Imidazole Catalyst Research Articles

Tailoring peel strength in UV-responsive, nonconductive adhesives via photocleavable epoxy for micro-LED bonding and repair

To develop a UV-responsive epoxy-based nonconductive adhesive (NCA) with adjustable peel strength, a bifunctional epoxy (NBE) was synthesized. This compound included an ortho-nitrobenzyl ester that decomposes upon UV absorption, exhibiting absorption in the 240350 nm wavelength range and a thermal decomposition temperature at 1% weight loss of 214 ℃. When coupled with an imidazole catalyst, the curing of NBE began at 100 ℃ and reached a maximum exothermic peak at 136 ℃. The NCA was formulated using NBE together with bisphenol F epoxy, cresol novolac epoxy, and nadic methyl anhydride as a curing agent. Despite the increasing NBE content in the NCA, the curing behaviour remained almost the same. However, the decomposition temperature of the NCA decreased in proportion to the NBE content. NCA tapes bonded to quartz glass substrates exhibited a 90° peel strength of 7.1910.39 N/in, depending on the NBE content. When exposed to excimer laser irradiation at 100 mJ/cm2, the 90° peel strength decreased significantly to nearly 0 N/in.

Design, Synthesis, and Application of Chiral Bicyclic Imidazole Catalysts.

Asymmetric organocatalysis has been considered to be an efficient and reliable strategy for the stereoselective preparation of optically active chemicals. In particular, chiral tertiary amines as Lewis base organocatalysts bearing core structures including quinuclidine, dimethylaminopyridine (DMAP), N-methylimidazole (NMI), amidine, etc. have provided new and powerful tools for various chemical transformations. However, due to the limitations in structural complexity, synthetic difficulty, low catalytic efficiency, and high cost, the industrial application of such catalysts is still far from being widely adopted. Therefore, the development of new chiral tertiary amine catalysts with higher activity and selectivity is greatly desired.In order to address the contradiction between activity and selectivity caused by the ortho group, a bicyclic imidazole structure bearing a relatively large bond angle ∠θ was designed as the skeleton of our new catalysts. 6,7-Dihydro-5H-pyrrolo[1,2-a]imidazole (abbreviated as DPI) and 5,6,7,8-tetrahydroimidazo[1,2-a]pyridine (abbreviated as TIP) are two of the utilized skeletons. In addition to obtaining satisfactory catalytic activity, excellent enantioselectivity would also be expected because the stereocontrol R group is neither far nor close to the catalytic active site (sp2-N atom) and is adjustable. Based on this skeleton, a family of chiral bicyclic imidazole catalysts were easily prepared and successfully applied in several enantioselective reactions for the synthesis of a variety of valuable chiral compounds.6,7-Dihydro-5H-pyrrolo[1,2-a]imidazole (abbreviated as DPI) is the predominantly utilized skeleton. First, HO-DPI, the key intermediate of the designed chiral bicyclic imidazole catalysts, could be efficiently synthesized from imidazole and acrolein, then separated by kinetic resolution or optical resolution. Second, Alkoxy-DPI, the alkyloxy-substituted chiral bicyclic imidazole catalysts, were synthesized by a one-step alkylation from HO-DPI. This type of catalyst has been successfully applied in asymmetric Steglich rearrangement (C-acylation rearrangement of O-acylated azlactones), asymmetric phosphorylation of lactams, and a sequential four-step acylation reaction. Third, Acyloxy-DPI, the acyloxy-substituted chiral bicyclic imidazole catalysts, were synthesized with a one-step acetylative kinetic resolution from racemic HO-DPI or acylation from enantiopure HO-DPI. The catalyst AcO-DPI has been successfully applied in enantioselective Black rearrangement and in direct enantioselective C-acylation of 3-substituted benzofuran-2(3H)-ones and 2-oxindoles. Fourth, Alkyl-DPI was synthesized via a two-step reaction from racemic HO-DPI and separated easily by resolution. The catalyst Cy-DPI has been successfully applied in dynamic kinetic resolution of 3-hydroxyphthalides through enantioselective O-acylation. Cy-PDPI was synthesized through a Cu-catalyzed amidation from Cy-DPI and successfully applied in the kinetic resolution of secondary alcohols with good to excellent enantioselectivities. Finally, the carbamate type chiral bicyclic imidazole catalysts, Carbamate-DPI, were readily synthesized from HO-DPI, and the catalyst Ad-DPI bearing a bulky adamantyl group was successfully applied in the synthesis of the anti-COVID-19 drug remdesivir via asymmetric phosphorylation. Alongside our initial work, this Account also introduces four elegant studies by other groups concerning asymmetric phosphorylation utilizing chiral bicyclic imidazole catalysts.In summary, this Account focuses on the chiral bicyclic imidazole catalysts developed in our group and provides an overview on their design, synthesis, and application that will serve as inspiration for the exploration of new organocatalysts and related reactions.

