Resorcinarene-Functionalised Imidazolium Salts as Ligand Precursors for Palladium-Catalysed Suzuki-Miyaura Cross-Couplings.
Résumé
Three imidazolium salts based on a rigid resorcinarene platform (1-3) were synthesised and used as catalyst precursors in the Suzuki-Miyaura cross-coupling of aryl halides with phenylboronic acid. In these pro-carbene ligands, the heterocyclic moiety has one N atom connected to a C2 atom of a resorcinolic ring, and the other is substituted by an alkyl group (R=n-propyl, iso-propyl, benzyl). The methinic C atoms of the macrocyclic core are all substituted by a pentyl group. The best catalytic performances were obtained by using an imidazolium/Pd ratio of 1:1. The catalytic systems displayed high activities, which increased in the order R=n-propyl (1)