Catalytic Reduction of Dinitrogen via Hydroboration

The conversion of dinitrogen (N2) into ammonia (NH3) or other nitrogenous compounds under mild conditions remains highly desirable, given the extremely harsh conditions required by the typically employed Haber–Bosch process, which reacts N2 with dihydrogen (H2) to produce NH3. However, the catalytic conversion of N2 using H2 or related compounds containing H–E bonds (where E represents a general element) as reductants under mild conditions has remained elusive. Herein, we report the catalytic reduction of N2 via hydroboration, wherein N2 (1 atm) reacts with catecholborane in the presence of molybdenum–nitride complexes bearing PCP-type pincer ligands as catalysts at 60 °C, yielding up to 32 equiv of borylamines based on the molybdenum atom. The catalytic reaction proceeds through three successive 1,2-additions of hydroborane to the molybdenum–nitrogen bond, disproportionation of the molybdenum–hydride complex, and regeneration of the molybdenum–nitride complex via cleavage of the nitrogen–nitrogen triple bond. The catalytic reduction of N2 with a “H2 equivalent” under mild reaction conditions represents a notable advance toward the development of ideal nitrogen fixation systems.