Acetylene hydroformylation with HCo(CO)3 as catalyst.: A density functional study

The mechanism of acetylene hydroformylation with HCo(CO)3 as active catalyst has been proposed and discussed on the basis of B3LYP density functional theory computation. It is found that the characteristic catalytic cycle is similar to that for olefin hydroformylation: (a) acetylene coordination and insertion, (b) CO coordination and insertion, and (c) H2 coordination and oxidative addition as well as unsaturated aldehyde elimination. Acetylene hydroformylation is computed to be more favored energetically than the competitive acetylene hydrogenation, and the production of saturated aldehyde is therefore due to the subsequent hydrogenation of the initially formed α,β-unsaturated aldehyde rather than the proposed hydrogenation of acetylene prior to hydroformylation. In contrast to olefin, acetylene insertion into the Co-H bond is an irreversible process, which determines the regioselectivity of terminal alkynes. CO coordination is found to be an exergonic process, while the corresponding H2 process is endergonic, and therefore, H2 is not competitive with CO. On the basis of the computed free energies of activation, the rate-determining step can be one of the reactions of the acyl tricarbonyl complex ((H2C = CHCO)Co(CO)3) with variation of the reaction conditions.