Borohydride Ionic Liquids as Reductants of CO2 in the Selective N‐formylation of Amines

Abstract Borohydride imidazolium ionic liquids, [IL]BH 4 , used for the first time as reductants in the N‐formylation of various amines with CO 2 , provided an excellent yield of formamides. Under the same conditions, 5 bar CO 2 and 80 °C, NaBH 4 produced a mixture of N‐formylated and N‐methylated products in a ratio of 1 : 2. An alternative approach, based on the addition of halide imidazolium salts ([IL]Cl or [IL]Br) to the reactions of amine with NaBH 4 and CO 2 , resulted in a significant increase of selectivity to formamide. However, no effect was noted for [IL]BF 4 and [IL]PF 6 . Monitoring the reaction course in time using 1 H NMR brought about new insight into the role of BH 3 in the reduction of CO 2 and the functionalization of amines. The formation of N‐methylaniline – borane intermediate was evidenced.