Carbenium Salts Research Articles

7-Benzyl-3-methyl-6-phenylimidazo[2,1-b][1,3]thiazol-7-ium chloride 0.75-hydrate

Theasymmetric unit of the title salt, C19H17N2S+·Cl−·0.75H2O, contains two symmetrically independent formula units of the carbenium salt along with three water mol­ecules. The water mol­ecules are only 50% occupated, and one of them is positioned in a hydro­phobic pocket not forming any hydrogen bonds. The conformation of the independent cations is very similar, with dihedral angles of 61.0 (2) and 61.5 (3)° between the benzene rings. They form quasi-centrosymmetric couples via π–π stacking inter­actions between the benzene and imidazo[2,1-b]thia­zole rings [centroid–centroid distances = 3.718 (3) and 3.663 (3) Å]. In the crystal, O—H⋯Cl hydrogen bonds lead to the formation of a helical anion–water chain along the c-axis direction. The cations connect to the anion–water chain through C—H⋯Cl inter­actions, generating a three-dimensional supra­molecular network. O—H⋯S hydrogen bonds and C—H⋯O inter­actions also occur.

Fluorescent and Highly Stable Unimodal DMPC Based Unilamellar Vesicles Formed by Spontaneous Curvature

The formation of uniform and highly stable unilamellar vesicles (ULVs) and the theory behind it are ongoing tasks within the vesicle community. Herein, we report the formation of highly stable, fluorescent, and unimodal 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) based ULVs with an average size of ~100 nm, as determined by cryogenic transmission electron microscopy (cryo-TEM) and dynamic light scattering (DLS). The ULVs are formed by mixing a two-component powder mixture or mixed lipid film of DMPC and 5 mol % of a novel amphiphilic carbenium salt, sodium 2-didecylamino-6,10-bis(N-methyltaruino)-4,8,12-trioxatriangulenium (Na-DSA) in aqueous solution when subjected to shaking. We propose that the high stability and the unimodal size distribution of the 5% DSA ULVs confirmed by DLS studies are a product of spontaneous curvature. UV-vis absorption/emission studies reveal that the structure of DSA promotes a strong interaction between the DMPC and the DSA to take place due to the complementary charge distribution of the DSA and DMPC head groups. The strong interaction may introduce an asymmetric amphiphile composition in the inner and outer leaflet of the bilayer which drives the spontaneous curvature.

Columnar Self-Assembly and Alignment of Planar Carbenium Ions in Langmuir−Blodgett Films

Structural and optical properties of multilayer Langmuir-Blodgett (LB) films of two amphiphilic carbenium salts 2-didecylamino-6,10-bis(dimethylamino)-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-1) and 2,6-bis(decylmethylamino)-10-dimethylamino-4,8,12-trioxatriangulenium hexafluorophosphate (ATOTA-2) are described. The LB films were prepared on lipophilic glass by standard vertical dipping. Grazing incidence X-ray diffraction (GIXD) measurements show that the planar organic cores, in spite of their positive charge, form closely packed columns with a repeating distance of ∼3.45 Å. Specular X-ray reflectivity (SXR) reveals the LB multilayers to consist of Y-type bilayers with thickness 31 Å for ATOTA-1 and 41 Å for ATOTA-2. This significant difference is ascribed to the different packing motifs of the alkyl chains in the two LB films. GIXD and polarized UV-vis absorption and emission spectroscopy show that the columnar aggregates in the LB films are oriented along the dipping direction. This alignment is attributed to shear effects during LB transfer. The main absorption band of the LB films is blue-shifted compared to that in solution, while the fluorescence is red-shifted by more than 100 nm. These findings suggest the presence of H-aggregates in agreement with the cofacial packing derived from the X-ray measurements. Polarized absorption spectroscopy with variable angle of incidence was used to resolve two perpendicular optical transitions in the visible range, one at 460 nm polarized perpendicular to the columnar direction, in the plane of the film, and one at 420 nm polarized along the film normal.

