Facile Synthesis of Unsolvated Alkali Metal Octahydrotriborate Salts MB3H8 (M=K,Rb, and Cs), Mechanisms of Formation,and the Crystal Structure of KB3H8

A facile synthesis of heavy alkali metal octahydrotriborates (MB₃H₈; M=K, Rb, and Cs) has been developed. It is simply based on reactions of the pure alkali metals with THF?BH₃, does not require the use of electron carriers or the addition of other reaction media such as mercury, silica gel, or inert salts as for previous procedures, and delivers the desired products at room temperature in very high yields. However, no reactions were observed when pure Li or Na was used. The reaction mechanisms for the heavy alkali metals were investigated both experimentally and computationally. The low sublimation energies of K, Rb, and Cs were found to be key for initiation of the reactions. The syntheses can be carried out at room temperature because all of the elementary reaction steps have low energy barriers, whereas reactions of LiBH₄/NaBH₄ with THF?BH₃ have to be carried out under reflux. The high stability and solubility of KB₃H₈ were examined, and a crystal structure thereof was obtained for the first time.     

Comparative Computational Studies of Gaseous Alkali Metal Amidoboranes MNH2BH3 and their Carbon Analogs MC2H5 (M = Li – Cs): Formation and Unimolecular Hydrogen Evolution

Comparative computational studies of reaction mechanisms of formation and unimolecular hydrogen evolution from alkali metal amidoboranes MNH₂BH₃ and their carbon analogs MC₂H₅ (M = Li – Cs) were performed at the B3LYP/def2‐TZVPPD level of theory. Transition states (TS) for the consecutive dehydrogenation reactions were optimized. In contrast to endergonic dehydrogenation of carbon analogs, dehydrogenation reactions of alkali metal amidoboranes are exergonic at room temperature. The nature of the alkali metal does not significantly affect the thermodynamic characteristics and activation energies of unimolecular gas phase dehydrogenation reactions. The influence of the alkali metal is qualitatively similar for amidoboranes and their carbon analogs.     

Präparative,röntgenographische und 1 H-Breitlinienresonanzuntersuchungen an Germylalkaliverbindungen,GeH 3 M

Preparation, X-Ray and 1 H-Wide-Line-Resonance Studies of Alkali Germyl Compounds, GeH ₃ M The alkali germyls GeH ₃ M (M = Li, Na, K, Rb, Cs) have been prepared from germane and the corresponding alkali metals. GeH ₃ K, GeH ₃ Rb and GeH ₃ Cs could be obtained as crystalline solids. It has been shown from X-ray single-crystal studies that GeH ₃ Cs has a structure of the TlI-type with the unusual coordination number 7. 1 H-wide-line-resonance investigations show that the rotations of the germyl groups are frozen in at low temperatures. From the observed 2. moment of the fixed germyl groups a H? Ge? H valence augle of 92.5±4°has been determined.     

Beiträge zur Chemie des Phosphors. 239 [1]. Reaktion von Diphosphan(4) mit Diboran(6) und mit THF-Boran: Bildung von Diphosphan-boran,P2H4 · BH3, und Diphosphan-1,2-bis(boran), BH3 · P2H4 · BH3

Contributions to the Chemistry of Phosphorus. 239. On the Reaction of Diphosphane(4) with Diborane(6) and with THF-Borane: Formation of Diphosphane-borane, P₂H₄ · BH₃, and Diphosphane-1,2-bis(borane), BH₃ · P₂H₄ · BH₃ Diphosphane(4) always reacts with diborane(6) in the temperature range of ?118 to ?78°C, to furnish a mixture of diphosphane-borane, P₂H₄ · BH₃ ( 1 ), and diphosphane-1,2-bis(borane), BH₃ · P₂H₄ · BH₃ ( 2 ), in addition to small amounts of triphosphane-1,3-bis(borane), BH₃ · P₃H₅ · BH₃, and phosphane-borane, BH₃ · PH₃, irrespective of the molar ratios of the reactants employed. The formation of the 1 : 1 adduct P₂H₄ · B₂H₆ reported in the literature [4] could not be confirmed. The structures of compounds 1 and 2 were investigated by nuclear magnetic resonance spectroscopy which revealed the complete, homolytic cleavage of diborane(6). As a result of the bonding of one BH₃ group to diphosphane(4), the Lewis basicity of the other PH₂ group is markedly reduced. Similar mixtures of products are obtained when the borane adduct THF · BH₃ is employed in an analogous reaction. In the case of a 1 : 1 molar ratio of P₂H₄ : THF · BH₃ at ?78°C, the reaction furnishes compound 1 exclusively. This product can be isolated in the pure state and is found to be appreciably more stable than diphosphane(4).     

