Lithium Amide Research Articles

Lithium Amide Protected against Hydrolysis by Aggregated Lithium Halides: An MS + DFT Investigation.

Supported by mass spectrometry experiments, DFT computations indicate that the lithium amide of a 3-aminopyrrolidine (lithium benzhydryl(1-benzylpyrrolidin-3-yl)amide, 1-Li) is protected, up to a certain limit, against hydrolysis when it is aggregated with a strongly polar partner such as LiCl, LiBr, or MeLi.

Lithium Hydrazinidoborane Ammoniate LiN₂H₃BH₃·0.25NH₃, a Derivative of Hydrazine Borane.

Boron- and nitrogen-based materials have shown to be attractive for solid-state chemical hydrogen storage owing to gravimetric hydrogen densities higher than 10 wt% H. Herein, we report a new derivative of hydrazine borane N2H4BH3, namely lithium hydrazinidoborane ammoniate LiN2H3BH3·0.25NH3. It is easily obtained in ambient conditions by ball-milling N2H4BH3 and lithium amide LiNH2 taken in equimolar amounts. Both compounds react without loss of any H atoms. The molecular and crystallographic structures of our new compound have been confirmed by NMR/FTIR spectroscopy and powder X-ray diffraction. The complexation of the entity LiN2H3BH3 by some NH3 has been also established by thermogravimetric and calorimetric analyses. In our conditions, LiN2H3BH3·0.25NH3 has been shown to be able to release H2 at temperatures lower than the parent N2H4BH3 or the counterpart LiN2H3BH3. It also liberates non-negligible amounts of NH3 at temperatures lower than 100 °C. This is actually quite detrimental for chemical H storage, but alternatively LiN2H3BH3·0.25NH3 might be seen as a potential NH3 carrier.

Asymmetric Synthesis of the Tetraponerine Alkaloids.

The asymmetric syntheses of all eight tetraponerine alkaloids (T1-T8) were achieved using the diastereoselective conjugate additions of lithium amide reagents in the key stereodefining steps. Conjugate addition of either lithium (R)-N-allyl-N-(α-methylbenzyl)amide or lithium (R)-N-(but-3-en-1-yl)-N-(α-methylbenzyl)amide to tert-butyl sorbate was followed by ring-closing metathesis of the resultant N-alkenyl β-amino esters, reduction to the corresponding aldehydes, and reaction with tert-butyl (triphenylphosphoranylidene)acetate. Subsequent conjugate addition of the requisite antipode of lithium N-benzyl-N-(α-methylbenzyl)amide to the resultant α,β-unsaturated esters gave a range of diamines for elaboration to T1-T8 via a sequence involving reduction of the ester moiety to give the corresponding aldehyde, olefination, tandem hydrogenation/hydrogenolysis, and cyclization upon reaction with 4-bromobutanal to give the tricyclic skeleton.

Structural Insights into the Lithium Amide-Imide Solid Solution

Solid solutions of lithium amide (LiNH2) and lithium imide (Li2NH) are present during ammonia decomposition catalysis by lithium imide and hydrogen storage and release reactions in the lithium amide–lithium hydride composite. As such, they are important materials in facilitating the use of hydrogen as a sustainable energy store. In order to understand the properties of these solutions, a series of samples spanning the full stoichiometry range of the solid solution between lithium amide and lithium imide were synthesized. Powder diffraction measurements showed that a nonstoichiometric cubic phase isostructural to the high-temperature phase of lithium imide was observed in all of the samples. In average stoichiometry values close to lithium amide, incomplete formation of a solid solution was observed, with tetragonal lithium amide observed in addition to the cubic nonstoichiometric phase. In analysis of neutron diffraction data, the variable stoichiometry in the structure was modeled using a “golf-ball” of scattering density around the nitrogen atom. This analysis revealed a greater degree of disorder in hydrogen distribution in the nonstoichiometric samples compared with lithium imide. Raman spectroscopy indicated that amide and imide groups in stoichiometric and nonstoichiometric environments can be differentiated by the frequency of the N–H stretch, with distinct bands observed for both amide and imide N–H stretches in both environments.

