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

The catalytic hydrogenation of CO 2 to formate was achieved using the previously reported dichloro(η 6 ‐ 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 κ 1 ‐ P coordination mode. The catalytic activity was achieved in the presence of DBU as a base providing a TON max 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(η 6 ‐ p ‐cymene){diphenyl(3‐methyl‐2‐indolide)phosphine}ruthenium ( 2 ). Structural characterization of complex 2 confirmed a κ 2 ‐ P,N coordination mode for the ligand resulting in a four membered metallacycle. Reaction of 2 with H 2 led to the formation of hydrochloro(η 6 ‐ p ‐cymene){diphenyl(3‐methyl‐indolyl)phosphine}ruthenium ( 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 synthesized via an alternative route involving the reaction of complex 1 with Me 2 NH • BH 3 as a means of converting Ru−Cl to Ru−H