Insertion, migratory involving radicals

Alkylzirconocene derivatives can be converted to alcohols with H202/NaOH, /BuOOH, or m-chloroperbenzoic acid (m-CPBA) [98], These reactions appear to involve migratory insertion processes (Pattern 14) similar to those observed with organoboranes (Scheme 1.20). On the other hand, oxidation with 02 may be a radical process. 

The enthalpy of activation for the turnover-limiting hydrogen-atom transfer step depends upon the affinity of tire anthracene substrate for free radicals. The 9,10-dihydroanthracene is formed as the product because the radical is most stable in these positions, and the mixture of stereoisomers is formed because the process does not involve migratory insertion. This mechanism also explains why simple benzene derivatives are imreactive. The 1,4-hexadienyl radical lies too far uphill of benzene and the cobalt hydride to be a product from a reaction of a catalytic cycle that occurs under mild conditions. 

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