Reactivity with Electrophiles of Imido Groups Supported on Trinuclear Titanium Systems

Several trinuclear titanium complexes bearing amido μ-NHR, imido μ-NR, and nitrido μ_<i>n</i>-N ligands have been prepared by reaction of [{Ti­(η⁵-C₅Me₅)­(μ-NH)}₃(μ₃-N)] (<b>1</b>) with 1 equiv of electrophilic reagents ROTf (R = H, Me, SiMe₃; OTf = OSO₂CF₃). Treatment of <b>1</b> with triflic acid or methyl triflate in toluene at room temperature affords the precipitation of compounds [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NH₂)­(OTf)] (<b>2</b>) or [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)­(μ-NH₂)­(μ-NMe)­(OTf)] (<b>3</b>). Complexes <b>2</b> and <b>3</b> exhibit a fluxional behavior in solution consisting of proton exchange between μ-NH₂ and μ-NH groups, assisted by the triflato ligand, as could be inferred from a dynamic NMR spectroscopy study. Monitoring by NMR spectroscopy the reaction course of <b>1</b> with MeOTf allows the characterization of the methylamido intermediate [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NHMe)­(OTf)] (<b>4</b>), which readily rearranges to give <b>3</b> by a proton migration from the NHMe amido group to the NH imido ligands. The treatment of <b>1</b> with 1 equiv of Me₃SiOTf produces the stable ionic complex [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NHSiMe₃)]­[OTf] (<b>5</b>) with a disposition of the nitrogen ligands similar to that of <b>4</b>. Complex <b>5</b> reacts with 1 equiv of [K­{N­(SiMe₃)₂}] at room temperature to give [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-N)­(μ-NH)­(μ-NHSiMe₃)] (<b>6</b>), which at 85 °C rearranges to the trimethylsilylimido derivative [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NSiMe₃)] (<b>7</b>). Treatment of <b>7</b> with [K­{N­(SiMe₃)₂}] affords the potassium derivative [K­{(μ₃-N)­(μ₃-NH)­(μ₃-NSiMe₃)­Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>8</b>), which upon addition of 18-crown-6 leads to the ion pair [K­(18-crown-6)]­[Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-N)­(μ-NH)­(μ-NSiMe₃)] (<b>9</b>). The X-ray crystal structures of <b>2</b>, <b>5</b>, <b>6</b>, and <b>8</b> have been determined

Reactivity with Electrophiles of Imido Groups Supported on Trinuclear Titanium Systems

Several trinuclear titanium complexes bearing amido μ-NHR, imido μ-NR, and nitrido μ_<i>n</i>-N ligands have been prepared by reaction of [{Ti­(η⁵-C₅Me₅)­(μ-NH)}₃(μ₃-N)] (<b>1</b>) with 1 equiv of electrophilic reagents ROTf (R = H, Me, SiMe₃; OTf = OSO₂CF₃). Treatment of <b>1</b> with triflic acid or methyl triflate in toluene at room temperature affords the precipitation of compounds [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NH₂)­(OTf)] (<b>2</b>) or [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)­(μ-NH₂)­(μ-NMe)­(OTf)] (<b>3</b>). Complexes <b>2</b> and <b>3</b> exhibit a fluxional behavior in solution consisting of proton exchange between μ-NH₂ and μ-NH groups, assisted by the triflato ligand, as could be inferred from a dynamic NMR spectroscopy study. Monitoring by NMR spectroscopy the reaction course of <b>1</b> with MeOTf allows the characterization of the methylamido intermediate [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NHMe)­(OTf)] (<b>4</b>), which readily rearranges to give <b>3</b> by a proton migration from the NHMe amido group to the NH imido ligands. The treatment of <b>1</b> with 1 equiv of Me₃SiOTf produces the stable ionic complex [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NHSiMe₃)]­[OTf] (<b>5</b>) with a disposition of the nitrogen ligands similar to that of <b>4</b>. Complex <b>5</b> reacts with 1 equiv of [K­{N­(SiMe₃)₂}] at room temperature to give [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-N)­(μ-NH)­(μ-NHSiMe₃)] (<b>6</b>), which at 85 °C rearranges to the trimethylsilylimido derivative [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NSiMe₃)] (<b>7</b>). Treatment of <b>7</b> with [K­{N­(SiMe₃)₂}] affords the potassium derivative [K­{(μ₃-N)­(μ₃-NH)­(μ₃-NSiMe₃)­Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>8</b>), which upon addition of 18-crown-6 leads to the ion pair [K­(18-crown-6)]­[Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-N)­(μ-NH)­(μ-NSiMe₃)] (<b>9</b>). The X-ray crystal structures of <b>2</b>, <b>5</b>, <b>6</b>, and <b>8</b> have been determined

