LiHMDS Research Articles

Interface-Engineered Atomic Layer Deposition of Li4Ti5O12:Toward High-Capacity 3D Thin-Film Batteries

Atomic layer deposition (ALD) of lithium (Li)-based thin films has aroused significant interest in recent years. Promising applications are Li-ion thin-film batteries (TFBs), protective particle coatings, interface model systems, and neuromorphic computing [1,2]. Here, we demonstrate high footprint capacities and excellent high-rate performance of Li4Ti5O12 (LTO) fabricated by ALD for three-dimensional (3D) solid-state TFBs to power upcoming energy-autonomous sensor systems.The simultaneous increase of power and energy density of full-cell 3D TFBs by coating the battery layer stack over microstructured substrates was recently demonstrated [3]. The required conformal, pinhole-free deposition, and stoichiometric control of nanometer-thin films on highly structured surfaces are only accessible via ALD. The vapor-phase technique based on sequential, self-limiting surface reactions is well understood. However, the direct deposition of Li-based anodes remains challenging [1].In previous studies, we developed a thermal three-step ALD process for Li-containing mixed oxides on 200 mm silicon wafers [4, 5]. Lithium-tert-butoxide (LTB) and lithium hexamethyldisilazide (LiHMDS) were proven as suitable precursors, forming high-quality spinel LTO with low impurities after rapid thermal processing. The excellent electrochemical behavior of ALD LTO with LiHMDS was examined and linked to the film texture [5].In this work, we optimize the LTO ALD process with LTB towards high-capacity 3D TFBs and evaluate the electrochemical performance for the first time. A process with tetrakis (dimethylamino) titanium (TDMAT) and H2O at 300 °C was developed, leading to a saturated growth per cycle of 1.06 Å cycle-1 for 7 s LTB pulses. An ALD temperature window between 240 and 320 °C was identified. The effect of the substrate on the initial growth and crystallization behavior was investigated. To overcome the crystallization-inhibiting effect of the titanium nitride current collector, we introduced an ultrathin AlOx interlayer.Planar ALD LTO films with various thicknesses of up to 75 nm were manufactured, increasing the footprint capacity from 1.5 to 4.3 μAh cm-2. We observed a higher surface capacity contribution due to an increased roughness and an inferior C-rate performance with increasing film thickness. 50 nm LTO films demonstrate the optimum energy and power density. A footprint capacity of 1.95 μAh cm-2, corresponding to 67 % of the initial capacity, was achieved at 50 C with an average Coloumb efficiency of 99.9975 %.Next, we evaluate ALD LTO films as 3D TFB anodes for the first time. The conformality of the ALD process on microstructured substrates was improved by extending the LTB pulse and purge times. The purge time is the key factor enabling a step coverage of 70 % for holes with an aspect ratio of 10:1. The 3D samples with an area-enhancement factor (AEF) of 9 coated with 50 nm LTO obtained a footprint capacity of 20.2 μAh cm-2 at 1 C. The significant capacity enhancement of 6.9 compared to planar samples is according to the conformality. The remarkable high-power capability of 3D LTO is demonstrated with 7.75 μAh cm-2 at extreme currents of 5 mA cm-2. A capacity retention of 97.4 % after 500 cycles at 1 mA cm-2 shows the high-rate cyclability. The superior high-rate performance of ALD LTO compared to other 3D anode materials illustrates the enormous potential for realizing high-energy and high-power on-chip 3D TFBs.

Role of the Coreactant on the Dual-Source Behavior of Lithium Hexamethyldisilazide for ALD Li-Containing Films.

