Electrochemistry of Bis(pyridine)cobalt (Nitrophenyl)corroles in Nonaqueous Media

Abstract

A series of bis(pyridine)cobalt corroles with one or three nitrophenyl groups on the meso positions of the corrole macrocycle were synthesized and characterized as to their electrochemical and spectroscopic properties in dichloromethane, benzonitrile, and pyridine. The potentials for each electrode reaction were measured by cyclic voltammetry and the electron-transfer mechanisms evaluated by analysis of the electrochemical data combined with UV-visible spectra of the neutral, electroreduced, and electroxidized forms of the corroles. The proposed electronic configurations of the initial compounds and the prevailing redox reactions involving the electroactive central cobalt ion, the electroactive conjugated macrocycle, and the electroactive meso-nitrophenyl groups are all discussed in terms of solvent binding and the number of the nitrophenyl groups and other substituents on the meso-nitrophenyl rings of the compounds.

Cobalt Corroles with Bis‐Ammonia or Mono‐DMSO Axial Ligands. Electrochemical, Spectroscopic Characterizations and Ligand Binding Properties

“…There is also a shoulder on the Soret band at about 414–417 nm. These spectra are similar to previously reported UV/Vis spectra for a related series of mono‐DMSO ligated cobalt nitrophenylcorroles under the same solution conditions …”

“…As seen in Figure , b, the UV/Visible spectrum of each bis‐NH 3 derivative is characterized by a split Soret band and two or three visible bands, the most intense of which is located at 615–628 nm and is considered as a marker band for the hexacoordinate Co III corrole. The overall spectral patterns of the 1NH 3 to 4NH 3 derivatives are similar to spectral patterns earlier reported for structurally related cobalt corroles containing two axially bound pyridine ligands …”

“…It should be noted that 1DMSO is the only cobalt corrole among the currently investigated compounds which possesses six electron‐withdrawing substituents on the meso ‐phenyl rings, and this seems to facilitate the binding of a second DMSO molecule to the cobalt center of the neutral compound. Stronger pyridine binding constants were also earlier reported for cobalt corroles with electron‐withdrawing substituents on the meso ‐phenyl rings …”

“…Recently, we reported the synthesis and electrochemical characterization of nitrophenyl‐substituted cobalt corroles axially ligated with DMSO or pyridine molecules in their air‐stable form , . The current manuscript is an expansion of these studies and characterizes in greater detail the properties of cobalt corroles with a single DMSO axial ligand or two NH 3 axial ligands in their air‐stable form.…”

“…Particularly, cobalt corroles exhibit a rich redox chemistry which depends on both the type of macrocycle and axial coordination at the cobalt metal center. Electron‐withdrawing groups anchored at the periphery of the macrocyclic core will also change electron density at the cobalt central metal ion, thus directly affecting the magnitude and degree of axial coordination …”