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Radical reactions in the co‐ordination field of transition metals. VIII —σ‐phenoxy and σ‐cyclohexadienoneoxy radicals co‐ordinated to cobalt (III) and their generation by tert ‐butylperoxy radicals or by molecular oxygen complexed to cobalt
Author(s) -
Tkáč A.,
Omelka L.
Publication year - 1980
Publication title -
organic magnetic resonance
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0030-4921
DOI - 10.1002/mrc.1270140207
Subject(s) - radical , chemistry , unpaired electron , cobalt , homolysis , photochemistry , phenols , alkoxy group , acetone , delocalized electron , phenol , intramolecular force , benzene , electron paramagnetic resonance , medicinal chemistry , organic chemistry , nuclear magnetic resonance , alkyl , physics
The formation of a ternary complex between phenols, Co (II)‐acetylacetonate and molecular oxygen has been established at ambient temperature and in non‐polar solvents. After intramolecular electron transfer the transientradical enhances the homolytic scission of the OH bond of the complexed phenol. The low g value of the observed ESR spectra, the net spin delocalization to the cobalt nucleus and the interaction of the unpaired electron with only a limited number of benzene ring protons, indicate the presence of co‐ordinated s̀‐phenoxy radicals generated from unhindered phenols ( g = 2.0006 ∼ 1.9997) and of co‐ordinated s̀‐cyclohexadienoneoxy radicals generated from hindered phenols ( g =1.9990 ∼ 1.9980). Without the cobalt‐chelating acetylacetonate ligands neither the co‐ordinated s̀‐phenoxy nor the co‐ordinated s̀‐cyclohexadienoneoxy radicals can be prepared, whereas co‐ordinated π‐ tert ‐butylperoxy radicals [Co(III)BuO 2 ·] are generated in a high concentration during the reaction of tert ‐butyl hydroperoxide with CoCl 2 in acetone.