Electrochemical and Spectroelectrochemical Investigations of “Figure-Eight” Octapyrrolic Macrocycles, Free Bases, and Their Mononuclear, Homo- and Heterodinuclear Complexes with Divalent Transition Metals

Abstract

This work reports on electrochemical investigations of ''figure-eight''-shaped cyclooctapyrrolic macrocycles (octaphyrins) 1−3 and of some of their mono-and dinuclear transition metal complexes. The octaphyrins 1−3 differ mainly in the size of the main conjugation pathway, which involves either 4n π-electrons for 1 and 3, or (4n + 2) π-electrons for 2. All species studied undergo six redox steps, namely two reductions and four oxidations. The two reductions and the first three oxidations are reversible one-electron transfers. The fourth oxidation is either reversible, or irreversible due to a subsequent chemical reaction. Depending on the complex studied, the third and fourth oxidations occur either at similar potentials, so that a global two-electron step is observed, or at distinct potentials, leading to two well-separated signals.

Dinuclear iridium and rhodium complexes with bridging arylimidazolide-N3,C2ligands: synthetic, structural, reactivity, electrochemical and spectroscopic studies

“…Spectroelectrochemical experiments were carried out as described elsewhere, 30 using a Zeiss MCS 601 UV-vis-NIR diode array spectrometer.…”

Bimetallic Figure‐Eight Octaphyrins Split into Four‐Pyrrolic Macrocycles

“…Representative examples of such coordination chemistry have been demonstrated by amethyrins,2 accordion porphyrins,3 N‐confused hexaphyrins,4 calix[4]pyrrole Schiff base macrocycles,5 rubyrins,6 structural analogues of Pac‐Man porphyrins,7 and other macrocycles containing a pyrrolic unit 8. Bimetallic complexes were also obtained for octaphyrins,9 and these are the primary topic of this Highlight 10–14…”

“…23 As regards to this effect, one has to be aware of the figure‐eight geometry compared to prototypical planar conjugated porphyrins or extended porphyrins. The marked influence of the size of the main conjugation pathway, which involves either 4 n π electrons for 2 and 3 or (4 n +2) π electrons for 4 , was demonstrated by the electronic spectra: a correlation between the wavelength of the most intense band versus the number of conjugated π electrons was observed for a series of species formed in the course of redox processes 10. The spectra of the (4 n +2) π‐electron species in particular exhibit an intense and sharp absorption band which reflects an intense conjugation in the ligand.…”

Expandierte Porphyrine: überraschende Strukturen, elektronische Eigenschaften und Reaktivitäten

“…Gruppe wurden Metallierungen mit Zn II am besten untersucht. Im Fall von (a) und (b) in Abbildung 10 nimmt der Makrocyclus eine verdrillte Konformation an, wie bei den achtförmigen Octaphyrinen (Abbildung 11 a, 73 ),73a, b wohingegen Koordinationen vom Typ (c) und (g) für “giebelförmige” oder planare Hexaphyrine beobachtet werden (Abbildung 11 b, 74 ) 73c. d Eine metallorganische Spezies eines expandierten Porphyrins mit einer C‐Zn‐Bindung ist nicht bekannt 74.…”