Bis-chelates of nickel(II) and copper(II) with an O,S-donor piperazine ligand

Abstract

A bidentate O,S-donor ligand N-(4-benzoyl-piperazine-1-carbothioyl)-benzamide (HL) was synthesized from the reaction of in situ generated benzoylisothiocyanate with piperazine and benzoyl chloride. Reaction of HL with the perchlorate salts of NiII and CuII in DMF–MeOH mixture using NEt3 as base afforded complexes 1 and 2 as crystalline solids in moderate yields. Physico-chemical and spectroscopic studies confirmed the chemical compositions of both the free ligand and its M(O,S)2 type metal complexes. The ligand undergoes keto-thione to keto-thiol tautomerization during metalation which is the driving force for the formation of neutral bis-chelates. The X-ray crystal structure of complex 2 shows bis-chelation with a cis-conformation in an overall square planar environment. M(O,S)2 complexes have been stabilized in cis-conformation from a piperazine based thiourea ligand through keto-imine-thiol tautomerization.