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Dendritic Chiral Salen Titanium(IV) Catalysts Enforce the Cooperative Catalysis of Asymmetric Sulfoxidation
Author(s) -
Chen Yaju,
Tan Rong,
Zhang Yaoyao,
Zhao Guangwu,
Yin Donghong
Publication year - 2015
Publication title -
chemcatchem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.497
H-Index - 106
eISSN - 1867-3899
pISSN - 1867-3880
DOI - 10.1002/cctc.201500900
Subject(s) - chemoselectivity , catalysis , chemistry , ionic liquid , dendrimer , enantioselective synthesis , intramolecular force , selectivity , combinatorial chemistry , polymer chemistry , organic chemistry
A series of new dendritic chiral salen Ti IV catalysts was prepared by the covalent confinement of multiple chiral salen Ti IV complexes on the periphery of a polyamidoamine (PAMAM) dendrimer through a flexible ionic liquid (IL) linker. The characterization results suggested the presence of a dendritic PAMAM scaffold, IL spacer, and intact peripheral active sites in the catalysts. The unique dendritic structure of catalysts together with a flexible IL spacer enforced the intramolecular, cooperative catalysis of asymmetric sulfoxidation to result in improved catalytic efficiency and, especially, a remarkably high selectivity. A chemoselectivity of 90 % with an enantioselectivity of 85 % was obtained in the asymmetric sulfoxidation of methyl phenyl sulfide catalyzed by the dendritic catalyst, which was significantly higher than that observed for the neat complex (64 % chemoselectivity with 68 % enantioselectivity). Furthermore, the catalysts could be recovered easily by solvent precipitation for efficient reuse.