Chemical Properties
off-white to beige powder
Uses
1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride is used as a phosphine-free ligand in various metal-catalyzed coupling reactions, often with advantageous results in difficult cases. For use in the Pd-catalyzed cross-coupling of aryl Grignards with aryl chlorides (Kumada reaction). Many examples have been recorded of the use of NHC ligands in the Suzuki coupling reaction, for examples utilizing 1,3-dimesitylimidazol-2-ylidene, in the coupling of arylboronic acids with relatively unreactive aryl chlorides.
Preparation
In a flask, the imine(3 g, 10 mmol) was dissolved in tetrahydrofuran(25 ml), followed by dropwise addition of chloromethyl ethyl ether(1.04 g, 11 mmol). the mixture was stirred under N2 at 40 °C for 18 h, and then ethyl ether(25 ml) was added to separate white solid. The solid was filtered and washed with ethyl ether. Finally, the white solid was dried under vacuum affording 1,3-Bis(2,4,6-trimethylphenyl)imidazolium chloride.
Reactions
Precursor to the nucleophilic carbene that serves as a bulky, electron-rich "phosphine mimic" for metal-catalyzed reactions.
(a) Palladium-catalyzed Suzuki cross-coupling of aryl chlorides.
(b) Palladium-catalyzed Kumada cross-coupling of aryl chlorides.
(c) Ruthenium-carbene catalysts for ring-closing metathesis.
(d) Suzuki coupling of aryltrimethylammonium salts.
(e) Sonogashira coupling of aryl bromides.
Precursor to a nucleophilic carbene that serves as catalyst.
Ligand for arylation of aldehydes.
Ligand for carbene catalyzed intermolecular arylation of C-H bonds.
Catalyst for boron conjugate additions to cyclic and acyclic α,β-unsaturated carbonyls.
Ligand for dehydrogenative cyclocondensation of aldehydes, alkynes, and dialkylsilanes.
Precursor for carbene for conjugate silylation of alpha, beta-unsaturated carbonyls.
reaction suitability
reagent type: ligand
Synthesis
The general procedure for the synthesis of 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride from N,N'-bis(2,4,6-trimethylphenyl)ethane-1,2-diimine and chloromethyl ethyl ether is as follows: in a dry flask, N,N'-bis(2,4,6-trimethylphenyl)ethane-1,2-diimine (3 g, 10 mmol) was dissolved in anhydrous tetrahydrofuran ( 25 ml) followed by slow dropwise addition of chloromethyl ethyl ether (1.04 g, 11 mmol). The reaction mixture was stirred at 40 °C for 18 h under nitrogen protection. After completion of the reaction, ether (25 ml) was added to precipitate a white solid. The solid product was collected by filtration and washed with ether and finally dried under vacuum to afford 1,3-bis(2,4,6-trimethylphenyl)imidazole chloride (IMes-HCl) 2.2 g in 65% yield. The structure of the product was confirmed by 1H NMR (CDCl3, 400 MHz) and 13C NMR (CDCl3, 100 MHz): 1H NMR δ 2.15 (s, 12H), 2.33 (s, 6H), 7.00 (s, 4H), 7.70 (s, 2H), 10.73 (s, 1H); 13C NMR δ 17.6, 21.1, 124.8, 129.8, 130.7, 134.1, 139.2, 141.1.
References
[1] Journal of Organic Chemistry, 2008, vol. 73, # 7, p. 2784 - 2791
[2] Tetrahedron Letters, 2012, vol. 53, # 7, p. 815 - 818
[3] Tetrahedron, 2012, vol. 68, # 38, p. 7949 - 7955
[4] Chemical Communications, 2011, vol. 47, # 5, p. 1559 - 1561
[5] Journal of Organometallic Chemistry, 2013, vol. 743, p. 44 - 48