Theoretical Investigation on the Chemistry of Entrapment of the Elusive Aminoborane (H2NBH2) Molecule

Aminoborane (H₂N?BH₂) is an elusive entity and is thought to be produced during dehydropolymerization of ammonia borane, a molecule of prime interest in the field of chemical hydrogen storage. The entrapment of H₂N?BH₂ through hydroboration of exogenous cyclohexene has emerged as a routine technique to infer if free H₂N?BH₂ is produced or not during metal‐catalyzed ammonia borane dehydrogenation reactions. But to date, the underlying mechanism of this trapping reaction remains unexplored. Herein, by using DFT calculations, we have investigated the mechanism of trapping of H₂N?BH₂ by cyclohexene. Contrary to conventional wisdom, our study revealed that the trapping of H₂N?BH₂ does not occur through direct hydroboration of H₂N?BH₂ on the double bond of cyclohexene. We found that autocatalysis by H₂N?BH₂ is crucial for the entrapment of another H₂N?BH₂ molecule by cyclohexene. Additionally, nucleophilic assistance from the solvent is also implicated for the entrapment reaction carried out in nucleophilic solvents. In THF, the rate‐determining barrier for formation of the trapping product was predicted to be 16.7 kcal mol^?1 at M06 L(CPCM) level of theory.     

THF-solvated Heavy Alkali Metal Benzyl Compounds (Na,Rb, Cs): Defined Deprotonation Reagents for Alkali Metal Mediation Chemistry

The incorporation of heavy alkali metals into substrates is both challenging and essential for many reactions. Here, we report the formation of THF-solvated alkali metal benzyl compounds [PhCH₂M ⋅ (thf)_n] (M=Na, Rb, Cs). The synthesis was carried out by deprotonation of toluene with the bimetallic mixture n-butyllithium/alkali metal tert-butoxide and selective crystallization from THF of the defined benzyl compounds. Insights into the molecular structure in the solid as well as in solution state are gained by single crystal X-ray experiments and NMR spectroscopic studies. The compounds could be successfully used as alkali metal mediating reagents. The example of caesium showed the convenient use by deprotonating acidic C−H as well as N−H compounds to gain insight into the aminometalation using these reagents.     

Darstellung und Kristallstruktur der Alkalithiochromate (III), ACr5S8 (A ≙ Cs,Rb und K)

Preparation and Crystal Structure of the Alkali Thiochromates (III), ACr₅S₈ (A ? Cs, Rb und K) The alkali thiochromates (III), ACr₅S₈ (A ? Cs, Rb und K), can be obtained by the reaction of chromium powder with the corresponding alkali metal carbonate in a current of dry hydrogensulfide at about 1320 K. X-ray investigations on single crystals revealed that the compounds crystallize isotypic in the space group C2/m (No. 12), z = 2. Chromium is surrounded by six sulphur atoms in form of an octahedron. These sulphur octahedrons are sharing edges and partly faces, building up a frame with tubes which contain the alkali metal ions in a linear arrangement. Remarkable is the very short cesium-cesium distance of 346 pm, in CsCr₅S₈.     

