Modeling Coadsorption of Titanium Tetrachloride and Bidentate Electron Donors on Magnesium Dichloride Support Surfaces

Coadsorption of titanium tetrachloride and two representative bidentate electron donors on magnesium dichloride surfaces is systematically studied by means of periodic quantum chemical calculations. The two catalytically relevant surfaces in the Ziegler–Natta catalysis, (104) and (110) surfaces of the MgCl₂ support, are taken into account. Adsorption of TiCl₄ leads to formation of three types of mononuclear species on the magnesium dichloride surfaces. However, TiCl₄ alone cannot properly stabilize the support. Coadsorption of electron donors along with TiCl₄, on the other hand, is shown to significantly improve the strength of TiCl₄ adsorption on the magnesium dichloride surfaces. Our findings indicate the importance of electron donors as promoters of titanium tetrachloride adsorption. The model is readily extendable to evaluate other electron donors and binuclear titanium species

Polyethylenimines: Multidentate Electron Donors for Ziegler–Natta Catalysts

Polyethylenimines, polymers bearing amino functionalities, are studied for the first time as internal electron donors for Ziegler–Natta catalysts. An advantage of polyethylenimines (PEIs) compared to the conventional phthalate electron donors is their relative harmlessness. Interaction of PEI with MgCl₂ support was studied using computational (DFT; M06-2X) and experimental (PXRD, DRIFT, CP/MAS ¹³C NMR) methods. Quantum chemical calculations suggest that the structural variations in PEIs significantly affect their ability to stabilize the catalytically relevant MgCl₂ surfaces. Coordination on the (104) surface seems to be favored upon consideration of the layered structure of MgCl₂. The surface stabilization energies of branched PEIs are of the same magnitude with a phthalate electron donor reference. Experimental results indicate, in agreement with theoretical results, a strong coordination ability of branched PEI through nitrogen atoms to MgCl₂. Based on spectroscopic data, nitrogen atoms of primary, secondary, and tertiary amino groups can participate in coordination to MgCl₂. Calculations indicate that the strongest coordination of branched PEI occurs through primary amino groups. A Ziegler–Natta catalyst containing branched PEI as an internal electron donor (MgCl₂/PEI/TiCl₄) showed a reasonably high activity in ethylene/1-butene copolymerization. Overall, the combined computational and experimental results provide detailed information about coordination of nitrogen-containing polymeric electron donors to MgCl₂ support and indicate their potential as a new type of internal electron donors for Ziegler–Natta catalysts

Toward Luminescence Vapochromism of Tetranuclear Au^I–Cu^I Clusters

A family of triphosphine gold–copper clusters bearing aliphatic and hydroxyaliphatic alkynyl ligands of general formula [HC­(PPh₂)₃Au₃Cu­(C₂R)₃]⁺ (R = cyclohexyl (<b>1</b>), cyclopentyl (<b>2</b>), Bu^t (<b>3</b>), cyclohexanolyl (<b>4</b>), cyclopentanolyl (<b>5</b>), 2,6-dimethylheptanolyl (<b>6</b>), 2-methylbutanolyl (<b>7</b>), diphenylmethanolyl (<b>8</b>)) was synthesized via a self-assembly protocol, which involves treatment of the (AuC₂R)_<i>n</i> acetylides with the (PPh₂)₃CH ligand in the presence of Cu⁺ ions and NEt₃. Addition of Cl^– or Br^– anions to complex <b>8</b> results in coordination of the halides to the copper atoms to give neutral HC­(PPh₂)₃Au₃CuHal­(C₂COHPh₂)₃ derivatives (Hal = Cl (<b>9</b>), Br (<b>10</b>)). The title compounds were characterized by NMR and ESI-MS spectroscopy, and the structures of <b>1</b>, <b>4</b>, <b>7</b>, and <b>8</b> were determined by single-crystal X-ray diffraction analysis. The photophysical behavior of all of the complexes has been studied to reveal moderate to weak phosphorescence in solution and intense emission in the solid state with a maximum quantum yield of 80%. Exposure of the solvent-free X-ray amorphous samples <b>8</b>–<b>10</b> (R = diphenylmethanolyl) to vapors of the polar solvents (methanol, THF, acetone) switches luminescence with a visible hypsochromic shift of emission of 50–70 nm. The vapochromism observed is tentatively ascribed to the formation of a structurally ordered phase upon absorption of organic molecules by the amorphous solids

