Catalytic Reduction of Dinitrogen to Ammonia at a Single Molybdenum Center

Dinitrogen (N 2 ) was reduced to ammonia at room temperature and 1 atmosphere with molybdenum catalysts that contain tetradentate [HIPTN 3 N] 3– triamidoamine ligands {such as [HIPTN 3 N]Mo(N 2 ), where [HIPTN 3 N] 3– is [{3,5-(2,4,6-i-Pr 3 C 6 H 2 ) 2 C 6 H 3 NCH 2 CH 2 } 3 N] 3– } in heptane. Slow addition of the proton source [{2,6-lutidinium}{BAr′ 4 }, where Ar′ is 3,5-(CF 3 ) 2 C 6 H 3 ]and reductant (decamethyl chromocene) was critical for achieving high efficiency (∼66% in four turnovers). Numerous x-ray studies, along with isolation and characterization of six proposed intermediates in the catalytic reaction under noncatalytic conditions, suggest that N 2 was reduced at a sterically protected, single molybdenum center that cycled from Mo(III) through Mo(VI) states.