Crystalline Hybrid Solid Materials of Palladium and Decamethylcucurbit[5]uril as Recoverable Precatalysts for Heck Cross‐Coupling Reactions

A series of M? Pd? Me₁₀CB[5] (M=Li, Na, K, Rb, and Cs; Me₁₀CB[5]=decamethylcucurbit[5]uril) hybrid solid materials have been successfully synthesized for the first time through a simple diffusion method. These as‐prepared hybrid solids have been applied as phosphine‐free precatalysts for Heck cross‐coupling reactions with excellent catalytic performance and good recyclability. In the processes of the catalytic reactions, the activated Pd^II species were released from the crystalline hybrid precatalysts and transformed into catalytically active Pd nanoparticles, which have been demonstrated as key to carry on the catalytic reactions for the recoverable precatalysts M? Pd? Me₁₀CB[5] (M=K, Rb, and Cs). It has also been rationalized that the introduction of different alkali metals afforded crystalline hybrid precatalysts with different crystal structures, which are responsible for their diversified stability and reusability presented in Heck reactions.     

Complex amidoboranes M<Superscript>2</Superscript>[M<Superscript>1</Superscript>(NH<Subscript>2</Subscript>BH<Subscript>3</Subscript>)<Subscript>4</Subscript>] (M<Superscript>1</Superscript> = Al,Ga; M<Superscript>2</Superscript> = Li,Na, K,Rb, Cs)

Structural, spectral, and thermodynamic characteristics of complex amidoboranes M²[M¹(NH₂BH₃)₄] (M¹ = Al, Ga; M² = Li, Na, K, Rb, Cs) were calculated by the B3LYP/def2-SVPD quantum-chemical method. The procedure for the synthesis of these compounds by reactions of alkali metal amidoboranes with aluminum and gallium chlorides was suggested and experimentally tested. Reaction products were characterized by the NMR and IR spectroscopy and X-ray phase analysis.     

Über die Alkaliselenoarsenate(III) KAsSe3 · H2O,RbAsSe3 · 1/2 H2O und CsAsSe3 · 1/2 H2O

On the Alkali Selenoarsenates(III) KAsSe₃ · H₂O, RbAsSe₃ · 1/2 H₂O, and CsAsSe₃ · 1/2 H₂O The alkali selenoarsenates(III) KAsSe₃ · H₂O, RbAsSe₃ · 1/2 H₂O, and CsAsSe₃ · 1/2 H₂O have been prepared by hydrothermal reaction of the respective alkali carbonate with As₂Se₃ at a temperature of 135°C. Their X-ray structural analyses demonstrated that the compounds contain polyselenoarsenate(III) anions (AsSe₃^?)_n, in wich the basic units are ψ-AsSe₃ tetrahedra, which are linked together through Se? Se bonds into infinite zweier single chains. The Rb and Cs salts are isotypic.     

Darstellung und schwingungsspektroskopische Untersuchung von [H3B?Se?Se?BH3]2− und [H3B-μ2-Se(B2H5)]− Kristallstruktur und theoretische Untersuchung der Molekülstruktur von [H3B-μ2-Se(B2H5)]−

Synthesis and Vibrational Spectroscopic Investigation of [H₃B? Se? Se? BH₃]^2? and [H₃B-μ₂-Se(B₂H₅)]^? Crystal Structure and Theoretical Investigation of the Molecular Structure of [H₃B-μ₂-Se(B₂H₅)]^? M₂[H₃B? Se? Se? BH₃] 1 is produced by the reaction between elemental selenium and MBH₄ (1 : 1) in triglyme (diglyme), under dehydrogenation. 1 reacts with an excess of B₂H₆ to give M[H₃B-μ₂-Se(B₂H₅)] 2 which is also formed in the reaction of THF · BH₃ with 1 . These reactions proceed under cleavage of the Se? Se bond and hydrogen evolution. [(C₆H₅)₄]Br reacts with Na · 2 to form [(C₆H₅)₄P] · 2 which crystallizes in the tetragonal space group I4 (Nr. 82). An X-ray structure determination failed because of disordering of the cation and anion. ¹¹B, ⁷⁷Se NMR shifts and ¹J(¹¹B¹H) coupling constants as well as IR- and Raman spectroscopic investigations convey further structural information. Structural data of 2 have been calculated by SCF methods. The anion of 2 may be viewed either as an adduct of Se with B₃H₈^?, or as a bridge substituted selena derivative of B₂H₆.     

