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 Pd 0 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.