Lithium Methoxide Research Articles

Methoxide‐Enabled Zirconium‐Catalyzed Migratory Alkene Hydrosilylation

AbstractA zirconocene dichloride‐catalyzed alkene hydrosilylation is reported that can be applied to non‐activated and conjugated terminal and internal alkenes. It involves a catalytic Zr‐walk process and leads to a selective conversion to the linear product. Lithium methoxide serves as mild catalyst activating agent, which significantly increases the applicability and operational simplicity in comparison to earlier zirconium(II)‐based protocols. Supported by additional experiments and calculations, a mechanism via zirconium(IV) intermediates is proposed. Due to the benign nature and ready‐availability of the zirconium catalyst, the reaction is an attractive alternative to established alkene hydrosilylation methods.

Methoxide-Enabled Zirconium-Catalyzed Migratory Alkene Hydrosilylation.

A zirconocene dichloride-catalyzed alkene hydrosilylation is reported that can be applied to non-activated and conjugated terminal and internal alkenes. It involves a catalytic Zr-walk process and leads to a selective conversion to the linear product. Lithium methoxide serves as mild catalyst activating agent, which significantly increases the applicability and operational simplicity in comparison to earlier zirconium(II)-based protocols. Supported by additional experiments and calculations, a mechanism via zirconium(IV) intermediates is proposed. Due to the benign nature and ready-availability of the zirconium catalyst, the reaction is an attractive alternative to established alkene hydrosilylation methods.

Aminolysis-mediated single-step surface functionalization of poly (butyl cyanoacrylate) microbubbles for ultrasound molecular imaging

Molecular ultrasound imaging with actively targeted microbubbles (MB) proved promising in preclinical studies but its clinical translation is limited. To achieve this, it is essential that the actively targeted MB can be produced with high batch-to-batch reproducibility with a controllable and defined number of binding ligands on the surface. In this regard, poly (n-butyl cyanoacrylate) (PBCA)-based polymeric MB have been used for US molecular imaging, however, ligand coupling was mostly done via hydrolysis and carbodiimide chemistry, which is a multi-step procedure with poor reproducibility and low MB yield. Herein, we developed a single-step coupling procedure resulting in high MB yields with minimal batch-to-batch variation. Actively targeted PBCA-MB were generated using an aminolysis protocol, wherein amine-containing cRGD was added to the MB using lithium methoxide as a catalyst. We confirmed the successful conjugation of cRGD on the MB surface, while preserving their structure and acoustic signal. Compared to the conventional hydrolysis protocol, aminolysis resulted in higher MB yields and better reproducibility of coupling efficiency. Optical imaging revealed that under flow conditions, cRGD- and rhodamine-labelled MB, generated by aminolysis, specifically bind to tumor necrosis factor-alpha (TNF-α) activated endothelial cells in vitro. Furthermore, US molecular imaging demonstrated a markedly higher binding of the cRGD-MB than of control MB in TNF-α activated mouse aortas and 4T1 tumors in mice. Thus, using the aminolysis based conjugation approach, important refinements on the production of cRGD-MB could be achieved that will facilitate the production of clinical-scale formulations with excellent binding and ultrasound imaging performance.Graphical

Borylated Cyclopentanes via Atom Transfer Radical [3+2] Annulation

AbstractAn atom transfer radical [3+2] annulation (ATRAn) reaction involving alkenyl boronic esters and homoallylic iodides provides a rapid access to polysubstituted borylated cyclopentanes. A variety of α‐substituted vinylboronic esters are suitable substrates and offer unique opportunities for further modification of the formed 5‐membered ring. For instance, the oxidation of the boronic ester to an alcohol allows the preparation of products that corresponds to an annulation involving the enol form of acetone. Substitution of the iodide by a nucleophile such as lithium methoxide without modifying the boronic ester moiety is also feasible. Finally, by using a (3‐acetoxyprop‐1‐en‐2‐yl)boronic ester, a facile 1,2‐elimination reaction provided a methylenecyclopentane. In this case, the alkenylboronate radical trap acts as an equivalent to allene, a building block so far elusive for preparative radical reactions.

Alcohol splitting with bipolar membranes for the production of metal alkoxides: Alcohol splitting behaviour and ion transport kinetics

In this study, an electrochemical route was proposed for metal alkoxides preparation by taking advantage of alcohol dissociation (ROH → RO− + H+) in a bipolar membrane. A current density of 25 mA cm−2 was optimized for lithium methoxide and magnesium methoxide production with energy consumption of 28.84 kWh∙kg−1 and 27.98 kWh∙kg−1, respectively. Electrochemical impedance spectroscopy (EIS) characterization indicated that the threshold voltage for alcohol dissociation for the Neosepta BP-1E bipolar membrane is 6.02 V, which is much higher than that for water splitting of 0.72 V. For a bipolar membrane, the resistance of the alcohol dissociation (RAD) and the resistance of the diffusion boundary layer (RDBL) are the major contributors to the impedance for methanol splitting, while only the latter is the predominant contributor to the impedance for water splitting. Overall, alcohol splitting in bipolar membrane provides a versatile platform for green preparation of metal alkoxides.