Atomic layer deposition (ALD) of Li-containing thin films is deemed as highly relevant for the development of next-generation Li-ion batteries. Lithium hexamethyldisilazide (LiHMDS), as Li-containing precursor, is preferred over the widely used lithium tert-butoxide because of its lower melting point of 70 °C. However, the presence of silyl groups in the LiHMDS chemical structure can result in the undesired incorporation of Si in the film. Therefore, understanding the reaction mechanism of LiHMDS is required to control its dual-source behavior and grow Si-free Li-containing thin films. For this purpose LiHMDS was combined with O2 plasma or water as coreactant. In situ spectroscopic ellipsometry (SE) and X-ray photoelectron spectroscopy (XPS) revealed that using O2 plasma as coreactant results in linear growth and Si-containing films, whereas using H2O as coreactant leads to fast, nonsurface-reaction-limited growth and Si-free films. To shed light on the role of the coreactant on the reaction mechanism of LiHMDS, in situ studies by time-resolved quadrupole mass spectrometry (QMS) were performed on the O2 plasma and H2O-based ALD processes. Measurements taken during full ALD cycles and half-cycles were carefully compared to identify which half-cycle surface reaction products lead to silicon incorporation in the film. The QMS results of the LiHMDS + H2O process showed that LiHMDS both chemisorbs and physisorbs. Furthermore, it is concluded that Si incorporation occurs during the O2 plasma step, when the physisorbed ligands are combusted and Si-containing products are redeposited. This work also demonstrates that the incorporated Si can be abstracted from the film by means of a H2 plasma step following the O2 plasma step. These insights on the role of the coreactant in the synthesis of Li-containing films contribute to the development of LiHMDS-based ALD processes for Li-ion battery applications.

Open-vessel polymerization of N-carboxyanhydride (NCA) for polypeptide synthesis.

Synthetic polypeptides, also known as poly(α-amino acids), have the same polyamide backbone structures as natural proteins and peptides. As an important class of biomaterials, polypeptides have been widely used because of their biocompatibility, bioactivity and biodegradability. Ring-opening polymerization of N-carboxyanhydride (NCA) is a classical and widely used method for the synthesis of polypeptides. The dominantly used primary amine-initiated NCA polymerization can yield well-defined polymers and complex macromolecular architectures, but the reaction is slow and sensitive to moisture, making it necessary to use anhydrous solvents and a glovebox. One solution is to use lithium hexamethyldisilazide (LiHMDS) as the initiator, as described in this protocol. LiHMDS-initiated NCA polymerization is less sensitive to moisture and can be carried out in an open vessel outside the glovebox. It is also very fast; the reaction can be complete within 5 min to produce 30-mer polypeptides. In this protocol, poly(γ-benzyl-L-glutamate) is prepared as an example, but the protocol can easily be adapted to the synthesis of other polypeptides by generating NCAs from different amino acids, making it particularly suitable for the efficient parallel synthesis of polypeptide libraries. We provide detailed procedures for NCA synthesis and purification, the method of polymer end-group modification and measurement of polymerization kinetics and reactivity ratio. The procedure for synthesis of monomers and polymerization to form polypeptides requires <1 d. The superfast and open-vessel NCA polymerization method described here will probably enable a wide range of applications in the synthesis and functional study of polypeptide biomaterials.

The Identification of Structural Changes in the Lithium Hexamethyldisilazide-Toluene System via Ultrasonic Relaxation Spectroscopy and Theoretical Calculations.

Ultrasonic absorption measurements were carried out over a wide concentration and temperature range by means of a pulse technique to examine the structural mechanisms and the dynamical properties in lithium hexamethyldisilazide (LiHMDS)-toluene solutions. Acoustic spectra revealed two distinct Debye-type relaxational absorptions attributed to the formation of trimers from dimeric and monomer units and to the formation of aggregates between a LiHMDS dimer and one toluene molecule in low and high frequencies, respectively. The formation of aggregates was clarified by means of molecular docking and DFT methodologies. The aggregation number, the rate constants and the thermodynamic properties of these structural changes were determined by analyzing in detail the concentration-dependent relaxation parameters. The low-frequency relaxation mechanism dominates the acoustic spectra in the high LiHMDS mole fractions, while the high-frequency relaxation influences the spectra in the low LiHMDS mole fractions. In the intermediate mole fraction region (0.25 to 0.46), both relaxations prevail in the spectra. The adiabatic compressibility, the excess adiabatic compressibility and the theoretically estimated mean free length revealed a crossover in the 0.25 to 0.46 LiHMDS mole fractions that signified the transition from one structural mechanism related with the hetero-association of LiHMDS dimers with toluene molecules to the other structural mechanism assigned to the formation of LiHMDS trimers. The combined use of acoustic spectroscopy with theoretical calculations permitted us to disentangle the underlying structural mechanisms and evaluate the volume changes associated with each reaction. The results were compared with the corresponding theoretically predicted volume changes and discussed in the context of the concentration effect on intermolecular bonding.

