 cm3) and the mixture was stirred for 5 h and filtered. 4,49-Dimethyl-2,29-bipyridyl (0.4 g, 2.2 mmol) in benzene (10 cm3) was added and the solution refluxed for 2 h, filtered and the volatiles were removed. The residue was washed with cold benzene (5 × 1 cm3) leaving a yellow solid (0.8 g) which was extracted with hot benzene (120 cm3), the solution filtered and the volume reduced to give yellow microcrystals. Yield 0.5 g (37%). IR spectrum: 1765w, 1610s, 1595m, 1480m, 1410s, 1370m, 1280s, 1235w, 1220w, 1155w, 1110w, 1070w, 1018m, 918w, 895w, 835w, 822m, 770m, 765m, 695m, 590w, 545w, 522w, 500w, 455w, 420w and 295s cm21.[WCl2(NCH2Me)(PhC2Ph)(dmbipy)] cis-chloro isomer 9. A solution of Me3SiNHEt (0.4 cm3, 2.5 mmol) in benzene (25 cm3) was added to a suspension of [{WCl4(PhC2Ph)}2] (0.6 g,2028 J. Chem. Soc., Dalton Trans., 1999, 2021–2029 0.6 mmol) in benzene (35 cm3) and the mixture stirred for 16 h. The solution was filtered, 4,49-dimethyl-2,29-bipyridyl (0.25 g, 1.36 mmol) in benzene (15 cm3) added and the mixture refluxed for 1 h.The solution was filtered while hot, the solvent reduced to ca. 45 cm3 and on standing the complex formed as a noncrystalline solid. Yield 0.24 g (30%). IR spectrum: 1785w, 1618s, 1595m, 1410m, 1325w, 1295s, 1258w, 1240w, 1065w, 1020m, 925m, 840w, 835w, 765m, 700m, 585w, 560w, 550w, 522w, 305m and 212w cm21. [WCl2(NCH2Me)(PhC2Ph)(dmbipy)] trans-chloro isomer 10. The solution remaining after isolation of complex 9 was reduced in volume to ca. 20 cm3 and on standing the complex formed as yellow crystals. Yield 0.46 g (52%). IR spectrum: 1770w, 1618s, 1595w, 1410w, 1330w, 1305s, 1285m, 1265w, 1242w, 1075w, 1025m, 928w, 910w, 835m, 775m, 745w, 690s, 550w, 520w, 420w and 300m cm21. [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(NH2C6H3Pri 2-2,6)] 11. The compound Me3SiNHC6H3Pri 2-2,6 (3.8 g, 15.3 mmol) in diethyl ether (30 cm3) was added to [{WCl4(PhC2Ph)}2] (3.8 g, 3.8 mmol) suspended in diethyl ether (120 cm3) and the mixture stirred for 24 h followed by a gentle reflux for 1 h.The solution was filtered, the solvent removed and the solid washed with light petroleum (60 cm3, 0 8C) and dried under vacuum. Yield 5.7 g (96%). The complex did not mull well in Nujol giving a poorly resolved spectrum. [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(dmbipy)] 12. Complex 11 (0.9 g, 1.2 mmol) and dmbipy (0.25 g, 1.4 mmol) were mixed and degassed. Tetrahydrofuran (25 cm3) was added and the mixture refluxed for 2 h.The solution was filtered and the solvent reduced to ca. 8 cm3 giving the complex as a yellow microcrystalline solid. Yield 0.48 g (53%). IR spectrum: 1790w, 1615s, 1590w, 1360s, 1340s, 1300w, 1240w, 1070w, 1020w, 900w, 830w, 802w, 760m, 730m, 695m, 580w, 560w, 518w, 455w and 300w cm21. [WCl2(NC6H3Me2-2,6)(PhC2Ph)(dmbipy)] 13. The compound Me3SiNHC6H3Me2-2,6 (0.8 g, 4.2 mmol) in benzene (15 cm3) was added to a suspension of [{WCl4(PhC2Ph)}2] (1.0 g, 1.0 mmol) in benzene (35 cm3) and the mixture stirred for 18 h.The yellow-brown solution was filtered and the solvent removed to give a yellow crystalline solid. Yield 1.3 g (98%). The complex (1.0 g, 1.5 mmol) and 4,49-dimethyl-2,29-bipyridyl (0.3 g, 1.6 mmol) were refluxed in benzene (35 cm3) for 2 h. The solution was filtered, the solvent removed and the yellow solid washed with light petroleum (60 cm3). Yield 1.0 g (99%). The complex was characterised by NMR spectroscopy.[WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(py)2] 14. Neat pyridine (1 cm3) was added to complex 11 (0.8 g, 1.0 mmol) in diethyl ether (30 cm3) and the mixture was stirred for 2 h. The solution was filtered and the solvent removed to give a yellow gum which solidified on standing under light petroleum (50 cm3). The solid was dissolved in toluene (20 cm3), the solution filtered and light petroleum (60 cm3) added to precipitate the complex. Yield 0.45 g (58%). This procedure failed to give an analytically pure sample [Found: C, 52.6; H, 4.6; N, 4.6.C36H37Cl2N3W requires C, 56.4; H, 4.9; N, 5.5%] and the sample would not crystallise from other solvents so it was characterised by NMR spectroscopy. [WCl2(NC6H3Pri 2-2,6)(PhC2Ph)(PMe3)2] 15. Complex 11 (0.8 g, 1.0 