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] ( L 1 ) and [N,N-bis(2-quinolylmethyl)-N-bis(2-pyridyl)methylamine] ( L 2 ) were employed to prepare Cu II and Cu I complexes for spectroscopic and structural characterization. [ L 1 Cu II (H 2 O)](NO 3 ) 2 and [ L 2 Cu II (NO 3 )]NO 3 have Jahn-Teller distorted octahedral geometries, and give rise to isotropic EPR spectra in frozen solution. [ L 1 Cu I (CH 3 CN)]OTf and [ L 2 Cu I (CH 3 CN)]OTf have distorted trigonal bipyramidal and tetrahedral solid-state structures, respectively. The N-donors display labile behavior in solution, based on variable-temperature 1 H NMR studies. Addition of trimethylamine N-oxide (Me 3 NO) to solutions of [ L 1 Cu I (CH 3 CN)]OTf and [ L 2 Cu I (CH 3 CN)]OTf resulted in diamagnetic species tentatively assigned as the corresponding adducts upon replacement of coordinated acetonitrile, based on 1 H NMR spectroscopy. Heating [ L 1 Cu I (CH 3 CN)]OTf to 50-60 °C in the presence of Me 3 NO resulted in its cupric analogue [ L 1 Cu II (CH 3 CN)] 2+ , as well as a small amount of 2-dipyridylketone, along with other oxidation byproducts. In the case of [ L 2 Cu I (CH 3 CN)]OTf, the reaction with Me 3 NO resulted in the cupric complex bis(2-quinolinecarboxamidato)copper(II), along with 2-dipyridylketone as oxidation products.