IMes explained

IMes is an abbreviation for an organic compound that is a common ligand in organometallic chemistry. It is an N-heterocyclic carbene (NHC). The compound, a white solid, is often not isolated but instead is generated upon attachment to the metal centre.

First prepared by Arduengo,^[1] the heterocycle is synthesized by condensation of 2,4,6-trimethylaniline and glyoxal to give the diimine. In the presence of acid, the resulting glyoxal-bis(mesitylimine) condenses with formaldehyde to give the dimesitylimidazolium cation. This cation is the conjugate acid of the NHC.^{[2] [3]}

Related compounds

Bulkier than IMes is the NHC ligand IPr (CAS 244187-81-3). IPr features diisopropylphenyl in place of the mesityl substituents.^[4]

Some variants of IMes and IPr have saturated backbones, two such ligands are SIMes and SIPr.^[5] They are prepared by alkylation of substituted anilines with dibromoethane followed by ring closure and dehydrohalogenation of the dihydroimidazolium salt.^[6]

Further reading

• 10.1038/nprot.2010.177. Synthesis of N-heterocyclic carbene ligands and derived ruthenium olefin metathesis catalysts. 2011. Bantreil. Xavier. Nolan. Steven P.. Nature Protocols. 6. 1. 69–77. 21212784. 30604456.

Notes and References

1. 10.1021/ja00040a007. Electronic stabilization of nucleophilic carbenes. 1992. Arduengo. Anthony J.. Dias. H. V. Rasika. Harlow. Richard L.. Kline. Michael. Journal of the American Chemical Society. 114. 14. 5530–5534.
2. 10.1021/ed300243s. Synthesis of Well-Defined Copper N-Heterocyclic Carbene Complexes and Their Use as Catalysts for a "Click Reaction": A Multistep Experiment That Emphasizes the Role of Catalysis in Green Chemistry. 2012. Ison. Elon A.. Ison. Ana. Journal of Chemical Education. 89. 12. 1575–1577. 2012JChEd..89.1575I.
3. Late-Stage Deoxyfluorination of Phenols with PhenoFluorMix . Junting . Chen . Tobias . Ritter . Org. Synth. . 2019 . 96 . 16 . 10.15227/orgsyn.096.0016 . free.
4. Morgan Hans. Lionel Delaude. Microwave-Assisted Synthesis of 1,3-Dimesitylimidazolium Chloride. Org. Synth. . 2010 . 87 . 77 . 10.15227/orgsyn.087.0077 . free.
5. Book: Steven P. Nolan . N-Heterocyclic Carbenes in Synthesis . Wiley-VCH . 2006 . 978-3-527-60940-6 .
6. 10.1038/protex.2012.048 . 31 January 2024 . Arnaud Gautier, Federico Cisnetti, Silvia Díez González, Clémentine Gibard . Synthesis of 1,3–bis(2,4,6–trimethylphenyl)–imidazolinium salts: SIMes·HCl, SIMes·HBr, SIMes·HBF₄ and SIMes·HPF₆ . Protocol Exchange . 10 October 2012 .