Ligand Degradation Study of Unsymmetrical β-Diketiminato Copper Dioxygen Adducts: The Length Chelating Arm Effect.

An investigation on the reactivity of O binding to unsymmetrical β-diketiminato copper(I) complexes by spectroscopic and titration analysis was performed. The length of chelating pyridyl arms (pyridylmethyl arm vs pyridylethyl arm) leads to the formation of mono- or di-nuclear copper-dioxygen species at -80 °C. The pyridylmethyl arm adduct (CuO) forms mononuclear copper-oxygen species and shows ligand degradation, resulting in the formation of (2,3)--(2,6-diisopropylphenyl)-4-((()-pyridin-2-ylmethylene)amino)pent-3-en-2-imine, which slowly converts to its cyclization isomer 1-(2,6-diisopropylphenyl)-4,6-dimethyl-2-(pyridin-2-yl)-1,2-dihydropyrimidine after addition of NHOH at room temperature. On the other hand, the pyridylethyl arm adduct [(Cu)(μ-O)] forms dinuclear species at -80 °C and does not show any ligand degradation product. Instead, free ligand formation was observed after the addition of NHOH. These experimental observations and product analysis results indicate that the chelating length of pyridyl arms governs the Cu/O binding ratio and the ligand degradation behavior.