An Unsaturated Nickel(0) NHC Catalyst: Facile Preparation and

Structure of Ni(0)(NHC)2, Featuring a Reduction Process from

Ni(II)(NHC)(acac)2

Organometallics 2008, 27, 6020–6024

Synthesis of Ni(NHC)(acac)2 (1a and 1b). In a typical example,bis(2,6-diisopropylphenyl)imidazolium chloride (468 mg, 1.10mmol), NaOtBu (115 mg, 1.20 mmol), and THF (15 mL) wereadded to a 50 mL flask and stirred at room temperature for 30 min,followed by addition of Ni(acac)2 (257 mg, 1.00 mmol) in THF (5mL). After stirring for 2 h, the resulting suspension was filteredwith Celite and evaporated. Wash with with hexane and dryingunder reduced pressure gave a pale green solid (536 mg, 83%) as1a. Anal.

Synthesis of Ni(NHC)2 (2a) from 1a. The complex 1a (129mg, 0.20 mmol), bis(2,4,6-trimethylphenyl)imidazolium chloride(85.0 mg, 0.20 mmol), NaH (96.0 mg, 4.00 mmol), and 1,4-dioxane(15 mL) were added to a 50 mL flask and stirred at 100 °C for12 h. After the volatile solvent was removed under reduced pressure,the residual solid was extracted with hexane. The resultingsuspension was filtered through Celite and evaporated to give adeep purple crystalline solid containing 2a and IPr carbene.Recrystallization from hexane at -30 °C afforded 2a in 45% yield(74.7 mg)

Synthesis and Structures of Nickel Halide Complexes BearingMono- and Bis-coordinated N-Heterocyclic Carbene Ligands,

Catalyzing Grignard Cross-Coupling Reactions

Organometallics 2006, 25, 3422-3427

Preparation of 1a, 1b, 2a, and 2b. The general procedure forpreparation of 1a, 1b, 2a, and 2b is as follows. In a typical example,bis(2,6-diisopropylphenyl)imidazolium chloride (117.0 mg, 0.270mmol) and THF (1.5 mL) were added to a 20 mL Schlenk tubeand stirred for 15 min, followed by addition of KOtBu (36.7 mg,0.327 mmol) and stirring for 20 min. The resulting pale yellowsuspension was filtered through a small amount of Celite and addedto a THF solution of [NiCl2(PPh3)2] (73.5 mg, 0.112 mmol) withvigorous stirring. The solution was then stirred for 10 min, and thevolatile reagents were removed under reduced pressure. Afterextracting with hexane, sublimation of the evaporated residue at80-110 °C for 1 h removed the triphenylphosphine, giving 2a (81.4mg, 0.089 mmol, 80% yield). No contaminating phosphine wasconfirmed on the basis of 1H and 31P NMR spectroscopy.

First Chelated Chiral N-HeterocyclicBis-Carbene Complexes

ORGANIC LETTERS 2000 Vol. 2, No. 8 1125-1128

Trans-diiodo-[1,1′-(2,2′-dimethyl-1,1′-binaphthyl)-3,3′-dimethyldiimidazoline-2,2′-diylidene] nickel (II) (2a) (a) Preparation in hot NMP Imidazolium salt 7 (29 mg, 0.041mmol) and nickel acetoacetate (21 mg, 0.082 mmol) were stirred in NMP (0.20 mL) at 200 °C for 1 h. The solvent was removed by distillation under high vacuum, and the residue was dissolved in CH2Cl2. Chromatography of the residue with CH2Cl2 as eluant gave complex 2a (7.9 mg, 26%) as a red solid. (b) Preparation from pre-formed carbene at rt Imidazolium salt 7 (15 mg, 0.022 mmol) and potassium t-butoxide (6.0 mg, 0.053 mmol) were stirred in THF (8 mL) at rt under N2 for 10 minutes. Bis(triphenylphosphine)nickel chloride (17 mg, 0.026 mmol) was added in THF (2mL) and the reaction was stirred for 19 hours and then concentrated. Column chromatography of the resultant residue with CH2Cl2 as eluant gave complex 2a (7.4 mg,45%) as a red solid.