Chemical evidence of polynuclear intermediates in a ligand redistribution equilibrium between dinuclear rhodium complexes. X-ray structure of [Rh 2(μ-bzta) 2(CO) 3(PPh 3)] (bzta = benzothiazole-2-thiolate)

Abstract

The monosubstituted dinuclear complex [Rh 2(μ-bzta) 2(CO) 3(PPh 3)] ( 3) has been isolated from the reaction of the tetracarbonyl complex [{Rh(μ-bzta)(CO)) 2} 2] ( 1) with triphenylphosphine. The crystal structural analysis of 3 has confirmed this complex to be dinuclear. The two metal centres exhibit distorted square-planar coordination and are bridged by two bzta ligands in a cis, cis and head-to-tail arrangement. The added PPh 3 group has been located trans to a S atom of the bridging ligand. In solution, complex 3 is in dynamic equilibrium with 1 and the disubstituted complex [{Rh(μ-bzta)(CO)(PPh 3)} 2] ( 2) as a result of a reorganization process. Scrambling experiments carried out with related 6-methylbenzothiazole-2-thiolate complexes suggest that polynuclear intermediates are responsible for the ligand-redistribution equilibrium. Addition of further triphenylphosphine to the equilibrium mixture gives 2 quantitatively. Complex 2 reacts with triphenylphosphine to give the mononuclear complex trans-[Rh(bzta)(CO)(PPh 3) 2] ( 8) in high yield, as a result of a bridge-splitting reaction.