How to insulate a reactive site from a perfluoroalkyl group: photoelectron spectroscopy, calorimetric, and computational studies of long-range electronic effects in fluorous phosphines P((CH(2))(m)(CF(2))(7)CF(3))(3)

Phosphorus-Recycling Wittig Reaction: Design and Facile Synthesis of a Fluorous Phosphine and Its Reusable Process in the Wittig Reaction

This study shows that phosphorus sources can be recycled using the appropriate fluorous phosphine in the Wittig reaction. The designed fluorous phosphine, which has an ethylene spacer between its phosphorus atom and the perfluoroalkyl group, was synthesized from air-stable phosphine reagents. The synthesized phosphine can be used for the Wittig reaction process to obtain various alkenes in adequate yields and stereoselectivity. The concomitantly formed fluorous phosphine oxide was extracted from the reaction mixture using a fluorous biphasic system. The fluorous phosphine was regenerated by reducing the fluorous phosphine oxide with diisobutylaluminum hydride. Finally, a series of gram scale phosphorus recycling processes were performed, which included the Wittig reaction, separation, reduction, and reuse.

Fluorous Soluble Cyanine Dyes for Visualizing Perfluorocarbons in Living Systems

The bioorthogonal nature of perfluorocarbons provides a unique platform for introducing dynamic nano- and microdroplets into cells and organisms. To monitor the localization and deformation of the droplets, fluorous soluble fluorophores that are compatible with standard fluorescent protein markers and applicable to cells, tissues, and small organisms are necessary. Here, we introduce fluorous cyanine dyes that represent the most red-shifted fluorous soluble fluorophores to date. We study the effect of covalently appended fluorous tags on the cyanine scaffold and evaluate the changes in photophysical properties imparted by the fluorous phase. Ultimately, we showcase the utility of the fluorous soluble pentamethine cyanine dye for tracking the localization of perfluorocarbon nanoemulsions in macrophage cells and for measurements of mechanical forces in multicellular spheroids and zebrafish embryonic tissues. These studies demonstrate that the red-shifted cyanine dyes offer spectral flexibility in multiplexed imaging experiments and enhanced precision in force measurements.

Fluorous-Phase Ion-Selective pH Electrodes: Electrode Body and Ionophore Optimization for Measurements in the Physiological pH Range

Because of their low polarity and polarizability, fluorous sensing membranes are both hydrophobic and lipophobic and exhibit very high ion selectivities. Here, we report on a new fluorous-membrane ion-selective electrode (ISE) with a wide sensing range centered around physiologically relevant pH values. The fluorophilic tris[perfluoro(octyl)butyl]amine (N[(CH₂)₄R_f8]₃) was synthesized and tested as a new H⁺ ionophore using a redesigned electrode body that provides excellent mechanical sealing and much improved measurement reliability. In a challenging 1 M KCl background, these fluorous-phase ISEs exhibit a sensing range from pH 2.2 to 11.2, which is one of the widest working ranges reported to date for ionophore-based H⁺ ISEs. High selectivities against common interfering ions such as K⁺, Na⁺, and Ca²⁺ were determined (selectivity coefficients: logK _H, K ^pot = - 11.6; logK _H, Na ^pot = - 12.4; logK _H, Ca ^pot < - 10.2). The use of the N[(CH₂)₄R_f8]₃ ionophore with its -(CH₂)₄- spacers separating the amino group from the strongly electron-withdrawing perfluorooctyl groups improved the potentiometric selectivity as compared to the less basic tris[perfluoro(octyl)propyl]amine ionophore. The use of N[(CH₂)₄R_f8]₃ also made the ISE less prone to counter anion failure (i.e., Donnan failure) at low pH than the use of tris[perfluoro(octyl)pentyl]amine with its longer -(CH₂)₅- spacers, which more effectively shield the amino center from the perfluorooctyl groups. In addition, we exposed both conventional plasticized PVC-phase pH ISEs and fluorous-phase pH ISEs to 10% serum for 5 days. Results show that the PVC-phase ISEs lost selectivity while their fluorous-phase counterparts did not.