Development of Tg-less epoxy thermosets by introducing crosslinking points into rigid mesogenic moiety via Schiff base-derived self-polymerization

Novel glass-transition-temperature-less (Tg-less) epoxy thermosets were prepared by a Schiff base (CH=N)-derived self-polymerization of mesogenic epoxy. The self-polymerization mechanism was verified by differential scanning calorimetry, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The epoxy–CH=N addition reaction formed a new tertiary amine, introducing a crosslinking point into the rigid mesogenic moiety. Dynamic mechanical analysis of the cured system showed a slight α-relaxation in tanδ, and a high storage modulus was maintained at > 250 ℃. Also, no drastic increase in the coefficient of thermal expansion related to the glass-transition behavior was observed. The results suggested that the crosslinking point formed in the rigid mesogenic moiety effectively suppressed the thermal motion of networked chains, resulting in Tg-less behavior. An imidazole catalyst was used to enhance the self-polymerization reactivity. The imidazole content effect on the temperature-dependency of the mean free volume in the network structure was investigated by positron annihilation lifetime spectrometry.

Chiral Bicyclic Imidazole-Catalyzed Direct Enantioselective C -Acetylation of Indolones

Chiral Bicyclic Imidazole-Catalyzed Direct Enantioselective <i>C</i> -Acetylation of Indolones

Chemical control of the aromatic disulfide exchange kinetics for tailor-made epoxy vitrimers

Aromatic disulfides containing epoxy vitrimers are one of the most versatile materials and the top candidates for employment in industrial applications, as they offer many advantages compared to other existing vitrimers (scalability, simplicity, easy processing and excellent mechanical properties) and their use in industrial applications is straight forward. The capability of tuning the mechanical and dynamic properties of vitrimers is one of the most explored fields in vitrimer materials. Herein we present tailor-made aromatic disulfide containing epoxy vitrimers trough the understanding of the effect of having: i) different hardener structure (Ortho or Para); ii) free pending amine groups or; iii) catalyst in the system. Our study shows that the relaxation time is highly dependent on regioisomerism of the aromatic hardener, stoichiometry and presence of catalyst. In the present study we found that equivalent Ortho and Para vitrimers show huge difference in the activation energy (Ea) ranging from 200 kJ/mol for Para vitrimers up to 350 kJ/mol for Ortho vitrimers. In the absence of free pending amine groups, the exchange kinetics are slowed down limiting their use for continuous processing techniques. In contrast, both free pending amine groups and imidazole catalyst permit to reduce the stress relaxation time ending up in relaxation times below 5 s at 180 °C. These results confirm the high tuning capability of aromatic disulfide containing epoxy vitrimers providing a methodology to tune the dynamic properties to design the right vitrimer for the right application and processing technology.

Catalytic Asymmetric Synthesis of the anti‐COVID‐19 Drug Remdesivir

AbstractThe catalytic asymmetric synthesis of the anti‐COVID‐19 drug Remdesivir has been realized by the coupling of the P‐racemic phosphoryl chloride with protected nucleoside GS441524. The chiral bicyclic imidazole catalyst used is crucial for the dynamic kinetic asymmetric transformation (DyKAT) to proceed smoothly with high reactivity and excellent stereoselectivity (96 % conv., 22:1 SP:RP). Mechanistic studies showed that this DyKAT is a first‐order visual kinetic reaction dependent on the catalyst concentration. The unique chiral bicyclic imidazole skeleton and carbamate substituent of the catalyst are both required for the racemization process, involving the phosphoryl chloride, and subsequent stereodiscriminating step. A 10 gram scale reaction was also conducted with comparably excellent results, showing its potential for industrial application.

