Three-coordinated isocyanide copper(I) complex: synthesis, characterization and catalytic activity

The growth of click chemistry is attributable to the combination of high yields and simple synthetic steps. One of the most famous reaction in this field is the copper alkyne-azine cycloaddition (CuAAC), widely applied to afford 1,4-disubstituted-1,2,3-triazoles to be used for a large variety of applications such as polymers, pharma or ligands.1 The most common catalytic system is composed by a Cu(II) salt, normally CuSO4·5H2O or Cu(OAc)2, together with sodium ascorbate as reducing agent in order to generate the Cu(I) species in situ. The use of Cu(I) derivatives such as halides or triflate salts normally requires bulky ligands, that can prevent the disproportion to Cu0 and Cu(II) and increase the solubility in organic solvents. The investigation on the catalytic activity of copper(I) species is mostly limited to linear and tetrahedral species, while much less attention was devoted to three-coordinated derivatives. In this communication, we report the synthesis and characterization of a tris-isocyanide copper(I) complex, having general formula [Cu(CNAr)3][BF4] (CNAr = 2,6-dimethylphenyl isocyanide). The structure of the complex was unambiguously defined by single crystal X-ray diffraction. Since the non-innocent role of isocyanide derivatives is widely recognized,2 we tested this complex for CuAAC. Remarkable catalytic activity was detected both in water and in neat conditions, opening up the way towards the use of three-coordinated species for copper alkyne-azine cycloaddition.