Cationic ring-opening polymerization of carbazolyl-containing epoxy monomers by triphenyl carbenium salts as thermal- and photolatent initiators

Photoinitiated cationic polymerizations of various epoxy monomers bearing a carbazole moiety, 9-[3-(allyloxy)-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[3-methoxy-2-(oxiran-2-ylmethoxy)propyl]-9H-carbazole, 9-[2-(oxiran-2-ylmethoxy)ethyl]-9H-carbazole, as well as a composition of 3,6-dibromo-9-(oxiran-2-ylmethyl)-9H-carbazole with 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate were investigated in bulk using triphenyl carbenium salts having anions such as BF4 −, SnCl5 −, and SbCl6 −. Dark polymerizations of the carbazolyl monomers in the presence of the initiators are studied. These photoinduced polymerization reactions give oligomers of degree of polymerization 4-22. The effect of the anion of the photoinitiator and polymerization time on the polymerization reaction is discussed.

2,6,10-Tris(dialkylamino)trioxatriangulenium salts: a new promising fluorophore. Ion-pair formation and aggregation in non-polar solvents

The D3h symmetric tris(dialkylamino)trioxatriangulenium ((R2N)3TOTA+) ions are structurally related to classical stains and fluorophores such as triphenylmethane dyes and rhodamines. New derivatives of (R2N)3TOTA+, in which long flexible alkyl chains surround the planar and rigid aromatic core, have been synthesized and isolated as hexafluorophosphate salts. In contrast to short-chain derivatives of triphenylmethane dyes, the new compounds described here are soluble in hydrocarbon solvents. The photophysical properties of these carbenium salts are investigated. Characteristic alterations of the photophysical properties as a function of solvent polarity, concentration and temperature are observed. A model to rationalize the phenomena is presented comprising three states of aggregation, i.e. freely solvated ions, tight ion-pairs, and dimers of ion-pairs. Reduced symmetry in the tight ion-pairs is held responsible for the observed splitting of the long wavelength absorption band. Exciton coupling in the ion-pair dimers leads to reduced oscillator strength of the S0-S1 transition. The model is supported by semi-empirical calculations of the structures and electronic transitions of the free cation and its ion-pair(s).

Octahedral Bis(phenoxy-imine)tin(IV) Alkyl Complexes: Synthesis, Characterization, and Reactivity toward Ionizing Species and Ethylene

The synthesis of new organotin compounds of the general formula L2SnR2 (L = N-(3-tert-butylsalicylidene)-2,3,4,5,6-pentafluoroaniline; R = CH3 (1), n-C4H9 (3)) and L‘2SnR2 (L‘ = N-(3-tert-butylsalicylidene)aniline; R = CH3 (2), n-C4H9 (4)) is described herein. The compounds were characterized by 1H, 13C, and 119Sn NMR in solution; in some cases a fluxional behavior was observed by variable-temperature experiments. Characterization by single-crystal X-ray diffraction analysis has been obtained for compounds 1, 2, and 4. The reactivity of the synthesized compounds toward ionizing agents was studied by an NMR-tube reaction. Compounds 2 and 4 underwent an alkyl abstraction reaction with the carbenium salt [C(C6H5)3]+[B(C6F5)4]-. The obtained cationic species exhibited some activity in the oligomerization of ethylene under mild conditions, producing short-chain oligomers, with saturated end groups and methyl branches.

Preparation and Properties of a Huge, Crystalline, and Water-Soluble Compound (C72H132N12Br6S12) That Possesses Six Carbenium Salt Units

Abstract The reaction of hexakis(bromomethyl)benzene with six molar amounts of 2,2-bis(diethylamino)-2-ethylium-1-dithiocarboxylate furnished a huge, crystalline, and water-soluble compound (C72H132N12Br6S12, MW = 2030) that possesses six carbenium bromide units.

Synthesis, structure, and properties of azatriangulenlenium salts.

