Calcium Bis Research Articles

Synthesis of Sterically Encumbered Alkaline-Earth Metal Amides Applying the In Situ Grignard Reagent Formation.

Magnesium and calcium are too inert to deprotonate amines directly. For the synthesis of bulky amides alternative strategies are required and in the past, N-bound trialkylsilyl groups have been used to ease metalation reactions. The in situ Grignard reagent formation in stirred suspensions of magnesium or calcium with hydryl halide and imine in THF allows the synthesis of a plethora of amides with bulky silyl-free substituents. Ball milling protocols partially favor competitive side reactions such as aza-pinacol coupling reactions. Calcium is the advantageous choice for the in situ Grignard reagent formation and subsequent addition onto the imines yielding bulky calcium bis(amides) whereas the stronger reducing heavier alkaline-earth metals strontium and barium are less selective and hence, the aza-pinacol coupling reaction becomes competitive. Exemplary, the solid-state molecular structures of [(Et2 O)Mg(N(Ph)(CHPh2 )2 ] and [(Et2 O)2 Ca(N(Ph)(CHPh2 )2 ] have been determined.

(Localized) Highly Concentrated Electrolytes for Calcium Batteries

AbstractThe concept of non‐aqueous highly concentrated electrolytes (HCEs) for modern rechargeable batteries has recently evolved further by also adding a non‐coordinating solvent, i. e., a diluent, to create localized HCEs (LHCEs). LHCEs rely on a charge carrier design similar to that of HCEs in synergy with tailored macroscopic properties, especially reduced viscosity. LHCEs have now been extensively investigated for monovalent Li+ and Na+ based batteries, but here we investigate both HCEs and LHCEs for divalent Ca2+ conducting systems. Here we systematically map both molecular and macroscopic features as function of composition of Ca(TFSI)2 (calcium bis(trifluoromethane)sulfonimide) in PC (propylene carbonate) based HCEs as well as the corresponding LHCEs created using TTE (1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropyl ether) as diluent. Some unique HCE properties arise already at ca. 2.00 m, which is at a lower salt concentration than for monovalent systems, and in addition the local structure of the HCE can be maintained even within a nominal 0.45 m LHCE (starting from a 3.26 m parent HCE). The combined observations made at molecular and macro levels pave the way for further optimization of important physico‐chemical properties, proper design of electrochemical investigations, and eventually a better understanding of how to best improve the desolvation kinetics at e. g., the electrolyte/electrode interfaces of a Ca metal anode.

Vinylimidazole-Based Polymer Electrolytes with Superior Conductivity and Promising Electrochemical Performance for Calcium Batteries.

Calcium batteries are next-generation energy storage technologies with promising techno-economic benefits. However, performance bottlenecks associated with conventional electrolytes with oxygen-based coordination chemistries must be overcome to enable faster cation transport. Here, we report an imidazole-based polymer electrolyte with the highest reported conductivity and promising electrochemical properties. The polymerization of vinylimidazole in the presence of calcium bis(trifluoromethanesulfonyl)imide (Ca(TFSI)2) salt creates a gel electrolyte comprising a polyvinyl imidazole (PVIm) host infused with vinylimidazole liquid. Calcium ions effectively coordinate with imidazole groups, and the electrolytes present room temperature conductivities of >1 mS/cm. Reversible redox activity in symmetric Ca cells is demonstrated at 2 V overpotentials, stable cycles at 0.1 mA/cm2, and areal capacities of 0.1 mAh/cm2. Softer coordination, polarizability, and closer coordinating site distances of the imidazole groups can explain the enhanced properties. Hence, imidazole is a suitable chemical benchmark for the future design and advancement of polymer electrolytes for calcium batteries.

