Phenoxyl radical metal complexes compounds

The most thoroughly studied class of phenoxyl radical complexes was prepared by oxidation of first-row transition metal complexes of the type of macrocyclic phenolate ligands shown in Figure 4. Studies of those compounds that contain Ga , Sc , and have been particularly useful for differentiating and establishing the properties of coordinated vs. uncoordinated phenoxyl radicals. Due to their closed shell nature, these ions are both spectroscopically silent and redox inactive, thus enabling the properties of phenoxyl radicals in their complexes to be seen unmasked from those of the metal ion. Data for oxidized forms of the complexes [L M] ((l)-(4) are illustrative). These compounds undergo three reversible one-electron oxidations at approximately equally spaced... 

A number of ligands comprising protected phenols, exemplified by (30) and (31), have been complexed to metal ions and oxidized in attempts to generate compounds with uncoordinated phenoxyl radicals. In most cases, UV-vis, IR, and/or EPR spectroscopic evidence was provided in support of phenoxyl radical formation, but in few cases were the compounds isolated as pure solids, and no X-ray structural data is available. A survey of these systems has been published. ... 

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