Mechanochemical Strategy Research Articles

Triphasic Hydroxysilylation of Alkenes by Mechanically Piezoelectric Catalysis

AbstractThe 1,2‐hydroxysilylation of alkenes is crucial for synthesizing organosilicon compounds which are key intermediates in material science, pharmaceuticals, and organic synthesis. The development of strategies employing hydrogen atom transfer pathways is currently hindered by the existence of various competing reactions. Herein, we reported a novel mechanochemical strategy for the triphasic 1,2‐hydroxysilylation of alkenes through a single‐electron‐transfer pathway. Our approach not only circumvents competitive reactions to enable the first‐ever 1,2‐hydroxysilylation of unactivated alkenes but also pioneers the research in mechanic force‐induced triphasic reactions under ambient conditions. This gentle method offers excellent compatibility with various functional groups, operates under simple and solvent‐free conditions, ensures rapid reaction time. Preliminary mechanistic investigations suggest that silylboronate can be transformed to a silicon radical by highly polarized Li2TiO3 particles and oxygen under ball‐milling condition.

Electro- and Mechanochemical Strategy as a Dual Synthetic Approach for Biologically Relevant 3-Nitro-imidazo-[1,2-a]pyridines.

We herein disclose a dual synthetic approach involving electrochemical and mechanochemical strategies for diversely functionalized 3-nitro-2-aryl-immidazo[1,2-a]pyridines. Both methods offer a practical and straightforward alternative route for accessing this important class of biologically promising nitrogen-containing heterocycles. Significant advantages of the newly developed methods include mild and energy-efficient reaction conditions, avoidance of transition metal catalysts, external heating and additional oxidants, shorter reaction times, good to excellent yields, broad substrate scope, gram-scale applicability, operational simplicity, and eco-friendliness. Furthermore, a synthetic application was extended by successfully reducing synthesized 3-nitro-2-aryl-immidazo[1,2-a]pyridines to their corresponding amino derivatives.

Triphasic Hydroxysilylation of Alkenes by Mechanically Piezoelectric Catalysis.

The 1,2-hydroxysilylation of alkenes is crucial for synthesizing organosilicon compounds which are key intermediates in material science, pharmaceuticals, and organic synthesis. The development of strategies employing hydrogen atom transfer pathways is currently hindered by the existence of various competing reactions. Herein, we reported a novel mechanochemical strategy for the triphasic 1,2-hydroxysilylation of alkenes through a single-electron-transfer pathway. Our approach not only circumvents competitive reactions to enable the first-ever 1,2-hydroxysilylation of unactivated alkenes but also pioneers the research in mechanic force-induced triphasic reactions under ambient conditions. This gentle method offers excellent compatibility with various functional groups, operates under simple and solvent-free conditions, ensures rapid reaction time. Preliminary mechanistic investigations suggest that silylboronate can be transformed to a silicon radical by highly polarized Li2TiO3 particles and oxygen under ball-milling condition.

Rationally Integrating Charge-Transfer Cocrystal and Ni(II) Organometallics for Visualized Photo/Thermochromic Sensors.

Smart materials demonstrate fascinating responses to environmental physical/chemical stimuli, including thermal, photonic, electronic, humidity, or magnetic stimuli, which have attracted intensive interest in material chemistry. However, their limited/harsh stimuli-responsive behavior or sophisticated postprocessing leads to enormous challenges for practical applications. Herein, we rationally designed and synthesized thermochromic Ni(II) organometallic [(C2H5)2NH2]2NiCl4-xBrx via a facile mechanochemical strategy, which demonstrated a reversible switch from yellow to blue color with a tunable phase-transition temperature from 75.6 to 61.7 °C. The simple electrospinning technology was applied to fabricate thermochromic Ni(II) organometallic-based nanofiber membranes for temperature monitoring. Furthermore, the organic charge-transfer cocrystal with a wide spectral absorption of 300-1950 nm and a high-efficiency photothermal conversion was combined with thermochromic Ni(II) organometallics for the desired dual-stimuli photo/thermochromism. This work supplies a new strategy for realizing multiple stimuli-responsive applications, such as thermal/light sensor displays and information storage.

