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Ethene Polymerization Activity and Coordination Gap Aperture in non‐ ansa Alkyl‐substituted Cyclopentadienyl‐ and Phospholyl‐zirconium/MAO Catalysts
Author(s) -
Janiak Christoph,
Lange Katharina C. H.,
Versteeg Uwe,
Lentz Dieter,
Budzelaar Peter H. M.
Publication year - 1996
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19961291219
Subject(s) - chemistry , cyclopentadienyl complex , lewis acids and bases , alkyl , adduct , zirconium , polymerization , metallocene , catalysis , crystallography , medicinal chemistry , stereochemistry , polymer chemistry , inorganic chemistry , organic chemistry , polymer
The ethene polymerization activities of a series of Cp'(C 5 H 5 )ZrCl 2 and Cp' 2 ZrCl 2 pre‐catalysts (Cp' = C 5 HMe 4 , C 4 Me 4 P, C 5 Me 5 , C 5 H 4 t Bu, C 5 H 3 ‐1,3‐ t Bu 2 , C 5 H 2 ‐1,2,4‐ t Bu 3 ) together with (C 5 H 5 ) 2 ZrCl 2 have been correlated with the coordination gap aperture. In the case of the mixed substituted C 5 R 5‐ n R' 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 (C 4 Me 4 P) 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 31 P NMR. Ab initio calculations on model L 2 TiMe + complexes (L = C 5 H 5 , C 5 H 4 N and C 5 H 4 P) for the insertion of ethene in the TiMe bond suggest a high electronic similarity for phospholyl and cyclopentadienyl. The 91 Zr‐NMR data (chemical shift and line width) for the above zirconocene series are reported. The 91 Zr 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 (C 5 H 3 ‐1,3‐ t Bu 2 )(C 5 H 5 )ZrCl 2 has been determined (monoclinic, P 2 1 / n , a = 6.631(3), b = 18.843(9), c = 15.265(5) Å, β = 91.3°, Z = 4).