Oxonium Cation Research Articles

The evidence of hydrated proton in eudialyte‐group minerals based on Raman spectroscopy data

AbstractHydronium (oxonium) cation H3O+ plays an important role in mineralogy and mineral structures. However, it is rather difficult to detect it using conventional methods of crystal structure analysis. In particular, hydronium‐bearing eudialyte‐group minerals (EGMs) are well known. In this paper, we provide data on a low‐temperature X‐ray structure analysis and vibrationl spectroscopy study of previously described “potassium‐oxonium eudialyte” from the Khibiny alkaline massif (Kola Peninsula, Russia) as well as new data on vibrational spectra and hydrogen bonding of a series of sodium‐deficient hydrated EGMs including new samples and minerals whose crystal structures were investigated earlier. Based on single‐crystal X‐ray structural analysis and Raman spectroscopy, it is shown that natural sodium‐deficient hydrated zirconosilicates related to eudialyte contain different hydrated proton complexes with extremely strong hydrogen bonds. The data obtained have been compared with recent high‐level quantum electronic and vibrational calculations. Some hydrated proton complexes in hydrated eudialyte‐related minerals have Zundel‐ and Eigen‐type configurations with the O˙˙˙O distances of ~2.40 and ~2.55 Å, respectively.

Selective Metal-Ligand Bond-Breaking Driven by Weak Intermolecular Interactions: From Metamagnetic Mn(III)-Monomer to Hexacyanoferrate(II)-Bridged Metamagnetic Mn2Fe Trimer.

Metal-ligand coordination interactions are usually much stronger than weak intermolecular interactions. Nevertheless, here, we show experimental evidence and theoretical confirmation of a very rare example where metal-ligand bonds dissociate in an irreversible way, helped by a large number of weak intermolecular interactions that surpass the energy of the metal-ligand bond. Thus, we describe the design and synthesis of trinuclear Mn2Fe complex {[Mn(L)(H2O)]2Fe(CN)6},2- starting from a mononuclear Mn(III)-Schiff base complex: [Mn(L)(H2O)Cl] (1) and [Fe(CN)6]4- anions. This reaction implies the dissociation of Mn(III)-Cl coordination bonds and the formation of Mn(III)-NC bonds with the help of several intermolecular interactions. Here, we present the synthesis, crystal structure, and magnetic characterization of the monomeric Mn(III) complex [Mn(L)(H2O)Cl] (1) and of compound (H3O)[Mn(L)(H2O)2]{[Mn(L)(H2O)]2Fe(CN)6}·4H2O (2) (H2L = 2,2'-((1E,1'E)-(ethane-1,2-diylbis(azaneylylidene))bis(methaneylylidene))bis(4-methoxyphenol)). Complex 1 is a monomer where the Schiff base ligand (L) is coordinated to the four equatorial positions of the Mn(III) center with a H2O molecule and a Cl- ion at the axial sites and the monomeric units are assembled by π-π and hydrogen-bonding interactions to build supramolecular dimers. The combination of [Fe(CN)6]4- with complex 1 leads to the formation of linear Mn-NC-Fe-CN-Mn trimers where two trans cyano groups of the [Fe(CN)6]4- anion replace the labile chloride from the coordination sphere of two [Mn(L)(H2O)Cl] complexes, giving rise to the linear anionic {[Mn(L)(H2O)]2Fe(CN)6}2- trimer. This Mn2Fe trimer crystallizes with an oxonium cation and a mononuclear [Mn(L)(H2O)2]+ cation, closely related to the precursor neutral complex [Mn(L)(H2O)Cl]. In compound 2, the Mn2Fe trimers are assembled by several hydrogen-bonding and π-π interactions to frame an extended structure similar to that of complex 1. Density functional theoretical (DFT) calculations at the PBE1PBE-D3/def2-TZVP level show that the bond dissociation energy (-29.3 kcal/mol) for the Mn(III)-Cl bond is smaller than the summation of all the weak intermolecular interactions (-30.1 kcal/mol). Variable-temperature magnetic studies imply the existence of weak intermolecular antiferromagnetic couplings in both compounds, which can be can cancelled with a critical field of ca. 2.0 and 2.5 T at 2 K for compounds 1 and 2, respectively. The magnetic properties of compound 1 have been fit with a simple S = 2 monomer with g = 1.959, a weak zero-field splitting (|D| = 1.23 cm-1), and a very weak intermolecular interaction (zJ = -0.03 cm-1). For compound 2, we have used a model with an S = 2 monomer with ZFS plus an S = 2 antiferromagnetically coupled dimer with g = 2.009, |D| = 1.21 cm-1, and J = -0.42 cm-1. The metamagnetic behavior of both compounds is attributed to the weak intermolecular π-π and hydrogen-bonding interactions.

