Trityl Cation Research Articles

A BH3 masked H-phosphonate for coupling in oligonucleotide synthesis

A method of masking 3′-H-phosphonate group for the solution-phase synthesis of ribonucleotide by H-phosphonate approach was described. The phosphonic acid group was masked by bis-(2-cyanoethyl) boranophosphate during the reactions. After a successive demasking treatment by triethylamine, trityl cation, and triethylamine, the triethylammonium 3′-H-phosphonate nucleotide can be obtained efficiently ready for the coupling cycle in synthesis of oligonucleotide.

Cation affinity numbers of Lewis bases.

Using selected theoretical methods the affinity of a large range of Lewis bases towards model cations has been quantified. The range of model cations includes the methyl cation as the smallest carbon-centered electrophile, the benzhydryl and trityl cations as models for electrophilic substrates encountered in Lewis base-catalyzed synthetic procedures, and the acetyl cation as a substrate model for acyl-transfer reactions. Affinities towards these cationic electrophiles are complemented by data for Lewis-base addition to Michael acceptors as prototypical neutral electrophiles.

Hydride Abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz = C5(CH2Ph)5): New Cationic Complexes Stabilized by η5:η2-C5H4:C6H5 Bonding of the Pentabenzylcyclopentadienyl Ligand

Hydride abstraction from [MCpBz(CO)3H] (M = Mo, W; CpBz = C5(CH2Ph)5) using trityl cations led to [M{η5:η2-C5Bz4CH2Ph}(CO)3]BArF (BArF = B(3,5-C6H3(CF3)2)4; M = Mo (3), W (4)) or [MCpBz(CO)3(FBF3)] (M = Mo (5), W (6)) depending on the trityl counterions. The stabilization of the acidic metal centers in 3 and 4 is made through the coordination of a C═C bond of one phenyl ring, generating ansa-bridged cyclopentadienyl–phenyl carbonyl complexes. 5 and 6 are zwitterionic compounds stabilized by the coordination of the BF4 anion. An exchange process between coordinated and noncoordinated phenyl rings occurs in dichloromethane solutions of 3. VT NMR experiments gave the exchange rate at various temperatures and ΔG⧧298 = 10.1 ± 0.2 kcal mol–1. In 4 the phenyl bonding is static at room temperature, on the NMR time scale. Reactions of 3 and 4 with CO and H2O led to [MCpBz(CO)4]BArF (M = Mo (7), W (8)) and [MCpBz(CO)3(OH2)]BArF (M = Mo (11), W (12)). In CH2Cl2 solutions 3 and 4 convert slowly to 7 and 8, respectively. DFT calculations attest to the stability of 3 to H2O bonding and also show that the replacement of phenyl coordination by CO is a favorable process (ΔH = −13.8 kcal mol–1).

Structural and Solvent Effects on the C–S Bond Cleavage in Aryl Triphenylmethyl Sulfide Radical Cations

Steady-state and laser flash photolysis (LFP) studies of a series of aryl triphenylmethyl sulfides [1, 3,4-(CH(3)O)(2)-C(6)H(3)SC(C(6)H(5))(3); 2, 4-CH(3)O-C(6)H(4)SC(C(6)H(5))(3); 3, 4-CH(3)-C(6)H(4)SC(C(6)H(5))(3); 4, C(6)H(5)SC(C(6)H(5))(3); and 5, 4-Br-C(6)H(4)SC(C(6)H(5))(3)] has been carried out in the presence of N-methoxyphenanthridinium hexafluorophosphate in CH(3)CN, CH(2)Cl(2), CH(2)Cl(2)/CH(3)CN, and CH(2)Cl(2)/CH(3)OH mixtures. Products deriving from the C-S bond cleavage in the radical cations 1(•+)-5(•+) have been observed in the steady-state photolysis experiments. Time-resolved LFP showed first-order decay of the radical cations accompanied by formation of the triphenylmethyl cation. A significant decrease of the C-S bond cleavage rate constants was observed by increasing the electron-donating power of the arylsulfenyl substituent, that is, by increasing the stability of the radical cations. DFT calculations showed that, in 2(•+) and 3(•+), charge and spin densities are mainly localized in the ArS group. In the TS of the C-S bond cleavage an increase of the positive charge in the trityl moiety and of the spin density on the ArS group is observed. The higher delocalization of the charge in the TS as compared to the initial state is probably at the origin of the observation that the C-S bond cleavage rates decrease by increasing the polarity of the solvent.

