Heteroleptic Copper Complexes as Catalysts for the CuAAC Reaction: Counter-Ion Influence in Catalyst Efficiency

A series of nine cationic heteroleptic aryl-BIAN-copper(I) (BIAN = bis-iminoacenaphthene) complexes with the general formula [Cu((E-C₆H₄)₂BIAN)(PPh₃)₂][X] (E = p-Me, p-iPr, o-iPr; X = BF₄, OTf, NO₃) 1^X–3^X were synthesized and fully characterized using several analytical techniques, including NMR spectroscopy and single-crystal X-ray diffraction. Except for complexes 2^BF₄ and 3^BF₄, which were already reported in our previous works, all remaining complexes are herein described for the first time. Two different strategies were used for the preparation of the complexes: complexes bearing BF₄⁻ or OTf⁻ counter-ions (1^BF₄, 1^OTf, 2^OTf, and 3^OTf) were obtained using the appropriate copper(I) precursors [Cu(NCMe)₄][BF₄] or [Cu(NCMe)₄][OTf], whereas for derivatives 1^NO₃–3^NO₃, [Cu(PPh₃)₂NO₃] was used. Their activity as catalysts for the copper azide-alkyne cycloaddition (CuAAC) was assessed alongside other high activity, previously reported Cu(I) complexes. Comparative studies to determine the influence of the counter-ion and of the aryl substituents were performed. All complexes behaved as active catalysts under neat reaction conditions, at 25 °C and in short reaction times without requiring the use of any additive, with complex 2^NO₃ being the most efficient derivative, along with other NO₃⁻-bearing complexes.