Mechanistic insights into CO hydrogenation to methanol mediated by a manganese pincer catalyst: a DFT study

Abstract

The catalytic hydrogenation of carbon monoxide (CO) to methanol using manganese pincer complexes remains a significant challenge, requiring a deeper mechanistic understanding to guide the development of more efficient systems. In this study, we performed a comprehensive density functional theory (DFT) investigation to elucidate the reaction mechanism of CO hydrogenation catalyzed by a manganese complex bearing a pincer ligand. Our theoretical results reveal that the catalytic cycle proceeds through four key stages: (i) formation of N-formylpyrrole; (ii) formation of 1-pyrrolylmethanol; (iii) regeneration of the pyrrole (Pyr) and formation of formaldehyde; and (iv) the formation of the final product methanol. Among these, the cleavage of the C–N bond during the Pyr regeneration step was identified as the rate-determining step (RDS), with a free energy barrier (ΔΔG^‡) of 22.1 kcal mol⁻¹. In addition, our study highlights the essential role of K₃PO₄ in the reaction. Rather than acting as a simple base, K₃PO₄ functions also as a promoter that facilitates CO activation and promotes C–N bond formation in the early stages of the catalytic cycle. Based on these mechanistic insights, we further designed a modified catalyst structure with the potential to enhance the efficiency of Mn-catalyzed CO hydrogenation. This work provides valuable theoretical guidance for the rational design of next-generation catalysts aimed at sustainable methanol production from CO.