title: Influence of the N-Substituents on the Nucleophilicity and Lewis Basicity of N-Heterocyclic Carbenes.
abstract: The ability to modulate the nucleophilicity and Lewis basicity of N-heterocyclic carbenes is pivotal to their application as organocatalysts. Herein we examine the impact of the N-substituent on the nucleophilicity and Lewis basicity. Four N-substituents popular in NHC organocatalysis, namely, the N-2,6-(CH3O)2C6H3, N-Mes, N-4-CH3OC6H4, and N-tert-butyl groups, have been examined and found to strongly affect the nucleophilicity. Thus, the N-2,6-(CH3O)2C6H3 group provides the most nucleophilic imidazolylidene NHC reported and the N-tert-butyl group one of the least. This difference in nucleophilicity is reflected in the catalyst efficiency, as observed with a recently reported trienyl ester rearrangement.
authors.affiliation: School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
authors.forename: Alison
authors.initials: A
authors.lastname: Levens
authors.affiliation: Department Chemie, Ludwig-Maximilians-Universität München , Butenandtstraße 5-13 (Haus F), 81377 München, Germany.
authors.forename: Feng
authors.initials: F
authors.lastname: An
authors.affiliation: Department für Chemie, Universität zu Köln , Greinstraße 4, 50939 Köln, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Breugst
authors.affiliation: Department Chemie, Ludwig-Maximilians-Universität München , Butenandtstraße 5-13 (Haus F), 81377 München, Germany.
authors.forename: Herbert
authors.initials: H
authors.lastname: Mayr
authors.affiliation: School of Chemistry, Monash University , Clayton, Victoria 3800, Australia.
authors.forename: David W
authors.initials: DW
authors.lastname: Lupton