Selective Alcohol Oxidation by a Copper TEMPO Catalyst: Mechanistic Insights by Simultaneously Coupled Operando EPR/UV-Vis/ATR-IR Spectroscopy

Jabor Rabeah; Ursula Bentrup; Reinhard Stößer; Angelika Brückner

doi:10.1002/anie.201504813

Selective Alcohol Oxidation by a Copper TEMPO Catalyst: Mechanistic Insights by Simultaneously Coupled Operando EPR/UV-Vis/ATR-IR Spectroscopy

Angew Chem Int Ed Engl. 2015 Sep 28;54(40):11791-4. doi: 10.1002/anie.201504813. Epub 2015 Jul 14.

Authors

Jabor Rabeah¹, Ursula Bentrup², Reinhard Stößer³, Angelika Brückner⁴

Affiliations

¹ Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock (Germany). jabor.rabeah@catalysis.de.
² Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock (Germany). ursula.bentrup@catalysis.de.
³ Institut für Chemie-Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, 12489 Berlin-Adlershof (Germany).
⁴ Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock (Germany). angelika.brueckner@catalysis.de.

PMID: 26174141
DOI: 10.1002/anie.201504813

Abstract

The first coupled operando EPR/UV-Vis/ATR-IR spectroscopy setup for mechanistic studies of gas-liquid phase reactions is presented and exemplarily applied to the well-known copper/TEMPO-catalyzed (TEMPO=(2,2,6,6-tetramethylpiperidin-1-yl)oxyl) oxidation of benzyl alcohol. In contrast to previous proposals, no direct redox reaction between TEMPO and Cu(I) /Cu(II) has been detected. Instead, the role of TEMPO is postulated to be the stabilization of a (bpy)(NMI)Cu(II) -O2 (⋅-) -TEMPO (bpy=2,2'-bipyridine, NMI=N-methylimidazole) intermediate formed by electron transfer from Cu(I) to molecular O2 .

Keywords: TEMPO; UV/Vis spectroscopy; alcohol oxidation; homogeneous catalysis; operando spectroscopy.