Utilisation of a dianionic pentadentate ligand in group 13 chemistry

Using the pentadentate tetrapyrazolylpyridyl diborate (B2Pz4Py) ligand allowed for the isolation of overall seven group 13 complexes, which have been fully characterised and whose solid-state structures were obtained by single-crystal X-ray diffraction analysis. The aluminium chloride (1) and bromide (2) complexes as well as the gallium chloride (3) and iodide (4) complexes are accessible by deprotonation of the ligand precursors [B2Pz4LiPyH]2 with lithium hexamethyldisilazide and subsequent reaction with aluminium and gallium trihalides. Using indium(I) chloride instead gives rise to the indium(III) bis(trimethylsily)amide complex 5. Chloride abstraction from the aluminium(III) complex 1 using a combination of TlBArF24 and TlPF6 affords the related aluminium(III) fluoride complex 6 while using the gallium(III) complex 3 yields the dinuclear cationic PF2O2-bridged gallium(III) complex 7.

Plasma-Enhanced Atomic Layer Deposition of Lithium Nickel Oxide Thin Film Model Systems

The main bottleneck in the development of the next generation of Li-ion batteries with higher energy densities, as demanded for long-range electrical mobility, is the lack of understanding and control of the reactions at the electrode-electrolyte interfaces. Reactions at the cathode side cause rapid capacity loss during cycling and represent a major issue for batteries with high-voltage cathodes, which are crucial in reaching the required energy densities. Promising candidates for use in next generation of batteries are Ni-rich Li(Ni1-x-yMnxCoy)O2 (NMC) cathodes, which show high capacity, high potential, and contribute to address the geopolitical issue of decreasing the Co content in the cathode. Ni-rich NMCs exhibit similar electrochemical properties as pure LiNiO2 and therefore LiNiO2 thin films can be used as model systems to gain fundamental understanding of the interfacial processes that hinder the large-scale implementation of Ni-rich NMCs. Atomic layer deposition (ALD) is a suitable technique to fabricate these model systems, as it gives precise control over film thickness, uniformity, chemical composition, and crystal orientation.Previous work on LiNiO2 by ALD is not extensively reported in literature. Moreover, films grown by a supercycle process, in which two ALD subcycles are alternated, suffered from a low Ni at.% and a large C content because of precursor ligand residues, and films fabricated using a complex multilayered approach showed severe Si contamination from the Li precursor [1]. In this contribution we report on ALD lithium nickel oxide (LNO) thin films with stoichiometries close to LiNiO2 and low levels of contaminants.The ALD process is based on lithium hexamethyldisilazide (LiHMDS) and nickel bis(N,N’-di-tert-butylacetamidinate) (Ni(tBu-MeAMD)2) as precursors and O2 plasma as co-reactant. 1 ALD cycle of Li2O is combined with x cycles of NiO using a supercycle approach. In this contribution we explore the relation between the Ni/Li cycle ratio x and material properties of the LNO films.The growth of the LNO films is monitored by means of in-situ spectroscopic ellipsometry. The ellipsometric data of films with a high Ni/Li cycle ratio are fitted with a general oscillator model used for NiO films, while a Cauchy model was adopted in case of a low Ni/Li cycle ratio and Li2O films. The growth per supercycle (GPSC) of LNO shows an intermixing effect, as it does not follow the linear trend calculated from the growth per cycle (GPC) values of the individual Li2O and NiO ALD processes, which are 1.0 Å/cycle and 0.34 Å/cycle respectively.XPS surface measurements show that the Ni/Li atomic ratio is tuned from 0 to 10 as function of the Ni/Li cycle ratio x. Low levels of Si and N contamination, below 4% and 2% respectively, are observed. A shift of the main peak in the Ni 2p3/2 spectrum to higher binding energies indicates a shift in oxidation state from Ni2+ to Ni3+ as decreases [2]. According to surface measurements, the LNO film with x=5 shows a stoichiometry close to LiNiO2, but depth profile measurements indicate that the Ni at.% is significantly higher in the bulk than on the surface of the films, most certainly attributed to the formation of a Li2CO3 surface layer upon air exposure. Li2CO3 is also present in the bulk of the LNO films, but the bulk C at.% stays below 4%.These results show that we can use ALD to fabricate a high-voltage cathode model system, which we plan to characterize in-situ and post-mortem in combination with both liquid and solid electrolytes to study the cathode-electrolyte interface.[1] Maximov et al., Energies, 13 (2020) 2345[2] Fu et al., Applied Surface Science 441 (2018) 1048 This work is part of the ‘BatteryNL – Next Generation Batteries based on Understanding Materials Interfaces’ project (with project number NWA.1389.20.089) of the NWA research programme ‘Research on Routes by Consortia (ORC)’ funded by the Dutch Research Council (NWO). Figure:(a) The GPSC of LNO ALD process shows an intermixing effect when comparing the experimental results with the expected GPSC based on the two processes (b) Ni 2p3/2 XPS spectrum for different Ni/Li cycle ratios x. A shift to higher binding energies is observed with decreasing x, indicating a shift from Ni2+ to Ni3+. (c) XPS surface measurements of LNO films show low levels of contaminants and a Ni/Li atomic ratio varying with the Ni/Li cycle ratio. (d) Depth profile of LNO with x=5 shows an increased Ni at.% and a low C at.% in the bulk of the film. Figure 1

