Dinickel(II) complexes of bis(N-heterocyclic carbene) ligands containing [Ni2(μ-OH)] cores as highly efficient catalysts for the coupling of aryl chlorides

Abstract

[Ni2(3,5-bis(N-methylimidazolylidenylmethyl)pyrazolate) 2](PF6)2 (1), [Ni2(μ-OH)(3,5- bis(N-pycolylimidazolylidenylmethyl)pyrazolate)](PF6)2 (2), and [Ni2(μ-OH)(3,5-bis(N-pyridylimidazolylidenylmethyl) pyrazolate)] (PF6)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 S.S-bis(N-methylimidazolylidenylmethyl)pyrazolates behaving as anionic tetradentate ligands. Complexes 2 and 3 contain Ni2(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. © 2008 American Chemical Society.