Fluorous compounds

Fluorous compounds with Integral (permanent) fluorinated domains ... 

Fluorous compounds with removable (temporary) fluorinated domains (tags) ... 

Despite their vast untapped potential, techniques like fluorous biphasic catalysis still have limitations. These limitations center on solubility and emanate directly from the strengths of the technique heavily fluorous compounds tend to be highly insoluble in organic solvents while organic compounds (especially polar ones) tend to be highly... 

Fluorous compounds with appropriate melting and boiling points can be used as solvents for reactions. Fluorous compounds that have been used as solvents for a variety of reactions include perfluoromethylcyclohexane (PP2) and perfluoro-hexane (Figure 3.1). 

Table 3.4 Partition coefficients for selected fluorous compounds in the (I 3 Cf, 11 ) 1 /(113 Cg H5 biphase system [25]...

Elute fluorous compounds with nonpolar solvent... 

Figure 3.6 Separation of a fluorous compound from an organic compound using FRPSG...

New Protocols Based upon Temperature-Dependent Solubilities of Fluorous Compounds and Solid/Liquid Phase Separations... 

As would be expected, fluorous compounds are preferentially retained on fluorous silica gel [62]. Similarly, fluorous catalysts can be adsorbed on fluorous silica gel. These materials have been applied to reactions in organic solvents and water, both at room temperature and above [63-69]. The investigators have usually interpreted the transformations as bonded fluorous phase catalysis , which corresponds to sequence B-II in Fig. 1. However, there remains the possibility that at least some catalysis proceeds under homogeneous conditions via desorbed species. To our knowledge, fish-out experiments analogous to that conducted with the Teflon tape in Fig. 8 have not been conducted. 

Gladysz JA, Tesevic V (2008) Temperature-Controlled Catalyst Recycling New Protocols Based upon Temperature-Dependent Solubilities of Fluorous Compounds and Solid/Liquid Phase Separations. 23 67-89... 

On the heels of work by Zhu and Horvath and Rabai, perfluorocarbon solvents and fluorous reagents have been used increasingly in organic syntheses. Ruorous compounds often partition preferentially into a fluorous phase in organic/fluorous liquid-liquid extraction, thus providing easy separation of the compounds. Tris[(2-perfluorohexyl)ethyl]tin hydride combines the favorable radical reaction chemistry of trialkyltin hydrides with the favorable separation features of fluorous compounds. 

Recently, the submitters have developed new separation procedures based on fluorous silica gel, and the separation of fluorous compounds by solid phase extraction... 

Table 5.1. Selected Fluorous Compounds with Potential Use as Solvents in Organic Synthesis 1...

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... 

Fluorous biphasic catalysis was pioneered by Horvath and Rabai [54, 55] who coined the term fluorous , by analogy with aqueous , to describe highly fluori-nated alkanes, ethers and tertiary amines. Such fluorous compounds differ markedly from the corresponding hydrocarbon molecules and are, consequently, immiscible with many common organic solvents at ambient temperature although they can become miscible at elevated temperatures. Hence, this provides a basis for performing biphasic catalysis or, alternatively, monophasic catalysis at elevated temperatures with biphasic product/catalyst separation at lower temperatures. A number of fluorous solvents are commercially available (see Fig. 7.16 for example), albeit rather expensive compared with common organic... 

Fluorous compounds and solvents have emerged as powerful tools in modem synthetic organic chemistry. The concept of fluorous biphasic system and fluorous biphasic catalysis is based on catalysis through the use of reagents that have perfluorinated carbon chains. 

---