Highly Conformal Solid Electrolyte for Li-Ion Batteries By Atomic Layer Deposition

Lithium phosphorus oxynitride (LiP x O y N z , commonly known as LiPON) is a state-of-the-art solid electrolyte material with suitably low resistivity and high ionic conductivity for all-solid-state thin-film microbatteries [1,2]. Thin and pinhole-free layers of LiPON can be fabricated using atomic layer deposition (ALD) [3]. Uniquely among thin-film fabrication methods, ALD is a technique that works for coating even challenging 3D interfaces [4,5]. In this work, LiPON ALD processes were optimized for two different lithium precursors at reasonable temperatures (~300 °C) and precursor pulse/purge lengths (< 5 s), and LiPON films were deposited onto PillarHall® lateral high-aspect-ratio (LHAR) test structures to investigate the conformality of the material. Comparative testing was performed between the two lithium precursors.The results indicated that more conformal LiPON films can be deposited using the appropriate precursors – in this case, lithium tert-butoxide (LiO t Bu) yielded greater penetration depths than lithium hexamethyldisilazide (Li-HMDS). The improved conformality observed when using LiO t Bu indicates that this precursor is a better choice for LiPON coatings on high-aspect-ratio structures. The ALD technique allowed for the deposition of highly conformal LiPON films, ~50–115 µm deep into 100–500 nm gaps. This opens possibilities for the use of LiPON as a solid electrolyte in batteries with high-surface-area electrodes. High surface areas are important not only for unlocking higher power densities (faster charging and discharging) in batteries, but also for enabling the use of thin-film technology in fabricating microbatteries with meaningful energy storage capacities.

Synthesis of inventive biphenyl and azabiphenyl derivatives as potential insecticidal agents against the cotton leafworm, Spodoptera littoralis

The emergence of pest resistance of Spodoptera littoralis (order; Lepidoptera, family; Noctuidae) towards the large scale of different classes of insecticides necessitates the development of some new poly-functionalized biphenyl and azabiphenyl with highly anticipated insecticidal bioresponse. Four new biphenyl carboxamidines 4a–d and four aza-analogue picolinamidine derivatives 8a–d were designed and prepared via the treatment of their corresponding carbonitriles with lithium-bis trimethylsilylamide [LiN(TMS)2], followed by hydrolysis with hydrogen chloride. Furthermore, these compounds were elucidated by spectral data, and their toxicity and insecticidal activity were screened against Spodoptera littoralis. Whereby, toxicological and biochemical aspects of the inventively synthesized biphenyl and azabiphenyl derivatives against the cotton leafworm, Spodoptera littoralis were inspected. As regards the indomitable LC50 and LC90 values, biphenyl and aza-analogues 8d, 8a, 4b, and 8b, revealed the furthermost forceful toxic effects with LC50 values of 113.860, 146.265, 216.624, and 289.879 ppm, respectively. Whereby, their LC90 values are 1235.108, 1679.044, 2656.296, and 3381.256 ppm, respectively, and toxicity index being 22.31%, 17.36%, 11.72%, and 8.76%, respectively, comparing with the already recommended, methomyl insecticide, lannate 90% SP (LC50, 25.396 and LC90, 57.860 and toxicity index, 100%). Additionally, electrochemical parameters via DFT studies were carried out for demonstrating and elucidation of structure–activity relationship (SAR) according to highly motived compounds, descriptors, and the in vivo insecticidal activities.Graphical

1,3‐Diketone‐Mediated Synthesis of Symmetrical Aryl Imides from Activated Amides

AbstractSymmetrical aryl imides are synthesized from the reaction of activated amides such as N‐phenyl‐N‐tosyl benzamides. The amine source is provided by lithium hexamethyldisilazide (LiHMDS), and a 1,3‐diketone mediates the generation of the N‐acyl donor from N,N‐bis(trimethylsilyl)amide. Various symmetrical aryl amides are thus formed in moderate to good yields.

