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Issue 25, 2013
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CO2/ethylene oxide copolymerization and ligand variation for a highly active salen–cobalt(III) complex tethering 4 quaternary ammonium salts

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Abstract

A cobalt(III) complex (1) of a salcy-type ligand tethering 4 quaternary ammonium salts, which is thought to act as a highly active catalyst for CO2/propylene oxide (PO) copolymerization, also shows high activity (TOF, 25 900 h−1; TON, 518 000; 2.72 kg polymer per g cat) and selectivity (>98%) for CO2/ethylene oxide (EO) copolymerization that results in high-molecular-weight polymers (Mn, 200 000–300 000) that have strictly alternating repeating units. The related cobalt(III) complexes 11–14 were prepared through variations of the ligand framework of 1 by replacing the trans-1,2-diaminocyclohexane unit with 2,2-dimethyl-1,3-propanediamine, trans-1,2-diaminocyclopentane, or 1,1′-binaphthyl-2,2′-diamine or by replacing the aldimine bond with ketimine. These ligand frameworks are thought to favour the formation of the cis-β configuration in complexation, and the formation of the cis-β configuration in 11–14 was confirmed through NMR studies or X-ray crystallographic studies of model complexes not bearing the quaternary ammonium salts. Complexes 11, 13, and 14, which adopt the cis-β configuration even in DMSO did not show any activity for CO2/PO copolymerization. Complex 12, which was constructed with trans-1,2-diaminocyclopentane and fluctuated in DMSO between the coordination and de-coordination of the acetate ligand as observed for 1, showed fairly high activity (TOF, 12 400 h−1). This fluctuating behaviour may play a role in polymerization. However, complex 12 did not compete with 1 in terms of activity, selectivity, and the catalyst cost.

Graphical abstract: CO2/ethylene oxide copolymerization and ligand variation for a highly active salen–cobalt(iii) complex tethering 4 quaternary ammonium salts

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Publication details

The article was received on 14 Aug 2012, accepted on 02 Oct 2012 and first published on 29 Oct 2012


Article type: Paper
DOI: 10.1039/C2DT31854G
Citation: Dalton Trans., 2013,42, 9245-9254
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    CO2/ethylene oxide copolymerization and ligand variation for a highly active salen–cobalt(III) complex tethering 4 quaternary ammonium salts

    J. Y. Jeon, J. J. Lee, J. K. Varghese, S. J. Na, S. Sujith, M. J. Go, J. Lee, M. Ok and B. Y. Lee, Dalton Trans., 2013, 42, 9245
    DOI: 10.1039/C2DT31854G

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