Synthesis of New Hybrid Hydroquinone/Cobalt Schiff Base Catalysts: Efficient Electron‐Transfer Mediators in Aerobic Oxidation

Abstract

Cultivating hybrids: The synthesis of new hybrid aerobic oxidation catalysts that include an oxygen‐activating motif and a hydroquinone is reported. These hybrid catalysts proved to be efficient for the aerobic reoxidation of palladium and ruthenium catalysts in a set of test oxidations (see graphic).

Redox‐Active Ligands in Catalysis

“…Covalently linking the hydroquinone, 20 with the metal complex further contributes to lowering the activation energy of the oxidation process, thereby highlighting the importance of a suitably positioned second coordination sphere redox-active moiety in catalysis (Scheme 9). [33] N-heterocyclic carbene ligands (NHC) are renowned for the strength of their M À C interaction, irrespective of the oxidation state of the metal center. [34] Adding a redox-active moiety to a NHC gives interesting properties to the resulting metal complexes.…”

Redoxaktive Liganden in der Katalyse

“…In der homogenen Katalyse wurden Chinone als wirksame ETMs eingesetzt, um die Pd II -Regeneration durch Luft bei oxidativen Wacker-Transformationen zu vermitteln. [32] Dieser chinonvermittelte niederenergetische [33] N-heterocyclische Carbenliganden (NHCs) sind bekannt für ihre starken, von der Oxidationsstufe des Metalls unabhängigen M-C-Wechselwirkungen. [34] Das Anbinden einer redoxaktiven Einheit an ein NHC führt zu interessanten Eigenschaften des resultierenden Komplexes.…”

Zeolite-encapsulated Co(II), Mn(II), Cu(II) and Cr(III) salen complexes as catalysts for efficient selective oxidation of benzyl alcohol

“…The dimmer species formation caused deactivation of the catalysts and as a consequence the re-used catalysts leads to lower substrate conversion [7][8][9]. Thus, heterogenization of metal salen-type catalysts, which can avoid the formation of dimerization species, has attracted many researcher attentions [10][11][12].…”