Strong Nucleophiles Research Articles

Catalytic Concerted SNAr Reactions of Fluoroarenes by an Organic Superbase.

We herein propose that the catalytic concerted SNAr reaction is a powerful method to prepare functionalized aromatic scaffolds. Classic stepwise SNAr reactions involving addition/elimination processes require the use of electron-deficient aromatic halides to stabilize Meisenheimer intermediates, despite their widespread use in medicinal chemistry research. Recent efforts have been made to develop concerted SNAr reactions involving a single transition state, allowing the use of electron-rich substrates based on the use of stoichiometric amounts of strong bases or reactive nucleophiles. This study demonstrates that, without the use of such reagents, the organic superbase t-Bu-P4 efficiently catalyzes the concerted SNAr reactions of aryl fluorides regardless of their electronic nature. The key to establishing this system is the dual activation of aryl fluoride and anionic nucleophiles by the t-Bu-P4 catalyst. Furthermore, this catalysis allows excellent functional group tolerance, utilization of diverse nucleophiles, and late-stage functionalization of bioactive compound derivatives. These findings make possible diverse applications in chemical synthesis and pharmaceutical development.

Direct Access to α,β‐Unsaturated γ‐Lactams via Palladium‐Catalysed Carbonylation of Propargylic Ureas

Abstract. Additive carbonylations typically necessitate strong nucleophiles, such as alcohols or amines. In this study, we carbonylated a poorly nucleophilic urea, under oxidant‐free conditions. Our straightforward carbonylative strategy enables access to versatile α,β‐unsaturated γ‐lactams featuring an aminocarbonyl fragment, utilizing readily available propargylic ureas as starting materials. The employment of the PdI2/KI catalytic system allowed complete regioselectivity (5‐endo‐dig), high functional group tolerance, broad substrate scope as well as operational simplicity (oxidant‐free, organic ligand‐free and base‐free protocol). The synthetic utility of these γ‐lactams is showcased through late‐stage functionalizations, such as Giese reactions and peptide couplings.

Superactivity of Bimetallic CuFeO2 Submicron Particles towards Selective Proteolysis, Depending on their Surface Hydroxyls.

Nano bimetallic oxides as nanoproteases have the great advantages in the heterogeneous hydrolysis of proteins. Here, we report that bimetallic delafossite CuFeO2 submicron particles (CuFeO2 SMPs) display a high protease activity towards selective cleavage of peptide bond involving hydrophobic residue at 25 °C. CuFeO2 SMPs have excellent regeneration performance with high structural stability. The strong Lewis acidity of Fe3+ and the strong nucleophilicity of Cu+ bound hydroxyl groups are both necessary for the high protease activity of CuFeO2 SMPs. Low-valent metal ion has a great advantage in that low-valent Cu+ bound hydroxyl has strong nucleophilicity, resulting in promotion of protein hydrolysis via high-efficient bimetallic catalysis. This study provides evidence that the protease activity of CuFeO2 SMPs depends on metal ion-bound hydroxyls on their surface. Our findings highlight that the valence of metal ions in artificial protease and their surface hydroxyls are two important factors that determine their catalytic efficiency.

Evaluating the Chemical Reactivity of DFT-Simulated Liquid Water with Hydrated Electrons via the Dual Descriptor.

