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.

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.

Triple C−H bond activation in the reaction of [Cp(R3PN)Ti(Me)2] with AlMe3 affords Ti‐Al‐C aggregates. These species 1 and 2 exist in equilibrium with AlMe3, thus demonstrating a highly facile interconversion of carbide species with distorted tetrahedral and five‐coordinate, pseudo‐trigonal‐bipyramidal geometries, respectively. R=iPr.

Multiple C-H bond activation occurs upon reaction of phosphinimide complexes of the form Cp′(R 3 PN)TiMe 2 (Cp′ ) Cp, indenyl; R ) i-Pr, Cy, Ph) with excess AlMe 3 , affording the carbide complexes Cp′Ti(µ 2 -Me)(µ 2 -NPR 3 )(µ 4 -C)(AlMe 2 ) 3 or in some cases [CpTi(µ 2 -Me)(µ 2 -NPR 3 )(µ 5 -C)(AlMe 2 ) 3 ‚(AlMe 3 )]. These species contain four-and five-coordinate carbide centers. VT-NMR studies established that such species exist in equilibrium. The four-coordinate carbide complexes retain Lewis acidity at a planar three-coordinate Al center, as evidenced by the reaction with diethyl ether, THF, or PMe 3 . This affords species of the form [CpTi-(µ 2 -Me)(µ 2 -NPR 3 )(µ 4 -C)(AlMe 2 ) 2 (AlMe 2 (L))] (L ) Et 2 O, THF, PMe 3 ). The Lewis acidity is also evidenced in the reaction of the carbide complexes with CpTi(NPR 3 )Me 2 . In this case, labeling studies affirm methyl group exchange processes. The analogous reactions of Cp(R 3 PN)Ti-(CH 2 SiMe 3 ) 2 or Cp*(R 3 PN)TiMe 2 with AlMe 3 afforded CpTi(µ 2 -Me)(µ 2 -NPR 3 )(µ 3 -CSiMe 3 )-(AlMe 2 ) 2 and Cp*Ti(µ 2 -Me)(µ 2 -NPR 3 )(µ 3 -CH)(AlMe 2 ) 2 , respectively. These observations confirm that steric congestion can impinge on the C-H activation process. The nature of the above products of C-H bond activation was confirmed employing NMR, isotopic labeling, and crystallographic methods. The implications of these results with respect to C-H bond activation and polymerization catalysis are considered.

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