Ionic Transformations in Extremely Nonpolar Fluorous Media: Easily Recoverable Phase-Transfer Catalysts for Halide-Substitution Reactions

Palladium-Catalyzed Decarbonylative Iodination of Aryl Carboxylic Acids Enabled by Ligand-Assisted Halide Exchange

We report an efficient and broadly applicable palladium-catalyzed iodination of inexpensive and abundant aryl and vinyl carboxylic acids via in situ activation to the acid chloride and formation of a phosphonium salt. The use of 1-iodobutane as iodide source in combination with a base and a deoxychlorinating reagent gives access to a wide range of aryl and vinyl iodides under Pd/Xantphos catalysis, including complex drug-like scaffolds. Stoichiometric experiments and kinetic analysis suggest a unique mechanism involving C-P reductive elimination to form the Xantphos phosphonium chloride, which subsequently initiates an unusual halogen exchange by outer sphere nucleophilic substitution.

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.

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 .

Tag and Capture Flow Hydrogen Exchange Mass Spectrometry with a Fluorous-Immobilized Probe

Analysis of complex mixtures of proteins by hydrogen exchange (HX) mass spectrometry (MS) is limited by one's ability to resolve the protein(s) of interest from the proteins that are not of interest. One strategy for overcoming this problem is to tag the target protein(s) to allow for rapid removal from the mixture for subsequent analysis. Here we illustrate a new solution involving fluorous conjugation of a retrievable probe. The appended fluorous tag allows for facile immobilization on a fluorous surface. When a target protein is passed over the immobilized probe molecule, it can be efficiently captured and then exposed to a flowing stream of deuterated buffer for hydrogen exchange. The utility of this method is illustrated for a model system of the Elongin BC protein complex bound to a peptide from HIV Vif. Efficient capture is demonstrated, and deuteration when immobilized was identical to deuteration in conventional solution-phase hydrogen exchange MS. Protein captured from a crude bacterial cell lysate could also be deuterated without the need for separate purification steps before HX MS. The advantages and disadvantages of the method are discussed in light of miniaturization and automation.

Fluoroponytailed crown ethers and quaternary ammonium salts as solid-liquid phase transfer catalysts in organic synthesis

Fluorous derivatives of dibenzo-18-crown-6 ether were prepared, and then successfully applied in representative solid-liquid phase transfer catalysis reactions, which were performed in standard organic solvents, such as chlorobenzene and toluene, as well as in fluorous solvents, such as perfluoro-1,3-dimethylcyclohexane. It was clearly shown that properly designed fluoroponytailed crown ethers could promote the disintegration of the crystal lattice of alkali salts, and transfer anions from the solid surface into an apolar, non-coordinating perfluorocarbon phase, for phase transfer catalysis reactions in organic synthesis. Furthermore, 3,5-bis(perfluorooctyl)benzyl bromide and triethylamine were reacted under mild conditions to provide an analogue of the versatile phase transfer catalyst, benzyltriethylammonium chloride, containing two fluoroponytails. This fluoroponytailed quaternary ammonium salt was also successfully employed as a catalyst in a variety of organic reactions conducted under solid-liquid phase transfer catalysis conditions, without a perfluorocarbon phase. Thus, being both hydrophobic and lipophobic, fluorous crown ethers and ammonium salts, could be rapidly recovered in quantitative yields, and reused without loss of activity, over several reaction cycles.

Hydrolysis of p-nitrophenyl esters in mixtures of water and a fluorous solvent

Hydrolyses of p-nitrophenyl hexanoate (PNPH) and diethyl p-nitrophenyl phosphate (Paraoxon) were carried out in mixtures of basic aqueous solutions and HFE-7200 (an isomeric mixture of perfluorobutyl and perfluoroisobutyl ethyl ether). Hexadecyltrimethylammonium bromide (CTAB), a perfluoroalklpylpyridinium chloride surfactant, tetrabutylammonium salts, and colloidal particles of cross-linked copolymers of 2-ethylhexyl methacrylate and styrylmethyl(trimethyl)ammonium chloride dispersed in either the aqueous phase or the HFE phase were used to promote the reactions. In a pH 9.4 borate buffer, the surfactants and the aqueous colloidal particles were the most active for PNPH hydrolysis, the PNPH preferred the HFE phase, and the rates depended both on mass transfer of the PNPH from HFE to water and on the intrinsic rate of hydrolysis in the aqueous phase. In 0.10 M NaOH, CTAB and the aqueous colloidal particles were the most active for Paraoxon hydrolysis, Paraoxon preferred the aqueous phase, and the rates followed pseudo-first-order kinetics.