Modeling the various properties of liquid water, particularly its reactivity, has been a longstanding challenge for simulation methods. Recently, ab initio simulations based on density functional theory (DFT) have come to the fore as tenable methods for calculating the properties and reactivity of water, with varying degrees of success for different exchange-correlation functionals. In particular, hybrid-GGA and meta-GGA functionals have been shown to reproduce many of the structural, dynamical, and energetic properties of water to a high degree of accuracy relative to their computational cost. Here, we show that the dual descriptor (DD) measure of nucleophilicity and electrophilicity, which is sometimes used to elucidate organic chemistry reaction mechanisms, can also be used to characterize the reactivity of DFT-simulated liquid water. The DD is especially apt for understanding the reactivity of excess electrons with water as its calculation explicitly involves adding and removing an excess electron from a reference system. We use the DD to explore the reactivity of water simulated using three different DFT functionals: the LDA functional (LDA), a hybrid-GGA functional (PBE0), and a hybrid meta-GGA functional (SCAN0). Using the DD, we show that the SCAN0 functional with the standard 25% Hartree-Fock exchange produces simulated liquid water with many regions that are far more reactive than either PBE0 or LDA. To understand the implications of these highly reactive regions, we then add a strong nucleophile in the form of an excess electron and find that although PBE0 and LDA predict stable hydrated electrons, the excess electron reacts nearly instantaneously with SCAN0 water via proton abstraction to form a hydrogen atom and hydroxide ion. We show that the DD provides the ability to not only predict whether or not liquid water will react with a hydrated electron but also which particular waters will be involved solely from analyzing pure water configurations generated with each functional. We rationalize this result in terms of the known trap-seeking behavior of injected hydrated electrons, which are able to find the most electronegative region in bulk water. These results highlight the utility of the dual descriptor as a fast and interpretable method for investigating condensed-phase reactivity with excess electrons.

Selective elimination of organic pollutants and analysis of effects and novel mechanisms of aged microplastics on wavelength-dependent UV-LED/H2O2 system

The selective removal of organic pollutants and potential impact of aged microplastics (MPs) as emerging pollutants in wavelength-dependent UV-LED/H2O2 system are not fully understood. This study found that cefalexin (CFX) degradation efficiency in UV-LED alone system was highly correlated with its UV molar absorbance (R2=0.994), while in UV-LED/H2O2 system, it was correlated with ·OH yield (R2=0.991) across various wavelengths. Quantitative structure-activity relationship (QSAR) analysis showed selective degradation of six pollutants based on their e--donating capabilities (R2=0.748–0.916). The coexistence of aged MPs, introducing C-O/C=O groups and rearranging their surface e-, potentially affected the elimination efficiency of CFX. Aged polystyrene (PS) decreased the degradation efficiency of CFX by shorting the O-O bond length (lO-O) in H2O2 and capturing e- from H2O2, whereas aged polyethylene (PE), polypropylene (PP) and polyvinyl chloride (PVC) had negligible effects as the lO-O elongation balanced the e--donating effect of H2O2. Additionally, phenol released from aged PS, with strong nucleophilicity, competing with CFX for ·OH, further decreasing CFX degradation efficiency. This study provides valuable insights into organic pollutant selective removal and reveals a novel inhibitory mechanism of aged PS on the performance of UV-LED/H2O2 technology.

Efficient Polycrystalline Single-Cation Perovskite Light-Emitting Diodes by Simultaneous Intracrystal and Interfacial Defect Passivation.

Polycrystalline perovskite light-emitting diodes (PeLEDs) have shown great promise with high efficiency and easy processability. However, PeLEDs using single-cation polycrystalline perovskite emitters have demonstrated low efficiency due to defects within the grains and at the interfaces between the perovskite layer and the charge injection contact. Thus, simultaneous defect engineering of perovskites to suppress exciton loss within the grains and at the interfaces is crucial for achieving high efficiency in PeLEDs. Here, 1,8-octanedithiol which is a strong nucleophile, is used to increase the luminescence efficiency of a single-cation perovskite by suppressing non-radiative recombination within the grains of their polycrystalline emitter film as well as at their interface with an anode. The dithiol additive performs a multifunctional role in defect passivation, spatial confinement of excitons, and prevention of exciton quenching at the interface between the perovskite layer and the underlying hole-injection layer. Photoluminescence studies demonstrate that incorporating the dithiol additive significantly enhances the charge carrier dynamics in perovskites, resulting in an external quantum efficiency (EQE) of up to 23.46% even in a simplified PeLED that does not use a hole-injection layer. This represents the highest level of EQE achieved among devices utilizing polycrystalline single-cation perovskites.

Beyond KRAS(G12C): Biochemical and Computational Characterization of Sotorasib and Adagrasib Binding Specificity and the Critical Role of H95 and Y96.

