Androgynous Porphyrins. Silver(II) Quinoxalinoporphyrins Act as Both Good Electron Donors and Acceptors

The metal-centered and macrocycle-centered electron-transfer oxidations and reductions of silver(II) porphyrins were characterized in nonaqueous media by electrochemistry, UV−vis spectroelectrochemistry, EPR spectroscopy, and DFT calculations. The investigated compounds are {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)porphyrinato}silver(II), {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)quinoxalino[2,3-b′]porphyrinato}silver(II), {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b′:7,8-b′′]porphyrinato}silver(II), and {5,10,15,20-tetrakis(3,5-di-tert-butylphenyl)bisquinoxalino[2,3-b′:12,13-b′′]porphyrinato}silver(II). The first one-electron oxidation and first one-electron reduction both occur at the metal center to produce stable compounds with Ag(III) or Ag(I) metal oxidation states, irrespective of the type of porphyrin ligand. The electrochemical HOMO−LUMO gap, determined by the difference in the first oxidation and first reduction potentials, decreases by introduction of quinoxaline gro...