Redox Effects and Interchange Substitution

Two ways to make a coordination inert 18e complex give fast substitution are oxidation or reduction to a coordination labile 17e or 19e 

With an electron in an M-L a orbital, 19e species are much more dissociatively labile than their 18e counterparts. For example, Fe(CO)5 can be substituted with electrochemical catalysis by a D mechanism, where 19e [Fe(CO)5]- is the chain carrier in the catalytic cycle of Eq. 4.39. The initial product radical reduces the starting Fe(CO)5 so the cycle can continue. 

Similarly, oxidation of a (f 18e complex gives a coordination labile 

Theraial M-M bond cleavage of L M-ML or abstraction of X from L M-X by a radical initiator, Q, also provide ways of accessing sub-stitutionally labile 17e ML intermediates. 

Certain soft nucleophiles show a second-order, A component for substitution of Mo(CO)6, a molecule that cannot rearrange to avoid 20e on 1 binding. Although 20e intermediates are not favored, a 20e transition state seems possible. An intermediate has to survive for many molecular vibrations, while a transition state need only survive for one s). Although both L and L bind simultaneously to the 

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