Oxygen Transfer from Trimethylamine N‐Oxide to CuI Complexes Supported by Pentanitrogen Ligands

Abstract

[N,N‐bis(1‐methyl‐2‐benzimidazolyl)methyl‐N‐(bis‐2‐pyridylmethyl)amine] (L1) and [N,N‐bis(2‐quinolylmethyl)‐N‐bis(2‐pyridyl)methylamine] (L2) were employed to prepare CuII and CuI complexes for spectroscopic and structural characterization. [L1CuII(H2O)](NO3)2 and [L2CuII(NO3)]NO3 have Jahn–Teller distorted octahedral geometries and give rise to isotropic EPR spectra in frozen solution. [L1CuI(CH3CN)]OTf and [L2CuI(CH3CN)]OTf have distorted trigonal bipyramidal and tetrahedral solid‐state structures, respectively. The N‐donors display labile behavior in solution, based on variable‐temperature 1H NMR studies. Addition of trimethylamine N‐oxide (Me3NO) to solutions of [L1CuI(CH3CN)]OTf and [L2CuI(CH3CN)]OTf resulted in diamagnetic species tentatively assigned as the corresponding adducts upon replacement of coordinated acetonitrile, based on 1H NMR spectroscopy. Heating [L1CuI(CH3CN)]OTf to 50–60 °C in the presence of Me3NO resulted in its cupric analogue [L1CuII(CH3CN)]2+, as well as a small amount of 2‐dipyridylketone, along with other oxidation by‐products. In the case of [L2CuI(CH3CN)]OTf, the reaction with Me3NO resulted in the cupric complex bis(2‐quinolinecarboxamidato)copper(II), along with 2‐dipyridylketone as oxidation products.