Redox Instability of Copper(II) Complexes of a Triazine‐Based PNP Pincer. Issue 12 (2nd March 2021) - Mohammadnezhad, Gholamhossein
Abstract: The new Cu(I) complex [Cu(PNP NTPh ‐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 . 0.5Et2 O. 1 was independently obtained from a reaction mixture containing the ligand and the Cu(II) precursor CuCl2 . 2H2 O in 50 % yield alongside with the Cu(II) coordination polymer [Cu(O2 PPh2 )2 ] n (2 ). From the reaction of Cu(NO3 )2 ⋅ 3H2 O with PNP NTPh ‐Ph in the presence of pyridine the complexes [Cu(O2 PPh2 )2 (Py)2 (H2 O)] (3 ), [Cu(O2 PPh2 )(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(PNP NTPh ‐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‐1 H ‐1, 2, 3‐triazoles. The environmentally benign ("green") and cheap EtOH/H2 O solvent mixture turned out to be very suitable. Melting points, FT‐IR, and NMR spectra of the triazole products were analysed. Abstract : From the tridentate PNP pincer ligand N, N ′‐bis(diphenylphosphino)‐2, 6‐diamino‐4‐phenyl‐1, 3, 5‐triazine a Cu(I) chlorido complex was synthesised, while the corresponding Cu(II) complex undergoes electron transfer resulting in Cu(I) and oxidised ligand. The stable Cu(I) complex can be used for azide‐alkyne 1, 3‐cycloaddition (AAC) catalysis.