Theoretical study on Dehydrogenative Lactonization of 1,2-benzenedimethanol using a Water-Soluble Iridium Complex Bearing 6,6’-dihydroxy-2,2’-bipyridine

Abstract

Cp^*Ir (Cp*=η⁵C₅Me₅) complexes catalyze efficiently both dehydrogenation from alcohols and hydrogenation to ketones. For example, the dehydrogenation reaction of 1,2-benzenedimethanol using a Cp^*Ir complex proceeds to form 2-(hydroxymethyl)benzaldehyde as a product in aqueous solution. It is possible to consider two types of catalyst cycles, which include Cp^*Ir complex of six and five coordination environment. In the present study, we investigated theoretically the mechanism of the catalytic cycle. All the structures were optimized and characterized as minima or transition states at the B3LYP/BSI level of theory (BSI designates the basis set combination of 541/541/111/1 for Ir and 6-311+g(2d,2p) for all nonmetal atoms). The free energy profiles including solvent effects were calculated to analyze the reaction mechanisms in detail. The SMD continuum model was used to include implicit solvent effects. For the catalytic cycles using Cp^*Ir complex with the six co ordination environment, the barrier heights for the hydrogen transfer was calculated to be 33.1 [kcal/mol].