The critical role of boron hybridization (sp3vs. sp2vs. sp) in hydrogenation mechanisms by boron-based Ru catalysts†

Abstract

Boron–transition metal (B–TM) catalysts have emerged as promising systems for hydrogenation reactions due to their unique bifunctional reactivity. However, the electronic structure–activity relationships of B–TM systems with different boron hybridizations remain poorly understood. This study systematically investigates how the sp³, sp², and sp hybridizations influence the catalytic mechanisms of B–Ru complexes in hydrogen activation and ethylene hydrogenation. For hydrogen activation, the sp³-B–Ru system follows a hydride mechanism (ΔG = 31.2 kcal mol⁻¹), while sp²/sp-B–Ru systems adopt a more efficient proton mechanism with lower barriers (15.3 and 20.8 kcal mol⁻¹, respectively). Orbital analysis demonstrates that the Ru contribution to bridging hydrides increases progressively from sp³ (9.4%) to sp (13.9%) systems, correlating with enhanced catalytic activity. For the hydrogenation reaction, the 2c–2e terminal is more favorable than the 3c–2e bridging hydrogen mechanism. Moreover, in the bridging hydrogen mechanism, the metal oxidation state remains unchanged for the sp² and the sp systems, which is superior to that for the sp³ system. These findings provide molecular-level insights for the rational design of B–TM catalysts with improved hydrogenation performance.