Nickel(II) Complexes of Bidentate N‐Heterocyclic Carbene/Phosphine Ligands: Efficient Catalysts for Suzuki Coupling of Aryl Chlorides

Nickel(II) complexes of bidentate N‐heterocyclic carbene (NHC)/phosphane ligand L were prepared and structurally characterized. Unlike palladium, which forms [PdCl 2 (L)], the stable nickel product isolated is the ionic [Ni(L) 2 ]Cl 2 . These Ni II complexes are highly robust in air. Among different N‐substituents on the ligand framework, the nickel complex of ligand L bearing N ‐1‐naphthylmethyl groups ( 2 a ) is a highly effective catalyst for Suzuki cross‐coupling between phenylboronic acid and a range of aryl halides, including unreactive aryl chlorides. The activities of 2 a are largely superior to those of other reported nickel NHC complexes and their palladium counterparts. Unlike the previously reported [NiCl 2 (dppe)] (dppe=1,2‐bis(diphenylphosphino)ethane), 2 a can effectively catalyze the cross‐coupling reaction without the need for a catalytic amount of PPh 3 , and this suggests that the PPh 2 functionality of hybrid NHC ligand L can partially take on the role of free PPh 3 . However, for unreactive aryl chlorides at low catalyst loading, the presence of PPh 3 accelerates the reaction.