Bimacrocyclic concave N-heterocyclic carbenes (NHCs): synthesis, structure, and application in catalyses
Résumé
Imidazolinium moieties have been incorporated into bimacrocycles to generate precursors for concave N-heterocyclic carbenes (NHCs). Starting from 2-nitroresorcinol and alkenols, symmetric concave imidazolinium salts 1 were obtained. Bimacrocyclization was achieved via ring closing metathesis (RCM). In an analogous fashion, axially chiral concave imidazolinium salts 2 were obtained by using a naphthalene bridgehead devoid of local C2-symmetry. The concave NHCs derived from the symmetric precursors 1 were used as nucleo-philic catalysts for the synthesis of Γ-butyrolactones and as ligands for transition metal catalysts. Copper complex 18 was used as catalyst for the cyclopropanation of styrene and indene with ethyl diazoacetate (EDA). Palladium complex 24 was used as catalyst for Mizoroki-Heck and Suzuki-Miyaura cross-coupling reactions.
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