Tandem copper hydride–Lewis pair catalysed reduction of carbon dioxide into formate with dihydrogen

The reduction of CO2 into formic acid or its conjugate base, using dihydrogen, is an attractive process. While catalysts based on noble metals have shown high turnover numbers, the use of abundant first-row metals is underdeveloped. The key steps of the reaction are CO2 insertion into a metal hydride and regeneration of the metal hydride with H2, along with the concomitant production of formate. For the first step, copper is known as one of the most efficient metals, as shown by the numerous copper-catalysed carboxylation reactions, but this metal has difficulties activating H2 to achieve the second step. Here, we report a catalytic system involving a stable copper hydride that activates CO2, working in tandem with a Lewis pair that heterolytically splits H2. In this system, unprecedented turnover numbers for copper are obtained. Surprisingly, through a combination of stoichiometric and catalytic reactions, we show that classical Lewis pairs outperform frustrated Lewis pairs in this process.