Pure and Applied Chemistry

Abstract: The synthesis of rare earth metal half-sandwich hydrido complexes [Ln (h⁵:h¹-C₅Me ₄SiMe₂NCMe₃) (THF) (µ-H) ] ₂ (Ln = Y, Lu) through s-bond metathesis of the easily accessible alkyl complexes [Ln (h⁵:h¹-C₅Me ₄SiMe₂NCMe₃) (CH₂ SiMe₃) (THF) ] was developed. The dimeric yttrium hydrido complexes are highly fluxional, and a monomer-dimer equilibrium is present. They were tested as single-site, single-component catalysts for the polymerization of ethylene and styrene, as well as alkyl acrylate and acrylonitrile. The hydrido complexes polymerize ethylene slowly and form isolable mono (insertion) products with styrene. The yttrium n-alkyl complexes [Y (h⁵:h¹-C₅Me ₄SiMe₂NCMe₃) (R) (THF) ] [R = (CH₂) _nCH₃, n = 3-9], prepared by the mono (insertion) of a-olefins, initiate polymerization in a relatively controlled manner. Thus, styrene was polymerized by the n-alkyl complex to give atactic polystyrenes with somewhat enriched syndiotacticities.