Dioxygen activation using schiff base macrocyclic dinuclear copper(I) complexes: Structurally characterized dioxygen reaction products

Schiff-base condensation of diethylenetriamine with a series of dialdehydes [isophthalaldehyde (2a), 5-tert-butylisophthalaldehyde (2b), 2-methylisophthalaldehyde (2c), and p-phthalaldehyde (2d)] affords four hexaaza macrocyclic ligands [L^H,H (3a), L^tBu,H (3b), L^H,Me (3c), L^p-H,H (3d)] bearing different substituents on the aromatic units that connect the two metal ion binding sites. The dinuclear copper(I) complexes [L^H,HCu₂(MeCN)₂] (ClO₄)₂ (4a), [L^tBu,HCu₂(MeCN)₂] (ClO₄)₂ (4b), [L^H,MeCu₂(MeCN)₂] (ClO₄)₂ (4c), and [L^p-H,HCu₂(MeCN)₂] (CF₃SO₃)₂ (4d) are obtained in good yields by reaction with Cu¹ salts, X-ray diffraction studies performed on 4a and 4d reveal a distorted tetrahedral coordination geometry around each Cu^Iion, which is constructed by three nitrogen donors of the macrocyclic ligand and one acetonitrile solvent molecule. Treatment of these complexes with molecular dioxygen shows that their reactivity can be fine-tuned by the nature of the aromatic unit of the dialdehyde building blocks. Thus two different dinuclear Cu^II complexes resulting from the reaction of 4a and 4b with dioxygen were isolated and characterized by single crystal X-ray diffraction, XPS and magnetic measurements. The introduction of a methyl group in the 2-position of the aromatic spacers in 4c hinders such oxygen transfer reactions but may allow the characterization of stable dioxygen binding species.