Direct CO Capture and Reduction to High-End Chemicals with Tetraalkylammonium Borohydrides.

We demonstrate the ability of tetraalkylammonium borohydrides to capture large amounts of CO , even at low CO concentrations, and reduce it to formate under ambient conditions. These materials show CO absorption capacities up to 30 mmol  g at room temperature and 1 bar CO . Every BH anion can react with three CO molecules to form triformatoborohydride ([HB(OCHO) ] ). The thermodynamics and kinetics of the reaction were monitored by a magnetic suspension balance (MSB). Direct CO capture and reduction from air was achieved with tetraethyl, -propyl, and -butylammonium borohydride. The alkyl chain length played an important role in the kinetics and thermodynamics of the reaction, especially in CO diffusivity (crystallinity and free-volume), activation energy (charge-transfer dependent on the alkyl chain), and hydrophobicity. Adding HCl gave formic acid and the corresponding chloride ammonium salt, which can be recycled. In addition, transfer of formate was achieved for the N-formylation of an amine.