Synthesis, structure, and catalytic behavior of rac-1,1 '-(3-oxapentamethylene)-bridged bis(indenyl) ansa-lanthanidocenes

A series of chiral 1,1 '-(3-oxapentamethylene)-bridged bis(indenyl) ansa-la nthanidocenes have been high stereoselectively synthesized. The reaction of YbCl3 with O(CH2CH2C9H6K)(2) in THF provided a rac / meso mixture of [O(CH 2CH2C9H6)(2)]YbCl(THF); the major diastereomer formed is racemic. The rac-[ O(CH2CH2C9H6)(2)]YbCl(THF) (1) was isolated after recrystallization of a ra c / mese mixture of [O(CH2CH2C9H6)(2)]YbCl(THF) in THF. Direct amidation (o r alkylation) of the rac/meso lanthanidocene chloride mixtures in toluene p rovided solely pure racemic ansa-lanthanidocene amides [O(CH2CH2C9H6)(2)] L nN(SiMe3)(2) (Ln = Y (2), Pr (3), Nd (4), Yb (5), Lu (6)) and pure racemic ansa-lanthanidocene hydrocarbyls [O(CH2CH2C9H6)(2)]-LnCH(2)SiMe(3) (Ln = Dy (7), Yb (8)). The structures of 1 and 5 were determined by X-ray diffracti on. The amide and hydrocarbyl complexes are efficient single-component cata lysts for methyl methacrylate polymerization. The effects of solvent and re action temperature on the polymerization were studied. Very high molecular weight (M-n > 10(6)) iso-rich poly(MMA) was obtained at lower temperature, while low molecular weight moderately syndiotactic poly(MMA) was obtained a t higher temperature. The polymerization behavior is proposed to be associa ted with rac/meso interconversion of the active center.