Tetracoordinate borates as catalysts for reductive formylation of amines with carbon dioxide

Abstract

We report sodium trihydroxyaryl borates as the first robust tetracoordinate organoboron catalysts for reductive functionalization of CO₂. These catalysts, easily synthesized from condensing boronic acids with metal hydroxides, activate main group element–hydrogen (E–H) bonds efficiently. In contrast to BX₃ type boranes, boronic acids and metal-BAr₄ salts, under transition metal-free conditions, sodium trihydroxyaryl borates exhibit high reactivity of reductive N-formylation toward a variety of amines (106 examples), including those with functional groups such as ester, olefin, hydroxyl, cyano, nitro, halogen, MeS–, ether groups, etc. The over-performance to catalyze formylation of challenging pyridyl amines affords a promising alternative method to the use of traditional formylation reagents. Mechanistic investigation supports electrostatic interactions as the key for Si/B–H activation, enabling alkali metal borates as versatile catalysts for hydroborylation, hydrosilylation, and reductive formylation/methylation of CO₂.