m‐Benziporphyrin(1.1.0.0)s as a Rare Example of Ring‐Contracted Carbaporphyrins with Metal‐Coordination Ability: Distorted Coordination Structures and Small HOMO‐LUMO Gaps

Abstract

m‐Benziporphyrin(1.1.0.0) and m‐pyreniporphyrin(1.1.0.0) were prepared as ring‐contracted carbaporphyrins. While m‐Benziporphyrin(1.1.0.0) was unstable, m‐pyreniporphyrin(1.1.0.0) was fairly stable. Both of their Pd ^II complexes showed distorted coordination structures with extremely short Pd−C bonds. As compared with the reported m‐benziporphyrin Pd ^II complexes, these Pd ^II complexes showed considerably small HOMO‐LUMO gaps, despite their smaller molecular size. Pd ^II metalation of the m‐pyreniporphyrin(1.1.0.0) dimer gave the corresponding Pd ^II complex, which showed similar distorted coordination and a smaller HOMO‐LUMO gap. Finally, Pd ^II metalation of a pyrene‐sharing formal p‐benziporphyrin(1.1.1.1) dimer gave a nonaromatic Pd ^II dimer, which rearranged to an aromatic Pd ^II complex upon treatment with alumina.