Mass spectrometry of d-ribose molecules

The results of mass spectra of d-ribose molecular beam study by electron impact for the 20–70 eV energy range at the evaporation temperature 310–430 K are presented. The experiment was carried out in two stages: first the mass spectra were measured in the range of 0–200 Da at different ionization energies, then relative cross-sections of single ionization of fragment ions were investigated in the electron energy range of 5–60 eV. The measured temperature dependences show the competing character of water and oxonium cation formation processes. It is the first determination of the appearance energy (AE) for the d-ribose molecule from the threshold region of the energy dependence of the effective ionization cross section. For the most intense fragment ions in the mass spectrum, the potentials of appearance are determined at the threshold of the dissociative ionization cross sections. Schemes for the fragmentation of positive d-ribose ions are proposed.

Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers

AbstractZwitterionic structure is necessary for NiII complexes to catalyze carbonylative polymerization (COP) of cyclic ethers. The cationic charge at the NiII center imparts sufficient electrophilicity to the Ni–acyl bond for it to react with cyclic ethers to give an acyl‐cyclic ether oxonium intermediate, while the ligand‐centered anionic charge ensures that the resultant oxonium cation is ion‐paired with the Ni0 nucleophile. The current catalysts give non‐alternating copolymers of carbon monoxide and cyclic ethers and are the most effective when both ethylene oxide and tetrahydrofuran are present as the cyclic ether monomers.

Zwitterionic Design Principle of Nickel(II) Catalysts for Carbonylative Polymerization of Cyclic Ethers.

Zwitterionic structure is necessary for NiII complexes to catalyze carbonylative polymerization (COP) of cyclic ethers. The cationic charge at the NiII center imparts sufficient electrophilicity to the Ni-acyl bond for it to react with cyclic ethers to give an acyl-cyclic ether oxonium intermediate, while the ligand-centered anionic charge ensures that the resultant oxonium cation is ion-paired with the Ni0 nucleophile. The current catalysts give non-alternating copolymers of carbon monoxide and cyclic ethers and are the most effective when both ethylene oxide and tetrahydrofuran are present as the cyclic ether monomers.

Surprisingly Flexible Oxonium/Borohydride Ion Pair Configurations.

We investigate the geometry of oxonium/borohydride ion pairs [ether-H(+)-ether][LA-H(-)] with dioxane, THF, and Et2O as ethers and B(C6F5)3 as the Lewis acid (LA). The question is about possible location of the disolvated proton, [ether-H(+)-ether], with respect to the hydride of the structurally complex [LA-H(-)] anion. Using Born-Oppenheimer molecular dynamics and a comparison of the potential and free energies of the optimized configurations, we show that herein considered ion pairs are much more flexible geometrically than previously thought. Conformers with different locations of cations with respect to anions are governed by a flat energy-landscape. We found a novel configuration in which oxonium is below [LA-H(-)], with respect to the direction of borane → hydride vector, and the proton-hydride distance is ca. 6 Å. With calculations of the vibrational spectra of [ether-H(+)-ether][(C6F5)3B-H(-)] for dioxane, THF, and Et2O as ethers, we investigate the manifestation of SSLB-type (short, strong, low-barrier) hydrogen bonding in the OHO motif of an oxonium cation.

Decomposition of a β-O-4 lignin model compound over solid Cs-substituted polyoxometalates in anhydrous ethanol: acidity or redox property dependence?

