Ruthenium Catalyzed Additive-Free N-Formylation of Amines with CO₂ and H₂: Exploring Carbon Neutral Hydrogen Cycle

The N-formylation of amines using CO₂ hydrogenation, conducted under additive-free conditions, represents a crucial methodology in organic synthesis. Herein, we demonstrated a highly efficient ruthenium pincer complex for the selective conversion of a wide array of amines into their corresponding formamides under additive-free condition with a turnover number (TON) of 980,000 within a single-batch. Controlled studies suggested the initial reduction of CO₂ to ammonium formate, followed by dehydration to generate formamide. NMR experiments revealed the potential intermediates and indicated the involvement of metal-ligand cooperativity of catalyst during substrate activation. In addition, this methodology was examined to establish a carbon neutral hydrogen storage cycle by capitalizing on the reversible transformation of formamides.