Copper complexes bearing an NHC–calixarene unit: synthesis and application in click chemistry
The synthesis of N-heterocyclic carbene (NHC) copper complexes supported by calixarene is reported. Mono-substituted calixarene was prepared through conventional procedures, followed by the attachment of an imidazolyl group to create the precursor of NHC ligands. Alkylation with two alkyl bromides followed by metalation resulted in fully characterized original complexes. The X-ray structure showed an “out” conformation for copper. The catalytic activity of the complexes was studied in click chemistry, and revealed good performances. In particular, three new triazoles were synthesized in high yields, under solvent-free conditions and a fast reaction time. The newly synthesized chiral complex was tested in the kinetic resolution of racemic azide.