Remote Perfluoroalkyl Substituents are Key to Living Aqueous Ethylene Polymerization

In various nickel(II) salicylaldiminato ethylene polymerization catalysts, which are a versatile mechanistic probe for substituent effects, longer perfluoroalkyl groups exert a strong effect on catalytic activities and polymer microstructures compared to the trifluoromethyl group. This effect is accounted for by a reduced electron density on the active sites, and is also supported by electrochemical studies. Thus, β‐hydride elimination, the key step of chain transfer and branching pathways, is disfavored while chain‐growth rates are enhanced. This enhancement occurs to an extent that enables living polymerizations in aqueous systems to afford ultra‐high‐molecular‐weight polyethylene for various chelating salicylaldimine motifs. These findings are mechanistically instructive as well as practically useful for illustrating the potential of perfluoroalkyl groups in catalyst design.

Perfluorinated phosphine and hybrid P–O ligands for Pd catalysed C–C bond forming reactions in solution and on Teflon supports

The synthesis of two types of phosphine ligands that feature perfluorinated ponytails is reported. A bidentate (RfCH₂CH₂)₂PCH₂CH₂P(CH₂CH₂Rf)₂ (Rf = CF₃(CF₂)_n; n = 5, 7) and an alkoxyphosphine made by ring opening a fluorous epoxide, RfCH₂CH(OH)CH₂PR₂ (Rf = CF₃(CF₂)₇), have been prepared and spectroscopically characterised. The electronic effects of the fluorous chains have been elucidated from either the ¹J_Pt–P or ¹J_P–Se coupling constants in Pt(ii) or phosphine selenide compounds. Whilst the bidentate phosphines do not give stable or active Pd catalysts, the hybrid ligand does allow Susuki, Heck and Sonogashira catalysis to be demonstrated with low catalyst loadings and good turnovers. Whilst a fluorous extraction methodology does not give good performance, the ligand can be adsorbed onto Teflon tape and for the Suzuki cross coupling reaction the catalytic system can be run 6 times before activity drops and this has been traced to oxidation of the ligand. Additionally the crystal structure of the hybrid phosphine oxide is reported and the non-covalent interactions discussed.

Phosphine ligands containing a perfluorous ponytail can be sorbed onto Teflon tape and used as ligands for C–C cross coupling reactions with little leaching.

A rationally designed perfluorinated host for the extraction of PFOA from water utilising non-covalent interactions

Three hosts for the encapsulation of perfluorooctanoic acid have been synthesized. The host:guest complexes have been characterized by multinuclear NMR spectroscopy in solution and the solid state.

A direct route from white phosphorus and fluorous alkyl and aryl iodides to the corresponding trialkyl- and triarylphosphines

The title reaction is effected with samarium(ii) reductants that generate fluorous radicals that add to P₄ with phosphorus–phosphorus bond cleavage.

Impact of the Long-Range Electronic Effect of a Fluorous Ponytail on Metal Coordination during Solvent Extraction

With the need for a precise description of the long-range electronic effects of a perfloroalkyl chain (F-ponytail) grafted onto metal chelators, we studied in detail the effect of a spacer inserted between the polar complexing head and the F-ponytail, in relation to the metal coordination ability of the resulting molecules. The prepared molecules were then applied for the extraction of various metals from an aqueous phase into an organic phase, and the optimum spacer length could be estimated to be between three and four methylene units, according to the extraction conditions. The study also revealed the difficulty of modeling and anticipating the tiny energy differences involved in the extraction process and the importance in peculiar cases to go beyond only these studied inductive effects to understand better the factors that govern the stabilization of a metallic cation in a complex fluorous phase.

