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Living β-selective cyclopolymerization using Ru dithiolate catalysts

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Abstract

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.

Graphical abstract: Living β-selective cyclopolymerization using Ru dithiolate catalysts

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Publication details

The article was received on 18 Mar 2019, accepted on 22 Jul 2019 and first published on 22 Jul 2019


Article type: Edge Article
DOI: 10.1039/C9SC01326A
Chem. Sci., 2019, Advance Article
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    Living β-selective cyclopolymerization using Ru dithiolate catalysts

    K. Jung, T. S. Ahmed, J. Lee, J. Sung, H. Keum, R. H. Grubbs and T. Choi, Chem. Sci., 2019, Advance Article , DOI: 10.1039/C9SC01326A

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