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 .