Synthesis of Molsidomine and Mesocarb Analog via Mechanochemistry

AbstractIminosydnones (ImSyds) have renowned biological activities and attractive chemical properties for chemical biology. However, access to N6‐functionalized iminosydnones involves tricky and hazardous procedures. Thanks to an innovative mechanochemical strategy using 1,1’‐carbonyldiimidazole (CDI) as an activating agent, a straightforward synthesis of molsidomine and of a mesocarb analog, two bioactive iminosydnones, was achieved. The whole process, involving 4 linear steps, was carried out in the solid state by ball‐milling and with safe reagents, offering efficient and sustainable access to N‐carbonylated iminosydnones, in agreement with the principles of green chemistry.

Charge Redistribution in Mechanochemical Reactions for Solid Interfaces.

Mechanochemical strategies are widely used in various fields, ranging from friction and wear to mechanosynthesis, yet how the mechanical stress activates the chemical reactions at the electronic level is still open. We used first-principles density functional theory to study the rule of the stress-modified electronic states in transmitting mechanical energy to trigger chemical responses for different mechanochemical systems. The electron density redistribution among initial, transition, and final configurations is defined to correlate the energy evolution during reactions. We found that stress-induced changes in electron density redistribution are linearly related to activation energy and reaction energy, indicating the transition from mechanical work to chemical reactivity. The correlation coefficient is defined as the term "interface reactivity coefficient" to evaluate the susceptibility of chemical reactivity to mechanical action for material interfaces. The study may shed light on the electronic mechanism of the mechanochemical reactions behind the fundamental model as well as the mechanochemical phenomena.

Upgrading anode graphite from retired lithium ion batteries via solid-phase exfoliation by mechanochemical strategy

Vast quantities of anode graphite from waste lithium ion batteries (LIBs), as a type of underrated urban mine, has enormous potential to be exploited for resource recovery. Herein, we propose a benign process integrating low-temperature pyrolysis and mechanochemical techniques to upcycle spent graphite (SG) from end-of-life LIBs. Pyrolysis at 500 °C leads to about 82.2 % PVDF dissociation in thermal treated graphite (TG). Solid-phase exfoliation via ball milling assisted by urea successfully produces abundant graphite flakes and a small amount of monolayer graphene nanosheet at the edge of mechanochemically processed graphite (MG). Subsequent rinsing removes the residual LiF salts. High purity and unique edge structural features of the as-prepared MG offer more active sites and storage reservoir for intercalation and de-intercalation of lithium ions, resulting in enhanced lithium-ion diffusion kinetics, excellent reversible specific capacity and desirable rate capability. Inspiringly, MG exhibits a remarkably enhanced initial specific charge capacity of 521.3 mAh g−1 during the first charge–discharge, and only declines from 569.9 mAh g−1 to 538 mAh g−1 with slight attenuation after 50 consecutive cycles at 0.1 A/g, indicating satisfactory cycle stability. Additionally, the purification and reconstruction mechanism for MG have been illustrated in detail. This study offers a green strategy to reconstruct and upgrade anode graphite from LIBs, which can realize sustainable waste management.

Ultra-fast mechanochemical strategy to obtain stable colloidal dispersions of MWCNT in hydrophilic media: Never has been so easy

In this paper, we present a new protocol that allows the dispersion of multi-wall carbon nanotubes (MWCNT) in the form of stable colloids in a hydrophilic medium up to concentrations of ca. 0.06 % (w/w). The strategy involves using a combination of mechanochemical treatment and surfactants. In this study, we processed MWCNTs with surfactants in a ball mill without using any solvents. The mechanochemical treatment consists of processing mixtures of MWCNTs (0.35 g) with different surfactants (4.5 g of CTAB, 3.6 g of SDS and 4.5 g of F127 as cationic anionic and neutral surfactants, respectively) in a ball mill for only 20 min at 300 rpm. The resulting black powder is then used directly to prepare dispersions in hydro-alcoholic media, which maintain colloidal stability for at least 25 days. Although various strategies for dispersal have been proposed in the literature, many involve time-consuming and multi-step processes with low yields. The MWCNTs modified non-covalently using our protocol are synthesised in a single step with a 100 % yield without any loss of reagents. MWCNT have shown potential in many emerging applications of great interest. Its use necessarily implies the achievement of a good dispersion in different solvents, and this aspect, in the case of hydrophilic media, still does not have a satisfactory answer. The absence of solvent during the mechanochemical treatment is the key aspect of our strategy. This small change represents a significant improvement. We demonstrate the outstanding stability of the obtained suspensions and the preservation of the nano-/microstructure of the MWCNTs, which remains unaltered during their preparation. Furthermore, using environmentally friendly solutions for dispersion makes this protocol a Green Chemistry approach.

Mechanochemical C-H Arylation and Alkylation of Indoles Using 3 d Transition Metal and Zero-Valent Magnesium.

