Molecular dynamics simulations of triflic acid and triflate ion/water mixtures: a proton conducting electrolytic component in fuel cells

Triflic acid is a functional group of perflourosulfonated polymer electrolyte membranes where the sulfonate group is responsible for proton conduction. However, even at extremely low hydration, triflic acid exists as a triflate ion. In this work, we have developed a force-field for triflic acid and triflate ion by deriving force-field parameters using ab initio calculations and incorporated these parameters with the Optimized Potentials for Liquid Simulations - All Atom (OPLS-AA) force-field. We have employed classical molecular dynamics (MD) simulations with the developed force field to characterize structural and dynamical properties of triflic acid (270-450 K) and triflate ion/water mixtures (300 K). The radial distribution functions (RDFs) show the hydrophobic nature of CF(3) group and presence of strong hydrogen bonding in triflic acid and temperature has an insignificant effect. Results from our MD simulations show that the diffusion of triflic acid increases with temperature. The RDFs from triflate ion/water mixtures shows that increasing hydration causes water molecules to orient around the SO(3)(-) group of triflate ions, solvate the hydronium ions, and other water molecules. The diffusion of triflate ions, hydronium ion, and water molecules shows an increase with hydration. At λ = 1, the diffusion of triflate ion is 30 times lower than the diffusion of triflic acid due to the formation of stable triflate ion-hydronium ion complex. With increasing hydration, water molecules break the stability of triflate ion-hydronium ion complex leading to enhanced diffusion. The RDFs and diffusion coefficients of triflate ions, hydronium ions and water molecules resemble qualitatively the previous findings using per-fluorosulfonated membranes.     

Iodonium Metathesis Reactions

A metathesis reaction occurs when a diaryliodonium triflate is heated with an aryl iodide, resulting in the formation of a new diaryliodonium triflate.     

A Two‐in‐one Pincer Ligand and its Diiron(II) Complex Showing Spin State Switching in Solution through Reversible Ligand Exchange

A novel pyrazolate‐bridged ligand providing two {PNN} pincer‐type compartments has been synthesized. Its diiron(II) complex LFe₂(OTf)₃(CH₃CN) ( 1 ; Tf=triflate) features, in solid state, two bridging triflate ligands, with a terminal triflate and a MeCN ligand completing the octahedral coordination spheres of the two high‐spin metal ions. In MeCN solution, 1 is shown to undergo a sequential, reversible, and complete spin transition to the low‐spin state upon cooling. Detailed UV/Vis and ¹⁹F NMR spectroscopic studies as well as magnetic measurements have unraveled that spin state switching correlates with a rapid multistep triflate/MeCN ligand exchange equilibrium. The spin transition temperature can be continuously tuned by varying the triflate concentration in solution.     

An efficient synthesis of imidazolinium salts using vinyl sulfonium salts

The synthesis of imidazolinium salts from the reaction of formamidines and (2-bromoethyl)diphenylsulfonium triflate is described. A variety of symmetrical and unsymmetrical imidazolinium triflate salts were synthesized in high yield in short reaction times under mild conditions. Aromatic and aliphatic N-substituents work well. The reaction is proposed to proceed via generation of a vinyl sulfonium salt intermediate from the bromoethylsulfonium triflate.     

Highly efficient one-pot synthesis of D-ring chloro-substituted neocryptolepines via a condensation—Pd-catalyzed intramolecular direct arylation strategy

D-ring chloro-substituted neocryptolepines have been synthesized in excellent yield starting from 3-bromo-2-chloro-1-methylquinolinium triflate via a one-pot condensation—Pd-catalyzed intramolecular direct arylation strategy involving chloroanilines. The 3-bromo-2-chloro-1-methylquinolinium triflate was obtained via methylation of commercial 3-bromo-2-chloroquinoline with methyl triflate.     

Influence of the alkyl group of triflate esters on their initiation ability for the cationic ring-opening polymerization of tetrahydrofuran

Esters of trifluoromethane sulfonic acid have been synthesized by reaction of different alcohols with triflic anhydride and used in situ as initiators for the polymerization of tetrahydrofuran. Kinetic studies of the polymerization showed that allyl triflate has the highest reactivity and that an increase of the alkyl chain length of the initiator leads to a significant decrease of the initiation rate. “Non-linear” triflate ester such as isobutyl triflate leads to incomplete initiation. It was impossible to synthesize quantitatively the triflate from tert-butyl alcohol due to spontaneous elimination leading to isobutylene.     

Iodonium Metathesis Reactions

A metathesis reaction occurs when a diaryliodonium triflate is heated with an aryl iodide, resulting in the formation of a new diaryliodonium triflate.     

