Catalytic reduction of dinitrogen to ammonia at well-defined single metal sites.

Dinitrogen (N2) is reduced to ammonia at room temperature and 1atm with molybdenum catalysts that contain tetradentate [HIPTN3N]3- triamidoamine ligands {[HIPTN3N]3-=[{3,5-(2,4,6-i-Pr3C6H2)2C6H3NCH2CH2}3N]3-, an example being [HIPTN3N]Mo(N2)} in heptane. Slow addition of the proton source ({2,6-lutidinium}{BAr'4}; Ar'=3,5-(CF3)2C6H3) and reductant (decamethyl chromocene) assure a high yield of ammonia (63-65% in four turnovers) versus dihydrogen formation. Numerous X-ray studies, along with isolation and characterization of seven intermediates in the proposed catalytic reaction (under noncatalytic conditions), suggest that N2 is being reduced at a sterically protected, single Mo centre that cycles between states Mo(III), Mo(IV), Mo(V) and Mo(VI).