Mechanistic insight into the dehydrogenation reaction catalyzed by an MLC catalyst with dual ancillary ligand sites†

Abstract

Metal–ligand cooperative (MLC) catalysis is central to modern catalytic chemistry, notable for its ability to enhance efficiency. Traditional MLC catalysts with a single auxiliary ligand site have limitations in optimizing catalytic activity, prompting increased interest in employing dual active sites for improved performance. In this study, density functional theory (DFT) is employed to explore the catalytic mechanism of a ruthenium complex featuring a 2-(2-benzimidazolyl)pyridine ligand in the dehydrogenation of benzyl alcohol. This catalyst is distinguished by its ability to use both the O–H group of hydroxy pyridine and the N–H group of benzimidazole as auxiliary sites during the reaction. The research uncovers a dynamic switching mechanism of ligand active sites across different catalytic stages. Specifically, the catalyst utilizes the oxygen site of the pyridone ligand as the proton acceptor during the proton transfer stage, while the N–H group of the benzimidazole ligand serves as the active site during the critical hydride transfer stage. This site-switching mechanism is elucidated through molecular plane parameter (MPP) analysis and Extended Transition State – Natural Orbitals for Chemical Valence (ETS-NOCV) analysis, which reveal that the N-site-assisted pathway during hydrogen transfer is characterized by reduced ligand deformation and enhanced orbital interactions. These factors contribute to the observed mechanistic selectivity. This dynamic site-switching strategy effectively lowers the reaction energy barrier and improves catalytic efficiency. The insights gained from this study not only clarify the roles of the ligand in various catalytic stages but also offer valuable theoretical guidance for the development of novel MLC catalysts with dual active sites.