Sulphonium Cation Research Articles

Ionic Liquid Synthesis of (Et3S)[Ag4I5] – A Structure Containing Basket‐Like Silver‐Iodide Cages with Ag22+ Pairs

AbstractThe compound (Et3S)[Ag4I5], 1, is readily synthesized from room‐temperature, ionic‐liquid media and displays a complex network structure of Ag6I6 cages with Ag22+ pairs forming 1D‐chains linked into layers distinctly separate from the disordered sulphonium cations. The compound should be regarded as a large‐bandgap semiconductor, but its significant structural voids qualify the compound a candidate for optoelectronic applications through the inclusion of suitable guest molecules.

On electronic structure of tris(dimethylamino)sulphonium heptafluoro-oxocyclotetraphosphazenate

The results of 3D periodic B3LYP calculations of tris(dimethylamino)sulphonium heptafluoro-oxocyclotetraphosphazenate in experimental geometry are compared with the analogous results for its isolated anion and cation in experimental and B3LYP optimized geometry. The electronic structure structure is evaluated in the terms of QTAIM topological analysis of electron density. P N bonds alternation and an increased cyclotetraphosphazene ring puckering is not due to solid state effects but due to O/F substitution. Tris(dimethylamino)sulphonium cation in experimental geometry has two S N bonds with positive electron density Laplacians at bond critical points (BCP) whereas the third S N bond has this value negative as expected for covalent bonds. Its B3LYP optimized structure of C 3 symmetry has all S N bonds with negative BCP electron density Laplacians.

Can thioglycosides imitate the oxonium intermediate in glycosyl hydrolases?

Glycosyl hydrolases catalyse the acid hydrolysis of the glycosidic bond of glycans. The structure of barley β- d-glucan glucohydrolase in complex with a thiol substrate analogue presents very short contacts between the carboxyl oxygen atoms of the catalytic acid and the sulphur atom of the inhibitor. The geometries of acetic acid and dimethylsulfide in various ionisation states from ab initio molecular orbital calculations predict similar short contacts when an acetate anion forms a complex with a sulphonium cation. The energy of this complex is, however, significantly greater than the energy of the complex where both acetic acid and dimethylsulfide are neutral. Calculations on an active site model of barley β- d-glucan glucohydrolase indicate that the protein environment is able to significantly reduce this energy. The energy required for mechanical constraint of the short S⋯O separations, however, is identical to that required for the transfer of the proton from the acid to the sulphur. The identity of the species participating in the short contacts remains unanswered.

Properties of junctions of crystalline networks of complex TCNQ salts in polymer matrix with silicon

The properties of junctions formed by conductive organic polymer composites with networks of two complex tetracyanoquinodimethane (TCNQ) salts (of N-n-butyl-isoquinolinium and of diethyl methyl sulphonium cations) with silicon were studied. We show that it is possible to prepare junctions with quite good rectifying properties, comparable to those using other organic semiconductors. The observed current-voltage characteristics can be satisfactorily fitted using the modified Schottky equation. C-V characteristics show that the transport mechanism, especially in the case of p-Si junctions is more complicated and probably tunnelling between localized levels plays an important role.

A unique example of an octahedral iron(II) complex containing four triflate anions and two nitrile-like organometallic cations

The action of MeSO3CF3 on [Fe2(cp)2(CO)2(µ-CO){µ-C(CN)SMe}]1(cp =η5-C5H5) yields [Fe2(cp)2(CO)2(µ-CO){µ-C(CN)SMe2}][SO3CF3]2. The sulphonium cation is also obtained, trapped in the unusual triflate complex Fe(OSO2CF3)4{Fe2(cp)2(CO)2(µ-CO)[µ-C(CN)SMe2}2]3, by treating the thiolcarbamate [Fe2(cp)2(CO)2(µ-CO){µ-C(CN)N(Me)C(O)SMe}]4 with MeSO3CF3. The X-ray crystal structure of 3 shows the iron(II) centre co-ordinated by four O-bonded triflate anions and by two, mutually trans-disposed, N-co-ordinated organometallic cations in an octahedral geometry.

Kinetics and mechanism of oxidation of organic sulphides by lead tetraacetate

Kinetics of oxidation of thirty-three organic sulphides, comprising monosubstituted aryl methyl sulphides and alkyl phenyl sulphides, by lead tetraacetate (LTA), to yield the corresponding sulphoxides, have been studied. The reaction is first order with respect to both sulphide and LTA and is catalysed by hydrogen ions. The observed solvent effect (m= 0.90 for MeSPh) is explained by a nucleophilic attack of the sulphide sulphur on LTA yielding a polar transition state. The rates of oxidation of meta- and para-substituted phenyl methyl sulphides were correlated with Taft′s and Swain′s dual substituent parameter equations. For the para-compounds, the best correlation is obtained with σ1 and σR+; the meta-substituted compounds correlate best with σ1 and σR0 values. The reaction constants are negative. The oxidation rates of ortho-substituted compounds yield an excellent correlation with a triparametric equation involving Taft′s σ1, and σR+ parameters, and Charton′s steric parameter V. The oxidation of alkyl phenyl sulphides is susceptible to both polar and steric effects of the alkyl groups. A mechanism involving formation of a sulphonium cation, in the rate-determining step, has been proposed.

