Metals In Liquid Ammonia Research Articles

Potassium- and Lithium-Ammonia Intercalation into Excitonic Insulator Candidate Ta2NiSe5.

Two new reduced phases derived from the topical excitonic insulator candidate Ta2NiSe5 have been synthesized via the intercalation of lithium and potassium from solutions of the metals in liquid ammonia. Li(NH3)Ta2NiSe5 and KTa2NiSe5 both crystallize in orthorhombic space group Pmnb with the following lattice parameters: a = 3.5175(1) Å, b = 18.7828(7) Å, and c = 15.7520(3) Å and a = 3.50247(3) Å, b = 13.4053(4) Å, and c = 15.7396(2) Å, respectively. They have increased unit cell volumes of 48% and 31%, respectively, relative to that of Ta2NiSe5. Significant rearrangement of the transition metal selenide layers is observed in both intercalates compared to the parent phase. In Li(NH3)Ta2NiSe5, neutron diffraction experiments confirm the location of the light Li, N, and H atoms, and solid-state nuclear magnetic resonance (NMR) experiments show that H, N, and Li each occupy a single environment at ambient temperature on the NMR time scale. Magnetometry data show that both intercalates have increased magnetic susceptibilities relative to that of Ta2NiSe5, consistent with the injection of electrons during intercalation and an enhancement of the Pauli paramagnetism.

Synthesis and Derivatives of Beryllium Triflate.

Various pathways for the synthesis of beryllium triflate were investigated. The reaction of triflic acid or trimethylsilyl triflate with beryllium metal in liquid ammonia led to the formation of mono-, di-, and tetra-nuclear beryllium ammine complexes. Utilization of SMe2 as a solvent gave homoleptic Be(OTf)2. Various beryllium triflate complexes with N- and O-donor ligands as well as the complex anions [Be(OTf)4]2- and [Be2(OTf)6]2- were synthesized to evaluate the reactivity and solution properties of beryllium triflate. This showed that OTf- is not a weakly coordinating anion for Be2+ cations and that it exhibits good bridging properties.

Formation of amidoberyllates from beryllium and alkali metals in liquid ammonia

Abstract Beryllium metal was dissolved in liquid ammonia at ambient temperature through addition of alkali metals. Thereby, the amidoberyllates Cs[Be(NH2)3], [Na4 (NH2)2][Be(NH2)4] and K4[Be2O(NH2)4][Be(NH2)3]2 were isolated and structurally characterized via single crystal X-ray diffraction. In the case of Li we were able to synthesize Be(NH2)2 at ambient temperature. We present the first example of a [Be(NH2)4]2− anion as well as the first oxyamidoberyllate anion [Be2O(NH2)4]2−.

Safe and scalable electroreduction

When chemists at Pfizer examined routes to make anti-Parkinson’s drug candidate sumanirole at the kilogram scale, they saw only one option for the final step. They would need to do a Birch reduction—a reaction that involves using sodium or lithium metal in liquid ammonia. This was a reaction of last resort: It required cryogenic temperatures, custom equipment to deliver the lithium metal, and enough gaseous ammonia to fill three Boeing 747 airliners. When the leftover lithium was quenched, it generated 2,300 L of hydrogen gas. “They vowed never to do that again,” says Phil S. Baran, an organic chemist at Scripps Research. Having learned of Pfizer’s difficulty, Baran joined forces with University of Utah electrochemist Shelley D. Minteer and University of Minnesota computational chemist Matthew Neurock to lead a group that explored the possibility of doing the reduction electrochemically. Although there are many examples of electrochemical oxidations, reductions are rare.

Synthesis of K2Se solar cell dopant in liquid NH3 by solvated electron transfer to elemental selenium

This study explores the rich chemistry of elemental selenium reduction to monoselenide anions. The simplest possible homogeneous electron transfer occurs with free electrons, which is only possible in plasmas; however, alkali metals in liquid ammonia can supply unbound electrons at much lower temperatures, allowing in situ analysis. Here, solvated electrons reduce elemental selenium to K2Se, a compound relevant for alkali metal doping of Cu(In,Ga)Se2 solar cell material. It is proposed that the reaction follows pseudo first-order kinetics with an inner-sphere or outer-sphere oxidation semi reaction mechanism depending on the concentration of solvated electrons.

