Living β-selective cyclopolymerization using Ru dithiolate catalysts
| Autor: | Kijung Jung, Hyeyun Keum, Tonia S. Ahmed, Robert H. Grubbs, Tae-Lim Choi, Jaeho Lee, Jong-Chan Sung |
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| Rok vydání: | 2019 |
| Předmět: |
chemistry.chemical_classification
Steric effects 010405 organic chemistry General Chemistry Polymer 010402 general chemistry 01 natural sciences 0104 chemical sciences Catalysis Chemistry chemistry.chemical_compound Monomer chemistry Polymerization Polymer chemistry Steric factor Copolymer Living polymerization |
| Zdroj: | Chemical Science Chemical Science, 10 (39) |
| ISSN: | 2041-6520 2041-6539 |
| Popis: | Cyclopolymerization (CP) of 1,6-heptadiyne derivatives is a powerful method for synthesizing conjugated polyenes containing five- or six-membered rings via α- or β-addition, respectively. Fifteen years of studies on CP have revealed that user-friendly Ru-based catalysts promoted only α-addition; however, we recently achieved β-selective regiocontrol to produce polyenes containing six-membered-rings, using a dithiolate-chelated Ru-based catalyst. Unfortunately, slow initiation and relatively low catalyst stability inevitably led to uncontrolled polymerization. Nevertheless, this investigation gave us some clues to how successful living polymerization could be achieved. Herein, we report living β-selective CP by rational engineering of the steric factor on monomer or catalyst structures. As a result, the molecular weight of the conjugated polymers from various monomers could be controlled with narrow dispersities, according to the catalyst loading. A mechanistic investigation by in situ kinetic studies using 1H NMR spectroscopy revealed that with appropriate pyridine additives, imposing a steric demand on either the monomer or the catalyst significantly improved the stability of the propagating carbene as well as the relative rates of initiation over propagation, thereby achieving living polymerization. Furthermore, we successfully prepared diblock and even triblock copolymers with a broad monomer scope. Chemical Science, 10 (39) ISSN:2041-6520 ISSN:2041-6539 |
| Databáze: | OpenAIRE |
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