Synthesis and DFT, Multinuclear Magnetic Resonance, and X‑ray Structural Studies of Iminoacyl Imido Hydridotris(3,5-dimethylpyrazolyl)borate Niobium and Tantalum(V) Complexes

Reaction of alkyl imido [MTp*XR­(N<i>t</i>Bu)] (M = Nb/Ta; Tp* = HB­(3,5-Me₂C₃HN₂)₃; X = Cl, R = Me (<b>1a</b>/<b>1b</b>), CH₂CH₃ (<b>2a</b>/<b>2b</b>), CH₂Ph (<b>3a</b>/<b>3b</b>), CH₂<i>t</i>Bu (<b>4a</b>/<b>4b</b>), CH₂SiMe₃ (<b>5a</b>/<b>5b</b>), CH₂CMe₂Ph (<b>6a</b>/<b>6b</b>); X = R = Me (<b>7a</b>/<b>7b</b>)) complexes with 1 equiv of the isocyanide 2,6-Me₂C₆H₃NC takes place with migration of an alkyl group and leads to the formation of the series of chlorido or methyl imido iminoacyl derivatives [MTp*X­(N<i>t</i>Bu)­{C­(R)­NAr-κ²<i>C</i>,<i>N</i>}] (M = Nb/Ta; Ar = 2,6-Me₂C₆H₃; X = Cl, R= Me (<b>8a</b>/<b>8b</b>), CH₂CH₃ (<b>9a</b>/<b>9b</b>), CH₂Ph (<b>10a</b>/<b>10b</b>), CH₂<i>t</i>Bu (<b>11a</b>/<b>11b</b>), CH₂SiMe₃ (<b>12a</b>/<b>12b</b>), CH₂CMe₂Ph (<b>13a</b>/<b>13b</b>); X = R = Me (<b>14a</b>/<b>14b</b>)). The molecular structure of <b>10b</b> was determined by X-ray diffraction methods. An irreversible <i>endo</i> → <i>exo</i> isomerization was detected by ¹H NMR in compounds <b>10a</b>–<b>13a.</b> The insertion–isomerization reaction coordinate was computed by DFT calculations

Hydridotris(3,5-dimethylpyrazolyl)borate Dimethylamido Imido Niobium and Tantalum Complexes: Synthesis, Reactivity, Fluxional Behavior, and C–H Activation of the NMe₂ Function

The pseudo-octahedral dichlorido imido hydridotris­(3,5-dimethylpyrazolyl)­borate niobium and tantalum compounds [MTp*Cl₂(N<i>t</i>Bu)] (M = Nb (<b>1a</b>), Ta (<b>1b</b>); Tp* = BH­(3,5-Me₂C₃HN₂)₃) were prepared in better yields by treatment of equimolar quantities of MCl₃(N<i>t</i>Bu)­py₂ and KTp* in toluene at reflux. Reactions of <b>1a</b>,<b>b</b> with a small excess of LiNMe₂ (1:1.2 ratio) in toluene gave the corresponding chlorido dimethylamido derivatives [MTp*Cl­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>2</b>), Ta (<b>3</b>)). Mixed methyl dimethylamido [MTp*Me­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>4</b>), Ta (<b>5</b>)) complexes were synthesized in good yields by heating for several days a mixture of <b>2</b> or <b>3</b> and MgClMe, in a 1:1 molar ratio. However, the reactions of <b>1a</b>,<b>b</b> with excess LiNMe₂ led to bis­(dimethylamido) complexes [MTp*­(NMe₂)₂(N<i>t</i>Bu)] (M = Nb (<b>6</b>), Ta (<b>7</b>)) as unitary species. <b>4</b> and <b>5</b> reacted with B­(C₆F₅)₃ to give the cation-like complexes [MTp*­(NMe₂)­(N<i>t</i>Bu)]⁺[BMe­(C₆F₅)₃]⁻ (M = Nb (<b>8</b>), Ta (<b>9</b>)), whereas in the case of complexes <b>6</b> and <b>7</b> the reaction led to [MTp*­(NMe₂)­{N­(Me)CH₂-κ¹<i>N</i>}­(N<i>t</i>Bu)]⁺[BH­(C₆F₅)₃]⁻ (M = Nb (<b>10</b>), Ta (<b>11</b>)) derivatives as result of the C–H_methyl bond activation into a NMe₂ function. The restricted rotation process of the NMe₂ moiety around the M–N_amido bond in complexes <b>2</b>–<b>7</b>, the pseudo-rotation process of the Tp* ligand into the cationic species <b>8</b> and <b>9</b>, and the CH₂ terminal group around the NCH₂ bond in compounds <b>10</b> and <b>11</b> were observed and studied by ¹H DNMR spectroscopy. The isomerization of two enantiomers in the mixtures of <b>4</b> and <b>5</b> with B­(C₆F₅)₃ was detected, and their mechanism was proposed. All compounds were studied by IR and multinuclear NMR (¹H, ¹³C, and ¹⁵N) spectroscopy, and the molecular structures of complexes <b>1a</b>,<b>b</b> and <b>3</b> were determined by X-ray diffraction methods

