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Issue 10, 2010
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Anion variation on a cobalt(iii) complex of salen-type ligand tethered by four quaternary ammonium salts for CO2/epoxidecopolymerization

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Abstract

Anion exchange of BF4 occurs by stirring a cobalt(III) complex of salen-type ligand tethered by four quaternary ammonium BF4 salts over a slurry of NaX in CH2Cl2, affording a complex containing four X's per cobalt (X = 2,4,5-trichlorophenolate, 6; X = 4-nitrophenolate, 10; X = 2,4-dichlorophenolate, 12). The 1H and 13C NMR spectra are in agreement with an unusual imine uncoordinated structure. The two salen-phenoxys and the two X's persistently coordinate with cobalt(III) to form a square planar cobaltate complex while the other two X's scramble through coordination and decoordination to the axial sites of the square plane. Another form of the complex (X = 2,4,5-trichlorophenolate, 14; X = 4-nitrophenolate, 15; X = 2,4-dichlorophenolate, 16) is also prepared, in which the scrambling two X's in 6, 10, or 12 are replaced with the corresponding [X⋯H⋯X] homoconjugate. These complexes, which adopt an unusual imine uncoordinated structure, are excellent catalysts for CO2/propylene oxide copolymerization (turnover frequency (TOF), 8300–16 000 h−1). In all cases, the complex containing the homoconjugate [X⋯H⋯X] shows higher activity than the corresponding phenol-free complex. Among the prepared complexes, 4-nitrophenol-4-nitrophenolate homoconjugate complex 15 showed the best performance (TOF, 16 000 h−1; selectivity, 98%; Mn, 273 000), allowing for replacement of the explosive 2,4-dinitrophenolate complex.

Graphical abstract: Anion variation on a cobalt(iii) complex of salen-type ligand tethered by four quaternary ammonium salts for CO2/epoxide copolymerization

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Article information


Submitted
07 Oct 2009
Accepted
17 Dec 2009
First published
28 Jan 2010

Dalton Trans., 2010,39, 2622-2630
Article type
Paper

Anion variation on a cobalt(III) complex of salen-type ligand tethered by four quaternary ammonium salts for CO2/epoxide copolymerization

J. Yoo, S. J. Na, H. C. Park, A. Cyriac and B. Y. Lee, Dalton Trans., 2010, 39, 2622
DOI: 10.1039/B920992A

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