Dinickel(II) Complexes of Bis(N-heterocyclic carbene) Ligands Containing [Ni2(μ-OH)] Cores as Highly Efficient Catalysts for the Coupling of Aryl Chlorides

[Ni 2 (3,5-bis( N -methylimidazolylidenylmethyl)pyrazolate) 2 ](PF 6 ) 2 ( 1 ), [Ni 2 (μ-OH)(3,5-bis( N -pycolylimidazolylidenylmethyl)pyrazolate)](PF 6 ) 2 ( 2 ), and [Ni 2 (μ-OH)(3,5-bis( N -pyridylimidazolylidenylmethyl)pyrazolate)](PF 6 ) 2 ( 3 ) have been prepared from the corresponding imidazolium salts via in situ generated silver-carbene complexes. The complexes and imidazolium salts were characterized by elemental analyses and NMR spectroscopy. The structures of 1 − 3 were identified by X-ray diffraction analysis. In complex 1, two nickel(II) ions are sandwiched by two 3,5-bis( N -methylimidazolylidenylmethyl)pyrazolates behaving as anionic tetradentate ligands. Complexes 2 and 3 contain Ni 2 (μ-OH) cores with two nickel centers bridged by anionic hexadentate imidazolylidene ligands. Complexes 2 and 3 show excellent catalytic activities in Suzuki−Miyaura and Kumada−Corriu coupling reactions of various aryl chlorides. The cross-coupling reactions of deactivated aryl chlorides with arylboronic acids and Grignard reagents have been accomplished in excellent yields at low catalyst loadings.