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

• Published in: Angewandte Chemie International Edition Vol. 54; no. 40; pp. 11791 - 11794
• Main Authors: Rabeah, Jabor, Bentrup, Ursula, Stößer, Reinhard, Brückner, Angelika
• Format: Journal Article
• Language: English
• Published: Weinheim WILEY-VCH Verlag 28-09-2015; WILEY‐VCH Verlag; Wiley Subscription Services, Inc
• Edition: International ed. in English
• Subjects: Alcohol; alcohol oxidation; Alcohols; Benzyl alcohol; Catalysts; Copper; Electron transfer; homogeneous catalysis; Infrared spectroscopy; Joining; Liquid phases; operando spectroscopy; Oxidation; Proposals; Redox reactions; Spectrum analysis; Stabilization; TEMPO; UV/Vis spectroscopy; alcohol oxidation; TEMPO; homogeneous catalysis; UV/Vis spectroscopy; operando spectroscopy
• ISSN: 1433-7851; 1521-3773
• DOI: 10.1002/anie.201504813

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 CuI/CuII has been detected. Instead, the role of TEMPO is postulated to be the stabilization of a (bpy)(NMI)CuII‐O2⋅−‐TEMPO (bpy=2,2′‐bipyridine, NMI=N‐methylimidazole) intermediate formed by electron transfer from CuI to molecular O2.
All good things come in threes: Simultaneous operando EPR/UV‐vis/ATR‐IR spectroscopy provides new mechanistic insights in TEMPO‐catalyzed aerobic alcohol oxidation. TEMPO=(2,2,6,6‐tetramethylpiperidin‐1‐yl)oxyl.