Fluorous solvents solubility

These alternative processes can be divided into two main categories, those that involve insoluble (Chapter 3) or soluble (Chapter 4) supports coupled with continuous flow operation or filtration on the macro - nano scale, and those in which the catalyst is immobilised in a separate phase from the product. These chapters are introduced by a discussion of aqueous biphasic systems (Chapter 5), which have already been commercialised. Other chapters then discuss newer approaches involving fluorous solvents (Chapter 6), ionic liquids (Chapter 7) and supercritical fluids (Chapter 8). 

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... 

Further efficient ligands for the epoxidation of alkenes have been reported by Pozzi, but using PhIO as the oxidant and pyridine V-oxide as an additive in FBS.[7, 51-53] Chiral (salen)Mn complexes have been synthesised, which are soluble in fluorous solvents and active in the epoxidation of a variety of alkenes. The catalysts were of the form shown in Figure 6.14. 

Bayardon and Sinou have reported the synthesis of chiral bisoxazolines, which also proved to be active ligands in the asymmetric allylic alkylation of l,3-diphenylprop-2-enyl acetate, as well as cyclopropanation, allylic oxidations and Diels-Alder reactions. [62] The ligands do not have a fluorine content greater than 60 wt% and so are not entirely preferentially soluble in fluorous solvents, which may lead to a significant ligand loss in the reaction system and in fact, all recycling attempts were unsuccessful. However, the catalytic results achieved were comparable with those obtained with their non-fluorous analogues. 

Studies of the phase behaviour at ambient temperature within the separator [43] show that there is significant solubility of the product nonanal within the fluorous phase and vice versa. Although this does not present a problem for the nonanal (it will simply be recycled to the reactor and create a steady state, it does mean that fluorous solvent is always being lost. The loss of the fluorous solvent (2.8 mol% into pure nonanal), as for the catalyst and the free ligand [41] is much more significant at low conversion, so... 

Organic compounds can be rendered soluble in fluorous solvents by attaching them to highly fluorinated tags, and some representative fluorous molecules are shown in Figure 1. The tags are often long... 

Reducing the number of fluorines on the fluorous tag also provides a general solution to the reaction solvent problem as the number of fluorines is reduced, the solubility in organic solvents tends to go up. Of course, the solubility in fluorous solvents tends to go down at the same time, and the residual tag must strike a balance between too many fluorines (low solubility in organic solvents) and too few fluorines (cannot easily be separated from organic compounds). However, thanks to the technique of fluorous solid-liquid extraction, there is surprisingly broad latitude here. 

Figure 1.6 Like dissolves like perfluoroalkyl ponytails make phosphines more soluble in a fluorous solvent. These phosphines are suitable ligands for metal catalysts, and will therefore aid the solubility of these catalysts in fluorous solvents...

The term fluorous was coined as an analogy to aqueous for highly fluorinated alkanes, ethers and tertiary amines [1], These compounds differ markedly from the corresponding hydrocarbon compounds to the extent that such compounds commonly give bilayers with conventional organic solvents. In this chapter, we will discuss the different approaches towards carrying out reactions in fluorous media and describe how reactants and catalysts can be engineered to be preferentially soluble in fluorous solvents. 

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

Aldehydes may be converted to carboxylic acids using Ni(acac)2 immobilized in [bmim][PF,5], with oxygen as the oxidant, as shown in Scheme 9.14 [27], A similar reaction has also been performed using perfluorinated solvents, and it was found that there was little difference between the two systems [28], However, the Ni(acac)2 catalyst could not be used directly in the fluorous solvent and therefore the 1,3-diketonate was modified with long perfluorinated chains prior to use to ensure solubility. 

The fluorous boronate is highly soluble in fluorous solvents, but when the nonfluorous R-group combines with another nonfluorous R-group the resulting product becomes preferentially soluble in the organic phase into which it is automatically extracted. 

From our cooperation partners. Profs. Gladysz and Dinjus, we received ligands with perfluorinated chains ( ponytails ), which show a thermomorphic solubility in organic solvents (P(et-Rf8)2(m-me-bz)) or maybe extracted with fluorous solvents (P(et-Rfs)3). P(et-Rf6)(z-pr)2 with only one perfluorinated... 

As shown in Scheme 3, the PCP ligand coifld be palladated in high yield. The resulting complexes 14-Rf were very soluble in fluorous solvents, insoluble in hexane, slightly soluble in ether, and moderately soluble in THF, CH2CI2, and acetone. However, 14-Rf readily dissolved in hot hexane, and with 14-Rfs single crystals were obtained upon coohng. X-ray analysis afforded the structures shown in Fig. 6. 

J.L. Panza, A.J. Russell, E.J. Beckman, Synthesis of fluorinated NAD as a soluble coenzyme for enzymatic chemistry in fluorous solvents and carbon dioxide. Tetrahedron 58 (2002) 4091-4104. 

---