Reactions of N-Monosubstituted Amidines with AlMe₃ and AlMeCl₂: Formation of Fused Triazaalane Heterocycles

Reactions of N-monosubstituted amidines of the formula HNC­(R)–NH­(R′) (R = Ph, 4-<i>tert</i>-butylphenyl, Me; R′ = 2,6-diisopropylphenyl, Ph) with AlMe₃ and AlMeCl₂ are reported. All the <i>N</i>-(Dipp)­amidines (Dipp = 2,6-diisopropylphenyl) react with AlMe₃ in a 1:1 ratio to yield tetrameric aluminum amidinates (<b>1</b>, <b>2</b>, and <b>3</b>) in good yields. In these compounds, the amidinate ligand chelates to Al while bridging to another Al. However, when <i>N</i>-phenylamidines are employed, tetracyclic (<b>4</b>–<b>9</b>) and pentacyclic (<b>10</b>) Al–N–C heterocycles are formed. In the case of <i>N</i>-phenylbenzamidine, formation of a hexacyclic Al–N–C heterocycle (<b>11</b>) is observed when a slight excess of AlMe₃ (1:1.2 equiv) is used. In these compounds, the amidinate ligand coordinates to Al atoms in a bridging fashion. Further, <i>N</i>-(Dipp)­acetamidine and <i>N</i>-(Dipp)­benzamidine are also treated with AlMeCl₂. Whereas <i>N</i>-(Dipp)­acetamidine affords an ionic 15-membered aluminum amidinate chain (<b>12</b>), <i>N</i>-(Dipp)­benzamidine gives a bicyclic heterocycle (<b>13</b>) and the AlCl₃ adduct of <i>N</i>-(Dipp)­benzamidine (<b>14</b>). However, from a reaction between <i>N</i>-phenylbenzamidine and AlMeCl₂, only the AlCl₃ adduct, <b>15</b>, was isolated. Compounds <b>3</b>, <b>4</b>, <b>6</b>, <b>8</b>, and <b>10</b>–<b>15</b> have been structurally characterized

Synthesis of Aluminum Complexes of Triaza Framework Ligands and Their Catalytic Activity toward Polymerization of ε‑Caprolactone

The synthesis and characterization of 1,5-bis­(2,6-diisopropylphenyl)-2,4-diphenyl-1,3,5-triazapenta-1,3-diene (L¹H), a triaza ligand, and Al complexes of its anion are reported. A neat condensation reaction between <i>N</i>-(Dipp)­benzamidine (Dipp = 2,6-diisopropylphenyl) and <i>N</i>-(Dipp)­benzimidoyl chloride affords L¹H in good yield. The Al complexes [L¹AlMe₂] (<b>1</b>), [L¹AlMe­(Cl)] (<b>2</b>), and [L¹AlCl₂] (<b>3</b>) are prepared by treating L¹H with a slight excess of AlMe₃, AlMe₂Cl, and AlMeCl₂, respectively, in toluene. Further, the aluminum complexes [L²AlMe₂] (<b>5</b>), [L²AlMe­(Cl)] (<b>6</b>), and [L²AlCl₂] (<b>7</b>) are obtained in good yields from 1,3-bis­(2-pyridylimino)­isoindoline (L²H) in a similar fashion. The ligand L¹H and complexes <b>1</b>, <b>2</b>, and <b>4</b>–<b>6</b> have been structurally characterized. All of the complexes have been explored for their catalytic activity toward the ring-opening polymerization (ROP) of ε-caprolactone. It has been found that [L¹AlMe₂], upon the addition of cocatalyst (benzyl alcohol), gives a tetranuclear Al alkoxide (<b>8</b>), which is highly efficient in catalyzing the ROP of ε-caprolactone. [L²AlMe₂] has also been found to be a good catalyst. The crystal structure of <b>8</b> and the catalytic activities of all the complexes in detail are reported

Synthesis of Aluminum Complexes of Triaza Framework Ligands and Their Catalytic Activity toward Polymerization of ε‑Caprolactone

