59: Electrochemical conversion of metallated Oligotetrapyrroles to 10,10-disubstituted Isocorroles complexes

Abstract: Tetrapyrrole derivatives have been well studied with applications in photomedicine, catalysis, and a variety of other arenas. Recent work has placed emphasis on non-aromatic tetrapyrrole scaffolds, in which the aromaticity has been disrupted by introducing a sp3-hybridized meso-carbon at the framework 10-position. One such non-traditional oligotetrapyrrole is known as the biladiene, which has been investigated as a triplet photosensitizer. In this work, we will discuss how oxidative ring closure of the biladiene results in the generation of another scaffold, named the isocorrole, which displays enhanced light absorption properties in the visible and near-IR region as well as unique redox properties. Nickel 10,10-dimethylbiladiene (Ni[DMBil1]) complexes were synthesized and found to exhibit multielectron redox behavior. These redox properties enable their electrochemical conversion to nickel 10,10-dimethylisocorroles (Ni[10-DMIC]) through a ligand-centered oxidative ring-closing pathway. To elucidate this transformation, scan-rate- and temperature-dependent cyclic voltammetry (CV) analyses, electrochemical quartz crystal microbalance (EQCM) measurements, and computational studies were performed. This work demonstrates that electrochemical, ligand-based oxidation provides a controlled method for converting biladiene to isocorrole, obviates the need for harsh oxidants, and offers mechanistic insight for designing redox-active tetrapyrrolic systems.