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

Oxidation of 10,15,20-triaryl Ni(ii)-porphyrins bearing an electron-withdrawing substituent at the 5-position with DDQ and FeCl(3) 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.