Copper(I) complexes with heteroaromatic hydrazone ligands: Synthesis, crystal structure and catalytic insights for tetrazole synthesis

The reaction between [Cu(PPh₃)₂(CH₃COO)] and hydrazone ligands derived from heteroaromatics (L_1-3) [L₁ = 2-(2-benzothiazole-2-yl)hydrazineylidene)acenaphthylen-1-one, L₂ = 2-(2-isoquinolin-3-yl)hydrazineylidene)acenaphthylen-1-one, L₃ = 2-(2-oxoacenaphthylen-1-ylidene)hydrazineyl)nicotinic acid] gives rise to a novel series of Cu(I) complexes of the type [Cu(PPh₃)₂(L_1-3)]. The structural confirmation of these complexes has been achieved through comprehensive analysis utilizing FT-IR, UV–Vis, NMR, and ESI-MS techniques. By utilizing single crystal X-ray diffraction, it has been established that the copper(I) ion is surrounded by a tetrahedral geometry, and a Schiff base is bound to it via a bidentate N^N coordination mode. These newly synthesized copper complexes exhibit excellent catalytic activity in three components reactions, involving diverse aldehydes, hydroxylamine hydrochloride, and sodium azide, leading to the production of variety of tetrazole derivatives. Remarkably, using 1.0 mol % of Cu(I) catalyst loading and an oxygen (O₂) environment, a vast diversity of substituted tetrazoles have been efficiently synthesized with yields ranging from good to outstanding.