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Issue 17, 2019
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Heterodinuclear zinc and magnesium catalysts for epoxide/CO2 ring opening copolymerizations

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Abstract

The ring-opening copolymerization of carbon dioxide and epoxides is a useful means to make aliphatic polycarbonates and to add-value to CO2. Recently, the first heterodinuclear Zn(II)/Mg(II) catalyst showed greater activity than either homodinuclear analogue (J. Am. Chem. Soc.2015, 137, 15078–15081). Building from this preliminary finding, here, eight new Zn(II)/Mg(II) heterodinuclear catalysts featuring carboxylate co-ligands are prepared and characterized. The best catalysts show very high activities for copolymerization using cyclohexene oxide (TOF = 8880 h−1, 20 bar CO2, 120 °C, 0.01 mol% catalyst loading) or cyclopentene oxide. All the catalysts are highly active in the low pressure regime and specifically at 1 bar pressure CO2. The polymerization kinetics are analysed using in situ spectroscopy and aliquot techniques: the rate law is overall second order with a first order dependence in both catalyst and epoxide concentrations and a zero order in carbon dioxide pressure. The pseudo first order rate coefficient values are compared for the catalyst series and differences are primarily attributed to effects on initiation rates. The data are consistent with a chain shuttling mechanistic hypothesis with heterodinuclear complexes showing particular rate enhancements by optimizing distinct roles in the catalytic cycles. The mechanistic hypothesis should underpin future heterodinuclear catalyst design for use both in other (co)polymerization and carbon dioxide utilization reactions.

Graphical abstract: Heterodinuclear zinc and magnesium catalysts for epoxide/CO2 ring opening copolymerizations

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Publication details

The article was received on 23 Jan 2019, accepted on 06 Mar 2019 and first published on 26 Mar 2019


Article type: Edge Article
DOI: 10.1039/C9SC00385A
Chem. Sci., 2019,10, 4618-4627
  • Open access: Creative Commons BY-NC license
    All publication charges for this article have been paid for by the Royal Society of Chemistry

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    Heterodinuclear zinc and magnesium catalysts for epoxide/CO2 ring opening copolymerizations

    G. Trott, J. A. Garden and C. K. Williams, Chem. Sci., 2019, 10, 4618
    DOI: 10.1039/C9SC00385A

    This article is licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported Licence. Material from this article can be used in other publications provided that the correct acknowledgement is given with the reproduced material and it is not used for commercial purposes.

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