mmol) was dissolved in diethyl ether (45 cm3) and an excess of PMe3 (0.25 cm3) added. The mixture was stirred for 3 h, the solution filtered and the solvent removed to give a gum which solidified on standing under light petroleum (50 cm3).Yield 0.75 g (97%). The complex had identical NMR spectra to those of an authentic sample.3 [NEt4][WCl4(NHC6H3Pri 2-2,6)(PhC2Ph)] 16. The salt [Et4N]- Cl (0.33 g, 2.0 mmol) in CH2Cl2 (25 cm3) was added to [{WCl4(PhC2Ph)}2] (1.0 g, 1.0 mmol) suspended in CH2Cl2 (25 cm3) and the mixture stirred for 1 h. The compound Me3- SiNHC6H3Pri 2-2,6 (0.5 g, 2.0 mmol) in CH2Cl2 (15 cm3) was added and the solution stirred for 20 h.The solution was filtered, the solvent removed and the solid held under vacuum for several hours. Yield 1.6 g (94%). The complex did not mull well in Nujol giving a poorly resolved spectrum. Crystallography Data collection was performed on a Nonius CAD-4 diVractometer using graphite monochromated Mo-Ka radiation (l = 0.71069 Å). The intensities were reduced to F2 and an empirical absorption correction applied based on y scan data.21 The structures were solved by Patterson and Fourier methods followed by full-matrix refinement on F2 using programs SHELXS 8622 and SHELXL 93.23 Hydrogen atoms were introduced in calculated positions and allowed to ride on the carrier atom.The thermal parameters of the methyl groups in complex 6 show large thermal motion indicative of some disorder. With C4 and C12 the electron density could be resolved into two peaks and these atoms have been allowed to refine as two half-weighted atoms with isotropic thermal parameters.Crystal data for complex 6. C24H37Cl2NP2W, M = 656.24, monoclinic, space group P21/c, a = 16.674(2), b = 10.159(4), c = 17.196(2) Å, b = 106.63(2)8, U = 2791.0(12) Å3, T = 173 K, Z = 4, m(Mo-Ka) = 4.45 mm21, 3969 observed reflections. Final wR(F2) was 0.0942; R1 = 0.0334. Crystal data for complex 10. C6H6. C34H33Cl2N3W, M = 738.38, triclinic, space group P1� , a = 10.091(2), b = 11.584(4), c = 14.098(2) Å, a = 87.00(2), b = 100.68(1), g = 97.31(2)8, U = 1605.6(2) Å3, T = 173 K, Z = 2, m(Mo-Ka) = 3.79, 4143 observed reflections.Final wR(F2) was 0.1080; R1 = 0.0429. CCDC reference number 186/1441. References 1 A. J. Nielson, P. D. W. Boyd, G. R. Clark, T. A. Hunt, J. B. Metson, C. E. F. Rickard and P. Schwerdtfeger, Polyhedron, 1992, 11, 1419; A. J. Nielson, P. D. W. Boyd, G. R. Clark, P. A. Hunt, M. B. Hursthouse, J. B. Metson, C. E. F. Rickard and P. A. Schwerdtfeger, J. Chem. Soc., Dalton Trans., 1995, 1153. 2 G. R. Clark, A. J. Nielson, A.D. Rae and C. E. F. Rickard, J. Chem. Soc., Dalton Trans., 1994, 1783. 3 G. R. Clark, M. W. Glenny, A. J. Nielson and C. E. F. Rickard, J. Chem. Soc., Dalton Trans., 1995, 1147. 4 M. D. Curtis, J. Real and D. Kwan, Organometallics, 1989, 8, 1644; F. A. Cotton and M. Shang, Inorg. Chem., 1990, 29, 508; K. H. Theopold, S. J. Holmes and R. R. Schrock, Angew. Chem., Int. Ed. Engl., 1983, 22, 1010; J. B. Hartung and S. F. Pedersen, J. Am. Chem. Soc., 1989, 111, 5468. 5 T. E. Baroni, J. A. Heppert, R. R. Hodel, R. P. Kingsborough, M. D. Morton, A. L. Rheingold and G. P. A. Yap, Organometallics, 1996, 15, 4872; P. M. Boorman, M. Wang and M. Parvez, J. Chem. Soc., Dalton Trans., 1996, 4533. 6 G. R. Clark, A. J. Nielson, C. E. F. Rickard and D. C. Ware, J. Chem. Soc., Chem. Commun., 1989, 343; A. J. Nielson and D. C. Ware, Polyhedron, 1990, 9, 603. 7 J. L. Templeton, Adv. in Organomet. Chem., 1989, 29, 1. 8 B. R. Ashcroft, D. C. Bradley, G. R. Clark, R. J. Errington, A. J. Nielson and C. E. F. Rickard, J. Chem. Soc., Chem. Commun., 1987, 170; B. R. Ashcroft, A. J. Nielson, D. C. Bradley, R. J. Errington, M. B. Hursthouse and R. L. Short, J. Chem. Soc., Dalton Trans., 1987, 2059. 9 A. J. Nielson, P. D. W. Boyd. G. R. Clark, P. A. Hunt, J. B. Metson, C. E. F. Rickard and P. Schwerdtfeger, Polyhedron, 1995, 14, 1255. 10 M. Kersting, K. Dehnicke and D. Fenske, J. Organomet. Chem. 1988, 346, 201. 11 T. C. Jones, A. J. Nielson and C. E. F. Rickard, J. Chem. Soc., Chem. Commun., 1984, 205; P. A. Bates, A. J. Nielson and J. M. Waters, Polyhedron, 1985, 4, 1391; A. J. Nielson, Polyhedron, 1988, 7, 67.J. Chem. Soc., Dalton Trans., 1999, 2021–2029 2029 12 D. D. Devore and E. A. Maatta, Inorg. Chim. Acta, 1986, 112, 87. 