Substitution in Polynuclear Complexes

Substitution reactions under ETC conditions are orders of magnitude faster than thermal substitutions in the neutral substrate. For example, reaction (18) occurs slowly and in only 10% yield after 3 h of refluxing in 

Application of a reducing potential, or addition of a small amount of benzophenone ketyl (BPK) gives 100% yield within 1 min. CO displacement from (13) by various phosphines and phosphites also occurs in high yield within 1 min when BPK is added. Another example of ETC is given in equation (19), which proceeds readily when a slight cathodic current is applied. 

Reaction (20) is unusually rapid compared to complexes containing smaller phosphines. It was shown that the rate-limiting step is not Co-Co 

The rate of ligand addition shown in equation (21) is in the following order in cyclohexane L = PBU3 (-BuNC = EtCN CO. The question of M-M bond cleavage vs. CO dissociation in the reactions of [M2(CO)io] (M = Mn or Re) has been debated for some time. It is now known that 

The substitution of E2Ph2 in (14) (E == Se or Te) by CO follows a dissociative pathway with Se Te in rate/ Photosubstitution of CO by PPh3 and P(0-i-Pr)3 in [Cp2pe2(CO)4] does not occur via [CpFe(CO)2] radicals as might be expected. Instead, (15) is postulated to be the reactive intermediate formed by photolysis that actually leads to observed products.  

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