Onium Research Articles

Visible light induced free radical promoted cationic polymerization using acylsilanes

Within this work, a novel visible light photoinitiation system for cationic polymerization of oxiranes such as cyclohexene oxide (CHO) and vinyl monomers such as isobutyl vinyl ether (IBVE) and N-vinylcarbazole (NVC) using tetrakis(2,4,6-trimethylbenzoyl)silane (TTBS) is described. Polymerizations were successfully initiated at room temperature upon irradiation in the visible region (λinc > 400) in bulk or methylene chloride solutions of these monomers and TTBS, in the presence of onium salts such as diphenyliodonium hexafluorophosphate (Ph2I+PF6−) and triphenylsulfonium hexafluorophosphate (Ph3S+PF−). Partial decomposition of TTBS by short irradiation time and keeping the polymerization solution in the dark yielded poly(cyclohexene oxide) (PCHO) bearing acyl silane terminal groups. Further use of the resultant polymer as photoinitiator in free radical polymerization of MMA and free radical promoted cationic polymerizations of CHO yielded PCHO-b-PMMA and chain extended PCHO, respectively.

Novel advances in the synthesis of bisphosphonates, containing heterocyclic and macrocyclic structure

Herein we describe our recent advances in the synthesis of new bisphosphonates, containing adenosines, adenine moiety as well as reactive aminoacetal fragment and calix[4]resorcinols framework. For the synthesis of these compounds we used three main approaches: Michael addition of nucleophilic amines (adenosines, adenines and aminoacetaldehyde) to (tetraethyl)ethenylidene-1,1-bisphosphonate and tetrakis(trimethylsilyl)ethenylidene-1,1-bisphosphonate); acid catalyzed condensation of bisphosphonic acid derivatives, containing acetal group with polyphenols; formation of onium salts of bisphosphonic acids with adenosine and aminomethylated calix[4]resorcinols.

Direct access to poly(glycidyl azide) and its copolymers through anionic (co-)polymerization of glycidyl azide

Glycidyl azide polymer or poly(glycidyl azide) which is considered as an excellent energetic binder or plasticizer in advanced solid propellants is generally obtained by post-modification or azidation of poly(epichlorohydrin). Here we report that glycidyl azide can be directly homopolymerized through anionic ring-opening polymerization to access poly(glycidyl azide) using onium salts as initiator and triethyl borane as activator. Molar masses of poly(glycidyl azide) up to 11.0 Kg/mol are achieved in a controlled manner with a narrow polydispersity index (PDI ≤ 1.2). Similarly, alternating poly(glycidyl azide carbonate) are also prepared through alternating copolymerization of glycidyl azide with carbon dioxide. Lastly, the copolymerization of glycidyl azide with other epoxide monomers is carried out; the azido functions carried by glycidyl azide which are successfully incorporated into the backbones of polyethers and polycarbonates based on cyclohexene oxide and propylene oxide subsequently served to introduce other functions by click chemistry.

Organic Selenocyanates as Halide Receptors: From Chelation to One-Dimensional Systems

Organic selenocyanates were recently identified as strong chalcogen bond donors. They also play an important role in biochemistry. Here, we show that 1,2-bis(selenocyanatomethyl)benzene (1) and 1,2,4,5-tetrakis(selenocyanatomethyl)-benzene (2) crystallize from dimethylformamide (DMF) to afford solvates where two ortho-SeCN moieties act as a chelate toward the carbonyl oxygen atom of DMF through strong Se···O chalcogen bonds. This result led us to explore their ability to also chelate halide anions (Cl–, Br–) in solution as well as in the solid state, an important issue in view of applications in crystal engineering or organocatalysis. NMR titration experiments provide an association constant between 1 and Cl– of 148 M–1. We also observed the recurrent formation of cocrystal salts from the association of the ChB donors 1 and 2 with the onium salts Ph4PCl, Ph4PBr, and Bu4NCl. We demonstrate that not only μ2-halide but also μ4-halide structures can be stabilized though ChB interactions, leading to the format...