13 M. R. Churchill, Y.-J. Li, K. H. Theopold and R. R. Schrock, Inorg. Chem., 1984, 23, 4472. 14 G. R. Clark, A. J. Nielson, A. D. Rae and C. E. F. Rickard, J. Chem. Soc., Chem. Commun., 1992, 1069; J. Chem. Soc., Dalton Trans., 1994, 1783. 15 C. D. Wagner, W. M. Riggs, L. F. Davis, J. F. Moulder and G. E. Muslenberg, Handbook of X-Ray Photoelectron Spectroscopy, Perkin-Elmer, Eden Prairie, St Paul, MN, 1979, p. 146. 16 G. R. Clark, A. J. Nielson and C. E. F. Rickard, J. Chem. Soc., Dalton Trans., 1995, 1907. 17 A. J. Nielson, G. R. Clark and C. E. F. Rickard, Aust. J. Chem., 1997, 50, 259. 18 Y.-W. Chao, P. A. Wexler and D. E. Wigley, Inorg. Chem., 1989, 28, 3860. 19 E. Hay, F. Weller and K. Dehnicke, Z. Anorg. Allg. Chem., 1984, 514, 25. 20 M. L. Luetkens, jun., A. P. Sattelberger, H. H. Murray, J. D. Basil, J. P. Fackler, jun., R. A. Jones and D. E. Heaton, Inorg. Synth., 1990, 28, 305. 21 A. C. North, D. C. Phillips and F. S. Mathews, Acta Crystallogr. Sect. A, 1968, 24, 351. 22 G. M. Sheldrick, SHELXL 86, Acta Crystallogr., Sect. A, 1990, 46 467. 23 G. M. Sheldrick, SHELXL 93, Program for the refinement of crystal structures, University of Göttingen, 1993. Paper 8/0917

ISSN:1477-9226    

DOI:10.1039/a809171d

出版商:RSC    

年代:1999

数据来源: RSC

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DALTON FULL PAPER J. Chem. Soc., Dalton Trans., 1998, Pages 2023–2027 2023 Self-assembling iron and manganese metal–germanium–selenide frameworks: [NMe4]2MGe4Se10, where M 5 Fe or Mn Homayoun Ahari, Armando Garcia, Scott Kirkby, GeoVrey A. Ozin,* David Young and Alan J. Lough Materials Chemistry Research Group, Lash Miller Chemical Laboratories, University of Toronto, 80 St. George Street, Toronto, Ontario, Canada M5S 3H6 The hydrothermal synthesis mixture Ge–Se–(TMA)OH–H2O (TMA1 = NMe4 1) yielded crystals of the material (TMA)4Ge4Se10.A single-crystal X-ray diVraction structure showed the presence of adamantanoid Ge4Se10 42 clusters and TMA1 cations. The TMA1 template-mediated aqueous synthesis of (TMA)2MGe4Se10 (M = Mn or Fe) from Ge4Se10 42 and M21 building-blocks is described. Rietveld powder X-ray diVraction full profile structure refinements of (TMA)2MGe4Se10 established that these novel metal–germanium–selenide frameworks are isostructural with the analogous metal–germanium–sulfides, (TMA)2MGe4S10. The selenide materials have a zinc blende-type of open-framework structure. Charge-balance of the anionic open-framework [MGe4Se10]22 is maintained by two TMA1 template cations that reside within the cavity spaces.Trends in the tetragonal unit cell dimensions and metal–chalcogenide bond lengths of (TMA)2MGe4X10 (X = S or Se) are those expected based upon increases in metal and chalcogenide radii on passing from S2II to Se2II and FeII to MnII.Controlled compositional variations of solid-state inorganic materials using isomorphous substitution, doping and defect chemistry is the foundation of tailoring their synthesis, structure, property and function relations.1 Nowhere is this more apparent than in silicon, gallium arsenide and zinc sulfide semiconductor materials and devices, where their properties are controlled through compositional tuning between isostructural end-members, exemplified by Si/Ge, GaAs/AlAs and ZnS/ ZnSe.Thus, SixGe1 2 x alloys are used in high mobility transistors, AlxGa1 2 xAs to engineer the electronic band structure of quantum devices, Ga1 1 xAs/GaAs1 1 x to control the number of charge carriers in pn-doped laser diodes, ZnSxSe1 2 x to tailor the absorption properties of IR detectors and the emission characteristics of blue-green laser diodes.2 These devices function on the principle of a random distribution of the elemental constituents over the tetrahedral sites of close-packed diamond- and zinc blende-types of crystal lattices. Recently, we applied this paradigm to isostructural tin(IV) thioselenide open-framework materials.3 The end-members have a framework that is based upon 2-D parallel-stacked microporous anionic [Sn3X7]22 layers, where X = S or Se. The individual layer topology is a 24-atom-ring