Abstract and subjects
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, H-2 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](2) as precatalyst, we demonstrate a novel example of a highly selective aldehyde-water shift in the absence of a hydrogen acceptor or base.