Photo‐induced association behavior of poly(sodium acrylate) bearing a small amount of malachite green

AbstractThe photo‐induced association and dissociation of poly(sodium acrylate) containing a small amount of photoresponsive malachite green (MG) in aqueous solution were studied. It is known that MG dissociates into ion pairs under UV irradiation to produce the green triphenylmethyl cation. The cation thermally recombines with its counter anion to regenerate the colorless neutral compound. The random copolymer of acrylic acid with 0.05 mol % of MG monomer [P(A/MG0.05)] was soluble in aqueous 0.01 M NaCl at pH 12 as a unimer due to electrostatic repulsion between carboxylate pendent groups when the MG moieties were in the neutral form. On the other hand, these MG groups were converted to the cationic form on UV irradiation, leading to polymer aggregation driven by electrostatic interactions between the cationic MG and anionic carboxylate pendent groups. These aggregates could be dissociated by heating in the dark, as the cationic MG reverted to its neutral form, eliminating these attractive electrostatic interactions. The association and dissociation of the copolymer was monitored by dynamic light scattering (DLS). When the salt concentration in aqueous solutions of P(A/MG0.05) was increased from 0.01 to 0.5 M at pH 12, no aggregation was observed on UV irradiation because of ionic screening of the aforementioned electrostatic interactions. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Heterobimetallic Nitride Complexes from Terminal Chromium(V) Nitride Complexes: Hyperfine Coupling Increases with Distance

Terminal nitride complexes of rhenium, osmium and molybdenum can form complexes with either alkylating agents, Lewis acidic metal halides, or low-valent, coordinatively unsaturated metal complexes. The few reactions of this type with a first-row transition-metal complex are limited to vanadium. Recently, the nitride chemistry of the chromium(V) cation has been significantly expanded by introduction of a preparative route which is based on nitrogen transfer from [Mn(N)(salen)] (salen=N,N’-bis(salicylidene)ethylenediamine) to the chromium(V) cation. With a range of chromium nitride complexes at hand we have investigated their reactivity and found that nucleophilicity is a general property which can be observed during formation of imide complexes with, for example, the trityl cation, tris(pentafluorophenyl)boron, and methyl triflate. In addition we report that terminal chromium(V) nitride complexes coordinate through the nitride ligand to low-valent complexes of the platinum metals. These compounds are possible precursors to bimetallic nitride phases which are gaining in importance as heterogeneous catalysts in, for example, the Haber–Bosch process. Solutions of terminal chromium nitride complexes in noncoordinating solvents treated with electrophiles such as B(C6F5)3 or C(C6H5)3 + quickly yield intensely colored orangered or green solutions. The reactions proceed cleanly as shown by EPR spectra which display a signal from a single S= =2 spin species. Similar reactivity was observed in reactions with either [Rh(cod)Cl]2 or cis-[PtCl2(dmso)2] (cod= 1,5cyclooctadiene, dmso= dimethyl sulfoxide). Structures of some of these systems, characterized by single-crystal X-ray diffraction, are shown in Scheme 1. Experimental and crystallographic details such as ORTEP drawings andmetric parameters of complexes 1–5 (Scheme 1) are available in the Supporting Information (Tables S1 and S1a). Inspection of the structures reveals a number of general aspects: there is a strong propensity for the chromium center to increase its coordination number from five to six upon coordination of the nitride ligand. This propensity is expected and a consequence of the trans influence of either an imide or a bridging nitride ligand which is significantly lower than that of a terminal nitride ligand. Accompanying this, the displacement of Cr out of the plane spanned by the equatorial ligators is diminished from about 0.5 to about 0.2 . The Cr N bond length is elongated from 1.55 in the terminal nitride complexes to approximately 1.60–1.62 in the functionalized systems. Comparison of structure 1 with that of [Cr(N)(salen)] reveals that the metal–salen ligand bonds are significantly shorter when the nitride ligand is functionalized, as expected when two ligands compete for electron donation. However, for the systems derived from [Cr(N)(dbm)2] the situation is less clear (dbm= dibenzoylmethanolate). In complex 2 all the Cr–dbm bonds are longer than in the parent terminal nitride complex, while they are shorter or similar within the limits of uncertainty in complex 5. The B N and C N bonds in 1, 4, and 5 are unexceptional but the N Rh and N Pt bond lengths in 2 and 3 are at about 1.970 and 1.906 , respectively, and very short; the first value belongs to the top 5% of the shortest Rh N bonds and the second belongs to the top 1% of the shortest Pt N bonds. Table 1 compares the Pt N bond of 3 with Pt N bonds of other cis[PtCl2(dmso)L] structures. Scheme 1. Schematic representation of the chromium(V) imide and chromium(V) bridging-nitride complexes.

