Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine–Titanium Complex

Catalytic reduction of N(2) to NH(3) 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 NH(3) 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(CH(2)CH(2)NSiMe(3))(3)) with KC(8) affords [Ti(III)(Tren(TMS))] (2). Addition of N(2) affords [{(Tren(TMS))Ti(III)}(2)(μ‐η(1):η(1)‐N(2))] (3); further reduction with KC(8) gives [{(Tren(TMS))Ti(IV)}(2)(μ‐η(1):η(1):η(2):η(2)‐N(2)K(2))] (4). Addition of benzo‐15‐crown‐5 ether (B15C5) to 4 affords [{(Tren(TMS))Ti(IV)}(2)(μ‐η(1):η(1)‐N(2))][K(B15C5)(2)](2) (5). Complexes 3–5 treated under N(2) with KC(8) and [R(3)PH][I], (the weakest H(+) source yet used in N(2) reduction) produce up to 18 equiv of NH(3) with only trace N(2)H(4). When only acid is present, N(2)H(4) is the dominant product, suggesting successive protonation produces [{(Tren(TMS))Ti(IV)}(2)(μ‐η(1):η(1)‐N(2)H(4))][I](2), and that extruded N(2)H(4) reacts further with [R(3)PH][I]/KC(8) to form NH(3).