Hydridotris(3,5-dimethylpyrazolyl)borate Dimethylamido Imido Niobium and Tantalum Complexes: Synthesis, Reactivity, Fluxional Behavior, and C–H Activation of the NMe₂ Function

The pseudo-octahedral dichlorido imido hydridotris­(3,5-dimethylpyrazolyl)­borate niobium and tantalum compounds [MTp*Cl₂(N<i>t</i>Bu)] (M = Nb (<b>1a</b>), Ta (<b>1b</b>); Tp* = BH­(3,5-Me₂C₃HN₂)₃) were prepared in better yields by treatment of equimolar quantities of MCl₃(N<i>t</i>Bu)­py₂ and KTp* in toluene at reflux. Reactions of <b>1a</b>,<b>b</b> with a small excess of LiNMe₂ (1:1.2 ratio) in toluene gave the corresponding chlorido dimethylamido derivatives [MTp*Cl­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>2</b>), Ta (<b>3</b>)). Mixed methyl dimethylamido [MTp*Me­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>4</b>), Ta (<b>5</b>)) complexes were synthesized in good yields by heating for several days a mixture of <b>2</b> or <b>3</b> and MgClMe, in a 1:1 molar ratio. However, the reactions of <b>1a</b>,<b>b</b> with excess LiNMe₂ led to bis­(dimethylamido) complexes [MTp*­(NMe₂)₂(N<i>t</i>Bu)] (M = Nb (<b>6</b>), Ta (<b>7</b>)) as unitary species. <b>4</b> and <b>5</b> reacted with B­(C₆F₅)₃ to give the cation-like complexes [MTp*­(NMe₂)­(N<i>t</i>Bu)]⁺[BMe­(C₆F₅)₃]⁻ (M = Nb (<b>8</b>), Ta (<b>9</b>)), whereas in the case of complexes <b>6</b> and <b>7</b> the reaction led to [MTp*­(NMe₂)­{N­(Me)CH₂-κ¹<i>N</i>}­(N<i>t</i>Bu)]⁺[BH­(C₆F₅)₃]⁻ (M = Nb (<b>10</b>), Ta (<b>11</b>)) derivatives as result of the C–H_methyl bond activation into a NMe₂ function. The restricted rotation process of the NMe₂ moiety around the M–N_amido bond in complexes <b>2</b>–<b>7</b>, the pseudo-rotation process of the Tp* ligand into the cationic species <b>8</b> and <b>9</b>, and the CH₂ terminal group around the NCH₂ bond in compounds <b>10</b> and <b>11</b> were observed and studied by ¹H DNMR spectroscopy. The isomerization of two enantiomers in the mixtures of <b>4</b> and <b>5</b> with B­(C₆F₅)₃ was detected, and their mechanism was proposed. All compounds were studied by IR and multinuclear NMR (¹H, ¹³C, and ¹⁵N) spectroscopy, and the molecular structures of complexes <b>1a</b>,<b>b</b> and <b>3</b> were determined by X-ray diffraction methods

Hydridotris(3,5-dimethylpyrazolyl)borate Dimethylamido Imido Niobium and Tantalum Complexes: Synthesis, Reactivity, Fluxional Behavior, and C–H Activation of the NMe₂ Function

