Calix[4]arene‐Supported <i>N</i>‐Heterocyclic Carbene Ligands as Catalysts for Suzuki Cross‐Coupling Reactions of Chlorotoluene

Abstract

Abstract Stable N ‐heterocyclic carbenes are generated starting from 5,17‐(bis‐imidazolium)‐substituted calix[4]arenes. Addition of Pd(OAc) 2 to these carbenes leads to macrocyclic cis ‐palladium chelate complexes in which the distal bridging of the upper rim leads to a strong distortion of the calix[4]arene skeleton which was proven by X‐ray crystal structure determination. Using an in‐situ catalytic system consisting of a calixarene‐imidazolium salt, Cs 2 CO 3 as a base and a source of palladium, a species is formed which can be used to catalyse the Suzuki cross‐coupling of 4‐chloro toluene. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2004)