Highly efficient Pd/tetraphosphine catalytic system for copper-free sonogashira reactions of aryl bromides with terminal alkynes

In this study, an easily synthesized polydentate ligand N,N,N',N'-tetra(diphenylphosphinomethyl)-1,2-ethylenediamine (1) in combination with [Pd(C ₃H ₅)Cl] ₂ was found to be an active catalyst in copper-free Sonogashira reactions. Most substrates, including steric hindered phenyl bromides and heteroaryl bromides, could couple efficiently with terminal alkynes in the presence of low catalyst loading (0.1 mol%) and this catalytic system showed excellent functional group tolerance. The influence of water in this system was also preliminarily investigated via 31P NMR in situ; that is, appropriate water favors the reaction while excess hindered this reaction.