Oxygen atom transfer to half-sandwich complexes of iridium and rhodium

The oxidation chemistry of half-sandwich iridium and rhodium complexes was explored. Iridium(Cp*) and rhodium(Cp*) complexes were prepared with various bidentate ligands and then reacted with oxygen atom transfer reagents. While oxidative degradation of the organic ligands was observed when using the oxygen atom transfer reagents iodosylbenzene and dimethyldioxirane, clean products were obtained when using a soluble derivative of iodosylbenzene, 2- tert-butylsulfonyliodosylbenzene (sPhIO). Oxidation reactions with sPhIO were typically conducted at low temperatures to increase the chance of observing reactive intermediates. It was found that the bidentate ligand 2-phenylpyridine was susceptible to insertion reactions at both metal centers. Oxygen atom insertion was observed into the rhodium-carbon bond of coordinated 2-phenylpyridine in a rhodium(Cp*) complex. Oxygen atom insertion was not observed in the analogous iridium complex; instead, an isoelectronic nitrene insertion into the iridium-carbon bond of 2-phenylpyridine occurred upon oxygen atom transfer to a coordinated nitrile ligand of the iridium(Cp*) complex. Subsequent oxygen atom transfer to the nitrene insertion compound occurred, but the iridium product could not be identified. The possible intermediacy of high-valent iridium and rhodium complexes is discussed. In addition, model iridium complexes were prepared with oxidized phenylpyridine ligands. Their reactivity suggested deactivation pathways involving the bidentate ligands of common water oxidation catalysts.