Recent developments in the chemistry of low valent Group 14 hydrides

This Perspective discusses the synthesis and reactivity of low valent Group 14 hydrides of germanium and tin. The use of hindered terphenyl ligands has facilitated the isolation of a number of unusual new main group hydride structural types (each predicted by computational work), and has culminated in the use of these species as precursors to new cluster archetypes.     

Formation region and hydrogen storage abilities of perovskite-type hydrides

Formation region and hydrogen desorption and absorption properties of the perovskite-type structure in Li_xNa_1−xMgH₃ with x = 0, 0.17, 0.33, 0.50 and 1.00 were studied in the present work. The experimental results are reasonably explained from the viewpoint of the geometric restrictions of ions that are described by so-called Goldschmidt tolerance factors. In NaMgH₃ (x = 0), two plateau pressures of about 0.040 and 0.15 MPa were clearly detected by hydrogen pressure–composition (p–c) isotherm measurement at 673 K. Moreover, NaMgH₃ can be reversibly formed in 1.0 MPa of hydrogen at 673 K, from the decomposed phase of elemental Na and Mg.     

Catalytic Enantioselective Reduction of Ketones by a Chiral Gallium Complex and Catecholborane

A catalytically active version of Noyori's famous BINAL reagent Li[AlH(OEt)(BINOL dianion)] is formed by the combination of LiGaH₄, monothiobinaphthol (MTB), and catecholborane. With this mixture unsymmetrical ketones can be reduced in high enantioselectively. Un=unsaturated unit; R=alkyl.     

Comparison of the reactivities of neutral and cationic transition metal alkyls and hydrides

Comparisons of the reactivities of neutral and cationic alkyl- and aryl-palladium and platinum complexes revealed that the creation of a vacant site adjacent to the alkyl or aryl ligand bound to the palladium center causes marked enhancement in the reactivities of these Group 10 metal alkyls and aryls toward β-hydrogen elimination, and olefin or CO insertion. The implications of the results on the fundamental processes of the transition metal alkyls and aryls with the mechanisms of palladium-catalyzed organic synthesis such as arylation of olefins and carbonylation of aryl halides are discussed. Comparisons of the reactivities of the neutral and cationic ruthenium hydrides also indicated enhancement in reactivity of the neutral hydride complex by its conversion to a cationic complex.     

Lithium Aluminium Hydride and Metallic Iron: A Powerful Team in Alkene and Arene Hydrogenation Catalysis

Alkenes that normally do not react with LiAlH₄ (3-hexene, cyclohexene, 1-Me-cyclohexene), can be reduced to the corresponding alkanes by a mixture of LiAlH₄ and Fe⁰ (the iron was activated by Metal-Vapour-Synthesis). This alkene-to-alkane conversion with a stoichiometric quantity of LiAlH₄/Fe⁰ does not need quenching with water or acids, implying that both H's originate from LiAlH₄. The LiAlH₄/Fe⁰ combination is also a remarkably potent cooperative catalyst for hydrogenation of multi-substituted alkenes and benzene or toluene. An induction period of circa two hours and the minimally required temperature of 120 °C, suggests that the actual catalyst is a combination of Fe⁰ and the decomposition product of LiAlH₄ (LiH and Al⁰). A thermally pre-activated LiAlH₄/Fe⁰ catalyst did not need an induction time and is also active at room temperature and 1 bar H₂. A combination of AliBu₃ and Fe⁰ is an even more active hydrogenation catalyst. Without pre-activation, tetra-substituted alkenes like Me₂C=CMe₂ and toluene could be fully hydrogenated.     

