Synthesis, Structure, Spectral and Electrochemical Properties of [20]Dioxahomoporphyrins and ­Covalently Linked Dioxahomoporphyrin–Porphyrin Dyads

A series of new [20]dioxahomoporphyrins have been synthesized by [2+2] condensation of (but-2-ene-2,3-diyldifuran-2,5-diyl)bis(p-methoxyphenylmethanol) with appropriate meso-aryldipyrromethanes under mild acid-catalyzed conditions. The X-ray structure determined for one of the dioxahomoporphyrins revealed that the macrocycle is significantly distorted and the two furan rings are completely out-of-plane from the mean plane. The [20]dioxahomoporphyrin macrocycles are stable and non-aromatic, and have been characterized in detail by HRMS, 1D and 2D NMR spectroscopy, UV/Vis spectrophotometry and electrochemical techniques. The iodo-functionalized [20]dioxahomoporphyrin was used to synthesize a covalently linked diphenylethyne-bridged [20]dioxahomoporphyrin–porphyrin dyad by coupling with an ethynyl-functionalized porphyrin under mild copper-free Pd0 catalytic conditions. The metallation of the porphyrin macrocycle of the [20]dioxahomoporphyrin–porphyrin dyad was carried out by treating the dyad with the appropriate metal salt under standard conditions and the resulting [20]dioxahomoporphyrin–metalloporphyrin dyads were characterized by various spectral and electrochemical techniques. The results of the studies indicated that in the dyads the dioxahomoporphyrin and porphyrin/metalloporphyrin units interact weakly and retain their individual features.