The Complexation between Amide Groups of Polyamide‐6 and Polysulfides in the Lithium–Sulfur Battery

Lithium–sulfur batteries have attracted considerable attention due to its high theoretical specific capacity, low cost, environmental friendliness, etc. However, the dissolution of polysulfide intermediate in the electrolyte leads to rapid capacity decay in the charge–discharge process. A sulfur‐based cathode with the specific discharge capacity of 630 mAh g−1 and ultrahigh capacity retention ratio of 0.11% per cycle after 400 cycles at 0.5 C that simply blend the sublimed sulfur and acetylene black in the mortar with the polyamide‐6 (PA6) as binder is reported. The intense complexation between the lithium polysulfide and amide groups (CONH) in PA6 can effectively inhibit the “shuttling effect” and reduce the loss of active materials during the charge–discharge process. The discovery provides a handy and practicable strategy for developing the excellent cycling stability lithium–sulfur batteries. image

Trans-Metal-Trapping Meets Frustrated-Lewis-Pair Chemistry: Ga(CH2SiMe3)3-Induced C-H Functionalizations.

Merging two topical themes in main-group chemistry, namely, cooperative bimetallics and frustrated-Lewis-pair (FLP) activity, this Forum Article focuses on the cooperativity-induced outcomes observed when the tris(alkyl)gallium compound GaR3 (R = CH2SiMe3) is paired with the lithium amide LiTMP (TMP = 2,2,6,6-tetramethylpiperidide) or the sterically hindered N-heterocyclic carbene (NHC) 1,3-bis(tert-butyl)imidazol-2-ylidene (ItBu). When some previously published work are drawn together with new results, unique tandem reactivities are presented that are driven by the steric mismatch between the individual reagents of these multicomponent reagents. Thus, the LiTMP/GaR3 combination, which on its own fails to form a cocomplex, functions as a highly regioselective base (LiTMP)/trap (GaR3) partnership for the metalation of N-heterocycles such as diazines, 1,3-benzoazoles, and 2-picolines in a trans-metal-trapping (TMT) process that stabilizes the emerging sensitive carbanions. Taking advantage of related steric incompatibility, a novel monometallic FLP system pairing GaR3 with ItBu has been developed for the activation of carbonyl compounds (via C=O insertion) and other molecules with acidic hydrogen atoms such as phenol and phenylacetylene. Shedding new light on how these non-cocomplexing partnerships operate and showcasing the potential of gallium reagents to engage in metalation reactions or FLP activations, areas where the use of this group 13 metal is scant, this Forum Article aims to stimulate more interest and activity toward the advancement of organogallium chemistry.

Lithium imide systems for high temperature heat storage in concentrated solar thermal systems

Hydrogen is touted as one of the solutions for future energy requirements. Metal hydrides typically studied for their high hydrogen capacity can be used as a thermal storage system by taking advantage of their endothermic/exothermic reactions with hydrogen. This allows the harnessing of solar energy by utilising thermal storage to alleviate its intermittent nature. Lithium amide (LiNH2), imides (Li2NH) and nitrides (Li3N) have been widely studied for their hydrogen storage at relatively low operating temperatures, typically suited for mobile applications. However, little work has been done involving the imide to nitride reaction of lithium-based materials due to their high temperature range. The following techniques were used to characterise this system: temperature programmed desorption (TPD), temperature programmed photographic analysis (TPPA), x-ray diffraction (XRD) and pressure-composition-temperature (PCT) measurements. TPD results revealed that only a single-step reaction occurred between 100 and 600 °C. TPPA revealed that having a molten solid solution of the sample, depreciated the reversibility of hydrogen absorption and desorption. The molten sample behaved quite vigorously in TPPA measurements and consequently blocked sample filters and sintering sample cell walls; creating engineering problems at higher temperatures. The results revealed that for reactions involving Li2NH and lithium hydride (LiH), the temperature range required for thermal storage is above the melting point of the system. The diffusion and absorption of hydrogen through stainless steel would also occur in the sample cells used, resulting in further problems. The reaction pathway of Li2NH and LiH was also found to be far more complex than generally reported: XRD revealed that the expected final product of Li3N could not be identified, instead a lithium imide-nitride hydride phase (Li4‑2xN1‑xH1‑x(NH)x) was identified as the final product of this system. PCT measurements were conducted to identify the kinetic and thermodynamics of this system, but because of the molten solid-solution problem, an accurate result could not be obtained.