Mutated KRAS proteins are frequently expressed in some of the most lethal human cancers and thus have been a target of intensive drug discovery efforts for decades. Lately, KRAS(G12C) switch-II pocket (SII-P)-targeting covalent small molecule inhibitors have finally reached clinical practice. Sotorasib (AMG-510) was the first FDA-approved covalent inhibitor to treat KRAS(G12C)-positive nonsmall cell lung cancer (NSCLC), followed soon by adagrasib (MRTX849). Both drugs target the GDP-bound state of KRAS(G12C), exploiting the strong nucleophilicity of acquired cysteine. Here, we evaluate the similarities and differences between sotorasib and adagrasib in their RAS SII-P binding by applying biochemical, cellular, and computational methods. Exact knowledge of SII-P engagement can enable targeting this site by reversible inhibitors for KRAS mutants beyond G12C. We show that adagrasib is strictly KRAS- but not KRAS(G12C)-specific due to its strong and unreplaceable interaction with H95. Unlike adagrasib, sotorasib is less dependent on H95 for its binding, making it a RAS isoform-agnostic compound, having a similar functionality also with NRAS and HRAS G12C mutants. Our results emphasize the accessibility of SII-P beyond oncogenic G12C and aid in understanding the molecular mechanism behind the clinically observed drug resistance, associated especially with secondary mutations on KRAS H95 and Y96.

Exploring the molecular solvatochromism, stability, reactivity, and non-linear optical response of resveratrol.

This work analyzes the isomerization effects and solvent contributions to the stability, electronic excitations, reactivity, and non-linear optical properties (NLO) of resveratrol molecules within the formalism of the Density Functional Theory. The findings suggest that resveratrol solvatochromism is significantly influenced by solvent polarization. The electronic and free energies (E and G) indicate that trans is the most stable conformer. The system is classified as a strong nucleophile. However, the analysis of the Fukui functions and the Mulliken charges indicate that cis-trans isomerization jointly affects the reactive indices of the carbon and hydrogen atoms. The results also suggest that solvent is relevant to solvatochromism and the NLO response. Both cis and trans conformers present strong excitations that undergo a visible hypsochromic change when the polarity of the solvent increases. Once the absorption spectra are connected to the first hyperpolarization ( ) by the Oudar and Chemla relation, the hypsochromism of resveratrol is the reason for the drop in the generation of the second harmonic when the ambient polarity decreases. The CAM-B3LYP DFT results suggest that resveratrol is interesting for NLO applications. Depending on the choice of solvent, values 50 times those observed for urea ( esu), which is a standard NLO material. The optimized geometries of cis and trans isomers of resveratrol in vacuum were obtained using Density Functional Theory (DFT) with the hybrid exchange-correlation function (CAM-B3LYP) and Pople basis set functions, specifically 6-311++G(d,p). The solvent effect on the geometries of both isomers was included using the polarizable continuum model (PCM) with the same level of QM calculation. Vibrational analysis was conducted to confirm that all optimized geometries correspond to the minimum energy. Various electronic properties, including dipole moments, molecular orbitals, transition energy, dipole polarizabilities, and global reactivity parameters, were calculated using both continuum and discrete solvation models based on the sequential QM/MM methodology. All QM calculations were performed with the Gaussian 09 program and the MC simulations with the DICE program. All NLO analysis was carried out using the Multiwfn code.

Reactivity of N terminal histidine of peptides towards excipients/impurity of excipients: A case study of liraglutide excipient compatibility study

The selection of quality excipients is a crucial step in peptide formulation development. Apart from excipient incompatibility, process-related impurities or degradants of an excipient can interact with peptide-active pharmaceutical ingredients, forming the interaction products. The formaldehyde has been reported as an impurity of excipient in polyethylene glycol, glycerol, magnesium stearate, microcrystalline cellulose, mannitol, etc. The peptide contains various amino acids such as histidine, lysine, and arginine having free amine groups. These amine groups act as strong nucleophile and can increase the reactivity of peptides. PLGA is the most widely used biodegradable polymer in sustained-release formulations. The hydrolysis of PLGA generates glycolic acid and lactic acid impurities, which can form the interaction product with the amines of peptides. During the formulation development of Liraglutide, we have found few interaction products. The systematic characterization and mechanistic understanding of these interaction products lead us to imidazopyrimidine, glycolyl, and lactolyl moieties. These interaction products have been characterized thoroughly with the use of LC-HRMS, MS/MS, and hydrogen-deuterium exchange mass studies. The study revealed that the reactivity of N-terminal histidine must be considered for formulation development. Moreover, the quality of excipients with respect to presence of impurities must be considered as critical material attributes.

