Aldehyde Decarbonylation by a Cobalt(I) Pincer Complex

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