Synthesis and Reactivity of 1-Allenyltriazenes

1-Aryl-3,3-dialkyltriazenes have received considerable attention in the context of synthetic and medicinal chemistry. In contrast, the chemistry of other unsaturated triazenes is largely unexplored. The synthesis of 1-allenyltriazenes is described. This new class of compounds can be obtained by base-induced isomerization of 1-alkynyltriazenes. The latter are accessible by reaction of alkynyl Grignard reagents with lithium amides and nitrous oxide. 1-Allenyltriazenes were found to be thermally labile, but they can be stored without degradation at lower temperatures. In the presence of ZnCl2, 1-allenyltriazenes rearrange into N-aminopyrazoles.

Novel and practical asymmetric synthesis of β2,3-amino esters using asymmetric Michael addition of chiral amine

A practical method for the synthesis of chiral β2,3-amino esters having various substituents was developed, which is characterized by an asymmetric Michael addition reaction of a chiral lithium amide with trisubstituted (E)-α,β-unsaturated esters. We found that a highly face-selective protonation occurred by the quick addition of water to the enolate intermediate derived from the Michael addition reaction to afford N-protected β2,3-amino esters in moderate to excellent yields. This finding was made possible by the facile preparation of geometrically pure trisubstituted (E)-α,β-unsaturated esters, which was established recently by our group. The subsequent deprotection of the amino group in the Michael adduct by using N-iodosuccinimide (NIS) efficiently provided β2,3-amino esters having various substituents.

Molecular design of melt-spinnable co-polymers as Si-B-C-N fiber precursors.

Two series of co-polymers with the general formula [B(C2H4SiCH3(NH)x(NCH3)y)3]n, i.e., composed of C2H4SiCH3(NH)x and C2H4SiCH3(NCH3)y (C2H4 = CHCH3, CH2CH2) building blocks in a well defined x : y ratio, have been synthesized by hydroboration of dichloromethylvinylsilane with borane dimethyl sulfide followed by successive reactions with lithium amide and methylamine according to controlled ratios. The role of the chemistry behind their syntheses has been studied in detail by solid-state NMR, FT-IR and elemental analyses. Then, the intimate relationship between the chemistry and the melt-spinnability of these polymers was discussed. By keeping x = 0.50 and increasing y above 0.50, i.e., obtaining methylamine excess, the co-polymers contained more ending groups and especially more tetracoordinated boron, thus allowing tuning very precisely the chemical structure of the preceramic polymer in order to meet the requirements for melt-spinning. The curing treatment under ammonia at 200 °C efficiently rendered the green fibers infusible before their subsequent pyrolysis under nitrogen at 1000 °C to generate Si-B-C-N ceramic fibers. Interestingly, it could be possible to produce also low diameter hollow fibers with relatively high mechanical properties for a further exploration as membrane materials.

Synthesis of GaN crystals through the reaction of gallium with lithium amide

Synthesis of GaN crystals through the reaction of gallium with lithium amide

Lithium Enolates in the Enantioselective Construction of Tetrasubstituted Carbon Centers with Chiral Lithium Amides as Noncovalent Stereodirecting Auxiliaries.

Lithium enolates derived from carboxylic acids are ubiquitous intermediates in organic synthesis. Asymmetric transformations with these intermediates, a central goal of organic synthesis, are typically carried out with covalently attached chiral auxiliaries. An alternative approach is to utilize chiral reagents that form discrete, well-defined aggregates with lithium enolates, providing a chiral environment conducive of asymmetric bond formation. These reagents effectively act as noncovalent, or traceless, chiral auxiliaries. Lithium amides are an obvious choice for such reagents as they are known to form mixed aggregates with lithium enolates. We demonstrate here that mixed aggregates can effect highly enantioselective transformations of lithium enolates in several classes of reactions, most notably in transformations forming tetrasubstituted and quaternary carbon centers. Easy recovery of the chiral reagent by aqueous extraction is another practical advantage of this one-step protocol. Crystallographic, spectroscopic, and computational studies of the central reactive aggregate, which provide insight into the origins of selectivity, are also reported.

