Nonclassical Oxygen Atom Transfer Reactions of Oxomolybdenum(VI) Bis(Catecholate)


Mechanistic studies indicate that the oxomolybdenum(VI) bis(3,5-di-tert-butylcatecholate) fragment deoxygenates pyridine-N-oxides in a reaction where the oxygen is delivered to molyb-denum but the electrons for substrate reduction are drawn from the bound catecholate ligands, forming 3,5-di-tert-butyl-1,2-benzoquinone. Inner-sphere redox reactions involve both changes in oxida-tion state and changes in bonding. Classically, in reactions such as the oxygen atom transfer (OAT) 1 reaction depicted in eqn (1a), the changes in oxidation state and those in bonding are co-localized: molybdenum is both oxidized and forms a new bond to oxygen, while nitrogen is reduced and the N– O bond is broken. Co-localization is not, however, obligatory. For example, in complexes with redox-active ligands, bonding changes may take place at a redox-inert metal center while the corresponding changes in oxidation state take place at the coordinated ligand (eqn (1b)). The most thoroughly studied example of such a ‘ʼnon-classical’’ inner-sphere redox reaction is proton-coupled electron transfer (PCET), where the motion of the hydrogen nucleus may be quite separated from the motion of the electron. 2 In contrast to PCET, nonclassical OAT (eqn (1b)) would be a two-electron redox process. ð 1aÞ

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