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 3 H 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 31 P NMR in situ; that is, appropriate water favors the reaction while excess hindered this reaction. Graphical Abstract A simple ligand N,N,N’,N’ -tetra(diphenylphosphinomethyl)-1,2-ethylenediamine was employed in Sonogashira reaction with relatively low catalyst loading and isolated yield up to 99 % was obtained in the absence of copper or any other additives. This catalytic system performed high efficiency and excellent functional group tolerance.