Structural characterization of the extracellular stalk material of the diatom Didymosphenia geminata.

The study represents new bioanalytical characterization of mainly organic components of the poorly investigated extracellular polymeric substances (EPS) of the enigmatic diatom Didymosphenia geminata, an invasive, worldwide expanding species endangering diverse ecosystems. This microalga attaches its siliceous cells to rocky substrates using fibrous stalks, which are made of an EPS-based matrix stabilized by crystalline calcite. The EPS were analyzed using selected methods, including microscopic, spectroscopic, and spectrometric techniques. We identified diverse types of biomolecules. The presence of lipids, condensed aromatics, and heteroaromatic compounds in the EPS has been confirmed using high-resolution mass spectrometry (HR-MS). Additionally, both sulfur-containing functionalities and carboxylic acids were determined too using infrared (IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy. For the first time, lignin compounds have been detected as one of the components of the EPS of the D. geminata diatom, using HR-MS and fluorescence microscopy (FM) in combination with specific staining techniques. By increasing the understanding of the chemistry and structural features of the stalks, we aim to develop potential applications and methods for removing these stalks from affected regions in the future, or, alternatively, to use them as a large-scale source of sustainable biocomposite material.

Isolation and Structure Analysis of Chitin Obtained from Different Developmental Stages of the Mulberry Silkworm (Bombyx mori).

Chitin, a ubiquitous biopolymer, holds paramount scientific and economic significance. Historically, it has been primarily isolated from marine crustaceans. However, the surge in demand for chitin and the burgeoning interest in biopolymers have necessitated the exploration of alternative sources. Among these methods, the mulberry silkworm (Bombyx mori) has emerged as a particularly intriguing prospect. To isolate chitin from Bombyx mori, a chemical extraction methodology was employed. This process involved a series of meticulously orchestrated steps, including Folch extraction, demineralization, deproteinization, and decolorization. The resultant chitin was subjected to comprehensive analysis utilizing techniques such as attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), 13C nuclear magnetic resonance (NMR) spectroscopy, and wide-angle X-ray scattering (WAXS). The obtained results allow us to conclude that the Bombyx mori represents an attractive alternative source of α-chitin.

75As Nuclear Magnetic Resonance Spectroscopic Investigation of the Thioarsenate Speciation in Strongly Alkaline Sulfidic Leaching Solutions.

Copper ores and concentrates thereof feature an increasingly notable content of impurities such as arsenic and other hazardous elements. As an alternative to the state-of-the-art partial roasting process, arsenic could be removed by the alkaline sulfide leaching of the copper concentrates. In order to optimize and understand the processes, knowledge of the speciation and oxidation states is essential. In addition to methods such as UV/Vis spectroscopy, chromatography and ICP/MS methods, 75As NMR spectroscopy may be useful for the differentiation and quantification of the various species. Although arsenate(V) has been characterized by 75As NMR some time ago, to our knowledge, there are no data on tetrathioarsenate(V) AsS43- and the mixed oxygen/sulfur substituted mono-, di- and trithioarsenates(V) AsOxS4-x3-, x = 3, 2, 1, respectively. Therefore, we investigated several model solutions and samples from Cu-As leaching with 75As NMR. The strongly alkaline conditions of the leaching solution proved to be very advantageous for that purpose. Both the tetrathioarsenate(V) and the mixed species AsOxS4-x3- (x = 1-3) could be characterized and provide valuable data for the quantification of the material flows in the leaching process.

P-Ru-Complexes with a Chelate-Bridge-Switch: A Comparison of 2-Picolyl and 2-Pyridyloxy Moieties as Bridging Ligands.

