7 research outputs found
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 MgCl<sub>2</sub> support, are taken
into account. Adsorption of TiCl<sub>4</sub> leads to formation of
three types of mononuclear species on the magnesium dichloride surfaces.
However, TiCl<sub>4</sub> alone cannot properly stabilize the support.
Coadsorption of electron donors along with TiCl<sub>4</sub>, on the
other hand, is shown to significantly improve the strength of TiCl<sub>4</sub> 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 MgCl<sub>2</sub> support was studied using
computational (DFT; M06-2X) and experimental (PXRD, DRIFT, CP/MAS <sup>13</sup>C NMR) methods. Quantum chemical calculations suggest that
the structural variations in PEIs significantly affect their ability
to stabilize the catalytically relevant MgCl<sub>2</sub> surfaces.
Coordination on the (104) surface seems to be favored upon consideration
of the layered structure of MgCl<sub>2</sub>. 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 MgCl<sub>2</sub>. Based on spectroscopic
data, nitrogen atoms of primary, secondary, and tertiary amino groups
can participate in coordination to MgCl<sub>2</sub>. 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 (MgCl<sub>2</sub>/PEI/TiCl<sub>4</sub>) 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 MgCl<sub>2</sub> support and indicate their potential
as a new type of internal electron donors for Ziegler–Natta
catalysts
Toward Luminescence Vapochromism of Tetranuclear Au<sup>I</sup>–Cu<sup>I</sup> Clusters
A family of triphosphine gold–copper
clusters bearing aliphatic
and hydroxyaliphatic alkynyl ligands of general formula [HCÂ(PPh<sub>2</sub>)<sub>3</sub>Au<sub>3</sub>CuÂ(C<sub>2</sub>R)<sub>3</sub>]<sup>+</sup> (R = cyclohexyl (<b>1</b>), cyclopentyl (<b>2</b>), Bu<sup>t</sup> (<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 (AuC<sub>2</sub>R)<sub><i>n</i></sub> acetylides with the (PPh<sub>2</sub>)<sub>3</sub>CH ligand
in the presence of Cu<sup>+</sup> ions and NEt<sub>3</sub>. Addition
of Cl<sup>–</sup> or Br<sup>–</sup> anions to complex <b>8</b> results in coordination of the halides to the copper atoms
to give neutral HCÂ(PPh<sub>2</sub>)<sub>3</sub>Au<sub>3</sub>CuHalÂ(C<sub>2</sub>COHPh<sub>2</sub>)<sub>3</sub> 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<sup>I</sup>–Cu<sup>I</sup> Clusters
A family of triphosphine gold–copper
clusters bearing aliphatic
and hydroxyaliphatic alkynyl ligands of general formula [HCÂ(PPh<sub>2</sub>)<sub>3</sub>Au<sub>3</sub>CuÂ(C<sub>2</sub>R)<sub>3</sub>]<sup>+</sup> (R = cyclohexyl (<b>1</b>), cyclopentyl (<b>2</b>), Bu<sup>t</sup> (<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 (AuC<sub>2</sub>R)<sub><i>n</i></sub> acetylides with the (PPh<sub>2</sub>)<sub>3</sub>CH ligand
in the presence of Cu<sup>+</sup> ions and NEt<sub>3</sub>. Addition
of Cl<sup>–</sup> or Br<sup>–</sup> anions to complex <b>8</b> results in coordination of the halides to the copper atoms