Synthesis of 2’,4‐Dibromo‐2,4’‐bithiazole Using Novel Long‐range Halogen Dance Reaction

AbstractThis study presents a novel halogen dance reaction using 4,5‐dibromo‐2,4’‐bithiazole, which demonstrates a long‐range effect. The reaction involves the migration of a bromo group from the C5‐position to the C2’‐position of another thiazole ring when treated with lithium hexamethyldisilazide (LiHMDS), resulting in the formation of a non‐symmetric brominated bithiazole. In contrast, the base‐induced C2’‐bromination of 4‐bromobithiazole was found to be inefficient in synthesizing the desired brominated bithiazole due to its poor deprotonation selectivity.

Investigation of the effect of structure modification of furamidine on the DNA minor groove binding and antiprotozoal activity

New analogs of the antiprotozoal agent Furamidine were prepared utilizing Stille coupling reactions and amidation of the bisnitrile intermediate using lithium bis-trimethylsilylamide. Both the phenyl groups and the furan moiety of furamidine were replaced by heterocycles including thiophene, selenophene, indole or benzimidazole. Based upon the ΔTm and the CD results, the new compounds showed strong binding to the DNA minor groove. The new analogues are also more active both in vitro and in vivo than furamidine. Compounds 7a, 7b, and 7f showed the highest activity in vivo by curing 75% of animals, and this merits further evaluation.

LiHMDS-Mediated Deprotonative Coupling of Toluenes with Ketones.

We demonstrate that lithium hexamethyldisilazide (LiHMDS) acts as an effective base for deprotonative coupling reactions of toluenes with ketones to afford stilbenes. Various functionalities (halogen, OCF3 , amide, Me, aryl, alkenyl, alkynyl, SMe, and SPh) are allowed on the toluenes. Notably, this system proved successful with low-reactive toluenes bearing a large pKa value compared to that of the conjugate acid of LiHMDS (hexamethyldisilazane, 25.8, THF), as demonstrated by 4-phenyltoluene (38.57, THF) and toluene itself (∼43, DMSO).

Lithium Hexamethyldisilazide Endows Li||NCM811 Battery with Superior Performance

The construction of stable cathode electrolyte interphase (CEI) is the key to improve the NCM811 particle structure and interfacial stability via electrolyte engineering. In He’s work, lithium hexamethyldisilazide (LiHMDS) as the electrolyte additive is proposed to facilitate the generation of stable CEI on NCM811 cathode surface and eliminate H2O and HF in the electrolyte at the same time, which boosts the cycling performance of Li||NCM811 battery up to 1000 or 500 cycles with 4.5 V cut-off voltage at 25 or 60 °C.

Observation and Stereochemistry of Betaine Intermediates in the Reaction of Phosphonium Ylide Containing a Phosphaboratatriptycene Skeleton with Benzaldehyde.

Betaine intermediates, rather than the corresponding 1,2-oxaphosphetanes, were observed in the reaction of the phosphonium ylide containing a phosphaboratatriptycene skeleton with PhCHO in THF. Their chemical shifts were -4.56, -4.92, -7.32, and -11.1 ppm at -10 °C in variable temperature (VT) 31P{1H} NMR experiments. These signals were observed by the deprotonations of β-hydroxyalkylphosphonium salts with lithium hexamethyldisilazide (LiHMDS) and sodium hexamethyldisilazide (NaHMDS). Their signals were assigned to betaine lithium complexes and salt-free betaines, respectively. The betaine lithium complexes were thermodynamically stable even at 25 °C and were converted to β-hydroxyalkylphosphonium salts by protonation, whereas the salt-free betaines were unstable, providing the corresponding ethylphosphonium salt and PhCHO at 0 °C, instead of olefins and phosphine oxide. The potential structures of the betaine lithium complexes and salt-free betaines were investigated by optimizing the expected stereoisomers and estimating the phosphorus chemical shifts by density functional theory (DFT) calculations. The results indicated that the erythro-syn- and threo-syn-betaines were more stable than their anti-forms. Erythro-syn-betaines were the most thermodynamically stable among the expected stereoisomers in both lithium complexes and salt-free betaines. The estimated phosphorus-31 signals were in good agreement with those experimental values.