Starting from [Ru(pyO)2(nbd)] 1 and a N,P,N-tridentate ligand (2a: PhP(pic)2, 2b: PhP(pyO)2) (nbd = 2,5-norbornadiene, pic = 2-picolyl = 2-pyridylmethyl, pyO = 2-pyridyloxy = pyridine-2-olate), the compounds [PhP(µ-pic)2(µ-pyO)Ru(κ2-pyO)] (3a) and [PhP(µ-pyO)3Ru(κ2-pyO)] (3b), respectively, were prepared. Reaction of compounds 3 with CO and CNtBu afforded the opening of the Ru(κ2-pyO) chelate motif with the formation of compounds [PhP(µ-pic)2(µ-pyO)Ru(κ-O-pyO)(CO)] (4a), [PhP(µ-pic)2(µ-pyO)2Ru(CNtBu)] (5a), [PhP(µ-pyO)4Ru(CO)] (4b) and [PhP(µ-pyO)4Ru(CNtBu)] (5b). In dichloromethane solution, 4a underwent a reaction with the solvent, i.e., substitution of the dangling pyO ligand by chloride with the formation of [PhP(µ-pic)2(µ-pyO)Ru(Cl)(CO)] (6a). The new complexes 3a, 4a, 5a, 5b and 6a were characterized by single-crystal X-ray diffraction analyses and multi-nuclear (1H, 13C, 31P) NMR spectroscopy. The different coordination behaviors of related pairs of molecules (i.e., pairs of 3, 4 and 5), which depend on the nature of the P-Ru-bridging ligand moieties (µ-pic vs. µ-pyO), were also studied via computational analyses using QTAIM (quantum theory of atoms in molecules) and NBO (natural bond orbital) approaches, as well as the NCI (non-covalent interactions descriptor) for weak intramolecular interactions.

Electrochemical Stimulation of Water-Oil Interfaces by Nonionic-Cationic Block Copolymer Systems.

Variable interfacial tension could be desirable for many applications. Beyond classical stimuli like temperature, we introduce an electrochemical approach employing polymers. Hence, aqueous solutions of the nonionic-cationic block copolymer poly(ethylene oxide)114-b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}171 (i.e., PEO114-b-PDPAEMA171 with a quaternized poly(diisopropylaminoethyl methacrylate) block) were investigated by emerging drop measurements and dynamic light scattering, analyzing the PEO114-b-qPDPAEMA171 impact on the interfacial tension between water and n-decane and its micellar formation in the aqueous bulk phase. Potassium hexacyanoferrates (HCFs) were used as electroactive complexants for the charged block, which convert the bishydrophilic copolymer into amphiphilic species. Interestingly, ferricyanides ([Fe(CN)6]3-) act as stronger complexants than ferrocyanides ([Fe(CN)6]4-), leading to an insoluble qPDPAEMA block in the presence of ferricyanides. Hence, bulk micellization was demonstrated by light scattering. Due to their addressability, in situ redox experiments were performed to trace the interfacial tension under electrochemical control, directly utilizing a drop shape analyzer. Here, the open-circuit potential (OCP) was changed by electrolysis to vary the ratio between ferricyanides and ferrocyanides in the aqueous solution. While a chemical oxidation/reduction is feasible, also an electrochemical oxidation leads to a significant change in the interfacial tension properties. In contrast, a corresponding electrochemical reduction showed only a slight response after converting ferricyanides to ferrocyanides. Atomic force microscopy (AFM) images of the liquid/liquid interface transferred to a solid substrate showed particles that are in accordance with the diameter from light scattering experiments of the bulk phase. In conclusion, the present results could be an important step toward economic switching of interfaces suitable, e.g., for emulsion breakage.

Ionic Dissociation of SiCl4 : Formation of [SiL6 ]Cl4 with L=Dimethylphosphinic Acid.

Reactions of SiCl4 with R2 PO(OH) (R=Me, Cl) yield compounds with six-fold coordinated silicon atoms. Whereas R=Me afforded the hexacoordinated tetra-cationic silicon complex [Si(Me2 PO(OH))6 ]4+ with chloride counter-ions, R=Cl caused release of HCl with formation of a cyclic dimeric silicon complex [Si(Cl2 PO(OH))(Cl2 PO2 )3 (µ-Cl2 PO2 )]2 with bridging bidentate dichlorophosphates.

Spider Chitin: An Ultrafast Microwave-Assisted Method for Chitin Isolation from Caribena versicolor Spider Molt Cuticle.

