Presence Of Lewis Acid Research Articles

Kinetic Studies of CO2 Insertion into Metal-Element σ-Bonds.

ConspectusDespite the plethora of metal catalyzed reactions for CO2 utilization that have been developed in academic laboratories, practical systems remain elusive. The understanding of the elementary steps in catalysis is a proven method to improve catalytic performance. In many catalytic cycles for CO2 utilization, the insertion of CO2 into a metal-element σ-bond, such as hydrides, alkyls, amides, or hydroxides, is a crucial step. However, despite the many demonstrations of CO2 insertion, there are a paucity of kinetic studies, and information about the reaction mechanism has been predominantly elucidated from computational investigations. In this Account, kinetic studies on CO2 insertion into late transition metal-element σ-bonds performed by my group are summarized, along with their implications for catalysis.A common pathway for CO2 insertion into a metal hydride involves a two-step mechanism. The first step is nucleophilic attack on CO2 by the hydride to generate an H-bound formate, followed by rearrangement to form an O-bound formate product. Kinetic studies on systems in which both the first and second steps are proposed to be rate-determining, known as inner-sphere and outer-sphere processes, respectively, show that insertion rates increase as (i) the ligand trans to the hydride becomes a stronger donor, (ii) the ancillary ligand becomes more electron-donating, and (iii) the Dimroth-Reichardt parameter of the solvent increases. However, the magnitude of these effects is generally smaller for inner-sphere processes because there is less buildup of charge in the key transition state. For similar reasons, the presence of Lewis acids only increases the rate of outer-sphere processes. These results suggest it may be possible to experimentally differentiate between inner- and outer-sphere processes.The insertion of CO2 into a metal-alkyl bond results in the formation of a C-C bond, which is important for the generation of fuels from CO2. For square planar Group 10 complexes, the presence of a strong donor ligand trans to the alkyl group is critical for kinetically promoting insertion. Further, the nucleophilicity of the alkyl ligand directly impacts the rate of CO2 insertion via an SE2 mechanism, as does the steric bulk of the complex, and the reaction solvent. In contrast to the relatively slow rates of insertion observed for metal alkyls, CO2 insertion is rapid for metal hydroxides and amides. Although kinetics trends could be determined for hydroxides, reactions with amides are too fast for quantitative studies.Overall, the rates of insertion correlate with the nucleophilicity of the element in the metal-element σ-bond, so amide > hydroxide > hydride > alkyl. Due to the related pathways for insertion, similar trends in ligand and solvent effects are observed for insertion into different metal-element σ-bonds. Thus, the same strategies can be used to control the rates of insertion across systems. Differences in the magnitude of solvent and ligand effects are caused by variation in the amount of charge build-up on the metal in the rate-determining transition state. Likely, given that CO2 is related to organic molecules such as aldehydes, ketones, and amides, the results described in this Account are general to a wider range of substrates.

Friedel Crafts Reactions Revisited: Some Applications in Heterogeneous Catalysis#

Abstract: Important organic reactions require the use of catalysts. The Friedel-Crafts reactions were discovered by Charles Friedel and James Mason Crafts in 1887. They are an essential catalytic process since they are widely applied in different areas such as fuels, cleaning, and pharmacological products. The reaction is usually carried out in the presence of Lewis acids or Brønsted acids in a homogeneous medium, with the nucleophilic aromatic substrate in excess. Although there is still work in the literature on the Friedel- Crafts reaction in a homogeneous medium using metal halides, the tendency is to replace these catalysts, which generate effluents that are harmful to the environment. Heterogeneous catalysts using solid acids show advantages over homogeneous catalysts, especially concerning separating products from the reaction medium, recycling, and reusing. This paper presents a mini-review focusing on the use of solid acids in Friedel-Crafts reactions.

Catalytic 1,1-diazidation of alkenes.