Nickel-Catalyzed Direct Arylation Polymerization for the Synthesis of Thiophene-Based Cross-linked Polymers.

An earth-abundant nickel(II) bipyridine catalyst, combined with lithium hexamethyldisilazide as base, demonstrates its wide applicability in the direct arylation polymerization of di- and tri-thiophene heteroaryls with poly(hetero)aryl halides. With a nickel catalyst loading of 2.5 mol%, a series of twenty highly cross-linked organic polymers is obtained in 34 to 99 % yields. Using mixed polytopic coupling partners allows obtaining alternating and optically active thiophene-based solids with intrinsic porosity.

Lithium hexamethyldisilazide as electrolyte additive for efficient cycling of high-voltage non-aqueous lithium metal batteries

High-voltage lithium metal batteries suffer from poor cycling stability caused by the detrimental effect on the cathode of the water moisture present in the non-aqueous liquid electrolyte solution, especially at high operating temperatures (e.g., ≥60 °C). To circumvent this issue, here we report lithium hexamethyldisilazide (LiHMDS) as an electrolyte additive. We demonstrate that the addition of a 0.6 wt% of LiHMDS in a typical fluorine-containing carbonate-based non-aqueous electrolyte solution enables a stable Li||LiNi0.8Co0.1Mn0.1O2 (NCM811) coin cell operation up to 1000 or 500 cycles applying a high cut-off cell voltage of 4.5 V in the 25 °C−60 °C temperature range. The LiHMDS acts as a scavenger for hydrofluoric acid and water and facilitates the formation of an (electro)chemical robust cathode|electrolyte interphase (CEI). The LiHMDS-derived CEI prevents the Ni dissolution of NCM811, mitigates the irreversible phase transformation from layered structure to rock-salt phase and suppresses the side reactions with the electrolyte solution.

Chemoselective Divergent Transformations of N-(Propargyl)indole-2-carbonitriles with Nitrogen Nucleophiles: Alkyne Hydroamination or Domino Cyclizations.

Interactions of N-(propargyl)indole-2-carbonitriles with nitrogen nucleophiles were studied. It was found that lithium hexamethyldisilazane (LiHMDS)-promoted reactions give mixtures of two product types, originating from an initial attack onto carbon-carbon or carbon-nitrogen triple bonds. Performing the reaction at reduced temperature and in the presence of catalytic amounts of LiHMDS delivered alkyne hydroamination products exclusively. On the contrary, the one-pot reaction of N-(propargyl)indole-2-carbonitriles with methanol and LiHMDS on heating, followed by the addition of a nitrogen nucleophile, allowed a selective domino cyclization sequence toward 1-aminopyrazino[1,2-a]indoles. Anilines and nitrogen heterocycles could be employed as N-nucleophiles to obtain products of both types. Moreover, an alternative one-pot route toward a third product type has been developed. When N-(propargyl)indole-2-carbonitrile was first combined with aniline and LiHMDS at reduced temperature, further heating of the in situ generated hydroamination product led to the intramolecular cyclization into 1-imino-2-phenylpyrazino[1,2-a]indoles. Thus, chemodivergent transformations of the same starting material into three compound classes were investigated. The possible reaction routes were studied, and N-(allenyl)indole-2-carbonitrile was identified as the key intermediate. Acyclic and cyclic products exhibit fluorescence emission in the blue to green range.

Simultaneous optimization of solvation structure and water-resistant capability of MgCl2-based electrolyte using an additive combination of organic and inorganic lithium salts