A convenient synthesis of triflate anion ionic liquids and their properties

A solvent- and halogen-free synthesis of high purity triflate ionic liquids via direct alkylation of organic bases (amines, phosphines or heterocyclic compounds) with methyl and ethyl trifluoromethanesulfonate (methyl and ethyl triflate) has been developed. Cheap and non-toxic dimethyl and diethyl carbonate serve as source for the methyl and ethyl groups in the preparation of methyl and ethyl triflate by this invented process. The properties of ionic liquids containing the triflate anion are determined and discussed.     

Experimental and computational insights into the stabilization of low-valent main group elements using crown ethers and related ligands

A series of tin(II) triflate and chloride salts in which the cations are complexed by either cyclic or acyclic polyether ligands and which have well-characterized single-crystal X-ray structures are investigated using a variety of experimental and computational techniques. M?ssbauer spectroscopy illustrates that the triflate salts tend to have valence electrons with higher s-character, and solid-state NMR spectroscopy reveals marked differences between superficially similar triflate and chloride salts. Cyclic voltammetry investigations of the triflate salts corroborate the results of the M?ssbauer and NMR spectroscopy and reveal substantial steric and electronic effects for the different polyether ligands. MP2 and DFT calculations provide insight into the effects of ligands and substituents on the stability and reactivity of the low-valent metal atom. Overall, the investigations reveal the existence of more substantial binding between tin and chlorine in comparison to the triflate substituent and provide a rationale for the considerably increased reactivity of the chloride salts.     

Vibrational spectroscopic and ab initio molecular orbital studies of the normal and 13C-labelled trifluoromethanesulfonate anion

Infrared and Raman spectra of both normal and ¹³C-labelled tetrabutylammonium trifluoromethanesulfonate (triflate) [Bu₄N·CF₃SO₃] and mercury triflate Hg(CF₃SO₃)₂ were recorded at room temperature. The observed isotopic frequency shifts and bandwidths in the vibrational spectra of the triflate anion were taken into account in the assignments of the vibrational modes of the triflate anion. These assignments were supported by ab initio Hartree—Fock self-consistent field (HF-SCF) calculations of vibrational frequencies and normal modes for the triflate anion.     

Cyclic vinylogous triflate hemiacetals as new surrogates for alkynyl aldehydes

Cyclic vinylogous triflate hemiacetals can serve as ‘synthetic equivalents’ for alkynyl aldehydes: treatment of a vinylogous triflate hemiacetal with excess amounts of Grignard reagents produces acyclic alkynyl alcohols in good to high yields. This transformation likely involves the Grob-type C-C bond cleaving fragmentation to form the alkynyl aldehyde in situ. Subsequent nucleophilic attack of the Grignard reagent furnishes secondary alkynols. Vinylogous triflate hemiacetals are easily prepared by DIBALH reduction of vinylogous acyl triflates, which are derived from cyclic 1,3-diketones.     

Direct functionalization of arenes by primary alcohol sulfonate esters catalyzed by gold(III)

Alkylation of arenes by primary alcohol triflate or methanesulfonate esters can be efficiently catalyzed by AuCl3 with silver triflate.     

Vinyl carbocations: solution studies of alkenyl(aryl)iodonium triflate fragmentations

Generation of vinyl cations is facile by fragmentation of alkenyl(aryl)iodonium trifluoromethanesulfonates. Kinetics and electronic effects were probed by (1)H NMR spectroscopy in CDCl(3). Products of fragmentation include six enol triflate isomers in addition to iodoarenes. The enol triflates arise from direct reaction of a triflate anion with the starting iodonium salts as well as triflate reaction with rearranged secondary cations derived from those salts. G2 calculations of the theoretical isodesmic hydride-transfer reaction between secondary vinyl cation 7 and primary vinyl cation 6 reveal that cation 6 is 17.8 kcal/mol higher in energy. Activation parameters for fragmentation of (Z)-2-ethyl-1-hexenyl(3,5-bis-trifluoromethylphenyl)iodonium triflate, 17e, were calculated using the Arrhenius equation: E(a) = 26.8 kcal/mol, Delta H(++) = 26.2 kcal/mol, and Delta S(++) = 11.9 cal/mol x K. Added triflate increases the rate of fragmentation slightly, and it is likely that for most beta,beta-dialkyl- substituted vinylic iodonium triflates enol triflate fragmentation products are derived from three competing mechanisms: (a) vinylic S(N)()2 substitution; (b) ligand coupling (LC); and (c) concerted aryliodonio departure and 1,2-alkyl shift leading to secondary rather than primary vinyl cations.     

