Iridium, rhodium, and ruthenium catalysts for the "aldehyde-water shift" reaction

Abstract

A series of half-sandwich complexes of iridium, rhodium, and ruthenium are shown to be active catalysts for the conversion of aldehydes and water to carboxylic acids. Depending on the catalyst, H2 is either released (the "aldehyde-water shift") or transferred to a second equivalent of aldehyde (aldehyde disproportionation). Mechanistic studies suggest hydride transfer to be the selectivity-determining step along the reaction pathway. Using [(p-cymene)Ru(bpy)OH2][OTf]2as precatalyst, we demonstrate a novel example of a highly selective aldehyde-water shift in the absence of a hydrogen acceptor or base. (Chemical Equation Presented).