title: Flexible Steric Bulky Bis(Imino)acenaphthene (BIAN)-Supported N-Heterocyclic Carbene Palladium Precatalysts: Catalytic Application in Buchwald-Hartwig Amination in Air.
abstract: To achieve efficient palladium-catalyzed cross-coupling reaction under mild reaction conditions with the flexible steric bulk strategy, a series of Pd-PEPPSI (PEPPSI: pyridine-enhanced precatalyst preparation, stabilization, and initiation) complexes C1-C6 were synthesized and characterized, in which unsymmetric flexible steric bulk was introduced on the N-aryl of ancenaphthyl skeleton. These well-defined palladium complexes were found to be excellent precatalysts for Buchwald-Hartwig amination of aryl chlorides with amines in air. The electronic effect of the Pd-PEPPSI complexes and the effect of ancillary pyridine ligands were evaluated, among which complex C3 exhibited the most efficiency. It was demonstrated that the cross-coupling products were obtained in excellent yields in the presence of 0.5-0.1 mol % palladium loading. A wide range of aryl- and heteroaryl chlorides as well as various amines were compatible. The oxidative addition of aryl chlorides is revealed to be the rate-determining step in the catalytic cycle. The catalytic activity can be enhanced by introducing electron-donating groups to the Pd-PEPPSI complexes. This type of Pd-PEPPSI precatalyst showed the most efficiency reported to date for the challenging C-N cross-coupling reactions requiring no anhydrous and inert atmosphere protections, suggesting flexible steric bulk as a promising catalyst design strategy.
authors.affiliation: School of Chemistry and Chemical Engineering, Guangdong Cosmetics Engineering and Technology Research Center, Guangdong Pharmaceutical University , Zhongshan, Guangdong 528458, China.
authors.forename: Xiao-Bing
authors.initials: XB
authors.lastname: Lan
authors.affiliation: School of Materials Science and Engineering, MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, Sun Yat-sen University , Guangzhou 510275, China.
authors.forename: Yinwu
authors.initials: Y
authors.lastname: Li
authors.affiliation: School of Chemistry and Chemical Engineering, Guangdong Cosmetics Engineering and Technology Research Center, Guangdong Pharmaceutical University , Zhongshan, Guangdong 528458, China.
authors.forename: Yan-Fang
authors.initials: YF
authors.lastname: Li
authors.affiliation: School of Chemistry and Chemical Engineering, Guangdong Cosmetics Engineering and Technology Research Center, Guangdong Pharmaceutical University , Zhongshan, Guangdong 528458, China.
authors.forename: Dong-Sheng
authors.initials: DS
authors.lastname: Shen
authors.affiliation: School of Materials Science and Engineering, MOE Key Laboratory of Bioinorganic and Synthetic Chemistry, Sun Yat-sen University , Guangzhou 510275, China.
authors.forename: Zhuofeng
authors.identifier: 0000-0001-9064-8051
authors.initials: Z
authors.lastname: Ke
authors.affiliation: School of Chemistry and Chemical Engineering, Guangdong Cosmetics Engineering and Technology Research Center, Guangdong Pharmaceutical University , Zhongshan, Guangdong 528458, China.
authors.forename: Feng-Shou
authors.identifier: 0000-0002-7525-3876
authors.initials: FS
authors.lastname: Liu