The synthesis and characterization of 1,5-bis­(2,6-diisopropylphenyl)-2,4-diphenyl-1,3,5-triazapenta-1,3-diene (L¹H), a triaza ligand, and Al complexes of its anion are reported. A neat condensation reaction between <i>N</i>-(Dipp)­benzamidine (Dipp = 2,6-diisopropylphenyl) and <i>N</i>-(Dipp)­benzimidoyl chloride affords L¹H in good yield. The Al complexes [L¹AlMe₂] (<b>1</b>), [L¹AlMe­(Cl)] (<b>2</b>), and [L¹AlCl₂] (<b>3</b>) are prepared by treating L¹H with a slight excess of AlMe₃, AlMe₂Cl, and AlMeCl₂, respectively, in toluene. Further, the aluminum complexes [L²AlMe₂] (<b>5</b>), [L²AlMe­(Cl)] (<b>6</b>), and [L²AlCl₂] (<b>7</b>) are obtained in good yields from 1,3-bis­(2-pyridylimino)­isoindoline (L²H) in a similar fashion. The ligand L¹H and complexes <b>1</b>, <b>2</b>, and <b>4</b>–<b>6</b> have been structurally characterized. All of the complexes have been explored for their catalytic activity toward the ring-opening polymerization (ROP) of ε-caprolactone. It has been found that [L¹AlMe₂], upon the addition of cocatalyst (benzyl alcohol), gives a tetranuclear Al alkoxide (<b>8</b>), which is highly efficient in catalyzing the ROP of ε-caprolactone. [L²AlMe₂] has also been found to be a good catalyst. The crystal structure of <b>8</b> and the catalytic activities of all the complexes in detail are reported

Reactions of N-Monosubstituted Amidines with AlMe₃ and AlMeCl₂: Formation of Fused Triazaalane Heterocycles

Reactions of N-monosubstituted amidines of the formula HNC­(R)–NH­(R′) (R = Ph, 4-<i>tert</i>-butylphenyl, Me; R′ = 2,6-diisopropylphenyl, Ph) with AlMe₃ and AlMeCl₂ are reported. All the <i>N</i>-(Dipp)­amidines (Dipp = 2,6-diisopropylphenyl) react with AlMe₃ in a 1:1 ratio to yield tetrameric aluminum amidinates (<b>1</b>, <b>2</b>, and <b>3</b>) in good yields. In these compounds, the amidinate ligand chelates to Al while bridging to another Al. However, when <i>N</i>-phenylamidines are employed, tetracyclic (<b>4</b>–<b>9</b>) and pentacyclic (<b>10</b>) Al–N–C heterocycles are formed. In the case of <i>N</i>-phenylbenzamidine, formation of a hexacyclic Al–N–C heterocycle (<b>11</b>) is observed when a slight excess of AlMe₃ (1:1.2 equiv) is used. In these compounds, the amidinate ligand coordinates to Al atoms in a bridging fashion. Further, <i>N</i>-(Dipp)­acetamidine and <i>N</i>-(Dipp)­benzamidine are also treated with AlMeCl₂. Whereas <i>N</i>-(Dipp)­acetamidine affords an ionic 15-membered aluminum amidinate chain (<b>12</b>), <i>N</i>-(Dipp)­benzamidine gives a bicyclic heterocycle (<b>13</b>) and the AlCl₃ adduct of <i>N</i>-(Dipp)­benzamidine (<b>14</b>). However, from a reaction between <i>N</i>-phenylbenzamidine and AlMeCl₂, only the AlCl₃ adduct, <b>15</b>, was isolated. Compounds <b>3</b>, <b>4</b>, <b>6</b>, <b>8</b>, and <b>10</b>–<b>15</b> have been structurally characterized

Copolymerization of CO₂ and Cyclohexene Oxide: β‑Diketiminate-Supported Zn(II)OMe and Zn(II)Et Complexes as Initiators

