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Download fileImplications of Indenyl Substitution for the Structural Chemistry of Rare-Earth Metal (Half-)Sandwich Complexes and Performance in Living Isoprene Polymerization
journal contribution
posted on 2019-07-18, 16:19 authored by Dominic Diether, Cäcilia Maichle-Mössmer, Reiner AnwanderLanthanum indenyl
half-sandwich complexes of the composition (IndR)La(AlMe4)2 were synthesized
in high crystalline yields by a salt-metathesis protocol applying
La(AlMe4)3 and Li(IndR). In
the solid state, the parent
indenyl (Ind) and 2-ethylindenyl (IndEt) complexes exhibit
a dimeric structural motif with the methyl groups of the linearly
aligned La(μ-CH3)Al moieties being cis-positioned to the indenyl ligand. In contrast, 1-trimethylsilyl
indenyl (IndSi) directs the η1-coordinated
methyl group of the bridging aluminato ligand into a trans-position, while 2-tert-butyl indenyl afforded the
monomeric half-sandwich complex (IndtBu)La(AlMe4)2. The reactions of Lu(AlMe4)3 with 1 or 2 equiv of Li(IndR) gave
predominantly bis(indenyl) sandwich complexes (IndR)2Lu(AlMe4). All (half-)sandwich complexes
were characterized by X-ray structure analysis, 1H/13C{1H} NMR and FTIR spectroscopy, and microanalysis.
The performance of all half-sandwich complexes in isoprene polymerization
was assessed upon activation with [Ph3C][B(C6F5)4], [PhNMe2H][B(C6F5)4], or B(C6F5)3. The choice of indenyl ligand and cocatalyst had a
major impact on the polymerization efficiency and stereospecificity.
The highest selectivities could be achieved with the binary catalyst
systems (IndEt)La(AlMe4)2/[Ph3C][B(C6F5)4] (cis/trans content 10.4/85.9)
and (IndSi)La(AlMe4)2/B(C6F5)3 (cis/trans content 77.0/13.0).