A general synthetic route to novel nitrogen-bridged heterocyclic carbenium ions of the acridinium and triangulenium type has been developed and investigated. The synthetic method is based on nucleophilic aromatic substitution (SNAr) on the tris(2,6-dimethoxyphenyl)carbenium ion (1) with primary amines and, by virtue of its stepwise and irreversible nature, provides a powerful tool for the preparation of a wide variety of new heterocyclic carbenium salts. Several derivatives of the three new oxygen- and/or nitrogen-bridged triangulenium salts, azadioxa- (6), diazaoxa- (7), and triazatriangulenium (4), have been synthesized and their physicochemical properties have been investigated. Crystal structures for compounds 2 b-PF6, 2 d-PF6, 4b-BF4, 4c-BF4, 6e-BF4, and 8 are reported. The different packing modes found for the triazatriagulenium salts are discussed in relation to the electrostatic and space-filling requirements of the ions. The stabilities of the cations 6a, 7b, and 4a, as expressed by their pKR+ values, have been determined in strongly basic nonaqueous solution by use of the C_ acidity function; the values obtained were 14.5, 19.4, and 23.7, respectively. This study further implied that the C_ scale in its present form is unsuitable for the precise determination of pKR+ values beyond 22.

Cyclic Voltammetric Characteristics of Tri- and Diarylcarbenium Salts Having Some Methoxyphenyl Groups

Abstract Triarylcarbenium salts (Φa3C+, ΦaΦb2C+, Φb3C+, ΦfΦb2C+, ΦeΦb2C+, PhΦb2C+, and FcC+ΦbPh [Φa, Φb, Φe, Φf, Ph, Fc = 2,4,6-(MeO)3C6H2, 2,6-(MeO)2C6H3, 2-(MeO)C6H4, 4-(MeO)C6H4, C6H5, Fe(η5-C5H5)(η5-C5H4)]) showed a reversible redox wave with one-electron transfer at a Pt electrode in 1,2-dichloroethane, while the reduction of diarylcarbenium salts (Φa2C+H, FcC+ΦaH, FcC+ΦbH, FcC+ΦcH, FcC+ΦeH, and FcC+PhH [Φc = 2,5-(MeO)2C6H3]) proceeded irreversibly. A wide range of cathodic shifts in the redox potentials (198—-377 mV for triarylcarbenium salts) and in the reduction peak potentials (-23—-311 mV for monoaryl(ferrocenyl)carbenium salts) could be observed as the number of o- and p-methoxy groups increased. Probably, the electron donation from the o- and p-methoxy substituents to the central carbon caused the wide negative shift in the redox potentials. These triarylcarbenium salts again showed reversible redox waves in their relatively low concentration region at an ITO electrode in an aqueous acidic medium. In the higher concentration region, an anodic wave was varied to a sharp peak, indicating the adsorption of triarylmethyl radicals. It is very interesting that the reversible redox behavior of these triarylcarbenium salts was observable even in an aqueous medium.

Facile synthesis of oxa- and azacyclic dienes via cycloalkenation of alkynyltungsten compounds. Stereoselective construction of tricyclic furan and pyran derivatives via intramolecular diels-alder reaction

A convenient and short synthesis of functionalized oxacyclic and azacyclic dienes is developed on the basis of organotungsten chemistry. Alkynyltungsten compounds bearing a tethered alcohol and amine are treated with aldehydes and BF(3).Et(2)O in cold diethyl ether to give tungsten-heterocyclic carbenium salts, further leading to tungsten-heterocyclic dienes via deprotonation with Et(3)N. Hydrodemetalation of these tungsten-heterocyclic dienes is performed by the action of anhydrous Me(3)NO in CH(3)CN. This method is applicable to the synthesis of a number of oxa- and azacyclic dienes, including those tethered with an electron-deficient olefin. The oxacyclic 1,3,8-nonatrienes and 1,3,9-decatrienes undergo intramolecular Diels-Alder reactions upon heating in toluene, yielding tricyclic tetrahydropyran and -furan derivatives with excellent diastereoselectivities.