Catalytic Asymmetric Synthesis of the anti-COVID-19 Drug Remdesivir.

The catalytic asymmetric synthesis of the anti-COVID-19 drug Remdesivir has been realized by the coupling of the P-racemic phosphoryl chloride with protected nucleoside GS441524. The chiral bicyclic imidazole catalyst used is crucial for the dynamic kinetic asymmetric transformation (DyKAT) to proceed smoothly with high reactivity and excellent stereoselectivity (96 % conv., 22:1 SP :RP ). Mechanistic studies showed that this DyKAT is a first-order visual kinetic reaction dependent on the catalyst concentration. The unique chiral bicyclic imidazole skeleton and carbamate substituent of the catalyst are both required for the racemization process, involving the phosphoryl chloride, and subsequent stereodiscriminating step. A 10 gram scale reaction was also conducted with comparably excellent results, showing its potential for industrial application.

Active centre and reactivity descriptor of a green single component imidazole catalyst for acetylene hydrochlorination.

A green catalyst for acetylene hydrochlorination yielding a VCM is presented using imidazole as a single component metal-free catalyst. The mechanisms and reactivities of imidazole-catalyzed acetylene hydrochlorination have been investigated by combined computational and experimental studies. The electronic effects of ortho-substituents on the reactivities have also been investigated. Through theoretical calculations and experimental studies, the nitrogen-atom including a lone pair active site of single component imidazole for metal-free acetylene hydrochlorination is proposed. It is suggested that the nitrogen-atom including a lone pair of imidazole adsorbs an HCl molecule to form an imidazole-HCl complex, which serves as the active catalyst to participate in the reaction process of acetylene hydrochlorination. Besides, the results show that C2H2 assists in the electrophilic addition of HCl, undergoing an almost planar six-membered ring transition state. Computational studies on the ortho-substitution of the active sites will have an important impact on the catalytic efficiency.

Cyclic Carbonates from CO2 and Epoxides on a Supported Imidazole Catalyst

Key words heterogeneous catalysis - bifunctional catalysis - carbon dioxide - epoxides - cyclic carbonates

Hydrothermal Synthesis of Platinum‐Group‐Metal‐Free Catalysts: Structural Elucidation and Oxygen Reduction Catalysis

AbstractA hydrothermal approach to generate a platinum‐group‐metal‐free (PGM‐free) Fe−N−C catalyst for the oxygen reduction reaction (ORR) is introduced. The process involves partial carbonization by hydrothermal means followed by thermal treatment to obtain the final catalysts. Detailed X‐ray scattering analysis of the glucose−imidazole catalysts (termed as GLU‐IMID‐C catalysts), obtained for the first time with the use of CarbonXS GUI program, reveals the presence of face‐centered cubic (FCC) iron nanoparticles embedded in partially graphitic carbon in all catalyst variations. We also report the physical characterization of these catalysts by using X‐ray photoelectron spectroscopy, Brunauer−Emmett−Teller surface area analysis, and transmission electron microscopy. The electrocatalytic behavior of the catalysts towards oxygen reduction is studied separately in acidic and alkaline electrolytes by rotating ring disk electrode measurements. The catalysts exhibit high ORR activity in acidic (0.5 M H2SO4) and alkaline (0.1 M KOH) electrolytes. A precursor structure−performance relationship of these catalysts and their performance trends in both electrolytes has been discussed in this work.

Direct enantioselective C-acylation for the construction of a quaternary stereocenter catalyzed by a chiral bicyclic imidazole.

A direct enantioselective C-acylation of 3-substituted benzofuran-2(3H)-ones (with up to 97% ee) was developed using a chiral bicyclic imidazole catalyst OAc-DPI and an achiral tertiary amine additive DIPEA. The reaction mechanism for the direct C-acylation has been investigated using both experimental and theoretical studies.

