Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 100. Synthesis of mixed-metal compounds via the salts [NEt4][Rh(CO)L(η5-C2B9H9R2)](L = PPh3, R = H; L = CO, R = Me); crystal structures of the complexes [WRhAu(µ-CC6H4Me-4)(CO)3(PPh3)(η-C5H5)(η5-C2B9H11)] and [WRh2Au2(µ3-CC6H4Me-4)(CO)6(η-C5H5)(η5-C2B9H9Me2)2]·0.5CH2Cl2

Abstract

The rhodacarbaborane salts [NEt₄][Rh(CO)L(η⁵-C₂B₉H₉R₂)] have been used to prepare the mixed-metal complexes [RhAu(CO)(PPh₃)L(η⁵-C₂B₉H₉R₂)](L = PPh₃, R = L = CO, R = Me), [WRhAu(µ-CC₆H₄Me-4)(CO)₃L(η-C₅H₅)(η⁵-C₂B₉H₉R₂)](L = PPh₃, R = H; L = CO, R = Me), and [WRh₂Au₂(µ₃-CC₆H₄Me-4)(CO)₆(η-C₅H₅)(η⁵-C₂B₉H₉Me₂)₂]. In relate studies treatment of the salt [WAuCl(µ-CC₆H₄Me-4)(CO)₂(η-C₅H₅)] with Na[Mn(CO)₅] or [N(PPh₃)₂][Co(CO)₄] yields, respectively, the trimetal compounds [WMAu(µ-CC₆H₄Me-4)(CO)_n(η-C₅H₅)](M = Mn, n= 7; M = Co, n= 6). The molecular structures of [WRhAu(µ-CC₆H₄Me-4)(CO)₃(PPh₃)(η-C₅H₅)(η⁵-C₂B₉H₁₁)] and [WRh₂Au₂(µ₃-CC₆H₄Me-4)(CO)₆(η-C₅H₅)(η⁵-C₂B₉H₉Me₂)₂] have been determined by single-crystal X-ray diffraction studies. In the trimetal species there is a bent [156.9(1)°] W–Au–Rh array of metal atoms [W–Au 2.732(1) and Rh–Au 2.640(1)Å] with the W–Au bond asymmetrically bridged by the p-tolylmethylidyne group [µ-C–W 1.90(1) and µ-C–Au 2.13(1)Å]. The W atom carries the C₅H₅ring and two CO groups, while the Rh atom is ligated by the η⁵-C₂B₉H₁₁ cage, a CO group, and the PPh₃ ligand [Rh–P 2.340(3)Å]. The pentanuclear metal cluster has a WAu₂triangular core [W–Au (average) 2.750(2) and Au ⋯ Au 2.969(2)Å] capped by the CC₆H₄Me-4 group [µ₃-C–W 2.02(2) and µ₃-C–Au (average) 2.05(2)Å]. The tungsten atom is co-ordinated by two CO groups and the C₅H₅ ring. Each gold atom is linked to a Rh(CO)₂(η⁵-C₂B₉H₉Me₂) fragment via both a Rh–Au bond [average 2.217(2)Å] and a B–H⇀Au three-centre two-electron bond. This linkage involves for each cage the unique boron atom in the face of the icosahedral C₂B₉H₉Me₂fragment which is β to the CMe groups. The spectroscopic properties (i.r., ¹H, ¹³C-{¹H}, ³¹P-{¹H}, and ¹¹B n.m.r.) of the new compounds are reported, and where appropriate the data are discussed in relation to their structures.