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 facile route provides the title compound 1 in only a few steps starting from bromopentafluorobenzene. Borane 1 is a very reactive hydroborating agent for a range of alkenes and alkynes. Reactions with unsymmetrical substrates display excellent regioselectivity, and interesting selectivities with silicon‐containing substrates are rationalized by electronic effects.

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.

The reactions of so called “tuck-in” permethyl zirconocene compounds Cp*(η5-η1-C5Me4CH2)ZrX (X = Cl (1a), C6H5 (1b), CH3 (1c)) with the highly electrophilic boranes HB(C6F5)2 and B(C6F5)3 are described. The products are zwitterionic olefin polymerization catalysts. Reactions with 1a and 1b yielded single products cleanly, but reactions with tuck-in methyl starting material 1c gave mixtures. Spectroscopic and structural studies showed that the electrophilic zirconium center in the product zwitterions was stabilized by a variety of mechanisms. In the products of reaction between 1a and 1b with HB(C6F5)2, Cp*[η5,η1-C5Me4CH2B(C6F5)2(μ-H)]ZrX (X = Cl (2a), 74%), C6H5 (2b, 62%)), the metal is chelated by a pendant hydridoborate moiety. Chloride product 2a was characterized crystallographically. In the reaction of B(C6F5)3 with 1a, the fluxional zwitterionic product Cp*[η5-C5Me4CH2B(C6F5)3]ZrCl (3a, 84%) is stabilized by a weak donor interaction between one of the ortho fluorine atoms of the −CH2B-(C6F5)3 counterion and the zirconium center (Zr−F = 2.267(5) Å). In the product of the reaction between 1b and B(C6F5)3, Cp*[η5-C5Me4CH2B(C6F5)3]ZrC6H5 (3b, 82%), a similar ortho-fluorine interaction was found in a yellow kinetic product (y-3b), which converted upon heating gently to a thermodynamic orange polymorph (o-3b) in which the zirconium center is compensated via an agostic interaction from an ortho C−H bond of the phenyl group and an interaction between the methylene group of the −CH2B-(C6F5)3 counteranion. These compounds were both characterized by X-ray crystallography. Zwitterion o-3b reacts with H2 to form the zwitterionic hydride Cp*[η5-C5Me4CH2B(C6F5)3]ZrH (4, 77%), characterized by NMR spectroscopy and X-ray crystallography to reveal a return to the ortho-fluorine mode of stabilization. Compounds 2a, 3a, o-3b, and 4 were all found to be active ethlyene polymerization catalysts; the chloride derivatives required minimal amounts of methylaluminoxane (MAO) to alkylate the zirconium center. Polymerization data are discussed in light of the structural findings for the catalysts employed.