Selective oxidative synthesis of meso-beta fused porphyrin dimers

An efficient route to meso-β doubly connected fused porphyrin dimers was developed. Synthesis of the dimers incorporated two successive C-C bond-forming steps selectively coupling unsubstituted meso-and β-positions. Using Cu(BF₄)₂ as an oxidant in nitromethane solvent, the radical coupling of Cu(II)-porphyrins occurred in high yield and without side-products, allowing chromatography-free purification. Efficient demetalation of the product yielded free-base derivatives and the possibility to incorporate other metals into the macrocycles. The absorption and electrochemical properties vary with the inserted metal, showing broad UV-visible-NIR absorption and multiple one-electron oxidations/reductions in a relatively narrow electrochemical window.