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Issue 8, 2018
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Cationic half-sandwich rare-earth metal alkyl species catalyzed polymerization and copolymerization of aryl isocyanides possessing polar, bulky, or chiral substituents

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Abstract

Two types of half-sandwich rare-earth metal dialkyl complexes (Cp)Ln(CH2SiMe3)2(THF) 1–6 (1: Cp = (3aR,4R,8R,8aR)-cyclopentadienyl ligand (Cpx*′), Ln = Sc; 2: Cp = Cpx*′, Ln = Y; 3: Cp = Cpx*′, Ln = Lu; 4: Cp = (3aR,8aS)-cyclopentadienyl ligand (Cpx*′′), Ln = Sc; 5: Cp = Cpx*′′, Ln = Y; 6: Cp = Cpx*′′, 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 [(1S,2R,5S)-2-isopropyl-5-methylcyclohexyl 4-isocyanobenzoate (D-IMCI) and (1R,2S,5R)-2-isopropyl-5-methylcyclohexyl 4-isocyanobenzoate (L-IMCI)] substituents with extremely high activities (up to 107 g of polymer molLn−1 h−1) under mild conditions. The resulting functional polyisocyanides have high molecular weights (Mn = 4.4–21.4 × 104 g mol−1) as well as broad molecular weight distributions (Mw/Mn = 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 106 g of polymer molLn−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.

Graphical abstract: Cationic half-sandwich rare-earth metal alkyl species catalyzed polymerization and copolymerization of aryl isocyanides possessing polar, bulky, or chiral substituents

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Publication details

The article was received on 02 Jan 2018, accepted on 17 Jan 2018 and first published on 18 Jan 2018


Article type: Paper
DOI: 10.1039/C8PY00007G
Citation: Polym. Chem., 2018,9, 984-993
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    Cationic half-sandwich rare-earth metal alkyl species catalyzed polymerization and copolymerization of aryl isocyanides possessing polar, bulky, or chiral substituents

    X. Yan, S. Zhang, D. Peng, P. Zhang, J. Zhi, X. Wu, L. Wang, Y. Dong and X. Li, Polym. Chem., 2018, 9, 984
    DOI: 10.1039/C8PY00007G

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