Although the 3 d transition-metal catalyzed C-H functionalization have been extensively employed to promote the formation of valuable carbon-carbon bonds, the persistent problems, including the use of sensitive Grignard reagents and the rigorous operations (solvent-drying, inert gas protection, metal pre-activation and RMgX addition rate control), still leave great room for further development of sustainable methodologies. Herein, we report a mechanochemical technology toward in-situ preparation of highly sensitive organomagnesium reagents, and thus building two general 3 d transition-metal catalytic platforms that enables regioselective arylation and alkylation of indoles with a wide variety of halides (including those containing post transformable functionalities and heteroaromatic rings). This mechanochemical strategy also brings unique reactivity and high step-economy in producing functionalized N-free indole products.

A contact-electro-catalysis process for producing reactive oxygen species by ball milling of triboelectric materials

Ball milling is a representative mechanochemical strategy that uses the mechanical agitation-induced effects, defects, or extreme conditions to activate substrates. Here, we demonstrate that ball grinding could bring about contact-electro-catalysis (CEC) by using inert and conventional triboelectric materials. Exemplified by a liquid-assisted-grinding setup involving polytetrafluoroethylene (PTFE), reactive oxygen species (ROS) are produced, despite PTFE being generally considered as catalytically inert. The formation of ROS occurs with various polymers, such as polydimethylsiloxane (PDMS) and polypropylene (PP), and the amount of generated ROS aligns well with the polymers’ contact-electrification abilities. It is suggested that mechanical collision not only maximizes the overlap in electron wave functions across the interface, but also excites phonons that provide the energy for electron transition. We expect the utilization of triboelectric materials and their derived CEC could lead to a field of ball milling-assisted mechanochemistry using any universal triboelectric materials under mild conditions.

Mechanochemical generation of aryl barium nucleophiles from unactivated barium metal.

Organobarium reagents are of interest as homologues of the Grignard reagents based on organomagnesium compounds due to their unique reactivity as well as regio- and stereoselectivity. However, reactions involving organobarium reagents are less developed in comparison to reactions involving Grignard reagents due to the lack of a simple and economical synthetic method and their high reactivity. To the best of our knowledge, there is no established method for the direct synthesis of organobarium compounds from commercially available bulk barium metal and organic halides. So far, the generation of organobarium compounds usually requires the use of activated barium (Rieke barium), which significantly reduces the practical utility of organobarium reagents and hinders the development of new organobarium-mediated transformations. Here, we present a mechanochemical strategy based on ball-milling that facilitates the direct generation of various aryl barium nucleophiles from commercially available unactivated barium metal and aryl halides without complicated pre-activation processes. Our simple mechanochemical protocol allows the rapid development of novel carbon-silicon-bond-forming reactions with hydrosilanes mediated by aryl barium nucleophiles; importantly, these reactions are difficult to achieve using other Grignard-type carbon nucleophiles. To the best of our knowledge, this is the first example of a nucleophilic substitution reaction involving an aryl barium species. Furthermore, this mechanochemical strategy established the first example of a nucleophilic addition to a carbonyl compound involving an aryl barium nucleophile. Preliminary theoretical calculations using the artificial force-induced reaction (AFIR) method to reveal the reaction mechanism of the hydrosilane arylation are also described.

Generic and facile mechanochemical access to versatile lattice-confined Pd(ii)-based heterometallic sites.

Metal-organic frameworks (MOFs) show remarkable potential in a broad array of applications given their physical and chemical versatility. Classical synthesis of MOFs is performed using solution chemistry at elevated temperatures to achieve reversible metal-ligand bond formation. These harsh conditions may not be suitable for chemical species sensitive to high temperature or prone to deleterious reactions with solvents. For instance, Pd(ii) is susceptible to reduction under solvothermal conditions and is not a common metal node of MOFs. We report a generic and facile mechanochemical strategy that directly incorporates a series of Pd(ii)-based heterobimetallic clusters into MOFs as metal nodes without Pd(ii) being reduced to Pd(0). Mechanochemistry features advantages of short reaction time, minimum solvent, high reaction yield, and high degree of synthetic control. Catalytic performances of lattice-confined heterobimetallic sites are examined for nitrene transfer reactions and we demonstrate that the chemoselectivity for allylic amination versus olefin aziridination is readily tuned by the identity of the first-row metal ion in Pd(ii)-based heterobimetallic clusters.