New developments in the chemistry of heteropolytungstates of rhodium and cerium

The heteropolytungstates [PW₁₁O₃₉RhCl]⁵⁻ (I), [PW₁₁O₃₉RhCH₂COOH]⁵⁻ (III), and [PW₁₁O₃₉Rh₂(OAc)₂]⁵⁻ (IV) are prepared by hydrothermal reaction of [PW₁₁O₃₉]⁷⁻ with RhCl₃ or Rh₂(OAc)₄ and characterized by NMR and X-ray structure determination. Electrolytic reduction of I yields the dimeric species [(PW₁₁O₃₉Rh₂)]¹⁰⁻ (II) which reacts with C₆H₅CH₂Br under photochemical conditions to yield dibenzyl and [PW₁₁O₃₉RhBr]⁵⁻ in a process analogous to Rh-porphyrins. Anion III and the corresponding Sicentered anion are rare examples of complexes with Rh-C bonds prepared in aqueous solution. Reaction of B-α [As^IIIW₉O₃₃]⁹⁻ with Ln^III yields new, massive heteropolytungstates [As₂Ln₂(H₂O)W₂₉O₁₀₃]¹⁷⁻ Ln = La, Ce(V), [Ce₄(H₂O)₄ − 4x(AsW₉O₃₃)₄As(WO₃)_{2 + x}(WO₅)]²⁵⁻, x < 0.5 (VI), and As₁₂Ln₁₆(H₂O)₃₆W₁₈₄O₃₂₄]⁷⁶⁻; Ln La,Ce (VII) with approximate relative molecular masses of 7 600, 10 500, and 40 000 respectively. Anion VII has a folded cyclic structure with a radius of 4 nm and is the largest heteropolytungstate so far reported. It is synthesized in yields of ca 30 % under mild conditions.     

New trends in methodological developments in clinical chemistry

Many new techniques have been introduced in clinical chemistry. Three important new methodologies are dry chemistry, gen technology and biosensors. Solid-phase chemistry systems. The two most common solid-phase systems are the Kodak-Ektachem and the Boehringer Mannheim Reflotron. The first one is working with serum and the second one mainly with whole blood. The determination of urea and the determination of the activity of AST (GOT) will be described. The greatest problems of these systems are the quality control of the analysis and the interferences by endogenous and exogenous substances. Analysis with the aid of gen technology. The major diagnostic applications of gen technology in human disease is the detection of genetic disorders and the tumor diagnosis. The beta-thalassemia will be the example for genetic disorders and the chronic myeloid leukemia (CML) for diagnosis of a tumor. Thalassemias are a group of inherited disorders caused by the defective or absent outpout of one of the globin chains of the Hb tetramere. The CML is an example of a specific translocation of a small region of chromosome 9 bearing the abl-oncogene to chromosome 22. Biosensors in biochemical analysis. Biosensors are analytical devices that respond selectively to analytes in an appropriate sample and convert their concentration into an electrical signal. As examples an in-vivo ferrocene-mediated glucose sensor and the determination of the isoenzyme LDH5 based on an antigene-antibody reaction are described.     

Synthesis and Crystal Structure of an Oligomeric Lithium Bis(amido)hydridooxidoaluminate Cluster, [{Li(C14H30N2)AlHO1/2}4]

The lithium bis(amido)hydridooxidoaluminate cluster [{Li(C₁₄H₃₀N₂)AlHO_1/2}₄] has been synthesized during systematic metallation/hydrometallation studies of a series of 1,4‐diazabut‐1‐enes with lithium aluminiumhydride. Formation of the complex is presumably derived from partial hydrolysis of the related lithium bis(amido)dihydridoaluminate and has been characterized using single crystal X‐ray diffraction. The complex crystallizes in the monoclinic space group C2/c (No. 15) with a = 25.012(2) Å, b = 10.673(2) Å, c = 28.673(3) Å, β = 115.855(7)°, V = 6887(1) ų, Z = 4. The complex exhibits an oligomeric structure of crystallographic C₂ symmetry, comprised of complex multicyclic units arising from extensive metal, hydride, oxide and ligand bridging interactions. These associations give rise to edge‐fused, non‐planar NAlOLi four‐membered rings tightly binding two of the diamido‐chelated aluminate units, with these in turn aggregating further via two of the μ²‐hydrides involving lithium atoms.     

Synthesis and structural characterisation of alkylaluminium and alkylgallium pinacolates

The influence of the steric repulsion of ligands on the structure of alkylaluminium and alkylgallium 2,3-dimethylbutane-2,3-diolates (pinacolates) has been studied. Reaction of Me₃Al and pinacol afforded the compound Me₅Al₃[OC(CH₃)₂C(CH₃)₂O]₂ (1) possessing two diolate ligands. The treatment of pinacol with the more sterically hindered ^tBu₃Al resulted in the formation of aluminium tripinacolate ^tBu₃Al₃[OC(CH₃)₂C(CH₃)₂O]₃ (2) as the only product. In contrast, the reaction of the less reactive ^tBu₃Ga with pinacol stopped at the stage of the compound ^tBu₃Ga₂[OC(CH₃)₃C(CH₃)₂O] [OC(CH₃)₃C(CH₃)₂OH] (3), which is an intermediate product of the reaction of 1,2-diols with group 13 trialkyls. Compounds 1, 2 and 3 were crystallographically characterised.     

