Ligand effects of 2,2'-bipyridine in the decomposition of 1,2,3,4-tetrahydro-1-naphthyl hydroperoxide catalyzed by cobalt(II) salt.

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The ligand effect of 2,2′-bipyridine on the rate of the decomposition of 1,2,3,4-tetrahydro-1-naphthyl hydroperoxide catalyzed by cobalt(II) decanoate in chlorobenzene was kinetically studied and compared with the redox potentials and the spectral data of cobalt(II) complexes. The activity of the anhydrous cobalt(II) decanoate increased by a factor of from three to seven by the addition of 2,2′-bipyridine when the molar ratio of 2,2′-bipyridine to cobalt was 0.25 to 2. It was found that the catalytic activity of the anhydrous cobalt(II) decanoate-2,2′-bipyridine complex shows a remarkable maximum value at the molar ratio of 2,2′-bipyridine to cobalt of 0.5. This novel finding can be explained on the basis of the redox potential measured by cyclic voltammetry in dichloromethane, the IR data, and the structure of the catalyst. The coordination of 2,2′-bipyridine causes the redox potential to change from 0.80–0.84 V to 0.60–0.64 V (<I>vs.</I> SCE) and also weakens the Co–O(decanoate) bond strength, resulting in a facile coordination of hydroperoxide to the cobalt ion as well as the acceleration of cleavage of hydro-peroxide. The maximum activity was explained by the proposed structure of the cobalt(II) decanoate-2,2′-bipyridine (1 : 1/2) complex with a fairly low redox potential and a vacant coordination site.
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