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.