Tetrachloroethylene dechlorination from sulfide-containing aquifers by biochar depends on hydrogeochemical conditions in two aspects: Adsorption and catalysis

Biochar can facilitate sulfide to reduce organic contaminants, such as tetrachloroethylene (PCE). However, the biochar interface catalytic performance in complex water matrices is rarely investigated, and the combined roles of sulfide and hydrogeochemical component in the dechlorination of PCE remains unclear. This study explore the influence of environmental parameters on PCE dechlorination by a wood-based biochar (WW800). The enhanced reductive dechlorination by WW800 was a two-site heterogeneous catalytic process in two stages: (1) adsorption and (2) reduction. In the absence of ions, the removal of PCE included both stages. Ca2+ cation bridge was important in enhancing the reducibility of –COOH on WW800 bound sulfide. The co-existence ionic conditions of six redox zones were simulated, HCO3– inhibited the binding of sulfide to WW800, and SO42− inhibited both adsorption and reduction stages. These inhibitory effects were prior to the promotion of Ca2+. The combination of multiple ions with WW800 consumed the active groups (pyridine N, C=O and O-C=O), which limited the transformation of sulfides to strong nucleophilicity. Among the single influencing factors, Ca2+, HCO3–, initial concentration of PCE and temperature were positively correlated with the removal kinetics of PCE (P<0.05). The low concentration of Fe2+ and Mn2+ in the simulated zones did not significantly promote the removal of PCE. According to the kinetic changes of dechlorination reaction, the inhibition of PCE conversion by humic acid was due to the change of sulfide species caused by pH value change. The aquifer environment with low temperature (10–15 °C) and DO (0–6.6 mg/L) had little effect on PCE dechlorination. Our results show that the hydrochemical components in aquifer enhance PCE dechlorination by biochar with different influence mechanisms, which provides theoretical guidance for application of this method in the aquifer.

Dicationic ionic liquid‐grafted UiO‐66 as efficient catalyst for CO2 conversion into cyclocarbonate under cocatalyst‐free and solventless conditions

CO2 chemical fixation offers a feasible approach for carbon mitigation and high‐value utilization, but it is still challenging to develop an efficient catalyst for CO2 conversion into cyclic carbonate. Herein, the triethylenediamine‐derived dicationic ionic liquids (DIL‐X, X = Cl, Br, and I) were grafted into UiO‐66 linkers through self‐assembly of Zr4+ ions and the mixed ligands of terephthalic acid and DIL‐bearing dicarboxylic acid, resulting in UiO‐66‐DIL‐Xn, (n designated as molar amount of the feeding DIL‐X). Their catalytic performance was evaluated by the epoxide cycloaddition reaction in the absence of solvent and cocatalyst. Among them, the UiO‐66‐DIL‐Cl0.4 catalyst exhibited outstanding performance, with a chloropropene carbonate yield of 92% and a high selectivity of 99% under 0.1 MPa CO2 at 110 °C for 16 h. Its high activity could be ascribed to the cooperativity among Lewis acidity of MOF nodes, the enhanced CO2 absorption, and the strong nucleophilicity offered by halogen ions of ionic liquid‐modified MOF. Moreover, UiO‐66‐DIL‐Cl0.4 presented excellent recyclability and substrate extension. A potential catalytic mechanism for the epoxide‐CO2 cycloaddition into cyclic carbonate has been proposed. This work will shed light on the rational design of functionalized MOFs‐based catalysts for CO₂ utilization.

