N-heterocyclic carbene adducts of cyclopalladated ferrocenylchloropyrimidine: synthesis, structural characterization and application in the Sonogashira reaction

Abstract

Three N-heterocyclic carbene (NHC) adducts of cyclopalladated ferrocenylchloropyrimidine, 2–4 [PdCl{[(η5-C5H5)]Fe[(η5-C5H3)-N2C4H2-Cl]}(NHCs)] have been prepared by reaction of the chloride-bridged palladacyclic dimer 1 [PdCl{[(η5-C5H5)]Fe[(η5-C5H3)-N2C4H2-Cl]}]2 with the corresponding imidazolium salts. These complexes were characterized by elemental analysis, IR, ESI–MS and NMR. The use of these complexes as catalysts for the Sonogashira reaction was examined. Complex 4 proved to be an efficient catalyst for the Sonogashira reaction of aryl bromides and some activated aryl chlorides under copper- and amine-free conditions. Typically, using 0.1–2 mol % of catalyst in the presence of 1.5 equivalents of CsOAc as base in dimethylacetamide at 120 °C provided coupling products in good yields.