Synthesis Of Imidazopyridine-Containing Ni Complex For Suzuki Cross-Coupling Reaction Of Aryl Tosylates

A novel nickelⅡ-imidazo[1,2-a]pyridine complex was designed and synthesized, and itsapplication in Suzuki cross-coupling reaction ofaryl tosylates with arylboric acid was investigated. 1.The synthesis of nickelⅡ-imidazo[1,2-α]pyridine complexA new kind of nickelⅡ-imidazo[1,2-a]pyridine metal compound was prepared from commerically available starting materials. The synthetic procedures were listed as follows in detail: (1)The a-bromoacetophenone reacted with 2-aminopyridine in ethanol solution under reflux for 7-8 h. Then, the solution mixture was evaporated and concentrated. The residue was purified through silica gel chromatography to give compound 1 as a white flocculent solid.(2)The obtained compound 1 reacted with NBS in acetonitrile under reflux for 1 h.(3)Finally, NiBr2, PPh3, compound 2, and zinc powder were refluxed in EtOH for 1.5 h to give compounds 3 as a red-brown solid.2.Nickel-catalyzed Suzuki cross-coupling reaction of aryl tosylates with arylboronic acids.4-Methoxy phenyl tosylates and phenyl boronic acid were utilized as the model substrates. The effects of bases, ligands, solvents, and time were extensively screened. The optimized conditions employed 10 mol% 3 as the catalyst,4-methoxy phenyl tosylates (1 eq) and phenylboronic acid (1.5 eq) as the substrates in toluene (2 mL) at 120℃ under argon for 10 h.Then the range of substrates was expanded. Aryl tosylates bearing electron-rich or electron-poor functional groups were well tolerated under the optimized conditions. The obtained coupling products were all confirmed by 1H NMR.