ISSN:
0009-2940
Keywords:
Zirconocenes
;
Metallocene-methylalumoxane catalysts
;
Ethene polymerization
;
Structure - reactivity correlation
;
Coordination gap aperture
;
Cone angles
;
91Zr NMR
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The ethene polymerization activities of a series of Cp'(C5H5)ZrCl2 and Cp'2ZrCl2 pre-catalysts (Cp' = C5HMe4, C4Me4P, C5Me5, C5H4tBu, C5H3-1,3-tBu2, C5H2-1,2,4-tBu3) together with (C5H5)2ZrCl2 have been correlated with the coordination gap aperture. In the case of the mixed substituted C5R5-nR'n ligands, the coordination gap aperture has been determined with the help of the cyclopentadienyl cone angle and the bending angle at zirconium. A hindered rotatability of the tert-butyl substituted systems has been evaluated by molecular modeling calculations and was included in the gap aperture estimation. Deviations from the activity - gap aperture correlation in the case of the phospholyl (C4Me4P) systems could be accounted for in terms of adduct formation between aluminum species and the phosphorus donors. These Lewis acid/base adducts form in an equilibrium reaction at high Al/Zr ratios, as shown by 31P NMR. Ab initio calculations on model L2TiMe+ complexes (L = C5H5, C5H4N and C5H4P) for the insertion of ethene in the Ti—Me bond suggest a high electronic similarity for phospholyl and cyclopentadienyl. The 91Zr-NMR data (chemical shift and line width) for the above zirconocene series are reported. The 91Zr chemical shift values increase with a good linear correlation to the number of methyl or tert-butyl groups, which is traced to the additive electron donating effect of the alkyl groups. The hyperconjugative donor effect of a tert-butyl group is found here to be 1.25 times that of a methyl group. The X-ray structure of (C5H3-1,3-tBu2)(C5H5)ZrCl2 has been determined (monoclinic, P21/n, a = 6.631(3), b = 18.843(9), c = 15.265(5) Å, β = 91.3°, Z = 4).
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19961291219
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