A tetranuclear thiocyanato-bridged copper(i) catalyst for the hydrogenation of carbon dioxide to formate under mild conditions

Abstract

The hydrogenation of carbon dioxide (CO₂) with a base to produce formate salts offers a method for storing hydrogen in an energy dense solid. This stored hydrogen (H₂) can be released later by acidifying the formate salts, or formic acid can be utilized directly in fuel cells. However, this process relies on catalytic CO₂ hydrogenation, which ideally should employ a catalyst made from an abundant earth metal. Recent research on molecular catalysts has led to improved rates for conversion of CO₂ to energy-rich products such as formate, but the catalysts based on first-row transition metals are under development. Copper(I) complexes containing the 1,2-bis[(di-tert-butylphosphino)methyl]benzene ligand are found to promote the catalytic hydrogenation of CO₂ to formate in the presence of NaOH/KOH as the base, where catalytic conversion of CO₂via hydrogenation using H₂ produces valuable energy-relevant chemicals and therefore is a promising safe and simple strategy to conduct reactions under ambient pressure at room temperature. Aiming at this goal, herein we report an efficient copper(I) complex [Cu₄(κ²-PCP^t-Bu)₂(μ₂-SCN)₄] as a catalyst to achieve ambient-pressure CO₂ hydrogenation to generate metal formate (HCO₂⁻M⁺) with turnover number (TON) values of 108 to 23 040 in 3 to 24 h of reaction at 25 °C to 60 °C. This outstanding catalytic performance makes [Cu₄(κ²-PCP^t-Bu)₂(μ₂-SCN)₄] a potential candidate for realizing the large-scale production of metal formate by CO₂ hydrogenation.