Complexes of the form (Cp†)TiCl2(NPR3)
and the analogous dimethyl derivatives (Cp†)TiMe2(NPR3) have been prepared. These species in the presence of MAO, B(C6F5)3, or [Ph3C][B(C6F5)4] are active
catalysts for ethylene polymerization.
The bis(tri-tert-butylphosphinimide) complexes (t-Bu3PN)2TiCl2 (1) and (t-Bu3PN)2TiMe2 (2) were
prepared and characterized crystallographically. Stoichiometric reactions of 2 with PhNMe2H[B(C6F5)4] in
the presence of PMe3 afforded [(t-Bu3PN)2TiMe(PMe3)][B(C6F5)4] (3), while reaction of 2 with B(C6F5)3 affords
(t-Bu3PN)2TiMe(μ-Me)B(C6F5)3 (4). Under laboratory
conditions these compounds are effective ethylene polymerization catalysts. Under commercially relevant
solution polymerization conditions, these catalysts are
exceptionally active. Complex 2, when activated with
Ph3C[B(C6F5)4], produces high molecular weight polyethylene with a narrow polydispersity at a rate approximately 4 times faster than the constrained geometry
catalyst ((C5Me4SiMe2N-t-Bu)TiX2). As such, these catalysts represent the first non-cyclopentadienyl, single-site
catalysts competitive with derivatives of metallocenes
under commercially relevant polymerization conditions.
A strategy for polymerization catalyst design has been developed based on the steric and
electronic analogy of bulky phosphinimides to cyclopentadienyl ligands. To this end, the
family of complexes of the form (Cp†)TiCl2(NPR3) has been prepared and characterized. Alkyl
and aryl derivatives of these species have also been synthesized, and a number have been
evaluated for use as catalyst precursors in olefin polymerization. The polymerization of
ethylene has been examined employing several types of cocatalyst activators. Trends and
patterns in the structure−activity relationship are discussed, and the implications for catalyst
design are evaluated.
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