Studies On The Suzuki-Miyaura Reaction Of Arenediazonium Salts Catalyzed By A Recyclable Polystyrene-supported NHC-Pd Complex

The unsymmetrical biaryls are widely present in numerous classes of organiccompounds, such as natural products, polymers, advanced materials, liquid crystals,ligands and molecules of medicinal interest. The Suzuki cross-coupling reactionwhich produces biaryls has proven to be one of the most versatile methods, althoughseveral other methods are available for this purpose. The key advantages of theSuzuki coupling are the mild reaction conditions and the commercial availability ofthe diverse boronic acids that are environmentally safer than other organometallicreagents. The scope of Suzuki reaction has been extensively studied for aryl bromideand iodide substrates, and the cross-couplings of less reactive aryl chlorides receivedconsiderable attention in view of their attractive cost and readily available diversity.Many haloarenes are prepared from arenediazonium salts throughSandermeiyer reaction. Therefore, unsymmetrical biaryls will be synthesized infewer steps though the Suzuki reaction of arenediazonium salts. Arenediazoniumsalts that can be easily prepared from the corresponding aniline in high yields havebeen proven to be more reactive than the corresponding aryl bromides and chloridesin the palladium-catalyzed coupling reactions and can be used as reactants in placeof the corresponding aryl halides in some cases.Heterogeneous catalysts have many advantages for industrial applications. TheNHC ligands bind to both Pd~â… and Pd~â…¡centers substantially stronger than those widely used phosphine ligands, and are highly suitable for attachment to solidsupports owing to its anticipated low level of metal leaching. However, only fewexamples of heterogeneous catalysts by anchoring NHC-Pd complexes for Suzukireaction have been reported, and there has been no general study on Suzuki-Miyaurareactions of arenediazonium salts under heterogenerous catalysis described to date.So it is meaningful to do research on polymer-supported NHC-Pd complex ascatalyst for Suzuki coupling reaction.Our work focused on the desulfitative Suzuki-Miyaura reaction ofarenediazonium salts and arylboronic acids in the presence of a recyclablepolystyrene-supported NHC-Pd Complex. Herein, five factors were considered: (1)the influence of solvent; (2) the effect of the amount of catalyst on the yield; (3) theeffect of reaction temperature on the reaction; (4) the recycling of the catalyst; (5)the generality of this strategy.