Theoretical study of iron acyl complexes modeling the active site of [Fe]-hydrogenase: Solvation effects play a significant role

Abstract

In this work, density functional theory (DFT) calculations were carried out to study the role of solvation effects on the reaction of diiron dithiolate complex with CO to form [Fe]-hydrogenase model complex. In the gas phase, the energy barrier of the first transition state TS1 species is ca. 6.1kcal/mol higher than the second transition state TS2 species. However, when the solvation effects were included, the energy order was reversed, i.e., the energy barrier of TS1 falls ca. 1.2kcal/mol lower than TS2, indicating that the insertion of the second CO to iron is the rate-determining step in the whole transformation process. The initial insertion of the CO plays an important role in increasing the reaction barrier of the binding of a second CO, which prevented the second step transformation. Thus, the solvation effects play a significant role in determining the reaction mechanism. In addition, the energy of PC species is lower than RC species, demonstrating that this transformation is a significantly exothermic process.