Electrochemically generated species transition metal complexes

Among the main goals of electrochemical research are the design, characterization and understanding of electrocatalytic systems, (1-2) both in solution and on electrode surfaces. (3.) Of particular importance are the nature and structure of reactive intermediates involved in the electrocatalytic reactions.(A) The nature of an electrocatalytic system can be quite varied and can include activation of the electrode surface by specific pretreatments (5-9) to generate active sites, deposition or adsorption of metallic adlayers (10-111 or transition metal complexes. (12-161 In addition the electrode can act as a simple electron shuttle to an active species in solution such as a metallo-porphyrin or phthalocyanine. 

The radical mechanism of OA occurs only for polar substrates. A free radical initiator (I) is made, typically by photolysis or electrochemical means. The initiator reacts with the metal complex to oxidize it by one electron, as shown in Figure 19.10. The species can then react with RX to generate R-. The R- radical undergoes a chain reaction with a second metal complex to make R-M " -X and another R- radical. This continues until chain termination by two R radicals coupling together or by radical trapping. The propagation step in the mechanism competes with isomerization or racemization of R-, so that the product is almost always a racemic mixture of optical isomers when a chiral C atom is used. Unlike the S 2 mechanism, the rate of the reaction is independent of steric bulk on the transition metal. Furthermore, the reaction sequence with respect to 3°>2°> I >CH3 (which maps with the... 

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