Toward Luminescence Vapochromism of Tetranuclear Au^I–Cu^I Clusters

A family of triphosphine gold–copper clusters bearing aliphatic and hydroxyaliphatic alkynyl ligands of general formula [HC­(PPh₂)₃Au₃Cu­(C₂R)₃]⁺ (R = cyclohexyl (<b>1</b>), cyclopentyl (<b>2</b>), Bu^t (<b>3</b>), cyclohexanolyl (<b>4</b>), cyclopentanolyl (<b>5</b>), 2,6-dimethylheptanolyl (<b>6</b>), 2-methylbutanolyl (<b>7</b>), diphenylmethanolyl (<b>8</b>)) was synthesized via a self-assembly protocol, which involves treatment of the (AuC₂R)_<i>n</i> acetylides with the (PPh₂)₃CH ligand in the presence of Cu⁺ ions and NEt₃. Addition of Cl^– or Br^– anions to complex <b>8</b> results in coordination of the halides to the copper atoms to give neutral HC­(PPh₂)₃Au₃CuHal­(C₂COHPh₂)₃ derivatives (Hal = Cl (<b>9</b>), Br (<b>10</b>)). The title compounds were characterized by NMR and ESI-MS spectroscopy, and the structures of <b>1</b>, <b>4</b>, <b>7</b>, and <b>8</b> were determined by single-crystal X-ray diffraction analysis. The photophysical behavior of all of the complexes has been studied to reveal moderate to weak phosphorescence in solution and intense emission in the solid state with a maximum quantum yield of 80%. Exposure of the solvent-free X-ray amorphous samples <b>8</b>–<b>10</b> (R = diphenylmethanolyl) to vapors of the polar solvents (methanol, THF, acetone) switches luminescence with a visible hypsochromic shift of emission of 50–70 nm. The vapochromism observed is tentatively ascribed to the formation of a structurally ordered phase upon absorption of organic molecules by the amorphous solids

Sky-Blue Luminescent Au^I–Ag^I Alkynyl-Phosphine Clusters

Treatment of the (AuC₂R)_<i>n</i> acetylides with phosphine ligand 1,4-bis­(diphenylphosphino)­butane (PbuP) and Ag⁺ ions results in self-assembly of the heterobimetallic clusters of three structural types depending on the nature of the alkynyl group. The hexadecanuclear complex [Au₁₂Ag₄(C₂R)₁₂(PbuP)₆]⁴⁺ (<b>1</b>) is formed for R = Ph, and the octanuclear species [Au₆Ag₂(C₂R)₆(PbuP)₃]²⁺ adopting two structural arrangements in the solid state were found for the aliphatic alkynes (R = Bu^t (<b>2</b>), 2-propanolyl (<b>3</b>), 1-cyclohexanolyl (<b>4</b>), diphenylmethanolyl (<b>5</b>), 2-borneolyl (<b>6</b>)). The structures of the compounds <b>1</b>–<b>4</b> and <b>6</b> were determined by single crystal X-ray diffraction analysis. The NMR spectroscopic studies revealed complicated dynamic behavior of <b>1</b>–<b>3</b> in solution. In particular, complexes <b>2</b> and <b>3</b> undergo reversible transformation, which involves slow interconversion of two isomeric forms. The luminescence behavior of the titled clusters has been studied. All the compounds exhibit efficient sky-blue room-temperature phosphorescence both in solution and in the solid state with maximum quantum yield of 76%. The theoretical DFT calculations of the electronic structures demonstrated the difference in photophysical properties of the compounds depending on their structural topology

