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 (-CH₂CH₂Py) group, were synthesized and structurally characterized. Reaction of the copper(II) complexes and cumene hydroperoxide (CmOOH) in the presence of triethylamine in CH₃CN gave the corresponding cumylperoxide complexes L8Cu^IIOOCm and L7Cu^IIOOCm. The UV-vis and EPR spectra suggested that L8Cu^IIOOCm takes a tetrahedrally distorted structure, whereas L7Cu^IIOOCm has a planar geometry in solution. Resonance Raman spectra of these alkylperoxide complexes indicated that the O-O stretching vibration energy of L8Cu^IIOOCm (ν_O-O=878cm^-1) is somewhat lower than that of L7Cu^IIOOCm (ν_O-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 L8Cu^IIOOCm toward CHD (1,4-cyclohexadiene) as well as solvent molecule (CH₃CN) is higher than that of L7Cu^IIOOCm 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.