Suzuki Coupling Reaction Mechanism Catalyzed By NCN-type Pincer Palladium Complex

Palladium catalyzed suzuki coupling reaction was an important reaction of organometallic reactions, which was the most common way to build Aryl-Aryl bond. The palladium catalyst with phosphorus showed high catalytic activity. However, phosphorus palladium catalysts were so sensitive for air and moisture that hard handing and saving. The NCN-Pincer palladium catalyst could overcome the most shortcomings. The mechanism of Pincer palladium-catalyzed Suzuki coupling reaction still have a lot of controversy.In this article, density functional theory (DFT) and organic experiments were used to test the mechanism of NCN-pincer palladium catalyzed Suzuki coupling reactions. Briefly, a series of NCN-pincer palladium catalysts were synthesized through screening catalysts and optimizating the reaction conditions, which greatly improved the yield of Suzuki coupling reactions, one of synthesized NCN-pincer palladium showed good activity for catalyzing Suzuki coupling reaction, especially for aryl iodides, TON was up to190million. There also had excellent catalytic activity for low active chlorinated aromatic hydrocarbons. In this paper, through determining chemical spatial structure of the NCN-pincer complex by X-ray single crystal diffraction, we built the caculation model of the catalyst’s spatial structure in Suzuki coupling reaction. At the same time, we used density functional theory B3LYP and experiments to study mechanism of the coupling reaction NCN-pincer palladium catalyzed Suzuki.Through using density functional theory calculations and experiments, we found NCN-pincer palladium-catalyzed Suzuki coupling reaction have four steps:(1) bromine of NCN-pincer palladium loss;(2) oxidative addition;(3) transmetallation;(4) release the catalyst by reductive elimination process. The aboved evidence provided a theory for experimental chemists to design better catalysts...