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

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.

Visible-Light Photoredox Catalysis: Selective Reduction of Carbon Dioxide to Carbon Monoxide by a Nickel N-Heterocyclic Carbene–Isoquinoline Complex

“…The Ni-N and Ni-C bond lengths are within the typical range for these types of donors. 76,[102][103][104] Evaluation of Nickel N-Heterocyclic Carbene-Amine Complexes for Electrocatalytic CO 2 Reduction. The electrochemical behaviors of complexes 1c-4c were interrogated by cyclic voltammetry.…”

Nickel N-heterocyclic carbene complexes and their utility in homogeneous catalysis

“…The transmetllation method (Scheme 13) was reported for the synthesis of the (775−777) [238] and (778) [239] complexes that were obtained from the reaction of the in situ generated Ag(I)−NHC complexes with NiCl 2 (PPh 3 ) 2 and (DME)NiCl 2 .…”

“…The compounds (187−188), [83] (216), [108] (256), [93] (264), [108] (684−685), [207] (717), [219] (729−732), [230] (756) [234,249] and (776−777) [238] have been reported for the Suzuki coupling of aryl bromide and chloride substrates. The complex (721) [222] is versatile for the Suzuki coupling towards all of the aryl chloride, bromide and iodide substrates.…”

“…The complex (721) [222] is versatile for the Suzuki coupling towards all of the aryl chloride, bromide and iodide substrates. [93] (392), [61] (403), [143] (453−454), [107] (458), [143] (756) [230] and (775) [238] have been reported for the Suzuki coupling of aryl bromide substrates.…”

“…The nickel complexes (124), [68] (128), [68] (622) [185] and (626) [190] were reported for the Kumada coupling of the fluoride and the chloride substrates, while the complex (756) [249] showed activity towards all of the three fluoride, chloride and the bromide substrates. Extending the substrate scope even further, the complexes (278) (319−320), [253] (322), [253] (324), [253] (391), [114] (392), [61] (586−587), [181] (604−605), [185] (609), [185] (623), [185] (624−625), [190] (627−630), [190] (684−685), [214] (691), [211] (708), [214] (711), [205] (722), [214] (741), [211] (755), [228] (757−760) [235] and (775−777) [238] have been reported of the Kumada coupling of only the chloride substrates. It is interesting to note that the compounds (129) and (132) are not analytically pure as they were found to be comprised of 70:30 mixture of Br/Cl atoms as observed in the single crystal X-ray diffraction studies [68].…”