Convenient protocols for Mizoroki-Heck reactions of aromatic bromides and polybromides with fluorous alkenes of the formula H2C[double bond, length as m-dash]CH(CF2)n-1CF3 (n = 8, 10)

The fluorous alkenes H₂C[double bond, length as m-dash]CHR_fn (R_fn = (CF₂)_n-1CF₃; n = 8, 10) undergo the Mizoroki-Heck reaction with a variety of aromatic monobromides and polybromides such as 1,3- and 1,4-C₆H₄Br₂, 1,3,5-C₆H₃Br₃, 1,3,5-C₆H₃Br₂Cl, 1,4-XC₆H₄Br (X = CF₃, R_f8, COCH₃, CN, 1,4-OC₆H₄Br), 1,2-O₂NC₆H₄Br, 5-bromoisoquinoline, 5-bromopyrimidine, 3-bromo-5-methoxypyridine, and 3,5-dibromopyridine (sixteen examples, 78% average isolated yield). Typically, 1.2-2.4 equiv. of alkene are employed per Ar-Br bond, together with Pd(OAc)₂ catalyst (4-5 mol%/Ar-Br bond), n-Bu₄N⁺ Br^- (0.8-1.0 equiv./Ar-Br bond), NaOAc (1.2-2.4 equiv./Ar-Br bond), and 3 : 1 w/w DMF/THF as solvent (120 °C). No effort is necessary to exclude air or moisture, and reactions may be conducted on >10 g scales. Only E isomers of the products Ar(CH[double bond, length as m-dash]CHR_fn)_m are detected. Thirteen representative examples are hydrogenated (Pd/C, balloon pressure H₂), giving Ar(CH₂CH₂R_fn)_m (92% average isolated yield).

Phase and redox shifted four iron/four sulfur clusters: fluorous analogs of metalloenzyme cofactors

Reactions of (1) [Q]2[Fe4S4(SC(CH3)3)4] and the fluorous thiols HS(CH2)nRf8 (n = 2, 3; Rf8 = (CF2)7CF3)), or (2) [Na]2[Fe4S4(S(CH2)nRf8)4] (n = 2, 3) and [PhCH2P((CH2)3Rf6)3][Br] or [PPN][Cl] (PPN = Ph3P[horiz bar, triple dot above]N[horiz bar, triple dot above]PPh3), give the title compounds [Q]2[Fe4S4(S(CH2)nRf8)4], comprised of a fluorous dianion and in some cases fluorous cations, with (1) Q/n = Ph4P/2 (, 67%), Ph4P/3 (, 67%), Me4N/3 (69%), and Ph3P(CH2)2Rf6/2 (73%) or (2) PhCH2P((CH2)3Rf6)3/2 (, 39%), PhCH2P((CH2)3Rf6)3/3 (, 63%), and PPN/2 (36%). The educt [Ph3P(CH2)2Rf6]2[Fe4S4(SC(CH3)3)4] is in turn prepared from FeCl3, HSC(CH3)3/CH3ONa, and [Ph3P(CH2)2Rf6][I], and the educts [Na]2[Fe4S4(S(CH2)nRf8)4] from [Na]2[Fe4S4(SC(CH3)3)4] and HS(CH2)nRf8. The SCH2(1)H and (13)C NMR signals of these paramagnetic salts appear 8.7-10.3 and 32.3-34.9 ppm downfield from those of the corresponding thiols, but the chemical shifts of other signals are nearly normal. The UV-visible spectra show bands similar to those of non-fluorous analogs (290-298 nm and 406-415 nm; ε = 25 700 and 19 200 M(-1) cm(-1) for ). The singly fluorous salts are soluble in organic solvents of moderate polarity, but not in fluorous solvents. The doubly fluorous salts , are soluble in all fluorous solvents assayed, with partition coefficients of >99.65 : <0.35 (CF3C6F11/toluene) and 93.2-93.1 : 6.9-6.8 (FC-72/THF). Cyclic voltammograms carried out using a platinum working microelectrode show that is 0.08 V thermodynamically easier to reduce than .

Fluorofluorophores: fluorescent fluorous chemical tools spanning the visible spectrum

"Fluoro" refers to both fluorescent and fluorinated compounds. Despite the shared prefix, there are very few fluorescent molecules that are soluble in perfluorinated solvents. This paucity is surprising, given that optical microscopy is a ubiquitous technique throughout the physical sciences and the orthogonality of fluorous materials is a commonly exploited strategy in synthetic chemistry, materials science, and chemical biology. We have addressed this shortage by synthesizing a panel of "fluorofluorophores," fluorescent molecules containing high weight percent fluorine with optical properties spanning the visible spectrum. We demonstrate the utility of these fluorofluorophores by preparing fluorescent perfluorocarbon nanoemulsions.

