Co-SAC catalyzed utilization of methanol and ethanol in the transfer hydrogenation of azo bonds: experimental and theoretical studies

Abstract

Transfer hydrogenation (TH) of non-polar bonds using methanol and ethanol as hydrogen sources is a great challenge, and the development of an efficient 3d metal-based catalyst to accomplish such reactions is an exciting area to explore. Selective TH of amine surrogates to their corresponding primary amines using methanol or ethanol is difficult as mono/di-alkylated amines are produced as the major products. Notably, the TH of azo bonds to amines has not been reported yet. Herein, using Co-SAC, various azo compounds including commercially used dyes were effectively transfer hydrogenated to the corresponding primary amines, using ethanol and methanol as the hydrogen sources. Several control experiments were conducted to understand this catalytic process. Hammett studies revealed that transfer hydrogenation was more favorable with the substrates having electron-donating substituents. DFT calculations were performed to get a deeper insight into the mechanism, which disclosed that alcohol dehydrogenation and –NN– bond hydrogenation transpired through β-hydride elimination and Co-hydride insertion pathways, respectively.