Copper-based catalysts derived from salen-type ligands: synthesis of 5-substituted-1H-tetrazoles via [3+2] cycloaddition and propargylamines via A3-coupling reactions

Abstract

Base-metal copper(II) complexes derived from unsymmetrical salen-type ligands were designed and synthesized using ligands L¹H to L⁴H in moderate yield. The synthesized unsymmetrical ligands L¹H to L⁴H and the corresponding copper complexes (1–4) were characterized by UV-visible, IR and ESI-MS spectroscopic studies. Molecular structures of complexes 1, 2 and 4 were determined by X-ray crystallography. Copper complexes 1–4 were employed as catalysts for [3+2] cycloaddition and A³-coupling reactions. The mutual approach of salen-type ligands and metals via active participation of ligands allow to achieve the catalytic reactions. Reaction pathways were proposed and possible intermediate species during the catalytic cycle were successfully characterized by ESI-MS spectroscopic studies.