hexagonal net.The pores are made up of broken cube Sn3X4 clusters connected via Sn(m-X)2Sn bridges. The tetramethylammonium (TMA1) charge balancing cations are positioned within the pores and between the layers.In the ternary (TMA)2Sn3SxSe7 2 x materials where 0 < x < 7, it was established that the distribution of the chalcogenides is random (solid–solution, Vegard law) at the length scale of the unit cell but site-selective at the level of the trigonal bipyramidal building blocks.4 In a related system, the self-assembly of Ge4S10 42 and M21 building blocks, mediated by the TMA1 template, produces an isostructural family of (TMA)2MGe4S10 materials (where M = Mn, Fe, Co or Zn).5–8 Their structure is based upon a zinc blende-type open framework with the tetragonal space group I4� and unit cell dimensions in the range a = 9.400–9.513 and c = 14.026–14.281 Å.The tetrahedral sites in the lattice are alternately substituted by pseudo-tetrahedral M21 and adamantanoid Ge4S10 42 building blocks, all covalently linked together by M(m-S)Ge bridge bonds. Charge balance of the anionic framework [MGe4S10]22 is maintained by two TMA1 template cations that reside within the cavity spaces. The isostructurality of the family of zinc blende-type openframeworks (TMA)2MGe4S10 provides an excellent opportunity for compositional tuning of their properties via the synthesis of (TMA)2MxM91 2 xGe4S10 solid solutions, where 0 < x < 1.6 The distribution of the M21/M921 cations over the pseudotetrahedral sites that link together the Ge4S10 42 adamantanoid modules controls the properties of these materials.Another approach for property tailoring in this system involves crystallizing mixtures of the precursors M21, xGe4S10 42 and (1 2 x)Ge4Se10 42 to give (TMA)2M(Ge4S10)x(Ge4Se10)1 2 x, where 0 < x < 1. As a step in this direction we report the synthesis and singlecrystal X-ray diVraction (XRD) structure determination of the adamantanoid (TMA)4Ge4Se10 precursor as well as Rietveld powder X-ray diVraction (PXRD) full profile structure refinements of (TMA)2MGe4Se10, where M = Mn or Fe, which establishes that these metal–germanium–selenide frameworks are isostructural with the analogous metal–germanium–sulfides, (TMA)2MGe4S10.5–8 Experimental Synthesis A note of safety.All the synthetic procedures outlined in this paper must be carried out in a fumehood. A self-contained aspirator pump is essential for this type of work in order to prevent discharge of volatile amines and alkyl selenides from the filtrate.(TMA)4Ge4Se10. Yellow cube-shaped crystals were obtained from the hydrothermal synthesis system with a reaction ratio of 4.1(TMA)OH?5H2O:4Ge: 10Se :130H2O. A reaction mixture, consisting of 2.28 g (TMA)OH?5H2O, 4.4 g H2O, 2.43 g Se and 0.89 g Ge, following the same order of addition, was placed into a TeflonTM-lined stainless steel reactor and heated hydrothermally at 150 8C for 3 d in a rolling oven. The product was recovered using suction filtration. The mass yield was 1.39 g which corresponded to a yield of 33% assuming no hydration in the final dry product.(TMA)2MGe4Se10 (M 5 Mn or Fe). These compounds can2024 J. Chem. Soc., Dalton Trans., 1998, Pages 2023–2027 Fig. 1 Observed (1, Io), calculated (--, Ic) and diVerence (Io 2 Ic) high resolution room-temperature PXRD patterns of (a) (TMA)2MnGe4Se10 and (b) (TMA)2FeGe4Se10 be synthesized and crystallized from water by simply mixing together aqueous solutions of the M21 and adamantanoid Ge4Se10 42 building-blocks.Control over the rates of nucleation and crystal growth has been achieved through reaction profiles that examine the eVects of temperature, selective complexation, mineralization and transporting agents and diVusion crystal growth. Optimization of the product yield, phase purity and degree of crystallinity (PXRD) of (TMA)2MGe4Se10 was achieved in syntheses that employed the following reaction stoichiometries and weights of reagents: (TMA)4Ge4Se10 (0.35 g, 0.25 mmol), FeSO4?7H2O (0.078 g, 0.28 mmol), H2O (9.15 g, 510 mmol) giving a yield of 0.20 g for (TMA)2FeGe4Se10; and (TMA)4Ge4Se10 (0.35 g, 0.25 mmol), Mn(OAc)2?4H2O (0.069 g, 0.28 mmol), H2O (9.15 g, 510 mmol) giving a yield of 0.18 g for (TMA)2MnGe4Se10. The products (TMA)2MGe4Se10 are essentially phase pure (aside from a trace of poorly crystalline selenium formed on storage of the materials in air at room temperature; they appear indefinitely stable when stored below 0 8C under an Ar atmosphere).The (TMA)2MGe4Se10 products are orange (Mn) and red (Fe) in color. The crystal morphology is best described as a tetragonal tetrahedron or tetragonal disphenoid, which is characterized by four isosceles triangular faces with the four-fold improper rotation axis bisecting two opposite edges. The crystals varied in size between 1 and 20 microns. Powder X-ray diVraction and Rietveld structure refinement Room-temperature X-ray powder diVraction data of (TMA)2- MGe4Se10 were collected on a Siemens D-5000 diVractometer (Fig. 1) using a Cu tube source and a ‘drifted Li–Si’ solid-state detector whose energy window was centered at 8.04 keV (eV ª 1.602 × 10219 J).The detector was set to discriminate against Cu-Kb, leaving the Cu-Ka1,2 X-ray lines. Voltage and current settis of the X-ray tube were 50 kV and 35 mA, respectively. The samples were packed onto low background flat plates. For practical reasons the data were collected in two sections from 10 to 428 and from 42 to 758 2q.This allowed the collection of high signal-to-noise data in the upper range while still keeping total collection times within acceptable limits for the X-ray facility. The Rietveld refinements were carried out using the General Structure Analysis System (GSAS).9 The two ranges of each data set were fitted as two histograms for a single structural model. The unit cell starting values were obtained from indexing the lower range histogram.The single-crystal data for (TMA)2MnGe4S10 were used to provide the initial atom positions within the unit cell and the I4� space group. The atom positions were translated within the unit cell to place a Ge4Se10 42 unit at the body center, rather than TMA1. This was done for convenience during the refinement. The histograms were fitted by first refining the lattice parameters and the background function. Next the atom positions were allowed to vary, followed by the peak profile coeYcients.The peaks were modeled as pseudo-Voigt functions. The starting values for the coeYcients were determined by refining LaB6, a line-shape standard [National Institute of Standards and Technology instrument line position and profile shape (SRM 660) LaB6 diVraction standards]. Isotropic thermal parameters were constrained to positive values. Any factor that ran negative was replaced with GSAS’s default value of 0.0250 and fixed before final refinement.The TMA1 cations present in the void spaces of the framework were fitted as ‘NC4 rigid bodies’ which maintained their structure. No attempt was made to fit the TMA1 cations with the hydrogen atoms attached since past experience with room-temperature data Rietveld refinements has demonstrated no improved correlation of the results to those obtained by single-crystal diVraction methods. EVorts to fit the TMA1 as independent atoms resulted in the failure of the refinement to converge to a sensible structure.This resulted from slight background electron density within the cavity. The most reasonable explanation is delocalization (likely thermal motion) of the TMA1 cations about the special positions on which they are centered. All the refinements gave Rp values of less than 9% indicating acceptable fits.J. Chem. Soc., Dalton Trans., 1998, Pages 2023–2027 2025 Table 1 Pertinent crystallographic information for (TMA)2MGe4X10, where M = Mn or Fe; X = S or Se Tetragonal I4� Parameter a/Å c/Å U/Å3 r(GeXt)/Å r(GeXb)*/Å r(MXt)*/Å a(XtMXt)/8 b(XtMXt)/8 (TMA)2MnGe4S10 528 9.513(1) 14.281(2) 1292.4 2.159 2.243–2.218 2.440 124.5 102.5 (TMA)2FeGe4S10 8 9.429(4) 14.206(6) 1263.0 2.132 2.259–2.107 2.298 119.0 104.9 (TMA)2MnGe4Se10 9.767(4) 14.833(6) 1415.0 2.289 2.380–2.304 2.552 127.5 101.3 (TMA)2FeGe4Se10 9.696(5) 14.705(8) 1382.5 2.241 2.401–2.317 2.502 125.5 102.1 * Range of three distinct germanium–chalcogenide Ge4X10 intracluster bond lengths.As expected the Rietveld refinements confirmed that (TMA)2- MGe4X10 (M = Mn21 or Fe21; X = S or Se) are all