Calcium Solvation Dynamics Probed By in-Situ/Operando Soft X-Ray Absorption Spectroscopy

Calcium is considered a promising candidate in multivalent battery technologies due to its safe, economic, and nontoxic nature. It has received considerable attention since the recent work showing that calcium can be plated and stripped at room temperature with good stabilities and capacities. It offers the promise of a more than two-fold increase in the volumetric capacity compared to the monovalent lithium-ion batteries. Additionally, because of the higher mobility of Ca2+ compared to that of Mg2+ because of the lower charge density of Ca2+, the interest in calcium batteries has been growing rapidly. The understanding of the solvation and charge transfer mechanism at the electrolyte/electrode interface and how different types of cations and anions will affect the calcium solvation at this interface is the key to develop novel calcium batteries. To probe the Ca2+ coordination at the electrolyte/electrode interface as a function of the type of anions, total electron yield (TEY) mode soft X-ray absorption spectroscopy (XAS) sensitive to the interfacial speciation has been used under operando electrochemical conditions. Meanwhile, total fluorescence yield (TFY) mode XAS is sensitive to bulk speciation. By comparing the operando TEY and TFY mode XAS from 0.5 M calcium bis(trifluoromethanesulfonyl)imide (CaTFSI2) in THF, the Ca L3,2-edge TEY-XAS intensity increased at positive potentials while the Ca L3,2-edge TFY-XAS intensity decreases at these positive potentials. Such a comparison clearly shows the solvation and desolvation dynamics of calcium at the electrolyte/electrode interface, which will benefit the future development of next-generation multivalent batteries.

Synthesis of polycalciumphenylsiloxane and composites based on the skeleton of a sea urchin with the resulting polymer

In this work, we obtained polycalciumphenylsiloxane (PCPS) by the interaction of calcium bis (acetylacetonate) with polyphenylsiloxane. The first method consisted in boiling the starting reagents in toluene for several hours; the second was as follows: the mixture of the starting reagents was preliminarily treated mechanically in a ball mill, followed by boiling in toluene for several hours. Two fractions, soluble and insoluble, were isolated in both syntheses. They were investigated using IR, NMR spectroscopy, thermogravimetric analysis, and gel permeation chromatography. It was shown that the insoluble fraction is a mixture of calcium acetylacetonate and polyphenylsiloxane with a small calcium ion content. The soluble fraction is polycalciumphenylsiloxane. The yield of the soluble fraction is higher in the second synthesis method. The polymers obtained in the first and second synthesis methods are similar in composition and structure, which was confirmed by physicochemical methods. Next, the skeleton of the sea urchin Strongylocentrotus intermedius was treated with a soluble fraction in toluene. In this case, a composite was obtained, which was treated with 2–3% hydrochloric acid and then calcined at a temperature of 600 °C. At each stage, the composition of the composites was investigated using elemental analysis and IR spectroscopy. The morphology was investigated using scanning electron microscopy.

Concentrated Electrolyte for High‐Performance Ca‐Ion Battery Based on Organic Anode and Graphite Cathode

AbstractDue to the large abundance, low redox potential, and multivalent properties of calcium (Ca), Ca‐ion batteries (CIBs) show promising prospects for energy storage applications. However, current research on CIBs faces the challenges of unsatisfactory cycling stability and capacity, mainly restricted by the lack of suitable electrolytes and electrode materials. Herein, we firstly developed a 3.5 m concentrated electrolyte with a calcium bis(fluorosulfonyl)imide (Ca(FSI)2) salt dissolved in carbonate solvents. This electrolyte significantly improved the intercalation capacity for anions in the graphite cathode and contributed to the reversible insertion of Ca2+ in the organic anode. By combining this concentrated electrolyte with the low‐cost and environmentally friendly graphite cathode and organic anode, the assembled Ca‐based dual‐ion battery (Ca‐DIB) exhibits 75.4 mAh g−1 specific discharge capacity at 100 mA g−1 and 84.7 % capacity retention over 350 cycles, among the best results known for CIBs.

Metalation of Aryl‐bis(3‐alkyl‐5‐methylpyrazol‐1‐yl)‐ methane (Alkyl=Me, Ad; Aryl=Ph, C6H4‐2−OH) with NaN(SiMe3)2, KN(SiMe3)2, and Ca{N(SiMe3)2}2