Improving lithium-ion cells by replacing polyethylene terephthalate jellyroll tape.

Polyethylene terephthalate (PET) tape is widely used by well-known lithium-ion battery manufacturers to prevent electrode stacks from unwinding during assembly. PET tape is selected since it has suitable mechanical and electrical properties, but its chemical stability has been largely overlooked. In the absence of effective electrolyte additives, PET can depolymerize into its monomer dimethyl terephthalate, which is an unwanted redox shuttle that induces substantial self-discharge in a lithium-ion cell. This study presents a chemical screening experiment to probe the PET decomposition mechanism involving in situ generated methanol and lithium methoxide from dimethyl carbonate, one of the most common electrolyte solvents in lithium-ion cells. By screening other polymers, it is found that polypropylene and polyimide (Kapton) are stable in the electrolyte. Finally, it is demonstrated that reversible self-discharge of LiFePO4-graphite cells can be virtually eliminated by replacing PET jellyroll tape with chemically stable polypropylene tape.

Oxidation stability of N-ethyl-2-pyrrolidinone under high voltage environments

This work was aimed at investigating the electrochemical oxidation behavior of poly(vinylpyrrolidone) (PVP, a popular dispersant in the process of battery production) under high voltage environments. N-ethyl-2-pyrrolidone (NEP) was selected as a compound representative of PVP. Working electrodes were designed and prepared with a mixture of NEP and ethylene vinyl alcohol (EVOH) as a vehicle, and conductive carbon black as the electron transport material. Linear sweep voltammetry (LSV) was used to monitor the reactions underwent by NEP. The oxidative products were analyzed with X-ray photoelectron spectroscopy (XPS) and gas chromatography coupled with mass spectrometry (GC–MS). LSV revealed electrochemical oxidation of NEP taking place at voltages higher than 4 V. XPS and GC–MS revealed that the electrochemical oxidative products contained an ammonium group derived from the loss of electrons of the NEP under the electric field. Two types of ammonium species were identified: (i) species resulting from the loss of four electrons followed by hydrolysis and; (ii) species of higher molecular weight as a result of the replacement of ethyl group on NEP with methoxy (from lithium methoxide) followed by loss of protons and electrons (two-electron-two-proton process) with hydrogen being exchanged with fluorine. A reasonable mechanism was proposed to explain these results.

Identification of Redox Shuttle Generated in LFP/Graphite and NMC811/Graphite Cells

Unwanted self-discharge of LFP/AG and NMC811/AG cells can be caused by in situ generation of a redox shuttle molecule after formation at elevated temperature with common alkyl carbonate electrolyte. This study investigates the redox shuttle generation for several electrolyte additives, e.g., vinylene carbonate and lithium difluorophosphate, by measuring the additive reduction onset potential, first cycle inefficiency and gas evolution during formation at temperatures between 25 and 70 °C. After formation, electrolyte is extracted from pouch cells for visual inspection and quantification of redox shuttle activity in coin cells by cyclic voltammetry. The redox shuttle molecule is identified by GC-MS and NMR as dimethyl terephthalate. It is generated in the absence of an effective SEI-forming additive, according to a proposed formation mechanism that requires residual water in the electrolyte, catalytic quantities of lithium methoxide generated at the negative electrode and, surprisingly, polyethylene terephthalate tape within the cell.

Generation of fluoro(thio)carbenes from Me3SiCF2SAr

Generation of carbenes bearing a fluorine atom and an arylthio group from the difluorinated silicon reagents is described. The carbene generation is performed using a combination of lithium methoxide and lithium chloride, which behave as Lewis basic and Lewis acidic activators, respectively. The reactivity of fluoro(thio)carbenes was evaluated by trapping with an alkene and an aminoborane. Quantum chemical calculations allowed comparison of the fluoro(thio)carbene with difluorocarbene.

Primary Amine Functionalization of Alkoxysilanes: Synthesis, Selectivity, and Mechanistic Insights.

