Redox cycle turnover efficiency

The reoxidation rate of the reduced metal is important in an efficient catalyst system. The metal-centered catalyst may have the proper redox potential for O2 oxidation, but if the rate of catalyst decomposition is competitive, then loss of the active catalyst results. To overcome issues of low turnover number (TON) and turnover frequency (TOE), added reagents are often used to couple multiple catalytic cycles in a biomimetic fashion [18]. Transition metals known to activate O2 based on biological precedence are commonly used as coupling reagents, including Cu(II), Co(II), Ee(II) and Mn(II) [2]. Many other organic molecules, such as quinones and catechols, can also act as redox couples. 

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