β-Diketiminate ligands with varying degrees of steric bulkiness and having −CN and −NO₂ groups on <i>N</i>-aryl substituents were synthesized. The catalytic activity of some of their [LZnEt] and [LZnOMe]₂ complexes (L = β-diketiminato) toward the copolymerization of carbon dioxide and cyclohexene oxide was explored. All the catalysts were found to be highly active and showed very good turnover frequency, and the polycarbonates produced have a very high percentage of carbonate linkages. The complex [L^iPr,Me‑CNZnEt] showed very high activity and selectivity on par with its zinc methoxide analogue. The polymers produced by [LZnEt] complexes displayed a bimodal molecular weight distribution

Copolymerization of CO₂ and Cyclohexene Oxide: β‑Diketiminate-Supported Zn(II)OMe and Zn(II)Et Complexes as Initiators

β-Diketiminate ligands with varying degrees of steric bulkiness and having −CN and −NO₂ groups on <i>N</i>-aryl substituents were synthesized. The catalytic activity of some of their [LZnEt] and [LZnOMe]₂ complexes (L = β-diketiminato) toward the copolymerization of carbon dioxide and cyclohexene oxide was explored. All the catalysts were found to be highly active and showed very good turnover frequency, and the polycarbonates produced have a very high percentage of carbonate linkages. The complex [L^iPr,Me‑CNZnEt] showed very high activity and selectivity on par with its zinc methoxide analogue. The polymers produced by [LZnEt] complexes displayed a bimodal molecular weight distribution

Insertion of Benzonitrile into Al–N and Ga–N Bonds: Formation of Fused Carbatriaza-Gallanes/Alanes and Their Subsequent Synthesis from Amidines and Trimethyl-Gallium/Aluminum

Insertion of aromatic nitriles into Al–N and Ga–N bonds are reported. Sterically less hindered aluminum amide [PhNHAlMe₂]₂ (<b>1</b>) undergoes CN insertion with benzonitrile to give an isomeric mixture of tetracyclic triazaalanes {[PhNC­(Ph)­N]₃[PhNC­(Ph)­NH]­Al­[AlMe]­[AlMe₂]₂} (<b>2</b> and <b>3</b>). A similar reaction with analogous gallium amide affords a tetracyclic triazagallane {[PhNC­(Ph)­N]₃[PhNC­(Ph)­NH]­Ga­[GaMe]­[GaMe₂]₂} (<b>6</b>) along with a novel bowl shaped carbon containing Ga–N cluster {[PhNC­(Ph)­N]­[PhN]­[GaMe]₂}₃ (<b>5</b>). On the other hand, when sterically bulky gallium amide (Dipp on N, Dipp = 2,6-diisopropylphenyl) is employed, a tetrameric gallium amidinate {[(Dipp)­NC­(Ph)­N]­GaMe}₄ (<b>8</b>) is obtained. Tetracyclic triazagallazane <b>6</b> is also synthesized from the condensation reaction of <i>N</i>-phenylbenzamidine with GaMe₃·OEt₂. Unlike AlMe₃, this reaction produces only one isomer. In case of amidines with bulkier substituents on N such as Dipp, formation of a bicyclic triazagallane {[(Dipp)­NC­(Ph)­NH]₂[(Dipp)­NC­(Ph)­N]­[GaMe]₂} (<b>14</b>) is also observed along with tetrameric gallium amidinate <b>8</b>, whereas <i>N</i>-<i>tert</i>-butylbenzamidine affords exclusively a tetrameric gallium amidinate {[(<i>tert</i>-Bu)­NC­(Ph)­N]­GaMe}₄ (<b>15</b>) similar to its Al analogue. However, treating <i>N</i>-(Dipp)­acetamidine with GaMe₃·OEt₂ gives only a bicyclic triazagallane {[(Dipp)­NC­(Me)­NH]₂[(Dipp)­NC­(Me)­N]­[GaMe]₂} (<b>16</b>). An intermediate [(<i>tert</i>-Bu)­N­(H) C­(Ph)­NGaMe₂]₂ (<b>17</b>), which is involved in the formation of tetrameric gallium amidinate <b>15</b>, is also characterized. A comparison of the structural parameters of Ga–N–C and Al–N–C frameworks synthesized in this study is reported

