Cyclometalated Palladium NHC Complexes Bearing PEG Chains for Suzuki–Miyaura Cross-Coupling in Water

Abstract

We present the synthesis and characterization of four new polyethylene glycol (PEG) substituted palladium complexes bearing a cyclometalated 2-phenylimidazole ligand and an N-heterocyclic carbene (NHC) ligand. A solid-state structure reveals the chelating binding mode and the coiling of the PEG chain in the auxiliary ligand. The PEG substitution significantly increased the solubility of the complexes in several solvents, enabling the efficient Suzuki–Miyaura cross-coupling reaction of aryl chlorides in an aqueous medium. Under optimized reaction conditions, sterically demanding biphenyl compounds with up to three ortho substituents were accessible in good to excellent yields.