Carbonylation Reactions of a Metallapentalyne: Synthesis of Its Ester and Amide Derivatives

Comprehensive SummaryCarbonylation reactions are a valuable synthetic method to construct carbonyl compounds and carbonylation reactions of aryl halides stand out as a highly significant tool for generating carbonyl substituted arenes. However, the important reactions have never been realized in aromatic metallacycles. Herein, we present the first carbonylation reactions of metallaaromatics, specifically alkoxycarbonylation and aminocarbonylation reactions of an osmapentalyne. During the carbonylation process, the electronic and steric properties of nucleophiles are regarded as critical factors. The alcohols with bulky substituents (isopropanol) require more reaction time and tert‐butyl alcohol is inert in the reaction. Comparatively, amines, being stronger nucleophiles, exhibit divergent behaviors. Bulky amines undergo aminocarbonylation, whereas small amines prefer direct nucleophilic additions. Control experiments revealed that the intermediate derived from coupling of metal carbyne with CO plays a significant role in the carbonylation reaction. According to these observations, a divergent pathway for the reaction is proposed. Furthermore, the photophysical properties of these carbonyl‐functionalized osmapentalene complexes are studied, and the maximum absorption peak of compound with a carboxylic group exhibits a significant red‐shift due to the smaller HOMO‐LUMO gap. These findings contribute to expanding the reactivity of metallaaromatics and offer new opportunities for the synthesis of carbonyl‐functionalized metallacycles.

Transpersulfidation or H2S Release? Understanding the Landscape of Persulfide Chemical Biology.

Persulfides (RSSH) are biologically important reactive sulfur species that are endogenously produced, protect key cysteine residues from irreversible oxidation, and are important intermediates during different enzymatic processes. Although persulfides are stronger nucleophiles than their thiol counterparts, persulfides can also act as electrophiles in their neutral, protonated form in specific environments. Moreover, persulfides are electrophilic at both sulfur atoms, and the reaction with a thiolate can lead to either H2S release with disulfide formation or alternatively result in transpersulfidation. Despite the broad acceptance of these reaction pathways, the specific properties that control whether persulfides react through the H2S-releasing or transpersulfidation pathway remain elusive. Herein, we use a combined computational and experimental approach to directly investigate the reactivity between persulfides and thiols to answer these questions. Using density functional theory (DFT) calculations, we demonstrate that increasing steric bulk or electron withdrawal near the persulfide can shunt persulfide reactivity through the transpersulfidation pathway. Building from these insights, we use a synthetic persulfide donor and an N-iodoacetyl l-tyrosine methyl ester (TME-IAM) trapping agent to experimentally monitor and measure transpersulfidation from a bulky penicillamine-based persulfide to a cysteine-based thiol, which, to the best of our knowledge, is the first direct observation of transpersulfidation between low-molecular-weight species. Taken together, these combined approaches highlight how the properties of persulfides are directly impacted by local environments, which has significant impacts in understanding the complex chemical biology of these reactive species.

On the Question of Uncatalyzed CO Insertion into a Hydrazone Double Bond: A Comparative Study Using Different CO Sources and Substrates.

Because of endogenous signaling roles of carbon monoxide (CO) and its demonstrated pharmacological effects, there has been extensive interests in developing fluorescent CO probes. Palladium-mediated CO insertion has been successfully used for such applications. However, recent years have seen many publications of using uncatalyzed CO insertion into a hydrazone double bond as a way to sense CO. Such chemistry has no precedents otherwise. Further, the rigor of the CO-sensing work was largely based on using ruthenium-carbonyl complexes such as CORM-3 as CO surrogates, which have been reported to have extensive chemical reactivity and to release largely CO2 instead of CO unless in the presence of a strong nucleophile such as dithionite. For all of these, it is important to reassess the feasibility of such a CO-insertion reaction. By studying two of the reported "CO probes" using CO gas, this study finds no evidence of CO insertion into a hydrazone double bond. Further, the chemical reaction between CO gas and a series of eight hydrazone compounds was conducted, leading to the same conclusion. Such findings are consistent with the state-of-the-art knowledge of carbonylation chemistry and do not support uncatalyzed CO insertion as a mechanism for developing fluorescent CO probes.

Competing C and N as Reactive Centers for Microsolvated Ambident Nucleophiles CN-(H2O)n=0-3: A Theoretical Study of E2/SN2 Reactions with CH3CH2X (X = Cl, Br, I).

