Controlled Reduction of Carboxamides to Alcohols or Amines by Zinc Hydrides

New protocols for controlled reduction of carboxamides to either alcohols or amines were established using a combination of sodium hydride (NaH) and zinc halides (ZnX₂). Use of a different halide on ZnX₂ dictates the selectivity, wherein the NaH‐ZnI₂ system delivers alcohols and NaH‐ZnCl₂ gives amines. Extensive mechanistic studies by experimental and theoretical approaches imply that polymeric zinc hydride (ZnH₂)_∞ is responsible for alcohol formation, whereas dimeric zinc chloride hydride (H?Zn?Cl)₂ is the key species for the production of amines.     

Iodination of 6-aryl-2-pyrones

The iodination of 6-aryl-2-pyrones with iodine chloride in glacial acetic acid leads to the corresponding 3-iodo derivatives. 3-Cyano-6-phenyl-2-pyrone and 3-phenylethynyl-6-phenyl-2-pyrone were obtained by replacement of the iodo group by cyano and phenylethynyl groups.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 616–618, May, 1884.     

Oxidation of Metal Hydrides with Molecular Oxygen

The oxidation of metal hydrides MH _x in the systems M-H₂-O₂ (M = Ti, Zr, Sc, Y, V) with molecular oxygen was carried out, and the optimal ranges of temperature and pressure were determined. The resistivity and electron work function for the oxyhydrides synthesized were measured.     

Proton Tunneling Distances for Metal Hydrides Formation Manage the Selectivity of Electrochemical CO2 Reduction Reaction

A series of manganese polypyridine complexes were prepared as CO₂ reduction electrocatalysts. Among these catalysts, the intramolecular proton tunneling distance for metal hydride formation (PTD-MH) vary from 2.400 to 2.696 Å while the structural, energetic, and electronic factors remain essentially similar to each other. The experimental and theoretical results revealed that the selectivity of CO₂ reduction reaction (CO₂RR) is dominated by the intramolecular PTD-MH within a difference of ca. 0.3 Å. Specifically, the catalyst functionalized with a pendent phenol group featuring a slightly longer PTD-MH favors the binding of proton to the [Mn−CO₂] adduct rather than the Mn center and results in ca. 100 % selectivity for CO product. In contrast, decreasing the PTD-MH by attaching a dangling tertiary amine in the same catalyst skeleton facilitates the proton binding on the Mn center and switches the product from CO to HCOOH with a selectivity of 86 %.     

Application of Alkali Metal Hydrides of Nanometric Size in Reduction,Cyclotrimerization and Metalation

Abstract: Reactions of some representative organic functional compounds by the alkali metal hydrides of nanometric size have been studied. Nitrobenzene, some aldehydes, esters and organic halides are reduced with good yield and high selectivity in many cases. Nitriles are cyclotrimerized and dimethyl sulfoxide is rapidly deprotonated.     

Vinyl Polymerization with Transition Metal Alkyls and Hydrides

Transition metal alkyls and hydrides isolated from Ziegler-type catalyst mixtures serve as appropriate models for coordination polymerization. These transition metal complexes initiate the polymerization of some vinyl compounds and aldehydes. In some cases the monomer-coordinated complexes may be isolated and the interaction of the monomer with the transition metal complexes may be studied. Comparison of the polymerization kinetics of the vinyl compounds with the decay kinetics of the initial transition metal complexes on interaction with the monomer provided important information with respect to the mechanism of coordination polymerization by these complexes. The effect of organoaluminum compounds on the reactivity of the transition metal complexes has been also studied. These transition metal alkyls initiate the polymerization of acetaldehyde to give a polyether-type polymer at -78°C and a polymer with OH groups at room temperature.     

过渡金属氢化物的合成方法

概述了过渡金属氢化物尤其是钌氢配合物的氧化加成、M-X还原、质子化、过渡金属氢化物转化和原子簇过渡金属配合物氢聚等合成方法的进展情况.     

