Imidazolium salts carboxylic acid amide

An example of a more standard, carboxyhc acid amide functionalised imidazolium salt and its apphcations come from the Ghosh group [120]. They reacted chloroacetic acid anilide with A-mesityl imidazole and obtained the respective carboxylic acid amide functionalised imidazolium salt which was reacted with sUver(I) oxide to form the corresponding silver(l) carbene complex featuring two trans-coordinated carbene ligands on the silver(I) ion (see Figure 4.39). 

Figure 4.39 A carboxylic acid amide functionalised imidazolium salt and its silver I) carbene...

Liao et al. also synthesised an imidazolium salt carrying two carboxylic acid amide functionalities and generated its silver carbene complex. It is distinguished by absolute linearity of the C-Ag-Cl vector and rather short Ag-C and Ag-Cl bond lengths. 

Carboxylic acid amide functionalised imidazolium salts can be reacted with group 10 halides directly in the presence of an inorganic base (e.g. K COj) to form homoleptic complexes (see Figure 4.41) [122]. Interestingly, the carbene units are cis to each other and not trans as would be expected (see Figures 4.30 and 4.38). The cis complexation is not aided by hydrogen bonding as the carboxylic acid amide functionality loses its proton upon complexation to nickel. 

A corresponding imidazolium salt carrying two carboxylic acid amide functionalised wingtip groups shows similar behaviour, but obviously without cis/trans isomers [123] (see Figure 4.43). 

Activation of the carboxylic acid amide proton occurs only after addition of potassium carbonate, similar to the reactivities observed with the monofunctionalised imidazolium salt in Figure 4.42. 

A very simple procedure for the preparation of amidinium salts is the condensation of carboxylic acids with excess amine in the presence of POCb. Using this method, the selfcondensation reaction of amide-POCb adducts is suppressed. The salts are usually isolated as perchlorates (132 Scheme 14). In a related reaction benzoic acid is transformed by means of iVA( -dimethylethylenediamine and TiCU to the imidazolium chloride, which was separated as the PFe salt (133). 4... 

---