A Pd^II Carbene Complex with Anthracene Side‐Arms for π‐Stacking on Reduced Graphene Oxide (rGO): Activity towards Undirected C–H Oxygenation of Arenes

Abstract

An N-heterocyclic carbene palladium(II) complex containing two anthracene side arms was immobilized on the surface of reduced graphene oxide (rGO) by π-stacking. The activity of the homogeneous analogue and the supported complex in undirected C-H acetoxylation reaction of arenes was [a]

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

“…The oxidation state of Pd was determined to +II. 11 This information is consistent with the analysis of the XANES spectra of 1 and its structure determined by EXAFS ( Table 1). The XANES and EXAFS spectra of 1@rGO are similar to those of 1 indicating a successful immobilization of 1 onto rGO.…”

“…However, our previous results based on XPS show that the pyridine ligand dissociates from Pd and is stacked on the support. 11 One possibility is that Pd atoms are pi-bound to a CC double bond and 2.18 Å is a reasonable bond length in such configuration. [31][32][33] Scheme 1 describes the immobilization process based on our understanding.…”

“…Materials 1@rGO (2.5 wt% Pd loading) and 1 were used as catalysts and synthesized according to procedures reported previously. 8,11 All reagents and solvents used in the experiments were purchased from commercial suppliers without further purification.…”

“…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 shows that PdIJII)-NHC complexes are effective as supported catalysts for arene acetoxylation. Ex situ studies indicate that the catalyst is not reduced during catalysis but there is little information on the mechanism.…”

“…Ex situ studies indicate that the catalyst is not reduced during catalysis but there is little information on the mechanism. 4,11 It can be noted that there are also systems based on Pd(0) pre-catalysts but these were applied for directed C-H activation. 3 Although a previous study by Tato et al has shed light on our understanding of the reaction mechanism of C-H acetoxylation catalyzed by PdIJII)-NHC complexes, 12 such efforts were limited to homogeneous reaction conditions due to the complexity of heterogeneous systems.…”