An efficient, sustainable organocatalyst, glycine betaine, was developed for the reductive functionalization of CO with amines and diphenylsilane. Methylamines and formamides were obtained in high yield by tuning the CO pressure and reaction temperature. Based on identification of the key intermediate, that is, the aminal, an alternative mechanism for methylation involving the C silyl acetal and aminal is proposed. Furthermore, reducing the CO amount afforded aminals with high yield and selectivity. Therefore, betaine catalysis affords products with a diversified energy content that is, formamides, aminals and methylamines, by hierarchical two-, four- and six-electron reduction, respectively, of CO coupled with C-N bond formation.

An effective and inexpensive organocatalyst tetrabutylammonium fluoride (TBAF) was developed for the reductive functionalization of CO with amines to selectively afford formamides or methylamines by employing hydrosilanes. Hydrosilanes with different substituents show discriminatory reducing activity. Thus, the formation of formamides and further reduction products, that is, methylamines could be controlled by elegantly tuning hydrosilane types. Formamides were obtained exclusively under an atmospheric pressure of CO with triethoxysilane. Using phenylsilane as a reductant, methylamines were attained with up to 99 % yield at 50 °C coupled to a complete deoxygenation of CO . The crucial intermediate silyl formate in the formylation step was identified and thereby a tentative mechanism involving the fluoride-promoted hydride transfer from the hydrosilane to CO /formamide was proposed. Striking features of this metal-free protocol are formylation and methylation of amines by reductive functionalization of CO with hydrosilanes and mild reaction conditions.

A tungstate catalyst for reductive functionalization of CO2 with amines and phenylsilane is successfully developed by simply varying the pressure to respectively form formamides and methylamines.

Various oxygen-nucleophiles prove to be efficient for reductive functionalization of CO2 with amines to methylamines, realizing both 6-electron reduction of CO2 and formation of a C–N bond in a one-pot operation.