A vitamin B12 derivative, heptapropyl cobyrinate perchlorate, was readily trapped onto an indium tin oxide (ITO) electrode by a sol–gel reaction. The complex was physically retained in a silica gel film which is formed on an ITO electrode. The thickness of the film could be controlled by the withdrawing speed of the dip coating process. Formation of a sol–gel film was confirmed by SEM measurements, and the total amount of the complex in the film was determined by UV–VIS absorption spectra. The complex exhibits the CoII/CoI redox couple at −0.42 V vs. Ag–AgCl. The amount of the electroactive complex in the sol–gel film deduced from electrochemical measurements is 3.0 × 10−11 and 6.2 × 10−11 mol cm−2 for thicknesses of 170 and 330 nm, respectively. This electroactive complex shows a high reactivity towards organic halides, and the controlled-potential electrolysis of benzyl bromide using the sol–gel modified electrode at −1.20 V vs. Ag–AgCl in aqueous solution containing 0.1 M KCl afforded dehalogenated products, bibenzyl and toluene, with a total turnover number of >1000 for 1 h.
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