Zur Kenntnis der Fluoride zweiwertiger Lanthanoide. II. Über die Synthese von MLnF3 aus MLnF4

On Fluorides of Divalent Lanthanoids. II. Synthesis of MLnF₃ from MLnF₄ CsEuF₃, CsYbF₃, and RbYbF₃, which had already been prepared via reduction of the corresponding trifluorides with alkali metal, were also obtained by reducing MLnF₄ with M (M = Cs, Rb, K; Ln = Eu, Yb). No additional alkali fluoroperovskites of lanthanoids were detected either by reduction of LnF₃ or MLnF₄ with metallic Cs, Rb, or K or by other reactions, e.g. 3CsF + 2SmF₃ + Sm. It was shown that the reaction of CsF with EuF₂ (350–850°C) produced only very little CsEuF₃.     

Alkalimetall-Cluster im Zeolith Y Darstellung,Eigenschaften, Reaktionen

Alkali Metal Clusters in Zeolite Y. Preparation, Properties, Reactions Alkali metal clusters (Type AB₃³⁺) were synthesized by reaction of alkali metal A (Li, Na, K, Rb, Cs) with the cations B (alkali, alkaline earth, and rare earth metals) of zeolite Y. The compounds were characterized by UV/VIS spectroscopy, oxidation by carbon oxides and organic halides, and adsorption of gases and polar molecules. The clusters are less reactive than the free alkali metals, the redox potential depends on the alkali metal as well as the cation of zeolite. Chemical interactions with typical ligands and with N₂, Ar, Kr, CO, CO₂, Benzene, and n-Hexane were observed. Reaction with ammonia leads to solvated electrons in zeolite's super-cage, stable up to 240 K.     

Structural Study of Alkaline 1-Phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate Salts: An Example of Periodicity in Alkaline Cations

The alkaline 1-phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate salts, M[C₆H₅N₄CS] (M = Li ( 1 ), Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 )) were obtained and characterized by means of mass spectrometry (FAB⁺) and NMR (¹H; ¹³C) spectroscopy. The structures of Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 ) compounds were determined by X-ray diffraction methods. The ligand shows a rich variety of coordination patterns with the alkaline cations. The formation of a four-membered ring MSCN in the compounds with heavier alkali cations (K, Rb and Cs) is shown. In all the cations the coordination number around it increases with the ionic radius. Compounds with Cs⁺ and Rb⁺ exhibited the formation of Cs-C and Rb-C interactions with the phenyl group.     

Zintl-Verbindungen mit Gold: M3AuSn4 mit M = K,Rb, Cs und M3AuPb4 mit M = Rb,Cs

Zintl-Compounds with Gold: M₃AuSn₄ with M = K, Rb, Cs and M₃AuPb₄ with M = Rb, Cs Silver coloured, brittle single crystals of the compounds M₃AuSn₄ with M = K, Rb, Cs and M₃AuPb₄ with M = Rb, Cs were synthesized by reactions of alkali metal azides (MN₃) with gold sponge and tin (lead) powder at T = 923 K. The structures of the isotypic compounds (space group Pmmn, Z = 2) were determined from X-ray single-crystal diffractometry data (see ‘‘Inhaltsübersicht”︁”︁). The Zintl-compounds M₃AuE(14)₄ with E(14) = Sn, Pb contain [AuE(14)₄]-chains with P₄-analogous E(14)₄-tetrahedra which are connected by μ₂-bridging gold atoms.     

Reaction of secondary phosphine selenides with the system Se/MOH (M = Li, Na, K, Rb, Cs): A novel three-component synthesis of diorganodiselenophosphinates

Secondary phosphine selenides, R₂P(Se)H (R = PhCH₂CH₂, PhCH(Me)CH₂, 4-t-BuC₆H₄CH₂CH₂, NaphthylCH₂CH₂, Ph), react with the system Se/MOH (M = Li, Na, K, Rb, Cs) in the system THF/EtOH at ambient temperature unusually fast (20–30 s) to give cleanly and almost quantitatively (in 94–100% yield) earlier unknown diorganodiselenophosphinates of alkali metals.     