New acid photogenerators based on thioxanthen-9-one sulfonium derivatives for detritylation in the oligonucleotide synthesis

Photochemical activity of a number of cationic thioxanthen-9-one derivatives for the formation of the trityl cation was studied, which resulted in the selection of compounds suitable for photodetritylation. 10-(4-Heptyloxyphenyl)-9-oxo-2-(N,N,N-triethylammonio)methyl-9H-thioxanthenium bis(hexafluorophosphate) and 2-methyl-, 2-(2-methyl-1-propanoyl-2-tosyl)-, 1-chloro-4-propoxy-, and 2,4-diethyl-10-(4-heptyloxyphenyl)-9-oxo-9H-thioxanthenium hexafluorophosphates were found to be photoactivators of detritylation of 5′-O-(4,4′-dimethoxytrityl)thymidine. The detritylation reaction is the most efficient in dichloromethane. 2,4-Diethyl-10-(4-heptyloxyphenyl)-9-oxo-9H-thioxanthenium hexafluorophosphate was used as a detritylation photoactivator in the oligonucleotide synthesis using an automated DNA synthesizer. The yield in the elongation step of the oligonucleotide chain was 98%.

ChemInform Abstract: Mechanism of the Cleavage Reaction of (Methylthio)methyl Ether with Triphenylmethyl Cation.

ChemInform Abstract: Mechanism of the Cleavage Reaction of (Methylthio)methyl Ether with Triphenylmethyl Cation.

ChemInform Abstract: Azulene Analogues of Triphenylmethyl Cation. Extremely Stable Hydrocarbon Carbocations.

Abstract A series of azulene analogues of triphenylmethyl cation; tri(1-azulenyl)methyl cation, di(1-azulenyl)phenylmethyl cation, (1-azulenyl)diphenylmethyl cation, and their methyl and methoxycarbonyl derivatives were synthesized. Their pKR+ values showed that the stability of these cations dramatically increases with the number of azulene rings, and the pKR+ values of tri(1-azulenyl)methyl cation (11.3) and its trimethyl derivative (11.4) are the highest ever reported for methyl cations substituted with hydrocarbon groups.

ChemInform Abstract: Preparation, X-Ray Crystal Structures, and Reactivity of Alkynylcyclopropenylium Salts.

