Reactions

Initiation: Prior to the catalytic cycle, the pre-catalyst Co₂(CO)₈ reacts with dihydrogen to generate the species HCo(CO)₄ (A). The latter undergoes loss of one carbon monoxide ligand to afford the 16-electron active species HCo(CO)₃ (B).

Catalytic cycle: The active cobalt complex coordinates an alkene substrate (1), followed by migratory insertion of the Co-H bond into the alkene (2). The regioselectivity of this step is predominantly governed by steric and electronic effects. The hydride is preferentially transferred to the terminal, less hindered carbon atom and the more electrophilic in the case where R is an electron-donating group, yielding the linear intermediate. If R is an electron-withdrawing group and the terminal carbon is hindered, the branched intermediate is possibly obtained. The resulting alkyl-cobalt complex then undergoes coordination of carbon monoxide (3), followed by migratory insertion into the Co-C bond, forming an acyl-cobalt species (4). Subsequently, oxidative addition of H₂ to the cobalt(I) center gives a cobalt(III) dihydride complex (5). Finally, reductive elimination releases the desired aldehyde product and regenerates the active catalyst (6).