<i>N</i>‑Benzoylbenzamidinate Complexes of Magnesium: Catalysts for the Ring-Opening Polymerization of ε‑Caprolactone and CO₂/Epoxide Coupling

A series of amidinate-based N,O-chelated magnesium complexes [(<b>L</b>^<b>1</b>)₂(THF)₂Mg] (<b>1</b>), [(<b>L</b>^<b>2</b>)₂(THF)₂Mg] (<b>2</b>), [(<b>L</b>^<b>3</b>)₂(THF)₂Mg] (<b>3</b>), and [(<b>L</b>^<b>4</b>)₂Mg] (<b>4</b>) were prepared by treating <i>N</i>-benzoyl-<i>N</i>′-arylbenzamidines (<b>L</b>^{<b>1</b>–<b>4</b>}H) with 0.5 equiv of di-<i>n</i>-butylmagnesium in THF. Analogous CH₃CN-coordinated complexes [(<b>L</b>^<b>1</b>)₂(CH₃CN)₂Mg] (<b>5</b>) and [(<b>L</b>^<b>3</b>)₂(CH₃CN)₂Mg] (<b>6</b>) were prepared in a similar way using CH₃CN as solvent. All of the compounds were characterized by ¹H/¹³C NMR spectroscopy, and the molecular structures of <b>1</b>, <b>2</b>, and <b>4</b>–<b>6</b> were further confirmed by single-crystal X-ray diffraction studies. Complexes <b>1</b>, <b>2</b>, <b>5</b>, and <b>6</b> displayed good catalytic activity toward the ring-opening polymerization (ROP) of ε-caprolactone. In addition, <b>1</b>, <b>5</b>, and <b>6</b> were also found to be excellent catalysts for making cyclic carbonates from CO₂ and epoxides in the presence of a cocatalyst, <i>n</i>-Bu₄NBr

CO₂/Epoxide Coupling and the ROP of ε‑Caprolactone: Mg and Al Complexes of γ‑Phosphino-ketiminates as Dual-Purpose Catalysts

γ-Phosphino-ketimines Ph₂PC­[C­(Me)­O]­[C­(Me)­NAr] (Ar = 2,6-diisopropylphenyl, <b>L</b>^<b>1</b>H; Ar = 2,6-difluorophenyl, <b>L</b>^<b>2</b>H) were synthesized by treating deprotonated ketimines with PPh₂Cl. Their Mg complexes [(<b>L</b>^<b>1</b>)₂(THF)­Mg] (<b>1</b>) and [(<b>L</b>^<b>2</b>)₂(THF)₂Mg] (<b>2</b>) were obtained in excellent yields from a reaction between <b>L</b>H and di-<i>n</i>-butylmagnesium in THF. Addition of a slight excess of trimethylaluminum to <b>L</b>H in toluene yielded the Al complexes [<b>L</b>^<b>1</b>AlMe₂] (<b>3</b>) and [<b>L</b>^<b>2</b>AlMe₂] (<b>4</b>). Complexes <b>1</b> and <b>3</b> displayed high catalytic activity in the synthesis of cyclic carbonates from CO₂ and epoxides and also in the ring-opening polymerization (ROP) of ε-caprolactone. However, complexes <b>2</b> and <b>4</b>, which contain fluoro substituents, showed poor activity in the synthesis of cyclic carbonates and could not initiate the ROP reaction. The pentacoordinated Mg complex <b>1</b> was found to be a better catalyst than the aluminum complex <b>3</b>. It was also observed that the complexes <b>1</b> and <b>3</b> were more efficient than the unsubstituted ketiminate complexes reported in the literature