Several 1,2-diphenyl-3-alkynylcyclopropenes were prepared by the reaction of acetylenic nucleophiles with diphenylcyclopropenylium perchlorate. The cyclopropenes were converted into alkynylcyclopropenylium salts via hydride abstraction with triphenylmethyl cation. Attempts to prepare a dication from either ethyne-bridged or butadiyne-bridged biscyclopropenes produced only the corresponding monocations. A dication was prepared when an ethylene spacer was inserted between the acetylene groups of the butadiyne-bridged biscyclopropene. Single-crystal X-ray structures of three of the cyclopropenylium ions were obtained. pKR+ titrations were carried out on two of the salts, which showed that acetylene substituents provide about the same degree of stability to the cyclopropenylium core as a phenyl group. Nucleophilic addition to the alkynylcyclopropenylium ions under kinetic conditions gave a statistical mixture of products; however, under thermodynamic reaction conditions, nucleophilic addition followed by ring...

A Lipophilic, Fluorine‐Free, Thermostable, Inexpensive, S4‐Symmetric, Highly Soluble, Weakly Coordinating, Protolabile Aluminate

AbstractThis communication presents the facile and cost‐effective synthesis as well as properties of salts of a lipophilic aluminate anion. Its unprecedented solubility in pentane makes possible tetrabutylammonium salt extraction with pentane. Nevertheless, its symmetry leads to high melting points of its thermostable salts. Several single crystals for X‐ray diffraction studies have been obtained. The anion is devoid ofhalogens, but is stable against sterically demanding electrophiles such as the trityl cation. However, it is unstable in protic media and hydrolyzes in the presence of water within days.

Preparation of trityl cations in faujasite micropores through supercritical CO 2 impregnation

In this paper, we investigated on the preparation of three zeolite encapsulated-trityl cations (trityl, dimethoxytrityl and methoxytrityl) using supercritical CO 2 (scCO 2) as the processing media. Since the studied trityl cations had a size larger than the diameter of the zeolite channels, the fabrication was based on a ship-in-a-bottle procedure using benzene, benzaldehyde, anisole, diphenylcarbinol and benzophenone as building blocks. The different cations were prepared by nucleophilic substitution, using the inner supercage of the acid zeolite as both a microreactor and a negative counterion for the trityl cation. The obtained impregnated samples were purified by cleaning with a continuous flow of scCO 2. Loaded amounts of ca. 8 wt.% were obtained following the supercritical procedure. The successful formation of the cation was confirmed by using optical spectroscopies, such as UV–vis diffuse reflectance and FTIR spectroscopies.

Direct Synthesis of a Photoactive Inorganic–Organic Mesostructured Hybrid Material and its Application as a Photocatalyst

A photoactive, hexagonally structured mesoporous material (Tyl-MCM41) is produced through co-hydrolysis of SiO(2) and a trialkoxysilane-functionalized trityl cation as photoactive species. The formation of the corresponding triphenylmethanol precursor in the material is confirmed by spectroscopic techniques. The hybrid material has an ordered structure with a narrow pore size distribution typical of ordered mesoporous MCM-41-type materials. The triarylcarbinol molecules incorporated into this hybrid structure (Triphol-MCM41) generate trityl cations under acidic conditions, which are photoactive and able to promote the photosensitized dimerization of 1,3-cyclohexadiene in a heterogeneous solid-liquid system. The material is stable and can be recycled without loss of the photochemical activity.

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.

Regioselective Oxidative Cation-Olefin Cyclization of Poly-enes: Catalyst Turnover via Hydride Abstraction

Electrophilic P2Pt2+ complexes are shown to catalyze the regio- and diastereoselective oxidative cascade cyclization of poly-enes. The reactions are stereospecific with respect to the initiating alkenes geometry and suggest an all-chair, semiconcerted transition structure. Catalyst turnover after cyclization apparently occurs via β-hydride elimination and subsequent hydride abstraction (from P2Pt−H+) by added Trityl cation (in the form of trityl methyl ether or a resin version thereof) to regenerate the active P2Pt2+ state. One intriguing possibility is that the high regioselectivity observed in the β-H elimination is due to a regio-defining β-agostic resting state.

