Computational insights into three-centre four-electron bridging hydride bond in boryl type PBP-M dihydride complexes✰

Abstract

Metal hydrides serve as crucial intermediates in many chemical processes, facilitating the utilization of hydrogen resources. Traditionally, three-centre metal hydrides have been viewed as less reactive due to their multi-stabilization effects. However, recent discoveries show the "three-centre four-electron" (3c-4e) bridging hydride bond exhibits significant activity in boryl transition metal systems. This research employs computational techniques to explore the factors that influence the formation of the 3c-4e bridging hydride, focusing on boryl 3d non-noble transition metals ranging from chromium (Cr) to nickel (Ni). By analyzing bond distances and bond orders, the study sheds light on the electronic and structural characteristics of the B-H-M bridging hydride. It reveals a clear link between the metal centre's redox properties and the emergence of bridging hydrides. Specifically, metal centres like Cr and Co, which have lower oxidation states and electronegativity, are more inclined to form active 3c-4e bridging hydrides. These insights, derived from computational analyses, offer valuable guidelines for the development of active 3c-4e bridging metal hydrides, thereby contributing to the advancement of new hydrogen transformation catalysts.