Reduction of 5,6-Dimethylidene-exo-2,3-epoxynorbornane with Metal Hydrides. Efficient syntheses of 6-methyl-5-methylidene-anti-3- nortricyclanol and of 2,3-dimethylidene-anti-7-norbornanol

5,6-Dimethylidene-exo-2,3-epoxynorbornane ( 1 ) is reduced slowly by LiAlH₄ in boiling tetrahydrofuran (THF) and furnishes a mixture of 5,6-dimethylidene-exo-2-norbornanol ( 2 ), 2,3-dimethylidene-anti-7-norbornanol ( 3 ) and principally 6-methyl-5-methylidene-anti-3-nortricyclanol ( 4 ). The yield of 4 is the highest for low initial concentrations of LiAlH₄; it decreases in favour of alcohols 2 and 3 at high concentration of LiAlH₄. The reduction of 1 with AlH₃ in THF yields 3 as the major product, thus revealing an efficient synthesis of 7-substituted-2, 3-dimethyl-idenenorbornane derivatives. No alcohol 2 could be isolated by LiEt₃BH reduction of 1 . LiAlD₄ reduces 1 into the monodeuterated alcohols 2 -d, 3 -d and 4 -d. The deuterium label is found in the endo-position at C (3) in 2 -d, in the exo-position at C(5) in 3 -d and in the methyl group of the tricyclic alcohol 4 -d. Mechanistic limits for the formation of 2 , 3 and 4 are discussed briefly.     

Synthesis of 3, 4, 6-triaryl-2-pyrones

A preparative method was worked out for the synthesis of 3,4,6-triaryl-2-pyrones by 1,3-dipolar cycloaddition of selenium arylacylmethylides to diphenylcyclopropenone.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1475–1478, November, 1977.     

Ion Segregation and Electrostatic Imbalance in Metal Hydrides

Crystal chemical indices of ion segregation and electrostatic imbalance after Beck help to rationalize inorganic crystal structures and sometimes even to predict them. Metal hydrides, from hydrido‐aluminates and ‐gallates, to complex transition metal hydrides, ternary ionic magnesium hydrides and mixed anionic hydrides, were investigated using these tools. Beck's ion segregation and electrostatic imbalance indices are found to work well in explaining crystal structures of most metal hydrides, although the electronegativity differences between cations and hydride anions are often much smaller in ionic metal hydrides, as compared to metal fluorides and oxides. This includes complex transition metal hydrides, despite the fact that formal oxidation states do not describe the actual charges properly. Rare cases of violations can be explained by the chemical bonding situation, e.g. the presence of weak metal–metal bonds in Li₃RhH₄.     

Reactivity of Coinage Metal Hydrides for the Production of H2 Molecules

The formation of molecular hydrogen as well as the possibility of using coinage metal hydrides as a prospective complex to produce hydrogen was presented in this work. Therefore, the reactions involving the interaction between two coinage metal hydrides, MH (M=Cu, Ag and Au, homo and heterodimers), were studied. The free energy profiles corresponding to aforementioned complexation were analysed by means of ab initio methods of quantum chemistry. The characteristics of these intermediates, final complexes and the electron density properties of the established interactions were discussed.     

Zn 还原过渡金属化合物制备金属粉体的过程

用Zn粉还原过渡金属Fe、Co、Ni和Cu的硫酸盐和硫酸铵复盐溶液，获得了相应金属的纳米粉体.详细研究了此反应的还原过程.用XRD、SEM、TEM和ED等方法对产物进行了表征，发现析出的粉体不同程度上均生成有Zn置换的固溶体. Fe在Zn粒外层生成薄层Fe-Zn固溶体，Ni和Co为粒径分别为7.5 nm和12.1 nm的Zn饱和固溶体， Cu则在外层生成Cu5Zn8的新相.讨论了还原过程的机制，认为和M-Zn电池电动势的驱动力有关.     

