Regioselective phenylene-fusion reactions of Ni(ii)-porphyrins controlled by an electron-withdrawing meso-substituent

Abstract

Oxidation of 10,15,20-triaryl Ni(II)-porphyrins bearing an electron-withdrawing substituent at the 5-position with DDQ and FeCl₃ gave 10,12- and 18,20-doubly phenylene-fused Ni(II)-porphyrins regioselectively. A doubly phenylene-fused meso-chloro porphyrin thus prepared was reductively coupled to give a meso–meso linked dimer, which was further converted to a quadruply phenylene-fused meso–meso, β–β, β–β triply linked Zn(II)–diporphyrin via inner-metal exchange followed by oxidation with DDQ and Sc(OTf)₃. As compared to the usual meso–meso, β–β, β–β triply linked Zn(II)-diporphyrin, this π-extended porphyrin dyad exhibits a smaller HOMO–LUMO gap and a larger two-photon absorption cross-section.