AbstractDeprotonation of phenyl‐bis(3,5‐dimethylpyrazolyl)methane (HC(Ph)(PzMe2)2, 1 a) with [(thf)2Ca{N(SiMe3)2}2] in THF at −40 °C yields heteroleptic [(thf)2Ca{N(SiMe3)2}{C(Ph)(PzMe2)2}] (2 a) and finally homoleptic [(thf)Ca{C(Ph)(PzMe2)2}2] (2 b). However, these complexes degrade at room temperature to calcium bis(pyrazolate) and 2‐phenyl‐4,6‐dimethylpyrimidine (3 a). This degradation is accelerated when bulky phenyl‐bis(3‐adamantyl‐5‐methylpyrazolyl)methane (HC(Ph)(PzAd,Me)2, 1 b) is treated similarly and 2‐phenyl‐4‐adamantyl‐6‐methylpyrimidine (3 b) forms quickly. Sodiation of 1 a and 1 b with NaN(SiMe3)2 yields [{HC(Ph)(PzMe2)2}Na{C(Ph)(PzMe2)2}] (4 a) and [{HC(Ph)(PzAd,Me)2}Na{C(Ph)(PzAd,Me)2}] (4 b). The stronger metalation reagent benzylpotassium is able to quantitatively deprotonate 1 b leading to dinuclear [K{C(Ph)(PzAd,Me)2}]2 (4 c). The metathetical approach and the reaction of 4 c with metal(II) halides of Mg, Ca and Zn again leads to degradation and formation of pyrimidine 3 b. This decomposition of the ligand can be circumvented when the sidearm contains the anionic charge. Thus, 2‐hydroxyphenyl‐bis(3‐adamantyl‐5‐methylpyrazol‐1‐yl)methane (1 c) reacts with [(thf)2Ca{N(SiMe3)2}2] in THF to the homoleptic complex [(thf)4Ca{O−C6H4−CH(PzAd,Me)2}] (2 c). In this complex, THF and pyrazolyl bases compete in the coordination sphere and preparation of a heteroleptic complex fails. To avoid the binding competition between THF and pyrazolyl bases and to stabilize heteroleptic calcium complexes, the reaction has been repeated in toluene yielding [Ca{N(SiMe3)2}{O−C6H4−CH(PzAd,Me)2}]2 (2 d).

A new approach to the synthesis of nanosized powder CaO and its application as precursor for the synthesis of calcium borates

A procedure for the synthesis of calcium oxide has been developed, which consists in heat treatment of an aqueous solution of calcium acetate and d-glucose at 350 and then at 700 °C. The process parameters have been determined. It has been shown that when d-glucose is used and the reaction mixture is heat treated at 700 °C, highly dispersed calcium oxide with an average particle size of 77 nm is formed. CaO formed has been used as a precursor for the synthesis of priceite (Ca2(B5O7)(OH)5 · H2O) during hydrothermal treatment of CaO in an aqueous solution of boric acid. It has been found that the optimal conditions for the synthesis of monophase priceite under hydrothermal conditions include the temperature range of 170–200 °C and the heating time of 12 h. When heating priceite at 800 °C in air for 1 h, highly dispersed powder calcium bis(borate) Ca(BO2)2 has been isolated as the final product. It is shown that the use of synthesized powder CaO leads to the formation of fine-crystalline powders of calcium borates. Samples obtained at each stage of the proposed synthesis of highly dispersed calcium oxide and calcium borates, using the example of priceite and calcium bis(borate), have been studied by powder X-ray diffraction, SEM, TEM, BET, IR spectroscopy, and DTA.

Calcium mediated efficient synthesis of N-arylamidines from organic nitriles and amines.

Amidines are a preeminent group of organic compounds having wide applications in various industries. Here, we have developed a simple one-step reaction protocol for the facile synthesis of N-arylamidines catalysed by calcium bis(hexamethyldisilazide) [Ca{N(SiMe3)2}2(THF)2]. The amidine synthesis was readily achieved from organic nitriles and amines which provided a broad substrate scope ranging from electron-withdrawing to electron-donating substitutions as well as heterocyclic substitution. The reaction was carried out in a solvent-free medium under ambient conditions. The nucleophilic addition of aromatic amines to aryl nitriles led to good to excellent yields of the corresponding amidines. The reactivity of the amidines was further examined and the respective urea derivatives were achieved in excellent yields. The plausible mechanism involves the generation of an active calcium amido pre-catalyst that helps in the activation of nitriles in the reaction course.