Compared to well-developed catalytic 1,2-diazidation of alkenes to produce vicinal diazides, the corresponding catalytic 1,1-diazidation of alkenes to yield geminal diazides has not been realized. Here we report an efficient approach for catalytic 1,1-diazidation of alkenes by redox-active selenium catalysis. Under mild conditions, electron-rich aryl alkenes with Z or E or Z/E mixed configuration can undergo migratory 1,1-diazidation to give a series of functionalized monoalkyl or dialkyl geminal diazides that are difficult to access by other methods. The method is also effective for the construction of polydiazides. The formed diazides are relatively safe by TGA-DSC analysis and impact sensitivity tests, and can be easily converted into various valuable molecules. In addition, interesting reactivity that geminal diazides give valuable molecules via the geminal diazidomethyl moiety as a formal leaving group in the presence of Lewis acid is disclosed. Mechanistic studies revealed that a selenenylation-deselenenylation followed by 1,2-aryl migration process is involved in the reactions, which provides a basis for the design of new reactions.

Study on the long-range chain degradation behavior of polylactic acid promoted by nanometer zinc oxide

Polylactic acid (PLA) is known for its degradative properties. Since PLA possesses a long chain macromolecular structure, its degradation behavior and characteristics have been the focus of research. In the presence of Lewis acid, the carbonyl oxygen in the ester group of PLA molecular chain can coordinate with it and be activated, so as to break the ester group and cause PLA degradation. However, there is still a lack of research strategies on the evolution of the remote structure of PLA chains, and there were few studies on the long-range degradation of PLA molecular chain in the effect of Lewis acid. In this work, a statistical method, combined with molecular weight testing, was proposed to investigate the long-range degradation behavior of PLA molecular chains. Results showed that in the presence of nano-ZnO, the long-range degradation of PLA molecular chain in solution was initially carried out in the form of terminal group biting-back and exchanging within 4 hours, and the molecular chain with new terminal-group was still long enough after degradation, gradually shortened over time. PLA began to degrade obviously after 8 h reaction. This chain scission method can provide a reaction platform for some reactions such as long-chain branching, which can be utilized to prepare PLA with special molecular chain topology and explore the mechanism of PLA chain structure transformation.

Trifluoromethylsulfinylation Reaction of Activated Arenes and Indoles with Trifluoromethanesulfinyl Chloride

AbstractThe trifluoromethylsulfinylation reaction of activated arenes with trifluoromethanesulfinyl chloride (CF3SOCl) in the presence of Lewis acid was achieved under mild and solvent‐free conditions. A series of aryl trifluoromethyl sulfoxides were obtained in moderate to high yields. The protocol could be extended to the perfluoroalkylsulfinylation of activated arenes, as well as the trifluoromethylsulfinylation of indoles without additive.

Competing interests during the key N-glycosylation of 6-chloro-7-deaza-7-iodopurine for the synthesis of 7-deaza-2'-methyladenosine using Vorbrüggen conditions.

A short 3-step synthesis of the antiviral agent 7DMA is described herein. The nature of a major by-product formed during the key N-glycosylation of 6-chloro-7-deaza-7-iodopurine with perbenzoylated 2-methyl-ribose under Vorbrüggen conditions was also investigated. Spectroscopic analyses support that the solvent itself is converted into a nucleophilic species competing with the nucleobase and further reacting with the activated riboside in an unanticipated fashion. These findings call for a revision of reaction conditions when working with weakly reactive nucleobases in the presence of Lewis acids. 7DMA thus obtained was evaluated for its efficacy against an emerging flavivirus in vitro.

Synthesis and studies of m/p-phenylene bridged bis(3-Pyrrolyl BODIPY)s

The first examples of m-/p-phenylene bridged bis(3-pyrrolyl BODIPY)s were synthesized by oxidizing the readily available m-/p-phenylene bridged bis(dipyrromethane) with DDQ in CH3CN followed by treatment with excess pyrrole and complexation with BF3⸱OEt2 in the presence of triethylamine. To the best of our knowledge, no straightforward synthetic method is available to prepare m-/p-phenylene bridged bis(3-pyrrolyl BODIPY)s. The bis(3-pyrrolyl BODIPY)s can be used as novel ligands for metal coordination chemistry by demasking BF2 units from bis(3-pyrrolyl BODIPY)s in the presence of Lewis acids. The bis(3-pyrrolyl BODIPY)s absorb at ∼585 nm with enhanced molar absorptivity compared to the monomer, 3-pyrrolyl BODIPY. The m-phenylene bridged bis(3-pyrrolyl BODIPY) emits strongly at ∼600 nm with a quantum yield of 0.34 whereas p-phenylene bridged bis(3-pyrrolyl BODIPY) emits relatively weakly in the same region with a quantum yield of 0.21. The electrochemical studies revealed that the two 3-pyrrolyl BODIPY units in bis(3-pyrrolyl BODIPY) dyads did not interact with each other. DFT/TD-DFT studies were used to understand the structure and electronic properties of bis(3-pyrrolyl BODIPY)s.