Production of aromatics from lignin has attracted much attention. Because of the coexistence of C–O and C–C bonds and their complex combinations in the lignin macromolecular network, a plausible roadmap for developing a lignin catalytic decomposition process could be developed by exploring the transformation mechanisms of various model compounds. Herein, decomposition of a lignin model compound, 2-phenoxyacetophenone (2-PAP), was investigated over several cesium-exchanged polyoxometalate (Cs-POM) catalysts. Decomposition of 2-PAP can follow two different mechanisms: an active hydrogen transfer mechanism or an oxonium cation mechanism. The mechanism for most reactions depends on the competition between the acidity and redox properties of the catalysts. The catalysts of POMs perform the following functions: promoting active hydrogen liberated from ethanol and causing formation of and then temporarily stabilizing oxonium cations from 2-PAP. The use of Cs-PMo, which with strong redox ability, enhances hydrogen liberation and promotes liberated hydrogen transfer to the reaction intermediates. As a consequence, complete conversion of 2-PAP (>99%) with excellent selectivities to the desired products (98.6% for phenol and 91.1% for acetophenone) can be achieved. The lignin model compound 2-phenoxyacetophenone can be completely cleaved into target products in a hydrogen-donating atmosphere over a catalyst with strong redox properties by the hydrogen transfer mechanism.

Challenges encountered during development of Mn porphyrin-based, potent redox-active drug and superoxide dismutase mimic, MnTnBuOE-2-PyP5 +, and its alkoxyalkyl analogues

We disclose here the studies that preceded and guided the preparation of the metal-based, redox-active therapeutic Mn(III) meso-tetrakis(N-n-butoxyethylpyridyl)porphyrin, MnTnBuOE-2-PyP5+ (BMX-001), which is currently in Phase I/II Clinical Trials at Duke University (USA) as a radioprotector of normal tissues in cancer patients. N-substituted pyridylporphyrins are ligands for Mn(III) complexes that are among the most potent superoxide dismutase mimics thus far synthesized. To advance their design, thereby improving their physical and chemical properties and bioavailability/toxicity profiles, we undertook a systematic study on placing oxygen atoms into N-alkylpyridyl chains via alkoxyalkylation reaction. For the first time we show here the unforeseen structural rearrangement that happens during the alkoxyalkylation reaction by the corresponding tosylates. Comprehensive experimental and computational approaches were employed to solve the rearrangement mechanism involved in quaternization of pyridyl nitrogens, which, instead of a single product, led to a variety of mixed N-alkoxyalkylated and N-alkylated pyridylporphyrins. The rearrangement mechanism involves the formation of an intermediate alkyl oxonium cation in a chain-length-dependent manner, which subsequently drives differential kinetics and thermodynamics of competing N-alkoxyalkylation versus in situ N-alkylation. The use of alkoxyalkyl tosylates, of different length of alkyl fragments adjacent to oxygen atom, allowed us to identify the set of alkyl fragments that would result in the synthesis of a single compound of high purity and excellent therapeutic potential.

Protonation and electronic structure of 2,6-dichlorophenolindophenolate during reduction. A theoretical study including explicit solvent

Protonation in the two-electron/two-proton reduction processes of 2,6-dichlorophenolindophenolate (DCIP) is investigated combining density functional theory (DFT) and molecular dynamics (MD) methods. DCIP (anion), DCIP•- (radical anion), and DCIP2- (dianion) are considered, including the electronic structure analysis from the prospective of quantum theory of atoms and molecules (QTAIM). It is shown that oxygen on the indophenolate moiety and nitrogen are the first and/or the second proton acceptor sites and their energetic order depends on the total charge of the system. MD simulations of differently charged species interacting with the solvent molecules have been performed for methanol, water, and oxonium cation (H3O+). Methanol and water molecules are found to form only hydrogen bonds with the solute irrespective of its charge. The calculated pKa values show that the imino group of DCIPH- is a weaker acid than water. While in the case of DCIP (and DCIP•-) plus oxonium cation, proton transfer from the solvent to the solute was evidenced for both aforementioned acceptor sites. In addition, MD simulations of bulks containing 15 and 43 molecules of water around the DCIP molecule have been performed, revealing the formation of 2-4 hydrogen bonds. Graphical Abstract 2,6-Dichlorophenolindophenolate interacts with solvent molecules (water, oxonium cation and methanol). Hydrogen transfer and electronic structure are studied by DFT and molecular dynamics methods.