Imidazole Derivatives as Accelerators for Ruthenium‐Catalyzed Hydroesterification and Hydrocarbamoylation of Alkenes: Extensive Ligand Screening and Mechanistic Study

AbstractImidazole derivatives are effective ligands for promoting the [Ru3(CO)12]‐catalyzed hydroesterification of alkenes using formates. Extensive ligand screening was performed to identify 2‐hydroxymethylated imidazole as the optimal ligand. Neither carbon monoxide gas nor a directing group was required, and the reaction also showed a wide substrate generality. The Ru–imidazole catalyst system also promoted intramolecular hydrocarbamoylation to afford lactams. A Ru–imidazole complex was unambiguously analyzed by X‐ray crystallography, and it had a trinuclear structure derived from one [Ru3(CO)12] and two ligands. This complex was also successfully used for hydroesterification. The mechanism was examined in detail by using D‐ and 13C‐labeled formates, indicating that the hydroesterification reaction proceeds by a decarbonylation–recarbonylation pathway.

Aggregation-induced emission: a simple strategy to improve chemiluminescence resonance energy transfer.

The emergence of aggregation-induced emission (AIE) has opened up a new avenue for scientists. There is a great demand for the development of a new generation chemiluminescence resonance energy transfer (CRET) acceptors with AIE characteristics due to the aggregation-caused chemiluminescence (CL) quenching effect commonly observed in the conventional fluorophore CL acceptors at high concentrations. However, the systematical studies involving in AIE-amplified CL are still scarce. Herein, it is the first report that the gold nanocluster aggregates (a type of well-defined AIE molecules) are used to study their influence on the bis(2,4,6-trichlorophenyl) oxalate (TCPO)-H2O2 CL reaction. Interestingly, the AIE molecules in the diluted solution are unable to boost the CL signal of the TCPO-H2O2 system, but their aggregates display a strongly enhanced CL emission compared to their counterparts of fluorophore molecules, thanks to the unique AIE effect of gold nanoclusters. In comparison to rhodamine B with the aid of an imidazole catalyst, the detection limit of the gold nanocluster aggregate-amplified CL probe for H2O2 (S/N = 3) is low in the absence of any catalyst. Finally, the other two typical AIE molecules, Au(I)-thiolate complexes and 9,10-bis[4-(3-sulfonatopropoxyl)-styryl]anthracene (BSPSA), are investigated to verify the generality of the AIE molecule-amplified CL emissions. These results demonstrate effective access to highly fluorescent AIE molecules with practical applications in avoiding the aggregation-induced CL quenching at high concentrations, which can be expected to provide a novel and sensitive platform for the CL amplified detection.

Chiral Bicyclic Imidazole Nucleophilic Catalysts: Design, Synthesis, and Application to the Kinetic Resolution of Arylalkylcarbinols

AbstractA new type of chiral 5‐aminoimidazole nucleophilic catalyst, designated as Alkyl‐PDPI (PDPI=3‐pyrrolidinyl‐6,7‐dihydro‐5H‐pyrrolo[1,2‐a]imidazole), was rationally designed, synthesized and applied to the kinetic resolution of various arylalkylcarbinols with good to excellent enantioselectivities. In particular, for phenyl(tert‐butyl)methanol and 1‐mesitylethanol, the s factors are as high as 45 and 67, respectively. Additionally, this new kind of chiral imidazole catalyst also showed good enantioselectivity for heteroarylalkylcarbinols.magnified image

ChemInform Abstract: Cu‐Catalyzed Amidation of Halogenated Imidazoles.

AbstractThe product (IX) can be further used to prepare a novel chiral imidazole catalyst for the kinetic resolution of secondary alcohols.

