ETHENE POLYMERIZATION ACTIVITY AND COORDINATION GAP APERTURE IN NON-ANSA ALKYL-SUBSTITUTED CYCLOPENTADIENYL-ZIRCONIUM MAO AND PHOSPHOLYL-ZIRCONIUM/MAO CATALYSTS/
C. Janiak et al., ETHENE POLYMERIZATION ACTIVITY AND COORDINATION GAP APERTURE IN NON-ANSA ALKYL-SUBSTITUTED CYCLOPENTADIENYL-ZIRCONIUM MAO AND PHOSPHOLYL-ZIRCONIUM/MAO CATALYSTS/, Chemische Berichte, 129(12), 1996, pp. 1517-1529
The ethene polymerization activities of a series of Cp'(C5H5)ZrCl2 and
Cp(2)'ZrCl2 pre-catalysts (Cp' = C(5)HMe(4), C(4)Me(4)P, C(5)Me(5), C
(5)H(4)tBu, C5H3-1,3-tBu(2), C5H2-1,2,4-tBu(3)) together with (C5H5)(2
)ZrCl2 have been correlated with the coordination gap aperture. In the
case of the mixed substituted C(5)R(5-n)R(n)' ligands, the coordinati
on gap aperture has been determined with the help of the cyclopentadie
nyl cone angle and the bending angle at zirconium. A hindered rotatabi
lity of the tert-butyl substituted systems has been evaluated by molec
ular modeling calculations and was included in the gap aperture estima
tion. Deviations from the activity-gap aperture correlation in the cas
e of the phospholyl (C(4)Me(4)P) systems could be accounted for in ter
ms of adduct formation between aluminum species and the phosphorus don
ors. These Lewis acid/base adducts form in an equilibrium reaction at
high Al/Zr ratios, as shown by P-31 NMR. Ab initio calculations on mod
el L(2)TiMe(+) 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 Zr-91-NMR data (chemical shift an
d Line width) for the above zirconocene series are reported. The Zr-91
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 do
nor effect of a tert-butyl group is found here to be 1.25 times that o
f a methyl group. The X-ray structure of (C5H3-1,3-tBu(2))(C5H5)ZrCl2
has been determined (monoclinic, P2(1)/n, a = 6.631(3), b = 18.843(9),
c = 15.265(5) Angstrom, beta = 91.3 degrees, Z = 4).