A highly active phosphine-borane organocatalyst for the reduction of CO2 to methanol using hydroboranes

Abstract

In this work, we report that organocatalyst 1-Bcat-2-PPh2-C 6H4 ((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·SMe2 and BH 3·THF) to generate CH3OBR2 or (CH 3OBO)3, products that can be readily hydrolyzed to methanol. The yields can be as high as 99% with exclusive formation of CH 3OBR2 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. © 2013 American Chemical Society.