Reaction of trimethylaluminum with [(Bu-t)Al(mu(3)-O)](6): Hybrid tert-butylmethylalumoxanes as cocatalysts for olefin polymerization

Citation
M. Watanabi et al., Reaction of trimethylaluminum with [(Bu-t)Al(mu(3)-O)](6): Hybrid tert-butylmethylalumoxanes as cocatalysts for olefin polymerization, ORGANOMETAL, 20(3), 2001, pp. 460-467
Citations number
47
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANOMETALLICS
ISSN journal
0276-7333 → ACNP
Volume
20
Issue
3
Year of publication
2001
Pages
460 - 467
Database
ISI
SICI code
0276-7333(20010205)20:3<460:ROTW[H>2.0.ZU;2-#
Abstract
The reaction of trimethylaluminum with the hexameric tert-butylalumoxane, [ (Bu-t)Al-(mu (3)-O)](6), has been investigated. Reaction of [((BU)-B-t)Al(m u (3)-O)](6) with 1 equiv of AlMe3 results in the formation of two isomers (A and B) of the hybrid tert-butylmethylalumoxane, [Al-7(mu (3)-O)(6)(Bu-t) (6)Me-3]. The structures of compounds A and B, as determined by NMR spectro scopy and mass spectrometry, consist of [Al-6(mu (3)-O)(6)((BU)-B-t)(5)Me] alumoxane cages, formed via tert-butyl/ methyl exchange, in which one of th e edges of the Al6O6 cage is complexed to the (Bu-t)AlMe2 formed during alk yl exchange. The difference between the isomers results from the geometric relationship of the cage Al-Me group and the opened edge. The activity of [ Al-7-(mu (3)-O)(6)(Bu-t)(6)Me-3], for the [Me2C(Cp)(Flu)] ZrBz(2)-catalyzed polymerization of 1,5-hexadiene, is significantly increased in comparison to [(Bu-t)Al(mu (3)-O)](6). The effect of additional equivalents of AlMe3 o n the cocatalytic activity of [Al-7(mu (3)-O)(6)(Bu-t)(6)Me-3] suggests tha t a maximum activity is obtained at a [(Bu-t)Al(mu (3)-O)](6) to AlMe3 rati o of 1:6. Under conditions of equal Al:Zr ratio the [(tBu)Al(mu (3)-O)](6)( AlMe3)(6) system has a higher activity than a representative sample of comm ercial methylalumoxane (MAO). H-1 NMR suggests that the reaction of [(Bu-t) Al(mu (3)-O)](6) With 6 equiv of AlMe3 yields (Bu-t)AlMe2 as the only tert- butyl-containing species and a proposed AlMe3 "free" form of MAO. Whereas t he activity of [Al-7(mu (3)-O)(6)(Bu-t)(6)Me-3] and MAO shows slight inhibi tion by the addition of Al(Bu-i)(3), the activity of the [(Bu-t)Al(mu (3)-O )](6)/(AlMe3)(6) system is unaffected. The reaction of Cp2Zr(CD3)(2) with [ Al-7(mu (3)-O)(6)(Bu-t)(6)Me-3] demonstrates that methyl exchange does not occur between a metallocene and the alkyls of the alumoxane cage, but does occur with the complexed (Bu-t)AlMe2.