Fluorine-fluorine interactions in the solid state: an experimental and theoretical study

The solid state structures of three compounds that contain a perfluorinated chain, CF(3)(CF(2))(5)CH(2)CH(CH(3))CO(2)H, CF(3)(CF(2))(5)(CH(2))(4)(CF(2))(5)CF(3) and {CF(3)(CF(2))(5)CH(2)CH(2)}(3)P═O have been compared and a number of C-F···F-C and C-F···H-C interactions that are closer than the sum of the van der Waals radii have been identified. These interactions have been probed by a comprehensive computational chemistry investigation and the stabilizing energy between dimeric fragments was found to be 0.26-29.64 kcal/mol, depending on the type of interaction. An Atoms-in-Molecules (AIM) study has confirmed that specific C-F···F-C interactions are indeed present, and are not due simply to crystal packing. The weakly stabilizing nature of these interactions has been utilized in the physisorption of a selected number of compounds containing long chain perfluorinated ponytails onto a perfluorinated self-assembled monolayer, which has been characterized by IRRAS (Infrared Reflection Absorption Spectroscopy).

Highly selective detection of silver in the low ppt range with ion-selective electrodes based on ionophore-doped fluorous membranes

Ionophore-doped sensing membranes exhibit greater selectivities and wider measuring ranges if their membrane matrixes are noncoordinating and solvate interfering ions poorly. This is particularly true for fluorous phases, which are the least polar and polarizable condensed phases known. In this work, fluorous membrane matrixes were used to prepare silver ion-selective electrodes (ISEs). Sensing membranes composed of perfluoroperhydrophenanthrene, sodium tetrakis[3,5-bis(perfluorohexyl) phenyl]borate, and one of four fluorophilic Ag(+)-selective ionophores with one or two thioether groups were investigated. All electrodes exhibited Nernstian responses to Ag(+) in a wide range of concentrations. Their selectivities for Ag(+) over interfering ions were found to depend on host preorganization and the length of the -(CH(2))(n)- spacers separating the coordinating thioether group from the strongly electron withdrawing perfluoroalkyl groups. ISEs based on the most selective of the four ionophores, that is, 1,3-bis(perfluorodecylethylthiomethyl)benzene, provided much higher selectivities for Ag(+) over many alkaline and heavy metal ions than most Ag(+) ISEs reported in the literature (e.g., log K(Ag,J)(pot) for K(+), -11.6; Pb(2+), -10.2; Cu(2+), -13.0; Cd(2+), -13.2). Moreover, the use of this ionophore with a linear perfluorooligoether as membrane matrix and solid contacts consisting of three-dimensionally ordered macroporous (3DOM) carbon resulted in a detection limit for Ag(+) of 4.1 ppt (3.8 × 10(-1)1 M).

Acid dissociation versus molecular association of perfluoroalkyl oxoacids: environmental implications

Perfluorooctanoate (PFO) and perfluorooctanesulfonate (PFOS) surfactant anions, once released, may rapidly reach remote regions. This phenomenon is puzzling because the water-bound anions of strong F-alkyl acids should be largely transported by slow oceanic currents. Herein, we investigate whether these hydrophobic F-alkyl oxoanions would behave anomalously under environmental conditions, as suggested elsewhere. Negative electrospray ionization mass spectra of micromolar aqueous PFO or PFOS solutions from pH 1.0 to 6.0 show (1) m/z = 499 (PFOS) signals that are independent of pH and (2) m/z = 413 (PFO) and 369 (PFO-CO(2)) signals, plus m/z = 213 (C(3)F(7)CO(2)(-)) and 169 (C(3)F(7)(-)) signals at higher collision energies, and, below pH approximately 4, m/z = 827 signals from a remarkably stable (PFO)(2)H(-) cluster that increase with decreasing pH. Since the sum of the m/z = 369, 413, and 827 signal intensities is independent of pH, that is, effectively encompasses all major species, we infer that pK(a)(PFOSA) < 1.0 and pK(a)(PFOA) < 1.0. We also derive K(2) < or = 4 x 10(7) M(-2) for the clustering equilibrium 2PFO + H(+) <==> (PFO)(2)H. Thus, although (PFO)(2)H is held together by an exceptionally strong homonuclear covalent hydrogen bond, neither PFOS nor PFO will associate or protonate significantly at environmentally relevant subnanomolar concentrations above pH approximately 1.

