Rare-earth Metal Dialkyl Complexes Supported by 1,3-Disubstituted Indolyl Ligand: Synthesis, Characterization and Catalytic Activity for Isoprene Polymerization

Rare-earth metal dialkyl complexes [1-Bn-3-(DippN=CH)C8H4N]RE(CH2SiMe3)(2)(thf)(2) (Dipp = 2,6-Pr2C6H3, RE = Y (1) and Er (2)) were prepared through the cyclometalation reactions of the N-Bn-3-imino-functionalized indolyl ligand 1-Bn-3-(DippN=CH)C8H5N with one equivalent of rare-earth metal trialkyl precursors. The structures of compounds 1 and 2 were confirmed by X-ray crystal analyses and characterized by elemental analysis, IR, NMR spectroscopy wherein applicable. In the presence of cocatalysts, these rare-earth metal dialkyl complexes initiated isoprene polymerization with a high activity (95% conversion of 2000 equivalent of isoprene in 360 min), producing polymers with high regioselectivity (1,4-polymers up to 91%).