The electric properties of AOT reverse micelles by molecular dynamics simulations

Reverse micelles (RMs) are the main component of a reverse microemulsion. The ionic RMs of sodium and calcium bis(2-ethylhexyl)sulfosuccinate (AOTNa and AOT2Ca, respectively), and water clusters of different size in isooctane were simulated by the united-atom molecular dynamics method. The radial density profiles characterized the local structure. The local electric potential and the electric field were calculated to describe the electric layer (EL). The behavior of these functions differs principally from the related quantities in the classical electric double layer. The decrease in the size of RMs leads to a noticeable compression of the EL. The value of the local electric field near the surface of the RM increases significantly with the replacement of Na+ counterions by Ca2+. The mutual compensation of the contributions from water and ions calculated separately was revealed, which results in poor sensitivity of the electric properties of the RMs to salt addition. The mean-square dipole moment was calculated for all considered aggregates. It was shown that this quantity strongly depends on the aggregate size as could be expected due to its fluctuation nature. Comparison of the mean-square dipole moment value obtained by the atomistic simulation with the one obtained within the primitive model witnesses that the strong overestimation of the dielectric permittivity of confined water in the primitive model of the RM leads to a significant decrease in the value of the micellar mean-square dipole moment.

Influence of Echeveria gibbiflora DC aqueous crude extract on mouse sperm energy metabolism and calcium-dependent channels.

In traditional Mexican medicine, Echeveria gibbiflora DC has been used as a vaginal post-coital rinse to prevent pregnancy. The aqueous crude extract (OBACE) induces sperm immobilization/agglutination and a hypotonic-like effect, likely attributed to the high concentration of calcium bis-(hydrogen-1-malate) hexahydrate [Ca2+ (C4H5O5)2•6H2O]. Likewise, OBACE impedes the increase of [Ca2+]i during capacitation. Evaluate the effect of OBACE on sperm energy metabolism and the underlying mechanism of action on sperm-specific channel. In vitro, we quantified the mouse sperm immobilization effect and the antifertility potential of OBACE. The energetic metabolism status was also evaluated by assessing the ATP levels, general mitochondrial activity, mitochondrial membrane potential, and enzymatic activity of three key enzymes of energy metabolism. Furthermore, the effect of the ion efflux of Cl- and K+, as well as the pHi, were investigated in order to elucidate which channel is suitable to perform an in silico study. Total and progressive motility notably decreased, as did fertility rates. ATP levels, mitochondrial activity and membrane potential were reduced. Furthermore, the activities of the three enzymes decreased. Neither Cl- or K+ channels activities were affected at low concentrations of OBACE; nevertheless, pHi did not alkalinize. Finally, an in silico analysis was performed between the Catsper channel and calcium bis-(hydrogen-1-malate) hexahydrate, which showed a possible blockade of this sperm cation channel. The results were useful to elucidate the effect of OBACE and to propose it as a future male contraceptive.

Comments on the paper "Growth and optical studies of tris (thiourea) potassium barium sulphate crystal: a novel semiorganic NLO bimetallic crystal"

ABSTRACTIn a recent paper Azhar et al., (Mater. Res. Innov. https://doi.org/10.1080/14328917.2017.1392694) claim to have grown a tris (thiourea) potassium barium sulphate (TTPBS) crystal, which according to them is a novel NLO bimetallic crystal. In this comment, we prove that the so called TTPBS is a dubious crystal. In addition, we show that the so called barium thiourea chloride (Raju et al Mater. Res. Innov, 2016) thiourea barium chloride (Mahendra et al Optik 2017) and calcium bis(thiourea) chloride (Anis et al Optik 2016) single crystals are all dubious materials and do not contain any alkaline-earth metal but are simply thiourea.

Straightforward One-Pot Syntheses of Silylamides of Magnesium and Calcium via an In Situ Grignard Metalation Method

Calcium bis[bis(trimethylsilyl)amide] (Ca(HMDS)2) is a widely used reagent in diverse stoichiometric and catalytic applications. These processes necessitate a straightforward and large-scale access of this complex. Calcium does not react with primary and secondary amines, but the addition of excess bromoethane to a mixture of calcium turnings and amines in THF at room temperature yields the corresponding calcium bis(amides), calcium bromide and ethane. This in situ Grignard metalation method (iGMM) allows the preparation of calcium bis(amides) from secondary and primary trialkylsilyl-substituted amines and anilines on a multigram scale.1 Background2 The In Situ Grignard Metalation Method (iGMM)3 Properties of [(thf)2M(HMDS)2]4 Applications and Perspective

Enhanced Electrochemical Stability of Molten Li Salt Hydrate Electrolytes by the Addition of Divalent Cations.