Silver- and Acid-Free Catalysis by Polyoxometalate-Assisted Phosphanegold(I) Species for Hydration of Diphenylacetylene

A DMSO-soluble intercluster compound consisting of a tetra{phosphanegold(I)}oxonium cation and an α-Keggin polyoxometalate (POM) anion, [{Au(PPh3)}4(μ4-O)]3[α-PW12O40]2 (1), was found to be an effective precatalyst for the silver- and acid-free catalysis of diphenylacetylene hydration (0.67 mol % catalyst; conversions 36.1%, 55.2%, and 93.7% after 4, 6, and 24 h reactions, respectively). The reaction proceeded in the suspended system in 6 mL of 1,4-dioxane/water (4:1) at 80 °C because of the low solubility of 1. Similar POM-based phosphanegold(I) compounds [{{Au(PPh3)}4(μ4-O)}{{Au(PPh3)}3(μ3-O)}][α-PW12O40]·EtOH (5), which is composed of a heptakis{triphenylphosphanegold(I)}dioxonium cation and an α-Keggin POM anion, and [Au(CH3CN)(PPh3)]3[α-PMo12O40] (6), which consists of an acid-free monomeric phosphanegold(I) acetonitrile cation and an α-Keggin molybdo-POM anion, also exhibited acid-free catalysis for the hydration of diphenylacetylene. An induction period was observed in the catalysis by 5. On the ot...

Cationic polymerization behavior of β‐methylglycidyl ether derivatives and physical properties of their cationically cured materials

ABSTRACTβ‐Methylglycidyl ethers have been applied to Electrical and Electronic adhesives. However, there is no report about the detailed polymerization behavior and physical properties of their cured products. Hence, we investigated cationic polymerization behavior of bisphenol A di(β‐methylglycidyl) ether (Me‐BADGE) and physical properties of the cured products containing Me‐BADGE. DSC analysis suggested that Me‐BADGE could be cured completely at lower temperature than bisphenol A diglycidyl ether (BADGE). Physical properties were analyzed by dynamic viscoelastic analysis. Glass transition temperature (Tg) of BADGE homopolymer was 194°C. In contrast, the copolymer of BADGE (50 wt %) with Me‐BADGE (50 wt %) showed Tg at 124°C. According to the data of E’ and tan δ, crosslink density of the cured products decreased with increasing the Me‐BADGE content. The analysis of cationic polymerization of monofunctional β‐methylglycidyl ether suggested that the cationic polymerization proceeded not only through oxonium cation but also through carbocation formed by ring‐opening reaction of oxonium cation. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42377.

Functionalized Oxatriquinanes and Their Structural Equilibrium in Protic Solvent

We synthesized oxatriquinane hexafluorophosphate bearing an ethoxycarbonylmethyl group 7 or a 2-oxopropyl group 11. Both of these organic oxonium cation compounds were obtained as stable solids. However, (1)H-NMR analysis showed that oxatriquinane 7 was present as the oxonium cation in aprotic solvent CD₃CN, but was in rapid equilibrium with ring-opened bicyclic compound 8 in protic solvent CD₃OD. The oxatriquinane 11 also showed similar behavior in protic solvent. Phenyl-substituted oxatriquinanes 12 and 14 were also obtained as stable solids, and showed similar properties to 7 and 11.

Novel Intercluster Compounds Composed of a Tetra{phosphanegold(I)}oxonium Cation and an α-Keggin Polyoxometalate Anion Linked by Three Monomeric Phosphanegold(I) Units

Abstract Using highly negatively charged Keggin polyoxometalates (POMs), [α-XW12O40]5− (X = Al and B), novel intercluster compounds composed of a tetrakis{triphenylphosphanegold(I)}oxonium cation and an α-Keggin POM linked by three monomeric triphenylphosphanegold(I) units were prepared. A single peak was observed in the solution 31P{1H} NMR for these clusters, which is consistent with rapid exchange of the phosphanegold(I) units in the tetra{phosphanegold(I)}oxonium cluster cation with the three monomeric phosphanegold(I) species linked to the POM. Importantly, these compounds may be relevant transition states or intermediates in POM-mediated tetra{phosphanegold(I)}oxonium cluster formation.