We report a highly selective substitution of silicon-bound methoxy groups by primary lithium amides. This unusual reactivity is possible because of the formation of particularly stable lithium methoxide, which compensates for the decreased Si-N bond enthalpy compared to Si-O bonds. In contrast to substitution reactions on halosilanes, highly selective monosubstitutions under mild conditions are possible, even in the presence of further reactive methoxy groups. A combination of experiments and density functional theory calculations was carried out in order to get an extensive understanding of the reaction. The calculations reveal a possible reaction mechanism with considerably low activation barriers and the entry of the nucleophile to be the rate-determining step. The low activation energies allow for the substitutions to be carried out at low temperatures, therefore preventing side reactions from occurring. The presented investigations expand the view of fundamental transformation processes on silicon and give access to a wide variety of functionalized silicon-based building blocks for various fields of chemistry.

Synthesis of a Neutral Mononuclear Four-Coordinate Co(II) Complex Having Two Halved Phthalocyanine Ligands That Shows Slow Magnetic Relaxations under Zero Static Magnetic Field.

Syntheses of a novel pseudotetrahedral four-coordinate mononuclear Co(II) complex that has two halved phthalocyanine moieties as the ligands, [Co(half-Pc)2] (1), and its magnetic properties as a single molecule magnet (SMM) are reported. A one pot reaction of phthalonitrile and lithium methoxide followed by the coordination to a Co(II) ion gave 1 as an orange solid in a moderate yield. X-ray crystallography on 1 reveals tetragonally distorted coordination geometry around the Co(II) ion. The M- HT-1 plots suggest that 1 has large axial magnetic anisotropy. The ac magnetic susceptibility data of the magnetically diluted 1 (dil.1) clearly show that the complex acts as an SMM even in the absence of the external static magnetic field ( Hdc). The influence of intermolecular and intramolecular interactions for the magnetic relaxation behaviors has been discussed by comparison of the magnetic data of 1 and dil.1. The Orbach process is suggested as the predominant mechanism of magnetic relaxations in the high-temperature range, and the Arrhenius plots provide the effective relaxation energy barrier and pre-exponential factor of Ueff = 54.0 cm-1 and τ0 = 3.17 × 10-10 s, respectively. The direct estimation of the axial anisotropic parameter of 1 was successfully performed by high-field, multifrequency ESR measurements up to 55 T and 2.5 THz. The evaluated axial zero-field splitting (ZFS) energy of 57.0 cm-1 is comparable to the Ueff energy, confirming that the magnetic relaxations are initiated by the thermal excitation from the ground | M S⟩ = |±3/2⟩ states to the |±1/2⟩ states in the high-temperature range. The results of the ab initio calculations based on the CAS(7,5) SCF wave functions indicate that the ground states of 1 consist mainly of | M S⟩ = |±3/2⟩ states, while the first excited states are the mixture of | M S⟩ = |+1/2⟩ and |-1/2⟩.

Hofmann Rearrangement of Carboxamides Mediated by N-Bromo­acetamide

An efficient, one-pot procedure for the Hofmann rearrangement of aromatic and aliphatic amides has been developed. Methyl and benzyl carbamates are produced with N-bromoacetamide in the presence of lithium hydroxide or lithium methoxide, in high yields. β-Phenylamino amides gave five-membered cyclic ureas stereospecifically. Side products of aryl or benzyl bromination were minimized. This procedure offers an easy access to various protected amines or diamines, which represent important synthetic precursors.

Formation and Crystal Structure of a Novel Zinc Phthalocyanine Analogue Having an Axial Isoindole Ligand Obtained by Lithium-mediated Reactions under Mild Conditions

Abstract The reaction of phthalonitrile and lithium methoxide at 70 °C in methanol yields a half-phthalocyanine intermediate, which coordinates to a zinc(II) ion in a subsequent reaction step to afford a novel five-coordinate zinc phthalocyanine analogue 2, having axially coordinating diiminoisoindole and methoxy moieties bonded at diagonal positions of the pyrrole α-carbons. Although the chromatographic isolation of 2 is problematic, its crystal structure has been determined unambiguously. The importance of the effective ionic radius of the zinc(II) ion for the resultant molecular structures is discussed.

Self-assembly of 2-hydroxy-tri-tert-butylphthalocyaninato zinc into J-type dimer: UV-vis, DFT and spectropotentiometric study

The role of the base nature during complexation of 2-hydroxy-9(10),16(17),23(24)-tri-tert-butyl-29H,31H-phthalocyanine ligand (1) with zinc acetate was studied by the UV-vis spectroscopy and DFT calculations. The latter allowed us to explain the selective formation of double-coordinated J-type dimer in the presence of lithium methoxide. Spectropotentiometry was used to study the nucleophilic properties of the dimeric complex in comparison with the corresponding monomer and has demonstrated the strong intramolecular interactions of macrocycles.

