Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine–Titanium Complex

Abstract

Catalytic reduction of N2 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 N2 reduction and protonolysis under homogeneous, abiological conditions. Reduction of [TiIV(TrenTMS)X] (X=Cl, 1A; I, 1B; TrenTMS=N(CH2CH2NSiMe3)3) with KC8 affords [TiIII(TrenTMS)] (2). Addition of N2 affords [{(TrenTMS)TiIII}2(μ-η1:η1-N2)] (3); further reduction with KC8 gives [{(TrenTMS)TiIV}2(μ-η1:η1:η2:η2-N2K2)] (4). Addition of benzo-15-crown-5 ether (B15C5) to 4 affords [{(TrenTMS)TiIV}2(μ-η1:η1-N2)][K(B15C5)2]2 (5). Complexes 3–5 treated under N2 with KC8 and [R3PH][I], (the weakest H+ source yet used in N2 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 [{(TrenTMS)TiIV}2(μ-η1:η1-N2H4)][I]2, and that extruded N2H4 reacts further with [R3PH][I]/KC8 to form NH3.