Aldehyde Decarbonylation by a Cobalt(I) Pincer Complex

Abstract

The cobalt(I) pincer complex, [Co(N2)(CyPNP)] (CyPNP = anion of 2,5-bis((dicyclohexylphosphino)methyl)pyrrole), reacts with aromatic, vinylic, and aliphatic aldehydes to produce the corresponding hydrocarbon products and [Co(CO)(CyPNP)]. The pathway for aldehyde decarbonylation is found to involve initial coordination of the aldehyde to Co(I), followed by oxidative addition of the C–H bond to produce a cobalt(III) acyl hydride. The acyl hydride species then undergoes CO deinsertion, followed by reductive elimination to afford the decarbonylated product and [Co(CO)(CyPNP)]. Reactions of [Co(N2)(CyPNP)] with other carbonyl containing groups such as carboxylic acids and amides also proceed via oxidative addition to give Co(III) intermediates arising from activation of the X–H (X = O or NH) bond. In these cases, however, the Co(III) species extrude molecular hydrogen to produce Co(II) species of the form [Co(X{O}CR)(CyPNP)] (X = O or NH). The ability of [Co(N2)(CyPNP)] to undergo facile oxidative addition is discussed in the context of potential bond activation processes mediated by well-defined Co species.