The Decomposition Products of Sulfur Hexafluoride (SF6) with Metals Dissolved in Liquid Ammonia

Sulfur hexafluoride is a highly chemically inert gas with several important industrial applications. It is stable against fused alkali, oxygen and ammonia, even at several hundred degrees Celsius. In this work, the reactions between metals (Li–Cs, Sr, Ba, Eu, Yb) dissolved in liquid ammonia and SF6 are reported, leading to mono- or bivalent fluorides and sulfides. To this end, SF6 was passed into a cooled solution of the respective metal in liquid ammonia. The identity of the products was confirmed by powder X-ray diffraction and IR spectroscopy. The reactions could lead to a cheap and effective disposal method of the present amounts of stored SF6, for possible generation of H2S and HF.

ChemInform Abstract: Preparation of Vinylcyclopropanes by Sodium Mediated Reductive Isomerization of Methylenecyclopropanes.

We disclosed therein a new reaction of reductive isomerization of methylenecyclopropanes (MCPs) to vinylcyclopropanes (VCPs). On treatment with sodium metal in liquid ammonia, MCPs bearing a C–O bond at allylic position undergo both a reductive cleavage of the C–O bond and an isomerization of the C–C double bond giving rise to VCPs. The scope of the reductive isomerization was investigated and showed a broad applicability since various functional groups are tolerated. MCP substrates were straightforwardly prepared by a palladium-promoted [2 + 1] cycloaddition between norbornene derivatives with alkynes.

Preparation of Vinylcyclopropanes by Sodium Mediated Reductive Isomerization of Methylenecyclopropanes.

We disclosed therein a new reaction of reductive isomerization of methylenecyclopropanes (MCPs) to vinylcyclopropanes (VCPs). On treatment with sodium metal in liquid ammonia, MCPs bearing a C-O bond at allylic position undergo both a reductive cleavage of the C-O bond and an isomerization of the C-C double bond giving rise to VCPs. The scope of the reductive isomerization was investigated and showed a broad applicability since various functional groups are tolerated. MCP substrates were straightforwardly prepared by a palladium-promoted [2 + 1] cycloaddition between norbornene derivatives with alkynes.

Convenient access to the tricyanoborate dianion B(CN)₃²⁻ and selected reactions as a boron-centred nucleophile.

Alkali metal tricyanoborates M2B(CN)3 (M = Na, K) are accessible by the reaction of tricyanofluoroborates with alkali metals (i) in liquid NH3 or (ii) in THF-naphthalene. The M2B(CN)3 are versatile starting materials for the synthesis of K[RB(CN)3] (R = Et, C6F5, CH2=CHCH2).

Mechanisms of Two Reduction Reactions under the Condition of Alkali Metal in Liquid Ammonia

Mechanisms of Two Reduction Reactions under the Condition of Alkali Metal in Liquid Ammonia

Ultrafast Dynamics of Electrons in Ammonia

Solvated electrons were first discovered in solutions of metals in liquid ammonia. The physical and chemical properties of these species have been studied extensively for many decades using an arsenal of electrochemical, spectroscopic, and theoretical techniques. Yet, in contrast to their hydrated counterpart, the ultrafast dynamics of ammoniated electrons remained completely unexplored until quite recently. Femtosecond pump-probe spectroscopy on metal-ammonia solutions and femtosecond multiphoton ionization spectroscopy on the neat ammonia solvent have provided new insights into the optical properties and the reactivities of this fascinating species. This article reviews the nature of the optical transition, which gives the metal-ammonia solutions their characteristic blue appearance, in terms of ultrafast relaxation processes involving bound and continuum excited states. The recombination processes following the injection of an electron via photoionization of the solvent are discussed in the context of the electronic structure of the liquid and the anionic defect associated with the solvated electron.

