Imidazolium salts functionalised alkyl groups

Danopoulos and co-workers reported on the preparation of NHC ligands with pendant indenyl and fluorenyl groups.19 Deprotonation of the alkyl -indene or -fluorene imidazolium salts with one equivalent of potassium hexamethyldisilazide leads to NHCs functionalised with neutral indene or fluorene moieties (IndH-NHC and F1H-NHC). Further deprotonation with... 

Another example for methoxy functionalised imidazolium salts comes from the group of Cetinkaya [185,186] featuring an -alkyl tether. Cetinkaya etal.me the traditional route to transition metal carbene complexes employing the electron-rich olefins as carbene source [57-59], Thermal cleavage of the olefinic double bond in the presaice of the metal precursor complex yields the desired transition metal carbene complex (see Figure 3.66). Using this method, Cetinkaya et al. synthesised rhodium(l) [185,186] and ruthenium(ll) [185] complexes. 

Having introduced the golden rule of phosphine chemistry to its carbene analogues we will proceed to break it several times in the following brief sununary of routes to synthesise phosphino functionalised carbenes. The best way to synthesise an imidazolium salt is to react an N-substituted imidazole with an alkyl or aryl halide [235], Thus, it is a good idea to utilise a functionalised alkyl halide. The functional group can then be used to introduce the phosphino group. 

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