Unsaturated Cyclopentadienyl-Molybdenum and Tungsten Carbonyl Cluster Complexes Containing Pd- and Pt(PBu^t₃) Groups

A series of new bimetallic cluster compounds, Cp2M2(CO)4[M‘(PBut3)]2 [M = Mo, M‘ = Pt (9); M = Mo, M‘ = Pd (10); M = W, M‘ = Pt (11); M = W, M‘ = Pd (12)], have been synthesized from reactions of [CpM(CO)3]2 (M = Mo, W) with an excess of M‘(PBut3)2 (M‘ = Pt, Pd) at various temperatures. Each compound was fully characterized by IR, 1H and 31P NMR, and single-crystal X-ray diffraction analyses. The metal atoms in the structure of 9 are arranged in a butterfly configuration, while the metal atoms of 10−12 adopt a tetrahedral geometry. Compounds 9 and 12 contain two edge-bridging and two triply bridging carbonyl ligands, 10 contains four triply bridging carbonyl ligands, and 11 contains two terminal and two edge-bridging carbonyl ligands. Each of the products is electron-deficient and the M−M bonds, M = Mo and W, are short, Mo−Mo = 2.6535(4) Å in 9 and 2.6362(4) Å in 10, W−W = 2.6168(9) Å in 11 and 2.6320(7) Å in 12, which is indicative of some localized multibond character between these metal atoms within the cluster framework. The nature of the bonding within the clusters was explored with DFT calculations (ADF 2004.01, PW91) for the title compounds in C2 symmetry as well as for a hypothetical, two-electron-reduced [Cp2Mo2Pd2(CO)4(PBut3)2]2- species.