ChemInform Abstract: Ambident Reactivities of Carbenium Salts Possessing a Thiocarbonyl Group at the β‐Position.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Stability and reactivity of ferrocenyl(2,4,6-trimethoxyphenyl)carbenium salts

Ferrocenyl(phenyl)methanols, Fc–CHΦOH [Fc=Fe(η 5-C 5H 5)(η 5-C 5H 4), Φ a=2,4,6-(MeO) 3C 6H 2 ( 1a); Φ b=2,6-(MeO) 2C 6H 3 ( 1b)], were prepared by the reactions of FcCHO with ΦLi. 1a reacted with only a slight excess of perchloric acid or tetrafluoroboric acid even in methanol and in 1 M HCl acid to give dark violet crystals of the carbenium salts, [FcCHΦ a]X [X=ClO 4 ( 2a), BF 4 ( 2a′)]. 1b reacted with these acids in diethylether to give the carbenium salts, [FcCHΦ b]X [X=ClO 4 ( 2b), BF 4 ( 2b′) (dark red–brown crystals)] in good yields. The p K R + values could be measured in HCl acid for 1a (3.0) and for 1b (1.6). 2a and 2b were labile in hot 2-propanol to give the reduced compounds, FcCH 2Φ. 1a and 1b reacted with 1,3,5-trimethoxybenzene, Φ aH, in 2-methyl-2-propanol containing only a slight excess of HCl acid to give diphenyl(ferrocenyl)methanes, FcCHΦ a 2 and FcCHΦ aΦ b, respectively. While 1a decomposed in neat 1,3-dimethoxybenzene, Φ bH, in the presence of acid, 1b reacted to give 2,4-dimethoxyphenyl(2,6-dimethoxyphenyl)ferrocenylmethane, FcCHΦ bΦ d [Φ d=2,4-(MeO) 2C 6H 3]. The 1H-NMR spectrum of 2a was temperature-dependent and indicated that the free rotations of both Fc and Φ a groups in 2a existed at r.t. but were frozen at −60°C.

Ambident Reactivities of Carbenium Salts Possessing a Thiocarbonyl Group at the β-Position

Abstract A stable, crystalline carbenium iodide, which possesses a thiocarbonyl group at the β-position, shows ambident reactivities, thereby reacting with a hard nucleophile OH− at the carbenium carbon atom and with a soft nucleophile RLi at the thiocarbonyl sulfur atom. Thermal dissociation of the MeLi adduct to a carbene and a ketene dithioacetal is also presented.

ChemInform Abstract: Unusual Stabilities and Reactivities of Tris‐ and Bis(2,4,6‐trimethoxyphenyl)carbenium Salts.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Palladium-catalyzed syntheses of oxygen- and nitrogen heterocycles via transmetalation of functionalized alkynyl stannanes

The reaction between CpFe(CO) 2I, hydroxy- or aminoalkynyl stannanes, and PdCl 2(CH 3CN) 2 (8.0 mol. %) generates a reactive iron-alkynyl intermediate that reacts in situ with RCHO BF 3·Et 2O to yield an iron oxa- or azacarbeniums quantitatively, further producing oxygen- and nitrogen heterocycles in high yields after Me 3NO-oxidation of these carbenium salts.

Seleno- and Tellurocarbenium Ions

: α-Chalcogeno substituted carbenium salts [(RX)3C]+ PF6-(X = S, Se, Te; R = 2,4,6-iPr3C6H2) obtained from reaction of the copper complexes [(bipy)CuXR] with CBr4 are stabilized to the same extent; but the electronic mechanism is very different.

