Redox Instability of Copper(II) Complexes of a Triazine-Based PNP Pincer

The new Cu(I) complex [Cu(PNPNTPh-Ph)Cl] (1) containing the tridentate PNP pincer ligand N,N '-bis(diphenylphosphino)-2,6-diamino-4-phenyl-1,3,5-triazine was obtained from the reaction of [Cu(SMe2)Cl](n) with the ligand as ether solvate 1(.)0.5Et(2)O. 1 was independently obtained from a reaction mixture containing the ligand and the Cu(II) precursor CuCl(2)(.)2H(2)O in 50 % yield alongside with the Cu(II) coordination polymer [Cu(O2PPh2)(2)](n) (2). From the reaction of Cu(NO3)(2) . 3H(2)O with PNPNTPh-Ph in the presence of pyridine the complexes [Cu(O2PPh2)(2)(Py)(2)(H2O)] (3), [Cu(O2PPh2)(Py)(2)(NO3)](2) (4), and [Cu(Py)(4)(NO3)(2)]Py-. (5), were obtained, 2, 3, and 4 contain diphenyl-phosphinate ligands. The underlying redox reaction of the ligand and Cu(II) yielding the oxidised ligands observed in the by-products and the Cu(I) product complex was further studied using electrochemistry and UV-vis spectroelectrochemistry. Attempts to synthesise the Cu(II) complex [Cu(PNPNTPh-Ph)(NO3)(2)] (6) in a mechanochemical experiment gave evidence for this unprecedented species from ESI-MS(+) and EPR spectroscopy but also revealed its very high sensitivity to air and moisture. The catalytic activity of 1 was investigated in the azide-alkyne cycloaddition yielding various 1-benzyl-4-phenyl-1H-1,2,3-triazoles. The environmentally benign (green) and cheap EtOH/H2O solvent mixture turned out to be very suitable. Melting points, FT-IR, and NMR spectra of the triazole products were analysed.

Automated summary

The study describes the synthesis of a new Cu(I) complex and its catalytic activity, investigates the redox reaction between the ligand and Cu(II), and discusses the effect of different solvents on the reaction.