Waste-Minimized, Ecofriendly, and Chemoselective Room-Temperature Hydrogenation of C=C Bonds Using a Homogeneous Recyclable Imidazole-Based Ru(II)-p-Cym Catalyst

Abstract

Catalytic hydrogenation of C=C bonds is crucial in fine chemical and pharmaceutical synthesis, yet the efficient recovery and reuse of homogeneous catalysts remain a challenge. Herein, we report a well-defined Ru-1 catalyst derived from 2,2′-bisbenzimidazole (BiBzImH₂) and Ru(II)-para-cymene, enabling chemoselective C=C hydrogenation at room temperature under moderate H₂ pressure without additives or base. Ru-1 exhibits high turnover frequencies (TOFs), a broad substrate scope (61 examples), and remarkable functional group tolerance. Notably, Ru-1 is 2 to 85 times more cost-effective than reported catalysts and can be efficiently recovered via solvent-mediated precipitation, maintaining its efficiency over multiple cycles. Mechanistic studies, including spectroscopic and isotopic labeling experiments, suggest that hydrogen activation requires vacant coordination sites at high pressure, proceeding without metal-ligand cooperativity. Moreover, the catalyst can be easily separated through solvent-mediated precipitation followed by product isolation through solvent evaporation without column chromatographic separation, minimizing solvent use and waste. Scalability and reusability studies confirm the practicality of this system, while green chemistry assessments (CHEM21 toolkit, E-factor, and EcoScale analysis) highlight its environmental sustainability.