Dual Nickel(II)/Mechanoredox Catalysis: Mechanical-Force-Driven Aryl-Amination Reactions Using Ball Milling and Piezoelectric Materials

The combination of a nickel(II) catalyst and a mechanoredox catalyst under ball-milling conditions promotes mechanical-force-driven C−N cross-coupling reactions. In this nickel(II)/mechanoredox cocatalyst system, the modulation of the oxidation state of the nickel center, induced by piezoelectricity, is used to facilitate a highly efficient aryl-amination reaction, which is characterized by a broad substrate scope, an inexpensive combination of catalysts (NiBr₂ and BaTiO₃), short reaction times, and an almost negligible quantity of solvents. Moreover, this reaction can be readily up-scaled to the multi-gram scale, and all synthetic operations can be carried out under atmospheric conditions without the need for complicated reaction setups. Furthermore, this force-induced system is suitable for excitation-energy-accepting molecules and poorly soluble polyaromatic substrates that are incompatible with solution-based nickel(II)/photoredox cocatalysts.     

Selective Synthesis of Oligosaccharides by Mechanochemical Hydrolysis of Chitin over a Carbon-Based Catalyst

Oligosaccharides possess fascinating functions that are applicable in a variety of fields, such as agriculture. However, the selective synthesis of oligosaccharides, especially chitin-oligosaccharides, has remained a challenge. Chitin-oligosaccharides activate the plant immune system, enabling crops to withstand pathogens without harmful agrichemicals. Here, we demonstrate the conversion of chitin to chitin-oligosaccharides using a carbon catalyst with weak acid sites and mechanical milling. The catalyst produces chitin-oligosaccharides with up to 94 % selectivity in good yields. Monte-Carlo simulations indicate that our system preferentially hydrolyzes larger chitin molecules over oligomers, thus providing the desired high selectivity. This unique kinetics is in contrast to the fact that typical catalytic systems rapidly hydrolyze oligomers to monomers. Unlike other materials carbons more strongly adsorb large polysaccharides than small oligomers, which is suitable for the selective synthesis of small oligosaccharides.     

Mechanochemical synthesis of N-tert-butanesulfinyl imines under metal-free conditions

A simple and convenient mechanochemical method for the condensation of aldehydes with tert-butanesulfinamide using catalytic amounts of iodine under metal- and solvent-free conditions is described.     

Spectroscopic Characterization of Complexes Obtained by Mechanochemical Reactions of Hemin

The solid state reactions of hemin with potassium acetate, KSCN, and Ag₂SO₄ were monitored using IR, Mössbauer and XRD techniques. These salts do not react at the peripheral propionic acid groups of hemin but form high spin complexes with hemin at the iron site. These complexes can be considered as ionic where the anions are coordinated to the metal through electrostatic interactions.     

Mechanochemical degradation of the crosslinked and foamed EVA multicomponent and multiphase waste material for resource application

Effects of mechanochemical degradation of the crosslinked and foamed ethylene-vinyl acetate copolymer (EVA) multicomponent and multiphase waste material in a solid state are studied with a HAAKE rheometer. The ruptures of chemical bonds in its net and stereo-structures are caused by external mechanical energy input by the Roller rotors of the HAAKE rheometer. A resource application method of the degradation product is obtained. The optimum mechanochemical degradation conditions are at 120–130 °C in a Roller rotor rotation speed range of 40–60 rpm for 24 min. Smaller polymer molecules have been generated so that the interfacial morphology, phase compatibility and plastic flow properties of the degradation product are all improved. The sol extracted from the degradation product is characterized with thermogravimetric analysis, gel permeation chromatography, nuclear magnetic resonance and Fourier transform infrared spectroscopy. Free radical reaction mechanisms are demonstrated in the degradation process. The degradation product partly replaces pure EVA in preparing the crosslinked and foamed material. Results show that the degradation product could be in resource application.     

Higher enantioselectivities in thiourea-catalyzed Michael additions under solvent-free conditions

Enantioselective Michael additions catalyzed by hydrogen-bonding catalysts produce many important compounds. Solvent-free reaction conditions in a ball mill can provide an improved enantioselectivity over the reaction in solution, due to lack of disruptive solvation of reagents. A range of 15 structurally different hydrogen-bonding organocatalysts were tested in two Michael additions to β-nitrostyrene under solvent-free conditions and compared with corresponding experiments in solution. With several thiourea catalysts, these Michael additions proceeded with higher enantioselectivities under solvent-free conditions than in solution.     

Solvent-free mechanochemical chlorination of hydrocarbons with CuCl2

Solvent-free chlorination of biphenyl and naphthalene was performed under mechanochemical stressing by high-energy ball milling (HEM) of a mixture of CuCl₂ (95 wt %) and the hydrocarbon (5 wt %). The reactivity of the selected hydrocarbons towards CuCl₂ during HEM partially correlates with their ionisation potentials (IP): hexadecane (9.91 eV) > biphenyl (8.27 eV) > naphthalene (8.14 eV).     

Solid-state mechanochemical synthesis of ferrocene

Solid-state mechanochemical reactions of iron(II) chloride with cyclopentadienides of alkaline metals or thallium, which lead to the formation of ferrocene, were studied. The dependence of the yield of the product on the parameters of mechanical loading for the reaction with cyclopentadienylthallium was determined.     

Characterization of solid electrolytes prepared from ionic glass and ionic liquid for all-solid-state lithium batteries

Glassy solid electrolytes were prepared by combining the 50Li₂SO₄·50Li₃BO₃ (mol%) ionic glass and the 1-ethyl-3-methyl-imidazolium tetrafluoroborate ([EMI]BF₄) ionic liquid. High-energy ball milling was carried out for the mixture of the inorganic ionic glass and the organic ionic liquid. The ambient temperature conductivity of the glass electrolyte with 10 mol% [EMI]BF₄ was 10⁻⁴ S cm⁻¹, which was three orders of magnitude higher than that of the 50Li₂SO₄·50Li₃BO₃ glass. The addition of [EMI]BF₄ to the ionic glass decreased glass transition temperature (T_g) of the glass and the decrease of T_g is closely related to the enhancement of conductivity of the glass. Morphology and local structure of the glass electrolyte was characterized. The dissolution of an ionic liquid in an ionic glass with Li⁺ ion conductivity is a novel way to developing glass electrolytes for all-solid-state lithium secondary batteries.     

The Mechanism of Flex-Activation in Mechanophores Revealed By Quantum Chemistry

Flex-activated mechanophores can be used for small-molecule release in polymers under tension by rupture of covalent bonds that are orthogonal to the polymer main chain. Using static and dynamic quantum chemical methods, we here juxtapose three different mechanical deformation modes in flex-activated mechanophores (end-to-end stretching, direct pulling of the scissile bonds, bond angle bendings) with the aim of proposing ways to optimize the efficiency of flex-activation in experiments. It is found that end-to-end stretching, which is a traditional approach to activate mechanophores in polymers, does not trigger flex-activation, whereas direct pulling of the scissile bonds or displacement of adjacent bond angles are efficient methods to achieve this goal. Based on the structural, energetic and electronic effects responsible for these observations, we propose ways of weakening the scissile bonds experimentally to increase the efficiency of flex-activation.