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

Dr. Jabor Rabeah^1,*, Dr. Ursula Bentrup^1,*, Prof. Dr. Reinhard Stößer² and Prof. Dr. Angelika Brückner^1,*

1.Leibniz-Institut für Katalyse e.V. an der Universität Rostock, Albert-Einstein-Str. 29a, 18059 Rostock (Germany) 

2.Institut für Chemie-Humboldt-Universität zu Berlin, Brook-Taylor-Str. 2, 12489 Berlin-Adlershof (Germany)

Article first published online: 14 JUL 2015

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.

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.

Visit Website