Phenol-functionalized polymerization control additives for negative tone epoxide crosslinking molecular resists

Controlling undesired polymerization in nominally unexposed regions is critical to achieving high-resolution, defect-free patterns when using negative tone molecular resists based on the crosslinking of epoxides. Two onium salt additives, a photodecomposable nucleophile (PDN) and a photoacid generator (PAG), were functionalized with phenols in order to investigate their use as generalized additives capable of slowing crosslinking and improving the resolution of a variety of epoxide resists. Presented here is a phenol-functionalized PDN [tris(4-hydroxyphenyl)sulfonium triflate (TPS-OH-Tf)] and a phenol-functionalized PAG [tris(4-hydroxyphenyl)sulfonium antimonate (TPS-OH-SbF6)] used in combination with a model epoxide resist (4-Ep). Utilizing additives that contained phenols resulted in a decrease in resist sensitivity, but enabled higher additive loadings which could be used to offset this loss in sensitivity. Using TPS-OH-SbF6 did not provide enough polymerization control to prevent line broadening, and the use of TPS-OH-Tf was still required to achieve sub 35 nm 1:1 line:space patterns. Adding TPS-OH-Tf was also found to improve pattern collapse behavior at reduced (<25 nm) feature sizes. Initial patterning using 100 keV electron-beam lithography showed that the resolution of 4-Ep was improved to 15 nm 1:1 line:space patterns using these phenol-functionalized additives and demonstrate the potential of these additives to improve the resolution of a variety of epoxide crosslinking molecular resists.

Macrocyclic Hosts in Asymmetric Phase-Transfer Catalyzed Reactions

The introduction and development of neutral macrocyclic hosts capable of complexing ions within their pre-organized cavity, has been of utmost importance in supramolecular chemistry. Their ability to form stable organic-soluble metal–macrocycle complexes opened up the way to their application in phase-transfer catalysis (PTC) as a viable alternative to quaternary onium salts. In particular, their conformationally rigid preorganized backbone, accommodating organic substrates in defined orientations, promotes highly efficient stereoselective reactions. This short review summarizes the applications of neutral macrocyclic hosts in stereoselective PTC, highlighting the difference and possible complementarity with quaternary ammonium salts.1 Introduction2 Crown Ethers and Related Coronands2.1 Enantioselective PTC with Chiral Macrocyclic Coronands2.2 Enantioselective PTC Reactions Catalyzed by Chiral Quaternary Ammonium Salts with Achiral Crown Ether Co-catalysts3 Cyclic Peptoids4 Miscellaneous Chiral Macrocyclic Hosts5 Summary and Outlook

N-, P-, and S-doped graphene-like carbon catalysts derived from onium salts with enhanced oxygen chemisorption for Zn-air battery cathodes

Compared to currently studied metal-based catalysts, metal-free heteroatom-doped carbon catalysts have many advantages including no issues of degradation and contamination from metal dissolution. Relying on single type of doping usually cannot yield optimal electronic and geometric structures favorable for the oxygen reduction reaction (ORR). Herein, heteroatom N, P, and S simultaneously doped graphene-like carbon (NPS-G) was successfully synthesized from onium salts by a facile one-step pyrolysis method. The resulting metal-free NPS-G catalyst with optimized N, P, and S contents exhibits enhanced catalytic activity towards the ORR in alkaline media, relative to any single doping. In particular, this metal-free catalyst shows an encouraging half-wave potential (E1/2 = 0.857 V) comparable to that of metal-based catalysts. It also demonstrates excellent electrochemical stability and methanol tolerance. This catalyst was further studied as a cathode in a primary Zn-air battery, showing exceptional open-circuit voltage (1.372 V) and power density (0.151 W cm−2). The NPS-G cathode delivers a specific capacity of 686 mA h gZn-1 at a current density of 10 mA cm−2 while utilizing 82.2% of the theoretical capacity (835 mA h gZn-1). The origin of high activity associated with various heteroatom dopings is elucidated through X-ray photoelectron spectroscopy analysis and density functional theory studies. The enhanced chemisorption of oxygen species (*OOH, *O and *OH) onto the dopants of the NPS-G catalysts reduces charge transfer resistance and facilitate the ORR. The porous 2D structure also contributes to the increase of active site density and facile mass transport.

