Abstract
The cobalt(I) pincer complex, [Co(N-2)-((PNP)-P-cy)] ((cy)pNP = anion of 2,5-bis-((dicyclohexylphosphino)methyl)pyrrole), reacts with aromatic, vinylic, and aliphatic aldehydes to produce the corresponding hydrocarbon products and [Co(CO)-((PNP)-P-cy)]. 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)((PNP)-P-cy)]. Reactions of [Co(N-2)((PNP)-P-cy)] 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 = 0 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)((PNP)-P-cy)] (X = O or NH). The ability of [Co(N-2)((PNP)-P-cy)] to undergo facile oxidative addition is discussed in the context of potential bond activation processes mediated by well-defined Co species.