Electrochemical and spectroelectrochemical studies of β-phosphorylated Zn porphyrins

The electrochemical and spectroelectrochemical properties of two beta-phosphorylated Zn porphyrins, [2-diethoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (1) and [2-diisopropoxyphosphoryl-5,10,15,20-tetraphenylporphyrinato]zinc (2), are reported in CH2Cl2 and PhCN containing tetrabutylammonium perchlorate (TBAP) or tetrabutylammonium hexafluorophosphate (TBAPF6) as supporting electrolyte. Under certain solution conditions, three one-electron reductions are observed, with the last process being attributed to the product of a chemical reaction following formation of the porphyrin dianion. Two or three oxidations are observed for the same compounds, again depending upon the solution conditions. In some cases, two well-defined and well-separated one electron oxidations are observed but in others the first one-electron abstraction to give the porphyrin radical cation is split into two redox processes, separated from each other by 110-140 mV. This splitting of the first oxidation into two processes is attributed to linking of the two porphyrins which results when a P=O unit of the phosphoryl substituent on one porphyrin binds to the Zn(II) center of a second porphyrin, resulting in dimer formation. The interaction between the two macrocycles is discussed in terms of the difference in potentials between the two split redox processes (Delta E-1/2) and the overall data is compared with that for other porphyrin dimers and bis-macrocycles reported in the literature.