The synthesis, reactivity, and crystal and molecular structure of [Rh3(µ-PPh2)3(µ-Cl)2(µ-CO)(CO)3], an unusual 50-electron closed trinuclear cluster derivative of rhodium

Abstract

The reaction of [{Rh(µ-Cl)(CO)₂}₂] with PPh₂H in benzene affords the mononuclear complex [RhCl(CO)(PPh₂H)₂] for a molar ratio of 1 : 4 and the trinuclear derivative [Rh₃(µ-PPh₂)₃(µ-Cl)₂(µ-CO)(CO)₃], for a molar ratio of 1 : 2. The structure of the trinuclear derivative has been determined by X-ray crystallography. It crystallises in the monoclinic space group P2₁/n, with a= 12.461(5), b= 32.867(5), c= 11.149(5)Å, β= 99.29(1)°, Z= 4, and R= 0.085. The metal atoms adopt a triangular configuration with each edge of the triangle being bridged by a diphenylphosphido-group as well as by either a chloro or a carbonyl group. In spite of this compound being a 50-electron system, all of the Rh–Rh distances correspond with those normally associated with a formal rhodium–rhodium bond. The chloro-groups in this compound can be extracted as radicals by the addition of NEt₂H, affording, in the presence of CO, [Rh₃(µ-PPh₂)₃(CO)₅], or displaced as chloride ions by treatment of the complex with AgSbF₆; the former reaction is a reversible process with dissolution of [Rh₃(µ-PPh₂)₃(CO)₅] in CCl₄ resulting in the regeneration of the title complex. [Rh₃(µ-PPh₂)₃(µ-Cl)₂(µ-CO)(CO)₃] is only moderately stable in solution and converts slowly to an insoluble species formulated as [{Rh(µ-PPh₂)(µ-Cl)(CO)}_n].