From simple rings to one-dimensional channels with calix[8]arenes, water clusters, and alkali metal ions

The macrocycle 4-tert-butylcalix[8]arene (L) was reacted with alkali metal carbonates (Li₂CO₃, Na₂CO₃, K₂CO₃, Rb₂CO₃, and Cs₂CO₃) at the interface of a biphasic THF/water system. Needle-like crystals with a general formula [A_x(4-tert-butylcalix[8]arene-xH)(THF)_y(H₂O)_z] (with A=Li, Na, K, Rb, Cs, x=1, 2, y=4, 5, 8, and z=6, 7) were thereby obtained. The solid state structures were investigated by X-ray diffraction of single crystals and by TGA measurements. They do not appear to be maintained in solution.     

Syntheses and reactions of triethylgermyllithium,-sodium, -potassium, -rubidium and -caesium in weak solvating solvents

Germylmetallic compounds, Et₃GeM, where M = Li, Na, K, Rb and Cs, have been prepared in high yield in n-hexane or benzene by the reaction of bis(triethylgermyl)mercury with the appropriate alkali metal. Reactions of these compounds with trimethylchlorosilane afforded the coupled product Et₃GeSiMe₃. The interaction of Et₃GeM with benzophenone, acetophenone and phenylacetylene has also been examined. The course of these reactions (i.e. the composition and the yields of the various products) is strongly dependent on the solvating abitity of the solvent and the nature of the alkali metal M.     

ASc[SeO3]2 (A = Na – Cs): Pure Alkali‐Metal Scandium Oxoselenates(IV) and Their Representatives With Mixed Alkali‐Metal Occupation

Alkali‐metal scandium oxoselenates(IV) ASc[SeO₃]₂ (A = Na – Cs) are known since a few years and a hydrothermal synthesis was used to obtain them. In our new studies we applied a flux‐supported solid‐state reaction and produced colorless single crystals as well. All representatives ASc[SeO₃]₂ with A = Na – Cs crystallize in the orthorhombic space group Pnma, in contrast to earlier reports for hexagonal RbSc[SeO₃]₂. Furthermore we have extended this field with some crystals showing a mixed occupation on the alkali‐metal site, namely (K,Na)Sc[SeO₃]₂, (Rb,K)Sc[SeO₃]₂, and (Cs,Rb)Sc[SeO₃]₂. Since all of them contain [ScO₆]^9– octahedra and [SeO₃]^2– ψ¹‐tetrahedra the diverse connectivity of the distinct alkali‐metal centered oxygen polyhedra differentiates the compounds with the smaller alkali metals (A′ = Na and K) from those with the bigger ones (A′′ = Rb and Cs). For the mixed crystals the amount of smaller or bigger alkali metal is responsible, which design is chosen by the system. This forces the mixed crystal (Rb,K)Sc[SeO₃]₂ with a higher amount of potassium instead of rubidium to crystallize isotypically with KSc[SeO₃]₂ and NaSc[SeO₃]₂, whereas the pure rubidium compound RbSc[SeO₃]₂ adopts the CsSc[SeO₃]₂‐type structure. These findings are supported by single‐crystal Raman spectroscopy.     

Ternäre Chloride in den Systemen ACl/DyCl3 (A = Cs,Rb, K)

Ternary Chlorides in the Systems ACl/DyCl₃ (A = Cs, Rb, K) The phase diagrams of the pseudobinary systems ACl/DyCl₃ (A = Cs, Rb, K) were investigated by DTA. With all alkali metals compounds A₃DyCl₆ (elpasolite family) and Ady₂Cl₇ are formed. Compounds A₂DyCl₅ exist only with Cs (Cs₂DyCl₅-type) and K (K₂PrCl₅-type). By solution calorimetry the formation enthalpies of the ternary chlorides from (nACl + DyCl₃) were measured and ‘synproportionation enthalpies’ for the formation from the compounds, adjacent in the phase diagrams, calculated. K₃DyCl₆ is the only compound, which is formed with a loss in lattice enthalpy. E.m.f. measurements in dependence on the temperature have revealed that, as for the other compounds A₃DyCl₆, a remarkable gain in entropy exists, which stabilizes K₃DyCl₆ at T ≧ 312 K. This entropy gain correlates with the existence of isolated DyCl₆^3? octahedra.