CHEMICAL EVIDENCE OF POLYNUCLEAR INTERMEDIATES IN A LIGAND REDISTRIBUTION EQUILIBRIUM BETWEEN DINUCLEAR RHODIUM COMPLEXES - X-RAY STRUCTUREOF [RH2(MU-BZTA)2(CO)3(PPH3)] (BZTA = BENZOTHIAZOLE-2-THIOLATE)

The monosubstituted dinuclear complex [Rh2(mu-bzta)2(CO)3(PPh3)] (3) h as been isolated from the reaction of the tetracarbonyl complex [{Rh(m u-bzta)(CO)2)2] (1) with triphenylphosphine. The crystal structural an alysis of 3 has confirmed this complex to be dinuclear. The two metal centres exhibit distorted square-planar coordination and are bridged b y two bzta ligands in a cis,cis and head-to-tail arrangement. The adde d PPh3 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 disu bstituted complex [{Rh(mu-bzta)(CO)(PPh3)}2] (2) as a result of a reor ganization process. Scrambling experiments carried out with related 6- methylbenzothiazole-2-thiolate complexes suggest that polynuclear inte rmediates are responsible for the ligand-redistribution equilibrium. A ddition of further triphenylphosphine to the equilibrium mixture gives 2 quantitatively. Complex 2 reacts with triphenylphosphine to give th e mononuclear complex trans-[Rh(bzta)(CO)(PPh3)2] (8) in high yield, a s a result of a bridge-splitting reaction.