Ligand Assisted Cleavage of H₂ Across a Ru−N Bond within a Four‐membered Metallacycle and the Catalytic Hydrogenation of CO₂ to Formate

Abstract

The catalytic hydrogenation of CO2 to formate was achieved using the previously reported dichloro(ƞ6‐p‐cymene){diphenyl(3‐methyl‐2‐indolyl)phosphine}ruthenium (1) as a catalyst under mild conditions. In this complex, the phosphorus‐based ligand adopts a κ1‐P coordination mode. The catalytic activity was achieved in the presence of DBU as a base providing a TONmax value of 3,800. In order to explore potential transformations occurring within the catalytic reactions, a series of stoichiometric tests were performed. Complex 1 was reacted with DBU to form chloro(ƞ6‐p‐cymene){diphenyl(3‐methyl‐2‐indolide)phosphine}ruthenium (2). Structural characterization of complex 2 confirmed a κ2‐P,N coordination mode for the ligand resulting in a four membered metallacycle. Reaction of 2 with H2 led to the formation of hydrochloro(ƞ6‐p‐cymene){diphenyl(3‐methyl‐indolyl)phosphine}ruth‐enium (3), albeit not with a clean conversion. This is the product resulting from the formal addition of hydrogen across the Ru‒N bond of the metallacycle. Complex 3 was also synthesised via an alternative route involving the reaction of complex 1 with Me2NH•BH3.