Formation of novel anionic gold-tin cluster compounds

A straightforward procedure for the formation of mixed metal Au/Sn clusters is presented: reaction of the heteroborate [SnB11H11]2- with phosphine gold electrophiles gave the clusters [Bu3NH]3[{(Et3P)Au(SnB11H11)}3] and [Bu3MeN]4[{(dppm)Au2(SnB11H11)2}2], which were characterised by X-ray diffraction.     

Metalloid Cluster Compounds of Group 14: Bonding Properties and Subsequent Reactions

Abstract

Metalloid cluster compounds of group 14 of the general formulae E_nR_m with n > m (E = Si, Ge, Sn, Pb; R = ligand), where naked as well as ligand bound tetrel atoms are present, represent a novel class of cluster compounds in group 14 chemistry and can be seen as intermediates on the way to the elemental state. Therefore, interesting properties are expected for these compounds, which might complement results from nanotechnology. In this article, first results for germanium are discussed, together with novel build-up reactions on the way to novel materials based on metalloid cluster compounds.

GRAPHICAL ABSTRACT     

Structure and phase stability of binary zintl-phase compounds: lithium-group 13 intermetallics and metal-doped group 14 clathrate compounds

The structure/bonding relationship in a series of intermetallic phases of Li with Al, Ga, and In was investigated by density functional theory and complemented by a model based on tight-binding theory and the method of moments. The combination of these two approaches provides a simple scheme which allows for both a comprehensive understanding of structural trends and the ability to predict low-energy structures for a given composition. This analysis gives a straightforward picture of phase stability in terms of local geometric features such as triangular, square, and hexagonal arrangements of atoms. The approach was extended to examine the structural properties of metal-doped clathrate compounds of C, Si, Ge, and Sn. Clathrate-type phases based on the frameworks Si172, Ge172, Si40, and Ge40 are not only likely to be energetically favorable but may also exhibit high thermoelectric efficiency.     

Chemometrics in pharmaceutical analysis: an introduction, review, and future perspectives

Chemometrics is the application of statistical and mathematical methods to analytical data to permit maximum collection and extraction of useful information. The utility of chemometric techniques as tools enabling multidimensional calibration of selected spectroscopic, electrochemical, and chromatographic methods is demonstrated. Application of this approach mainly for interpretation of UV-Vis and near-IR (NIR) spectra, as well as for data obtained by other instrumental methods, makes identification and quantitative analysis of active substances in complex mixtures possible, especially in the analysis of pharmaceutical preparations present in the market. Such analytical work is carried out by the use of advanced chemical instruments and data processing, which has led to a need for advanced methods to design experiments, calibrate instruments, and analyze the resulting data. The purpose of this review is to describe various chemometric methods in combination with UV-Vis spectrophotometry, NIR spectroscopy, fluorescence spectroscopy, electroanalysis, chromatographic separation, and flow-injection analysis for the analysis of drugs in pharmaceutical preparations. Theoretical and practical aspects are described with pharmaceutical examples of chemometric applications. This review will concentrate on gaining an understanding of how chemometrics can be useful in the modern analytical laboratory. A selection of the most challenging problems faced in pharmaceutical analysis is presented, the potential for chemometrics is considered, and some consequent implications for utilization are discussed. The reader can refer to the citations wherever appropriate.     

The synthesis and structural characterisation of an homologous series of group 14 1-chloro-2,2-difluorovinyl compounds

A series of group 14 1-chloro-2,2-difluorovinyl compounds Ph₃E(CClCF₂) (E=Ge, Sn, Pb) has been prepared using the low temperature reactions of 1-chloro-2,2-difluorovinyllithium (LiCClCF₂), generated in situ from CF₃CH₂Cl (HCFC-133a) and n-butyllithium. These new materials have been fully characterised, including for E=Ge and Sn, by single crystal X-ray studies. This is the first time that any main-group 1-chloro-2,2-difluorovinyl compounds have been crystallographically studied.     

Addition of stable nitroxide radical to stable divalent compounds of heavier group 14 elements

The reactions of stable cyclic dialkylgermylene 2 and dialkylstannylene 3 with 2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) radical (2 equiv) gave the corresponding 1:2 adducts 4 and 5, respectively, which were characterized by NMR, MS, and X-ray analyses. The kinetics of the stepwise addition of two TEMPO molecules to germylene 2 revealed that the initial addition of TEMPO to 2 was 1010 times slower than the second TEMPO addition to the resulting germyl radical. The origin of the rate difference was discussed on the basis of the qualitative perturbation theory. In contrast to the reactions of 2 and 3, the reaction of dialkylsilylene 1 with TEMPO gave an interesting 1,3-dioxadisiletane derivative.     

