A Highly Active Phosphine-Borane Organocatalyst for the Reduction of CO2 to Methanol Using Hydroboranes

In this work, we report that organocatalyst 1-Bcat-2-PPh2-C6H4 ((1); cat = catechol) acts as an ambiphilic metal-free system for the reduction of carbon dioxide in presence of hydroboranes (HBR2 = HBcat (catecholborane), HBpin (pinacolborane), 9-BBN (9-borabicyclo[3.3.1]nonane), BH3 center dot SMe2 and BH3 center dot THF) to generate CH3OBR2 or (CH3OBO)(3), products that can be readily hydrolyzed to methanol. The yields can be as high as 99% with exclusive formation of CH3OBR2 or (CH3OBO)(3) with TON (turnover numbers) and TOF (turnover frequencies) reaching >2950 and 853 h(-1), respectively. Furthermore, the catalyst exhibits living behavior: once the first loading is consumed, it resumes its activity on adding another loading of reagents.