Synthesis and Olefin polymerization catalysis of new trivalent samarium and yttrium complexes with bridging bis(cyclopentadienyl) ligands

Article abstract of DOI:10.1021/om000226a

New trivalent samarium and yttrium complexes with bridging bis(cyclopentadienyl) ligands were synthesized, and olefin polymerization catalysis of the complexes having an alkyl group [R = CH(SiMe₃)₂] on the metal was investigated. Three types of the rare earth halides (rac, C₁, and meso) whose structures differed with respect to the bridging group and the positions of substituents on the cyclopentadienyl (Cp) rings were prepared: rac-Sm-Cl, Me₂Si[2,4-(Me₃Si)₂C₅ H₂]₂SmCl₂Li(THF)₂ (1a); C₁-Sm-Cl, Me₂Si[2,4-(Me₃Si)₂ C₅H₂][3,4-(Me₃Si)₂C₅ H₂]-SmCl₂Li(THF)₂ (2a); C₁(Ph₂Si)-Sm-Cl, Ph₂Si[2,4- (Me₃Si)₂C₅H₂][3,4- (Me₃Si)₂C₅H₂]SmCl₂- Li(THF)₂ (3); meso-Sm-Cl, [1,2-(Me₂Si)(Me₂SiOSiMe₂)](4-Me₃ CC₅H₂)₂SmCl₂Li(THF)₂ (4a);rac-Y-Cl, Me₂Si[2,4-(Me₃Si)₂C₅ H₂]₂YCL₂Li(THF)₂ (5a); C₁-Y-Cl, Me₂Si[2,4-(Me₃Si)₂ C₅H₂][3,4-(Me₃Si)₂C₅ H₂]YCl₂Li(THF)₂ (6a); meso-Y-Cl, [1,2-(Me₂Si)(Me₂SiOSiMe₂)](4-Me₃ SiC₅H₂)₂YCl-(THF) (7a). Although the rac and C₁ complexes (1a, 2a and 5a, 6a) were obtained as an isomeric mixture by the reaction of LnCl₃ (Ln = Sm, Y) with a dilithium salt of the ligand Me₂Si[(Me₃Si)₂C₅ H₃]₂, it could be separated into both the pure complexes by utilizing the difference of solubility in hexane in each case. Structural data were obtained on 1a, 2a, 3, and 7a to confirm the structures expected from NMR spectroscopy. The (ring centroid)- metal-(ring centroid) angles in these complexes are ca. 10-20° smaller than those in nonbridging bis(cyclopentadienyl) rare earth complexes. The rare earth halides 1a, 2a, 4a, 5a, 6a, and 7a reacted with LiCH(SiMe₃)₂ to afford rare earth alkyl complexes, rac-Sm-R, Me₂Si[2,4-(Me₃Si)₂C₅ H₂]₂SmCH(SiMe₃)₂ (1b); C₁-Sm-R, Me₂Si[2,4-(Me₃Si)₂ C₅H₂][3,4-(Me₃Si)₂C₅ H₂]SmCH(SiMe₃)₂ (2b); meso-Sm-R, [1,2-(Me₂Si)(Me₂SiOSiMe₂)] (4-Me₃CC₅H₂)₂SmCH (SiMe₃)₂ (4b); rac-Y-R, Me₂Si[2,4-(Me₃Si)₂C₅ H₂]₂YCH(SiMe₃)₂ (5b); C₁-Y-R, Me₂Si[2,4-(Me₃Si)₂ C₅H₂][3,4-(Me₃Si)₂C₅ H₂] YCH(SiMe₃)₂ (6b); meso-Y-R, and [1,2-(Me₂Si)(Me₂SiOSiMe₂)] (4-Me₃SiC₅H₂)₂YCH (SiMe₃)₂ (7b), respectively. Only C₁ type alkyl complexes (2b and 6b) polymerize ethylene, giving high molecular weight polyethylenes, and the precise structure of the active Sm complex 2b was determined by X-ray crystallography.