As an ambident nucleophile, CN- has both C and N atoms that can act as the reactive center to facilitate substitution reactions. We investigate in detail the potential energy profiles of CN-(H2O)0-3 with CH3CH2X (X = Cl, Br, I) to explore the influence of solvent molecules on competition between the different nucleophilic atoms C and N involving the SN2 and E2 pathways. The energy barrier sequence for the transition states follows C@inv-SN2 < N@inv-SN2 < C@anti-E2 < N@anti-E2. When two different atoms act as nucleophilic atoms, the SN2 reaction is always preferred over the E2 reaction, and this preference increases with microsolvation. For the ambident nucleophiles CN-(H2O)0-3, C as the reactive center always has stronger nucleophilicity and basicity than N acting as the reactive center. Regarding the leaving group, the height of the energy barrier is positively correlated with the acidity of the CH3CH2X substrate for the E2 pathway and with X-heterolysis for the SN2 pathway. Furthermore, we found that in the gas phase, the energy barrier for different leaving group systems decreases gradually in the order Cl > Br > I, while in the SMD solution, the energy barrier and product energy increase slightly in the system from X = Cl to Br; this change may be due to the significantly weakened transition-state interaction for the X = Br system. Our activation strain, quantitative molecular orbital, and charge analyses reveal the physical mechanisms underlying the various computed trends. In addition, we also demonstrate the two points recently proposed by Vermeeren, P. . Chem. Eur. J. 2020, 26, 15538-15548.

Activatable NIR Fluorescence Probe for Epinephrine Detection and Bioimaging Based on Anionic Heptamethine Cyanine.

Epinephrine (EP) is an essential catecholamine in the human body. Currently, most EP detection methods are not suitable for in vivo detection due to material limitations. An organic small molecule fluorescent probe based on a chemical cascade reaction for the detection of EP was designed. Anionic heptamethine cyanine dye was selected as a fluorescent dye because of its NIR fluorescence emission with excellent biocompatibility. The secondary amine of EP nucleophilically attacks the carbonate of the probe with its stronger nucleophilicity and further undergoes intramolecular nucleophilic cyclization to release the fluorophore. Other substances containing only primary amines or no β-OH lack reaction competitiveness due to their weaker nucleophilicity or inability to undergo further cyclization. The fluorescence recovery of the probe was linearly related to the EP concentration of 2-75 μmol/L. The detection limit was 0.4 μmol/L. The recovery rate was 94.78-111.32%. Finally, we successfully achieved bioimaging of EP in living cells and EP analogue in nematodes.

The Intramolecular Charge Transfer Mechanism by Which Chiral Self-Assembled H8-BINOL Vesicles Enantioselectively Recognize Amino Alcohols.

The chiral H8-BINOL derivatives R-1 and R-2 were efficiently synthesized via a Suzuki coupling reaction, and they can be used as novel dialdehyde fluorescent probes for the enantioselective recognition of R/S-2-amino-1-phenylethanol. In addition, R-1 is much more effective than R-2. Scanning electron microscope images and X-ray analyses show that R-1 can form supramolecular vesicles through the self-assembly effect of the π-π force and strong hydrogen bonding. As determined via analysis, the fluorescence of the probe was significantly enhanced by mixing a small amount of S-2-amino-1-phenylethanol into R-1, with a redshift of 38 nm, whereas no significant fluorescence response was observed in R-2-amino-1-phenylethanol. The enantioselective identification of S-2-amino-1-phenylethanol by the probe R-1 was further investigated through nuclear magnetic titration and fluorescence kinetic experiments and DFT calculations. The results showed that this mechanism was not only a simple reactive probe but also realized object recognition through an ICT mechanism. As the intramolecular hydrogen bond activated the carbonyl group on the probe R-1, the carbonyl carbon atom became positively charged. As a strong nucleophile, the amino group of S-2-amino-1-phenylethanol first transferred the amino electrons to a carbonyl carbocation, resulting in a significantly enhanced fluorescence of the probe R-1 and a 38 nm redshift. Similarly, S-2-amino-1-phenylethanol alone caused severe damage to the self-assembled vesicle structure of the probe molecule itself due to its spatial structure, which made R-1 highly enantioselective towards it.

