Synthesis, Electrochemical Behavior, and Catalytic Activity of Cobalt Complexes of 5,15-Diazaporphyrin and 5-Monoazaporphyrin Derivatives Bearing Meso-Aryl Groups.

Abstract

Cobalt (Co) complexes of porphyrin derivatives possess distinctive redox properties, and hence, their development has attracted significant interest across a wide range of fields. Herein, we report the new examples of the Co complexes of 5,15-diazaporphyrin (DAP) and 5-monoazaporphyrin (MAP) derivatives bearing meso-aryl groups. These Co complexes were prepared by metal-templated cyclization of Co-bis(dipyrrin) complexes, complexation of azaporphyrin freebases with a Co salt, and meso-N-functionalization of the Co complexes of DAP and MAP with diphenyliodonium hexafluorophosphate or methyl triflate. The structures as well as the optical and redox properties of these new Co complexes were elucidated by X-ray crystallography, spectroscopic and voltammetric measurements, and density functional theory calculations. The introduction of a positive charge to the DAP and MAP rings via meso-N-functionalization considerably altered the frontier-orbital energies, resulting in redshifts of the Q bands and anodic shifts of the ligand-centered redox processes. The addition of axial ligands also had notable effects on the metal-centered and ligand-centered redox processes. All the Co^II complexes catalyzed the intramolecular radical cyclization and 1,2-H-shift reactions of N-benzyl-N-Boc-3-diazopropane-1-amine in the presence of Cs₂CO₃ to yield two kinds of products via the corresponding σ-bonded alkyl Co-azaporphyrin intermediates.