Ullmann Reaction Catalyzed by Heterogeneous Mesoporous Copper/Manganese Oxide: A Kinetic and Mechanistic Analysis

Abstract

A heterogeneous copper oxide supported on mesoporous manganese oxide (meso Cu/MnO) was explored for Ullmann-type cross-coupling reactions. An inverse micelle-templated evaporation-induced self-assembly method with in situ addition of copper was adopted to synthesize the mesoporous catalyst. Broad substrate scope and excellent functional group tolerability in C-O, C-N, and C-S bond formation reactions were observed using the optimized reaction conditions. The catalytic protocol was ligand free, and the catalyst was reusable without any significant loss of activity. The kinetic and Hammett analyses provided evidence for oxidative addition to a Cu(I) reaction center followed by nucleophilic addition and reductive elimination at the active copper oxide surface. Rate acceleration was observed for aryl halides with electron-withdrawing groups. The Hammett analysis determined ρ = +1.0, indicative of an oxidative addition, whereas the electronic effect in the phenol ring (ρ = -2.9) was indicative of coordination to a metal ion. Theoretically, the oxidative addition of the aryl halides is assisted by the ligand environment of the copper center. Relevant mechanistic implications are discussed on the basis of the experimental and computational results.

Magnetically recyclable nano copper/chitosan in O‐arylation of phenols with aryl halides

“…A possible mechanism is proposed for the synthesis of diaryl ether that is consistent with the literature . Firstly, Fe 3 O 4 /CS‐Cu NPs inserts in the aryl halide bond via oxidative addition reaction (I).…”

A quinoxaline-based porous organic polymer containing copper nanoparticles CuNPs@Q-POP as a robust nanocatalyst toward C–N coupling reaction

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Visualizing and Understanding Ordered Surface Phases during the Ullmann Coupling Reaction

“…The Ullmann coupling reaction is a classic metal-catalyzed synthetic method for forming C–C bonds where two aryl halides are coupled over a copper catalyst to form a biaryl molecule. , The original Ullmann reaction traditionally required stoichiometric amounts of copper and aryl halides in order to proceed. However, modern iterations of the reaction have found that catalytic amounts of copper bound ligands and a wide range of copper species can be used to promote the reaction. − Unlike other metal-mediated reactions, the Ullmann mechanism is not as fully understood despite its widespread study and application. This is due to its unpredictable selectivity coupled with its sensitivity to functional groups and the need for extreme reaction conditions. − …”