Unusual Stabilities and Reactivities of Tris- and Bis(2,4,6-trimethoxyphenyl)carbenium Salts

Abstract 2,4,6-Trimethoxyphenyllithium, Φ′Li[Φ′ = 2,4,6-(MeO)3C6H2], reacted with diphenyl carbonate and with ethyl formate to give tris(2,4,6-trimethoxyphenyl)methanol, Φ′3COH (1), and bis(2,4,6-trimethoxyphenyl)methanol, Φ′2CHOH (2), respectively. Compound 1 reacted with a slight excess of perchloric acid in 2-propanol to give very dark-purple crystals of the triarylcarbenium salt, [Φ′3C]X (3, X = ClO4), which were inert even in hot ethanol. However, a treatment of 3 (X = Cl), prepared in situ in 1 M (1 M = 1 mol dm−3) hydrochloric acid, with 1 M sodium hydroxide resulted to give 4-bis(2,4,6-trimethoxyphenyl)methylene-3,5-dimethoxy-2,5-cyclohexadienone. Compound 2 also reacted with a slight excess of perchloric acid in methanol to give dark-red crystals of the diarylcarbenium salt, [Φ′2CH]X (5, X = ClO4). Compound 5 was considerably inert even in hot methanol, but was easily reduced in primary and secondary alcohols to give bis(2,4,6-trimethoxyphenyl)methane, Φ′2CH2. Measurements of the half-lives of 5 in these alcohols showed that 5 was more labile in secondary alcohols, such as 2-propanol and 2-butanol, than in primary alcohols. When a suspension of 5 (X = Cl), prepared in situ in 1 M hydrochloric acid, was heated, tris(2,4,6-trimethoxyphenyl)methane, Φ′3CH (7), was obtained. Analogous reactions to give 7 were observed in methanol containing a slight excess of hydrochloric acid or nitric acid in place of perchloric acid. The possible paths of these reactions are discussed.

ChemInform Abstract: Catalytic Activity of Bis(dialkylamino)carbenium Salts in Hydrosilylation Reactions.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

UV/VIS and NMR spectroscopic studies on the structure of cationically polymerized cyclopentadiene on the surface of silica particles

AbstractThe cationic polymerization of cyclopentadiene (CPD) in the presence of silica gel particles is initiated by triphenylmethyl chloride, triphenylmethyl bromide, and methyl triflate in 1,2‐dichloroethane. The suspension polymerization yields soluble colourless polycyclopentadiene (PCPD) and intensively blue coloured silica particles (PCPD+ silica). The formation of the polymer structure on the silica surface in suspension is followed by transmission UV/VIS spectroscopy and solution (1H and 13C) NMR spectroscopy. The structure of the novel solid materials (PCPD modified silica particles) is additionally investigated by DRIFT spectroscopy, solid‐state 13C CP/MAS NMR spectroscopy and scanning electron microscopy (SEM).The blue colour of the PCPD+ silica particles is caused by polyenylium sequences with five or six conjugated double bonds along the isomerized PCPD chains. The PCPD+ structures are compared with similar ionic model compounds derived from retinol and retinal, respectively. The remaining of the PCPD layer including the conjugated sequences on the surface is attributed to the formation of covalent SiOC bonds. Model reactions of the cationically active PCPD+ silica particles with benzyltriethylammonium chloride and hexachloroantimonate, as well as charge transfer complex formation of the PCPD polymer layer with carbenium salts, (C6H5)3C+AsF and C7HBF, are also investigated. A possible mechanism for the formation of crosslinked PCPD layers on the silica surface is suggested.

Ambident reactivities of bis(diethylamino)[(methylthio)thiocarbonyl]carbenium salts; reactions at the carbenium carbon atom vs. Thiocarbonyl sulfur atom

Bis(diethylamino)[(methylthio)thiocarbonyl]carbenium salts ( 1), a carbenium ion carrying an α-thiocarbonyl group, shown ambident reactivities toward a series of nucleophiles. Thus, they reacted with a typically hard nucleophile, hydroxide, at the carbenium carbon atom, whereas they smoothly reacted with soft nucleophiles, such as carbon, nitrogen, sulfur, and phosphorus nucleophiles, at the thiocarbonyl sulfur atom.