isostructural, but with variations in the unit-cell parameters and in some of the atom positions within the unit cell (see Table 1). Unit-cell parameters, atom positions and Rietveld refinement statistics are listed in Tables 2 and 3. CCDC reference number 186/979. Table 2 Fractional atomic parameters for (TMA)2MnGe4Se10 a Atomb Ge(1) Se(2) Se(3) Se(4) N(1) C(1) N(2) C(2) Mn(1) x 0.078 9(4) 0.260 4(4) 0.000 0 0.176 3(4) 0.500 0 0.374 680 0.500 0 0.422 350 0.000 0 y 0.176 3(4) 0.103 1(3) 0.000 0 0.345 5(4) 0.500 0 0.466 050 0.000 0 20.101 640 0.500 0 z 0.088 5(3) 20.006 7(3) 0.186 3(3) 0.173 9(3) 0.000 0 20.062 040 0.250 0 0.189 890 0.250 0 U(iso)/Å2 0.0250 0.0250 0.0250 0.0250 0.0250 0.06(1) 0.0250 0.0250 0.0250 a Rietveld refinement statistics for (TMA)2MnGe4Se10; histogram 1: Rwp = 11.78%; Rp = 8.72%; histogram 2: Rwp = 11.62%, Rp = 9.08%; powder totals: Rwp = 11.67%, Rp = 8.98%; cR 2 = 6.902.b The high precision for the carbon atom positions is the product of the rigid body refinement of the TMAs with the nitrogen atoms in the special positions. Table 3 Fractional atomic parameters for (TMA)2FeGe4Se10 a Atomb Ge(1) Se(1) Se(2) Se(3) N(1) C(1) N(2) C(2) Fe(1) x 0.078 9(5) 0.263 7(5) 0.000 0 0.173 8(5) 0.500 0 0.374 680 0.500 0 0.422 350 0.000 0 y 0.181 1(5) 0.106 5(4) 0.000 0 0.350 2(4) 0.500 0 0.466 050 0.000 0 20.101 640 0.500 0 z 0.089 2(4) 20.006 0(4) 0.187 7(5) 0.172 2(3) 0.000 0 20.062 040 0.250 0 0.189 890 0.250 0 U(iso)/Å2 0.047(3) 0.041(3) 0.040(3) 0.027(2) 0.40(8) c 0.0250 0.0250 0.33(6) c 0.086(7) a Rietveld refinement statistics for (TMA)2FeGe4Se10; histogram 1: Rwp = 10.83%; Rp = 8.04%; histogram 2: Rwp = 4.96%, Rp = 3.90%; powder totals: Rwp = 7.22%, Rp = 5.13%; cR 2 = 2.614.b The high precision for the carbon atom positions is the product of the rigid body refinement of the TMAs with the nitrogen atoms in the special positions. The large thermal parameters on the atoms of TMA1 cations may be due to some disorder of these molecules.Attempts to model these molecules as disordered atoms gave no improvement in the structure refinement and in fact the model using the anisotropic thermal displacement parameters gave the better results. c The void space in which the TMA1 sits is larger than the close-packing space of the molecules.It is therefore expected to rattle around in the cavity space at room temperature among four lowest energy sites given the S4 symmetry. However, the space group and coordinate system chosen puts the N on a special position where it cannot move. The result would be a large C]N displacement vector and a large thermal parameter for N which is what is found. When it is attempted to fit the system with the N oV the special position and using a complete TMA1 cation, the fit was not any better and there were so many new TMA1 parameters from all the symmetry requirements that it did not provide any more meaning and might just be mopping up errors.Results and Discussion The compound (TMA)4Ge4Se10 crystallizes in the cubic space group P4� 3n with a = 20.028(2) Å. There are eight Ge4Se10 42 clusters in the cubic unit cell with two crystallographically distinct sites. Two of these units are located on the mid line of each face for a total of six, while the others lie at the center and corners accounting for the remaining two.Fig. 2 shows a labeled thermal ellipsoid drawing (ORTEP)10 of the molecule. There are also two crystallographically distinct sites for the charge balancing TMA1 cations in the unit cell. They form Ge]Set ? ? ?H]C (3.053, 3.112 Å) and Ge]Seb ? ? ?H]C (3.028, 3.143 Å) hydrogen bonds involving methyl group hydrogen atoms of the TMA1 cations and terminal and bridging selenium atoms of the adamantanoid Ge4Se10 42 cluster.The purity of the as-synthesized (TMA)4Ge4Se10 material was determined by the comparison of the X-ray powder pattern of the material with the simulated pattern created by CERIUS“ software as shown in Fig. 3.11 Details of the structure and summary of data collection for (TMA)4Ge4Se10 are presented in Tables 4 and 5. The crystallographic information for (TMA)4Ge4X10, where X = S or Se, is compared in Table 6. The powder patterns of (TMA)2MGe4Se10 (M = Mn or Fe) have been recorded