Reaction of InCl3with Various Reducing Agents: InCl3–NaBH4-Mediated Reduction of Aromatic and Aliphatic Nitriles to Primary Amines

While alternative methods of preparing dichloroindium hydride (HInCl2) via the in situ reduction of InCl3 using lithium amino borohydride (LAB) were explored, generation of HInCl2 from the reduction of InCl3 by sodium borohydride (NaBH4) was also re-evaluated for comparison. The reductive capability of the InCl3/NaBH4 system was found to be highly dependent on the solvent used. Investigation by 11B NMR spectroscopic analyses indicated that the reaction of InCl3 with NaBH4 in THF generates HInCl2 along with borane–tetrahydrofuran (BH3·THF) in situ. Nitriles underwent reduction to primary amines under optimized conditions at 25 °C using 1 equiv of anhydrous InCl3 with 3 equiv of NaBH4 in THF. A variety of aromatic, heteroaromatic, and aliphatic nitriles were reduced to their corresponding primary amine in 70–99% isolated yields. Alkyl halide and nitrile functional groups were reduced in tandem by utilizing the reductive capabilities of both HInCl2 and BH3·THF in a one-pot reaction. Finally, the selective reduction of the carbon bromine bond in the presence of nitriles was achieved by generating HInCl2 via the reduction InCl3 with NaBH4 in CH3CN or with lithium dimethylaminoborohydride (MeLAB) in THF.