Showing papers in "Zeitschrift für anorganische und allgemeine Chemie in 2018"

200 Years of Lithium and 100 Years of Organolithium Chemistry.

Abstract: The element lithium has been discovered 200 years ago. Due to its unique properties it has emerged to play a vital role in industry, esp. for energy storage, and lithium-based products and processes support sustainable technological developments. In addition to the many uses of lithium in its inorganic forms, lithium has a rich organometallic chemistry. The development of organometallic chemistry has been hindered by synthetic problems from the start. When Wilhelm Schlenk developed the basic principles to handle and synthesize air- and moisture-sensitive compounds, the road was open to further developments. After more information was available about the stability and solubility of such compounds, they started to play an essential role in other fields of chemistry as alkyl or aryl transfer reagents.

The van der Waals Ferromagnets Fe5–δGeTe2 and Fe5–δ–xNixGeTe2 – Crystal Structure, Stacking Faults, and Magnetic Properties

Abstract: Fe5-delta GeTe2 was synthesized by heating the elements at 1050 K and characterized by single crystal and powder X-ray analysis. The structure [R3m, a = 4.0376(4) angstrom, c = 29.194(6) angstrom] consists of Fe5-delta Ge layers separated by tellurium double layers forming a van der Waals gap. The pronounced two-dimensional character of Fe5-delta GeTe2 causes stacking faults along the c direction. Simulations of different stacking variants using the DIFFaX software reveal disorder occurring in domains. Magnetic measurements of Fe5-delta GeTe2 show ferromagnetism below 279 K with a saturation moment of 1.80 mu(B) at 1.8 K. Nickel substitution of the iron sites has little influence on the structure but changes the saturation moment, which passes through a maximum of 2.11 mu(B) in Fe4.11Ni0.50GeTe2. This indicates that structural influences as well as the dilution of the magnetic iron atoms play a decisive role.

Synthesis and X‐ray Crystal Structures of Ga‐substituted Distibenes [L(X)GaSb]2

Abstract: This is the peer reviewed version of the following article: Z. Anorg. Allg . Chem. 2018, 644, 1028-1033, which has been published in final form at: https://doi.org/10.1002/zaac.201800204 Version of Record online: 13 July 2018