Chitin, as a fundamental polysaccharide in invertebrate skeletons, continues to be actively investigated, especially with respect to new sources and the development of effective methods for its extraction. Recent attention has been focused on marine crustaceans and sponges; however, the potential of spiders (order Araneae) as an alternative source of tubular chitin has been overlooked. In this work, we focused our attention on chitin from up to 12 cm-large Theraphosidae spiders, popularly known as tarantulas or bird-eating spiders. These organisms "lose" large quantities of cuticles during their molting cycle. Here, we present for the first time a highly effective method for the isolation of chitin from Caribena versicolor spider molt cuticle, as well as its identification and characterization using modern analytical methods. We suggest that the tube-like molt cuticle of this spider can serve as a naturally prefabricated and renewable source of tubular chitin with high potential for application in technology and biomedicine.

Tin(IV) Compounds with 2-C6F4PPh2 Substituents and Their Reactivity toward Palladium(0): Formation of Tin-Palladium Complexes via Oxidative Addition.

The tin(IV) compounds MexSn(2-C6F4PPh2)4-x (1, x = 1; 2, x = 2) and ClSn(2-C6F4PPh2)3 (3) were obtained from the reactions of 2-LiC6F4PPh2 with MeSnCl3 (3:1), Me2SnCl2 (2:1), or SnCl4 (3:1), respectively. The reactions of 2-LiC6F4PPh2 with SnCl4 in different stoichiometric ratios (4:1-1:1) gave 3 as the main product. Compound Cl2Sn(2-C6F4PPh2)2 (4) was formed in the transmetalation reaction of 3 and [AuCl(tht)] but could not be isolated. 1 and 2 react with palladium(0) sources {[Pd(PPh3)4] and [Pd(allyl)Cp]} by the oxidative addition of one of their Sn-CAryl bonds to palladium(0) with formation of the heterobimetallic complexes [MeSn(µ-2-C6F4PPh2)2Pd(κC-2-C6F4PPh2)] (5) and [Me2Sn(µ-2-C6F4PPh2)Pd(κ2-2-C6F4PPh2)] (6) featuring Sn-Pd bonds. The reaction of 3 with palladium(0) proceeds via the oxidative addition of the Sn-Cl bond to palladium(0), thus furnishing the complex [Sn(µ-2-C6F4PPh2)3PdCl] (7) featuring a Sn-Pd bond and a pentacoordinate Pd atom. Transmetalation of MexSn(2-C6F4PPh2)4-x (x = 1-3) with [Pd(allyl)Cl]2 gave MexClSn(2-C6F4PPh2)3-x and [Pd(allyl)(µ-2-C6F4PPh2)]2. For x = 1, the compound MeClSn(2-C6F4PPh2)2 (generated in situ) reacted with another 1 equiv of [Pd(allyl)Cl]2 by the oxidative addition of the Sn-Cl bond to palladium(0) and the reductive elimination of allyl chloride, thus leading to [MeSn(µ-2-C6F4PPh2)2PdCl] (8). The reductive elimination of allyl chloride was also observed in the reaction of 3 with [Pd(allyl)Cl]2, giving [Sn(µ-2-C6F4PPh2)3PdCl] (7). All compounds have been characterized by means of multinuclear NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction, and selected compounds by 119Sn Mössbauer spectroscopy. Computational analyses (natural localized molecular orbital calculations) have provided insight into the Sn-Pd bonding of 5-8.

2-Acylpyrroles as mono-anionic O,N-chelating ligands in silicon coordination chemistry.