The Role of Onium Salts in the Pro-Oxidant Effect of Gold Nanoparticles in Lipophilic Environments.

Metal nanoparticles are reported to be toxic due to the generation of free radicals at their surface. Relatively inert thiol-capped gold nanoparticles (AuNPs) have been reported to induce radical formation in the presence of hydroperoxides, which would conflict with their potential use as inert scaffolds for the design of novel nano-antioxidants. With the aim of clarifying this aspect, we investigated the pro-oxidant activity of dodecanethiol-capped AuNPs (∼5 nm diameter), prepared through the Brust-Schiffrin synthesis, by oxygen-uptake kinetic studies. The pro-oxidant activity was found to be proportional to the impurities of the transfer agent tetraoctylammonium bromide (TOAB) left from the synthesis and decreased on repeated washing of the nanoparticles. Under identical settings similar batches of AuNP (∼9 nm diameter) prepared through the Ulman method without onium salts showed no pro-oxidant behavior. The alternative onium phase-transfer agents Oct4 NBF4 (Oct=octyl), Hex4 NBF4 (Hex=hexyl), and Hex4 NPF6 were comparatively investigated and showed lower pro-oxidant activity depending on the counterion (Br- >PF6- >BF4- ).

Highly Active Organic Lewis Pairs for the Copolymerization of Epoxides with Cyclic Anhydrides: Metal-Free Access to Well-Defined Aliphatic Polyesters

Polyester synthesis from the alternating copolymerization of epoxides with cyclic anhydrides via a metal-free route remains a key challenge. This work reports the development of a highly active organocatalytic route for the copolymerization of a spectrum of epoxides and cyclic anhydrides. Fully alternating polyesters were synthesized by a variety of organic Lewis acid–base pairs including organoboranes and quaternary onium salts. The effect of the acidity, type, and size of Lewis pairs on the catalytic activity and selectivity of the copolymerization is presented. The undesirable transesterification and etherification were effectively suppressed even in the case of complete conversion of the cyclic anhydride. This could be ascribed to the formation of a unique tetracoordinate bond-carboxylate (or alkoxide) anion. The Lewis pairs are highly active, with a turnover frequency of 102 and 303 h–1 for the copolymerization of propylene oxide with maleic anhydride and phthalic anhydride, respectively, at 80 °C. B...

Catalytic Action of Water during Nucleophilic Substitution of Halogen in Hexachlorocyclotriphosphazatriene with Pyridine N-Oxide

The data on the kinetics of the reaction between hexachlorocyclotriphosphazatriene (the phosphazene) with pyridine N-oxide in mixed organic solvents in the presence of water are presented. The reaction of the phosphazene with pyridine N-oxide leads to the formation of the onium salt. It has been found that water catalyzes this reaction, the catalytic action resulting from the solvation of the polar transition state due to the formation of the phosphazene complex with hydrogen bonding, thus facilitating the rupture of the phosphorus bond with the leaving anion.

Temperature‐responsive Catalyst for the Coupling Reaction of Carbon Dioxide and Propylene Oxide

The selective synthesis of polypropylene carbonate (PPC) and cyclic propylene carbonate (CPC) from coupling reaction of CO2 and propylene oxide (PO) is a long term pursuing target. Here we report that a temperature controllable porphyrin aluminum catalyst using 5,10,15,20‐tetra(1,2,3,4,5,6, 7,8‐octahydro‐1,4:5,8‐dimethanoanthracen‐9‐yl)porphyrin as ligand, once in conjunction with suitable onium salt, achieved single cycloaddition or copolymerization reaction. Only cycloaddition reaction happened at temperature above 75 °C to produce 100% CPC, whereas copolymerization became dominant to afford PPC with selectivity over 99% at 25 °C, and the obtained PPC showed over 99% carbonate linkage and 92% head‐to‐tail structure. Based on systematic analysis of the electronic and steric feature in the porphyrin ligand, it was found that the electronic feature of the substituent in porphyrin ligand was decisive for PPC selectivity, porphyrin ligand bearing strong electron‐donating substituents displayed a significantly reduced tolerance towards increased temperature with respect to PPC formation. Therefore, temperature‐responsive catalyst could be designed by suitable modification in porphyrin ligand, and such accurate synthesis of target product by one catalyst may create a useful and facile platform for selective PPC or CPC production.

