Reduction of Carbon Dioxide with Ammonia-Borane under Ambient Conditions: Maneuvering a Catalytic Way

Abstract

In the development of alternatives to the traditional catalytic hydrogenation of CO2 with gaseous H2, employing nongaseous H2 storage compounds as potential reductants for catalytic transfer hydrogenation of CO2 is promising. Ammonia-borane, due to its high hydrogen storage capacity (19.6 wt %), has been used for catalytic transfer hydrogenation of several organic unsaturated compounds. However, a similar protocol involving catalytic transfer hydrogenation of less reactive CO2 with NH3BH3 is yet to be realized experimentally. Herein, we demonstrate the first catalytic CO2 transfer hydrogenation process for generating formate salt with NH3BH3 under ambient conditions (1 atm and 30 °C) employing a cationic "Ir(III)-abnormal NHC" catalyst via an electrophilic NH3BH3 activation route. It exhibited an initial turnover frequency of 686 h-1 and a high turnover number (TON) of ≈1300 in just 4 h. Most significantly, the catalyst was durable enough to maintain long-term activity, and upon only periodic recharging of NH3BH3, it furnished a total TON of >4200 in 10 h.