ELECTROCHEMICALLY INDUCED AROMATIC NUCLEOPHILIC-SUBSTITUTION WITH [(ETA(5)-C5H5)FE(CO)2]- AND [(ETA(5)-C5H5)MO(CO)3]- ANIONS

The reaction of low S(N)(Ar)-active and non-active aryl halides p-XC6H4Hal (X = CH3, H, Cl, COCH3, CN or NO2; Hal = I or Br) with [(eta5-C5H5)Fe(CO)2]- and [(eta5-C5H5)Mo(CO)3]- is studied using a number of electrochemical methods (cyclic voltammetry, rotating-ring-disk-electrode technique and preparative-scale electrolysis). It is shown that the electrode catalysis enables one to carry out aromatic nucleophilic substitution which generally leads to sigma-aryl derivatives of (eta5-cyclopentadienyl) irondicarbonyl. Nevertheless, a detailed study of the mechanism of the reduction and oxidation of [(eta5-C5H5)Fe(CO)2C6H4X-p] at a Pt electrode reveals that the irreversibility of their reduction processes imposes certain restrictions on performing electrode-initiated aromatic nucleophilic substitution. This results in the occurrence of the ''electrochemical activation window'', i.e. limitation of the potential region where electrochemically induced aromatic nucleophilic substitution is possible. For the [(eta5-C5H5)Mo(CO)3]- anion, we failed to obtain its sigma-aryl derivatives using electrochemical activation of aryl halides. The main product of the reaction is (eta5-C5H5)Mo(CO)3Hal.