Insight into Oxide-Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts

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• 作者：Dr. Cé ; dric Boulho ; Dr. Harmen S. Zijlstra ; Alexander Hofmann ; Prof.&ensp ; Dr. Peter H. M. Budzelaar and Prof.&ensp ; Dr. Sjoerd Harder
• 刊名：Chemistry - A European Journal
• 出版年：2016
• 出版时间：November 21, 2016
• 年：2016
• 卷：22
• 期：48
• 页码：17450-17459
• 全文大小：1231K
• ISSN：1521-3765

文摘

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]⁺.