Theoretical study on acetaldehyde and ethanol elimination from the hydrogenation of CH3(O)CCo(CO)(3)

A theoretical study based on density functional theory (DFT) has been carried out on the reaction pathways leading to acetaldehyde and ethanol formation from the hydrogenation of the coordinatively unsaturated CH3(O)CCo(CO)(3) complex (1). Hydrogenation of 1 represents the last step of the catalytic hydroformylation process. We have found that, in the H-2-induced acetaldehyde elimination reaction, the energy barrier for the oxidative addition/reductive elimination process is only 36.3 kJ . mol(-1). This process is kinetically favored over a sigma-bond metathesis pathway involving a four-center transition state with a barrier of 70.4 kJ . mol(-1). The possible formation of a hydroxycarbene complex which easily will add hydrogen yielding ethanol and regenerating the HCo(CO)(3) catalyst has also been discussed. This hydroxycarbene complex is thermodynamically accessible, although the energy barriers for the reaction pathways leading to its formation are larger than 95.5 kJ mol(-1). On the other hand, the production of ethanol from hydrogenation of acetaldehyde through a hydroxymethyl intermediate has an energy barrier of 42.3 kJ . mol(-1). It is concluded that the catalytic generation of alcohols does not proceed via the formation of a hydroxycarbene intermediate but rather through further hydrogenation of the aldehyde molecules.