Kryptopyrrole (2,4-dimethyl-3-ethylpyrrole) was acylated with, for example, benzoyl chloride to afford 2-benzoyl-3,5-dimethyl-4-ethylpyrrole (L(1)H). With SiCl4 this ligand reacts under liberation of HCl and formation of the complex L(1)2SiCl2. In related reactions with HSiCl3 or H2SiCl2, the same chlorosilicon complex is formed under liberation of HCl and H2 or liberation of H2, respectively. The chlorine atoms of L(1)2SiCl2 can be replaced by fluoride and triflate using ZnF2 and Me3Si-OTf, respectively. The use of a supporting base (triethylamine) is required for the complexation of phenyltrichlorosilane and diphenyldichlorosilane. The complexes L(1)2SiCl2, L(1)2SiF2, L(1)2Si(OTf)2, L(1)2SiPhCl, and L(1)2SiPh2 exhibit various configurations of the octahedral silicon coordination spheres (i.e. cis or trans configuration of the monodentate substituents, different orientations of the bidentate chelating ligands relative to each other). Furthermore, cationic silicon complexes L(1)3Si(+) and L(1) SiPh(+) were synthesized by chloride abstraction with GaCl3. In contrast, reaction of L(1)2SiCl2 with a third equivalent of L(1)H in the presence of excess triethylamine produced a charge-neutral hexacoordinate Si complex with a new tetradentate chelating ligand which formed by Si-templated C-C coupling of two ligands L(1).

Chemometric Combination of Ultrahigh Resolving Mass Spectrometry and Nuclear Magnetic Resonance Spectroscopy for a Structural Characterization of Lignin Compounds.

In recent years, the potential of lignins as a resource for material-based applications has been highlighted in many scientific and nonscientific publications. But still, to date, a lack of detailed structural knowledge about this ultracomplex biopolymer undermines its great potential. The chemical complexity of lignin demands a combination of different, powerful analytical methods, in order to obtain these necessary information. In this paper, we demonstrate a multispectroscopic approach using liquid-state and solid-state Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) and nuclear magnetic resonance (NMR) spectroscopy to characterize a fractionated LignoBoost lignin. Individual FT-ICR-MS, tandem MS, and NMR results helped to determine relevant information about the different lignin fractions, such as molecular weight distributions, oligomer sizes, linkage types, and presence of specific functional groups. In addition, a hetero spectroscopic correlation approach was applied to chemometrically combine MS, MS/MS, and NMR data sets. From these correlation analyses, it became obvious that a combination of tandem MS and NMR data sets gives the opportunity to comprehensively study and describe the general structure of complex biopolymer samples. Compound-specific structural information are obtainable, if this correlation approach is extended to 1D-MS and NMR data, as specific functional groups or linkages are verifiable for a defined molecular formula. This enables structural characterization of individual lignin compounds without the necessity for tandem MS experiments. Hence, these correlation results significantly improve the depth of information of each individual analysis and will hopefully help to structurally elucidate entire lignin structures in the near future.

Disilicon complexes with two hexacoordinate Si atoms: paddlewheel-shaped isomers with (ClN4 )Si-Si(S4 Cl) and (ClN2 S2 )Si-Si(S2 N2 Cl) skeletons.

The reaction of 1-methyl-3-trimethylsilylimidazoline-2-thione with hexachlorodisilane proceeds toward substitution of four of the disilane Cl atoms during the formation of disilicon complexes with two neighboring hexacoordinate Si atoms. The N,S-bidentate methimazolide moieties adopt a buttressing role, thus forming paddlewheel-shaped complexes of the type ClSi(µ-mt)4 SiCl (mt=methimazolyl). Most interestingly, three isomers (i.e., with (ClN4 )SiSi(S4 Cl), (ClN3 S)SiSi(S3 NCl), and (ClN2 S2 )SiSi(S2 N2 Cl) skeletons as so-called (4,0), (3,1), and cis-(2,2) paddlewheels) were detected in solution by using (29) Si NMR spectroscopic analysis. Two of these isomers could be isolated as crystalline solids, thus allowing their molecular structures to be analyzed by using X-ray diffraction studies. In accord with time-dependent NMR spectroscopy, computational analyses proved the cis-(2,2) isomer with a (ClN2 S2 )SiSi(S2 N2 Cl) skeleton to be the most stable. The compounds presented herein are the first examples of crystallographically evidenced disilicon complexes with two SiSi-bonded octahedrally coordinated Si atoms and representatives of the still scarcely explored class of Si coordination compounds with sulfur donor atoms.

