Sulfonium Triflate Research Articles

Synthesis of Heterocyclic Sulfonium Triflates by Cu-Catalyzed Selective Sarylation with Aryl(mesityl)iodonium Salts

Background: An efficient method for synthesizing cyclic arylsulfonium salts has been developed by selective aryl transfer to the sulfur atom from aryl(mesityl)iodonium triflates, a recyclable series of diaryliodonium salts. Methods: The utilization of sulfonium salts as valuable intermediates is well-established, as they exhibit high reactivity under conditions of heating or UV irradiation. However, their synthesis typically involves the reaction of diarysulfoxide with acid anhydride, which requires the oxidation of sulfur(II) to sulfoxide(IV) and thus limits the scope of synthesis. Hence, in this study, we employed recyclable mesityliodonium(III) salts and copper catalysis. Results: The method was used to synthesize cyclic arylsulfonium salts without the need for preoxidation of the sulfur atom, resulting in a facile and high-yield synthesis. Conclusion: The desired cyclic arylsulfonium salts were synthesized through selective transfer of the aryl group from mesityliodonium salts, demonstrating the effectiveness of the new approach.

Direct Vinylation of Activated Methines by a Vinylsulfonium Salt

Abstract: Vinylation of activated methines is a synthetically useful and challenging transformation. Traditional methods for this transformation always encounter multiple steps, limited generality and/or handling gaseous substrates. Herein, we report by using diphenyl(vinyl)sulfonium triflate as a vinylation component, a one-step direct vinylation of activated methines can be realized under mild conditions. This reaction, compatible with several kinds of activated methines, can lead to the construction of vinylated quaternary carbon centers concisely.

Base-Promoted Synthesis of Vinyl Sulfides from Sulfonium Triflates.

A new protocol has been developed for vinyl sulfide synthesis promoted by an alkoxy base under metal-free conditions. In this reaction, aryl and alkenyl sulfonium triflates with diverse functionalities are converted into vinyl sulfides with excellent reactivity. This transformation features mild and safe reaction conditions that avoid catalyst, transition metal, high-pressure gas, and high reaction temperature without compromising efficiency.

Water developable non-chemically amplified photoresist for electron beam and extreme ultraviolet lithography

Background: Non-chemically amplified resist (n-CAR) shows great potential as a unique lithographic material because it avoids some disadvantages of CAR, such as post-exposure instability and acid diffusion. Furthermore, since toxic and flammable developers are widely used in semiconductor manufacturing, the implementation of innovative environmentally friendly water-developable photoresists is of interest. Aim: A unique n-CAR, which could be developed with an environmentally friendly developer, was prepared for electron beam (e-beam) lithography (EBL) and extreme ultraviolet lithography (EUVL). Approach: A polymer containing radiation/photosensitive sulfonium triflate group (PSSF) was synthesized and characterized by infrared, H1 NMR, and gel permeation chromatography. The lithography performance of the PSSF photoresist was evaluated by EBL and EUVL. The patterns were analyzed with scanning electron microscope and atomic force microscope. Results: The PSSF photoresist can be used in EBL and EUVL. Post-exposure bake had no significant effect on the resolution of photoresist. Development in water should be kept at an appropriate time of 30 s to obtain the repeatable and high-resolution patterns. It shows a similar sensitivity to polymethyl methacrylate but higher contrast. Conclusions: The PSSF acts as n-CAR, and 20 nm line patterns and 35 nm 1:1 line/space patterns were achieved in EBL and EUVL, respectively. It can be developed in pure water with high contrast (γ = 5.49).

Convergent Synthesis of 1,4-Dicarbonyl Z-Alkenes through Three-Component Coupling of Alkynes, α-Diazo Sulfonium Triflate, and Water.