Highly Efficient One-Pot Synthesis of COS-Based Block Copolymers by Using Organic Lewis Pairs.

A one-pot synthesis of block copolymer with regioregular poly(monothiocarbonate) block is described via metal-free catalysis. Lewis bases such as guanidine, quaternary onium salts, and Lewis acid triethyl borane (TEB) were equivalently combined and used as the catalysts. By using polyethylene glycol (PEG) as the macromolecular chain transfer agent (CTA), narrow polydispersity block copolymers were obtained from the copolymerization of carbonyl sulfide (COS) and propylene oxide (PO). The block copolymers had a poly(monothiocarbonate) block with perfect alternating degree and regioregularity. Unexpectedly, the addition of CTA to COS/PO copolymerization system could dramatically improve the turnover frequency (TOF) of PO (up to 240 h−1), higher than that of the copolymerization without CTA. In addition, the conversion of CTA could be up to 100% in most cases, as revealed by 1H NMR spectra. Of consequence, the number-average molecular weights (Mns) of the resultant block copolymers could be regulated by varying the feed ratio of CTA to PO. Oxygen-sulfur exchange reaction (O/S ER), which can generate randomly distributed thiocarbonate and carbonate units, was effectively suppressed in all of the cases in the presence of CTA, even at 80 °C. This work presents a versatile method for synthesizing sulfur-containing block copolymers through a metal-free route, providing an array of new block copolymers.

Spectroscopic Characterization of a [C−F−C]+ Fluoronium Ion in Solution

AbstractWe report the first spectroscopic evidence for a [C−F−C]+ fluoronium ion in solution. Extensive NMR studies (19F, 1H, 13C) characterize a symmetric cage‐like species in which fluorine exhibits substantial covalent bonding to each of the two carbon atoms involved in the three‐center interaction. Experimental NMR data comport well with calculated values to lend credence to the structural assignment. As the culminating experiment, a Saunders isotopic perturbation test confirmed the symmetric structure. Congruent with the trend in other types of onium ions, the calculated charge at fluorine moves in a more positive (less negative) direction from the neutral. It is this important trend that explains in part the extraordinary historical difficulty in making theoretical predictions of fluoronium ions come true in solution, and why it takes fluorine captured in a cage to produce, finally, a stable ion and complete the historical arc of the organic halonium ion story.

Spectroscopic Characterization of a [C-F-C]+ Fluoronium Ion in Solution.

We report the first spectroscopic evidence for a [C-F-C]+ fluoronium ion in solution. Extensive NMR studies (19 F, 1 H, 13 C) characterize a symmetric cage-like species in which fluorine exhibits substantial covalent bonding to each of the two carbon atoms involved in the three-center interaction. Experimental NMR data comport well with calculated values to lend credence to the structural assignment. As the culminating experiment, a Saunders isotopic perturbation test confirmed the symmetric structure. Congruent with the trend in other types of onium ions, the calculated charge at fluorine moves in a more positive (less negative) direction from the neutral. It is this important trend that explains in part the extraordinary historical difficulty in making theoretical predictions of fluoronium ions come true in solution, and why it takes fluorine captured in a cage to produce, finally, a stable ion and complete the historical arc of the organic halonium ion story.

Forming a Stable CEI Layer on LiNi0.5Mn1.5O4 Cathode by the Synergy Effect of FEC and HDI

As a promising additive for film forming on anodes, fluoroethylene carbonate (FEC) has been applied widely in commercial lithium ion batteries (LIBs). However, the influence of FEC in high-voltage Li+ energy storage systems are still under disputing for the negative effects on cathodes. Considering a FEC molecule would be electro-oxidized to a radical onium ion, we investigate hexamethylene diisocyanate (HDI) as the additive which can react with the intermediate to form an amide-based polymer via thermodynamic processes. The polymer would be stable at high potential. In the FEC-containing electrolyte with HDI added, a surface layer is formed on the LiNi0.5Mn1.5O4 cathode, which would protect the compounds from decomposing and improve the performances of the batteries. The capacity retention of Li/LiNi0.5Mn1.5O4 cells cycled between 3.5–4.9 V (vs. Li+/Li) is significantly increased from 59.1% to 76.1% in 200 cycles, and the rate capability is also improved compared with the ones without HDI. The electrolyte system also shows a good compatibility with graphite, presenting a promising prospect for the practical application of high-voltage LIBs.

