Biphasic fluorous

The term fluorous biphase has been proposed to cover fully fluorinated hydrocarbon solvents (or other fluorinated inert materials, for example ethers) that are immiscible with organic solvents at ambient conditions. Like ionic liquids the ideal concept is that reactants and catalysts would be soluble in the (relatively high-boiling) fluorous phase under reaction conditions but that products would readily separate into a distinct phase at ambient conditions (Figure 5.5). 

Various other biphasic solutions to the separation problem are considered in other chapters of this book, but an especially attractive alternative was introduced by Horvath and co-workers in 1994.[1] He coined the term catalysis in the fluorous biphase and the process uses the temperature dependent miscibility of fluorinated solvents (organic solvents in which most or all of the hydrogen atoms have been replaced by fluorine atoms) with normal organic solvents, to provide a possible answer to the biphasic hydroformylation of long-chain alkenes. At temperatures close to the operating temperature of many catalytic reactions (60-120°C), the fluorous and organic solvents mix, but at temperatures near ambient they phase separate cleanly. Since that time, many other reactions have been demonstrated under fluorous biphasic conditions and these form the basis of this chapter. The subject has been comprehensively reviewed, [2-6] so this chapter gives an overview and finishes with some process considerations. 

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... 

Figure 6.1 The fluorous biphase concept illustrated for the hydro formylation of an alkene (substrate) to an...

Figure 6.2. Fluorous biphasic hydrogenation of methyl t/h-cinnamate catalysed by rhodium complexes.[23]...

Figure 6.6. Hydrosilation of alkenes under fluorous biphasic conditions.[34]...

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. 

Pozzi has also reported a fluoro-functionalised tetraazacyclotetradecane macrocycle, which is selectively soluble in fluorocarbons and active in the fluorous biphasic oxidation of hydrocarbons. [59] This ligand (Figure 6.17) was produced whilst... 

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