Comparing Isomeric Tridentate Carbazole‐Based Click Ligands: Metal Complexes and Redox Chemistry

Abstract

Two novel bis(triazolyl)carbazole ligands Hbtc1 (3,6-di(tert-butyl)-1,8-bis[(1-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-4-yl)]-9H-carbazole) and Hbtc2 (3,6-di(tert-butyl)-1,8-bis[(4-(3,5-di(tert-butyl)phenyl)-1,2,3-triazol-1-yl)]-9H-carbazole), differing in the regiochemistry of triazole attachment, have been synthesized by Cu-catalyzed azide-alkyne cycloaddition, the so-called "click-reactions". Metalation with Ru, Zn, and Ni precursors led to the formation of M(btc) complexes (M=Ru, Zn, Ni), with two deprotonated ligands coordinating to the metal center in tridentate fashion, forming almost perfectly octahedral coordination spheres. The redox properties of M(btc) complexes have been investigated by cyclic voltammetry, UV/Vis spectroscopy, spectroelectrochemistry, and chemically. The CV of the ruthenium complexes revealed three quasi-reversible one-electron oxidation processes, one assigned as the Ru couple and two originating from ligand-based oxidations. The CVs of both Zn and Ni complexes contained only two oxidation waves corresponding to the oxidation of the two ligands. The oxidation potentials of complexes derived from Hbtc1 ligands were found to be 300-400 mV lower than those of the corresponding complexes derived from Hbtc2, reflecting the significant difference in donation through the N(2) or N(3) atom of the triazole moiety.

Carbenaporphyrine: eine Lücke in der Chemie N‐heterocyclischer Carbene schließt sich

“…Der Schlüsselschritt der Synthese ist die kupferkatalysierte Alkin‐Azid‐Cycloaddition (CuAAC), [26] die so genannte “Klick”‐Reaktion, [27] bei der beide Triazoleinheiten unter Bildung des Makrocyclus aufgebaut werden. Sowohl das Alkin 3 als auch das Azid 4 sind literaturbekannt und können aus dem Carbazol 2 erhalten werden [28, 29] . Die Herstellung des Azids aus 1,8‐Dibromcarbazol gemäß der Literatur verlief in unseren Händen nicht erfolgreich [29] .…”

Oxygen‐Depleted Calixarenes as Ligands for Molecular Models of Galactose Oxidase

“…The different appearances of the three CVs can then be explained by the different degrees of electronic delocalization and communication after the first oxidation event: the electronic communication between the oxidized and the remaining second phenolate cannot be mediated effectively by the central ion in the case of zinc because of its completely filled d 10 configuration, leading to two oxidations at potentials that do not differ significantly; indeed there are also examples reported in which both electrons are removed simultaneously . The communication can be facilitated by the open‐shell 3d metal ions nickel(II) and copper(II), so that the removal of a second electron is affected more significantly .…”

Erich‐Hückel‐Preis: H.‐J. Werner / Hermann‐Staudinger‐Preis: B. Voit / Alfred‐Stock‐Gedächtnispreis: C. Limberg / Janssen Prize for Creativity in Organic Synthesis: F. D. Toste / EurJIC und EurJOC im 20. Jahrgang

“…Limberg interessiert sich für die Aktivierung kleiner Moleküle, für molekulare Metalloxide und für Moleküle mit ungewöhnlichen Metall‐Metall‐Wechselwirkungen. In Chemistry—A European Journal berichtete er über isomere Carbazol‐basierte Klick‐Liganden und in der Angewandten Chemie über einen Ni‐CO 2 2− ‐Komplex . Limberg ist einer der drei Herausgeber der Zeitschrift für anorganische und allgemeine Chemie .…”