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

Highly Recoverable Pd(II) Catalysts for the Mizoroki–Heck Reaction Based on N‑Heterocyclic Carbenes and Poly(benzyl ether) Dendrons

Two series of bis­(imidazolylidene)­palladium complexes of general formula [PdBr₂(NHC)₂] have been prepared. The molecular weight of the complexes was enlarged by bonding poly­(benzyl ether) dendrons of increasing size (G0 to G3) at the nitrogen atom of the NHC ligands. Complexes <b>1</b>–<b>4</b> contain monodentate NHC ligands coordinated in a <i>trans</i> mode, whereas complexes <b>9</b>–<b>12</b> contain a chelating ethylene-bridged bis­(NHC) ligand. The complexes were recovered from the product stream of a Mizoroki–Heck reaction by nanofiltration through thermally and chemically stable ceramic membranes. The recoverability is better for larger complexes and chelate ligands. In particular, chelate G3 complex <b>12</b> maintained a constant activity during the 13 recovery cycles performed, affording an accumulated turnover number (TON) of 13 000. On average, around 99.5% of the metal is recovered in each recovery cycle, and contamination by palladium is only 3 mg per kg of product. Several models to explain the efficiency of the recovery are discussed

Co-complexation of Lithium Gallates on the Titanium Molecular Oxide {[Ti(η⁵‑C₅Me₅)(μ-O)}₃(μ₃‑CH)]

Amide and lithium aryloxide gallates [Li⁺{RGaPh₃}⁻] (R = NMe₂, O-2,6-Me₂C₆H₃) react with the μ₃-alkylidyne oxoderivative ligand [{Ti­(η⁵-C₅Me₅)­(μ-O)}₃(μ₃-CH)] (<b>1</b>) to afford the gallium–lithium–titanium cubane complexes [{Ph₃Ga­(μ-R)­Li}­{Ti­(η⁵-C₅Me₅)­(μ-O)}₃(μ₃-CH)] [R = NMe₂ (<b>3</b>), O-2,6-Me₂C₆H₃ (<b>4</b>)]. The same complexes can be obtained by treatment of the [Ph₃Ga­(μ₃-O)₃{Ti­(η⁵-C₅Me₅)}₃(μ₃-CH)] (<b>2</b>) adduct with the corresponding lithium amide or aryloxide, respectively. Complex <b>3</b> evolves with formation of <b>5</b> as a solvent-separated ion pair constituted by the lithium dicubane cationic species [Li­{(μ₃-O)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-CH)}₂]⁺ together with the anionic [(GaPh₃)₂(μ-NMe₂)]⁻ unit. On the other hand, the reaction of <b>1</b> with Li­(<i>p</i>-MeC₆H₄) and GaPh₃ leads to the complex [Li­{(μ₃-O)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-CH)}₂]­[GaLi­(<i>p</i>-MeC₆H₄)₂Ph₃] (<b>6</b>). X-ray diffraction studies were performed on <b>1</b>, <b>2</b>, <b>4</b>, and <b>5</b>, while trials to obtain crystals of <b>6</b> led to characterization of [Li­{(μ₃-O)₃Ti₃(η⁵-C₅Me₅)₃(μ₃-CH)}₂]­[PhLi­(μ-C₆H₅)₂Ga­(<i>p</i>-MeC₆H₄)­Ph] <b>6a</b>

Learning about Steric Effects in NHC Complexes from a 1D Silver Coordination Polymer with Fréchet Dendrons

The complex (NHC)­AgBr, which bears G1 poly­(benzyl ether) dendritic substituents in the NHC ligand, forms a 1D coordination polymer based on unusual zigzag −Ag–halide– chains. The asymmetric distribution of the volume buried by the NHC ligand in the Ag coordination sphere is important to explain the formation of this structure. A <i>V</i>_bur eccentricity parameter has been introduced and used in conjunction with the %<i>V</i>_bur descriptor to analyze the X-ray structures of 100 (NHC)­AgX complexes

