Carbon dioxide hydrogenation catalysed by well-defined Mn(<scp>i</scp>) PNP pincer hydride complexes

Abstract

The catalytic reduction of carbon dioxide is of great interest for its potential as a hydrogen storage method and to use carbon dioxide as C-1 feedstock. In an effort to replace expensive noble metal-based catalysts with efficient and cheap earth-abundant counterparts, we report the first example of Mn(i)-catalysed hydrogenation of CO₂ to HCOOH. The hydride Mn(i) catalyst [Mn(PNP^NH-<i>i</i>Pr)(H)(CO)₂] showed higher stability and activity than its Fe(ii) analogue. TONs up to 10 000 and quantitative yields were obtained after 24 h using DBU as the base at 80 °C and 80 bar total pressure. At catalyst loadings as low as 0.002 mol%, TONs greater than 30 000 could be achieved in the presence of LiOTf as the co-catalyst, which are among the highest activities reported for base-metal catalysed CO₂ hydrogenations to date.