Selective Formylation and Methylation of Amines using Carbon Dioxide and Hydrosilane Catalyzed by Alkali-Metal Carbonates

The formylation and methylation of amines with carbon dioxide and hydrosilanes are emerging yet important types of transformations for CO2. Catalytic methods effective for both reactions with wide substrate scopes are rare because of the difficulty in controlling the selectivity. Herein, we report that simple and readily available inorganic bases—alkali-metal carbonates, especially cesium carbonate—catalyze both the formylation and methylation reactions efficiently under mild conditions. The selectivity can be conveniently controlled by varying the reaction temperature and silane. A "cesium effect" on both reactions was observed by comparing the catalytic activity of various alkali-metal carbonates. Combined experimental and computational studies suggested the following reaction mechanism: (i) activation of Si–H by Cs2CO3, (ii) insertion of CO2 into Si–H, (iii) formylation of amines by silyl formate, and (iv) reduction of formamides to methylamines.