A Non-Hydrolytic Sol-Gel Route to Organic-Inorganic Hybrid Polymers: Linearly Expanded Silica and Silsesquioxanes.

Condensation reactions of chlorosilanes (SiCl4 and CH3SiCl3) and bis(trimethylsilyl)ethers of rigid, quasi-linear diols (CH3)3SiO-AR-OSi(CH3)3 (AR = 4,4'-biphenylene (1) and 2,6-naphthylene (2)), with release of (CH3)3SiCl as a volatile byproduct, afforded novel hybrid materials that feature Si-O-C bridges. The precursors 1 and 2 were characterized using FTIR and multinuclear (1H, 13C, 29Si) NMR spectroscopy as well as single-crystal X-ray diffraction analysis in case of 2. Pyridine-catalyzed and non-catalyzed transformations were performed in THF at room temperature and at 60 °C. In most cases, soluble oligomers were obtained. The progress of these transsilylations was monitored in solution with 29Si NMR spectroscopy. Pyridine-catalyzed reactions with CH3SiCl3 proceeded until complete substitution of all chlorine atoms; however, no gelation or precipitation was found. In case of pyridine-catalyzed reactions of 1 and 2 with SiCl4, a Sol-Gel transition was observed. Ageing and syneresis yielded xerogels 1A and 2A, which exhibited large linear shrinkage of 57-59% and consequently low BET surface area of 10 m2⋅g-1. The xerogels were analyzed using powder-XRD, solid state 29Si NMR and FTIR spectroscopy, SEM/EDX, elemental analysis, and thermal gravimetric analysis. The SiCl4-derived amorphous xerogels consist of hydrolytically sensitive three-dimensional networks of SiO4-units linked by the arylene groups. The non-hydrolytic approach to hybrid materials may be applied to other silylated precursors, if the reactivity of the corresponding chlorine compound is sufficient.

Nonequilibrium Colloids: Temperature-Induced Bouquet Formation of Flower-like Micelles as a Time-Domain-Shifting Macromolecular Heat Alert.

Climate change requires enhanced autonomous temperature monitoring during logistics/transport. A cheap approach comprises the use of temperature-sensitive copolymers that undergo temperature-induced irreversible coagulation. The synthesis/characterization of pentablock copolymers (PBCP) starting from poloxamer PEO130-b-PPO44-b-PEO130 (poly(ethylene oxide)130-b-poly(propylene oxide)44-b-poly(ethylene oxide)130) and adding two terminal qPDMAEMA85 (quaternized poly[(2-dimethylamino)ethyl methacrylate]85) blocks is presented. Mixing of PBCP solutions with hexacyanoferrate(III)/ferricyanide solutions leads to a reduction of the decane/water interfacial tension accompanied by a co/self-assembly toward flower-like micelles in cold water because of the formation of an insoluble/hydrophobic qPDMAEMA/ferricyanide complex. In cold water, the PEO/PPO blocks provide colloidal stability over months. In hot water, the temperature-responsive PPO block is dehydrated, leading to a pronounced temperature dependence of the oil-water interfacial tension. In solution, the sticky PPO segments exposed at the micellar corona cause a colloidal clustering above a certain threshold temperature, which follows Smoluchowski-type kinetics. This coagulation remains for months even after cooling, indicating the presence of a kinetically trapped nonequilibrium state for at least one of the observed micellar structures. Therefore, the system memorizes a previous suffering of heat. This phenomenon is linked to an exchange of qPDMAEMA-blocks bridging the micellar cores after PPO-induced clustering. The addition of ferrous ions hampers the exchange, leading to the reversible coagulation of Prussian blue loaded micelles. Hence, the Fe2+ addition causes a shift from history monitoring to the sensing of the present temperature. Presumably, the system can be adapted for different temperatures in order to monitor transport and storage in a simple way. Hence, these polymeric "flowers" could contribute to preventing waste and sustaining the quality of goods (e.g., food) by temperature-induced bouquet formation, where an irreversible exchange of "tentacles" between the flowers stabilizes the bouquet at other temperatures as well.