Excited states in the radiation chemistry of gaseous diatomic hydrides

Although some uncertainty concerning the yield of triplet excited states exists, the yields of ions and atoms predicted from electron impact cross-sections and other information are in relatively good agreement with experimental data for the radiolysis of H₂. A substantial contribution to the atom yield comes from excited states lying just below and above the ionization potential. Less information is available for hydrogen halides. However, while rapid auto-ionization occurs for some superexcited states of HCl, there is again evidence for disscoiations- in this case to form H(1s) and excited Cl. The occurence of this type of process is supported by energy balance calculations for both HCl and HBr. The behaviour of the low-lying excited states of these molecules is relatively well understood.     

LiTMP Trans‐Metal‐Trapping of Fluorinated Aromatic Molecules: A Comparative Study of Aluminum and Gallium Carbanion Traps

Fluoroaromatic scaffolds pose a challenge to lithiation due to low stability of lithiated intermediates. Here we apply trans‐metal‐trapping (TMT) to a series of key fluorinated aromatics. In TMT, LiTMP performs the metalation, while an organometallic trap intercepts the emergent carbanion. This study contrasts the trapping abilities of i Bu₂AlTMP and Ga(CH₂SiMe₃)₃, structurally mapping their TMT reactions and probing relative stabilities of metalated fluoroaromatic intermediates by NMR studies. Results show the installed Al−C(aryl) bonds are more prone to decomposition by benzyne formation and Li‐F liberation, than the Ga−C(aryl) species. The latter are thus better for onward reactivity as demonstrated in cross‐coupling reactions with benzoyl chloride that produce ketones.     

Recent developments in the chemistry of azaferrocenes

The simplest heteroferrocene, azaferrocene, was first described in 1964, and until recently, the chemistry of these compounds has remained largely unexplored. This review will focus on recent advances in the chemistry of azaferrocenes including methods of azaferrocene synthesis and functionalization. The electrochemical behavior of azaferrocenes and their applications in catalysis and biology will also be emphasized here.     

Organometallic compounds of Group 13 elements containing the ligand C(SiMe3)2(SiMe2C5H4N-2)

The lithium derivative (1) reacted with AlCl₃ or Me₂AlCl to give, respectively, the monomeric compounds (2a) and (2b). The product from reaction with commercially available GaBr₃ was the analytically pure monomeric heterocycle (3), indicating that the starting halide had been partially hydrolysed before use. The reaction between 1 and commercially available InCl₃ gave a homogenous white solid (4) with X = Cl (59%) or OH (41%). The X-ray crystal structures of 2a, 3, and 4 have been determined.     

Modern aspects of the chemistry of complex boron and aluminum hydrides

The review deals with new methods of synthesis of complex tetrahydroborates and tetrahydroaluminates and their coordination compounds, initial reagents for synthesis of borides, catalyst precursors, and materials for hydrogen economy.     

Recent developments in the chemistry of perhydroindoles and perhydrocinnolines

Recent synthetic routes to the tetrahydro, hexahydro and octahydro derivatives of indoles are reviewed. An interesting one is the formation of 3-amino-4-oxo-4,5,6,7-tetrahydroindoles in the reaction of 2-phenacyl cyclohexane-l,3-diones with 1,1-disubstituted hydrazines. Antifertility, cns depressant and antiinflammatory activities have been encountered for perhydroindoles besides other biological activities. Hexahydrocinnolines are obtained from the reaction of 2-phenacyl (acetonyl) cyclohexanones and cyclohexane-1,3-diones with hydrazines, while octahydrocinnolines are formed from cyclohexanone-2-acetic acids and hydrazines in two steps. 5-oxo-5,6,7,8-hexahydrocinnolines and their oximes undergo anomalous and interesting aromatisation reactions. Some hexahydrocinnolines are cns depressants while octahydrocinnolines are analgesics. More importantly, they are precursors for interesting azamorphinans. Contribution No. 736 from Research centre