under high resolution conditions on a Siemens D5000 diVractometer.They both indexed quite well in the tetragonal space group I4� and yielded unit cell dimensions of a = 9.767(4), c = 14.833(6) Å (Mn) and a = 9.696(5), c = 14.705(8) Å (Fe). This provides evidence for isostructurality between all members of the family of materials, (TMA)2MGe4X10, where M = Mn or Fe; X = S or Se, Table 1. The structure of (TMA)2MGe4S10 has been determined from singlecrystal XRD (M = Mn),5 by ab initio structure determination 7 and Rietveld PXRD full profile (M = Fe, Co, Zn) structure analyses.14 The phase has an open-framework structure based on the alternation, in all three spatial ns, of pseudotetrahedral M21 and adamantanoid Ge4S10 42 building-blocks, all covalently linked together by M(m-S)Ge bridge-bonds and packed into a tetragonal I4� unit cell with dimensions a = 9.513(1), c = 14.281(2) Å (Mn)5–7 and a = 9.429(4), c = Fig. 2 An ORTEP diagram of single-crystal XRD structure of (TMA)4Ge4Se10, H atoms are omitted for clarity2026 J. Chem. Soc., Dalton Trans., 1998, Pages 2023–2027 14.206(6) Å (Fe).8 With these structures as a starting model, Rietveld PXRD full profile structure analyses were performed on the new materials (TMA)2MnGe4Se10 and (TMA)2FeGe4- Se10. The initially guessed structure refined fairly well in both cases, to yield final Rp values of 8.98% (Mn) and 5.13% (Fe) indicative of a reliable structure determination.A pertinent graphical projection of the Rietveld crystal structures of the (TMA)2MnGe4Se10 and (TMA)2FeGe4Se10 frameworks is shown in Fig. 4. Inspection of the unit-cell dimensions, pertinent bond lengths and angles of the precursors (TMA)4Ge4X10 and products (TMA)2MGe4X10, where M = Mn or Fe and X = S or Se, Fig. 3 X-Ray powder pattern for (TMA)4Ge4Se10 (top) compared with the simulated powder pattern (bottom) from single-crystal data, created by CERIUS“ software Table 4 Single-crystal XRD data and structure refinement for (TMA)4Ge4Se10* Empirical formula MT /K l/Å Crystal system Space group a/Å U/Å3, Z Dc/Mg m23 m/mm21 F(000) Crystal size/mm q Range/8 Limiting indices Reflections collected Independent reflections Absorption correction Data, restraints, parameters Goodness of fit on F2 Final R indices [I > 2s(I)]: R1, wR2 R indices (all data): R1, wR2 Absolute structure parameter Extinction coeYcient Largest diVerence peak, hole/e Å23 C16H48Ge4N4Se10 1376.54 168(2) 0.710 73 Cubic P4� 3n 20.028(2) 8033.3(13), 8 2.276 12.041 5120 0.31 × 0.29 × 0.27 2.88 to 24.97 2 < h < 23, 0 < k < 16, 0 < l < 16 2492 1297 (Rint = 0.0849) 0.3547, 0.4274 1297, 0, 81 0.708 0.0345, 0.0301 0.1333, 0.0394 0.34(8) 0.000 060(2) 0.529, 20.552 * Mo-Ka radiation, graphite-monochromator, Enraf-Nonius CAD4 diVractometer, absorption correction (SHELXA-90 program for absorption correction),12 structure solved by direct methods and refined by full-matrix least-squares on F2 using SHELXTL/PC.13 The Ge and Se atoms were refined with anisotropic displacement parameters and C and N atoms were refined isotropically.Hydrogen atoms were included in calculated positions and treated as riding atoms. reveals the expected trends on passing from the smaller S2II and FeII to the larger Se2II and MnII, respectively, Table 1. The similarity of the bond lengths and angles in the adamantanoid Ge4X10 cluster in both the modular precursors and the openframework products indicates that it is behaving as a rigid ‘pseudo-tetrahedral’ connecting unit.Particularly interesting is Fig. 4 A CERIUS“ molecular graphics representation of (TMA)2- MGe4Se10 showing the adamantanoid Ge4X10 42 and M21 on alternate tetrahedral sites of a zinc-blende lattice. The TMA1 charge balancing cations occupy the void space of the open framework structure (hydrogen atoms are omitted for clarity) Ge Ge Ge Ge Ge Ge M M M M Se Se Se Se Se Se Se Se C C C C N z y x Table 5 Atomic coordinates [×1024] and equivalent isotropic displacement parameters [Å2 × 1023] for (TMA)4Ge4Se10 Atom Ge(1) Ge(2) Se(1) Se(2) Se(3) Se(4) Se(5) N(1) C(1) C(2) N(2) C(3) C(4) C(5) C(6) x 675(1) 708(1) 1324(2) 00 1368(1) 1399(1) 3372(9) 2960(12) 3197(12) 1508(8) 1664(11) 2007(9) 1611(11) 826(9) y 675(1) 5634(1) 1324(2) 0 