Imidazolium ionic liquids as solvents for cerium(IV)-mediated oxidation reactions

Use of imidazolium ionic liquids as solvents for organic transformations with tetravalent cerium salts as oxidizing agents was evaluated. Good solubility was found for ammonium hexanitratocerate(IV) (ceric ammonium nitrate, CAN) and cerium(IV) triflate in 1-alkyl-3-methylimidazolium triflate ionic liquids. Oxidation of benzyl alcohol to benzaldehyde in 1-ethyl-3-methylimidazolium triflate was studied by in-situ FTIR spectroscopy and 13C NMR spectroscopy on carbon-13-labeled benzyl alcohol. Careful control of the reaction conditions is necessary because ammonium hexanitratocerate(IV) dissolved in an ionic liquid can transform benzyl alcohol not only into benzaldehyde but also into benzyl nitrate or benzoic acid. The selectivity of the reaction of cerium(IV) triflate with benzyl alcohol in dry ionic liquids depends on the degree of hydration of cerium(IV) triflate: anhydrous cerium(IV) triflate transforms benzyl alcohol into dibenzyl ether, whereas hydrated cerium(IV) triflate affords benzaldehyde as the main reaction product. Reactions of ammonium hexanitratocerate(IV) with organic substrates other than benzyl alcohol have been explored. 1,4-Hydroquinone is quantitatively transformed into 1,4-quinone. Anisole and naphthalene are nitrated. For the cerium-mediated oxidation reactions in ionic liquids, high reaction temperatures are an advantage because under these conditions smaller amounts of byproducts are formed.     

Synthesis and characterization of a β-diketiminate-supported aluminum dication

A base-stabilized mononuclear aluminum dication has been prepared by extrusion of two triflate anions from a precursor β-diketiminate-supported aluminum bis(triflate) using the tris(2-aminoethyl)amine (tren) ligand.     

Versatile application of trifluoromethyl triflate

Hydrolytically stable and easy to handle trifluoromethyl triflate was found to be a liquid reservoir of ‘masked’ difluorophosgene. Anhydrous F⁻ sources cleave the S-O bond in trifluoromethyl triflate yielding quantitatively the trifluoromethanolate salts, being useful trifluoromethoxy group carriers. Reaction of trifluoromethanolates with in situ generated from o-trimethylsilylphenyl triflate benzyne leads to (trifluoromethoxy)benzene and fluorobenzene (ratio 85:15). Whereas an addition of trifluoromethanethiolate anion across a triple bond of benzyne leads to [(trifluoromethyl)sulfanyl]benzene solely.     

Preparation of bis(heteroaryl)iodonium salts via an iodonium transfer reaction between di(cyano)iodonium triflate and organostannes

Di(cyano)iodonium triflate 5 generated in situ from iodosyl triflate (0 = I-OTf) and cyanotrimethylsilane is a preferred reagent for the preparation of various bis(heteroaryl)iodonium triflate salts 11–15 via an iodonium transfer reaction with the corresponding tributyltin substituted heterocycles 6–10 . Novel heteroaromatic iodonium salts 3, 11–15 were isolated in good yields as relatively stable microcrystalline solids and characterized by multinuclear nmr, ir and hrms data.     

Polycondensation of α‐amino acid esters in the presence of yttrium triflate as a Lewis acid

To develop polycondensation methods for poly(α‐amino acid)s, we describe a first examination to use yttrium triflate as a Lewis acid for polycondensation of α‐amino acid esters. In the absence of Lewis acid, no polycondensation of 2‐methoxyphenyl glycinate ( 1b ) at room temperature proceeded. While the polycondensation of 1b was carried out with 5 mol % yttrium triflate, a condensation product of glycine was obtained in 16% yield. Although polycondensation of 4‐nitrophenyl L ‐leucinate ( 1c ) and 4‐nitrophenyl L ‐valinate ( 1d ) were also promoted with 5 mol % yttrium triflate, the condensation products of both α‐amino acid esters were obtained in only a few percent yield. When 1d was polymerized in the presence of 100 mol % yttrium triflate, high molecular weight poly(L ‐valine) was obtained in 91% yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4731–4735, 2006     

Indium‐Catalyzed Synthesis of Keto Esters from Cyclic 1,3‐Diketones and Alcohols and Application to the Synthesis of Seratrodast

Esterification reactions from cyclic 1,3‐diketones and alcohols are carried out in the presence of several Lewis acids. In particular, indium(III) triflate, In(OTf)₃, iron(III) triflate, Fe(OTf)₃, copper(II) triflate, Cu(OTf)₂, and silver(I) triflate, AgOTf, show high catalytic activities. These reactions proceed through the carbon–carbon bond cleavage by a retro‐aldol reaction and were found to be highly regioselective even in the presence of other functional groups. This type of reaction can also be applied to the preparation of the keto esters during the synthesis of seratrodast, which is an antiasthmatic and eicosanoid antagonist.     

Bismuth(III) Triflate: A Safe and Easily Handled Precursor for Triflic Acid: Application to the Esterification Reaction

A series of carboxylic acids were converted into their corresponding methyl esters using bismuth(III) triflate as a catalyst in methanol. Good to excellent yields were obtained for different aliphatic or aromatic starting materials. In the reaction, bismuth triflate acts as a precursor that, upon hydrolysis, liberates sufficient triflic acid to catalyze the esterification.