Synthesis, structure, and modeling of a cyclic rhodium(III) porphyrin dimer with an encapsulated 4,4′-bipyridine ligand

We have shown that a covalently linked Rh(LII) porphyrin dimer with an encapsulated bipyridine ligand displays a ruffled distortion of the porphyrin units whereas complexes of monomeric Rh porphyrin with bipyridine and pyridine exhibit saddle distortions, The porphyrin distortion in the dimer is induced by the butadiyne linkers which are themselves only slightly distorted. The ligand is highly resistant to dissociation, thereby inhibiting attempts to assess the catalytic potential of the dimer. An analogous complex lacking the linker was found to have a tilted bipyridine ligand in the solid state, which appears to be a characteristic of porphyrin coordination oligomers.