A Convenient Diels-Alder Approach toward Potential Polyketide-like Antibiotics Using α-Activated α,β-Unsaturated 4,4-Dimethyl-1-tetralones as Dienophiles.

Making use of a Diels-Alder approach based on various α,β-unsaturated 2-carbomethoxy-4,4-dimethyl-1-tetralones as novel dienophiles, the corresponding polycyclic adducts could be efficiently synthesized in good to high yields (74~99%) in the presence of Lewis acid (e.g., SnCl4). Accordingly, a synthetically useful platform is established to provide a focused aromatic polyketide-like library for screening of potential natural and non-natural antimicrobial agents.

Conversion of Glucose to 5-Hydroxymethylfurfural Using Consortium Catalyst in a Biphasic System and Mechanistic Insights

We found an effective catalytic consortium capable of converting glucose to 5-hydroxymethylfurfural (HMF) in high yields (50%). The reaction consists of a consortium of a Lewis acid (NbCl5) and a Brønsted acid (p-sulfonic acid calix[4]arene (CX4SO3H)), in a microwave-assisted reactor and in a biphasic system. The best result for the conversion of glucose to HMF (yield of 50%) was obtained with CX4SO3H/NbCl5 (5 wt%/7.5 wt%), using water/NaCl and MIBK (1:3), at 150 °C, for 17.5 min. The consortium catalyst recycling was tested, allowing its reuse for up to seven times, while maintaining the HMF yield constant. Additionally, it proposed a catalytic cycle by converting glucose to HMF, highlighting the following two key points: the isomerization of glucose into fructose, in the presence of Lewis acid (NbCl5), and the conversion of fructose into HMF, in the presence of CX4SO3H/NbCl5. A mechanism for the conversion of glucose to HMF was proposed and validated.

Aluminum-Catalyzed Cross Selective C3–N1′ Coupling Reactions of N-Methoxyindoles with Indoles

C3–N1′ bond formation of bisindoles has been a great challenge due to the intrinsic reactivity of indoles as both C3 and N1-nucleophilic character. Herein, we demonstrate an C3–N1′ cross-coupling reaction of indoles using N-methoxyindoles as N-electrophilic indole reagents in the presence of Lewis acid. The bisindoles generated in this transformation are latent C3-nucleophile, allowing them to be used as strategic intermediates in sequential C3–N1′–C3′–N1″ triindole formations. The potential synthetic usefulness of this sequential transformation was highlighted upon application to the construction of C3–N1 looped polyindoles.

SYNTHESIS, PHYSICAL AND BIOLOGICAL STUDY OF SOME NEW GLUCOSE BASED GLYCOLIPIDS

New glycolipids on glucose have been synthesized according to well-known sequencing reactions. The series of reactions started with peracetylation of glucose to produce mainly β-anomer, which is reacted directly with long chain alcohol in presence of Lewis acid as catalyst. The deacetylation of sugar head group was achieved under basic conditions. The resulting glycolipids have been modified in more three reaction steps to get the final products. The modified glycolipids have been studied under POM and DSC to confirm the phase behavior of these type of amphiphilic molecules, which is indicate that most of them form lamellar phase. These materials were also studied against two types of cancer cells to confirm their ability to interfere the bi-layer membrane of the living cell.