Reactivity with Electrophiles of Imido Groups Supported on Trinuclear Titanium Systems

Several trinuclear titanium complexes bearing amido μ-NHR, imido μ-NR, and nitrido μ_<i>n</i>-N ligands have been prepared by reaction of [{Ti­(η⁵-C₅Me₅)­(μ-NH)}₃(μ₃-N)] (<b>1</b>) with 1 equiv of electrophilic reagents ROTf (R = H, Me, SiMe₃; OTf = OSO₂CF₃). Treatment of <b>1</b> with triflic acid or methyl triflate in toluene at room temperature affords the precipitation of compounds [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NH₂)­(OTf)] (<b>2</b>) or [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)­(μ-NH₂)­(μ-NMe)­(OTf)] (<b>3</b>). Complexes <b>2</b> and <b>3</b> exhibit a fluxional behavior in solution consisting of proton exchange between μ-NH₂ and μ-NH groups, assisted by the triflato ligand, as could be inferred from a dynamic NMR spectroscopy study. Monitoring by NMR spectroscopy the reaction course of <b>1</b> with MeOTf allows the characterization of the methylamido intermediate [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NHMe)­(OTf)] (<b>4</b>), which readily rearranges to give <b>3</b> by a proton migration from the NHMe amido group to the NH imido ligands. The treatment of <b>1</b> with 1 equiv of Me₃SiOTf produces the stable ionic complex [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NHSiMe₃)]­[OTf] (<b>5</b>) with a disposition of the nitrogen ligands similar to that of <b>4</b>. Complex <b>5</b> reacts with 1 equiv of [K­{N­(SiMe₃)₂}] at room temperature to give [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-N)­(μ-NH)­(μ-NHSiMe₃)] (<b>6</b>), which at 85 °C rearranges to the trimethylsilylimido derivative [Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-NH)₂(μ-NSiMe₃)] (<b>7</b>). Treatment of <b>7</b> with [K­{N­(SiMe₃)₂}] affords the potassium derivative [K­{(μ₃-N)­(μ₃-NH)­(μ₃-NSiMe₃)­Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>8</b>), which upon addition of 18-crown-6 leads to the ion pair [K­(18-crown-6)]­[Ti₃(η⁵-C₅Me₅)₃(μ₃-N)­(μ-N)­(μ-NH)­(μ-NSiMe₃)] (<b>9</b>). The X-ray crystal structures of <b>2</b>, <b>5</b>, <b>6</b>, and <b>8</b> have been determined

Group 4 Half-Sandwich Tris(trimethylsilylmethyl) Complexes: Thermal Decomposition and Reactivity with <i>N</i>,<i>N</i>‑Dimethylamine–Borane

The thermal decomposition of group 4 trimethylsilylmethyl derivatives [M­(η⁵-C₅Me₅)­(CH₂SiMe₃)₃] (M = Ti (<b>1</b>), Zr (<b>2</b>), Hf (<b>3</b>)) in solution and their reactivity with <i>N</i>,<i>N</i>-dimethylamine–borane were investigated. Heating of hydrocarbon solutions of compounds <b>2</b> and <b>3</b> at 130–200 °C results in the elimination of SiMe₄ and the clean formation of the singular alkylidene–alkylidyne zirconium and hafnium compounds [{M­(η⁵-C₅Me₅)}₃{(μ-CH)₃SiMe}­(μ₃-CSiMe₃)] (M = Zr (<b>4</b>), Hf (<b>5</b>)). The reaction of <b>2</b> and <b>3</b> with NHMe₂BH₃ (≥1 equiv) at room temperature affords the dialkyl­(dimethylamidoborane) complexes [M­(η⁵-C₅Me₅)­(CH₂SiMe₃)₂(NMe₂BH₃)] (M = Zr (<b>6</b>), Hf (<b>7</b>)). Compounds <b>6</b> and <b>7</b> are unstable in solution and decompose with formation of the alkyl­(dimethylamino)­borane [B­(CH₂SiMe₃)­H­(NMe₂)] (<b>8</b>), SiMe₄, and other minor byproducts, including the tetranuclear zirconium­(III) octahydride complex [{Zr­(η⁵-C₅Me₅)}₄(μ-H)₈] (<b>9</b>) in the decomposition of <b>6</b>. Addition of NHMe₂BH₃ to the titanium tris­(trimethylsilylmethyl) derivative <b>1</b> gives the trinuclear mixed valence Ti­(II)/Ti­(III) tetrahydride complex [{Ti­(η⁵-C₅Me₅)­(μ-H)}₃(μ₃-H)­(μ₃-NMe₂BH₂)] (<b>10</b>) at 45–65 °C. While the complete conversion of <b>1</b> under argon atmosphere requires excess NHMe₂BH₃ (up to 15 equiv), complex <b>10</b> is readily prepared with 3 equiv of NHMe₂BH₃ under a hydrogen atmosphere indicating that the formation of <b>10</b> involves hydrogenolysis of <b>1</b> in the presence of (NMe₂BH₂)₂. In absence of amine–borane, the reaction of <b>1</b> with H₂ leads to the tetranuclear titanium­(III) octahydride [{Ti­(η⁵-C₅Me₅)}₄(μ-H)₈] (<b>11</b>), which upon addition of NHMe₂BH₃ and subsequent heating at 65 °C affords complex <b>10</b>. The X-ray crystal structures of <b>2</b>, <b>4</b>, <b>5</b>, <b>10</b>, and <b>11</b> were determined