Preparation, characterization and evaluation of cefixime ternary inclusion complexes formated by mechanochemical strategy

Preparation, characterization and evaluation of cefixime ternary inclusion complexes formated by mechanochemical strategy

Improving the performance of geopolymer-based wood adhesives using a green mechanochemical strategy

Geopolymers are a new type of inorganic polymeric cementitious material with excellent properties such as flame retardancy and thermal stability. In this work, an environmentally friendly geopolymer-based adhesive was prepared using a one-step mechanochemical method, and the geopolymer-based adhesive was used to develop a low-cost, aldehyde-free, and highly flame-retardant plywood. Mechanical ball milling generated high temperatures through the collision of the agate balls and the material, which facilitated the polymerization reaction of the geopolymer. This method increased the viscosity of the adhesive and enhanced the “riveting” of the mechanical interlocks between the geopolymer and the wood. When the solid-liquid ratio of the synthetic geopolymer was 2.2, the bonding strength of the plywood developed using the adhesive prepared by the mechanochemical method was 43.0% higher than that of the plywood developed using the electromechanical stirring method, reaching 0.735 MPa, while in compliance with the GB/T 9846-2015 (China) standard for Class II plywood. In addition, the geopolymer-based adhesive had excellent thermal stability, and its mass retention rate was as high as 86.8% after treatment at 800oC. Meanwhile, the geopolymer-based adhesive endowed the flammable plywood with flame-retardant properties, and the heat release rate (HRR), total heat release (THR), and total smoke production (TSP) of the plywood were as low as 275.9 kW/m2, 27.4 MJ/m2 and 0.84 m2, respectively. Therefore, geopolymer-based adhesives show great potential in replacing traditional aldehyde-based adhesives in plywood production, providing a new idea for quick, green, and efficient preparation of inorganic adhesives with excellent bonding properties.

Opportunities and Challenges in Applying Solid-State NMR Spectroscopy in Organic Mechanochemistry.

In recent years it is shown that mechanochemical strategies can be beneficial in directed conversions of organic compounds. Finding new reactions proved difficult, and due to the lack of mechanistic understanding of mechanochemical reaction events, respective efforts have mostly remained empirical. Spectroscopic techniques are crucial in shedding light on these questions. In this overview, the opportunities and challenges of solid-state nuclear magnetic resonance (NMR) spectroscopy in the field of organic mechanochemistry are discussed. After a brief discussion of the basics of high-resolution solid-state NMR under magic-angle spinning (MAS) conditions, seven opportunities for solid-state NMR in the field of organic mechanochemistry are presented, ranging from ex situ approaches to structurally elucidated reaction products obtained by milling to the potential and limitations of in situ solid-state NMR approaches. Particular strengths of solid-state NMR, for instance in differentiating polymorphs, in NMR-crystallographic structure-determination protocols, or in detecting weak noncovalent interactions in molecular-recognition events employing proton-detected solid-state NMR experiments at fast MAS frequencies, are discussed.

Mechanochemical activation of NHC–CS2 adducts for the generation of N‐heterocyclic carbenes

AbstractStable N‐heterocyclic carbenes (NHCs) have garnered significant attention in synthetic chemistry due to their versatile applications. In this study, we explored a novel mechanochemical method for the generation of free carbenes, which could be a good complement to traditional approaches that require strong bases or reductants. Ball milling of NHC–CS2 adducts at room temperature successfully resulted in the quantitative formation of free carbenes that can be subsequently trapped by sulfur or selenium. Importantly, heating NHC–CS2 adducts in solution phase did not lead to the successful generation of free carbenes, in agreement with the high activation energy required for NHC–CS2 dissociation. These findings underscore the potential of ball milling as a robust and versatile approach for generating NHCs from stable NHC‐small molecule adducts, and opens new avenues for developing mechanochemical strategies for generating valuable NHC‐derived compounds.

Improving the Bioactivity and Stability of Embedded Enzymes by Covalent Organic Frameworks.

