Living cis-1,4-Selective Polymerization of 1,3-Dienes by Enamino-Oxazolinate Rare-Earth Metal Complexes

A series of enamino-oxazolinate rare-earth metal complexes were successfully synthesized and structurally characterized. The alkyl elimination of enamino-oxazolinate proligands [R1 = H, R2 = CF3 (L1-H); R1 = Me, R2 = CF3 (L2-H); R1 = iPr, R2 = CF3 (L3-H); R1 = iPr, R2 = Ph (L4-H)] with an equimolar amount of Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu, Sc) smoothly afforded the desired rare-earth metal complexes [L(1–4)-Ln(CH2SiMe3)2](THF). Upon activation by a borate, all of these complexes, especially 1-Y, exhibited high catalytic activities for the living polymerization of 1,3-dienes (isoprene, β-myrcene, and β-farnesene) to afford highly cis-1,4-regular polymers (up to 99.6% for polyisoprene, 99.6% for polymyrcene, and 99.9% for polyfarnesene). Noteworthily, the presence of the polar −CF3 group in the ligands had a positive effect on the rare-earth metal complexes to realize satisfactory catalytic performance.