Phosphine-substituted trigonal-prismatic and octahedral clusters

Abstract

The cluster [Rh₆C(CO)₁₅]^2– reacts with PPh₃ under mild conditions to give [Rh₆C(CO)₁₄(PPh₃)]^2–, the first reported substituted carbido cluster of rhodium with a trigonal-prismatic structure, which has been characterised by multinuclear NMR measurements (¹³C, ³¹P and direct ¹⁰³Rh). Thermal decarbonylation of [Rh₆C(CO)₁₄(PPh₃)]^2– gives the octahedral cluster [Rh₆C(CO)₁₂(PPh₃)]^2– which has been characterised by X-ray crystallography: space group P2₁/c, a= 12.837(3), b= 22.60(1), c= 21.181 (4)Å, Z= 4, R= 0.048, and R′= 0.055. The substituent PPh₃ is in the same plane as dppe (Ph₂PCH₂CH₂PPh₂) in [Rh₆C(CO)₁₁(dppe)]^2– but substitution has not occurred at the same site. The fluxional behaviour of both the PPh₃- and diphosphine-substituted octahedral clusters have been established from detailed multinuclear NMR variable-temperature measurements.