Ligand Exchange Processes in Abnormal N-heterocyclic Carbene Rhodium Complexes

Rhodium( III) complexes containing a mesoionic and strongly electron- donating abnormal dicarbene ligand and a phosphine in a facial coordination mode and three ancillary iodide ligands undergo spontaneous solvolysis to give a cationic complex with an iodide in the outer coordination sphere. The availability of this non- coordinating iodide promotes a halide exchange reaction and in chlorinated solvents such as chlorocyclohexane, chloroethyl benzene, 1,2- dichloro- ethane, and benzyl chloride, the metal- coordinated iodo ligands exchange for chlorides. Mechanistic investigations suggest that the role of the metal is to release the iodide anion, rather than being directly involved in the C- Cl bond activation. The release of the iodide from the metal coordination sphere is promoted by the strong donor ability of the abnormal dicarbene ligand.