Chiral Lithium Amides: Tuning Asymmetric Synthesis on the Basis of Structural Parameters.

An overview on the structural arrangements adopted by Chiral Lithium Amides (CLAs), alone or in mixed complexes, is presented. These species are important reagents for asymmetric synthesis and understanding their organization is essential to improve their design and the reaction conditions.

Two-Peak Mystery of LiNH2–NaH Dehydrogenation Is Solved? A Study of the Analogous Sodium Amide/Lithium Hydride System

Alkali metal amide and imide systems especially NaNH2 and Li2NH have recently been proposed as a catalyst for NH3 cracking. This finding ignites the interest of researchers worldwide to study amide–imide/amide–hydride systems. Although these systems have shown catalytic properties toward NH3 cracking and have also been proposed as a hydrogen storage material, the decomposition mechanism of sodium amide is still unclear due to the complexity and low melting point of NaNH2. Herein, pure NaNH2 and its composite with lithium hydride as well as sodium hydride in a molar ratio 1:1 has been investigated, and a detailed mechanism associated with their decomposition has been suggested. The sodium amide–lithium hydride system is found to be analogous to lithium amide–sodium hydride. It desorbs 4 wt % H2 through cation exchange in a temperature range of 25–200 °C followed by NH3 mediated reaction in the temperature range 200–400 °C. The desorbed product can be rehydrogenated at around 200 °C under 2.0 MPa. An import...

Structure of non-symmetric lithium amidinate complexes prepared by addition of lithium amides to various nitriles

Lithium amidinate complexes were prepared by direct reactions from various nitriles - R1-CN (R = Ph, n-Bu, t-Bu) and trimethylsilyl-substituted lithium amides - R2(Me3Si)NLi (R2 = Ph, 2,6-(CH3)2C6H3 (Dmp) and 2,6-[(CH3)2CH]2C6H3 (Dipp)). All the reactions proceed only in coordinating solvents as diethylether or THF where the migration of the trimethylsilyl group to the nitrogen atom of the parent nitrile is favoured. In the case of t-BuCN, virtually no conversion to appropriate lithium amidinate was observed under the same reaction protocol. Only the adduct of the composition {(t-BuCN){2,6-[(CH3)2CH]2C6H3}(Me3Si)NLi]}2 was isolated from the reaction of t-BuCN with {2,6-[(CH3)2CH]2C6H3}(Me3Si)NLi]} carried out in hexane or toluene solution. Lithium atoms in this adduct appear in trigonal planar to pyramidal coordination neighborhoods. The structure of lithium amidinates in the solid state is strongly dependent on the substitution pattern, when the Dipp substituent is present, complexes always crystallize as mononuclear species with isobidentate bonding fashion of the amidinate and two molecules of solvent being extra-coordinated to the lithium atom. On contrary, smaller peripheral groups do not protect the lithium atom from further association and those complexes are described as di- or trinuclear adducts with less than two coordinated molecules of solvent per lithium atom. In all lithium amidinates prepared, the central lithium atom has distorted tetrahedral coordination geometry with ligands going from anisobidenate or bidentate-bridging to tridentate bonding fashion except the trinuclear complex bearing the smallest combination of ligands where one of the lithium atoms is found in the trigonal planar vicinity.

Structural Diversity in Alkali Metal and Alkali Metal Magnesiate Chemistry of the Bulky 2,6-Diisopropyl-N-(trimethylsilyl)anilino Ligand.

Bulky amido ligands are precious in s‐block chemistry, since they can implant complementary strong basic and weak nucleophilic properties within compounds. Recent work has shown the pivotal importance of the base structure with enhancement of basicity and extraordinary regioselectivities possible for cyclic alkali metal magnesiates containing mixed n‐butyl/amido ligand sets. This work advances alkali metal and alkali metal magnesiate chemistry of the bulky arylsilyl amido ligand [N(SiMe3)(Dipp)]− (Dipp=2,6‐iPr2‐C6H3). Infinite chain structures of the parent sodium and potassium amides are disclosed, adding to the few known crystallographically characterised unsolvated s‐block metal amides. Solvation by N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) or N,N,N′,N′‐tetramethylethylenediamine (TMEDA) gives molecular variants of the lithium and sodium amides; whereas for potassium, PMDETA gives a molecular structure, TMEDA affords a novel, hemi‐solvated infinite chain. Crystal structures of the first magnesiate examples of this amide in [MMg{N(SiMe3)(Dipp)}2(μ‐nBu)]∞ (M=Na or K) are also revealed, though these breakdown to their homometallic components in donor solvents as revealed through NMR and DOSY studies.

