Alternating and Random Copolymerization of Isoprene and Ethylene Catalyzed by Cationic Half-Sandwich Scandium Alkyls

The acid−base reactions between the scandium trialkyl complex Sc(CH2SiMe3)3(THF)2 and 1 equiv of Cp′−H afforded straightforwardly the corresponding mono(cyclopentadienyl)scandium dialkyl complexes Cp′Sc(CH2SiMe3)2(THF) (Cp′ = C5H5 (1), C5MeH4 (2), C5Me4H (3), C5Me5 (4), C5Me4SiMe3 (5)) in 65−80% isolated yields. The analogous half-sandwich complexes having a heteroatom-containing side arm, (C5Me4R)Sc(CH2SiMe3)2 (R = CH2CH2PPh2 (6), C6H4OMe-ο (7)), were obtained by the one-pot metathetical reactions of ScCl3(THF)3 with 1 equiv of the potassium salts of the ligands and 2 equiv of LiCH2SiMe3. The similar reactions of ScCl3(THF)3 with KC5Me4(C6H4NMe2-ο) and LiCH2SiMe3 gave a methylene-bridged binuclear complex [{C5Me4(ο-C6H4N(Me)CH2-μ}Sc(CH2SiMe3)]2 (8). Complexes 1−8 were fully characterized by 1H, 13C NMR, X-ray, and microelemental analyses. The reactions of 5 and 7 with 1 equiv of [PhMe2NH][B(C6F5)4] in THF afforded quantitatively the structurally characterizable cationic monoalkyl complexes [(C5Me4SiMe3)S...