Luminescent Gold(I) Alkynyl Clusters Stabilized by Flexible Diphosphine Ligands

Treatment of the homoleptic decanuclear compounds (AuC₂R)₁₀ with the cationic gold diphosphine complexes [Au₂(PR′₂-X-PR′₂)₂]²⁺ results in high-yield formation of the new family of hexanuclear clusters [Au₆(C₂R)₄(PR′₂-X-PR′₂)₂]²⁺ (PR′₂-X-PR′₂ = PPh₂-(CH₂)_<i>n</i>-PPh₂, <i>n</i> = 2 (<b>1</b>, R = diphenylmethanolyl), <i>n</i> = 3 (<b>3</b>, R = diphenylmethanolyl; <b>4</b>, R = 1-cyclohexanolyl; <b>5</b>, R = 2-borneolyl), 4 (<b>6</b>, R = 1-cyclohexanolyl); PR′₂-X-PR′₂ = PCy₂-(CH₂)₂-PCy₂ (<b>2</b>, R = diphenylmethanolyl); PR′₂-X-PR′₂ = 1,2-(PPh₂-O)-C₆H₄ (<b>7</b>, R = diphenylmethanolyl); PR′₂-X-PR′₂ = (<i>R</i>,<i>R</i>)-DIOP (<b>8</b>, R = diphenylmethanolyl)). In the case of PPh₂-(CH₂)₄-PPh₂ phosphine and −C₂C­(OH)­Ph₂ alkynyl ligands an octanuclear cluster of a different structural type, [Au₈(C₂C­(OH)­Ph₂)₆(PPh₂-(CH₂)₄-PPh₂)₂]²⁺ (<b>9</b>), was obtained. Complexes <b>1</b>–<b>3</b>, <b>7</b>, and <b>9</b> were studied by X-ray crystallography. NMR and ESI-MS spectroscopic investigations showed that all but two (<b>2</b> and <b>9</b>) compounds are fluxional in solution and demonstrate dissociative chemical equilibria between major and a few minor forms. All of these complexes are intensely emissive in the solid state at room temperature and demonstrate very high quantum yields from 0.61 to 1.0 with weak influence of the alkynyl substituents R′ and the diphosphine backbones on luminescence energies. Two crystalline forms of the cluster <b>2</b> (<i>P</i>2₁/<i>n</i> and <i>P</i>2₁ space groups) exhibit unexpectedly contrasting yellow and sky blue emission, maximized at 572 and 482 nm, respectively. Electronic structure calculations with density functional methods demonstrate that the transitions responsible for the highly effective phosphorescence are dominated by contributions from the Au and π-alkynyl orbitals

Sky-Blue Luminescent Au^I–Ag^I Alkynyl-Phosphine Clusters

Treatment of the (AuC₂R)_<i>n</i> acetylides with phosphine ligand 1,4-bis­(diphenylphosphino)­butane (PbuP) and Ag⁺ ions results in self-assembly of the heterobimetallic clusters of three structural types depending on the nature of the alkynyl group. The hexadecanuclear complex [Au₁₂Ag₄(C₂R)₁₂(PbuP)₆]⁴⁺ (<b>1</b>) is formed for R = Ph, and the octanuclear species [Au₆Ag₂(C₂R)₆(PbuP)₃]²⁺ adopting two structural arrangements in the solid state were found for the aliphatic alkynes (R = Bu^t (<b>2</b>), 2-propanolyl (<b>3</b>), 1-cyclohexanolyl (<b>4</b>), diphenylmethanolyl (<b>5</b>), 2-borneolyl (<b>6</b>)). The structures of the compounds <b>1</b>–<b>4</b> and <b>6</b> were determined by single crystal X-ray diffraction analysis. The NMR spectroscopic studies revealed complicated dynamic behavior of <b>1</b>–<b>3</b> in solution. In particular, complexes <b>2</b> and <b>3</b> undergo reversible transformation, which involves slow interconversion of two isomeric forms. The luminescence behavior of the titled clusters has been studied. All the compounds exhibit efficient sky-blue room-temperature phosphorescence both in solution and in the solid state with maximum quantum yield of 76%. The theoretical DFT calculations of the electronic structures demonstrated the difference in photophysical properties of the compounds depending on their structural topology