Mild and efficient Pd(PtBu3)2‐catalyzed aminocarbonylation of aryl halides to aryl amides with high selectivity

This work describes a mild and efficient approach for the synthesis of aryl amides via catalytic aminocarbonylation of aryl halides with alicyclic amines using a Pd(P^t Bu₃)₂/NH₄Cl catalyst system. Under mild reaction temperature of 60°C and balloon pressure of CO, 5 mol% Pd(P^t Bu₃)₂ with a cheap NH₄Cl promoter is sufficient for high yields of aryl amides. The influence of reaction parameters such as reaction temperature, ligand type and promoter on catalytic activity was investigated. This work also discusses the catalytic intermediates in detail, and provides a plausible mechanism based on an acid chloride intermediate.     

The Formation of Surface Lithium–Iron Ternary Hydride and its Function on Catalytic Ammonia Synthesis at Low Temperatures

Lithium hydride (LiH) has a strong effect on iron leading to an approximately 3 orders of magnitude increase in catalytic ammonia synthesis. The existence of lithium–iron ternary hydride species at the surface/interface of the catalyst were identified and characterized for the first time by gas-phase optical spectroscopy coupled with mass spectrometry and quantum chemical calculations. The ternary hydride species may serve as centers that readily activate and hydrogenate dinitrogen, forming Fe-(NH₂)-Li and LiNH₂ moieties—possibly through a redox reaction of dinitrogen and hydridic hydrogen (LiH) that is mediated by iron—showing distinct differences from ammonia formation mediated by conventional iron or ruthenium-based catalysts. Hydrogen-associated activation and conversion of dinitrogen are discussed.     

The Formation of Surface Lithium–Iron Ternary Hydride and its Function on Catalytic Ammonia Synthesis at Low Temperatures

Lithium hydride (LiH) has a strong effect on iron leading to an approximately 3 orders of magnitude increase in catalytic ammonia synthesis. The existence of lithium–iron ternary hydride species at the surface/interface of the catalyst were identified and characterized for the first time by gas‐phase optical spectroscopy coupled with mass spectrometry and quantum chemical calculations. The ternary hydride species may serve as centers that readily activate and hydrogenate dinitrogen, forming Fe‐(NH₂)‐Li and LiNH₂ moieties—possibly through a redox reaction of dinitrogen and hydridic hydrogen (LiH) that is mediated by iron—showing distinct differences from ammonia formation mediated by conventional iron or ruthenium‐based catalysts. Hydrogen‐associated activation and conversion of dinitrogen are discussed.     

Schichtenweise Substitution von Kationen im Lithiumamid: Kaliumtrilithiumamid,KLi3(NH2)4 und Kaliumheptalithiumamid,KLi7(NH2)8

Substitution in Layers of Cations in Lithium Amide: Potassium Trilithium Amide, KLi₃(NH₂)₄, and Potassium Heptalithium Amide, KLi₇(NH₂)₈ Four ternary amides were characterized in the system KNH₂/LiNH₂ by x-ray techniques: K₂Li(NH₂)₃ (dimorphous), KLi(NH₂)₂, KLi₃(NH₂)₄, and KLi₇(NH₂)₈. The compounds were prepared by the reaction of ammonia with the metals in high-pressure autoclaves. The atomic arrangements of the potassium-poor amides, KLi₃(NH₂)₄, and KLi₇(NH₂)₈ which have been investigated by x-ray single crystal analysis are discussed: Layers of edge sharing aniontetrahedra occupied to three quarters by lithium are the dominating structural feature. These layers ? [Li₃(NH₂)₄^?] — are primitively stacked in such a manner that potassium occupies quadratic prismatic sites. In KLi₇(NH₂)₈ the layers are connected alternatively by lithium in tetrahedral sites and potassium in an eightfold coordination. The ordered distribution of the cations is controlled by the orientation of amide ions. KLi₃(NH₂)₄ can structure-geometricly be considered as a further example of an “ordered defect structure” of the ThCr₂Si₂ type structure.     

