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Insight into Oxide‐Bridged Heterobimetallic Al/Zr Olefin Polymerization Catalysts
Author(s) -
Boulho Cédric,
Zijlstra Harmen S.,
Hofmann Alexander,
Budzelaar Peter H. M.,
Harder Sjoerd
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201602674
Subject(s) - cationic polymerization , catalysis , polymerization , chemistry , aluminate , adduct , olefin polymerization , dissociation (chemistry) , metal , monomer , polymer chemistry , transition metal , medicinal chemistry , olefin fiber , crystallography , oxide , zirconium , materials science , inorganic chemistry , organic chemistry , cement , metallurgy , polymer
Reaction of (TBBP)AlMe ⋅ THF with [Cp* 2 Zr(Me)OH] gave [(TBBP)Al(THF)−O−Zr(Me)Cp* 2 ] (TBBP=3,3’,5,5’‐tetra‐ t Bu‐2,2'‐biphenolato). Reaction of [DIPPnacnacAl(Me)−O−Zr(Me)Cp 2 ] with [PhMe 2 NH] + [B(C 6 F 5 ) 4 ] − gave a cationic Al/Zr complex that could be structurally characterized as its THF adduct [(DIPPnacnac)Al(Me) − O−Zr(THF)Cp 2 ] + [B(C 6 F 5 ) 4 ] − (DIPPnacnac=HC[(Me)C=N(2,6‐ i Pr 2 −C 6 H 3 )] 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 (Δ G =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* 2 ZrMe] + .