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

m-Benziporphyrin(1.1.0.0) and mpyreniporphyrin(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 mpyreniporphyrin(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 pyrenesharing 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.