Fluorous biphase systems

Fluorous biphasic systems operate on the premise that the catalyst complex is preferentially soluble in the fluorous phase. This is achieved by synthesising fluorinated ligands that have a high weight-percentage of fluorine. It has been reported that for a complex to be preferentially soluble in fluorous solvents it must contain >60... 

Pozzi and co-workers have also reported a fluorous soluble cobalt complex, which is active in the aerobic epoxidation of alkenes in a fluorous biphasic system (FBS).[50] The ligand used in this complex was a fluorinated tetraarylporphyrin, with eight perfluorooctyl chains shown in Figure 6.13. The cobalt complex was dissolved in perfluorohexane and added to a solution of the alkene with 2-methylpropanal (aldehyde substrate — 2 1) at room temperature. 

Figure 6.30. Schematic diagram of a reactor used continuously for up to 500 h for fluorous biphasic reactions without gaseous reagents. [81] (A. Yoshidaetal, Development of the continuous-flow reaction system based on the Lewis acid-catalysed reactions in a fluorous biphasic system, Green Chemisty, 5, (2003), 555) Reproduced by permission of The Royal Society of Chemistry.

TABLE 6.3. Process for optimized nonanal production of 100 000 tonnes y1 using perfluoro-methylcyclohexane in a fluorous biphasic system a... 

M. Cavazzini, F. Montanari, G. Pozzi, S. Quia, Perfluorocarbon-Soluble Catalysts and Reagents and the Application of FBS (Fluorous Biphase System) to Organic Synthesis , J. Fluorine Chem. 1999, 94,183. 

In both the Ni(acac)2-[bmim][PF6] and fhtorous biphasic systems, catalyst leaching is very low and several further batch oxidation reactions may be carried out with similar results to those obtained in the first run. In the fluorous biphasic system, the yield of 4-chlorobenzoic acid dropped from 87 % to 70 % by the sixth reaction cycle using [bmim][PF6] as a solvent, the yield was essentially the same after four uses, and no catalyst was found to leach into the organic phase. 

A fluorous biphasic system has been used to reduce the metal contamination arising in the copper-catalysed living radical polymerization of vinyl monomers. 

Table 2. Substrate, structures, and turn-over frequencies obtained for hydrogenation reactions in fluorous biphasic systems employing dendrimer-encapsulated Pd nanoparticles ...

More recent conceptual advances in the liquid/liquid biphasic systems include the novel fluorous biphase system (FBS)12-14,70-73 and the use of ionic liquids15-22... 

Recently a fluorous biphase system, a mixture of perfluorocarbon and hydrocarbon, was recommended for performing homogeneous catalytic reactions.22 At the higher reaction temperature miscibility of the biphase system takes place. When the reaction is finished the temperature is lowered, phase separation occurs and the catalyst can easily be isolated from one layer. 

Vinylic Oxidation. Various alkenes are oxidized to the corresponding ketones using fm-BuOOH in the presence of Pd(II) catalysts bearing perfluorinated ligands in a fluorous biphasic system.1309 The catalyst can be reused, but progressively longer reaction times are required. 

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