Spotlight on the Winners of the DCO‐SCF 2021 Awards – An Ever Valuable Collaboration with EurJOC

Spotlight on the Winners of the DCO‐SCF 2021 Awards – An Ever Valuable Collaboration with EurJOC

Pentaleno[1,2-c]pyrroles: Tricyclic 5/5/5 Fused Rings.

A novel method for the preparation of tetrahydropentaleno[1,2-c]pyrroles (8) is described via the reaction of anilines with 1-en-4-yn-3-ols in the presence of Lewis acid. Oxidation of 8 with Br2 gave pentaleno[1,2-c]pyrroles (10), which is the first reported tricyclic 5/5/5 ring with a fully conjugated system. Structures of these obtained compounds were characterized by spectroscopic methods, and compounds 8a,b and 10c were further confirmed by X-ray crystallographic determination.

Nghiên cứu tổng hợp poly-β-pinen khối lượng phân tử thấp và khảo sát một số tính chất cơ bản

In this study, low-molecular-weight polyterpene was synthesized from the β-pinene monomer by controlled polymerization in the presence of Lewis Acid. The structure of the resulting polyterpene was determined by 1H and 13C nuclear magnetic resonance (NMR) and Infrared (IR) Spectroscopy. Gel permeation chromatography (GPC) showed the polyterpene product with a molecular weight of 890 and PDI of 1.48 due to the polymer synthesis. Differential scanning calorimetry (DSC) of the resulting polyterpene shows a melting point in the range of -3 to -15°C and a crystallization point in the range of -25 to -30⁰C. In addition, this study proved that the breakdown voltage, dielectric dissipation factor, washout resistance, acid number of the obtained polyterpene are suitable for making protective coatings for electrical and electronic equipment.

Density Functional Theory Study on [Ni0(1,10-Phenanthroline)]-Catalyzed Reductive Carboxylation of Alkyl and Aryl Halides with CO2: Effect of the Lewis Acid and β-H Elimination Side Reaction in the Crucial CO2 Insertion Step.

The [Ni0(phen)] (1)-catalyzed reductive carboxylation of propyl and phenyl chloride with a CO2 molecule has been compared using the density functional theory method. The reactivity of 1 in the initial oxidative addition with the propyl and phenyl chloride and in the subsequent single electron transfer step to form the NiI intermediates, [NiI(phen)(R'-CH2)], 4, (R' = CH3-CH2-), and [NiI(phen)(C6H5)], 4', is almost the same. However, an apparent reactivity difference is interpreted in the CO2 insertion step, which involves the NiI and the NiII intermediates. In both propyl and phenyl chloride, the NiI-mediated CO2 insertion is kinetically more preferred than that mediated by the analogues NiII intermediates (3 and 3') by +5.0 and +33.4 kcal/mol, respectively. This trend in energetics clearly shows that the CO2 insertion of phenyl chloride exclusively occurs via the NiI-mediated pathway, whereas in propyl chloride, it follows both NiI- and NiII-mediated pathways. Overall, the catalytic efficacy of 1 is found to be higher in phenyl chloride (by +11.3 kcal/mol) than that in propyl chloride. Furthermore, the effect of a plausible β-H elimination side reaction in the CO2 insertion step is modeled for propyl chloride. Herein, the β-H elimination of the NiII propyl species (3) is kinetically more feasible than its CO2 insertion, while the β-H elimination of NiI propyl (4) is rather difficult compared to its CO2 insertion by +16.3 kcal/mol. This strongly supports the suitability of the NiI intermediate in the CO2 insertion step. In addition, the role of the Lewis acid (X) in the CO2 insertion step is tested by incorporating various Lewis acids (X = MgCl2, ZnCl2, AlCl3, and LiCl) in the NiII propyl (7) and NiI propyl (5) intermediates. The Lewis acids effectively facilitate the CO2 insertion step, and the effect due to MgCl2 is found to be more evident. MgCl2 enhances the CO2 insertion of 5 and 7 by 89 and 84%, respectively, and hence, the NiI-mediated CO2 insertion of propyl halide (ΔG⧧ = +1.4 kcal/mol) is now comparable with that of phenyl halide (ΔG⧧ = +0.9 kcal/mol). This suggests that in the presence of Lewis acids, the catalytic efficacy of 1 is enhanced for the reductive carboxylation of propyl halide and exhibits similar reactivity to that of phenyl halide.

