Dinitrogen Binding at a Trititanium Chloride Complex and Its Conversion to Ammonia under Ambient Conditions

Reaction of [TiCp*Cl-3] (Cp*=eta(5)-C5Me5) with one equivalent of magnesium in tetrahydrofuran at room temperature affords the paramagnetic trinuclear complex [{TiCp*(mu-Cl)}(3)(mu(3)-Cl)], which reacts with dinitrogen under ambient conditions to give the diamagnetic derivative [{TiCp*(mu-Cl)}(3)(mu(3)-eta(1) : eta(2) : eta(2)-N-2)] and the titanium(III) dimer [{TiCp*Cl(mu-Cl)}(2)]. The structure of the trinuclear mixed-valence complexes has been studied by experimental and theoretical methods and the latter compound represents the first well-defined example of the mu(3)-eta(1) : eta(2) : eta(2) coordination mode of the dinitrogen molecule. The reaction of [{TiCp*(mu-Cl)}(3)(mu(3)-eta(1) : eta(2) : eta(2)-N-2)] with excess HCl in tetrahydrofuran results in clean NH4Cl formation with regeneration of the starting material [TiCp*Cl-3]. Therefore, a cyclic ammonia synthesis under ambient conditions can be envisioned by alternating N-2/HCl atmospheres in a [TiCp*Cl-3]/Mg(excess) reaction mixture in tetrahydrofuran.