title: Insight into Oxide-Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts.
abstract: Reaction of (TBBP)AlMe⋅THF with [Cp*2Zr(Me)OH] gave [(TBBP)Al(THF)-O-Zr(Me)Cp*2] (TBBP=3,3',5,5'-tetra-tBu-2,2'-biphenolato). Reaction of [DIPPnacnacAl(Me)-O-Zr(Me)Cp2] with [PhMe2NH]+[B(C6F5)4]-gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me)-O-Zr(THF)Cp2]+[B(C6F5)4]-(DIPPnacnac=HC[(Me)C=N(2,6-iPr2-C6H3)]2). The first complex polymerizes ethene in the presence of an alkylaluminum scavenger but in the absence of methylalumoxane (MAO). The adduct cation is inactive under these conditions. Theoretical calculations show very high energy barriers (ΔG=40-47 kcal mol-1) for ethene insertion with a bridged AlOZr catalyst. This is due to an unfavorable six-membered-ring transition state, in which the methyl group bridges the metal and ethene with an obtuse metal-Me-C angle that prevents synchronized bond-breaking and making. A more-likely pathway is dissociation of the Al-O-Zr complex into an aluminate and the active polymerization catalyst [Cp*2ZrMe]+.
authors.affiliation: Inorganic and Organometallic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany.|Dutch Polymer Institute (DPI), P. O. Box 902, 5600 AX, Eindhoven, Netherlands.
authors.forename: Cédric
authors.initials: C
authors.lastname: Boulho
authors.affiliation: Inorganic and Organometallic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany.|Dutch Polymer Institute (DPI), P. O. Box 902, 5600 AX, Eindhoven, Netherlands.|Stratingh Institute, University of Groningen, Nijenborgh 4, 9747 AG, Groningen, Netherlands.
authors.forename: Harmen S
authors.initials: HS
authors.lastname: Zijlstra
authors.affiliation: Inorganic and Organometallic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Hofmann
authors.affiliation: Dutch Polymer Institute (DPI), P. O. Box 902, 5600 AX, Eindhoven, Netherlands.|Department of Chemistry, University of Manitoba, Winnipeg, MB R3T 2N2, Canada.
authors.forename: Peter H M
authors.initials: PH
authors.lastname: Budzelaar
authors.affiliation: Inorganic and Organometallic Chemistry, University of Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany.|Dutch Polymer Institute (DPI), P. O. Box 902, 5600 AX, Eindhoven, Netherlands.
authors.forename: Sjoerd
authors.initials: S
authors.lastname: Harder
keywords: alkene polymerization; aluminum; bimetallic catalysis; synthetic methods; zirconium