Fixation of Dinitrogen at an Asymmetric Binuclear Titanium Complex

Alkaline earth metal-assisted dinitrogen activation at nickel

Rare examples of trinuclear [Ni-N2-M-N2-Ni] core (M = Ca, Mg) with linear bridged dinitrogen ligands are reported in this work. The reduction of [iPr2NN]Ni(μ-Br)2Li(thf)2 (1) (iPr2NN = 2,4-bis-(2,6-diisopropylphenylimido)pentyl) with elemental Mg or Ca in THF under an atmosphere of dinitrogen yields the complex {iPr2NNNi(μ-N2)}2M (thf)4 (M = Mg, complex 2 and M = Ca, complex 3). The bridging end-on (μ-N2)2M(thf)4 moiety connects the two [iPr2NNNi]- nickelate fragments. A combination of X-ray crystallography, solution and solid-state spectroscopy have been applied to characterize complexes 2 and 3, and DFT studies have been used to help explain the bonding and electronic structure in these unique Ni-N2-Mg and Ni-N2-Ca complexes.

Direct Incorporation of Dinitrogen into an Aliphatic C-H Bond

The activation of dinitrogen (N₂) and direct incorporation of its N atom into C-H bonds to create aliphatic C-N compounds remains unresolved. Incompatible conditions between dinitrogen reduction and C-H functionalization make this process extremely challenging. Herein, we report the first example of dinitrogen insertion into an aliphatic Csp³-H bond on the ligand scaffold of a 1,3-propane-bridged [N₂N]^2--type dititanium complex. Mechanistic investigations on the behaviors of dinuclear and mononuclear Ti complexes indicated the intramolecular synergistic effect of two Ti centers at a C-N bond-forming step. Computational studies revealed the critical isomerization between the inactive side-on N₂ complex and the active nitridyl complex, which is responsible for the Csp³-H amination. This strategy maps an efficient route toward the future synthesis of aliphatic amines directly from N₂.

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

Reaction of [TiCp*Cl₃] (Cp*=η⁵‐C₅Me₅) with one equivalent of magnesium in tetrahydrofuran at room temperature affords the paramagnetic trinuclear complex [{TiCp*(μ‐Cl)}₃(μ₃‐Cl)], which reacts with dinitrogen under ambient conditions to give the diamagnetic derivative [{TiCp*(μ‐Cl)}₃(μ₃‐η¹ : η² : η²‐N₂)] and the titanium(III) dimer [{TiCp*Cl(μ‐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 μ₃‐η¹ : η² : η² coordination mode of the dinitrogen molecule. The reaction of [{TiCp*(μ‐Cl)}₃(μ₃‐η¹ : η² : η²‐N₂)] with excess HCl in tetrahydrofuran results in clean NH₄Cl formation with regeneration of the starting material [TiCp*Cl₃]. Therefore, a cyclic ammonia synthesis under ambient conditions can be envisioned by alternating N₂/HCl atmospheres in a [TiCp*Cl₃]/Mg(excess) reaction mixture in tetrahydrofuran.

Formate Complexes of Tri- and Tetravalent Titanium Supported by a Tris(phenolato)amine Ligand

Titanium(III) and titanium(IV) formate complexes supported by the sterically encumbering tris(phenolato)amine ligand (H3(O3N) = tris(4,6-di-tert-butyl-2-hydroxybenzyl)amine) are described. Salt metathesis of the chlorido precursor [(O3N)TiCl] (1-Cl) with sodium formate in a...

Reduction of highly bulky triphenolamine molybdenum nitrido and chloride complexes

Transition metal nitrides are key intermediates in the catalytic reduction of dinitrogen to ammonia. To date, transition metal nitride complexes with the triphenolamine (TPA) ligand have not been reported and the system with the ligand has been much less studied for ammonia formation compared with other systems. Herein, we report a series of molybdenum complexes supported by a sterically demanding TPA ligand, including a nitrido complex NMo(TPA). We achieved the stoichiometric conversion of the nitride moiety into ammonia under ambient conditions by adding proton and electron sources to NMo(TPA). However, the catalytic turnover for N₂ reduction to ammonia was not observed in the triphenolamine ligand system unlike the Schrock system-triamidoamine ligand. Density functional theory calculation revealed that the molybdenum center favors binding NH₃ over N₂ by 16.9 kcal mol^-1 and the structural lability of the trigonal bipyramidal (TBP) molybdenum complex seems to prevent catalytic turnover. Our systematic study showed that the electronegativity and bond length of ancillary ligands determine the preference between N₂ and NH₃, suggesting a systematic design strategy for improvement.