to give neutral HCÂ(PPh<sub>2</sub>)<sub>3</sub>Au<sub>3</sub>CuHalÂ(C<sub>2</sub>COHPh<sub>2</sub>)<sub>3</sub> 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<sup>I</sup>–Ag<sup>I</sup> Alkynyl-Phosphine Clusters
Treatment of the (AuC<sub>2</sub>R)<sub><i>n</i></sub> acetylides with phosphine ligand
1,4-bisÂ(diphenylphosphino)Âbutane (PbuP) and Ag<sup>+</sup> ions results
in self-assembly of the heterobimetallic clusters of three structural
types depending on the nature of the alkynyl group. The hexadecanuclear
complex [Au<sub>12</sub>Ag<sub>4</sub>(C<sub>2</sub>R)<sub>12</sub>(PbuP)<sub>6</sub>]<sup>4+</sup> (<b>1</b>) is formed for R
= Ph, and the octanuclear species [Au<sub>6</sub>Ag<sub>2</sub>(C<sub>2</sub>R)<sub>6</sub>(PbuP)<sub>3</sub>]<sup>2+</sup> adopting two
structural arrangements in the solid state were found for the aliphatic
alkynes (R = Bu<sup>t</sup> (<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 (AuC<sub>2</sub>R)<sub>10</sub> with the cationic gold diphosphine complexes [Au<sub>2</sub>(PR′<sub>2</sub>-X-PR′<sub>2</sub>)<sub>2</sub>]<sup>2+</sup> results
in high-yield formation of the new family of hexanuclear clusters
[Au<sub>6</sub>(C<sub>2</sub>R)<sub>4</sub>(PR′<sub>2</sub>-X-PR′<sub>2</sub>)<sub>2</sub>]<sup>2+</sup> (PR′<sub>2</sub>-X-PR′<sub>2</sub> = PPh<sub>2</sub>-(CH<sub>2</sub>)<sub><i>n</i></sub>-PPh<sub>2</sub>, <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′<sub>2</sub>-X-PR′<sub>2</sub> = PCy<sub>2</sub>-(CH<sub>2</sub>)<sub>2</sub>-PCy<sub>2</sub> (<b>2</b>, R = diphenylmethanolyl); PR′<sub>2</sub>-X-PR′<sub>2</sub> = 1,2-(PPh<sub>2</sub>-O)-C<sub>6</sub>H<sub>4</sub> (<b>7</b>, R = diphenylmethanolyl); PR′<sub>2</sub>-X-PR′<sub>2</sub> = (<i>R</i>,<i>R</i>)-DIOP (<b>8</b>, R = diphenylmethanolyl)). In the case of
PPh<sub>2</sub>-(CH<sub>2</sub>)<sub>4</sub>-PPh<sub>2</sub> phosphine
and −C<sub>2</sub>CÂ(OH)ÂPh<sub>2</sub> alkynyl ligands an octanuclear
cluster of a different structural type, [Au<sub>8</sub>(C<sub>2</sub>CÂ(OH)ÂPh<sub>2</sub>)<sub>6</sub>(PPh<sub>2</sub>-(CH<sub>2</sub>)<sub>4</sub>-PPh<sub>2</sub>)<sub>2</sub>]<sup>2+</sup> (<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>2<sub>1</sub>/<i>n</i> and <i>P</i>2<sub>1</sub> 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<sup>I</sup>–Ag<sup>I</sup> Alkynyl-Phosphine Clusters
Treatment of the (AuC<sub>2</sub>R)<sub><i>n</i></sub> acetylides with phosphine ligand
1,4-bisÂ(diphenylphosphino)Âbutane (PbuP) and Ag<sup>+</sup> ions results
in self-assembly of the heterobimetallic clusters of three structural
types depending on the nature of the alkynyl group. The hexadecanuclear
complex [Au<sub>12</sub>Ag<sub>4</sub>(C<sub>2</sub>R)<sub>12</sub>(PbuP)<sub>6</sub>]<sup>4+</sup> (<b>1</b>) is formed for R
= Ph, and the octanuclear species [Au<sub>6</sub>Ag<sub>2</sub>(C<sub>2</sub>R)<sub>6</sub>(PbuP)<sub>3</sub>]<sup>2+</sup> adopting two
structural arrangements in the solid state were found for the aliphatic
alkynes (R = Bu<sup>t</sup> (<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