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Binuclear zirconocene cations with μ-CH<sub>3</sub>-bridges in homogeneous Ziegler-Natta catalyst systems

Binuclear zirconocene cations with μ-CH3-bridges in homogeneous Ziegler-Natta catalyst systems

Type of Publication: Journal article
URI (citable link): http://nbn-resolving.de/urn:nbn:de:bsz:352-239201
Author: Beck, Stefan; Prosenc, Marc-Heinrich; Brintzinger, Hans-Herbert; Goretzki, Ralf; Herfert, Norbert; Fink, Gerhard
Year of publication: 1996
Published in: Journal of Molecular Catalysis A: Chemical ; 111 (1996), 1-2. - pp. 67-79. - ISSN 1381-1169
DOI (citable link): https://dx.doi.org/10.1016/1381-1169(96)00168-9
Summary:
Binuclear zirconocene cations are observed by 1H-NMR in C6D6 solutions containing B(C6F5)3 and an excess of a zirconocene dimethyl complex. The CH3-bridged cation [((C5H5)2ZrCH3)2(μ-CH3)]+, solvent-separated from the anion H3CB(C6F5)−3, is present in equilibrium with (C5H5)2Zr(CH3)2 and the mononuclear ion pair [(C5H5)2ZrCH+3***H3CB(C6F5)−3]; in more concentrated solutions, a binuclear ion pair [((C5H5)2ZrCH3)2(μ-CH3)+***H3CB(C6F5)−3] is the dominant species. Similar equilibria are observed in C6D6 solutions containing B(C6F5)3 and (CH3)4C2(C5H4)2Zr(CH3)2, (CH3)2Si(C5H4)2Zr(CH3)2 or rac-(CH3)2Si(indenyl)2Zr(CH3)2. Complexes with sterically more demanding ligands, such as (C5(CH3)5)2Zr(CH3)2 or rac-(CH3)2Si(2-methyl-benz[e]indenyl)2Zr(CH3)2 do not form any binuclear species under these conditions. In the catalyst system rac-(CH3)2Si(indenyl)2Zr(CH3)2Bu3NH+B(C6F5)−4, activities for the polymerization of propene increase with excess of the dimethyl zirconocene complex. This effect is due in part to a sacrifice of some dimethyl zirconocene for the removal of impurities from the catalyst system and in part to a stabilization of the catalyst in the form of the binuclear cation [((CH3)2Si(indenyl)2ZrCH3)2(μ-CH3)]+. The latter appears to act, in the presence of propene, as a source of the mononuclear cation [(CH3)2Si(indenyl)2ZrCH3(C3H6)]+, rather than as a polymerization catalyst by itself.
Subject (DDC): 540 Chemistry
Keywords: NMR, Ziegler-Natta, zirconocene
Link to License: Terms of use

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BECK, Stefan, Marc-Heinrich PROSENC, Hans-Herbert BRINTZINGER, Ralf GORETZKI, Norbert HERFERT, Gerhard FINK, 1996. Binuclear zirconocene cations with μ-CH3-bridges in homogeneous Ziegler-Natta catalyst systems. In: Journal of Molecular Catalysis A: Chemical. 111(1-2), pp. 67-79. ISSN 1381-1169. Available under: doi: 10.1016/1381-1169(96)00168-9

@article{Beck1996Binuc-23920, title={Binuclear zirconocene cations with μ-CH3-bridges in homogeneous Ziegler-Natta catalyst systems}, year={1996}, doi={10.1016/1381-1169(96)00168-9}, number={1-2}, volume={111}, issn={1381-1169}, journal={Journal of Molecular Catalysis A: Chemical}, pages={67--79}, author={Beck, Stefan and Prosenc, Marc-Heinrich and Brintzinger, Hans-Herbert and Goretzki, Ralf and Herfert, Norbert and Fink, Gerhard} }

Beck, Stefan Brintzinger, Hans-Herbert Goretzki, Ralf Prosenc, Marc-Heinrich Fink, Gerhard Beck, Stefan Herfert, Norbert 2013-08-08T06:27:28Z 1996 Prosenc, Marc-Heinrich 2013-08-08T06:27:28Z Goretzki, Ralf Brintzinger, Hans-Herbert eng Herfert, Norbert terms-of-use Fink, Gerhard Binuclear zirconocene cations with μ-CH<sub>3</sub>-bridges in homogeneous Ziegler-Natta catalyst systems Binuclear zirconocene cations are observed by <sup>1</sup>H-NMR in C<sub>6</sub>D<sub>6</sub> solutions containing B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> and an excess of a zirconocene dimethyl complex. The CH<sub>3</sub>-bridged cation [((C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrCH<sub>3</sub>)<sub>2</sub>(μ-CH<sub>3</sub>)]<sup>+</sup>, solvent-separated from the anion H3CB(C<sub>6</sub>F<sub>5</sub>)<sup>−</sup><sub>3</sub>, is present in equilibrium with (C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub> and the mononuclear ion pair [(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrCH<sup>+</sup><sub>3</sub>***H<sub>3</sub>CB(C<sub>6</sub>F<sub>5</sub>)<sup>−</sup><sub>3</sub>]; in more concentrated solutions, a binuclear ion pair [((C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>ZrCH<sub>3</sub>)<sub>2</sub>(μ-CH<sub>3</sub>)<sup>+</sup>***H<sub>3</sub>CB(C<sub>6</sub>F<sub>5</sub>)<sup>−</sup><sub>3</sub>] is the dominant species. Similar equilibria are observed in C<sub>6</sub>D<sub>6</sub> solutions containing B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> and (CH<sub>3</sub>)<sub>4</sub>C<sub>2</sub>(C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub>, (CH<sub>3</sub>)<sub>2</sub>Si(C<sub>5</sub>H<sub>4</sub>)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub> or rac-(CH<sub>3</sub>)<sub>2</sub>Si(indenyl)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub>. Complexes with sterically more demanding ligands, such as (C<sub>5</sub>(CH<sub>3</sub>)<sub>5</sub>)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub> or rac-(CH<sub>3</sub>)<sub>2</sub>Si(2-methyl-benz[e]indenyl)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub> do not form any binuclear species under these conditions. In the catalyst system rac-(CH<sub>3</sub>)<sub>2</sub>Si(indenyl)<sub>2</sub>Zr(CH<sub>3</sub>)<sub>2</sub>Bu<sub>3</sub>NH<sup>+</sup>B(C<sub>6</sub>F<sub>5</sub>)<sup>−</sup><sub>4</sub>, activities for the polymerization of propene increase with excess of the dimethyl zirconocene complex. This effect is due in part to a sacrifice of some dimethyl zirconocene for the removal of impurities from the catalyst system and in part to a stabilization of the catalyst in the form of the binuclear cation [((CH<sub>3</sub>)<sub>2</sub>Si(indenyl)<sub>2</sub>ZrCH<sub>3</sub>)<sub>2</sub>(μ-CH<sub>3</sub>)]<sup>+</sup>. The latter appears to act, in the presence of propene, as a source of the mononuclear cation [(CH<sub>3</sub>)<sub>2</sub>Si(indenyl)<sub>2</sub>ZrCH<sub>3</sub>(C<sub>3</sub>H<sub>6</sub>)]<sup>+</sup>, rather than as a polymerization catalyst by itself. Journal of Molecular Catalysis A: Chemical ; 111 (1996), 1-2. - S. 67-79

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