Synthesis and Olefin Polymerization Catalysis of New Divalent Samarium Complexes with Bridging Bis(cyclopentadienyl) Ligands

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, Me 2 Si(2-Me 3 Si-4-tBuC 5 H 2 ) 2 Sm(THF) 2 ( 7 ); rac -tBuMe 2 Si, Me 2 Si(2-Me 3 Si-4-tBuMe 2 SiC 5 H 2 ) 2 Sm(THF) 3 ( 8 ); C 1 symmetric, Me 2 Si[2,4-(Me 3 Si) 2 C 5 H 2 ][3,4-(Me 3 Si) 2 C 5 H 2 ]Sm(THF) 2 ( 9 ); meso, [1,2-(Me 2 Si)(Me 2 SiOSiMe 2 )](3-tBuC 5 H 2 ) 2 Sm(THF) 2 ( 10 ); C 2 v symmetric (Ph 2 Si), Ph 2 Si[3,4-(Me 3 Si) 2 C 5 H 2 ] 2 Sm(THF) 2 ( 11 ); C 2 v symmetric [(SiOSi) 2 ], [1,2-(Me 2 SiOSiMe 2 ) 2 ](3-tBuC 5 H 2 ) 2 Sm(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 × 10 5 g of PE/(mol h)) and C 1 -symmetric 9 afforded the highest molecular weight of polyethylene ( M n = 145 × 10 4 ). 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).