Self‐organized Ruthenium–Barium Core–Shell Nanoparticles on a Mesoporous Calcium Amide Matrix for Efficient Low‐Temperature Ammonia Synthesis

A low‐temperature ammonia synthesis process is required for on‐site synthesis. Barium‐doped calcium amide (Ba‐Ca(NH₂)₂) enhances the efficacy of ammonia synthesis mediated by Ru and Co by 2 orders of magnitude more than that of a conventional Ru catalyst at temperatures below 300 °C. Furthermore, the presented catalysts are superior to the wüstite‐based Fe catalyst, which is known as a highly active industrial catalyst at low temperatures and pressures. Nanosized Ru–Ba core–shell structures are self‐organized on the Ba‐Ca(NH₂)₂ support during H₂ pretreatment, and the support material is simultaneously converted into a mesoporous structure with a high surface area (>100 m² g⁻¹). These self‐organized nanostructures account for the high catalytic performance in low‐temperature ammonia synthesis.     

Reaction Pathways Determined by Mechanical Milling Process for Dehydrogenation/Hydrogenation of the LiNH2/MgH2 System

The dehydrogenation/hydrogenation processes of the LiNH₂/MgH₂ (1:1) system were systematically investigated with respect to balller milling and the subsequent heating process. The reaction pathways for hydrogen desorption/absorption of the LiNH₂/MgH₂ (1:1) system were found to depend strongly on the milling duration due to the presence of two competing reactions in different stages (i.e., the reaction between Mg(NH₂)₂ and MgH₂ and that between Mg(NH₂)₂ and LiH), caused by a metathesis reaction between LiNH₂ and MgH₂, which exhibits more the nature of solid–solid reactions. The study provides us with a new approach for the design of novel hydrogen storage systems and the improvement of hydrogen‐storage performance of the amide/hydride systems.     

Wasserstoffbrückenbindungen in den Monoammoniakaten von Kalium‐ und Caesiumamid

Hydrogen Bonds in the Monoammoniates of Potassium and Cesium Amide X‐ray structure determination was carried out on the monoammoniates of potassium and cesium amide. Crystals of KNH₂ · NH₃ were grown from liquid NH₃ at 50 °C > T > 20 °C. They crystallize in the cold part of a pressure resistant glass apparatus. Single crystals of CsNH₂ · NH₃ were obtained by zone‐melting at —30 °C in x‐ray capillaries. The following data characterize the crystal chemistry of the compounds: KNH₂ · NH₃ Cmc2₁, Z = 4 21 °C a = 3, 938(1) Å, b = 10, 983(3) Å, c = 5, 847(1) Å CsNH₂ · NH₃ Pnma, Z = 4 30 °C a = 7, 103(1) Å, b = 5, 390(1) Å, c = 10, 106(2) Å For CsNH₂ · NH₃ all hydrogen atom positions were successfully refined. The structure of both ammoniates may be described by a distorted hexagonal close packed arrangement of cations with the NH₃ molecules in the octahedral and the NH₂^— anions in the trigonal bipyramidal interstices. The three H atoms of the NH₃ molecules are involved in hydrogen bridge bonds to two amide ions with d(N(NH₃)···N(NH₂^—)) = 2.60Å for the K and 3.19Å for the Cs compound and to a further NH₃ molecule with d(N(NH₃)···N(NH₃)) = 2.98Å for the K and 3.56Å for the Cs compound. Structural relationship of the ammoniates to the monohydrates of KOH and RbOH is discussed.     

Amminelithium Amidoborane Li(NH3)NH2BH3: A New Coordination Compound with Favorable Dehydrogenation Characteristics

The monoammoniate of lithium amidoborane, Li(NH₃)NH₂BH₃, was synthesized by treatment of LiNH₂BH₃ with ammonia at room temperature. This compound exists in the amorphous state at room temperature, but at ?20 °C crystallizes in the orthorhombic space group Pbca with lattice parameters of a=9.711(4), b=8.7027(5), c=7.1999(1) Å, and V=608.51 ų. The thermal decomposition behavior of this compound under argon and under ammonia was investigated. Through a series of experiments we have demonstrated that Li(NH₃)NH₂BH₃ is able to absorb/desorb ammonia reversibly at room temperature. In the temperature range of 40–70 °C, this compound showed favorable dehydrogenation characteristics. Specifically, under ammonia this material was able to release 3.0 equiv hydrogen (11.18 wt %) rapidly at 60 °C, which represents a significant advantage over LiNH₂BH₃. It has been found that the formation of the coordination bond between ammonia and Li⁺ in LiNH₂BH₃ plays a crucial role in promoting the combination of hydridic B? H bonds and protic N? H bonds, leading to dehydrogenation at low temperature.     