Water can be an attractive solvent for Li-ion battery electrolytes owing to numerous advantages such as high polarity, nonflammability, environmental benignity, and abundance, provided that its narrow electrochemical potential window can be enhanced to a similar level to that of typical nonaqueous electrolytes. In recent years, significant improvements in the electrochemical stability of aqueous electrolytes have been achieved with molten salt hydrate electrolytes containing extremely high concentrations of Li salt. In this study, we investigated the effect of divalent salt additives (magnesium and calcium bis(trifluoromethanesulfonyl)amides) in a molten salt hydrate electrolyte (21 mol kg–1 lithium bis(trifluoromethanesulfonyl)amide) on the electrochemical stability and aqueous lithium secondary battery performance. We found that the electrochemical stability was further enhanced by the addition of the divalent salt. In particular, the reductive stability was increased by more than 1 V on the Al electrode in the presence of either of the divalent cations. Surface characterization with X-ray photoelectron spectroscopy suggests that a passivation layer formed on the Al electrode consists of inorganic salts (most notably fluorides) of the divalent cations and the less-soluble solid electrolyte interphase mitigated the reductive decomposition of water effectively. The enhanced electrochemical stability in the presence of the divalent salts resulted in a more-stable charge–discharge cycling of LiCoO2 and Li4Ti5O12 electrodes.

Crystal structures of Z-Gly-Aib-O-·0.5Ca2+·H2O and Z-Gly-Aib-OH.

Both deprotonated and neutral achiral title dipeptides assume similar structures of two conformations, which are related by a unit-cell inversion centre. Two mol-ecules of both conformations of the metal-free neutral dipeptide are linked by two hydrogen bonds, while two mol-ecules of both conformations of the ionized form coordinate a calcium ion in calcium(II) bis-[2-(2-{[(benz-yl-oxy)carbon-yl]amino}-acetamido)-2-methyl-propano-ate] monohydrate, 0.5Ca2+·C14H17N2O5-·0.5H2O, which lies on an inversion centre and forms a distorted octa-hedral complex with the metal ion. These CaII complexes are connected in the crystal via hydrogen bonds in the b- and c-axis directions, whereas in the a-axis direction, they stack via apolar contacts. In the metal-free crystal, namely 2-(2-{[(benz-yloxy)carbon-yl]amino}-acetamido)-2-methyl-propanoic acid, C14H18N2O5, mol-ecules are hydrogen bonded in the a- and c-axis directions, and stack in the b-axis direction via apolar contacts.

Dimethylcalcium.

The salt metathesis reaction between homoleptic calcium bis(trimethylsilyl)amide [Ca{N(SiMe3)2}2]2 and "halide-free" methyllithium allowed for the isolation of X-ray-amorphous dimethylcalcium [CaMe2]n in good yields and purities. The formation of [CaMe2]n was proven by microanalysis and NMR/FTIR spectroscopic methods as well as a series of derivatization reactions. Despite slowly decomposing thf, [CaMe2]n could be crystallized from chilled thf solutions as the heptametallic adduct [(thf)10Ca7Me14]. Reaction of [CaMe2]n with CaI2 in thf led to the dimeric complex [(thf)3Ca(Me)(I)]2, whereas in tetrahydropyran (thp) the trinuclear complex [(thp)5Ca3(Me)5(I)] was obtained, both representing the first crystallographically characterized heavy-Grignard compounds with methyl groups as the hydrocarbyl ligand. While protonolysis of [CaMe2]n with the superbulky proligand HTptBu,Me in nonpolar solvents gave homoleptic (TptBu,Me)2Ca, reaction in donor solvents (thf, thp) afforded the monomeric complexes [(TptBu,Me)Ca(Me)(thf)] and [(TptBu,Me)Ca(Me)(thp)], which are the first examples bearing terminal Ca-CH3 functionalities. Grignard-type nucleophilic methyl-group transfer to hexamethylacetone gave access to the dimeric alkoxide complexes [(thf)Ca(OCtBu2Me)2]2 and [(tBu2CO)Ca(μ2-OCtBu2Me)3Ca(OCtBu2Me)]. Finally, addition of the Lewis acid GaMe3 to [CaMe2]n led to the corresponding tetramethylgallate compound [Ca(GaMe4)2]n.