Implanting multi-functional ionic liquids into MOF nodes for boosting CO2 cycloaddition under solventless and cocatalyst-free conditions

It is critical to design an effective catalyst for CO2 conversion into cyclocarbonate to achieve the carbon neutrality. Herein, MIL-101(Cr) tethered by hydrogen bond donors (HBD)-containing ionic liquids (denoted as MIL-101-ILs(R), R = OH, NH2, and COOH) were synthesized through the implantation of 4,4′-bipyridine into MOF nodes via the post-synthetic modification, followed by the decoration with bromoalkanes including bromoethanol, bromoethylamine, and bromoacetic acid. Their catalytic performance were evaluated by the epoxide cycloaddition reaction under 1.0 MPa CO2 and 80 ℃ for 6 h in the absence of solvent and cocatalyst. Compared to MIL-101-ILs without HBD, MIL-101-ILs(OH) and MIL-101-ILs(NH2) demonstrated the more chloropropene carbonate (CPC) yield of 88 % and 83 %, respectively. Notably, MIL-101-ILs(COOH) exhibited an uppermost activity with a CPC yield of 96 %, attributed to the cooperativity of Lewis acidity originating from Cr3O clusters, hydrogen-bond interaction afforded by carboxyl groups, and the strong nucleophilicity offered by Br- ions of ILs. Moreover, MIL-101-ILs(COOH) presented excellent recyclability. A potential catalytic mechanism for epoxide cycloaddition with CO2 into cyclic carbonate has been proposed.

Catalytic polymer self-cleavage for CO2 generation before combustion empowers materials with fire safety

Polymeric materials, rich in carbon, hydrogen, and oxygen elements, present substantial fire hazards to both human life and property due to their intrinsic flammability. Overcoming this challenge in the absence of any flame-retardant elements is a daunting task. Herein, we introduce an innovative strategy employing catalytic polymer auto-pyrolysis before combustion to proactively release CO2, akin to possessing responsive CO2 fire extinguishing mechanisms. We demonstrate that potassium salts with strong nucleophilicity (such as potassium formate/malate) can transform conventional polyurethane foam into materials with fire safety through rearrangement. This transformation results in the rapid generation of a substantial volume of CO2, occurring before the onset of intense decomposition, effectively extinguishing fires. The inclusion of just 1.05 wt% potassium formate can significantly raise the limiting oxygen index of polyurethane foam to 26.5%, increase the time to ignition by 927%, and tremendously reduce smoke toxicity by 95%. The successful application of various potassium salts, combined with a comprehensive examination of the underlying mechanisms, underscores the viability of this strategy. This pioneering catalytic approach paves the way for the efficient and eco-friendly development of polymeric materials with fire safety.

Backside versus Frontside SN2 Reactions of Alkyl Triflates and Alcohols.

Nucleophilic substitution reactions are elementary reactions in organic chemistry that are used in many synthetic routes. By quantum chemical methods, we have investigated the intrinsic competition between the backside SN2 (SN2-b) and frontside SN2 (SN2-f) pathways using a set of simple alkyl triflates as the electrophile in combination with a systematic series of phenols and partially fluorinated ethanol nucleophiles. It is revealed how and why the well-established mechanistic preference for the SN2-b pathway slowly erodes and can even be overruled by the unusual SN2-f substitution mechanism going from strong to weak alcohol nucleophiles. Activation strain analyses disclose that the SN2-b pathway is favored for strong alcohol nucleophiles because of the well-known intrinsically more efficient approach to the electrophile resulting in a more stabilizing nucleophile-electrophile interaction. In contrast, the preference of weaker alcohol nucleophiles shifts to the SN2-f pathway, benefiting from a stabilizing hydrogen bond interaction between the incoming alcohol and the leaving group. This hydrogen bond interaction is strengthened by the increased acidity of the weaker alcohol nucleophiles, thereby steering the mechanistic preference toward the frontside SN2 pathway.