Formation and Unimolecular Dehydrogenation of Gaseous Alkaline‐earth Metal Amidoboranes M(NH2BH3)2 (M = Be – Ba): Comparative Computational Study

Formation of alkaline‐earth metal amidoboranes M(NH₂BH₃)₂ (M = Be, Mg, Ca, Sr, Ba) and unimolecular dehydrogenation reactions were computationally studied at the B3LYP/def2‐TZVPPD level of theory. Formation of M(NH₂BH₃)₂ from ammonia borane and MH₂ is exergonic, but subsequent unimolecular dehydrogenation reactions are endergonic at room temperature. In contrast to alkali metal amidoboranes, for M(NH₂BH₃)₂ the nature of M significantly affects their reactivity. Activation energies for the dehydrogenation of first and second hydrogen molecules decrease from Be to Ba. In case of Be compounds, intramolecular M ··· H–B contacts play an important role, whereas for heavier analogs such contacts are much less pronounced.     

Hydrides,Amides and Imides Mediated Ammonia Synthesis and Decomposition

Ammonia is feeding nearly half the world population and also holds the promise as a carbon‐free energy carrier. The development of ammonia synthesis and decomposition processes under milder conditions is a grand challenge for more than a century. Increasing effort is devoted to this area in recent years and encouraging progress has been achieved. In this paper, we summarize our recent research using alkali or alkaline earth metal amides, imides and hydrides for ammonia synthesis and decomposition. These materials could serve as either indispensible component of active center in thermal catalytic process or nitrogen carrier for chemical looping ammonia synthesis. The synergy of amide, imide, or hydride with transition metals enables ammonia synthesis or decomposition with unprecedented high efficiency under milder reaction conditions, and thus opens an avenue to advance the chemistry or catalysis of N₂ fixation reaction. The compositional and structural diversity of the amide, imide and hydride materials provides plenty of opportunity and potential for further exploration and optimization.     

Chemical looping of metal nitride catalysts: low-pressure ammonia synthesis for energy storage

The activity of many heterogeneous catalysts is limited by strong correlations between activation energies and adsorption energies of reaction intermediates. Although the reaction is thermodynamically favourable at ambient temperature and pressure, the catalytic synthesis of ammonia (NH₃), a fertilizer and chemical fuel, from N₂ and H₂ requires some of the most extreme conditions of the chemical industry. We demonstrate how ammonia can be produced at ambient pressure from air, water, and concentrated sunlight as renewable source of process heat via nitrogen reduction with a looped metal nitride, followed by separate hydrogenation of the lattice nitrogen into ammonia. Separating ammonia synthesis into two reaction steps introduces an additional degree of freedom when designing catalysts with desirable activation and adsorption energies. We discuss the hydrogenation of alkali and alkaline earth metal nitrides and the reduction of transition metal nitrides to outline a promoting role of lattice hydrogen in ammonia evolution. This is rationalized via electronic structure calculations with the activity of nitrogen vacancies controlling the redox-intercalation of hydrogen and the formation and hydrogenation of adsorbed nitrogen species. The predicted trends are confirmed experimentally with evolution of 56.3, 80.7, and 128 μmol NH₃ per mol metal per min at 1 bar and above 550 °C via reduction of Mn₆N_2.58 to Mn₄N and hydrogenation of Ca₃N₂ and Sr₂N to Ca₂NH and SrH₂, respectively.     

Untersuchung des Systems Kalium/Europium/Ammoniak

Investigation of the System Potassium/Europium/Ammonia The reaction of the metals K and Eu in the molar ratios from K:Eu = 12:1 yo 1:40 with NH₃ as solvent and reactant at temperature from 300 to 500°C and pressure of 5000 bar led to the following compounds: EuN, Eu(NH₂)₂, KEu(NH₂)₃ and K₃Eu(NH₂)₆. Their conditions of preparation are explained. The thermal degradation of Eu(NH₂)₂ gives directly EuN; the ternary amides give EuN and undecomposed KNH₂. The x-ray investigation of single crystals gave the structures: For the crystal data see “Inhaltsübersicht”. The crystal chemistry of the compounds is discussed.     

Catalytic asymmetric hydroxylation of α-alkoxycarbonyl amides with a Pr(OPr)3/amide-based ligand catalyst

A catalytic asymmetric hydroxylation of N-nonsubstituted α-alkoxycarbonyl amides is described. A new effective catalyst comprising Pr(OⁱPr)₃ and a fluoro-substituted amide-based ligand was identified using oxaziridine as the oxidizing reagent. The catalyst components were in dynamic equilibrium in the reaction mixture, which assembled to form the associated transition state through metal coordination and hydrogen bonding.     