Comparison of low‐energy CAD spectra of sulphonium, ammonium and phosphonium cations, propene elimination from allyl‐substituted oniums

AbstractThe low‐energy collision‐activated dissociation of symmetrical n‐butyl‐substituted and of allyl‐substituted onium cations has been recorded using fast atom bombardment ionization and a tandem mass spectrometry quadrupole mass spectrometer. Structure of the fragments and decomposition pathways have been ascertained using a multi‐quadrupole MS/MS/MS triple analyser instrument. Whereas most sulphonium cations exhibit only heterolytic cleavages, fragmentation of ammonium and phosphonium is mainly homolytic. Allylic sulphonium, and to a lesser extent allylic ammonium, easily undergo propene elimination. This reaction, which does not occur in 1‐propenyl oniums, might involve a McLafferty type rearrangement.

Conducting salts of cyclic sulphonium cations with 7,7,8,8-tetracyano-p-quinodimethane (TCNQ): X-ray crystal structure of 1-methyl-1,4-dithianium TCNQ salt, (MDT)1 +(TCNQ)2 ?

Cyclic sulphonium cations (1)–(3) form 1 : 2 salts with TCNQ which are organic conductors at room temperature (σr.t. 1 × 10–3–2.0 S cm–1); the X-ray crystal structure of 1-methyl-1,4-dithianium TCNQ salt (MDT)1+(TCNQ)2–(1) has been determined.

Sulphonium ions: Collision‐activated dissociation using fast atom bombardment ionization and a triple quadrupole mass spectrometer

AbstractThe low‐energy collision‐activated dissociation of sulphonium cations, including symmetrical trialkyl R3S+, dimethylalkyl (CH3)2RS+, diphenylalkyl Ph2RS+ and cyclic (CH2)nS+R, has been recorded using fast atom bombardment ionization and a triple quadrupole mass spectrometer. The general trends are easy loss of sulphide to give [R]+, except for R  CH3, and loss of alkene to give protonated sulphide if β‐hydrogens are available. Loss of alkane, generally found in ammonium compounds, is not observed.

Synthesis of debromo-8,8a-dihydroflustramine c 1 , a model synthesis toward amauromine

Debromo-8,8a-dihydroflustramine C ( 4 ), a model compound of amauromine( 1 ), was synthesized utilizing thio-Claisen rearrangement of a sulphonium cation at the key step. This is the first synthesis of hexahydropyrrolo-[2,3-b]indole skeleton substituted with inverted prenyl group at position 3a.

Total synthesis of amauromine

A total synthesis of amauromine ( 1 ) is described. Starting with L-tryptophan, diketopiperazine 4 was synthesized in nine steps. Thio-Claisen rearrangement of the sulphonium cation derived from the key intermediate 4 proceeded at the two sites simultaneously to provide 3 along with 12 . Reductive desulphurization on 3 using TiCl 4-LiAlH 4 (1:2) resulted in concurrent cyclization to lead to amauromine ( 1 ).

Arene—onium cations—V. Preparative investigation concerning yields and selectivities for the anodic formation of some selected trisarene sulphonium cations

Based on kinetic data for the anodic oxidation of bisarenesulphonium cations[1] the preparative anodic oxidation of bisanisolesulphide, bisbenzenesulphide and bistoluenesulphide was performed in acetonitrile in presence of different arenes as coupling partners aiming to show that higher selectivities for the formation of desired trisarene sulphonium cations can be obtained provided appropriate process parameters are chosen. It is decisive to establish a concentration ratio {c(arene)/c(bisarenesulphide)} in the reaction layer which is high enough to keep the rate of anodic self-coupling vs the coupling with the desired arene low enough. For the formation of trisanisole sulphonium cations, where not self-coupling but coupling with water (yielding bisanisole oxide) is the most important competing reaction, a selectivity of 80% is already obtained if the ratio of the bulk concentrations of the competing coupling partners water and anisole is unity. In the case of the formation of tristoluenesulphide further advantage for obtaining a higher selectivity may be drawn from heterogeneous catalysis of the coupling reaction at carbon anodes. The yield for tristoluene sylphonium cations can be raised to nearly 90% at carbon anodes whereas oxidizing 0.1 M bistoluenesulphide in the presence of 0.1 M toluene at platinum anodes yields only undesired self-coupling products. From bisbenzenesulphide no trisbenzene sulphonium cations could be obtained; however, coupling with mesitylene, xylene and toluene was achieved.

