6533b831fe1ef96bd1298350

RESEARCH PRODUCT

Rare Earth Half-Sandwich Catalysts for the Homo- and Copolymerization of Ethylene and Styrene

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The synthesis of rare earth metal half-sandwich hydrido complexes [Ln(η5:η1-C5Me4SiMe2NCMe3)(THF)(μ-H)]2(Ln = Y, Lu, Yb, Er, Tb) through σ-bond metathesis of the alkyl complexes [Ln(η5:η1- C5Me4SiMe2NCMe3)(CH2SiMe3)(THF)], easily accessible by the reaction of the amino-cyclopentadiene with [Ln(CH2SiMe3)3(THF)2], was developed. The dimeric lanthanide hydrido complexes are highly fluxional involving THF dissociation and cis-trans isomerization of the linked amidocyclopentadienyl ligand. The presence of a monomer-dimer equilibrium is suggested by cross-over experiments. They were tested as single-site, single-component catalysts for the polymerization of ethylene, α-olefin, and styrene, as well as alkyl acrylate and acrylonitrile. The hydrido complexes polymerize ethylene slowly, whereas they form isolable mono(insertion) products with α-olefins and with styrene. The yttrium n-alkyl complexes [Y(η5:η1,-C5Me4SiMe2NCMe3)(R)(THF)n] (R = (CH2)nCH3, n = 3-9), prepared by the mono(insertion) of α-olefins, initiate polymerization of styrene in a relatively controlled manner. Thus, styrene was polymerized by the in-situ formed n-hexyl complex to give atactic polystyrenes with narrow molecular weight distributions and somewhat enriched syndiotacticities. Sequential addition of terf-butyl acrylate allows the synthesis of poly(styrene-block- tert-butyl acrylate).