DFT study of alkene hydrogenation catalyzed by Rh(acac)(CO)2

Hydrogenation of alkene catalyzed by the catalyst Rh(acac)(CO)2 has been investigated theoretically with the aid of density functional calculations. The findings are as follows: (1) An associative but not a dissociative mechanism is found favorable for substitution of a carbonyl by ethene. (2) The substitution step of a carbonyl by H2 is found to be involved prior to the oxidative addition of H2, and this step is predicted to be the rate-determining step. (3) The ethene inserts into the Rh–H trans to CO but not the one cis to CO. (4) Reductive elimination of ethane occurs directly from a five-coordinate intermediate where the hydride but not the ethyl group occupies the apical position of the square-pyramidal structure. Some other issues related to the reactions are also discussed.