Fluorous effects in amide-based receptors for anions

Hybrid receptors designed to recognize both the sulfonate headgroup and the fluorous tail of perfluorooctanesulfonate (CF(3)(CF(2))(7)SO(3)(-), "PFOS") were prepared by coupling fluorinated carboxylic acids onto poly(aminomethyl)benzene scaffolds. Binding to PFOS, CF(3)SO(3)(-), p-TsO(-), and Cl(-) was monitored by (1)H NMR and isothermal titration calorimetry (ITC). In chloroform solvent, hydrogen-bonding to anions is accompanied by downfield shifts in the amide NH protons of the fluorinated receptors and by evolution of heat. Association constants for 1:1 complexation (K(assoc)) are >1000 M(-1). An analogous hydrocarbon receptor binds weakly to anionic guests (K(assoc) < 50 M(-1)). Ab initio calculations indicate that the differences in 1:1 binding strengths between fluorous and nonfluorous hosts cannot be ascribed to differences in NH donor acidities.

Preparation of a Highly Fluorophilic Phosphonium Salt and its Use in a Fluorous Anion-Exchanger Membrane with High Selectivity for Perfluorinated Acids

Fluorous solvents are the most nonpolar, nonpolarizable phases known, whereas ions are inherently polar. This makes it difficult to create salts that are soluble in a fluorous solvent. Here we present the synthesis and characterization of a new fluorophilic phosphonium salt, tris{3,5-bis[(perfluorooctyl)propyl]phenyl}methylphosphonium methyl sulfate. The salt has a solubility of at least 14 mM in perfluoro(perhydrophenanthrene), perfluoro(methylcyclohexane), and perfluorohexanes. It also shows immediate potential for use as a phase-transfer catalyst in fluorous biphasic catalysis, but in this work it is used as an anion exchanger site in the first potentiometric fluorous-membrane anion-selective electrode. The membrane sensor exhibited the exceptional selectivity of 3.9 × 10(10) to 1 for perfluorooctanesulfonate over chloride, and of 2.5 × 10(7) to 1 for perfluorooctanoate over chloride. With improvements to the sensor's detection limit and lifetime, it has the potential to be an attractive alternative to the expensive, time-consuming methods currently employed for measurement of perfluorinated acids.

Coordinative properties of highly fluorinated solvents with amino and ether groups

Despite the widespread use of perfluorinated solvents with amino and ether groups in a variety of application fields, the coordinative properties of these compounds are poorly known. It is generally assumed that the electron withdrawing perfluorinated moieties render these functional groups rather inert, but little is known quantitatively about the extent of their inertness. This paper reports on the interactions between inorganic monocations and perfluorotripentylamine and 2H-perfluoro-5,8,11-trimethyl-3,6,9,12-tetraoxapentadecane, as determined with fluorous liquid-membrane cation-selective electrodes doped with tetrakis[3,5-bis(perfluorohexyl)phenyl]borate salts. The amine does not undergo measurable association with any ion tested, and its formal pK(a) is shown to be smaller than -0.5. This is consistent with the nearly planar structure of the amine at its nitrogen center, as obtained with density functional theory calculations. The tetraether interacts very weakly with Na(+) and Li(+). Assuming 1:1 stoichiometry, formal association constants were determined to be 2.3 and 1.5 M(-1), respectively. This disproves an earlier proposition that the Lewis base character in such compounds may be nonexistent. Due to the extremely low polarity of fluorous solvents and the resulting high extent of ion pair formation, a fluorophilic electrolyte salt with perfluoroalkyl substituents on both the cation and the anion had to be developed for these experiments. In its pure form, this first fluorophilic electrolyte salt is an ionic liquid with a glass transition temperature, T(g), of -18.5 degrees C. Interestingly, the molar conductivity of solutions of this salt increases very steeply in the high concentration range, making it a particularly effective electrolyte salt.

