Manganese-catalyzed hydroboration of carbon dioxide and other challenging carbonyl groups

Reductive functionalization of the C=O unit in carboxylic acids, carbonic acid derivatives, and ultimately in carbon dioxide itself is a challenging task of key importance for the synthesis of value-added chemicals. In particular, it can open novel pathways for the valorization of non-fossil feedstocks. Catalysts based on earth-abundant, cheap, and benign metals would greatly contribute to the development of sustainable synthetic processes derived from this concept. Herein, a manganese pincer complex [Mn(Ph 2 PCH 2 SiMe 2 ) 2 NH(CO) 2 Br] ( 1 ) is reported to enable the reduction of a broad range of carboxylic acids, carbonates, and even CO 2 using pinacolborane as reducing agent. The complex is shown to operate under mild reaction conditions (80–120 °C), low catalyst loadings (0.1–0.2 mol%) and runs under solvent-less conditions. Mechanistic studies including crystallographic characterisation of a borane adduct of the pincer complex ( 1 ) imply that metal-ligand cooperation facilitates substrate activation.