Trivalent Metal Lewis Acids Activate CO in Transfer Hydrogenations.

Using γ-terpinene as a bio-derived H surrogate, trivalent metal MX (M = Al, Ga, In, Yb, X = Cl, OTf) Lewis acids (LAs) catalyze CO hydrogenation to formate, yielding p-cymene as the by-product. The resulting formate produces up to 91% N-formamides in tandem hydrogenation-coupling reactions and up to 95% heterocycles, including azoles, via further in situ transfer formylation to ortho-substituted anilines and cyclization at 130 °C and 4 bar. But In(OTf) and a Lewis base fail to abstract a hydride from γ-terpinene. Unlike other LAs and transfer hydrogenation catalysts that induce hydride abstraction from 1,4-cyclohexadiene(s) over B(CF), alkali earth or noble metals, MX LAs activate CO, so CO can directly accept a hydride from γ-terpinene during formate synthesis, as shown by density functional theory calculations. This triple role of MX LAs in promoting (1) CO activation, (2) tandem coupling reactions, and (3) transfer formylation at low pressure paves the way for sustainable CO hydrogenation processes, leveraging bio-derived H surrogates to develop efficient carbon capture and utilization systems and to synthesize valuable compounds from renewable feedstocks.