Easily-preparable N-Heterocyclic Carbene (NHC) Precursors
- 1,3-Diisopropylimidazolium Hydrogencarbonate (contains varying amounts of 1,3-Diisopropylimidazolium-2-carboxylate)
- 1,3-Di-tert-butylimidazolium Hydrogencarbonate (contains varying amounts of 1,3-Di-tert-butylimidazolium-2-carboxylate)
• NHC ligands and catalysts are preparable by heating.
• No salt generated during preparation.
• Applicable under neutral conditions.
NHC-CO2 Adducts: Transition metal / NHC complex catalyst preparation1)
A mixture of [Rh(cod)Cl]2 (54 mg) and NHC-CO2 adduct (2 eq.) is stirred in acetonitrile (3 mL) for 5 min at room temperature in a Schlenk flask, followed by heating at 75 °C for 20 min under an atmosphere of argon. The reaction mixture is dried in vacuo, and washed three times with diethyl ether. The yellow solid is obtained.
NHC Hydrogencarbonate Salts: Transition metal / NHC complex catalyst preparation2)
(CH3)2SAuCl (11.4 mg), NHC hydrogencarbonate salt (1.2 eq.), and THF (0.7 mL) are put in a capped vial (air atmosphere). After 1 h of stirring at 50 °C, the solution is filtered over silica gel and dried in vacuo. The Au-NHC complex is obtained as a colorless solid.
NHC-CO2 Adducts: NHC-Catalyzed Conjugate Cyanations3)
1,4-Dioxane (0.5 mL) is added to a mixture of a p-quinone methide derivative (0.062 mmol), trimethylsilyl cyanide (1.3 eq.) and NHC-CO2 adduct (10 mol%) under argon atmosphere and the resulting mixture is stirred at room temperature. After the reaction is completed, the mixture is quenched with 5 mL of aqueous sodium thiosulfate and extracted with diethyl ether (3 x 5 mL). The combined organic layer is dried over anhydrous sodium sulfate and concentrated under reduced pressure. The residue is then purified through a silica gel column chromatography to give the pure product.
NHC Hydrogencarbonate Salts: NHC-Catalyzed Benzoin Condensations2)
NHC hydrogencarbonate salt (10 mol%) and molecular sieves 3A are introduced into a Schlenk tube. The powder is submitted to three Ar/vacuum cycles. Dry THF (2 mL), and then benzaldehyde (0.2 mL, 2 mmol) are added. Conversion to benzoin is calculated by 1H-NMR in CDCl3 after the reaction for 24 h at 60 °C.
- 1)A. M. Voutchkova, L. N. Appelhans, A. R. Chianese, R. H. Crabtree, J. Am. Chem. Soc. 2005, 127, 17624.
- 2)M. Fèvre, J. Pinaud, A. Leteneur, Y. Gnanou, J. Vignolle, D. Taton, J. Am. Chem. Soc. 2012, 134, 6776.
- 3)P. Goswami, G. Singh, R. V. Anand, Org. Lett. 2017, 19, 1982.
- B1045 Chloro(1,5-cyclooctadiene)rhodium(I) Dimer (= [Rh(cod)Cl]2)
- C1807 Chloro(1,5-cyclooctadiene)iridium(I) Dimer (= [Ir(cod)Cl]2)
- P2161 Palladium(II) Acetate (Purified) (= Pd(OAc)2)
- A1479 Allylpalladium(II) Chloride Dimer (= [Pd(allyl)Cl]2)
- C2719 Chloro(dimethylsulfide)gold(I) (= (CH3)2SAuCl)
Related Product Category Pages
- Carbon-Donor Ligands [Catalysis]
- N-Heterocyclic Carbene (NHC) Ligands [Cross-coupling Reaction using Transition Metal Catalysts]