title: Self-Supported N-Heterocyclic Carbenes and Their Use as Organocatalysts.
abstract: The study of N-heterocyclic carbenes (NHCs) as organocatalysts has proliferated in recent years, and they have been found to be useful in a variety of reactions. In an attempt to further expand their utility and to study their recyclability, we designed and synthesized a series of self-supported NHCs in which the catalytic carbene groups form part of a densely functionalized polymer backbone, and studied them as organocatalysts. Of the self-Supported NHCs examined, a benzimidazole derived polymer with flexible linkers connecting the catalytic groups was found to be the most efficient organocatalyst in a model benzoin condensation reaction, and thus it was used in a variety of such reactions, including some involving catalyst recycling. Furthermore, it was also used to catalyze a set of redox esterification reactions involving conjugated unsaturated aldehydes. In all of these reactions the catalyst afforded good yield of the desired product and its polymeric nature facilitated product purification.
authors.affiliation: Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, China. u3002732@connect.hku.hk.
authors.forename: Shuang
authors.initials: S
authors.lastname: Ma
authors.affiliation: Department of Chemistry, University of Hong Kong, Pokfulam Road, Hong Kong, China. phtoy@hku.hk.
authors.forename: Patrick H
authors.initials: PH
authors.lastname: Toy
mesh_terms: D001562:Benzimidazoles / Q000138:chemical synthesis* / Q000737:chemistry; D002384:Catalysis; D004951:Esterification; D008697:Methane / Q000031:analogs & derivatives* / Q000737:chemistry; D015394:Molecular Structure; D010084:Oxidation-Reduction; D011108:Polymers / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
chemical_list: D001562:Benzimidazoles; D011108:Polymers; C030011:carbene; D008697:Methane
keywords: N-heterocyclic carbene; benzoin condensation; organocatalyst; redox esterification; self-supported catalyst