• LiHMDS with water-resistant capability is found to assist the solvation of MgCl 2 in THF solvent by ion association. • A small amount of LiHMDS in MgCl 2 /THF contributes to reduce the de-solvation energy of Mg 2+ by forming [Mg x Li y HMDS z Cl 2x+ y -z · n THF] aggregates. • An increasing amount of LiHMDS in MgCl 2 /THF makes the functional [Mg x Li y HMDS z Cl 2x+ y -z · n THF] start to dissociate. • LiCl as co-additive can avoid the dissociation of [Mg x Li y HMDS z Cl 2x+ y -z · n THF]. • A Mg//Mo 6 S 8 full cell can be cycled for over 10,000 cycles with a superior capacity retention of 83 mA h g –1 even under an ultrahigh rate of 31.1 C (1 C = 128.8 mA g –1 ). The inefficient operation of Mg batteries associated with the high sensitivity of electrolyte to impurities (water, air, etc.) seriously impedes their practical use. Here, we report a water-resistant MgCl 2 -based electrolyte consisting of low-cost organic lithium hexamethyldisilazide (LiHMDS) and inorganic lithium chloride (LiCl) dual-salt additives. The electrolyte displays excellent electrochemical performance for reversible Mg stripping and plating, with overpotential of 0.15 V and 0.30 V at 5 mA cm –2 and 10 mA cm –2 , respectively, and Coulombic efficiency (CE) up to 100%. It keeps its reactivity even with the presence of 1000 ppm H 2 O or ∼3% impurities introduced by using impure reagents (MgCl 2 , 97%) during its synthesis. Experimental characterization and theoretical calculations reveal that the single-salt additive of organic LiHMDS in MgCl 2 /THF is a “double edged sword”:the upside is that, with a small amount added, it contributes to reduce the de-solvation energy of Mg 2+ by forming water-resistant [Mg x Li y HMDS z Cl 2x+ y -z · n THF] aggregates with MgCl 2 salts; the downside is that, while its amount increases, it starts to dissociate those functional aggregates. On the other hand, adding an inorganic salt LiCl as co-additive can reconstruct [Mg x Li y HMDS z Cl 2x+ y -z · n THF] aggregates and avoid their dissociation. With this hybrid electrolyte, a Mg//Mo 6 S 8 full cell can achieve a discharge specific capacity of 83 mA h g –1 even after 10,000 cycles at a high rate of 31.1 C (1 C = 128.8 mA g –1 ). This solvation structure reconstruction approach has far-reaching significance for the electrolyte design for rechargeable magnesium batteries.

Synthesis and Characterization of Pyridine Dipyrrolide Uranyl Complexes.

The first actinide complexes of the pyridine dipyrrolide (PDP) ligand class, (MesPDPPh)UO2(THF) and (Cl2PhPDPPh)UO2(THF), are reported as the UVI uranyl adducts of the bulky aryl substituted pincers (MesPDPPh)2– and (Cl2PhPDPPh)2– (derived from 2,6-bis(5-(2,4,6-trimethylphenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H2MesPDPPh, Mes = 2,4,6-trimethylphenyl), and 2,6-bis(5-(2,6-dichlorophenyl)-3-phenyl-1H-pyrrol-2-yl)pyridine (H2Cl2PhPDPPh, Cl2Ph = 2,6-dichlorophenyl), respectively). Following the in situ deprotonation of the proligand with lithium hexamethyldisilazide to generate the corresponding dilithium salts (e.g., Li2ArPDPPh, Ar = Mes of Cl2Ph), salt metathesis with [UO2Cl2(THF)2]2 afforded both compounds in moderate yields. The characterization of each species has been undertaken by a combination of solid- and solution-state methods, including combustion analysis, infrared, electronic absorption, and NMR spectroscopies. In both complexes, single-crystal X-ray diffraction has revealed a distorted octahedral geometry in the solid state, enforced by the bite angle of the rigid meridional (ArPDPPh)2– pincer ligand. The electrochemical analysis of both compounds by cyclic voltammetry in tetrahydrofuran (THF) reveals rich redox profiles, including events assigned as UVI/UV redox couples. A time-dependent density functional theory study has been performed on (MesPDPPh)UO2(THF) and provides insight into the nature of the transitions that comprise its electronic absorption spectrum.

Significant Broadening of the Substrate Scope for the Hydrated Imidazoline Ring Expansion (HIRE) via the Use of Lithium Hexamethyldisilazide

AbstractSubstrates that are insufficiently activated towards the hydrated imidazoline ring expansion (HIRE) process have been previously found to deliver exclusively the products of aminoalkyl side-chain ring expansion. Attempted reversal of the process by thermal activation towards HIRE failed. We have found that for such problematic substrates the HIRE-type ring expansion can be effectively achieved by applying lithium hexamethyldisilazide (LHMDS) in toluene. LHMDS is thought to promote intramolecular transamidation, which leads to ring-expanded 10- and 11-membered heterocyclic products in modest to good yields. The process significantly broadens the substrate scope amenable to the HIRE strategy.