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

Copper(II) complexes supported by N-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 (-CHCHPy) group, were synthesized and structurally characterized. Reaction of the copper(II) complexes and cumene hydroperoxide (CmOOH) in the presence of triethylamine in CHCN gave the corresponding cumylperoxide complexes L8CuOOCm and L7CuOOCm. The UV-vis and EPR spectra suggested that L8CuOOCm takes a tetrahedrally distorted structure, whereas L7CuOOCm has a planar geometry in solution. Resonance Raman spectra of these alkylperoxide complexes indicated that the O-O stretching vibration energy of L8CuOOCm (ν=878cm) is somewhat lower than that of L7CuOOCm (ν=881cm). Such a difference in O-O bond strength is reflected to the reactivity difference of these two alkylperoxide complexes. Namely, the reactivity L8CuOOCm toward CHD (1,4-cyclohexadiene) as well as solvent molecule (CHCN) is higher than that of L7CuOOCm 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.