Synthesis of Heterocyclic-Fused Cyclopentadienyl Scandium Complexes and the Catalysis for Copolymerization of Ethylene and Dicyclopentadiene

Heterocyclic-fused cyclopentadienyl scandium bis(alkyl) complexes L1-4Sc(CH2SiMe3)(2)THF ((5-Me-1-Ph-cyclopenta[b]pyrrol-4-yl)Sc(CH2SiMe3)(2)THF (1), (2,5-Me-2-3-Ph-6H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF (2), (2,4,5,6-Me-4-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF (3), (2,3,4,5,6-Me-5-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)(2)THF) (4)) were facilely synthesized by alkane elimination reaction of Sc(CH2SiMe3)3(THF)2 with the heterocyclic-fused cyclopentadienyl ligands HL1-4 in high yields. Complexes 1-4 were characterized by H-1 and C-13 NMR spectroscopies and X-ray diffraction analyses as THF-solvated monomers, adopting a half-sandwich geometry. Upon activation of [Ph3C][B(C6F5)(4)]/AliBu(3), these half-sandwich scandium complexes displayed various activities toward the copolymerization of ethylene (E) and dicyclopentadiene (DCPD). Complex 1, supported by the phenyl-substituted pyrrole-fused cyclopentadienyl ligand, showed a slightly higher activity than the phenyl-substituted thiophene-fused cyclopentadienyl complex 2. Among the thiophene-fused cyclopentadienyl complexes 2-4, 4, bearing pentamethyl substituents, showed the highest activity of 2.9 x 10 (6) g/molSc.h.bar. The resultant copolymers had adjustable DCPD incorporation varying from 14.0 up to 46.1 mol %, of which the alternating poly(E-alt-DCPD) had a high Tg of 166 degrees C. In addition, no cross-linking was observed in the copolymers, suggesting that these catalytic systems were highly regioselective for the two active double bonds within DCPD.