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

The reduction of CO 2 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 CO 2 insertion into a metal hydride and regeneration of the metal hydride with H 2 , 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 H 2 to achieve the second step. Here, we report a catalytic system involving a stable copper hydride that activates CO 2 , working in tandem with a Lewis pair that heterolytically splits H 2 . 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. Due to its ready availability and low cost, copper is an attractive metal for the homogeneous reduction of CO 2 to formate. However, although CO 2 can readily insert into copper hydrides to produce metal-bound formate, subsequent regeneration of the catalytic species with H 2 is more challenging. Here a dual strategy is used, whereby a copper hydride activates CO 2 and a Lewis pair heterolytically splits H 2 , leading to dramatically improved performance.