De novo embedding enzymes within reticular chemistry materials have shown the enhancement of physical and chemical stability for versatile catalytic reactions. Compared to metal-organic frameworks (MOFs), covalent organic frameworks (COFs) are usually considered to be the more superior host of enzymes because of their large channels with low diffusion barriers, outstanding chemical/thermal stability, and metal-free nature. However, detailed investigations on the comparison of COFs and MOFs in enhancing biocatalytic performance have not been explored. Here, we de novo encapsulated enzymes within two COFs via a mechanochemical strategy, which avoided the extreme synthetic conditions of COFs and highly maintained the biological activities of the embedded enzymes. The enzymes@COFs biocomposites exhibited a much higher activity (3.4-14.7 times higher) and enhanced stability than those in MOFs (ZIF-8, ZIF-67, HKUST-1, MIL-53, and CaBDC), and the rate parameter (kcat/Km) of enzyme@COFs was 41.3 times higher than that of enzyme@ZIF-8. Further explorations showed that the conformation of enzymes inside MOFs was disrupted, owing to the harmful interfacial interactions between enzymes and metal ions as confirmed by ATR-FTIR, fluorescence spectroscopy, and XPS data. In contrast, enzymes that were embedded in metal-free COFs highly preserved the natural conformation of free enzymes. This study provides a better understanding of the interfacial interactions between reticular supports and enzymes, which paves a new road for optimizing the bioactivities of immobilized enzymes.

Reinforced photoinduced behavior of a low-cost mechanochemical synthesized Fe-doped B12As2 nanocrystals

Icosahedral boron arsenide B12As2 is a self-healing semiconductor potentially applied in harshly irradiated environments. However, doping effects were rarely investigated to expand their applications. Hereby, a low-cost mechanochemical strategy is proposed to synthesize B12As2 nanocrystals with a boron transformation rate of ∼70%. Nano-B12As2 of 40–50 nm could be self-doped with Fe element and purified by aqua regia. Fe accounts from ∼0.00–1.77 at% with rotational speeds. Based on nano-size effects and Fe-doping effects, the photoluminescence process shows an indirect band-gap at Eg= 2.81 eV and the presence of impurity energy level at E′= 2.11 eV. The optical absorption is red-shifted from the reported UV region to the visible region. The multiply increased photocatalytic hydrogen production (249 μmol∙h−1∙g−1 vs. 92.2 μmol∙h−1∙g−1) and photocurrent density (∼6 times) indicate that Fe-doping enhances the photo-excitement and the separation of the photoinduced carrier. First-principles calculations reveal a robust B12As2 structure doped by Fe, bonding to icosahedral B12 clusters and its nearest As via the Fe(III) style. Doped-Fe alters HOMO and LUMO orbital components, reduces the optical band-gap and becomes the activated carrier-separation center. Overall, a novel synthetic method and mechanism of Fe-doping are revealed that would facilitate optical applications of B12As2 crystals under extreme conditions.

Mechanochemical strategy assisted morphology recombination of COFs for promoted kinetics and LiPS transformation in Li–S batteries

A covalent organic frameworks (COFs) material with regular pores and stable structure can be used as the host of lithium-sulfur batteries to improve battery kinetics and polysulfides conversion. Herein, we designed and synthesized two kinds of rod-liked bulk COFs by adjusting different pore sizes (COF-BTD and COF-TFB), unfortunately, the active sites masking and sluggish kinetics have not met our expectations. Generally, the available layered COFs prepared from mechanochemical can expose abundant active sites and favorable kinetics than bulk COFs. Thus, simple mechanical ball milling is applied to activate the above COFs (M-COFs group). It is worth noting that layered R–COF–BTD is directly synthesized from rod-liked precursors by simple morphological reconstruction. A series of characterization methods are used to systematically explore the advantages of the group of M-COFs@S electrodes in the cycling process, including the effects of specific morphology on the kinetics and transformation of polysulfides. Our research provides a feasible plan for the development and selection of the host material of lithium-sulfur batteries.

Facile construction of phosphorus-free and green organic-inorganic hybrid flame-retardant system: For improving fire safety of EP

As the contradiction intensifies both the increasing consumption of petroleum resources and environmental protection, the exploitation and utilization of biological resources have reached an unprecedented height. In this work, a phosphorus-free and green organic-inorganic hybrid flame-retardant system was facilely constructed based on oyster waste via mechanochemical strategies for flame-retardant epoxy (EP). The characterization results showed the successful exfoliation of the lamellar structure in oyster waste during the mill process. EP composites with TOSP exhibited a short combustion time during the vertical combustion test. And the limited oxygen index value of EP composites with TOSP increased from 24.4 % to 27.3 %. Remarkably, the introduction of environmentally friendly TOSP enhanced the fire safety of EP (e.g., ∼41.8 % and 55.0 % decline in peak heat release rate (pHRR) and total CO production (TCOP) at only 4 wt% content). Hence, the work offers novel insights into the facile construction of a phosphorus-free and green organic-inorganic hybrid flame-retardant system and recycling oyster waste.