Crosslinkable photoacid generators for ultrahigh loading in epoxide functionalized molecular resists

A series of ionic onium salt photoacid generators (PAGs) functionalized with epoxide or phenolic groups capable of participating in the cationic polymerization of epoxides have been synthesized and investigated for use in ultrahigh PAG loaded negative tone epoxide functionalized molecular resists. An epoxide functionalized PAG [tris(4-glycidylether-3,5-dimethylphenyl)sulfonium hexafluoroantimonate] was found to be capable of use at loadings up to 100 mol. % in an epoxide functionalized resist [1,1,2,2-tetrakis(4-(oxiran-2-ylmethoxy)phenyl)ethane (4-Ep)] without inhibiting its ability to form fully crosslinked features, and was able to resolve 50 nm features under 100 keV electron-beam lithography at PAG loadings exceeding 50 mol. %. A phenol functionalized PAG [tris(4-hydroxyphenyl)sulfonium hexafluoroantimonate] was similarly capable of use at loadings up to 50 mol. % in 4-Ep without inhibiting cross-linking, and was able to resolve both 50 and sub-50 nm features at PAG loadings exceeding 30 mol. % using 100 keV electron-beam lithography. Initial results from this study indicate that the functionalized PAGs can enable higher PAG loadings in these negative tone resists than was previously possible; however, increasing PAG loading beyond at least 30 mol. % has a negative impact on sensitivity when using 100-keV high energy e-beam exposures.

Antimony(V) Chloride, SbCl5 as a Labile Reagent in Organic Transformations

SbCl5 has been shown to be versatile reagent especially as a Lewis acid catalyst in many organic reactions such as electrophilic aromatic substitution, isomerization and rearrangements, halogenation, preparation of carbocation and onium ion complexes etc. Therefore in this paper applicably of antimony(V) chloride in organic transformations reactions is reviewed.

Driving Force Dependence of Electron Transfer from Electronically Excited [Ir(COD)(μ-Me2pz)]2 to Photo-Acid Generators.

We report the rates of electron transfer (ET) reactions of electronically excited [Ir(COD)(μ-Me2pz)]2 with onium salt photoacid generators (PAGs). The reduction potentials of the PAGs span a large electrochemical window that allows determination of the driving force dependence of the ET reactions. Rate constants of ET from electronically excited [Ir(COD)(μ-Me2pz)]2 to onium PAGs are determined by the reaction driving force until the diffusion limit in acetonitrile is reached.

Microstructure aspects of radiation-cured networks: Cationically polymerized aromatic epoxy resins

The thermo-mechanical properties and nanostructural features of epoxy aromatic resins cationically cured by UV–visible or electron beam radiation have been studied by FT-NIR spectroscopy, dynamic mechanical analysis (DMA), dielectric spectroscopy (DS), and atomic force microscopy (AFM). The influence of formulation (nature and content of onium salt) and of curing parameters (doses, thermal treatment) on the thermophysical have been investigated. The presence of several relaxation domains observed by DMA and DS analysis confirms the presence of heterogeneities in the cured materials. Network formation is described by the percolation of glassy nanoclusters which are evidenced by AFM analyses. AFM probing by quantitative nanomechanical measurements confirms the gradual build-up of the local Young's modulus in good agreement with the macroscopic value.

Generation of ferrocenylvinyl cation CpFeC5H4–C+=CH2 by protonation of ferrocenylacetylene with Nafion and its reactions with SMe2 and PPh3 in scCO2 giving onium salts

Cation CpFeC5H4–C+=CH2 was obtained by protonation of FcC CH with Nafion superacid in DMF or scCO2 and characterized by NMR spectroscopy. The protonation in the presence of SMe2 or PPh3 affords new onium derivatives, which were isolated as the tetrafluoroborate salts.