Fluorous Catalysts and Reagents

Another recent advance in this area is the development of fluorous ionic liquids.These can contain perffuoroalkyl groups in the cation or in the 

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Optimization of a fluorous-organic biphasic system requires knowledge of the solubility of the fluorous catalysts and reagents in the fluorous solvents with... 

Richter B, de Wolf E, van Koten G, Deelman BJ (2000) J Org Chem 65 3885 Gladysz JA, Correa da Costa R (2004) Strategies for the Recovery of Fluorous Catalysts and Reagents Design and Evaluation. In Gladysz JA, Curran DP, Horvdth IT (eds) Handbook of Fluorous Chemistry. WUey, Weinheim, p 24 Palo D, Erkey C (1998) J Chem Eng Data 43 47... 

L.P. Barthel-Rosa and J.A. Gladysz (1999) Coordination Chemistry Reviews, vol. 190-192, p. 587 - Chemistry in fluorous media A user s guide to practical considerations in the application of fluorous catalysts and reagents . 

In order to extract non-fluorous products from reactions involving fluorous solvents in a rational way, partition coefficients must be known. The design and optimization of fluorous catalysts and reagents require analogous data. In 1999, only a few partition coefficients involving fluorous and organic phases had been... 

IV. 15. L.P. Barthel-Rosa, J.A. Gladysz - Chemistry in Fluorous Media A User s Guide to Practical Considerations in the Application of Fluorous Catalysts and Reagents, Coord. Chem. Rev. 190-192,587,1999. 

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. 

Fluorous biphase reactions have been reviewed extensively in the past few years, and most important types of reaction may now be conducted under fluorous conditions [46,51], However, partitioning of catalysts and reagents into the fluorous phase is seldom perfect - even a loss of 1-2% of an expensive catalyst may be unacceptable. Solubility and partitioning between phases relies on a complex balance of properties and interactions, and rather than simply adding more fluorocarbon chains to a catalyst (which is a common approach to the problem of leaching of catalyst from the fluorous phase), studies have indicated that the partition coefficients of fluorous compounds may better be optimised by... 

Perfluorinated molecules are prepared from their hydrocarbon analogues by electrochemical fluorination or by fluorination using cobalt trifluoride. Functional perfluorinated molecules are then used to prepare the tagged catalysts and reagents (Figure 7.4). Therefore, in terms of life cycle analysis, fluorous solvents are not as green as a solvent that does not need to be prepared, e.g. water, or a solvent that requires little substrate modification, e.g. a renewable VOC. However, the ability of FBSs to perform efficient separations often reduces the overall amount of solvent that is required in a process and therefore they are considered green alternative solvents. 

An exciting recent development in this field is the application of the unusual solubility properties of perfluorocarbons as solvents in so-called fluorous biphase chemistry [7]. These novel synthetic procedures enable ready separation of suitably designed catalysts and reagents by simple phase separation of many hydrocarbon solvents (containing the product) from the fluorous phase containing the catalyst. Success in these procedures is of course contingent on the inert nature of the fluorous phase under the reaction conditions. 

The effects of fluorous solvents and reagents have been utilized since the beginning of the 1990s. The first practical applications were the immobilization and recovery of expensive or toxic catalysts [3] and the use of chemically inert fluorocarbons to stabilize reactive intermediates [4] (Scheme 3.1). 

As chemical synthesis moves from discovery to production, scales increase and the use of catalytic rather than stoichiometric quantities of reagents is increasingly advantageous from both the economic and environmental standpoints. The vast majority of fluorous catalysts prepared to date are best classified as heavy fluorous catalysts, and they are removed from the reaction mixture by liquid/liquid separation techniques. On the one hand, fluorous silica gel provides another option for these catalysts, which is to use a solid/liquid separation instead. On the other hand, fluorous silica gel enables the use of light fluorous catalysts, such as the palladium catalyst shown in Scheme 36. Mizoroki-Heck reactions are promoted by standard conductive heating (oil bath) or microwave heating. After cooling and solid-phase extraction. 

If nonvolatile liquids are to be used to avoid the problems associated with volatile organic solvents, then it is very desirable that there is some convenient way of recovering the reaction products from the liquid. This approach is used in the biphasic systems described in Chapters 2-5. In the fluorous biphase (Chapter 3), reagents and catalysts are fine-tuned by adding perfluoroalkyl chains, known as ponytails , to ensure that only those chemicals will mix with the fluorous layer. Purification is simply a matter of separating the two phases. Transition metal catalysts with fluorous ligands will remain in the fluorous phase, and the whole catalyst-solvent mixture may be reused for another batch of reactions, as shown schematically in Figure 1.20b. 

The enantioselective synthesis of a-amino acids employing easily available and reusable chiral catalysts or reagents presents clear advantages for large-scale applications. Accordingly, recyclable fluorous chiral phase-transfer catalyst 31 has been developed by the authors group, and its high chiral efficiency and reusability demonstrated in the asymmetric alkylation of 2. After the reaction, 31 could be easily recovered by simple extraction with FC-72 (perfluorohexanes) as a fluorous solvent and used for the next run, without any loss of reactivity and selectivity (Scheme 5.17) [23]. 

The fluorous biphasic concept was introduced by the Hungarian chemists Istvan Horvath and Jozsef Rabai in 1994 [148], A fluorous biphasic system consists of a fluorous phase (a perfluoroalkane-, perfluorodialkyl ether-, or perfluorotrialkylamine-rich phase) containing a fluorous-soluble reagent or catalyst, and a second phase,... 

Curran, D. P. (2006) Organic synthesis with light-fluorous reagents, reactants, catalysts, and... 

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