Catalytic reduction of dinitrogen to ammonia at a single molybdenum center.

This account explores the catalytic reduction of dinitrogen by molybdenum complexes that contain the HIPTN(3)N ligand (HIPTN(3)N) = (HIPTNCH(2)CH(2))(3)N, where HIPT = 3,5-(2,4,6-i-Pr(3)C(6)H(2))(2)C(6)H3) at room temperature and pressure with protons and electrons. A total of 7-8 equiv of ammonia is formed out of approximately 12 possible (depending upon the Mo derivative employed). No hydrazine is formed. Numerous X-ray studies of proposed intermediates in the catalytic cycle suggest that N(2) is being reduced at a sterically protected, single Mo center operating in oxidation states between Mo(III) and Mo(VI). Subtle variations of the HIPTN(3)N ligand are not as successful as a consequence of an unknown shunt in the catalytic cycle that consumes reduction equivalents to yield (it is proposed) dihydrogen [corrected]