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

An investigation on the reactivity of O-2 bindingtounsymmetrical beta-diketiminato copper-(I) complexes by spectroscopicand titration analysis was performed. The length of chelating pyridylarms (pyridylmethyl arm vs pyridylethyl arm) leads to the formationof mono- or di-nuclear copper-dioxygen species at -80 degrees C.The pyridylmethyl arm adduct (L-1 CuO2) forms mononuclear copper-oxygen species and shows ligand degradation,resulting in the formation of (2E,3Z)-N-(2,6-diisopropylphenyl)-4-(((E)-pyridin-2-ylmethylene)-amino)-pent-3-en-2-imine, which slowly convertsto its cyclization isomer 1-(2,6-diisopropylphenyl)-4,6-dimethyl-2-(pyridin-2-yl)-1,2-dihydropyrimidineafter addition of NH4OH at room temperature. On the otherhand, the pyridylethyl arm adduct [(L-2 Cu)(2)(mu-O)(2)] forms dinuclear species at -80 degrees C and does not show any ligand degradation product. Instead,free ligand formation was observed after the addition of NH4OH. These experimental observations and product analysis resultsindicate that the chelating length of pyridyl arms governs the Cu/O-2 binding ratio and the ligand degradation behavior.