Structural, physical, and chemical properties of fluorous compounds.

The sizes and structures of fluorous molecules are analyzed, particularly with respect to the helical conformations of perfluoroalkyl segments and their phase separation in crystal lattices. Basic molecular properties, bond energies, and special bonding motifs are reviewed. Solubility, adsorption, and related phenomena are treated. Miscibilities of fluorous solvents, and partition coefficients of solutes in fluorous/organic biphase mixtures, are analyzed. Electronic effects and NMR properties are discussed, and some reactions involving the fluorinated parts of fluorous substances are presented.

Synthesis and reactivity of fluorous and nonfluorous aryl and alkyl iodine(III) dichlorides: new chlorinating reagents that are easily recycled using biphasic protocols.

Fluorous aryl and alkyl iodine(III) dichlorides of the formulas (R(fn)(CH(2))(3))(2)C(6)H(3)ICl(2) (R(fn) = CF(3)(CF(2))(n-1); n = 8 for 3,5-disubstituted and n = 6, 8, 10 for 2,4-disubstituted) and R(fn)CH(2)ICl(2) (n = 8, 10) are prepared in 71-98% yields by reactions of Cl(2) and the corresponding fluorous iodides. These are effective reagents for the conversions of cyclooctene to trans-1,2-dichlorocyclooctene, anisole to 4-chloro- and 2-chloroanisole, 4-tert-butylphenol to 2-chloro-4-tert-butylphenol, PhCOCH(2)COPh to PhCOCHClCOPh, and PhCOCH(3) to PhCOCH(2)Cl and PhCOCHCl(2) (CH(3)CN, rt to 40 degrees C, 100-64% conversions). The chlorinated products and fluorous iodide coproducts are easily separated by organic/fluorous liquid/liquid biphase workups. The latter are obtained in 97-90% yields and reoxidized with Cl(2). Analogous chlorinations are conducted with 3-Cl(2)IC(6)H(4)COOH (16) and 4,4'-Cl(2)IC(6)H(4)C(6)H(4)ICl(2). With the former, the products and coproduct 3-IC(6)H(4)COOH (91-85% recoveries) are easily separated by organic/aqueous NaHCO(3) liquid/liquid biphase workups. The coproduct from the latter, 4,4'-IC(6)H(4)C(6)H(4)I, is insoluble in common organic solvents, allowing separation by liquid/solid phase workups (91-89% recoveries). The effect of the structure of the iodine(III) dichloride upon reactivity is analyzed in detail. The fluorous systems with R(f8) substituents are generally superior, but 16 is more reactive and gives higher selectivities.

Ionic transformations in extremely nonpolar fluorous media: easily recoverable phase-transfer catalysts for halide-substitution reactions.

Solutions of the fluorous alkyl halides R(f8)(CH(2))(m)X (R(fn)=(CF(2))(n-1)CF(3); m=2, 3; X=Cl, Br, I) in perfluoromethylcyclohexane or perfluoromethyldecalin are inert towards solid or aqueous NaCl, NaBr, KI, KCN, and NaOAc. However, halide substitution occurs in the presence of fluorous phosphonium salts (R(f8)(CH(2))(2))(R(f6)(CH(2))(2))(3)P(+)X(-) (X=I (1), Br (3)) and (R(f8)(CH(2))(2))(4)P(+)I(-) (10 mol %), which are soluble in the fluorous solvents under the reaction conditions (76-100 degrees C). Stoichiometric reactions of a) 1 with R(f8)(CH(2))(2)Br and b) 3 with R(f8)(CH(2))(2)I were conducted under homogenous conditions in perfluoromethyldecalin at 100 degrees C and yielded the same R(f8)(CH(2))(2)I/R(f8)(CH(2))(2)Br equilibrium ratio ( approximately 60:40). This shows that ionic displacements can take place in extremely nonpolar fluorous phases and suggests a classical phase-transfer mechanism for the catalyzed reactions. Interestingly, the nonfluorous salt (CH(3)(CH(2))(11))(CH(3)(CH(2))(7))(3)P(+)I(-) (4) also catalyzes halide substitutions, but under triphasic conditions with 4 suspended between the lower fluorous and upper aqueous layers. NMR experiments established very low solubilities in both phases, which suggests interfacial catalysis. Catalyst 1 is easily recycled, optimally by simple precipitation onto teflon tape.

Fluorophilic ionophores for potentiometric pH determinations with fluorous membranes of exceptional selectivity.

Ionophore-doped sensor membranes exhibit greater selectivities and wider measuring ranges when they are prepared with noncoordinating matrixes. Since fluorous phases are the least polar and least polarizable liquid phases known, a fluorous phase was used for this work as the membrane matrix for a series of ionophore-based sensors to explore the ultimate limit of selectivity. Fluorous pH electrode membranes, each comprised of perfluoroperhydrophenanthrene, sodium tetrakis[3,5-bis(perfluorohexyl)phenyl]borate, and one of four fluorophilic H(+)-selective ionophores were prepared. All the ionophores are highly fluorinated trialkylamines containing three electron withdrawing perfluoroalkyl groups shielded from the central nitrogen by alkyl spacers of varying lengths: [CF(3)(CF(2))(7)(CH(2))(3)](2)[CF(3)(CF(2))(6)CH(2)]N, [CF(3)(CF(2))(7)(CH(2))(3)](2)(CF(3)CH(2))N, [CF(3)(CF(2))(7)(CH(2))(3)](3)N, and [CF(3)(CF(2))(7)(CH(2))(5)](3)N. Their pKa values in the fluorous matrix are as high as 15.4 +/- 0.3, and the corresponding electrodes exhibit logarithmic selectivity coefficients for H(+) over K(+) as low as <-12.8. The pKa and selectivity follow the trends expected from the degree of shielding and the length of the perfluoroalkyl chains of the ionophores. These electrodes are the first fluorous ionophore-based sensors described in the literature. The selectivities of the sensor containing [CF(3)(CF(2))(7)(CH(2))(5)](3)N are not only greater than those of analogous sensors with nonfluorous membranes but were of the same magnitude as the best ionophore-based pH sensors ever reported.

Ionic transformations in extremely nonpolar fluorous media: phase transfer catalysis of halide substitution reactions.

Fluorous solutions of alkyl halides Rf8(CH2)mX (m = 2, 3; X = Cl, Br, I) are inert toward solid or aqueous NaCl, NaBr, and KI, but halide substitution occurs in the presence of fluorous phosphonium salts (10 mol %, 76-100 degrees C).