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

Abstract

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.

Putting on the Crown: Synthesis and Reactivity of Trimethyltitanium

“…The Ti–Cl distance of 2.4490(6) Å in 7 is markedly longer than the Ti–(μ 2 -Cl) distance in [(C 5 Me 5 )­Ti­(μ 2 -Cl)] 3 (μ 3 -Cl) (av. 2.383 Å) …”

“…2.383 Å). 21 Having in mind the preferred heteroaluminato formation when treating rare-earth-metal methyl complexes with HAlMe 2 , 22,23 we probed the reaction of 1 with dimethylalane. To our surprise, independent of the amount of HAlMe 2 employed, compound 1 was converted into formally divalent complex [{(Me 3 TACN)Ti} 2 {(μ-H) 2 AlMe 2 } 2 (μ-H)][AlMe 4 ] (8) (Scheme 3).…”

Monocyclopentadienyltitanium(III) Complexes with Hydridoborato Ligands

“…Reduction of the latter titanium(IV) trichloride precursor with an excess of magnesium led to a mixed-valence Ti II /Ti III trinuclear complex [{Ti(η 5 -C 5 Me 5 )(μ-Cl)} 3 (μ 3 -Cl)] capable of activating dinitrogen under ambient conditions. 27 Analogous treatment of [Ti(η 5 -C 5 Me 5 )X 3 ] with excess LiAlH 4 in ethereal solvents (L) produced titanium(II) species [{Ti(η 5 -C 5 Me 5 )(μ-H)} 2 {(μ-H) 2 AlXL} 2 ] (L = thf, X = Cl, Br; L = OEt 2 , X = Cl), while the reactions with the milder reductant LiBH 4 gave titanium-(III) tetrahydridoborato complexes. 28 In particular, the X-ray crystal structure of the bis(tetrahydridoborato) derivative showed a dimer [{Ti(η 5 -C 5 Me 5 )(BH 4 )(μ-BH 4 )} 2 ] with two bridging BH 4 ligands between the metal centers (Scheme 1).…”

“…As part of a project devoted to the development of new structures and reactivity patterns of low-valent titanium complexes, we recently reported a detailed study on monopentamethylcyclopentadienyltitanium­(III) dihalides. , Several [Ti­(η 5 -C 5 Me 5 )­Cl 2 ] derivatives were prepared by thermal homolysis or hydrogenolysis of the Ti–C­(methyl) bond of [Ti­(η 5 -C 5 Me 5 )­Cl 2 Me] or by reaction of [Ti­(η 5 -C 5 Me 5 )­Cl 3 ] with stoichiometric amounts of conventional reducing agents (Mg, LiAlH 4 ). Reduction of the latter titanium­(IV) trichloride precursor with an excess of magnesium led to a mixed-valence Ti II /Ti III trinuclear complex [{Ti­(η 5 -C 5 Me 5 )­(μ-Cl)} 3 (μ 3 -Cl)] capable of activating dinitrogen under ambient conditions . Analogous treatment of [Ti­(η 5 -C 5 Me 5 )­X 3 ] with excess LiAlH 4 in ethereal solvents (L) produced titanium­(II) species [{Ti­(η 5 -C 5 Me 5 )­(μ-H)} 2 {(μ-H) 2 AlXL} 2 ] (L = thf, X = Cl, Br; L = OEt 2 , X = Cl), while the reactions with the milder reductant LiBH 4 gave titanium­(III) tetrahydridoborato complexes .…”

Pentamethylcyclopentadienyltrimethylgermane: A Nontoxic Entry to Mid-Valent Monopentamethylcyclopentadienylvanadium Chloride Complexes

“…11,12 More recently, we described that reduction of [TiCp*Cl 3 ] with magnesium afforded a mixed-valence titanium(III)/titanium-(II) trinuclear complex [{TiCp*(μ-Cl)} 3 (μ 3 -Cl)] capable of performing a four-electron reduction of N 2 under ambient conditions to give a derivative with a μ 3 -η 1 :η 2 :η 2 -Ν 2 ligand among three titanium centers. 13 We speculated that the higher availability of stable oxidation states of vanadium could be beneficial to activate dinitrogen and other small molecules on monocyclopentadienyl-based systems. Thus, we decided to revisit complex [{VCp*(μ-Cl) 2 } 3 ] (1) to clarify some inconsistencies in the properties reported for this compound and to use it for further developing the chemistry of mid-valent monocyclopentadienylvanadium complexes.…”