Water-Soluble Mono- and Dimethyl N‑Heterocyclic Carbene Platinum(II) Complexes: Synthesis and Reactivity

A family of water-soluble dimethyl complexes of formula <i>cis</i>-[PtMe₂(dmso)­(NHC·Na)] (<b>2</b>), in which NHC is an anionic N-heterocyclic carbene bearing a sulfonatopropyl chain on one of the nitrogen atoms and a sulfonatopropyl (<b>a</b>), methyl (<b>b</b>), mesityl (<b>c</b>), or 2,6-diisopropylphenyl group (<b>d</b>) on the other, have been prepared. The hydrolytic stability of the Pt–C bonds in these complexes under different neutral, alkaline, and acidic aqueous conditions has also been studied. Complexes <b>2</b> were found to be quite stable at room temperature in water under neutral or alkaline conditions. Degradation occurred at higher temperatures but involved C sp³–H activation and C–C reductive elimination processes in addition to Pt–Me bond hydrolysis. Hydrolytic cleavage of the platinum–methyl bonds was favored by good nucleophiles. Thus, the addition of KCN to an aqueous solution of <b>2</b> resulted in formation of the monomethyl complexes K­[PtMe­(CN)₂(NHC·Na)] (<b>9</b>), whereas the dimethyl complexes K­[PtMe₂(CNR)­(NHC·Na)] (<b>10</b>) were formed with the isocyanide CNCH₂COOK. The addition of stoichiometric amounts of protic acids to aqueous solutions of <b>2</b> resulted in the clean cleavage of one or both platinum­(II)–methyl bonds. Thus, the reaction of <b>2</b> with HCl afforded the complexes [PtClMe­(dmso)­(NHC·Na)] (<b>3</b>) and [PtCl₂(dmso)­(NHC·Na)] (<b>4</b>), whereas [PtMe­(OH₂)­(dmso)­(NHC)] (<b>5</b>) and [Pt­(OH₂)₂(dmso)­(NHC)]­[BF₄] (<b>7</b>) were obtained upon treatment with HBF₄. The crystal structure of <b>9a</b> is remarkable in light of the longitudinal channels around 6 Å in diameter internally decorated with Pt–Me bonds

Sulfonated Water-Soluble N‑Heterocyclic Carbene Silver(I) Complexes: Behavior in Aqueous Medium and as NHC-Transfer Agents to Platinum(II)

This report describes the synthesis of water-soluble silver­(I) and platinum­(II) complexes bearing sulfonated mono- or dianionic N-heterocyclic carbene ligands. Thus, treatment of the corresponding zwitterionic imidazolium derivative with silver­(I) oxide in water afforded the light-sensitive bis­(carbene) complexes Ag­[Ag­(NHC)₂] (<b>2</b>^<b>Ag+</b>), which were transformed into the stable salts Na­[Ag­(NHC)₂] (<b>2</b>) by addition of sodium chloride. In contrast, the same reaction in dmso afforded mono­(carbenes) of general formula Na­[AgCl­(NHC)] (<b>3</b>). The solvent-dependence of the reaction product can be rationalized on the basis of the equilibrium [AgCl₂]⁻ ↔ AgCl + Cl^–. The precipitation of silver chloride is more favored in protic solvents than in aprotic solvents such as dmso, thus explaining the formation of bis­(carbenes) in water. The formation of silver chloride may also promote the hydrolysis of silver NHC complexes under some conditions. The water-soluble platinum­(II) complexes Na­[PtCl₂(dmso)­(NHC)] were synthesized by using either mono­(carbene) silver complexes <b>3</b> as carbene-transfer agents or by direct metalation of the imidazolium salt with <i>cis</i>-[PtCl₂(dmso)₂] in the presence of NaHCO₃ as base. The (NHC)­Pt­(II) complexes were tested as catalysts for the hydration of alkynes in the aqueous phase and found to be active in neat water without the need for acidic cocatalysts