Electrochemistry of TEMPO: an assessment of the water diffusion constant in the aqueous liquid/vapor interfacial region

TEMPO, 2,2,6,6-tetramethylpiperidnyl-1-oxy, is a weak surfactant exhibiting a reversible redox activity: a one-electron oxidation to its oxonium cation. In the course of our earlier work (ref. Wu et al. in J Am Chem Soc 127:4490–4496, 2005; Glandut et al. in J Phys Chem B 110:6101–6109, 2006; Glandut et al. in Langmuir 22:10697–10704, 2006), we developed a full understanding of TEMPO’s electrochemistry at line microband electrodes. In these experiments TEMPO diffuses to the line electrode residing in the plane of the air/water interface in two coupled media, bulk aqueous phase with D = 7.7 × 10−6 cm2/s and along the 2D air/water interface with at least an order of magnitude greater surface diffusion constant, Dsurf. The magnitude of the TEMPO oxidation current depends jointly on Dsurf and on the rate of surface partitioning expressed by the desorption rate constant, kdes. The population of TEMPO partitioned to the air/water interface is largely unsolvated and couples to the aqueous solution by hydrogen bonding to predominately one water molecule. Our experimental methodology allows us to simultaneously determine Dsurf and kdes by recording TEMPO voltammetric curves with line microband and barrier microband electrodes. In this report, we present a new methodology of producing and characterizing barrier microband electrodes using vapor-deposited SiO and introduce additional measures such as aspiration of the air/water interface designed to substantially reduce if not eliminate negative error due to surface impurities. These investigations generated a more accurate value of Dsurf of 1.0 ± 0.3 × 10−4 cm2/s which we discuss in terms of the dynamic properties of water in the air/water interfacial region.

Myths about the proton. The nature of H+ in condensed media.

Recent research has taught us that most protonated species are decidedly not well represented by a simple proton addition. What is the actual nature of the hydrogen ion (the "proton") when H(+), HA, H2A(+), and so forth are written in formulas, chemical equations, and acid catalyzed reactions? In condensed media, H(+) must be solvated and is nearly always dicoordinate, as illustrated by isolable bisdiethyletherate salts having H(OEt2)2(+) cations and weakly coordinating anions. Even carbocations such as protonated alkenes have significant C-H···anion hydrogen bonding that gives the active protons two-coordinate character. Hydrogen bonding is everywhere, particularly when acids are involved. In contrast to the normal, asymmetric O-H···O hydrogen bonding found in water, ice, and proteins, short, strong, low-barrier (SSLB) H-bonding commonly appears when strong acids are present. Unusually low frequency IR νOHO bands are a good indicator of SSLB H-bonds, and curiously, bands associated with group vibrations near H(+) in low-barrier H-bonding often disappear from the IR spectrum. Writing H3O(+) (the Eigen ion), as often appears in textbooks, might seem more realistic than H(+) for an ionized acid in water. However, this, too, is an unrealistic description of H(aq)(+). The dihydrated H(+) in the H5O2(+) cation (the Zundel ion) gets somewhat closer but still fails to rationalize all the experimental and computational data on H(aq)(+). Researchers do not understand the broad swath of IR absorption from H(aq)(+), known as the "continuous broad absorption" (cba). Theory has not reproduced the cba, but it appears to be the signature of delocalized protons whose motion is faster than the IR time scale. What does this mean for reaction mechanisms involving H(aq)(+)? For the past decade, the carborane acid H(CHB11Cl11) has been the strongest known Brønsted acid. (It is now surpassed by the fluorinated analogue H(CHB11F11).) Carborane acids are strong enough to protonate alkanes at room temperature, giving H2 and carbocations. They protonate chloroalkanes to give dialkylchloronium ions, which decay to carbocations. By partially protonating an oxonium cation, they get as close to the fabled H4O(2+) ion as can be achieved outside of a computer.

Oxonium picrate.

The title compound, H3O+·C6H2N3O7 −, consists of one picrate anion and one oxonium cation. The oxonium cation is located on a crystallographic twofold axis and both its H atoms are disordered, each over two symmetry-equivalent positions with occupancy ratios of 0.75. The picrate anions are also located on twofold axes bis­ecting the phenolate and p-nitro groups. π–π inter­actions between the rings of the picrates [centroid-to-centroid distances of 3.324 (2) Å] connect the anions to form stacks along the a-axis direction. The stacks are further joined together by the protonated water mol­ecules through hydrogen bonds to form two-dimensional sheets extending parallel to the ab plane. The sheets are stacked on top of each other along the c-axis direction and connected through C—H⋯O inter­actions between the CH groups of the benzene rings and the picrate nitro groups, with C⋯O distances of 3.450 (2) Å.

