Metallaantiaromaticity of 10-Platinacorrole Complexes

The aromaticity of cyclic pi-conjugated organometallic compounds is known as metallaaromaticity. pi-Conjugated metallacycles, such as metallabenzenes and metallapentalenes, have been investigated in order to understand the involvement of the d electrons from the metal center in the pi-conjugated systems of the organic ligands. Here, we report the synthesis of Pd-(II) 10-platinacorrole complexes with cyclooctadiene (COD) and norbornadiene (NBD) ligands. While the Pd-(II) 10-platinacorrole COD complex adopts a distorted structure without showing appreciable antiaromaticity, the corresponding NBD complex exhibits a distinct antiaromatic character due to its highly planar conformation. Detailed density functional theory (DFT) calculations revealed that two d orbitals are involved in macrocyclic pi-conjugation. We furthermore demonstrated that Craig-Mo''bius antiaromaticity is not present in the studied system. The synthesis of 10-platinacorroles enables a systematic comparison of the antiaromaticity and aromaticity of closely related porphyrin analogues, providing a better understanding of pi-conjugation that involves d orbitals.