Arene—onium cations—VI Electrode kinetics of the anodic formation of arene—sulphonium cations from bisarenesulphides

Electrode kinetic investigations (voltammetry at stationary electrodes, rotating ring—disc electrodes and rotating rod electrodes) of the anodic oxidation of bisanisole-, bismesitylene-, bisxylene-, bistoluene- and bisbenzenesulphide were performed in acetonitrile. Observed anodic half wave potentials increase in the given order. The S-radical cations of the bisarenesulphides form in a reversible one-electron oxidation step. The radical cations of bisanisole- and bismesitylenesulphide are unable to react, even with relatively strong bases like water, and they disproportionate to form the more reactive dications which react readily with different nucleophiles. The more reactive radical cations of bisxylene-, bistoluene- and bisbenzenesulphide react directly with nucleophiles, for instance with aromatic bases and with the more basic hydrocarbons (anisole, styrene). Participation of dications in their consecutive reactions cannot be detected. The anodic dimerization of these three bisarenesulphides is a relatively fast reaction and is due to the addition of the respective bisarenesulphide radical cation to bisarenesulphide molecules. The reason for the striking mechanistic difference for the two groups of radical cations is very likely an unfavourable disproportionation equilibrium for the more reaction bisarenesulphide radical cations.

X-ray crystallographic analysis of 3-(2'-phenyl-2,4'-bithiazole-4-carboxamido) propyldimethylsulphonium iodide, an analogue of the DNA-binding portion of bleomycin A2.

The crystal and molecular structure of the title compound, an analogue of the DNA binding region of bleomycin A2, has been determined by X-ray crystallography. All the three independent molecules in an asymmetric unit are approximately planar with fully extended side chains. A computer graphics model-building study has shown that the phenyl group and the second thiazole ring can be intercalated between the base pairs of the double-stranded deoxydinucleoside phosphate d(CpG), and also that the sulphonium cation can interact with a backbone phosphate group. This model is in accord with NMR spectral data.

13C13C vicinal coupling constants of sulphonium cations

AbstractThe 13C13C vicinal coupling constants of cyclic sulphonium cations, with the labelled carbon bound to the positively charged sulphur atom, cannotbe related to the dihedral angle ϕ by a Karplus type correlation.

A theoretical study of the sulphonium cation SH +3

Ab initio Hartree—Fock calculations with STO-3G functions have been performed to determine the structure (1.371 Å and 95.33°) of SH + 3 and the proton affinity (≈196 kcal/mol) of H 2S. Inclusion of a sulphur 3d function in the basis has been found essential to give a better geometry of SH + 3.

Kinetics and mechanism of decomposition of benzyldimethylsulphonium salts in chloroform

The decomposition of benzyldimethylsulphonium halides has been studied with chloroform as solvent, in which the reaction goes to completion, yielding the benzyl halide and dimethyl sulphide as the only products. The kinetics show an exact first-order relation with respect to the conductivity of the solution rather than the molar concentration of the salt. The first-order rate constant is controlled by the nucleophilicity of the anion. Addition of small amounts of ammonium salt causes a sharp decrease in rate constant which becomes more gradual and linear at higher concentrations of added salt. This salt effect is completely insensitive to the nature of the anion of the added ammonium salt. Activation parameters and the α-deuterium isotope effect are reported. A mechanism is proposed involving a unimolecular decomposition of a triple ion consisting of two sulphonium cations and one halide ion.

Stereochemistry of the hydrogen–deuterium base-catalysed exchange and conformation of cyclic five-membered sulphonium cations

Nuclear Overhauser experiments indicate that the ring protons of cation (1a) which undergo fast base-catalysed exchange are cis to S–Me; values of Jgem for conformationally rigid thiolanium cations suggest a half-chair conformation for (I).

Mechanism on the photorearrangements of phenylthiazoles

Various arylthiazoles have been subjected to photolysis. The resulting photorearrangements have been classified as type A or B. Type A involves formal exchange of positions 2 and 4, or 3 and 5. Type B involves formal interchange of positions 2 and 3 with concomitant inversion of positions 4 and 5. The mechanistic aspects of the reaction are discussed and we present a mechanism involving a tricyclic sulphonium cation and subsequent formation of a more stable bicyclic intermediate leading to the rearrangement product. Strong support for our proposed mechanism has been provided by deuterium incorporation during the rearrangement of 2-phenylthiazole (17) or 4-phenylthiazole (19) to 3-phenylisothiazole (18).

Photoisomerization of phenylisothiazoles

The photoisomerization of phenylisothiazoles into phenylthiazoles probably proceeds via tricyclic sulphonium cation intermediates.