Fluorous imidazolium salt

Recently, the present authors have achieved a facile recycling method for both catalyst and reachon medium using F-626 in a Mizoroki-Heck arylation reaction of acrylic acids [11]. The procedure employed a fluorous carbene complex, prepared in situ from a fluorous imidazolium salt, palladium acetate as the catalyst and F-626 as a single reaction medium. When acrylic acid was used as a substrate, separation of the product from the reaction mixture was performed simply by filtration with a small amount of FC-72. The FC-72 solution containing the fluorous Pd-catalyst and F-626 was evaporated and the residue containing the catalyst and F-626 (96% recovery) can be recycled for the next run (Scheme 3.5-6). They tried to reuse the catalyst, and observed no loss of catalytic activity in five re-use cycles. 

Another system, a mixture of Pd(OAc)2 and IPr HC1, can mediate this reaction in the presence of a fluorine source [121]. The use of TBAF is essential for this reaction as it can act as a base, deprotonating the imidazolium salt, as a fluorous medium for tin extraction and as a fluorinating agent. In fact, the in situ formation of a hypervalent organnostannate speeds up the trans-metallation step and therefore eases the coupling reaction. Unfortunately, the reaction is limited to aryl bromides and activated aryl chlorides, on the other hand vinylstannates can also be used as coupling partners (Scheme 14). 

Improvement of organic reactions by the use of fluorous components and ionic liquids has been the subject of intense research. Imidazolium salts that carry a polyfluori-nated chain (fluorous ionic liquids) are found to act as surfactants when added to conventional ionic liquids. Thus emulsification of fluoroalkanes with the ionic liquid phase is facilitated. ... 

In conclusion to this brief summary, let us emphasize that the development of catalysts that are well-defined, bring about efficient and selective transformations and can be separated from products and recycled-remains a key challenge for the XXI century. Indeed, the use of the above catalytic techniques along with that of ionic liquids (because of their lack of vapor tension and their ease of separation from apolar products the most used are imidazolium salts) and supercritical fluids (mostly sc. CO2 because it is a non-polluting easily removed solvent, also compatible with fluorous chemistry) reflects efforts to improve the Green Chemistry" aspects of catalytic processes. 

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