Electrochemically induced aromatic nucleophilic substitution with [(η 5-C 5H 5)Fe(CO) 2] − and [(η 5-C 5H 5Mo(CO) 3] − anions

Abstract

The reaction of low S N(Ar)-active and non-active aryl halides p-XC 6H 4Hal (X  CH 3, H, Cl, COCH 3, CN or NO 2; Hal  I or Br) with [(η 5-C 5H 5)Fe(CO) 2] − and [(η 5-C 5H 5)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 σ-aryl derivatives of (η 5-cyclopentadienyl) irondicarbonyl. Nevertheless, a detailed study of the mechanism of the reduction and oxidation of [(η 5-C 5H 5)Fe(CO) 2C 6H 4X- 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 [(η 5-C 5H 5)Mo(CO) 3] − anion, we failed to obtain its σ-aryl derivatives using electrochemical activation of aryl halides. The main product of the reaction is (η 5-C 5H 5)Mo(CO) 3Hal.