Synthesis and Metalation of Doubly o-Phenylene-Bridged Cyclic Bis(dipyrrin)s with Highly Bent Skeleton of Dibenzoporphyrin(2.1.2.1).

Facile synthesis of dibenzoporphyrins(2.1.2.1) has been successfully reported by the simple condensation reaction of o-dipyrrolylbenzene with various aldehydes in the presence of a Lewis acid. This reaction enables the preparation of various dibenzoporphyrin(2.1.2.1) derivatives with p-substituted phenyl groups, five-membered heterocycles, and ethynyl groups at the meso-positions. Dibenzoporphyrins(2.1.2.1) consist of two dipyrrin units that are connected by o-phenylene bridges, which adopt highly bent saddle-shaped structures; this was confirmed by X-ray diffraction analysis. We found that dibenzoporphyrin(2.1.2.1) can be described as a 20π antiaromatic conjugated system, but practically, it is not an antiaromatic macrocycle, which we revealed by (1) H NMR spectroscopy. The redox potentials had good correlations with Hammett substituent constant (σp ) of the substituents at the meso-positions. The free-base dibenzoporphyrin(2.1.2.1) was able to form the metal complexes with nickel(II), copper(II), palladium(II), platinum(II), and tin(IV) ions. These results suggested that dibenzoporphyrin(2.1.2.1) derivatives can be utilized as novel macrocyclic dianionic tetradentate ligands for various metal ions to give complexes with varying optical and electrochemical properties.