Mixed phosphine/N-heterocyclic carbene palladium complexes: synthesis, characterization and catalytic use in aqueous Suzuki–Miyaura reactions

Abstract

A series of N-heterocyclic carbene (NHC)/PR₃ palladium(II) and palladium(0) complexes has been synthesized and fully characterized. X-ray crystallographic data have allowed comparison of ligand steric properties. The NHC ligand was found to vary its steric properties as a function of the phosphine co-ligand. These complexes display interesting catalytic properties in the Suzuki–Miyaura reaction performed in aqueous media. The pre-catalyst [PdCl₂(IPr)(XPhos)] (IPr = N,N′-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene; XPhos = 2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl) was found to be the most efficient system, promoting the coupling of a wide range of aryl chlorides with boronic acids in aqueous media with a typical catalyst loading of 0.03 mol%.