Geometric effects on OO bond scission of copper(II)-alkylperoxide complexes.

Copper(II) complexes supported by N3 -tridentate ligands, consisting of a rigid cyclic diamine (8-membered cyclic-diamine; L8 or 7-membered cyclic-diamine; L7) and a 2-(2-pyridyl)ethyl (-CH2 CH2 Py) group, were synthesized and structurally characterized. Reaction of the copper(II) complexes and cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH3 CN gave the corresponding cumylperoxide complexes L8CuII OOCm and L7CuII OOCm. The UV-vis and EPR spectra suggested that L8CuII OOCm takes a tetrahedrally distorted structure, whereas L7CuII OOCm has a planar geometry in solution. Resonance Raman spectra of these alkylperoxide complexes indicated that the O-O stretching vibration energy of L8CuII OOCm (νO-O =878cm-1 ) is somewhat lower than that of L7CuII OOCm (νO-O =881cm-1 ). Such a difference in O-O bond strength is reflected to the reactivity difference of these two alkylperoxide complexes. Namely, the reactivity L8CuII OOCm toward CHD (1,4-cyclohexadiene) as well as solvent molecule (CH3 CN) is higher than that of L7CuII OOCm due to the weaker O-O bond of the former complex as compared to that of the latter complex. Geometric effects on the reactivity induced by the supporting ligands are discussed.