Atom Economical Multi-Substituted Pyrrole Synthesis from Aziridine

Multi-substituted pyrroles are synthesized from regiospecific aziridine ring-opening and subsequent intramolecular cyclization with a carbonyl group at the γ-position in the presence of Lewis acid or protic acid. This method is highly atom economical where all the atoms of the reactants are incorporated into the final product with the removal of water. This new protocol is applied to the synthesis of various pyrroles, including natural products.

Effect of the Synthesis Conditions of MIL-100(Fe) on Its Catalytic Properties and Stability under Reaction Conditions.

MIL-100(Fe) is a metal–organic framework (MOF) characterized by the presence of Lewis acid and Fe(II/III) redox sites. In this work, different synthesis methods for the preparation of MIL-100(Fe) are studied. Depending on the source of fluorine, different phases can be obtained: MIL-100(Fe) and an Fe trimesate with unknown structure which we call Fe(BTC). These materials were characterized using numerous techniques and applied in the reaction of CO2 cycloaddition with epichlorohydrin, a reaction catalyzed by Lewis acid sites. It was observed that samples with more Fe(BTC) phase were more active in the reaction. However, all samples, under reaction conditions, transformed into a less active phase.

Reactions of 1-C-acceptor-substituted glycals with nucleophiles under acid promoted (Ferrier-rearrangement) conditions

The reactivity of O-peracetylated and O-perbenzoylated 1-COOMe, 1-CONH2 and 1-CN-substituted glycals was studied against O-, S-, N- and C-nucleophiles in the presence of Lewis acids. Allylic substituted products with exclusive axial stereoselectivity were formed with simple alcohols, N3−, and Cl− ions, but with benzyl thiol the Ferrier rearrangement took place and thioglycosides were obtained. The use of a sugar derived thiol resulted in the formation of both the allylic substituted and the rearranged products.

Computational study of the transamination reaction in vinylogous acyls: Paving the way to design vitrimers with controlled exchange kinetics

AbstractOne of the key points in the design of vitrimers is controlling the associative exchange kinetics. One common chemistry used in vitrimers is based on the dynamic amine exchange reaction of vinylogous acyl compounds in presence of free amine. Understanding the reaction mechanism is essential to assist the optimization of the reaction conditions as well as the molecular structure of the reactant compounds in the pursuit of new materials. In this work, a computational study has been performed to explore different reaction mechanisms in neutral, acidic and in basic conditions or in the presence of Lewis acids, as well as the effect of chemical modifications in the exchange reaction. The results reveal that the formation of hydrogen bonds are a key feature and that the vinylogous urea improves the transamination compared to vinylogous urethane. The esteric hindrance of the amino group in the vinylogous compound also plays an important role. Finally, the nature of the free amine can improve the reactivity by equilibrating two contrary effects: the basicity favors the nucleophilic attack and the conjugated acidity favors the protonation. The findings of this theoretical work shed light in the design of new vitrimers with controlled exchange kinetics by chemical modifications.

Nucleophilic Substitution Reactions in the [B3H8]- Anion in the Presence of Lewis Acids.

As a result of our study on the interaction between the octahydrotriborate anion with nucleophiles (Nu = THF, Ph3P, Ph2P-(CH2)2-PPh2 (dppe), Ph3As, Et3N, PhNH2, C5H5N, CH3CN, Ph2CHCN)) in the presence of a wide range of Lewis acids (Ti(IV), Hf(IV), Zr(IV), Al, Cu(I), Zn, Mn(II), Co(II) halides and iodine), a number of substituted derivatives of the octahydrotriborate anion [B3H7Nu] are obtained. It is found that the use of TiCl4, AlCl3, ZrCl4, HfCl4, CuCl and iodine leads to the highest product yields. In this case, it is most likely that the reaction proceeds through the formation of an intermediate [B3H7-HMXnx], which was detected by NMR spectroscopy. The structures of [Ph3P·B3H7] and [PhNH2·B3H7] were determined by X-ray diffraction.