Synthesis and Nonenzymatic Template-Directed Polymerization of 2′-Amino-2′-deoxythreose Nucleotides

Threose nucleic acid (TNA) is a potential alternative genetic material that may have played a role in the early evolution of life. We have developed a novel synthesis of 2′-amino modified TNA nucleosides (2′-NH2-TNA) based on a cycloaddition reaction between a glycal and an azodicarboxylate, followed by direct nucleosidation of the cycloadduct. Using this route, we synthesized the thymine and guanine 2′-NH2-TNA nucleosides in seven steps with 24% and 12% overall yield, respectively. We then phosphorylated the guanine nucleoside on the 3′-hydroxyl, activated the phosphate as the 2-methylimidazolide, and tested the ability of the activated nucleotide to copy C4 RNA, DNA, and TNA templates by nonenzymatic primer extension. We measured pseudo-first-order rate constants for the first nucleotide addition step of 1.5, 0.97, and 0.57 h–1 on RNA, DNA, and TNA templates, respectively, at pH 7.5 and 4 °C with 150 mM NaCl, 100 mM N-(hydroxylethyl)imidazole catalyst, and 5 mM activated nucleotide. The activated nucleotide hydrolyzed with a rate constant of 0.39 h–1, causing the polymerization reaction to stall before complete template copying could be achieved. These extension rates are more than 1 order of magnitude slower than those for amino-sugar ribonucleotides under the same conditions, and copying of the TNA template, which best represented a true self-copying reaction, was the slowest of all. The poor kinetics of 2′-NH2-TNA template copying could give insight into why TNA was ultimately not used as a genetic material by biological systems.

Preparation and Impact Properties of Epoxy/ Epoxidized Palm Oil Blend Glass Fiber Reinforced Composite Systems

Green thermosetting resins are were prepared using Epoxidizided palm oil (EPO) and epoxy based petroleum. The polymer resins were cured through amine system with the addition of various percentage of imidazole catalyst (5, 10, 25 and 30%). The evaluation for thermal due to high cross link densities blend samples toward heat. All the blend samples presented thermoset characteristics that was dependent upon the quantity of catalyst. As expected, the Tg decreased as the amount of imidazole increased.

에폭시 접착제의 경화거동 및 접합강도에 미치는 경화촉매제의 영향

Adhesive bonding is one of the most promising joining methods which may substitute for conventional metallurgical joining processes, such as welding, brazing and soldering. Curing behavior and mechanical properties of adhesive joint are largely dependent on the curing agent including hardener and catalyst. In this study, effects of curing system on the curing behavior and single-lap shear strength of epoxy adhesive joint are investigated. Dihydrazide, anhydride and dicyandiamide(DICY) were chosen as hardener and imidazole and triphenylphosphine(TPP) were chosen as catalyst. In curing behavior, TPP showed the delay of the curing rate for DICY and ADH at <TEX>$160^{\circ}C$</TEX>, compared to imidazole catalyst due to the high curing onset/peak temperature. DICY seemed to be most beneficial in the joint strength for both steel and Al adherends, although the type of adherends affected the shear strength of epoxy adhesive joint.

Regiodivergent Reactions through Catalytic Enantioselective Silylation of Chiral Diols. Synthesis of Sapinofuranone A

Through the use of an amino acid based imidazole catalyst, a regiodivergent silylation of chiral diols in cases where there is not a significant steric and electronic difference between the regioisotopic hydroxyl groups has been developed. This transformation allows for the conversion of racemic diols into regioisomeric, enantiomerically enriched, monosilylated products. The utility of this process is highlighted in the efficient enantioselective preparation of a useful synthetic intermediate and the natural product, sapinofuranone A.

Insights into heterogeneous phosphodiester hydrolysis using a simple hydrogel-based copper(II)-imidazole catalyst

A family of copolymer hydrogels containing different mass percentages of vinylimidazole, acrylamide and N, N′-methylenebisacrylamide were used to bind copper(II) ions. The resultant copper-loaded gels demonstrated spectroscopic features that indicated copper was bound in a distorted square planar geometry. The hydrolysis activity of these the most active of these systems towards bis(3-nitrophenyl)phosphate at pH 8 was 2.78 × 10 −6 s −1, five orders of magnitude greater than the uncatalyzed reaction. While these systems obey Michaelis–Menten kinetics, they also subject both competitive and non-competitive inhibition from excess substrate and excess hydroxide due to constraints based in the coordination geometry of the copper(II) active sites.