über zweistufige Redoxsysteme, VII. Polarographie und Spektroskopie heterocyclischer Azine und ihrer höheren Oxydationsstufen

Abstract

Die Polarographie der heterocyclischen Redoxsysteme 6-10,14 und 15 zeigt reversible zweistufige Einelektroneniibergange mit Semichinonbildungskonstanten K M 107-1010 (6-10) bzw. -104 (14) und 120 (15) [Abbildung 61. Der SubstituenteneinfluD auf K und die Lage der Potentiale werden besprochen. Die Elektronenspektren von 6-10, 14 und 15 in ihren Oxydationsstufen RED, SEM und OX werden verglichen (Tabelle 3). Two-step Redox Systems, VII 1). Polarography and Spectroscopy of Heterocyclic Azines and their Higher Oxidation LevelsThe polarography of the heterocyclic redox systems 6-10, 14 and 15 reveals reversible oneelectron transfers in two steps. Semiquinone formation constants K are = lO7-lO10 (6-lo), In friiheren Untersuchungen haben sich die heterocyclischen Azine 15) und 2 -56) als vorzuglich reversible Redoxsysteme erwiesen. Sie tauschen in zwei deutlich getrennten Stufen El und E2 je ein Elektron aus, so daB Semichinonbildungskonstanten K von 106-1010 beobachtet werden und sich haufig alle drei Oxydationsstufen in Substanz darstellen oder wenigstens optisch messen lassen.Um den Existenzbereich derartiger Redoxsysteme kennenzulernen, wurden die in der voranstehenden Mitteilung 1) beschriebenen Azine 6 -13 und die Azoverbindungen

N-Heterocyclic Carbene Adducts of Main Group Elements and Their Use as Ligands in Transition Metal Chemistry

“…In addition, several electron-rich tetrakis- and even hexakis­(guanidino) benzene systems such as 331 and 332 were prepared by the Himmel group ,− and used as redox-active compounds with multistage redox behavior or as ligands for the preparation of coordination polymers. Another peculiar example is the urea azine 333 , which resembles the heterocyclic 2,2′-azines already described by Hünig and co-workers between 1964 and 1971. − 333 was obtained from the reaction of 2-chloro-1,3-dimethylimidazolium chloride and hydrazine hydrate, and it can be formally perceived as the lightest N-heterocyclic group 15 dicarbene–dielement complex. , Similar to Hünig’s azines, 333 represents a two-stage redox systems, which can be reversibly oxidzed to the corresponding radical cation and dication, and its reactivity toward ZnCl 2 , CoCl 2 , and CuCl 2 was also studied. , The latest additions to the family of chelating imidazolidine ligands stems from the Eisen group, who introduced imidazolidin-2-imine-aryloxide ligands of type 334 , which were used for the preparation of Ni­(II) and Pd­(II) complexes [( 334 )­M­(PPh 3 )­R] (M = Ni, R = Ph; M = Pd, R = Me) …”

Charge transfer complexes and cation radical salts of azino-diselenadiazafulvalene

“…In order to prepare the symmetrical azino-DSeDAF 1, we followed Hünig's strategy which consists of the reaction of quaternary heterocyclic salts with a half equivalent of hydrazine in a basic medium (Scheme 1) [3]. First, we prepared 3-methyl-2-methylthio-benzoselenazolium salt 3 from 2-methylthio-benzoselenazole 2 [6] with a new one-step approach in 91% yield.…”

“…Among the numerous variations realized on the fulvalene skeleton, the insertion of a conjugated spacer group such as an azino one between the two heterocyclic cores gave rise to an interesting family of compounds known as heterocyclic azines [2]. Hünig et al developed this strategy some years ago and showed that these derivatives present two monoelectronic oxidation waves with excellent reversibility [3]. Additionally, the presence of an azino spacer group increases the window potential stability of the cation radical species.…”