We report a general protocol for the convergent synthesis of 1,4-dicarbonyl Z-alkenes form alkynes using α-diazo sulfonium triflate and water. The C═O, C═C, and C-H bonds are formed under mild conditions with a wide range of functional groups tolerated. The reaction exhibits excellent Z-selectivity and complete regioselectivity. The resulting 1,4-dicarbonyl Z-alkenes can smoothly undergo follow-up conversion to a variety of heteroaromatic scaffolds. Moreover, the reaction also provides a facile access to the corresponding deuterated Z-alkenes and deuterated heteroarenes with a high level of deuterium incorporation (90-97% D-inc.) by directly using D2O, thus rendering the method highly valuable. The comprehensive mechanistic studies indicate that a free carbyne radical intermediate is formed via the photocatalytic single electron transfer process, and KH2PO4 plays a crucial role in significant improvements on yield and selectivity based on density-functional theory calculations, providing a new direction for radical coupling reactions of diazo compounds.

Rapid access to organic triflates based on flash generation of unstable sulfonium triflates in flow.

Flash (extremely fast) electrochemical generation of unstable arylbis(arylthio)sulfonium triflates [ArS(ArSSAr)]+ [OTf]- that are unsuitable for accumulation in batch processes was achieved within 10 s in a divided-type flow electrochemcial reactor, enabling one-flow access to vinyl triflates, short-lived oxocarbenium triflates and glycosyl triflates.

Study of Self-Patterned Zinc Tin Oxide Thin-Film Transistors Prepared from Photocurable Precursor Solution with Photoacid Generator

Solution-processed zinc tin oxide (ZTO) thin-film transistors (TFTs) have great potential uses in next-generation wearable and flexible electronic products. Zinc and tin precursor materials are naturally abundant and have low fabrication costs. To integrate a single ZTO TFT into logic circuits including inverters, NAND, and NOR gates will require the development of a facile patterning process to replace conventional and complicated photolithography techniques which are usually time-consuming and toxic. In this study, self-patterned ZTO thin films were prepared using a photo-patternable precursor solution including a photoacid generator, (4-methylthiophenyl)methyl phenyl sulfonium triflate. Solution-processed ZTO precursor films fabricated with the photoacid generator were successfully micropatterned by UV exposure, and transitioned to a semiconducting ZTO thin film by heat treatment. The UV-irradiated precursor films became insoluble in developing solvent as the generated proton from the photoacid generator affected the metal-containing ligand and changed the solubility of the metal oxide precursors. The resulting ZTO thin films were utilized as the active layers of n-type TFTs, which exhibited a typical n-type transfer, and output characteristics with appropriate threshold voltage, on/off current ratio, and field-effect mobility. We believe that our work provides a convenient solution-based route to the fabrication of metal-oxide semiconductor patterns.

α‐Diazo Sulfonium Triflates: Synthesis, Structure, and Application to the Synthesis of 1‐(Dialkylamino)‐1,2,3‐triazoles

AbstractThe one‐pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds is elucidated by X‐ray crystallography. Under photochemical conditions, reaction of these salts with N,N‐dialkyl hydrazones affords 1‐(dialkylamino)‐1,2,3‐triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene–metal complexes is also reported and the donor properties of these new ligands characterized.

α-Diazo Sulfonium Triflates: Synthesis, Structure, and Application to the Synthesis of 1-(Dialkylamino)-1,2,3-triazoles.

The one‐pot synthesis of a series of sulfonium salts containing transferable diazomethyl groups is described, and the structure of these compounds is elucidated by X‐ray crystallography. Under photochemical conditions, reaction of these salts with N,N‐dialkyl hydrazones affords 1‐(dialkylamino)‐1,2,3‐triazoles via diazomethyl radical addition to the azomethine carbon followed by intramolecular ring closure. The straightforward transformation of the structures thus obtained into mesoionic carbene–metal complexes is also reported and the donor properties of these new ligands characterized.

Synthesis and reactions of (E)-β-(bromotetrafluoroethyl)vinyl diphenyl sulfonium triflate

We have synthesized (E)-β-(bromotetrafluoroethyl)vinyl sulfonium salt as a novel vinyl sulfonium salt. The excellent performance of the salt was demonstrated in the efficient synthesis of the corresponding 2-(bromotetrafluoroethyl)-N-substituted aziridines and (bromotetrafluoroethyl)cyclopropane derivatives in high yields.

