Catalytic Dinitrogen Reduction to Ammonia at a Triamidoamine-Titanium Complex.

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(CH2 CH2 NSiMe3 )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 -N2 K2 )] (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 [R3 PH][I], (the weakest H+ source yet used in N2 reduction) produce up to 18 equiv of NH3 with only trace N2 H4 . When only acid is present, N2 H4 is the dominant product, suggesting successive protonation produces [{(TrenTMS )TiIV }2 (μ-η1 :η1 -N2 H4 )][I]2 , and that extruded N2 H4 reacts further with [R3 PH][I]/KC8 to form NH3 .