ChemInform Abstract: Enantioselective Synthesis of Silacyclopentanes.

AbstractFunctionalized silacyclopentanes are synthesized by enantioselective β‐elimination of silacyclopentene oxides and subsequent stereospecific transformations using a newly developed chiral lithium amide.

N,2,3,4‐Tetrasubstituted Pyrrolidines through Tandem Lithium Amide Conjugate Addition/Radical Cyclization/Oxygenation Reactions

Enantioselective syntheses of densely functionalized pyrrolidines deriving their chirality from (R)‐1‐(phenyl)ethylamine are reported. Allylic amines and β‐substituted‐α,β‐unsaturated esters are used as the building blocks in this one‐pot reaction. Single electron transfer (SET) oxidation served to merge the reactivities of anionic enolate and radical intermediates. Ferrocenium hexafluorophosphate, which is easy to prepare, store and handle, was applied as SET oxidant and persistent free radical TEMPO served as the oxygenating agent introducing a protected hydroxy function, which proved to be beneficial for further derivatization. Exclusive 2,3‐trans and up to 6:1 3,4‐cis/trans diastereoselectivities were achieved in the targeted tetrasubstituted pyrrolidines.

Hydrogenation Reaction Pathways in the Systems Li3N–H2, Li3N–Mg–H2, and Li3N–MgH2–H2 by in Situ X-ray Diffraction, in Situ Neutron Diffraction, and in Situ Thermal Analysis

The phase diagram Li–Mg–N–H offers ample opportunities for potential hydrogen storage systems. Three systems based on lithium nitride, Li3N, were investigated by time-resolved in situ methods (thermal analysis, X-ray and neutron diffraction) at temperatures up to 703 K and hydrogen gas pressures up to 9.4 MPa. Pure lithium nitride reacts in a one-step reaction to lithium amide according to Li3N + 2H2 → LiNH2 + 2LiH at 1.0 MPa hydrogen pressure. Equimolar mixtures of lithium nitride with magnesium hydride, both at 1.5 and 9.4 MPa hydrogen gas pressure, react in the same way up to 543 K, i.e., magnesium hydride does not participate in the reaction. At higher temperatures, lithium magnesium nitride is formed according to the endothermic reaction LiNH2 + MgH2 → LiMgN + 2H2 at moderate (≤1.5 MPa) and via the exothermic reaction Li3N + MgH2 → LiMgN + 2LiH at higher hydrogen gas pressures (5.0 MPa). Mixed imide Li2Mg(NH)2 is formed when an excess of Li3N is used in the reaction. The hydrogenation of mixtures of ...

Asymmetric syntheses of (−)-hastanecine, (−)-turneforcidine and (−)-platynecine

Concise total asymmetric syntheses of three diastereoisomeric 1-hydroxymethyl-7-hydroxy substituted pyrrolizidines, (−)-hastanecine, (−)-turneforcidine and (−)-platynecine, are reported. The doubly diastereoselective conjugate additions of lithium (R)- or (S)-N-benzyl-N-(α-methylbenzyl)amide to tert-butyl (R,E)-4-(triethylsilyloxy)hepta-2,6-dienoate [which was prepared (in 96:4 e.r.) via Lewis acid mediated catalytic asymmetric allylation of tert-butyl (E)-4-oxobut-2-enoate] proceeded in both cases under the dominant control of the lithium amide reagent. Subsequent diastereoselective enolate allylations installed the required stereogenic centres, and the pyrrolizidine ring system was rapidly accessed by a two-step protocol (viz. ozonolysis and one-pot hydrogenolysis/double reductive cyclisation), to complete the asymmetric syntheses of (−)-hastanecine, (−)-turneforcidine and (−)-platynecine in 17, 8 and 24% overall yield, respectively, in eleven steps from commercially available 2,2-dimethoxyacetaldehyde in each case.