5000 4926(1) 6269(2) 3372(9) 2960(12) 3203(11) 3392(7) 4123(10) 2968(10) 3257(10) 3223(10) z 675(1) 1823(1) 1324(2) 1381(2) 1113(1) 2508(1) 1202(1) 3372(9) 2960(12) 4096(10) 813(8) 712(10) 423(8) 1568(10) 624(9) U(eq) * 17(1) 16(1) 30(2) 21(1) 17(1) 19(1) 28(1) 26(8) 47(14) 36(7) 18(4) 33(5) 34(5) 38(7) 31(5) * U(iso) is defined as one third of the trace of the orthogonalized Uij tensor.Table 6 Pertinent crystallographic information for (TMA)4Ge4X10, where X = S or Se Cubic P4� 3n Parameter a/Å U/Å3 r(GeXt)/Å r(GeXb)/Å (TMA)4Ge4S10 * 19.390(3) 7290.1(2) 2.158(13) 2.244(3) (TMA)4Ge4Se10 20.028(2) 8033.3(13) 2.253(7) 2.378(2) * Single-crystal XRD structure determination on the material prepared from the elemental Ge–S precursors.5 The authors of this reference synthesized the same product from freshly prepared GeS2.J. Chem.Soc., Dalton Trans., 1998, Pages 2023–2027 2027 the local co-ordination geometry of the M21 linking site which is a squashed MX4 tetrahedral (S4 site symmetry) for all members of the family.The distortion from Td is most pronounced for (TMA)2MnGe4Se10 and least for (TMA)2FeGe4S10, although the angular spread is only Da = 8.5 and Db = 3.68 for the entire series. This structure-bonding model accounts for the roughly proportional expansion of the unit cell dimensions without any major angular distortions between the buildingblocks on passing from the smaller to the larger framework element constituents. From the X-ray diVraction results one can infer that there are local bond length and angular distortions for the 3d5, Mn21/ 3d6, Fe21 and Ge4X10 42 modular building-blocks in (TMA)2- MGe4X10 family members.These distortions are away from the regular Td symmetry sites in the archetype zinc blende-type lattice. They likely arise from the response of the entire system to co-operative TMA1–framework interactions (i.e. TMA1 template space-filling, charge-balancing and hydrogen-bonding considerations) in order to achieve a structure with the minimum energy configuration.Acknowledgements G. A. O. is deeply indebted to the Canada Council for the award of an Isaac Walton Killam Research Fellowship, 1995–1997. The generous financial assistance of the Natural Sciences and Engineering Research Council of Canada (NSERC), the Canadian Space Agency (CSA), and Universal Oil Products (UOP), is deeply appreciated. Dr. S. K. is deeply grateful to NSERC for a graduate scholarship in support of his research. In addition we thank Mr. G. Vovk for synthesizing the (TMA)4Ge4S10 material discussed in this paper. References 1 C. N. R. Rao and J. Gopalakrishnan, New Directions in Solid State Chemistry, Cambridge University Press, Cambridge, 1986. 2 R. Gunshor and A. V. Nurmikko, Mater. Res. Bull., 1995, 20, 15. 3 H. Ahari, R. L. Bedard, C. L. Bowes, T. Jiang, A. Lough, G. A. Ozin, S. Petrov and D. Young, Adv. Mater., 1995, 7, 375. 4 H. Ahari, R. L. Bedard, A. Lough, S. Petrov, G. A. Ozin and D. Young, Adv. Mater., 1995, 7, 370; H. Ahari, Ö. Dag, R. L. Bedard, S. Petrov and G. A. Ozin, J. Phys. Chem., 1998, 102, 2356. 5 O. M. Yaghi, Z. Sun, D. A. Richardson and T. L. Groy, J. Am. Chem. Soc., 1994, 116, 807. 6 O. M. Yaghi, D. A. Richardson, G. Li, C. E. Davis and T. L. Groy, Mater. Res. Soc. Symp. Proc., 1995, 371, 15. 7 O. Achak, J. Y. Pivan, M. Maunaye, D. Louër and M. Louër, J. Alloys Comp., 1995, 219, 111. 8 L. Bowes, A. Lough, A. Malek, G. A. Ozin, S. Petrov and D. Young, Chem. Ber., 1996, 129, 283. 9 C. Larson and R. B. Von Dreele, Los Alamos Laboratory Report No. LA-UR-86-748, 1987. 10 C. K. Johnson, ORTEP, Report ORNL-5138, Oak Ridge National Laboratory, Oak Ridge, TN, 1976. 11 CERIUS2.0“, Simulation Tools User’s Reference, Biosym/ Molecular Simulations, San Diego, CA, 1997. 12 G. M. Sheldrick, SHELXA-90, program for absorption correction, University of Göttingen, 1990. 13 G. M. Sheldrick, SHELXTL/PC V5.0, Siemens Analytical X-Ray Instruments, Madison, WI, 1993. 14 S. J. Kirkby, Ph.D. Thesis, Spectroscopy and Crystallography of Metal Germanium Chalcogenide Openframework Materials and Precursors, University of Toronto, 1996. Received 16th January 1998; Paper 8/

ISSN:1477-9226    

DOI:10.1039/a800449h

出版商:RSC    

年代:1998

数据来源: RSC