The cation cluster of heavier group 14 elements: a free germyl cation with trishomoaromaticity

The heavier group 14 element cation cluster compound, [(tBu3Si)6Ge10I]+.TTFPB- (3+. TTFPB-; TTFPB- = tetrakis(2,3,5,6-tetrafluorophenyl)borate), was unexpectedly obtained by thermolysis of in situ prepared iodocyclotrigermene, (tBu3Si)3Ge3I, in toluene in the presence of KI and K+.TTFPB-. The molecular structure of 3+.TTFPB- has been unambiguously determined by X-ray crystallography, showing that 3+ is a free germyl cation. The three "naked" cationic germanium atoms in the framework constitute a three-center two-electron (3c-2e) bond with a trishomocyclotrigermenylium character, which is well-supported by a theoretical calculation on the model compound Ge10H7+.     

Synthesis and structure of cluster compounds containing a novel cluster core {Re4STe3}

Three novel cluster compounds K₄[Re₄STe₃(CN)₁₂]·₄H₂O (I), [{Cu(en)₂}₂Re₄STe₃(CN)₁₂]·₅H₂O (II) and [{Cu(trien)}₂Re₄STe₃(CN)₁₂]·2H₂O (III) (en is ethylenediamine, trien is triethylenetetraamine) containing a new cluster core {Re₄STe₃} have been prepared and structurally characterized. According to single crystal X-ray diffraction data, compound I is ionic and represents the arrangement of ions K⁺ and [Re₄STe₃(CN)₁₂]^4?; compounds II and III are molecular and formed by two cationic moieties {Cu(en)₂}²⁺ and {Cu(trien)}²⁺, respectively, coordinated to one cluster anion. In the solid state, S atom positions in the tetrahedron Q₄ (Q = S, Te) are disordered for all three compounds: in I and III sulfur atoms are split over all four Q positions, while in II over two positions.     

Controlled introduction of allylic group to chlorosilanes

Allylation of chlorosilanes has been achieved with allylsamarium bromide, especially in a controlled manner. Thus allylation of trisubstituted chlorosilanes (R₃SiCl) afforded a variety of aryl, aralkyl, and alkenyl substituted allylsilanes. Dichlorosilanes (R₂SiCl₂) can either afford monoallylated silanes or diallylated silanes depending on the amount of allylsamarium bromide used. Similarly, trichlorosilanes (RSiCl₃) can selectively afford mono-, di-, and tri-allylation products. Finally, perchlorosilane (SiCl₄) was allylated stepwise and the corresponding silanes containing one, two, three or four allylic groups, respectively, were obtained in satisfactory yields.     

New perspectives for "non-classical" molecules: heavy [1.1.1]propellanes of group 14

Heavy analogues of hydrocarbons intrigue chemists for a number of reasons, not least because they are often fundamentally different from their carbon counterparts and have remained a challenge for both experimentalists and theoreticians for a long time. The appealing properties of [1.1.1]propellanes of group 14 consisting of inverted tetrahedral bridgehead atoms can mainly be attributed to the particular bonding between the latter. More than 20 years after the first member of this family has been published, several contributions to this area have impressively extended the spectrum of these so-called main-group biradicaloids. Still in its infancy, further perspectives for these "non-classical" molecules are now arising. In this tutorial review, early findings and recent developments in this area are presented. Particular attention is drawn on the relationship of unusual structures and unusual reactivities of main-group element compounds in general and in particular of heavy propellane scaffolds of group 14.     

Preparation and properties of novel palladium compounds containing a thiomethoxymethyl group

Oxidative addition of chloromethyl methyl sulfide to Pd(Ph₃P)₄ provided a good yield of Pd(Ph₃P)₂(CH₂SCH₃)Cl (I) whose ¹H NMR and molecular weight data showed that dissociation of either the phosphine or the chloride ligand occurs in CH₂Cl₂ solution. In accord with such equilibria, repeated crystallization of I from CH₂Cl₂ and Et₂O gradually removed the triphenylphosphine set free in these solvents to give the monomeric complex. Pd(Ph₃P)(CH₂SCH₃)Cl (III), while treatment of 1 with NH₄PF₆ in CH₂Cl₂ and acetone gave the cationic complex [Pd(Ph₃P)₂(CH₂SCH₃]PF₆ (II),¹H NMR spectra of II and III are discussed in terms of a three-membered chelate structure arising from coordination of sulfur with palladium     

Studies on organophosphorous compounds: IX. C-Phosphorylation of compounds bearing an active methylene group

The behaviour of carbanions of para-substituted benzylcyanides and ambident enolates toward phosphorylation has been examined. In the former case the C-phosphorylation proceeded smoothly, while the ambident enolate ions derived either from β-diketones or from β-ketoesters gave exclusively regiospecific O-phosphorylation products on reaction with diethyl phosphoryl chloride. The experimental results are well supported by reaction selectivity in terms of E_qo/E_C.OC/ based on EHMO calculation.     