Cs2Ba(O3)4 · 2 NH3, das erste ionische Erdalkaliozonid

Cs₂Ba(O₃)₄ · 2 NH₃, the First Ionic Alkaline Earth Metal Ozonide Cs₂Ba(O₃)₄ · 2 NH₃ is the first ionic ozonide containing an alkaline earth metal cation. Its synthesis has been achieved via partial cation exchange of CsO₃ dissolved in liquid ammonia. According to a single crystal X‐ray structure determination (Pnnm; a = 6.312(2) Å, b = 12.975(3) Å, c = 8.045(2) Å; Z = 2; R₁ = 4.6%; 848 independent reflections) ozonide anions, cesium cations and ammonia molecules form a CsCl‐type arrangement, where Cs⁺ and NH₃ occupy one half of the cation sites, each. Ba²⁺ is coordinated by four ozonide groups and two ammonia molecules. Because of a short hydrogen bond to one of the terminal oxygen atoms, the respective O–O‐distance in the ozonide ion is longer than the other. The shortest intermolecular O–O‐distance ever observed in ionic ozonides has been found in this compound, which can be taken as a first clue for the radical ozonide anion to dimerize like the isoelectronic SO₂^– does.     

A New Route to Metal Azides

Beside several other applications, metal azides can be used for the synthesis of nitridophosphates and binary nitrides. Herein we present a novel synthetic access to azides: Several metals, such as main‐group, transition metals, and rare‐earth metals, react with silver azide in liquid ammonia as a solvent giving the corresponding metal azides. In this work Mn(N₃)₂, Sn(N₃)₂, and Eu(N₃)₂, as well as their ammonia complexes were synthesized for the first time through low‐temperature methods. Also a simpler access to Zn(N₃)₂ was possible. At room temperature and the respective vapor pressure of NH₃, it became possible to grow single crystals of the dinuclear holmium azide [Ho₂(μ‐NH₂)₃(NH₃)₁₀](N₃)₃?1.25 NH₃. We are confident that this new route could lead to novel metal azides as well as nitrides of the main‐group, the transition, and the rare‐earth metals upon careful decomposition.     

Darstellung,Struktur und Reaktionsfähigkeit einiger Metall(I)- und-(II)-Derivate des Diäthylphosphono-Acetons

Metalation of diethylphosphono-acetone (DÄPA) with potassium or lithium in benzene and with KNH₂, LiNH₂, or calcium in liquid ammonia afforded the metal derivatives ofDEPA, which were isolated in a pure state. Their structure has been investigated by i.r.- and¹H n.m.r.-spectroscopy. In solution metallotropic conversion of thecis-enolate chelates intotrans-enolates and C-forms occurs. The reactivity of these metal derivatives towards some alkylating and acylating reagents as well towards carbonyl compounds has been investigated.

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Diese Mitteilung ist z. T. Inhalt der Diplomarbeit vonI. Velinov, Univ. Sofia (1968).     

Lithiumaluminiumamid,LiAl(NH2)4, Darstellung,röntgenographische Untersuchung,Infrarotspektrum und thermische Zersetzung

Lithium Aluminium Amide, LiAl(NH₂)₄-Preparation, X-Ray Investigation, I.R.Spectrum, and Thermal Decomposition The reaction of lithium and aluminium with liquid ammonia gives LiAl(NH₂)₄ within some days at temperatures from 80–100°C. Crystals for an X-ray structure determination must be grown very slowly from liquid NH₃ starting with thoroughly pulverized amide. The structure analysis was successful including the determination of the positions of the hydrogen atoms of the amide ions. Space group: P2₁/n; lattice constants: a = 9.478(1) Å, b = 7.351(1) Å, c = 7.398(1) Å, β = 90.26(1)°; Z = 4, R-values (unweighted, weighted with w = 1): 0.042/0.046. The atomic arrangement of LiAl(NH₂)₄ can formally be described as a new variant of the GaPS₄-type structure. The compound is characterized too by its i.r. spectrum. The thermal degradation of LiAl(NH₂)₄ gives at 180°C amorphous Al₂(NH)₃ and crystalline LiNH₂; at 220°C results already very fine AlN. Above 400°C this AlN reacts with LiNH₂ or Li₂NH forming Li₃AlN₂.     

