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 [(<i>p</i>-cymene)­Ru­(bpy)­OH₂]­[OTf]₂ as precatalyst, we demonstrate a novel example of a highly selective aldehyde–water shift in the absence of a hydrogen acceptor or base