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)2THF ((5-Me-1-Ph-cyclopenta­[b]­pyrrol-4-yl)­Sc­(CH2SiMe3)2THF (1), (2,5-Me2-3-Ph-6H-cyclopenta­[b]­thiophenyl)­Sc­(CH2SiMe3)2THF (2), (2,4,5,6-Me4-4H-cyclopenta­[b]­thiophenyl)­Sc­(CH2SiMe3)2THF (3), (2,3,4,5,6-Me5-4H-cyclopenta­[b]­thiophenyl)­Sc­(CH2SiMe3)2THF) (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 1H and 13C NMR
spectroscopies and X-ray diffraction analyses as THF-solvated monomers,
adopting a half-sandwich geometry. Upon activation of [Ph3C]­[B­(C6F5)4]/AliBu3, 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 × 106 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 °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.