Precedents for Metal Activation of Organic Substrates

In the presence of molecular oxygen and Co(II) or Co(III)salpr complexes, hindered phenols (11) are converted into peroxy-o-quinolato (13) or peroxy-/ -quinolato-Co(III) complexes (14) depending on the 

As cobalt complex-mediated oxygenation of these hindered phenols (11) occurs 30 times faster than base-catalyzed oxygenation 62), the phenolato Co(III) complex (12) evidently possesses special activation for reaction with molecular oxygen. In keeping with the desirability of a localized, soft anionic center in an oxygenase substrate, we can only assume that the metal is able to localize the n-anionic charge into an orbital with more [sp ] character. 

The essential point which is demonstrated by these examples is that, first, the oxygen is not activated by the cobalt complex, but the substrate is, and second, the metal does something more than impart radical character. We maintain that soft anion character is engendered in these substrates. As we will see later, these examples constitute valid precedents for substrate activation . 

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