Unexpected but convenient synthesis of soluble meso-tetrakis(3,4-benzoquinone)-substituted porphyrins

A new route to 3,4-benzoquinone-substituted porphyrins is reported. In attempted nitration reactions on the copper(II) or nickel(II) complexes of 5,10,15,20-tetrakis(3,5-di-t-butyl-4-hydroxyphenyl) porphyrin using lithium nitrate in acetic anhydride-acetic acid/chloroform no nitration products could be detected with the main products being the corresponding complexes of 5,10,15,20-tetrakis(3,4-dioxo-5-t-butylcyclohexa-1,5-dienyl) porphyrin. These o-quinone-substituted porphyrins are available in reasonable yield (> 50%), their synthesis is simple and they are of good solubility. The electrochemical and spectroelectrochemical properties of representative o-quinone-substituted Cu(II) and Ni(II) porphyrin derivatives are also reported.