A new class of stable, saturated N-heterocyclic carbenes with N-naphthyl substituents: synthesis, dynamic behavior, and catalytic potential

Abstract

A new family of easily accessible and stable imidazolin-2-ylidenes has been synthesized, where the side chains are comprised of substituted naphthyl units. This generates C2-symmetric (anti) and Cs-symmetric (syn) atropisomers. The interconversion between the isomers is studied in detail both for the N-heterocyclic carbene salts and the free carbenes through variable-temperature 1H NMR spectroscopic studies; activation free energies are calculated and can be linked to the substitution pattern of the naphthyl moieties. Palladium complexes comprising the new N-heterocyclic carbenes are synthesized and preliminary data show that these compounds behave well as precatalysts in the Buchwald-Hartwig amination reaction of aryl bromides and aryl chlorides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)