Chemistry of di- and tri-metal complexes with bridging carbene or carbyne ligands. Part 31. Synthesis and crystal structures of the compounds [AuW(µ-CHR)(CO)2(PPh3)(η-C5H5)]·CH2Cl2 and [AuPtW(µ3-CR)(CO)2(PMe3)3(η-C5H5)][PF6](R = C6H4Me-4)

Abstract

Treatment of a mixture of the salts [N(PPh₃)₂][W₂{µ-CH(C₆H₄Me-4)}(CO)₇(η-C₅H₅)] and TIPF₆ in tetrahydrofuran (thf) with [AuCl(PPh₃)] affords the bridged p-tolylmethylidene complex [AuW{µ-CH(C₆H₄Me-4)}(CO)₂(PPh₃)(η-C₅H₅)], the structure of which has been established by a single-crystal X-ray diffraction study. As expected, the Au–W bond [2.729(1)Å] is spanned by the CH(C₆H₄Me-4) group. The µ-C–W separation is relatively short [2.058(14)Å] whereas the µ-C–Au distance is relatively long [2.268(14)Å]. To account for these features a three-centre two-electron µ-C–Au–W interaction is postulated. Addition of [Au(PR′₃)]⁺[PR′₃= PPh₃ or P(cyclo-C₆H₁₁)₃] fragments, generated in situ from [AuCl(PR′₃)] and TIPF₆ in dichloromethane, to the alkylidynetungsten compounds [W(CR)(CO)₂(η-C₅H₅)](R = C₆H₄Me-4 or Me) affords the salts [AuW(µ-CR)(CO)₂(PR′₃)(η-C₅H₅)][PF₆][R = C₆H₄Me-4, PR′₃= PPh₃or P(C₆H₁₁)₃; R = Me, PR′₃= PPh₃]. N.m.r. studies (¹H, ³¹P-{¹H}, and ¹³C-{¹H}) on solutions of these salts, however, reveal that the cations dissociate, affording equilibrium mixtures containing the species [Au{W(CR)(CO)₂(η-C₅H₅)}₂]⁺ and [Au(PR′₃)₂]⁺. The trimetal compound [AuPtW(µ₃-CR)(CO)₂(PMe₃)₃(η-C₅H₅)][PF₆](R = C₆H₄Me-4) has been prepared by two routes: from the reaction between [Au{W(CR)(CO)₂(η-C₅H₅)}₂][PF₆] and [Pt(C₂H₄)(PMe₃)₂], and by addition of [Au(thf)(PMe₃)][PF₆] to [PtW(µ-CR)(CO)₂(PMe₃)₂-(η-C₅H₅)]. The structure of [AuPtW(µ₃-CR)(CO)₂(PMe₃)₃(η-C₅H₅)][PF₆] has been established by X-ray crystallography. A triangular array of metal atoms [Au–W 2.801 (2), Au–Pt 2.956(2), and Pt–W 2.770(2)Å] is asymmetrically bridged by the CR ligand [µ₃-C–Au 2.21 (4), µ₃-C–Pt 1.97(4), and µ₃-C–W 2.01 (4)Å]. The Au–Pt separation suggests that there is little or no direct metal–metal bonding between these two metal atoms. The tungsten atom carries the cyclopentadienyl ligand and two CO groups, but the latter are appreciably non-linear. The gold and platinum atoms are ligated by one and two PMe₃ groups, respectively.