Kaliumtriamidostannat(II), K[Sn(NH2)3] – Synthese und Kristallstruktur

Potassium Triamidostannate(II), K[Sn(NH₂)₃] – Synthesis and Crystal Structure Rusty‐red crystals of K[Sn(NH₂)₃] were obtained by the reaction of SnBr₂ and KNH₂ in a 1 : 3 molar ratio in liquid ammonia at 233 K in the form of platelets. The structure was determined from single crystal X‐ray diffractometer data: Space group P3; Z = 2; a = 6.560(1) Å, c = 7.413(2) Å. The structure contains trigonal pyramidal complex anions [Sn(NH₂)₃]^– and potassium cations. These ions are arranged to one another following the motif of a strongly distorted hexagonal close packing of sequence A(Sn) B(Sn) A′(K) B′(K) …     

Isotype Strukturen einiger Hexaamminmetall(II)-halogenide von 3d-Metallen: [V(NH3)6]I2, [Cr(NH3)6]I2, [Mn(NH3)6]Cl2, [Fe(NH3)6]Cl2, [Fe(NH3)6]Br2, [Co(NH3)6]Br2 und [Ni(NH3)6]Cl2

The Structures of some Hexaammine Metal(II) Halides of 3 d Metals: [V(NH₃)₆]I₂, [Cr(NH₃)₆]I₂, [Mn(NH₃)₆]Cl₂, [Fe(NH₃)₆]Cl₂, [Fe(NH₃)₆]Br₂, [Co(NH₃)₆]Br₂ and [Ni(NH₃)₆]Cl₂ Crystals of yellow [V(NH₃)₆]I₂ and green [Cr(NH₃)₆]I₂ were obtained by the reaction of VI₂ and CrI₂ with liquid ammonia at room temperature. Colourless crystals of [Mn(NH₃)₆]Cl₂ were obtained from Mn and NH₄Cl in supercritical ammonia. Colourless transparent crystals of [Fe(NH₃)₆]Cl₂ and [Fe(NH₃)₆]Br₂ were obtained by the reaction of FeCl₂ and FeBr₂ with supercritical ammonia at 400°C. Under the same conditions orange crystals of [Co(NH₃)₆]Br₂ were obtained from [Co₂(NH₂)₃(NH₃)₆]Br₃. Purple crystals of [Ni(NH₃)₆]Cl₂ were obtained by the reaction of NiCl₂ · 6H₂O and NH₄Cl with aqueous NH₃ solution. The structures of the isotypic compounds (Fm3 m, Z = 4) were determined from single crystal diffractometer data (see “Inhaltsübersicht”). All compounds crystallize in the K₂[PtCl₆] structure type. In these compounds the metal ions have high-spin configuration. The orientation of the dynamically disordered hydrogen atoms of the ammonia ligands is discussed.     

Lewis acid promoted dehydration of amides to nitriles catalyzed by [PSiP]-pincer iron hydrides

The dehydration of primary amides to their corresponding nitriles using four [PSiP]-pincer hydrido iron complexes 1–4 [(2-Ph₂PC₆H₄)₂MeSiFe(H)(PMe₃)₂ ( 1 ), (2-Ph₂PC₆H₄)₂HSiFe(H)(PMe₃)₂ ( 2 ), (2-(iPr)₂PC₆H₄)₂HSiFe(H)(PMe₃)₂ ( 3 ) and (2-(iPr)₂PC₆H₄)₂MeSiFe(H)(PMe₃)₂ ( 4 )] as catalysts in the presence of (EtO)₃SiH as dehydrating reagent was explored in the good to excellent yields. It was proved for the first time that Lewis acid could significantly promote this catalytic system under milder reaction conditions than other Lewis acid-promoted system, such as shorter reaction time or lower reaction temperature. This is also the first example that dehydration of primary amides to nitriles was catalyzed by silyl hydrido iron complexes bearing [PSiP]-pincer ligands with Lewis acid as additive. This catalytic system has good tolerance for many substituents. Among the four iron hydrides 1 is the best catalyst. The effects of substituents of the [PSiP]-pincer ligands on the catalytic activity of the iron hydrides were discussed. A catalytic reaction mechanism was proposed. Complex 4 is a new iron complex and was fully characterized. The molecular structure of 4 was determined by single crystal X-ray diffraction.