Intercluster Compound between a Tetrakis{triphenylphosphinegold(I)}oxonium Cation and a Keggin Polyoxometalate (POM): Formation during the Course of Carboxylate Elimination of a Monomeric Triphenylphosphinegold(I) Carboxylate in the Presence of POMs

The preparation and structural characterization of a novel intercluster compound, [{Au(PPh(3))}(4)(μ(4)-O)](3)[α-PW(12)O(40)](2)·4EtOH (1), constructed between a tetrakis{triphenylphosphinegold(I)}oxonium cation and a saturated α-Keggin polyoxometalate (POM) are described. The tetragold(I) cluster oxonium cation was formed during the course of carboxylate elimination of a monomeric phosphinegold(I) carboxylate complex, i.e., [Au((R,S)-pyrrld)(PPh(3))] [(R,S)-Hpyrrld = (R,S)-2-pyrrolidone-5-carboxylic acid], in the presence of the free acid form of a Keggin POM, H(3)[α-PW(12)O(40)]·7H(2)O. The liquid-liquid diffusion between the upper water/EtOH phase containing the Keggin POM and the lower CH(2)Cl(2) phase containing the monomeric gold(I) complex gave a pure crystalline sample of 1 in good yield (42.1%, 0.242 g scale). Complex 1 was formed by ionic interaction between the tetragold(I) cluster cation and the Keggin POM anion. As a matter of fact, the POM anion in 1 can be exchanged with the BF(4)(-) anion using an anion-exchange resin (Amberlyst A-27) in BF(4)(-) form. By using other Keggin POMs, such as H(4)[α-SiW(12)O(40)]·10H(2)O and H(3)[α-PMo(12)O(40)]·14H(2)O, the same tetragold(I) cluster cation was also formed, i.e., in the forms of [{Au(PPh(3))}(4)(μ(4)-O)](2)[α-SiW(12)O(40)]·2H(2)O (2) and [{Au(PPh(3))}(4)(μ(4)-O)](3)[α-PMo(12)O(40)](2)·3EtOH (3). Compounds 1-3, as dimethyl sulfoxide-soluble, EtOH- and Et(2)O-insoluble dark-yellowish white solids, were characterized by complete elemental analysis, thermogravimetric and differential thermal analyses, Fourier transform IR, X-ray crystallography, and solid-state (CPMAS (31)P and (29)Si) and solution ((31)P{(1)H} and (1)H) NMR spectroscopy. The molecular structures of 1 and 2 were successfully determined. The tetragold(I) cluster cation was composed of four PPh(3)Au(I) units bridged by a central μ(4)-oxygen atom in the geometry of a trigonal pyramid or distorted tetrahedron.

Why Oxonium Cation in the Crystal Phase is a Bad Acceptor of Hydrogen Bonds: A Charge Density Analysis of Potassium Oxonium Bis(hydrogensulfate)

Peculiarities of chemical bonding in the crystal of potassium oxonium bis(hydrogensulfate) were analyzed by means of R. Bader's "Atoms in Molecule" theory on the basis of the experimental data. The results obtained were shown to provide insight into the tendency of the oxygen atom of the oxonium moiety to avoid the H-bond formation in its crystalline salts.

Oxonium ammonio(cyclopropyl)methylenebis(hydrogenphosphonate) monohydrate

The title compound, H3O+·C4H10NO6P2 −·H2O, was obtained from the reaction of cyclo­propane­carbonitrile with PCl3, followed by dropwise addition of water. The asymmetric unit comprises an oxonium cation, a zwitterionic monoanion containing a positively charged ammonium group and two negatively charged phospho­nic acid residues and a water mol­ecule of crystallization. The hydroxonium cation and water mol­ecule are hydrogen bonded to the anion and further N—H⋯O and O—H⋯O bonds create a three-dimensional network.

Hg(OTf)2-Catalyzed Cyclization of N-Tosylanilinoallylic Alcohols to 2-Vinylindolines

The Hg(OTf) 2 -catalyzed cyclization of N-tosylanilino-allylic alcohols giving rise to vinyl-substituted indolines has been developed. The reaction takes place with a highly efficient catalytic turnover (up to 1000 times) under mild conditions. The hydroxyl group of the organomercuric intermediate is protonated by in situ formed TfOH generating an oxonium cation, which regenerates the catalyst after demercuration.