Fluorous biphasic catalysis reaction

These examples reveal the attractive features of fluorous biphasic catalysis methods for chemical processes. Reactions occur in the liquid phase and can be either homogeneous or biphasic. In either case, biphasic conditions are established at the end of the reaction so the separation is easy. Fluorous sol-... 

R. H. Fish, Fluorous Biphasic Catalysis A New Paradigm for the Separation of Homogeneous Catalysts from their Reaction Substrates and products , Chem. Fur. J. 1999, 5,1677. 

These critical aspects of the classical fluorous biphasic catalysis led in recent works to the development of protocols for the conversions with modified catalyst systems in non-fluorinated hydrocarbons as solvents. As part of the BMBE lighthouse project, Gladyzs and coworkers appHed this concept to C - C coupHng reactions (Suzuki reaction) and other metal-catalyzed addition reactions (hydrosilylation, selective alcoholysis of alkynes), which have direct relevance for the synthesis of fine chemicals and specialties [74]. 

The major problem associated with aqueous catalysis is the limited and often very low solubility of certain organic reactants in water. Much work is needed to find practical solutions for these hydrophobic reactants. Possibilities deserving further attention include the application of fluorous biphasic catalysis or nonaqueous ionic liquid catalysis. The potential of organic reactions compatible with or even promoted by water is not yet fully exploited. 

A chapter written in 1996 covers hydroformylation catalyzed by organometallic complexes in detail,219 whereas a review written 5 years later gives a summary of the advances on hydroformylation with respect to synthetic applications.220 A selection of papers in a special journal issue has been devoted to carbonylation reactions.221 A major area of the research has been the development of fluorous biphasic catalysis and the design of new catalysts for aqueous/organic biphasic catalysis to achieve high activity and regioselectivity of linear or branched aldehyde formation. 

Because of their low solubilities in the aqueous phase, the hydroformylation of higher alkenes (>C2) is still a challenging problem. In addition to fluorous biphasic catalysis, possible solutions, which have been addressed, include the addition of surfactants240,241 or the use of amphiphilic ligands242-244 to enhance mutual solubility or mobility of the components across the phase boundary and thereby increase the rate of reaction. The use of polar solvents such as alcohols,245 p-cyclodextrin,246 cyclodextrin ligands,247 248 thermoregulated phase-transfer... 

Fig. 2. Fluorous biphasic catalysis part II asymmetric alkylation, reduction, oxidation, and cross-coupling reactions with fluorous tagged catalysts.

Fluorous biphasic catalysis was first reported with the hydroformylation reaction depicted in Figure 12.16 (Curran and Lee, 2001). 

Supercritical fluids, especially SCCO2 (cf. Section 3.1.13), find increasing interest as environmentally friendly reaction media with unique properties for chemical reactions [285]. The problem of insufficient solubility of the ligand complexes has been solved by an approach similar to fluorous biphasic catalysis (cf. Section 3.1.1.2.1) [286-289]. 

Fish, R. H. (1999) Fluorous biphasic catalysis A new paradigm for the separation of homogeneous catalysts from their reaction substrates and products. Chemistry-A European Journal, 5(6), 1677-1680. 

For typical fluorous biphase catalysis the most important aspect is the simple recycling and re-use of the catalyst. Fluorous solvents have one special advantage over hydrocarbon solvents, however. Their very high oxygen dissolving capacity, combined with their extreme resistance to oxidative decomposition makes perfluorocarbons in combination with fluorous catalysts the optimum choice for oxidation reactions. Thus, the biomimetic oxidation of olefins with molecular oxygen and 2-methylpropanal as a co-reductand has been achieved with a fluorous cobalt porphyrin catalyst (22) [23], and also even without catalyst [24] (Scheme 3.7). 

This approach has now been applied to a broad range of catalytic reactions, such as hydrogenation, hydroformyla-tion, hydroboration, and many palladium-catalyzed cross-coupling reactions, and excellent catalyst recovery and reuse have been reported. Although there are many comprehensive reviews of fluorous biphase catalysis,the... 

Fiuorous catalysis is now regarded by some specialists as a well-established area providing complementary approaches to aqueous (see Chapter 2) or ionic-biphase (see Chapter 5) catalysis. So far, no economical application of fluorous-biphase catalysis is known (except for highly specialized lab uses) but fluorous-biphasic separation techniques without catalytic reactions involved may be the trailblazers of later catalytic uses. 

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