Catalytic Reduction of Dinitrogen to Ammonia at a Single Molybdenum Center

Dinitrogen (N2) was reduced to ammonia at room temperature and 1 atmosphere with molybdenum catalysts that contain tetradentate HIPTN3N3- triamidoamine ligands (such as HIPTN3NMo(N2), where HIPTN3N3- is (3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2)3N3-) in heptane. Slow addition of the proton source (2,6-lutidinium)(BAr'4), where Ar' is 3,5-(CF3)2C6H3and reductant (decamethyl chromocene) was critical for achieving high efficiency ( approximately 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 N2 was reduced at a sterically protected, single molybdenum center that cycled from Mo(III) through Mo(VI) states.