Diruthenium Catalyst for CO2 and (Bi)carbonate Hydrogenation to Formate in Aqueous media.

Highly efficient CO2 and (bi)carbonate hydrogenation to formate in water was achieved by exploiting the cooperative interaction of the two ruthenium centers in a series of water-soluble diruthenium complexes [{(η6-arene)RuCl}2(μ-κ2:κ2-benztetraimd)]2+ containing the bridging meta-/para-bis-imidazole methane-based ligands (m-/p-benztetraimd). Our findings revealed the pivotal role of the ligand structure in tuning the catalytic activity, where the catalyst p-C3 [{(η6-p-cymene)RuCl}2(μ-κ2:κ2-p-benztetraimd)]2+ outperformed others. Consequently, a high formate yield (2.73 mmol) with a turnover number (TON) of 1092 (1524 in 24 h) and a turnover frequency (TOF) of 137 h-1 was achieved over the catalyst p-C3 at 40 bar pCO2/pH2 (1:3) at 80°C. Advantageously, the catalyst p-C3 also efficiently hydrogenated potassium bicarbonate and potassium carbonate to formate. We further utilized the optimized process for demonstrating the conversion of CO2 captured (via direct air capture) to formate through an integrated carbon capture and CO2 hydrogenation process. Moreover, the catalyst p-C3 exhibited appreciable recyclability over multiple catalytic cycles for the reversible CO2/(bi)carbonate hydrogenation and formate dehydrogenation process. The key reaction intermediates, such as hydride species formed by treating the complex p-C3 with H2 gas, revealed the role of such intermediates in achieving high catalytic activity for CO2 hydrogenation over the diruthenium catalysts.