The First Structurally Characterized Salts of Deprotonated Urea: M(CN2H3O) with M = Na, K, Rb, and Cs

AbstractThe ureates of the alkali metals Na – Cs were synthesized from urea and the metals in liquid ammonia at temperatures below 50 °C. The crystal structures were determined using single‐crystal X‐ray diffraction. NaCN2H3O crystallizes in the monoclinic system [P21/c, Z = 16, a = 17.529(1) Å, b = 6.4784(5) Å, c = 10.8211(9) Å, β = 96.938(1)°]. All other ureates are orthorhombic, with KCN2H3O and RbCN2H3O being isotypic [Pbca, Z = 8, KCN2H3O: a = 7.102(4) Å, b = 7.221(4) Å, c = 13.533(8) Å; RbCN2H3O: a = 7.1973(8) Å, b = 7.3531(8) Å, c = 13.921(2) Å]. CsCN2H3O adopts a smaller unit cell [P212121, Z = 4, a = 6.3520(3) Å, b = 7.1645(4) Å, c = 9.0911(5) Å]. The ureates of K, Rb, and Cs contain hydrogen‐bond networks, the imino nitrogen atom acting as the hydrogen‐bond acceptor in CsCN2H3O. In KCN2H3O and RbCN2H3O, however, the carbonyl oxygen atom accepts the hydrogen bonds.

Synthesis of cyclohexa-1,4-dienephosphonoyl dichlorides

1,4-Cyclohexadiene and similar hydrocarbons can be prepared via the Birch reduction of aromatic hydrocarbons with metals in liquid ammonia [3]. However, this approach is limitedly applicable in the cases of functionalized derivatives. One of the convenient methods to prepare 1,4-cyclohexadiene derivatives is cycloaddition of conjugated dienes to the acetylenes containing acceptor substituents (the Diels–Alder reaction). The Diels–Alder reaction of dimethyl chloroacetylenephosphonate and tetramethyl acetylenediphosphonate with some dienes leads to formation of the phosphorus-containing 1,4-cyclohexadiene derivatives [4–6].

Reductive Deoxygenation of Alcohols: Catalytic Methods Beyond Barton–McCombie Deoxygenation

AbstractDeoxygenation is an extensively studied field in organic chemistry, and over the last decades many methods such as the Barton–McCombie deoxygenation reaction or deoxygenation with alkali metals in liquid ammonia have been established. Within this microreview, we discuss different strategies for the chemoselective catalytic deoxygenation of alcohols with special attention to their scope and limitations. The deoxygenation of derivatives of alcohols and their direct deoxygenation as step‐economic alternative are covered with current examples. Catalytic methods can serve as convenient and economic alternatives for established methods in the reduction of carbon–oxygen single bonds.

Solvothermal Synthesis, Crystal Growth, and Structure Determination of Sodium and Potassium Guanidinate

Phase-pure NaCN(3)H(4) and KCN(3)H(4) were synthesized from molecular guanidine and elemental metal in liquid ammonia at room temperature and elevated pressure close to 10 atm. The crystal structures were determined at 100 K using single-crystal X-ray diffraction. Both compounds crystallize in the monoclinic system (P2(1)/c, No. 14) but are far from being isotypical. NaCN(3)H(4) (a = 7.9496(12) Å, b = 5.0328(8) Å, c = 9.3591(15) Å, β = 110.797(3)°, Z = 4) contains a tetrahedrally N-coordinated sodium cation while KCN(3)H(4) (a = 7.1200(9) Å, b = 6.9385(9) Å, c = 30.404(4) Å, β = 94.626(2)°, Z = 16) features a very large c axis and a rather complicated packing of irregularly N-coordinated potassium cations. In the crystal structures, the guanidinate anions resemble the motif known from RbCN(3)H(4), that is, with one elongated C-((amino))N single bond and two shorter C-((imino))N bonds (bond order = 1.5) although the orientation of one N-H bond differs in the guanidinate anion of NaCN(3)H(4). Both crystal structures and infrared spectroscopy evidence the presence of hydrogen-bridging bonds, and the vibrational properties were analyzed by ab initio phonon calculations.

