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Poly(styrene)‐Supported Co–Salen Complexes as Efficient Recyclable Catalysts for the Hydrolytic Kinetic Resolution of Epichlorohydrin
Author(s) -
Zheng Xiaolai,
Jones Christopher W.,
Weck Marcus
Publication year - 2005
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200500786
Subject(s) - kinetic resolution , styrene , copolymer , metal salen complexes , polymer chemistry , ethylenediamine , monomer , epichlorohydrin , catalysis , chemistry , reactivity (psychology) , polymerization , hydrolysis , cobalt , polymer , enantioselective synthesis , organic chemistry , medicine , alternative medicine , pathology
Here we describe an unprecedented synthetic approach to poly(styrene)‐supported chiral salen ligands by the free radical polymerization of an unsymmetrical styryl‐substituted salen monomer (H 2 salen=bis(salicylidene)ethylenediamine). The new method allows for the attachment of salen moieties to the polymer main chain in a flexible, pendant fashion, avoiding grafting reactions that often introduce ill‐defined species on the polymers. Moreover, the loading of the salen is controlled by the copolymerization of the styryl‐substituted salen monomer with styrene in different ratios. The polymeric salen ligands are metallated with cobalt( II ) acetate to afford the corresponding supported Co–salen complexes, which are used in the hydrolytic kinetic resolution of racemic epichlorohydrin, exhibiting high reactivity and enantioselectivity. Remarkably, the copolymer‐supported Co–salen complexes showed a better catalytic performance (>99 % ee , 54 % conversion, one hour) in comparison to the homopolymeric analogues and the small molecule Co–salen complex. The soluble poly(styrene)‐supported catalysts were recovered by precipitation after the catalytic reactions and were recycled three times to afford almost identical enantiomeric excesses as the first run, with slightly reduced reaction rates.