Cationic half-sandwich rare-earth metal alkyl species catalyzed polymerization and copolymerization of aryl isocyanides possessing polar, bulky, or chiral substituentsElectronic supplementary information (ESI) available: Experiment section, UV-vis absorption spectra, 1H and 13C NMR spectra, FT-IR spectra, ESI-MS spectrum and GPC curves. CCDC 1588843, 1588845 and 1588851. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c8py00007g

Two types of half-sandwich rare-earth metal dialkyl complexes (Cp)Ln(CH 2 SiMe 3 ) 2 (THF) 1-6 ( 1 : Cp = (3a R ,4 R ,8 R ,8a R )-cyclopentadienyl ligand (Cp x *′), Ln = Sc; 2 : Cp = Cp x *′, Ln = Y; 3 : Cp = Cp x *′, Ln = Lu; 4 : Cp = (3a R ,8a S )-cyclopentadienyl ligand (Cp x *′′), Ln = Sc; 5 : Cp = Cp x *′′, Ln = Y; 6 : Cp = Cp x *′′, Ln = Lu) have been synthesized and structurally characterized by X-ray diffraction. The reaction of these half-sandwich rare-earth metal dialkyl complexes with almost one equivalent of activator (borate or borane) quantitatively afforded the cationic half-sandwich rare-earth metal alkyl species, which are the first example of rare-earth metal catalysts for the polymerization of five functional aryl isocyanides containing polar ester [4-ethoxycarbonyl phenyl isocyanide (EPI)], bulky naphthyl [2-naphthyl isocyanide (NI)] or tetraphenylethylene [4-isocyano-4′-(1,2,2-triphenylvinyl)-1,1′-biphenyl (ITPB)], or chiral ester [(1 S ,2 R ,5 S )-2-isopropyl-5-methylcyclohexyl 4-isocyanobenzoate ( d -IMCI) and (1 R ,2 S ,5 R )-2-isopropyl-5-methylcyclohexyl 4-isocyanobenzoate ( l -IMCI)] substituents with extremely high activities (up to 10 7 g of polymer mol Ln −1 h −1 ) under mild conditions. The resulting functional polyisocyanides have high molecular weights ( M n = 4.4-21.4 × 10 4 g mol −1 ) as well as broad molecular weight distributions ( M w / M n = 3.20-6.82) and exhibit good solubility, aggregation-caused quenching (ACQ) nature, or single-handed helical conformation. Moreover, the complex 1 /activator binary system can also promote the helix-sense-selective copolymerization of chiral d -IMCI or l -IMCI with achiral ITPB at high activities (up to 10 6 g of polymer mol Ln −1 h −1 ), affording new random poly( d / l -IMCI- co -ITPB)s with d / l -IMCI contents in the range of 9-76 mol% and different degrees of single-handed helical conformations. In contrast with the AIE nature of the ITPB monomer, these copolymers containing ITPB units exhibit ACQ nature similar to poly(ITPB). A plausible coordination-insertion mechanism is proposed based on ESI-MS spectroscopy, providing insight into the initiation and termination polymerization process of aryl isocyanides catalyzed by rare-earth metal catalysts. Cationic half-sandwich rare-earth metal alkyl species were first used for the coordination-insertion polymerization and copolymerization of aryl isocyanides.