Catalysts for Suzuki–Miyaura Coupling Reaction

Among the main reactions in organic chemistry, the Suzuki–Miyaura cross-coupling reaction catalyzed by a homogeneous or heterogeneous palladium complex is undoubtedly the most important. This reaction enables the synthesis of complex and functionalized organic molecules under mild experimental conditions compatible with many functional groups in batch and in continuous flow processes [1]. A review of the Suzuki–Miyaura cross-coupling reaction using nitroarenes as electrophilic coupling reagents instead of organic halides or triflates is reported [2]. The substitution of aryl halides and derivatives with nitro compounds could have an impact in terms of sustainability even if the use of nitroarenes requires a bulky biarylphosphine ligand. This review could open up a new green and sustainable method for the future of the Suzuki–Miyaura cross-coupling reaction with important applications in the pharmaceutical domain. Nitrogen-doped graphene (NDG) is used as a support for the preparation of an NDG@Pd nanocatalyst in a Suzuki–Miyaura cross-coupling reaction [3]. The precatalyst (Pd 5 mol%) is obtained by the simultaneous reduction of graphene oxide (GRO) and PdCl2 in the presence of hydrazine hydrate as a reducing agent, while ammonium hydroxide is used as a source of “N” on the surface of graphene. In the presence of phenyl halides, phenyl boronic acids, and sodium dodecyl sulfate in refluxing water for 5 minutes, the cross-coupling affords the target biaryl derivatives in good yields. Under these conditions, the N-doped catalyst displays excellent reusability even after several reactions. Three nanosized palladium catalysts (0.2 mol%) supported on graphene oxide (GO) and its composite with TiO2 (GO-TiO2) are prepared and fully characterized [4]. These catalysts are studied for the carbonylative coupling of iodobenzene with aryl boronic acids in anisole for 4 h at 100 ◦C and furnish the corresponding diarylketones at atmospheric pressure of CO. The best productivity (95%) is obtained in the presence of Pd/GO-TiO2, which is also successfully recycled in four subsequent runs. After a few recyclings, the selectivity to ketones decreases and normal Suzuki–Miyaura coupling occurs. Pd-nanodot-modified gold nanoparticles with or without a graphene interface layer are prepared using a wet-chemical synthetic method [5]. Among the different catalysts, Pd-rGO-AuNPs permit the highest catalytic activity for the visible-light-induced C–C bond coupling reaction. This work clearly indicates that the design and use of engineered interfaces are of importance to achieve enhanced catalytic activity with plasmonic hybrid nanomaterials. A mechanism study shows that the electron–hole pair generated by the absorption of light energy is responsible for the enhanced photocatalytic activity. Different titanium-dioxide-supported palladium catalysts are produced and characterized for a ligand-free Suzuki–Miyaura cross-coupling reaction [6]. Among these catalysts, Pd/TiO2 (anatase-type) obtained by acetonitrile solution impregnation between palladium acetate and anatase-type TiO2 demonstrates the best catalytic activity. Various aryl chloride and bromide derivatives and arylboronic acids in the presence of 5−10 mol% Pd/TiO2 in dimethylacetamide for 24 h at 80 ◦C furnish the target compounds in good yields. Novel magnetically recyclable catalysts which have Fe3O4@Pd nanoparticles (NPs) are prepared starting from Fe3O4 [7]. Adding glucose in a hydrothermal treatment and then PdCl2 in the presence of ascorbic acid furnishes Fe3O4@C/Pd, while adding glucose and ethylenediamine permit the creation