Synthesis of Benzonitrile from Dinitrogen

Abstract: The rhenium mediated synthesis of benzonitrile is reported with direct use of N2 as a nitrogen source. The reaction affords benzonitrile in about 30% overall yield upon N2 splitting and benzylation of resulting terminal nitride. Subsequent oxidation of an intermediate phenylketimido compound restores the parent rhenium complex within a full four-step synthetic cycle. The reaction shows that previously observed nitrile tautomerization is not a prerequisite for nitrile synthesis from N2 with this system. The Haber-Bosch process (HBP) currently provides synthetic ammonia at a massive scale (approx. 150 Mt/a).1 The high energy demand has fueled many efforts to develop bioinspired catalysts for nitrogen fixation at ambient conditions.2 Remarkable recent progress followed Schrock’s seminal work, 3 , 4 , 5 with turn-over numbers up to 230 for the currently most active catalysts.6 Scheme 1. Oxidative release of acetonitrile from ketimide complex 1 as part of a synthetic cycle for direct N-transfer from N2 to acetonitrile.[7e] About 20% of the industrially produced ammonia serves as feedstock for nitrogen containing chemicals, such as amines, nitriles or N-heterocyclic compounds. Direct N2 conversion to organic products therefore is an attractive goal from the point of atom, energy and redox economy. Stoichiometric C–N functionalization of N2, e.g. with C-electrophiles, 7 heterocummulenes, 8 or carbon monoxide, 9 is well established and several quasi-catalytic synthetic cycles were reported as a proof-of-principle.10 Inspired by Cummins’ work,7a,b we recently reported a synthetic cycle for the transformation of N2 to acetonitrile,7e which is an attractive target as judged by the similar bond energies of CoN and NoN triple bonds. The reaction proceeds via rhenium mediated splitting of N2, and subsequent functionalization of the resulting nitrides, by alkylation, deprotonation and ligand oxidation with N-chlorosuccinimide. Examination of this final oxidation step by stepwise 1-electron oxidation of ketimido intermediate 1Me (Scheme 1) gave an unprecedented rhenium(V) vinyl imido complex (2), i.e. a tautomer of the unobserved rhenium(III) nitrile species. Acetonitrile release is finally triggered by addition of a chloride source and catalytic amounts of base (e.g. DBU) presumably to enable vinylimide tautomerization. This observation raises the question whether nitriles that cannot tautomerize, such as arylnitriles ArCN, are also accessible through such a reaction sequence. We here present a full synthetic cycle for the direct synthesis of benzonitrile from dinitrogen via N2 splitting into nitrides. Chemical or electrochemical reduction of the rhenium pincer complexes [ReCl2(PNP)] or [ReCl3(PNP)] (3; PNP = N(CH2CH2PtBu2)2) under N2 (1 bar) affords the rhenium(V) nitride complex [Re(N)Cl(PNP)] (4).7d,e,11 Starting from the rhenium(IV) chloride, isolated yields between 60-70% are obtained with Na/Hg as reductant in THF at room temperature (Scheme 2). The terminal nitride complex can be selectively alkylated at the nitride moiety with alkyltriflates ROTf (R = Me, Et) giving the imido complexes [Re(NR)Cl(PNP)]OTf (R = Me (5H), Et (5Me)).7d,e In contrast to these triflate reagents, benzyltriflate is not stable at room temperature. PhCH2OTf was therefore prepared in situ according to published procedures for other alkyltriflates from excess benzylbromide and AgOTf. 12 Unlike with methyland ethyltriflate, only the previously reported protonation product of 4,7d i.e. the amine complex [Re(N)Cl{HN(CH2CH2PtBu2)2}]OTf, was obtained almost quantitatively as indicated by comparison of the NMR spectra. The origin of the proton remains unclear at this point. However, nitride benzylation is obtained upon addition of a non-nucleophilic base. The benzylimido complex [Re(NCH2Ph)Cl(PNP)]OTf (5Ph) is obtained in up to 90% yield with in situ generated benzyltriflate in the presence of ca. 2 eq of 2,6di-tert-butyl-4-methylpyridine (Scheme 2). The green benzylimido complex 5Ph exhibits Cs symmetry on the NMR timescale. The chemical shift of the 31P{1H} NMR signal (d(C6D6) = 90.3 ppm) resembles the respective methyland ethylimido complexes 5Me (d(C6D6) = 90.7 ppm) and 5Et (d(C6D6) = 90.1 ppm), respectively.7d,e Similarly, the 1H NMR signatures of their pincer ligands reveal closely related characteristics. The methylene protons of the benzylimido moiety (NCH2Ph) of 5Ph are found as a singlet resonance at 4.60 ppm in the 1H NMR spectrum. Furthermore, this signal and the aromatic 1H NMR signals exhibit cross peaks in the NOESY spectrum with the same set of tBu groups, yet not with pincer backbone protons. This observation confirms selective nitride rather than pincer amide benzylation. Benzylimide complex 5Ph is quantitatively deprotonated by strong bases, such as KOtBu or KN(SiMe3)2. For example, with KN(SiMe3)2 the azavinylidene complex [Re(NCHPh)Cl(PNP)] (1Ph, Scheme 2) is obtained in about 80% isolated yield. 31P, 1H and 13C NMR spectroscopic characterization indicates two full sets of Re Cl N

Ore Leashing Processing for Yellow Cake Production and Assay of their Uranium Content by Radiometric Analysis

Abstract: In this study, Ore granite samples were collected from Gattar site for leashing of yellow cake. The process involves heap leaching of uranium through four main steps; size reduction, leaching, uranium purification and finally precipitation and filtration. The separation process has been given in details and as flow chart. Gamma spectrometry based on HpGe detector and energy dispersive X-ray (EDX) were used to assay uranium content and activity before and after separation. The uranium weight percentage value as measured by EDX were found to be 40.5 and 67.5% before and after purification respectively. The results of the calculations based on gamma measurements show high uranium activity and that the uranium activity ratios values are 0.045 ±4.9%, 0.043 ±4.7% and 0.046 ±2.3%, before purification. While these values were found to be 0.050 ±3.3%, 0.049 ±3.3% and 0.050 ±2.7%, after purification, respectively. The results are discussed in details in the paper.