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)(2)BIAN)(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(4)(BF) and 3(4)(BF), 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(4)(BF), 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(3)(NO)-3(3)(NO), [Cu(PPh3)(2)NO3] 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 degrees C and in short reaction times without requiring the use of any additive, with complex 2(3)(NO) being the most efficient derivative, along with other NO3--bearing complexes.