ELECTRODE-REACTIONS OF P-OXO IRON(III) PORPHYCENE DIMERS - FORMATION OF STABLE [[(PC)FE]O-2](N) COMPLEXES WHERE N=-4 TO +4

This paper reports the first detailed electrochemistry of iron(III) mu -oxo porphycene dimers. The investigated compounds are represented as [(Pc)Fe]O-2 where Pc = the dianion of octaethylporphycene (OEPc), etio porphycene (EtioPc), tetrapropylporphycene (TPrPc) or tetra-tert-butyl porphycene (TBuPc). Each derivative undergoes four reversible one-elec tron reductions and four reversible one-electron oxidations, and this data is compared to that of the related iron(III) porphyrin mu-oxo dim ers which in non-aqueous media may undergo up to four one-electron oxi dations but only a single reversible one-electron reduction. The site of electroreduction during the first two one-electron transfers of [(P c)Fe]O-2 was evaluated utilizing thin-layer UV-visible spectroelectroc hemistry and indicated the stepwise addition of two electrons to the c onjugated pi-ring system of the porphycene rather than to the Fe(III) metal ions of the mu-oxo dimer. Comparisons are made between the elect rochemistry and UV-visible spectra of electroreduced [(EtioPc)Fe]O-2 a nd a related mu-oxo porphycene dimer possessing the same macrocycle bu t electroinactive metal ions, [(EtioPc)Al]O-2, as well as between dime ric [(OEPc)Fe]O-2 and monomeric (OEPc)FeCl. This data is self-consiste nt and clearly indicates that the first two reductions of [(Pc)Fe]O-2 occur at the porphycene macrocycle rather than at the Fe(III) center a s has been suggested for iron Il-oxo porphyrin dimers. The difference in reductive electrochemistry between [(Pc)Fe]O-2 and [(P)Fe]O-2 (wher e P = the dianion of a porphyrin ring) is interpreted in terms of diff erent sites of electron transfer and a lowering of the LUMO energy lev el.