INTRAMOLECULAR ION-ION INTERACTIONS IN ZWITTERIONIC METALLOCENE OLEFIN POLYMERIZATION CATALYSTS DERIVED FROM TUCKED-IN CATALYST PRECURSORS AND THE HIGHLY ELECTROPHILIC BORANES XB(C6F5)(2) (X=H, C6F5)

The reactions of so called ''tuck-in'' permethyl zirconocene compounds Cp(eta(5)-eta(1)-C5Me4CH2)ZrX (X = Cl (1a), C6H5 (1b), CH3 (1c)) wit h the highly electrophilic boranes HB(C6F5)(2) and B(C6F5)(3) are desc ribed. The products are zwitterionic olefin polymerization catalysts. Reactions with la and Ib yielded single products cleanly, but reaction s with tuck-in methyl starting material Ic gave mixtures. Spectroscopi c and structural studies showed that the electrophilic zirconium cente r 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[ eta(5) eta(1)-C5Me4CH2B(C6F5)(2)(mu-H)]ZrX (X = Cl (2a), 74%), C6H5 (2 b, 62%)), the metal is chelated by a pendant hydridoborate moiety. Chl oride product 2a was characterized crystallographically. In the reacti on of B(C6F5)(3) with 1a, the fluxional zwitterionic product Cp[eta(5 )-C5Me4CH2B(C6F5)(3)]ZrCl (3a, 84%) is stabilized by a weak donor inte raction between one of the ortho fluorine atoms of the -CH2B-(C6F5)(3) counterion and the zirconium center (Zr-F = 2.267(5) Angstrom). In th e product of the reaction between 1b and B(C6F5)(3), Cp[eta(5)-C5Me4C H2B(C6F5)(3)]ZrC6H5 (3b, 82%), a similar ortho-fluorine interaction wa s found in a yellow kinetic product (y-3b), which converted upon heati ng gently to a thermodynamic orange polymorph (o-3b) in which the zirc onium center is compensated via an agostic interaction from an ortho C -H bond of the phenyl group and an interaction between the methylene g roup of the -CH2B-(C6F5)(3) counteranion. These compounds were both ch aracterized by X-ray crystallography. Zwitterion o-3b reacts with H2 t o form the zwitterionic hydride Cp[eta(5)-C5Me4CH2B(C6F5)(3)]ZrH (4, 77%), characterized by NMR spectroscopy and X-ray crystallography to r eveal a return to the ortho-fluorine mode of stabilization. Compounds 2a, 3a, o-3b, and 4 were all found to be active ethylene polymerizatio n catalysts; the chloride derivatives required minimal amounts of meth ylaluminoxane (MAO) to alkylate the zirconium center. Polymerization d ata are discussed in light of the structural findings for the catalyst s employed.