One-pot Synthesis of Allyl Sulfides from Sulfinate Esters and Allylsilanes through Reduction of Alkoxysulfonium Intermediates

An efficient method to synthesize allyl sulfides from sulfinate esters and allylsilanes is described. Based on the reactivity of isolated allyl(methoxy)phenyl sulfonium triflate, we have developed a simple one-pot method for the allyl sulfide synthesis by S-allylation of sulfinate esters and subsequent reduction with sodium borohydride. A number of allyl sulfides were prepared by this method leaving various functional groups unreacted.

Ullmann-type N-arylation of anilines with alkyl(aryl)sulfonium salts.

A palladium/copper-cocatalyzed Ullmann-type N-arylation of anilines using alkyl(aryl)sulfonium triflates as arylation reagents has been accomplished. The reaction enabled Caryl-S bond cleavage over Calkyl-S bond breakage of alkyl(aryl)sulfoniums by Pd(P(tBu)3)2/CuI and gave the corresponding N-arylated products in good to high yields. It was also significant that the reactions of aniline with asymmetric butyl(mesityl)(aryl)sulfonium triflates showed excellent selectivity, in which the aryl groups other than the bulky and electron-rich mesityl moieties were transformed.

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.

EUV photofragmentation and oxidation of a polyarylene – Sulfonium resist: XPS and NEXAFS study

Secondary electrons play a vital role in Extreme Ultraviolet Lithography (EUVL). However, the mechanisms and chemical reactions after photon absorption in this high energy region only recently have been studied in more detail. The present work is an attempt to obtain more information about the photofragmentation process when EUV radiation is used in polymers. EUV irradiation on a non-chemically amplified resist (non-CAR), poly[methyl (4-(phenyl thio) - phenyl) – sulfonium trifluoromethanesulfonate] (PAS), was studied using monochromatic synchrotron radiation at 103.5 eV of excitation energy. XPS and NEXAFS spectroscopy were used to follow the surface chemical changes after the samples were irradiated and oxidized. The results showed the fast desorption of the sensitive sulfonium triflate with important rearrangements that kept the sulfur contents and polymer backbone with minor changes. This was confirmed by the detection of new SC and SS signals after irradiation. New carbonyl signals were also detected and it was also observed that the aromatic rings resisted the irradiation of EUV photons. The photofragmentation process showed a different mechanism in relation with similar resists that we have studied in the past. Angle resolved-NEXAFS results and semiempirical calculations showed that the PAS film adopted a random configuration in relation to the Si(100) plane. It may allow a strong interaction after EUV irradiation between the excited species or radicals formed and the polymer chains favoring rearrangement reactions. The present investigation shows the need to understand the photochemical mechanisms under EUV photon excitations which are different to UV light. This knowledgement may lead to prepare better resist formulations for EUVL. Based on our finding a simple mechanism was proposed.

Efficient cyclopropanation of aryl/heteroaryl acetates and acetonitriles with vinyl diphenyl sulfonium triflate

A convenient method was developed for the cyclopropanation of aryl acetates and aryl acetonitrile using vinyl diphenyl sulfonium triflate salt. The newly developed conditions are simple, mild, and compatible with a wide range of functional groups, without the need to apply an inert atmosphere, or alkali bases.

EUV photofragmentation study of hybrid nonchemically amplified resists containing antimony as an absorption enhancer.

A detailed investigation to understand the mechanism of the resist action at a fundamental level is essential for future Extreme Ultraviolet Lithography (EUVL) resists. The photodynamics study of a newly developed hybrid nonchemically amplified 2.15%-MAPDSA–MAPDST resist using synchrotron radiation excitation at 103.5 eV (12 nm) is presented. Antimony was incorporated in the resist as a heavy metal absorption center in the form of antimonate (2.15%). The results showed the fast decomposition rate of the radiation sensitive sulfonium triflate. HR-XPS and sulfur L-NEXAFS spectra of the copolymer films revealed that after irradiation the Ar–S+–(CH3)2 sulfonium group bonded to the phenyl ring resisted the EUV excitation. Those results confirmed the polarity switching mechanism from hydrophilic sulfonium triflates to hydrophobic aromatic sulfides obtained in previous results. The inorganic component SbF6− included in the resist formulations as an EUV absorption enhancer was particularly illustrative of the photofragmentation process. F 1s and O 1s HR-XPS spectra showed that fluorine remains linked to the antimony, even after 15 min of irradiation. A change of the antimony oxidation state was also observed with an increase in irradiation time. The presence of the heavy metal may control the high energy deposited on the resist which finally led to very well resolved 20 nm isolated line patterns by EUVL. The 10 times improved sensitivity compared with previous poly-MAPDST resists studied in the past showed the potential of this class of hybrid resists for next generation semiconductor industry applications.

