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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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Submitted
23 Jan 2019
Accepted
06 Mar 2019
First published
26 Mar 2019

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2019,10, 4618-4627
Article type
Edge Article

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

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