HCo(CO)₃-Catalyzed Propene Hydroformylation. Insight into Detailed Mechanism

The entire catalytic cycle of propene hydroformylation using HCo(CO) 3 as an active catalyst has been systematically investigated at the B3LYP density functional level of theory. It is found that the most stable π-complex HCo(CO) 3 (η 2 -H 2 C CHCH 3 ) has a C C double bond coordination in the equatorial position, and the subsequent olefin insertion (alkylation) process is reversible, in agreement with the experimental finding. The hydride migratory insertion is accompanied by Co(CO) 3 pseudorotation, leading to the Co···H−C agostic stabilized (iso)propyl complex (C 3 H 7 )Co(CO) 3 with the alkyl group at the axial position and thus does not take place on a C s symmetry potential energy surface. The regioselectivity is mainly determined by the relative stability of the alkyl cobalt tetracarbonyl complexes (C 3 H 7 )Co(CO) 4 from the exothermic and irreversible CO addition to the alkyl cobalt tricarbonyl complexes (C 3 H 7 )Co(CO) 3, which is therefore a thermodynamic controlled process. The CO insertion process (carbonylation) proceeds via two Co(CO) 3 pseudorotated transition states and a Co···H−C agostic stabilized intermediate. The resulting most stable complex (C 3 H 7 CO)Co(CO) 3 with the acyl group in the axial site has a η 2 -O C interaction at the equatorial site, and the computed characteristic vibrational modes agree well with the available experimental data. In contrast to the generally accepted conclusion, H 2 coordination to the acyl complex rather than oxidative addition is the rate-determining step after HCo(CO) 3 generation. This finding is supported by the high stability of the acyl complex toward further H 2 addition, as found experimentally.