New non-chemically amplified molecular resist design with switchable sensitivity for multi-lithography applications and nanopatterning

The development of new photoresist materials for multi-lithography applications is crucial but a challenging task for semiconductor industries. During the last few decades, given the need for new resists to meet the requirements of semiconductor industries, several research groups have developed different resist materials for specific lithography applications. In this context, we have successfully synthesized a new molecular non-chemically amplified resist (n-CAR) (C3) based on the functionalization of aromatic hydroxyl core (4,4′-(9H-fluorene-9,9-diyl)diphenol) with radiation sensitive sulfonium triflates for various lithography applications. While, micron scale features have been developed using i-line (365 nm) and DUVL (254 nm) exposure tools, electron beam studies on C3 thin films enabled us to pattern 20 nm line features with L/3S (line/space) characteristics on the silicon substrate. The sensitivity and contrast were calculated from the contrast curve analysis as 280 µC cm−2 and 0.025 respectively. Being an important parameter for any newly developed resists, the line edge roughness (LER) of 30 nm (L/5S) features were calculated, using SUMMIT metrology package, to be 3.66 ± 0.3 nm and found to be within the acceptable range. AFM analysis further confirmed 20 nm line width with smooth pattern wall. No deformation of patterned features was observed during AFM analysis which indicated good adhesion property between patterned resists and silicon substrates.

Sonogashira Reaction Using Arylsulfonium Salts as Cross-Coupling Partners.

Triarylsulfonium, alkyl- and fluoroalkyl(diaryl)sulfonium, and aryl(dialkyl)sulfonium triflates are successfully used as a new family of cross-coupling participants in the Sonogashira reaction as aryldiazonium, diaryliodonium, and tetraphenylphosphonium salts. It was found that terminal alkynes reacted mildly with triarylsulfonium or (2,2,2-trifluoroethyl)diphenylsulfonium triflate at room temperature under Pd- and Cu-cocatalysis to give the corresponding arylalkynes in up to >99% yield. This protocol represents the first use of arylsulfonium salts as cross-coupling partners in the Pd/Cu-catalyzed Sonogashira reaction.

Zinc triflate-mediated cyclopropanation of oxindoles with vinyl diphenyl sulfonium triflate: a mild reaction with broad functional group compatibility

The first use of Zn(OTf)2 for the cyclopropanation of unprotected oxindoles with vinyl diphenyl sulfonium triflate to show high regioselectivity.

Pd-catalyzed Suzuki–Miyaura cross-coupling of [Ph2SR][OTf] with arylboronic acids

The Pd-catalyzed Suzuki–Miyaura cross-coupling of alkyl- and fluoroalkyl(diphenyl)sulfonium triflates with arylboronic acids was compared. The fluorine substitution on the alkyl groups of [Ph2SR][OTf] had a big influence on the reaction. Perfluoroalkyl(diphenyl)sulfonium triflates (2b–d) were unsuccessful participants in the Pd-catalyzed phenylation of arylboronic acid under the standard conditions because of the strong electronegativity of the long-chain perfluoroalkyl groups, which underwent SRfn bond cleavage instead. Polyfluoroalkyl(diphenyl)sulfonium triflates (2f–h) reacted with arylboronic acid to afford the phenylation product in very low yields due to the tendency of deprotonation and β-F elimination of the sulfonium salts. Eventually, (2,2,2-trifluoroethyl)diphenylsulfonium triflate (2e), methyl- or ethyl(diphenyl)sulfonium triflate (2i or 2j), and triphenylsulfonium triflate (2m) were found to be more effective reagents than other tested phenylsulfounium salts for Pd-catalyzed phenylation, which provided much higher yields of the desired products under mild conditions.