Redox-Active Behavior of the [{Ti(η⁵‑C₅Me₅)(μ-NH)}₃(μ₃‑N)] Metalloligand

Treatment of [Cl₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] with [K­(C₅Me₅)] in toluene gives C₁₀Me₁₀ and the paramagnetic [K­(μ-Cl)₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>3</b>) derivative. Crystallization of <b>3</b> in pyridine affords the potassium-free [Cl₂(py)₂Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>4</b>) complex. Whereas the reaction of <b>3</b> with 1 equiv of 18-crown-6 leads to the molecular complex [(18-crown-6)­K­(μ-Cl)₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>5</b>), the analogous treatment of <b>3</b> with cryptand-222 affords the ion pair [K­(crypt-222)]­[Cl₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>6</b>). The X-ray crystal structures of <b>4</b>, <b>5</b>, and <b>6</b> have been determined. Density functional theory (DFT) calculations have elucidated the electronic structure of these species, which should be regarded as containing trivalent Y bonded to the {(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)} metalloligand radical anion

Partial Hydrogenation of a Tetranuclear Titanium Nitrido Complex with Ammonia Borane

The treatment of [{Ti­(η⁵-C₅Me₅)}₄(μ₃-N)₄] with NH₃BH₃ leads to the paramagnetic imidonitrido complex [{Ti­(η⁵-C₅Me₅)}₄(μ₃-N)₃(μ₃-NH)], which can also be obtained by stepwise proton and electron transfer with HOTf and [K­(C₅Me₅)]

Redox-Active Behavior of the [{Ti(η⁵‑C₅Me₅)(μ-NH)}₃(μ₃‑N)] Metalloligand

Treatment of [Cl₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] with [K­(C₅Me₅)] in toluene gives C₁₀Me₁₀ and the paramagnetic [K­(μ-Cl)₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>3</b>) derivative. Crystallization of <b>3</b> in pyridine affords the potassium-free [Cl₂(py)₂Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>4</b>) complex. Whereas the reaction of <b>3</b> with 1 equiv of 18-crown-6 leads to the molecular complex [(18-crown-6)­K­(μ-Cl)₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>5</b>), the analogous treatment of <b>3</b> with cryptand-222 affords the ion pair [K­(crypt-222)]­[Cl₃Y­{(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)}] (<b>6</b>). The X-ray crystal structures of <b>4</b>, <b>5</b>, and <b>6</b> have been determined. Density functional theory (DFT) calculations have elucidated the electronic structure of these species, which should be regarded as containing trivalent Y bonded to the {(μ₃-NH)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-N)} metalloligand radical anion

Synthesis, Optical Properties, and Regioselective Functionalization of 4a-Aza-10a-boraphenanthrene

4a-Aza-10a-boraphenanthrene has been synthesized in only four steps from commercially available materials with a remarkable overall yield of 62%. In contrast to other BN-isosteres of phenathrene, this isomer is weakly fluorescent, which has been explained by means of computational studies that found a low energy conical intersection for the nonradiative deactivation of the excited state. Moreover, a completely regioselective functionalization of 4a-aza-10a-boraphenanthrene at C-1 by reaction with activated electrophiles has been achieved