A theoretical approach for homogeneous CO2 reduction by Ni(cyclam): substituents with intra-molecular hydrogen transfer

Abstract

We explore the detailed mechanism for the reduction reaction through systematic theoretical calculations, and the Ni-cyclam catalyst for the homogeneous CO₂ reduction reaction exhibits high efficiency. We find that the first hydrogen transfer step is the rate-determining step for the reaction. Our simulation results show that both the acidity of the environment and substituents play critical roles in the CO₂ reduction reaction. The strong electron-withdrawing substituent perpendicular to the C atoms at the 5,6,12,14-position of cyclam decreases the energy barrier of the rate-determining step significantly. Moreover, we reveal the mechanism through density functional theory calculations, which exhibits the intra-molecular H-transfer feature and thus explains the extraordinary reactivity seen during the reaction in previous works. All the results ensure a good future for such series of Ni-cyclam catalysts.