Electrochemical studies of corrphycenes and metallocorrphycenes

Corrphycene 3 (Cn) is a structural isomer of porphyrin 1 that was synthesiz ed for the first time 5 years ago. This paper reports on the redox properti es of free-base octaethylcorrphycene E(2)OECn and 16 metal complexes derive d therefrom. In CH2Cl2 solution, the free base and the metallo(II) octaethy lcorrphycenes, M(II)OECn, typically undergo four distinct one-electron redo x steps involving the tetrapyrrolic macrocycle, of which two are reduction steps and two are oxidations. One exception to this general pattern is disp layed by the Co(II)OECn complex. In this instance, the first one-electron r eduction is metal-centered and produces Co(I)OECn. A comparison of the redo x potentials of corrphycenes with those of porphyrins and porphycenes indic ates that the first reduction potentials of the free base and of the metall o-octaethylcorrphycenes are between those of the porphycenes-the easiest to reduce molecules in this set of isomeric tetrapyrrolic systems-and those o f the porphyrins. The oxidation potentials of corrphycenes and porphyrins a re found to be quite similar. On the other hand, porphycenes are oxidized a t less positive potentials. The redox gap Delta E-1/2 = E(1/2)(Ox)1 - E(1/2 )(Red)1 is equal to 2.15 +/- 0.08 V for the free base corrphycene and the v arious metallocorrphycenes that were subjected to study. This redox gap is not much different from that observed in porphyrins (Delta E-1/2 = 2.25 +/- 0.1 V), whereas if differs significantly from that observed in porphycenes (Delta E-1/2 = 1.85 +/- 0.15 V). The sequence of these Delta E-1/2 values parallels the lowest energy absorption maxima observed in the UV-vis spectr a of these three isomers.