Theoretical Study of the Proton Transfer between Water and [FeH(CO)4]- in Aqueous Solution and Relevance to the Water-Gas Shift Reaction Catalyzed by Iron Pentacarbonyl in the Condensed Phase

Abstract

Proton transfer between H2O and FeH(CO)4-, the assumed slow step of the water-gas shift reaction catalyzed by Fe(CO)5, has been studied with Hartree−Fock and multiconfiguration CASSCF ab initio methods. The calculations have been performed in vacuo and in water solution at 298 K, simulating the solvent as a polarizable continuum medium. The process in solution has been found to be less endothermic than in the gas phase by about 50 kcal/mol. The valence bond analysis, made on the CASSCF wave function along the reaction path, explains the mechanism in terms of a single structure in which the transferred hydrogen is simultaneously bonded to iron and oxygen with a different polarization depending on the reaction coordinate.