Formic acid as the H2-carrier and the transfer hydrogenation reagent for Ru-catalyzed hydroaminomethylation of olefins

Formic acid (FA) is a potential hydrogen storage substance due to its abundant resources, ease of storage, and high hydrogen content. In this paper, the hydroaminomethylation of olefins with FA as the hydrogen source was accomplished over DPEPhos-based Ru catalyst for the first time. Under optimal conditions, alpha-olefins or cyclo-olefins with steric hindrance obtained 62%similar to 96% yields of the target amines. The influence of FA was investigated by in situ high-pressure H-1 NMR spectroscopy analyses, isotope labelling experiments, and the separated hydroformylation or reduction amination. It was indicated that FA was decomposed to provide H-2 for the hydroformylation, and was used as a reducing agent in the transfer hydrogenation of imines/enamines. The reversible amidation of FA with substrate amine could inhibit the side reaction of aldehydes transfer hydrogenation. Moreover, the involving FA would facilitate the formation of Ru-H species, thereby promoting the hydroaminomethylation.