Mechanisms of the transfer hydroformylation catalyzed by rhodium, cobalt, and iridium complexes: Insights from density functional theory study

Abstract

The mechanisms of the transfer hydroformylation reactions catalyzed by rhodium, cobalt, and iridium complexes were studied by using the density functional theory. There are nine stages in each catalytic cycle: oxidation addition and C−H activation, hydrogen transfer and benzoic acid dissociation, anti-insertion reaction (decarbonylation), β-H elimination, nucleophilic substitution 1 (SN1) of ligand, C=C insertion, C=O insertion, coordination of benzoic acid and hydrogen transfer, and reductive elimination and aldehyde dissociation for catalyst regeneration. The total free energy barriers of the reactions catalyzed by Rh, Co and Ir complexes are 25.1 (3Rh → TS11,12-Rh), 27.3 (1Co → TS5,6-Co) and 41.5 (14Ir → TS14,1-Ir) kcal/mol, respectively. Such barriers indicate that the newly proposed cobalt complex could be a potential low-cost catalyst for the transfer hydroformylation reaction under mild conditions. The electronic structures of key intermediates and transition states in the reactions were analyzed by using the natural bond orbital theory and the Multiwfn program.