Dimethylcalcium synthesis cracked

Dimethylcalcium may sound like a simple compound, but its synthesis has eluded chemists. Researchers reported a synthesis 60 years ago, but no one has reproduced it, casting doubt on whether dimethylcalcium was actually made that first time. Now, Reiner Anwander and coworkers at Eberhard Karls University of Tubingen have succeeded in synthesizing dimethylcalcium via a metathesis reaction between methyllithium and calcium bis(trimethylsilyl)amide (J. Am. Chem. Soc. 2018, DOI: 10.1021/jacs.7b12984). A synthesis of methylcalcium compounds could lead to new catalysts or reagents for forming carbon-carbon bonds. “Although methylcalcium compounds have been discussed for more than a century, they’ve always been ill defined and probably impure,” says Michael S. Hill of the University of Bath. “The isolation and definitive characterization of these compounds is a real synthetic achievement, and the paper as a whole is a striking piece of work.” The hardest part of making dimethylcalcium turned out to be finding ap...

Friedel-Crafts alkylation of benzo[b]furan with activated cyclopropanes catalyzed by a calcium(II) complex

The synthesis of γ-benzo[b]furanyl malonates was achieved through the addition of benzo[b]furan to activated cyclopropanes. These Friedel-Crafts reactions were catalyzed by calcium bis(trifluoromethanesulfonimide), Ca(NTf2)2 with tetrabutylammonium hexafluorophosphine as a co-catalyst. The additions proceeded with complete regioselectivity and in good to excellent yield. Optimization of the reaction conditions and investigation into the scope of the methodology with regards to substitution on the cyclopropane are reported.

Heavy Grignard Reagents: Synthesis, Physical and Structural Properties, Chemical Behavior, and Reactivity.

The Grignard reaction offers a straight forward atom-economic synthesis of organomagnesium halides, which undergo redistribution reactions (Schlenk equilibrium) yielding diorganylmagnesium and magnesium dihalides. The homologous organocalcium complexes (heavy Grignard reagents) gained interest only quite recently owing to several reasons. The discrepancy between the inertness of this heavy alkaline earth metal and the enormous reactivity of its organometallics hampered a vast and timely development after the first investigation more than 100 years ago. In this overview the synthesis of organocalcium reagents is described as is the durability in ethereal solvents. Aryl-, alkenyl-, and alkylcalcium halides are prepared by direct synthesis. Characteristic structural features and NMR parameters are discussed. Ligand redistribution reactions can be performed by addition of potassium tert-butanolate to ethereal solutions of arylcalcium iodides yielding soluble diarylcalcium, whereas sparingly soluble potassium iodide and calcium bis(tert-butanolate) precipitate. Furthermore, reactivity studies with respect to metalation and addition to unsaturated organic compounds and metal-based Lewis acids, leading to the formation of heterobimetallic complexes, are presented.

Synthesis and Reactivity of Discrete Calcium Imides.

Protonolysis of dibenzylcalcium with triphenylsilylamine affords a thf-coordinated tetrametallic calcium imide with a heterocuboid core structure. The use of calcium bis(tetramethylaluminate) as a precursor for tandem salt metathesis/protonolysis reactions with alkali metal amides of 2,6-diisopropylaniline and triphenylsilylamine provides access to Lewis acid stabilized monocalcium imides of the type [(thf)4 Ca(μ2 -NR)(μ2 -Me)AlMe2 ]. Treatment of [(thf)4 Ca(μ2 -NSiPh3 )(μ2 -Me)AlMe2 ] with phenylsilane results in H-Si addition across the Ca-N imido bond, producing a homoleptic calcium amidoaluminate complex and putative CaH2 whereas reaction with phenylacetylene leads to protonation of an AlMe moiety to yield the dimeric complex [(thf)Ca{NSiPh3 }{AlMe2 (CCPh)}]2 .