Nucleophilic attack bimolecular transfer

The reductions are usually bimolecular and are believed to take place by electron transfer at an activated complex resulting from attack of these nucleophiles at a coordinated ligand. Iodide, bromide, and thiocyanate commonly behave in this way. Scheme 10 outlines the interactions (138a). Quite often, ligand substitutions precede or compete with the reduction processes, which might then take place at several substitution products (138). 

The Gibbs energy profile involved in formation of the transition state for atom transfer is that shown in fig. 7.3. When the attacking nucleophile is the same as the leaving group, then the profile is that for a homonuclear bimolecular reaction. This type of system can be studied using radioactive isotopes. 

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