Coordination chemistry of iron porphycenes in the presence of CO, CO2, and N-methylimidazole:: Electrochemical, ESR, and UV-vis study

The electrochemical behavior of iron porphycenes in benzonitrile, tetrahydrofuran, N,N-dimethylformamide, and dichloromethane in the presence of Lewis bases is reported. This analysis combined the use of polarographic, steady-state voltammetric, cyclic voltammetric, and spectroelectrochemical methods. Iron(III) 2,7,12,17-tetra-n-propylporphycene ([Fe(III)TPrPn]Cl) is reduced in three one-electron steps and is oxidized in two one-electron steps: All the processes are reversible. The corresponding iron mu-oxo dimer [Fe(III)TPrPn](2)O undergoes four one-electron oxidations as well as four one-electron reductions. [Fe(III)TPrPn]Cl forms a stable [Fe(III)TPrPn](N-MeIm)(2)(+) complex in the presence of N-MeIm. This complex is reduced stepwise to [Fe(II)TPrPn]N-MeIm, the iron(II) radical anion [Fe(II)TPrPn(.)](-) and the iron(II) dianion [Fe(II)TPrPn](2-) as confirmed by UV-vis and ESR spectroscopy of the electrogenerated species. In the presence of CO, the seduction of iron(III) generates [Fe-II(CO)TPrPn]. In contrast to porphyrins, one- and two-electron reductions of the latter compound are shifted to more negative potentials in DMF and THF and these electron transfers remain reversible. UV-vis spectroelectrochemical experiments at an optically transparent thin layer electrode (OTTLE) demonstrate that the generated species are respectively [Fe-II(CO)TPrPn(.)](-) and [Fe-II(CO)TPrPn](2-). This redox behavior is distinctively different rom that of Fe-CO porphyrins. In the presence of CO2, electrocatalytic reduction of CO2 is observed, as for porphyrins.