In situ XAS study of the local structure and oxidation state evolution of palladium in a reduced graphene oxide supported Pd(ii) carbene complex during an undirected C–H acetoxylation reaction

Ning Yuan,A Ken Inge,Ola F Wendt,Xiaodong Zou,Éva G Bajnóczi,Ingmar Persson,Norbert Stock,L Reine Wallenberg,Maitham H Majeed,Axel R Persson,Niclas Heidenreich

doi:10.1039/c8cy02430h

Abstract

In situ XAS is used to reveal the evolution of palladium species during an undirected C–H acetoxylation reaction.

Highlights

In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladiumIJII) catalyzed undirected C–H acetoxylation reaction in the presence of an oxidant
The preparation procedure is depicted in Scheme 1.11 It was shown that 1@rGO works as an active heterogeneous catalyst in undirected C–H acetoxylation of benzene and its catalytic efficiency is slightly higher than its homogeneous analog.[11]
The oxidation state of Pd was determined to +II.[11]. This information is consistent with the analysis of the X-ray absorption near edge structure (XANES) spectra of 1 and its structure determined by extended X-ray absorption fine structure (EXAFS) (Table 1)

Summary

Introduction

In situ X-ray absorption spectroscopy (XAS) investigations have been performed to provide insights into the reaction mechanism of a palladiumIJII) catalyzed undirected C–H acetoxylation reaction in the presence of an oxidant. The mean average oxidation state of Pd decreases to the initial state at the end of the experiment which means that comparable amounts of Pd(0) and PdIJIV) are present These observations from heterogeneous catalysis are in good agreement with its homogeneous analog and they support a PdIJII)–PdIJIV)–PdIJII) reaction mechanism. Demand, because these supported systems are recyclable and easy to separate from the reaction mixture, and for their potential to introduce novel chemical reactivity.[3,4,5] Reduced graphene oxide (rGO) was successfully applied as a supporting material for different types of transition metal N-heterocyclic carbene (TM–NHC) complexes and applied for many transformations including C–H acetoxylation.[6,7,8,9,10] Recently, we developed an anthracene-tagged PdIJII)–NHC complex, 1, supported on rGO through π-stacking (here labeled 1@rGO) according to an adaptation of the procedure proposed by Peris and co-workers.[8] The preparation procedure is depicted in Scheme 1.11 It was shown that 1@rGO works as an active heterogeneous catalyst in undirected C–H acetoxylation of benzene and its catalytic efficiency is slightly higher than its homogeneous analog.[11] This, together with our previous work,[4]. The growing interest in in situ XAS measurements on solid–liquid and solution phase reactions has promoted the development of the reactors.[24,25] With improved control of the chemical conditions several successful examples have been reported.[26,27,28,29] These studies have proven that in situ XAS is a powerful tool to study the catalytic species in solution and solution–solid reaction mixtures

Objectives

Results

Conclusion