This paper deals with the preparation and olefin polymerization catalysis of six new divalent samarium complexes. These bridged bis(cyclopentadienyl) (Cp) complexes exhibit various structures with regard to the bridging group and the position of substituents on the Cp rings:  rac-tBu, Me2Si(2-Me3Si-4-tBuC5H2)2Sm(THF)2 (7); rac-tBuMe2Si, Me2Si(2-Me3Si-4-tBuMe2SiC5H2)2Sm(THF)3 (8); C 1 symmetric, Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]Sm(THF)2 (9); meso, [1,2-(Me2Si)(Me2SiOSiMe2)](3-tBuC5H2)2Sm(THF)2 (10); C 2 v symmetric (Ph2Si), Ph2Si[3,4-(Me3Si)2C5H2]2Sm(THF)2 (11); C 2 v symmetric [(SiOSi)2], [1,2-(Me2SiOSiMe2)2](3-tBuC5H2)2Sm(THF)2 (12). The structures of 7, 8, 10, and 12 were confirmed by X-ray crystallographic analysis. Among these divalent complexes, meso type complex 10 showed the highest activity for polymerizations of ethylene (5 × 105 g of PE/(mol h)) and C 1-symmetric 9 afforded the highest molecular weight of polyethylene (M n = 145 × 104). Only racemic complexes 7 and 8 could polymerize 1-olefins such as 1-pentene and 1-hexene, giving highly isotactic polymers. Moreover, rac-7 induces catalytic cyclopolymerization of 1,5-hexadiene to give poly(methylene-1,3-cyclopentane).

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, C 1, 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)2C5H2]2SmCl2Li(THF)2 (1a); C 1-Sm−Cl, Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]SmCl2Li(THF)2 (2a); C 1(Ph2Si)−Sm−Cl, Ph2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]SmCl2Li(THF)2 (3); meso-Sm−Cl, [1,2-(Me2Si)(Me2SiOSiMe2)](4-Me3CC5H2)2SmCl2Li(THF)2 (4a); rac-Y−Cl, Me2Si[2,4-(Me3Si)2C5H2]2YCl2Li(THF)2 (5a); C 1-Y−Cl, Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]YCl2Li(THF)2 (6a); meso-Y−Cl, [1,2-(Me2Si)(Me2SiOSiMe2)](4-Me3SiC5H2)2YCl(THF) (7a). Although the rac and C 1 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)2C5H3]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)2C5H2]2SmCH(SiMe3)2 (1b); C 1-Sm−R, Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]SmCH(SiMe3)2 (2b); meso-Sm−R, [1,2-(Me2Si)(Me2SiOSiMe2)](4-Me3CC5H2)2SmCH(SiMe3)2 (4b); rac-Y−R, Me2Si[2,4-(Me3Si)2C5H2]2YCH(SiMe3)2 (5b); C 1-Y−R, Me2Si[2,4-(Me3Si)2C5H2][3,4-(Me3Si)2C5H2]YCH(SiMe3)2 (6b); meso-Y−R, and [1,2-(Me2Si)(Me2SiOSiMe2)](4-Me3SiC5H2)2YCH(SiMe3)2 (7b), respectively. Only C 1 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.