Fluorous phase-transfer activation of catalysts: application of a new rate-enhancement strategy to alkene metathesis

Reactions of the bis(pyridine) complex (H2IMes)(Py)2(Cl)2Ru(=CHPh) and fluorous phosphines P(CH2CH2R(fn))3 (n = a, 6; b, 8; c, 10; R(fn) = (CF2)(n-1)CF3) give (H2IMes)(P(CH2CH2R(fn))3)(Cl)2Ru(=CHPh) (2a-c, 64-73%), which are analogs of Grubbs' second generation catalyst and effective alkene metathesis catalysts under organic monophasic and fluorous/organic biphasic conditions. The latter give rate accelerations, which are believed to arise from phase transfer of the dissociated fluorous phosphine.

“Heavy Fluorous” Cyclopentadienes and Cyclopentadienyl Complexes with Three to Five Ponytails: Facile Syntheses from Polybromocyclopentadienyl Complexes, Phase Properties, and Electronic Effects

The reactions between [(eta5-C5H(5-x)Br(x))M(CO)3] (M = Re, Mn; x = 1, 3, 4, 5) and [IZn[(CH2)(n)R(f8)]] (n = 2, 3; R(f8) = (CF2)7CF3) in the presence of [Cl2PdL2] catalysts give the title complexes [[eta5-C5H(5-x)[(CH2)(n)R(f8)]x]M(CO)3]. In the case of x = 5, the major product is actually [[eta5-C5H[(CH2)(n)R(f8)]4]M(CO)3], in which one of the bromides has been substituted by hydride. Minor amounts of multiple hydride substitution products are formed, all of them readily separable on fluorous silica gel. Irradiation of the manganese complexes in CF3C6H5/MeOH/ether gives uncoordinated cyclopentadienes, which can be deprotonated and reattached to other metals. Partition coefficients have been measured (CF3C6F11/toluene): complexes with three or more ponytails are highly fluorophilic, with values of > 99.8: < 0.2. The IR [symbol: see text]CO bands have been used to probe the inductive effects of the ponytails at the metal centers.

Light, Medium, and Heavy Fluorous Triarylphosphines Exhibit Comparable Reactivities to Triphenylphosphine in Typical Reactions of Triarylphosphines

[reaction: see text] The relative reactivities of triphenylphosphine (PPh(3)) and three fluorous triarylphosphines [(p-R(F)(CH(2))(2)C(6)H(4))(n)PPh(3)(-)(n), where n = 1-3] have been compared in internal competition experiments. Product ratios were determined by (31)P NMR spectroscopy. The four phosphines have about the same reactivities in oxidation, alkylation, and Staudinger reactions and give comparable yields in a preparative Mitsunobu reaction. Previously observed rate and yield differences in Staudinger reactions of the fluorous phosphines are attributed to solubility effects, not reactivity differences. A light fluorous phosphine [(p-C(8)F(17)(CH(2))(2)C(6)H(4))PPh(2)] outperforms a commercially available resin-bound phosphine in a competitive benzylation experiment by a factor of about 4.

Modular Synthesis of Fluorous Trialkylphosphines

A modular synthetic protocol was developed for the preparation of fluorous trialkylphosphines with a different number of methylene spacers and various lengths of the fluorous ponytails P[(CH(2))(A)R(FX)][(CH(2))(B)R(FY)][(CH(2))(C)R(FZ)] (A, B, C = 3 and 4; X, Y, Z = 4, 6, and 8). [reaction: see text]

Convenient syntheses of “heavy fluorous” cyclopentadienes and cyclopentadienyl complexes with three to five ponytails

Reactions of (eta5-C5H(5-x)Brx)M(CO)3(M = Re, Mn; x= 1, 3, 4, 5) and IZn(CH2)2R(f8) in the presence of Cl2PdL2 catalysts give the title complexes (eta5)-C5H(5-x)(CH2)2R(f8)x)M(CO3), accompanied in the case of x= 5 by hydride-transfer byproducts. Extremely high fluorophilicities are realized, and the cyclopentadienyl ligands are readily detached (hnu) from the manganese complexes.