Palladium Complexes of a P2C Ligand Containing a Central Carbene Moiety

Palladium(II) complexes of the PCHP pincer ligand were prepared from PdCl2, a “proto-pincer” P2CH2, and base. The resulting (PCHP)PdCl was converted to (PCHP)PdOTf. (PCHP)PdCl did not react with NaN(SiMe3)2 but produced (PCHP)PdR (R = Me, Et, Ph) upon reaction with the corresponding organolithium, Grignard, or organozinc reagent. Trityl cation abstracted a hydride from (PCHP)PdCl to yield cationic Pd carbene complex (P2C)PdCl. Analysis of the structural data points to minimal π-interaction between the carbene center and palladium.

Electrophilic Activation of Lewis Base Complexes of Borane with Trityl Tetrakis(pentafluorophenyl)borate

Borenium ions do not accumulate under the conditions of hydride abstraction from Lewis base borane complexes (L·BH3) using trityl cation because subsequent rapid reaction with L·BH3 occurs to form B−H−B bonds. The hydride-bridged cations are sufficiently stabilized to resist abstraction of the remaining hydride by excess trityl cation; however, reversible cleavage of the 3c2e bond does take place to release borenium ion equivalents, as evidenced by interaction with weak nucleophiles.

Photochemical micelle control by long‐alkyl‐chain Malachite Green

AbstractWe have designed a Malachite Green leuconitrile carrying a long‐alkyl‐chain which controls micelle formation photochemically. The Malachite Green derivative, when ionized photochemically, exhibits some hydrophilicity by its triphenylmethyl cation and some hydrophobicity by its long alkyl chain. The behavior of the photoresponsive Malachite Green surfactant was studied in mixed micelle solutions containing cetyltrimethylammonium chloride (CTAC) and a small quantity of the Malachite Green. We found that UV irradiation drastically decreased the critical micelle concentration (cmc) of the mixed micelle solutions and that the Malachite Green derivative realized photoinduced uptake of oily substances based on its photogenerated amphiphilicity. The mechanism of the photoinduced enhancement of solubilizing oily substances is discussed at the viewpoint of the microscopic location of the Malachite Green surfactant in the micelle. Copyright © 2007 John Wiley & Sons, Ltd.

Investigation of ion pair formation in the triphenylmethyl chloride–trimethyl aluminium system, as a model for the activation of olefin polymerization catalyst

Triphenylmethyl chloride (“trityl chloride”, Ph 3CCl) will transfer chloride ions to aluminium alkyls and methylaluminoxane and it is thereby converted into 1,1,1-triphenylethane (“trityl methyl” Ph 3CMe) and the triphenylcarbonium ion (“trityl ion”, Ph 3C +). IR spectra of these trityl species have been recorded. Assignments are supported by quantum chemical calculations, leading to significant revisions for some of the modes that are most influenced by reactions. A bright yellow colour shown to be due to the trityl cation, makes trityl chloride a useful indicator for ion pair formation. Trimethyl aluminium (TMA) is chlorinated by trityl chloride and forms dimethyl aluminium chloride (DMAC). DMAC will form a stable ion pair with trityl chloride, probably by forming the anion Al 2Cl 3Me 4 −. Large excess of trityl chloride causes the formation of AlCl 4 −, and probably AlCl 3Me − and AlCl 2Me 2 − anions. It appears that methyl aluminium chloride anions are formed if, and only if, the anions have at least three chlorine atoms, possibly because of the need to dissipate the negative charge enough to keep the anion dissolved in the hydrocarbon solvent. Methylaluminoxane (MAO) also forms ion pair with trityl chloride, although to lesser extent and less persistent.

Benzene Loss from Trityl Cations—A Mechanistic Study

Triarylmethyl cations eliminate substituted benzene in the gas phase, upon activation. The mechanism of this process has been studied using deuterium labeling, substituent effects, and density functional theory calculations. It is shown that this apparently simple dissociation is in fact a complicated stepwise process that involves several consecutive hydride shifts. The combination of experimental evidence and computational results leads to a clear description of transition states and reaction intermediates.