Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine-Titanium Complex

Catalytic reduction of N-2 to NH3 by a Ti complex has been achieved, thus now adding an early d-block metal to the small group of mid- and late-d-block metals (Mo, Fe, Ru, Os, Co) that catalytically produce NH3 by N-2 reduction and protonolysis under homogeneous, abiological conditions. Reduction of [Ti-IV(Tren(TMS))X] (X=Cl, 1A; I, 1B; Tren(TMS)=N(CH2CH2NSiMe3)(3)) with KC8 affords [Ti-III(Tren(TMS))] (2). Addition of N-2 affords [{(Tren(TMS))Ti-III}(2)(mu-eta(1):eta(1)-N-2)] (3); further reduction with KC8 gives [{(Tren(TMS))Ti-IV}(2)(mu-eta(1):eta(1):eta(2):eta(2)-N2K2)] (4). Addition of benzo-15-crown-5 ether (B15C5) to 4 affords [{(Tren(TMS))Ti-IV}(2)(mu-eta(1):eta(1)-N-2)][K-(B15C5)(2)](2) (5). Complexes 3-5 treated under N-2 with KC8 and [R3PH][I], (the weakest H+ source yet used in N-2 reduction) produce up to 18 equiv of NH3 with only trace N2H4. When only acid is present, N2H4 is the dominant product, suggesting successive protonation produces [{(Tren(TMS))Ti-IV}(2)(mu-eta(1):eta(1)-N2H4)][I](2), and that extruded N2H4 reacts further with [R3PH][I]/KC8 to form NH3.