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|Title:||Palladium complexes of abnormal n-heterocyclic carbenes as precatalysts for the much preferred cu-free and amine-free sonogashira coupling in air in a mixed-aqueous medium|
|Publisher:||ROYAL SOC CHEMISTRY|
|Abstract:||A series of new PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed precatalysts of abnormal N-heterocyclic carbenes for the highly desirable Cu-free and amine-free Sonogashira coupling in air in a mixed-aqueous medium is reported. Specifically, the PEPPSI themed (NHC) PdI(2)(pyridine) type precatalysts, 1b-4b, efficiently carried out the highly convenient Cu-free and amine-free Sonogashira coupling of aryl bromides and iodides with terminal acetylenes in air in a mixed aqueous medium. Complexes, 1b-4b, were synthesized by the direct reaction of the corresponding imidazo[1,2-a] pyridinium iodide salts, 1a-4a, with PdCl(2) in pyridine in the presence of K(2)CO(3) as a base while the imidazo[1,2-a] pyridinium iodide salts, 1a-4a, were in turn synthesized by the alkylation reactions of the respective imidazo[1,2-a] pyridine derivatives with alkyl iodides. The density functional theory (DFT) studies revealed that these imidazol-3-ylidene[1,2-a] pyridine derived abnormal carbenes are strongly sigma-donating and consequently significantly weaken the catalytically important labile trans pyridine ligand in 1b-4b.|
|Appears in Collections:||Review|
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