Protonation of cyclo-platinumdirhodium complexes. X-Ray crystal structure of [PtRh2(µ-H)(µ-CO)2(CO)(PPh3)(η-C5Me5)2][BF4]

Abstract

The cluster compounds [PtRh₂(µ-CO)₂(L)(L′)(η-C₅Me₅)₂](L = L′= CO; L = CO, L′= PPh₃; L–L′= cyclo-C₈H₁₂) react with HBF₄ in diethyl ether to give the salts [PtRh₂(µ-H)(µ-CO)₂(L)(L′)(η-C₅Me₅)₂][BF₄] which exhibit in solution novel dynamic behaviour, as revealed by n.m.r. studies. The structure of [PtRh₂(µ-H)(µ-CO)₂(CO)(PPh₃)(η-C₅Me₅)₂][BF₄] has been established by X-ray diffraction on a single crystal that was orthorhombic, space group Pbca, Z= 8 in a unit cell of dimensions a= 21.503(12), b= 23.728(8), and c= 15.896(5)Å. The structure was refined to R 0.048 (R′ 0.050) for 4 901 independent reflections (2θ⩽ 55°, Mo-K_αX-radiation) collected at room temperature. The cation consists of a Pt(H)(CO)(PPh₃) unit bonded to the dirhodium fragment Rh₂(µ-CO)₂(η-C₅Me₅), such that co-ordination about the Pt atom is essentially planar. The two rhodium–platinum bonds [2.805(1) and 2.705(1)Å] differ by 0.1 Å, and evidence is presented that the hydrido-ligand bridges the longer bond, cis to the PPh₃ ligand. The two carbonyl groups which bridge the rhodium–rhodium bond show much weaker interaction with the Pt atom [Pt–C 2.75(1)Å(mean)] than in the neutral precursor. Relationships between the platinumdirhodium cations, platinum–olefin complexes, and protonated cyclopropanes are discussed.