The pseudo-octahedral dichlorido imido hydridotris­(3,5-dimethylpyrazolyl)­borate niobium and tantalum compounds [MTp*Cl₂(N<i>t</i>Bu)] (M = Nb (<b>1a</b>), Ta (<b>1b</b>); Tp* = BH­(3,5-Me₂C₃HN₂)₃) were prepared in better yields by treatment of equimolar quantities of MCl₃(N<i>t</i>Bu)­py₂ and KTp* in toluene at reflux. Reactions of <b>1a</b>,<b>b</b> with a small excess of LiNMe₂ (1:1.2 ratio) in toluene gave the corresponding chlorido dimethylamido derivatives [MTp*Cl­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>2</b>), Ta (<b>3</b>)). Mixed methyl dimethylamido [MTp*Me­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>4</b>), Ta (<b>5</b>)) complexes were synthesized in good yields by heating for several days a mixture of <b>2</b> or <b>3</b> and MgClMe, in a 1:1 molar ratio. However, the reactions of <b>1a</b>,<b>b</b> with excess LiNMe₂ led to bis­(dimethylamido) complexes [MTp*­(NMe₂)₂(N<i>t</i>Bu)] (M = Nb (<b>6</b>), Ta (<b>7</b>)) as unitary species. <b>4</b> and <b>5</b> reacted with B­(C₆F₅)₃ to give the cation-like complexes [MTp*­(NMe₂)­(N<i>t</i>Bu)]⁺[BMe­(C₆F₅)₃]⁻ (M = Nb (<b>8</b>), Ta (<b>9</b>)), whereas in the case of complexes <b>6</b> and <b>7</b> the reaction led to [MTp*­(NMe₂)­{N­(Me)CH₂-κ¹<i>N</i>}­(N<i>t</i>Bu)]⁺[BH­(C₆F₅)₃]⁻ (M = Nb (<b>10</b>), Ta (<b>11</b>)) derivatives as result of the C–H_methyl bond activation into a NMe₂ function. The restricted rotation process of the NMe₂ moiety around the M–N_amido bond in complexes <b>2</b>–<b>7</b>, the pseudo-rotation process of the Tp* ligand into the cationic species <b>8</b> and <b>9</b>, and the CH₂ terminal group around the NCH₂ bond in compounds <b>10</b> and <b>11</b> were observed and studied by ¹H DNMR spectroscopy. The isomerization of two enantiomers in the mixtures of <b>4</b> and <b>5</b> with B­(C₆F₅)₃ was detected, and their mechanism was proposed. All compounds were studied by IR and multinuclear NMR (¹H, ¹³C, and ¹⁵N) spectroscopy, and the molecular structures of complexes <b>1a</b>,<b>b</b> and <b>3</b> were determined by X-ray diffraction methods

Hydridotris(3,5-dimethylpyrazolyl)borate Dimethylamido Imido Niobium and Tantalum Complexes: Synthesis, Reactivity, Fluxional Behavior, and C–H Activation of the NMe₂ Function

The pseudo-octahedral dichlorido imido hydridotris­(3,5-dimethylpyrazolyl)­borate niobium and tantalum compounds [MTp*Cl₂(N<i>t</i>Bu)] (M = Nb (<b>1a</b>), Ta (<b>1b</b>); Tp* = BH­(3,5-Me₂C₃HN₂)₃) were prepared in better yields by treatment of equimolar quantities of MCl₃(N<i>t</i>Bu)­py₂ and KTp* in toluene at reflux. Reactions of <b>1a</b>,<b>b</b> with a small excess of LiNMe₂ (1:1.2 ratio) in toluene gave the corresponding chlorido dimethylamido derivatives [MTp*Cl­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>2</b>), Ta (<b>3</b>)). Mixed methyl dimethylamido [MTp*Me­(NMe₂)­(N<i>t</i>Bu)] (M = Nb (<b>4</b>), Ta (<b>5</b>)) complexes were synthesized in good yields by heating for several days a mixture of <b>2</b> or <b>3</b> and MgClMe, in a 1:1 molar ratio. However, the reactions of <b>1a</b>,<b>b</b> with excess LiNMe₂ led to bis­(dimethylamido) complexes [MTp*­(NMe₂)₂(N<i>t</i>Bu)] (M = Nb (<b>6</b>), Ta (<b>7</b>)) as unitary species. <b>4</b> and <b>5</b> reacted with B­(C₆F₅)₃ to give the cation-like complexes [MTp*­(NMe₂)­(N<i>t</i>Bu)]⁺[BMe­(C₆F₅)₃]⁻ (M = Nb (<b>8</b>), Ta (<b>9</b>)), whereas in the case of complexes <b>6</b> and <b>7</b> the reaction led to [MTp*­(NMe₂)­{N­(Me)CH₂-κ¹<i>N</i>}­(N<i>t</i>Bu)]⁺[BH­(C₆F₅)₃]⁻ (M = Nb (<b>10</b>), Ta (<b>11</b>)) derivatives as result of the C–H_methyl bond activation into a NMe₂ function. The restricted rotation process of the NMe₂ moiety around the M–N_amido bond in complexes <b>2</b>–<b>7</b>, the pseudo-rotation process of the Tp* ligand into the cationic species <b>8</b> and <b>9</b>, and the CH₂ terminal group around the NCH₂ bond in compounds <b>10</b> and <b>11</b> were observed and studied by ¹H DNMR spectroscopy. The isomerization of two enantiomers in the mixtures of <b>4</b> and <b>5</b> with B­(C₆F₅)₃ was detected, and their mechanism was proposed. All compounds were studied by IR and multinuclear NMR (¹H, ¹³C, and ¹⁵N) spectroscopy, and the molecular structures of complexes <b>1a</b>,<b>b</b> and <b>3</b> were determined by X-ray diffraction methods