Borohydride Ionic Liquids as Reductants of CO in the Selective N-formylation of Amines.

Borohydride imidazolium ionic liquids, [IL]BH, used for the first time as reductants in the N-formylation of various amines with CO, provided an excellent yield of formamides. Under the same conditions, 5 bar CO and 80 °C, NaBH 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 and CO, resulted in a significant increase of selectivity to formamide. However, no effect was noted for [IL]BF and [IL]PF. Monitoring the reaction course in time using H NMR brought about new insight into the role of BH in the reduction of CO and the functionalization of amines. The formation of N-methylaniline - borane intermediate was evidenced.