Rare-earth metal complexes supported by indolyl-based NCN-pincer ligand and their efficient catalysis for isoprene polymerization

Rare-earth metal dialkyl complexes [1-CH2N(CH3)2–3-CH2CH2N(CH3)2C8H4N]RE(CH2SiMe3)2 (RE = 1-Y, 2-Er, 3-Yb and 4-Lu) were synthesized by the well-designed indolyl-based proligand 1-CH2N(CH3)2–3-CH2CH2N(CH3)2C8H4NH with rare-earth metal trialkyl complexes (RE(CH2SiMe3)2(THF)2) underwent direct alkane elimination. Single-crystal X-ray analyses and the NMR spectroscopy revealed these dialkyl complexes were analogous mononuclear NCN-pincer geometry via CH activation of 2-sp2 indole. Employing these complexes, upon activation by aluminum alkyls and borate, initiated isoprene polymerization with high conversion and high stereoselectivity (98% conversion of 2000 equivalent of isoprene, 1,4-cis polymers up to 91.5%).