In Situ Dearomatisation/Alkylation of Arylphosphane Derivatives (Eur. J. Org. Chem. 13/2012)

AbstractThe cover picture shows the in situ dearomatisation/alkylation of the aryl substituent in aryldialkylphosphane–borane by a solution of alkali metal in liquid ammonia and alkyl halide. This leads to the formation of α‐substituted (1,4‐cyclohexadien‐3‐yl)phosphane–borane where the “unreactive” phenyl substituent is replaced by a cyclohexadienyl fragment possessing a functionality in the α‐position. This reaction sequence can be regarded as a versatile tool in the “activation” of the aryl substituent in organophosphorus compounds both through aromaticity breaking and introduction of new functionalities at the quaternary α‐carbon atom. Details are discussed in the article by M. Stankevič et al. on p. 2521 ff. The authors would like to express their gratitude to Katarzyna Jaklińska for her efforts during the preparation of the cover picture. magnified image

Evolution of a strongly correlated liquid with electronic density

Systems created by dissolving elemental metals in liquid ammonia are strongly correlated liquid metals where the electronic correlation strength can be easily changed by altering the electronic density. We study the plasmon in the lithium ammonia system as a function of electronic density using nonresonant inelastic x-ray scattering and use this to determine the long wavelength plasmon energy ${E}_{0}$ and the plasmon dispersion $\ensuremath{\alpha}$ as a function of electronic density. These parameters show the increasing influence of electronic correlations as we go to lower concentrations. The plasmon width is found to increase as we go to lower concentration. The implications of these results are discussed.

Evidence for ammonia solvated electrons stabilized at the surface of magnesium oxide

We report on the magnetic properties of solvated electrons localized at the surface of magnesium oxide and obtained by reaction of ammonia with surface excess electrons. Excess electrons can be stabilized at the surface of insulating ionic oxides by strong local potentials of positive and negative ions in particular arrays and in some circumstances by single cations. Exposure of these centres to NH3 leads to ammoniated electrons analogous to those obtained by dissolution of alkali metals in liquid ammonia.

On the Mechanisms of Electride Induced Synthesis of Ytterbium Carbazolates, Formation of Coordination Polymers by Condensation and Polymer Degradation by Chemical Scissors

AbstractDissolution of ytterbium metal in liquid ammonia in the presence of carbazole at low temperatures and subsequent treatment with N‐phenylpiperazine gives single crystalline [Yb(Cbz)2(NH3)4] · 3Phpip (Cbz− = carbazolate anion, C12H8N−, Phpip = N‐phenylpiperazine, (C6H5)C4H8NNH). The highly air and moisture sensitive crystals are prone to release ammonia but can be successfully shielded in the interior of large crystals of CbzH · Phpip, a co‐crystallization of both ligands, whose crystal structure is also presented. Further heating transforms the monomeric molecules [Yb(Cbz)2(NH3)4] into dimeric [Yb2(Cbz)4(NH2)2(NH3)4] · 3CbzH and their condensation accompanied by release of ammonia consequently leads to the coordination polymer $^{1}_{\infty}\rm [Yb_{2}(Cbz)_{4}]$. This reaction path is compared to a high temperature reaction route without electride formation. Synthesis in molten carbazole directly leads to the one‐dimensional coordination polymer. Subsequent treatment with N‐phenylpiperazine yields dimeric [Yb2(Cbz)4(Phpip)4] · 2Phpip and monomeric [Yb(Cbz)2(Phpip)3][Yb(Cbz)3(Phpip)2], the final step of the degradation reaction. It can be shown that N‐phenylpiperazine functions as chemical scissors at higher temperatures and as crystallization matrix at lower temperatures.

Reductive Activation of Arenes. Part 21. Reaction of Products of Two‐Electron Reduction of Arenecarbonitriles by Alkali Metals in Liquid Ammonia with Bromo‐ and Dibromoalkanes.

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