17O NMR spectroscopy in the study of group 14 organometallic compounds

A study of Group 14 organometallic compounds using ¹⁷O NMR spectroscopy carried out at the Latvian Institute of Organic Synthesis has been reviewed. The main areas of ¹⁷O NMR application—studies of electronic effects, conformational analysis and coordinative interactions—have been characterized.     

High-pressure syntheses of novel binary nitrogen compounds of main group elements

The application of high-pressure methods in the search for novel materials usually requires additional effort compared to syntheses at ambient pressure. Depending on the desired p/T conditions different methods may be used. Special techniques and experimental apparatus such as shock waves, diamond anvil cells, and multianvil presses, which have been applied mainly by earth scientists and physicists in the past, are increasingly being applied by synthetic chemists and material scientists. A series of fascinating discoveries have been made recently as is demonstrated by three examples of binary nitrogen compounds: 1) Diazenides, compounds with N(2)(2-) ions, were obtained as single-phase products and structurally characterized for the first time. 2) At 11 GPa and 1800 K a phosphorus(V) nitride was prepared, which contains tetragonal PN(5) pyramids as a novel structural motif. 3) Macroscopic amounts of spinel silicon nitride were synthesized by shock-wave techniques, which allows the comprehensive characterization and possibly the implementation of this new hard material.     

Convenient method for introduction of cyano group into nitrogen,sulfur, and oxygen heterocyclic compounds

A number of heterocyclic aldehydes were transformed via their NN-dimethythydrazones to nitriles in high yields using a one-pot procedure.Department of Organic Chemistry, Slovak Technical University, Bratislava, Slovakia. Institute of Organic Chemistry. Technical University, Wroclaw, Poland. Published in Khimiya Geterotsiklicheskikh Soedinerui, No. 10, pp. 1356–1357, October, 1995. Original article submitted August 24, 1995.     

Preparation,properties and reactivities of novel platinum compounds containing a thiomethoxymethyl group

Oxidative addition of ClCH₂SCH₃ to PtL₄ afforded trans-PtL₂(CH₂SCH₃)Cl (Ia, L = Ph₃P;Ib, L = MePh₂P). Treatment of I with NH₄PF₆ or Et₃OBF₄ in CH₂C1₂ gave ionic species, [PtL₂(CH₂SCH₃)]X (II, L = Ph₃P, MePh₂P, X = BF₄, PF₆), while similar treatment with MeSO₃F in benzene yielded a new type of stable dimethylsulfonium methylide—platinum complex, trans-[PtL₂(CH₂SMe₂)Cl] SO₃F (IIIa, L = Ph₃P; IIIb, L = MePh₂P). Action of H₂O₂ on Ia gave [Pt(Ph₃P)(μ-CH₂SCH₃)C1]₂ (IV) and its triphenylarsine analog, [Pt(Ph₃As)(μ-CH₂SCH₃)C1]₂ (V) was prepared in one step by oxidative addition of ClCH₂SCH₃ to Pt(AsPh₃)₄. The structural difference between [Pt(Ph₃P)(μ-CH₂SCH₃)C1]₂ and Pd(Ph₃P)- (CH₂SCH₃)C1 is discussed in terms of the difference in the ionization potential from d¹⁰ to d⁸ electronic state of metals.     

A novel porous carbon and its perspectives for the solid phase extraction of volatile organic compounds

A porous carbon sorbent prepared by controlled pyrolysis of saccharose in a matrix of silica gel was tested for the preconcentration of a variety of compounds differing in polarity and volatility (hydrocarbons, halocarbons, oxygenated compounds) in simulated and real air samples. The trapped components were desorbed off-line by liquid-(carbon disulphide and carbon disulphide with 1% methanol) and on-line by thermo-desorption in combination with HRCGC. Adsorption-desorption properties of the sorbent were evaluated according to the determined recovery values, whereby physicochemical interactions of both the sorbent and solute were taken into consideration. With oxygenated compounds recovery data indicate the presence of active sites on the surface of the sorbent.Dedicated to Professor Dr. Dr. h.c. mult. J. F. K. Huber on the occasion of his 70th birthday