Synthesis of a stable J-type dimer based on the 2-hydroxy- 9(10),16(17),23(24)-tri(tert-butyl)phthalocyanine zinc complex

Interaction of 2-hydroxy-9(10),16(17),23(24)-tri( tert -butyl)phthalocyanine with zinc acetate in the presence of lithium methoxide affords a stable J-type dimer. Its formation was simulated by density functional theory (DFT).

First example of a hexadentate bicyclic phthalocyanine analogue containing a divalent metal center

A reaction of 1,2-dicyanobenzene and lithium methoxide at 70 °C in methanol yielded the half-phthalocyanine intermediate, which coordinates to a cadmium(II) ion in the subsequent reaction step to give the first example of a six-coordinate phthalocyanine analogue containing a divalent metal ion at the center.

ChemInform Abstract: One‐Step Conversion of Methoxysilanes to Aminosilanes: A Convenient Synthetic Strategy to N,O‐Functionalized Organosilanes.

AbstractThe driving force for the reaction is suggested to be the formation of lithium methoxide and aggregation effects.

Solubilization of SEI lithium salts in alkylcarbonate solvents

The SEI (Solid Electrolyte Interphase) at the surface of electrodes in lithium-ion batteries is composed of various lithium compounds, organic or mineral, which have a direct impact on cycling performance. The main lithium species constituting the SEI and selected in this study are lithium fluoride LiF, lithium carbonate Li 2CO 3, lithium hydroxide LiOH, lithium oxide Li 2O, lithium methoxide LiOCH 3 and lithium ethoxide LiOC 2H 5. Their solubilities were determined in ethylene, propylene, dimethyl, diethyl and vinylene carbonates (EC, PC, DMC, DEC and VC) and in one of their mixtures commonly used in lithium-ion batteries (EC/PC/3DMC) by mean of atomic absorption spectroscopy (AAS). These solutions were also investigated by EIS (Electrochemical Impedance Spectroscopy) and conductimetry measurements. Results show that while solubilization properties differ between LiF and other lithium compounds considered, their association pattern in solution is identical and solutions are mainly constituted of quadrupolar aggregates.

ChemInform Abstract: Direct Methoxylation of Nitroarenes and Nitroazaarenes with Alkaline Methoxides via Nucleophilic Displacement of an Aromatic Hydrogen Atom.

Treatment of 1,3-dinitrobenzene and 5-substituted derivatives with excess potassium or sodium methoxide in 1,3-dimethylimidazolidin-2-one (DMI) at room temperature results in the displacement of an aromatic hydrogen at the 4-position by methoxide, affording 2,4-dinitroanisole and its 6-substituted derivatives, respectively, in low to moderate yield. In contrast, an equimolar reaction under similar conditions leads to the replacement of the nitro group in preference to the ring hydrogen. The reaction does not take place with lithium methoxide as a base. Mono- and dinitronaphthalenes and nitroquinolines undergo similar displacement of a hydrogen atom at the position ortho or para to the nitro group, giving the corresponding methoxy derivatives in moderate yield. A slow addition of the nitro compound to a large excess of potassium methoxide under an oxygen atmosphere has been found to enhance the conversion and improve the product yield. On the basis of the product distribution as well as the kinetic isotope effect kH/kD = 2.1, direct displacement of a ring hydrogen atom by methoxide ion has been interpreted in terms of the rate-determining release of an ipso-hydrogen atom as a proton from the initially formed Meisenheimer adduct.

Computational Study on the Solubility of Lithium Salts Formed on Lithium Ion Battery Negative Electrode in Organic Solvents

The solubility of lithium salts, found in solid-electrolyte interface (SEI) films on the anode surface in lithium ion battery cells, has been examined in organic solvents through atomistic computer simulations. The salts included lithium oxide (Li2O), lithium carbonate (Li2CO3), lithium oxalate ([LiCO2]2), lithium fluoride (LiF), lithium hydroxide (LiOH), lithium methoxide (LiOCH3), lithium methyl carbonate (LiOCO2CH3), lithium ethyl carbonate (LiOCO2C2H5), and dilithium ethylene glycol dicarbonate (([CH2OCO2Li]2: LiEDC). The organic solvents were dimethyl carbonate (DMC) and ethylene carbonate (EC). The atomic charges in the force field have been fitted to the electrostatic potential obtained from density functional theory calculations for each salt. The heat of dissolution in DMC for the salts calculated from computer simulations ranged from exothermic heats for the organic salts in general to endothermic heats for the inorganic salts in the order of LiEDC < LiOCO2CH3 < LiOH < LiOCO2C2H5 < LiOCH3 < LiF ...