Ancillary aryloxide ligands in ethylene polymerization catalyst precursors

The compounds CpTiCl2(OC6H3-i-Pr-2) (1), CpTiCl(OC6H3-i-Pr-2)(2) (2), CpTi(R)(OC6H3-i-Pr-2)(2) (R = t-Bu 3, s-Bu 4, n-Bu 5, Me 6) have been prepared and characterized. Compounds 1 or 2 in the presence of 500 equivalents of methylaluminoxane (MAO) act as catalyst precursors for ethylene polymerization. While the catalysts derived from the monocyclopentadienyl complexes are much less active that the metallocenes, there is a clear enhancement in the activity of about 40% as a result of the inclusion of a second aryloxide ligand. Reactions of 1 with AlMe3 revealed stepwise formation of CpTi(Me)Cl(OC6H3-i-Pr-2) 7 and CpTi(Me)(2)(OC6H3-i-Pr-2) 8, while subsequent addition of AlMe3 afforded complete conversion to 8, with formation of the aluminum species [AlMe2(OC6H3-i-Pr-2)](n) 9. In contrast, the catecholate complex CpTi(O2C6H4)Cl 10 reacts with AlMe3 yielding the paramagnetic species [CpTi(O-2(C6H4)). AlClMe2], 11. Incorporation of aryloxide ligands in modified metallocenes was readily accomplished with the preparation of Cp2ZrCl(OC6H3-i-Pr-2) 12, Cp2ZrCl(OC6H5) 13, Cp2ZrMe(OC6H5) 14 and Cp2TiCl(OC6H3-i-Pr-2) 15. In combination with MAO, 12, 14 and 15 effect the polymerization of ethylene with an 11% increase in activity over the parent metallocenedichlorides. The implications of the increased activity are considered. Crystallographic data are reported for 2, 3, 6, 9, 11, 12 and 13. (C) 1999 Elsevier Science S.A. All rights reserved.