Reactions of 1-Trichloromethyl-2,4,6-trimethylbenzene with 2-Amino- and 2-Amino-5-bromopyridines

A new type of reaction has been discovered for trichloromethylarenes with pyridines. The reaction of 1-trichloromethyl-2,4,6-trimethylbenzene with 2-amino- and 2-amino-5-bromopyridines does not stop with formation of the pyridinium salt, but rather leads to unique amidines, namely, 1-[-(2-pyridylimino)-2,4,6-trimethylbenzyl]-2-pyridonimine and its 5-bromo derivative.     

In-Situ/Operando X-ray Characterization of Metal Hydrides

In this article, the capabilities of soft and hard X-ray techniques, including X-ray absorption (XAS), soft X-ray emission spectroscopy (XES), resonant inelastic soft X-ray scattering (RIXS), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD), and their application to solid-state hydrogen storage materials are presented. These characterization tools are indispensable for interrogating hydrogen storage materials at the relevant length scales of fundamental interest, which range from the micron scale to nanometer dimensions. Since nanostructuring is now well established as an avenue to improve the thermodynamics and kinetics of hydrogen release and uptake, due to properties such as reduced mean free paths of transport and increased surface-to-volume ratio, it becomes of critical importance to explicitly identify structure-property relationships on the nanometer scale. X-ray diffraction and spectroscopy are effective tools for probing size-, shape-, and structure-dependent material properties at the nanoscale. This article also discusses the recent development of in-situ soft X-ray spectroscopy cells, which enable investigation of critical solid/liquid or solid/gas interfaces under more practical conditions. These unique tools are providing a window into the thermodynamics and kinetics of hydrogenation and dehydrogenation reactions and informing a quantitative understanding of the fundamental energetics of hydrogen storage processes at the microscopic level. In particular, in-situ soft X-ray spectroscopies can be utilized to probe the formation of intermediate species, byproducts, as well as the changes in morphology and effect of additives, which all can greatly affect the hydrogen storage capacity, kinetics, thermodynamics, and reversibility. A few examples using soft X-ray spectroscopies to study these materials are discussed to demonstrate how these powerful characterization tools could be helpful to further understand the hydrogen storage systems.     

Synthesis of 2-hydroxy-3,5-diaryl-6-benzyl-γ-pyrones and their esters

Chemistry of Heterocyclic Compounds -     

A facile, general synthesis of 3,4-difluoro-6-substituted-2-pyrones

Reaction of (2E)-2,3-difluoro-3-iodoacrylic acid with a variety of terminal acetylenes under cocatalysis of PdCl2(PPh3)2 and CuI gave difluorinated 2-pyrones as the sole product in good yields.     

The Reaction of Bicyclo [3.2.1] octenyl Halides with Metal Hydrides

Reduction of 2-phenyl- and 2-methyl-exo-3,4-dichlorobicyclo[3.2.1]oct-2-enes with lithium aluminium hydride (LAH) or tributyltin hydride (TBTH) gave endo-2-phenyl-3-chlorobicyclo[3.2.1]oct-3-ene, 2-phenyl-3-chlorobicyclo[3.2.1]oct-2-ene and their methyl analogues. The action of both reagents on 2-phenyl-exo-3, 4-dibromobicyclo[3.2.1]oct-2-ene similarly resulted in reductive monodebromination to give normal and allylically rearranged products. Additionally, further reduction occurred to give endo-2-phenylbicyclo[3.2.1]oct-3-ene and 2-phenylbicyclo[3.2.1]-oct-2-ene. In all cases, LAH gave mainly the allylic rearrangement product whereas TBTH gave mostly unrearranged product. The reason for these differences could have been due either to the intervention of allylic radicals in the TBTH reduction or to differences in nucleophilicity. The results also show that LAH is equally efficaceous as TBTH in the reduction of these allylic halides and equally selective in the reduction of the vinyl bromides. The stereochemistry of the allylic rearrangement was shown to be synfacial in that hydride replaced halide on the same face of the molecule.