Atomic contributions from spin-orbit coupling to 29Si NMR chemical shifts in metallasilatrane complexes.

New members of a novel class of metallasilatrane complexes [X-Si-(µ-mt)(4)-M-Y], with M=Ni, Pd, Pt, X=F, Cl, Y=Cl, Br, I, and mt=2-mercapto-1-methylimidazolide, have been synthesized and characterized structurally by X-ray diffraction and by (29)Si solid-state NMR. Spin-orbit (SO) effects on the (29)Si chemical shifts induced by the metal, by the sulfur atoms in the ligand, and by heavy halide ligands Y=Cl, Br, I were investigated with the help of relativistic density functional calculations. Operators used in the calculations were constructed such that SO coupling can selectively be switched off for certain atoms. The unexpectedly large SO effects on the (29)Si shielding in the Ni complex with X=Y=Cl reported recently originate directly from the Ni atom, not from other moderately heavy atoms in the complex. With respect to Pd, SO effects are amplified for Ni owing to its smaller ligand-field splitting, despite the smaller nuclear charge. In the X=Cl, Y=Cl, Br, I series of complexes the Y ligand strongly modulates the (29)Si shift by amplifying or suppressing the metal SO effects. The pronounced delocalization of the partially covalent M←Y bond plays an important role in modulating the (29)Si shielding. We also demonstrate an influence from the X ligand on the (29)Si SO shielding contributions originating at Y. The NMR spectra for [X-Si-(µ-mt)(4)-M-Y] must be interpreted mainly based on electronic and relativistic effects, rather than structural differences between the complexes. The results highlight the sometimes unintuitive role of SO coupling in NMR spectra of complexes containing heavy atoms.

Linking 31P magnetic shielding tensors to crystal structures: experimental and theoretical studies on metal(II) aminotris(methylenephosphonates).

The (31)P chemical shift tensor of the phosphonate group [RC-PO(2)(OH)](-) is investigated with respect to its principal axis values and its orientation in a local coordinate system (LCS) defined from the P atom and the directly coordinated atoms. For this purpose, six crystalline metal aminotris(methylenephosphonates), MAMP·xH(2)O with M = Zn, Mg, Ca, Sr, Ba, and (2Na) and x = 3, 3, 4.5, 0, 0, and 1.5, respectively, were synthesized and identified by diffraction methods. The crystal structure of water-free BaAMP is described here for the first time. The principal components of the (31)P shift tensor were determined from powders by magic-angle-spinning NMR. Peak assignments and orientations of the chemical shift tensors were established by quantum-chemical calculations from first principles using the extended embedded ion method. Structure optimizations of the H-atom positions were necessary to obtain the chemical shift tensors reliably. We show that the (31)P tensor orientation can be predicted within certain error limits from a well-chosen LCS, which reflects the pseudosymmetry of the phosphonate environment.

Phenylarsonic acid-DMPS redox reaction and conjugation investigated by NMR spectroscopy and X-ray diffraction.

The reaction between 2,3-dimercaptopropane-1-sulfonate (DMPS, unithiol) and four phenylarsonic(V) acids, i.e. phenylarsonic acid (PAA), 4-hydroxy-3-nitrophenylarsonic acid (HNPAA), 2-aminophenylarsonic acid (o-APAA) and 4-aminophenylarsonic acid (p-APAA), is investigated in aqueous solution. The pentavalent arsenic compounds are reduced by DMPS to their trivalent analogs and instantly chelated by the vicinal dithiol, forming covalent As-S bonds within a five-membered chelate ring. The different types and positions of polar substituents at the aromatic ring of the arsonic acids influence the reaction rates in the same way as observed for reaction with glutathione (GSH), as well as the syn/anti molar ratio of the diastereomeric products, which was analyzed using time- and temperature-dependent nuclear magnetic resonance (NMR) spectroscopy. Addition of DMPS to the conjugate formed by a phenylarsonic(V) acid and the biologically relevant tripeptide GSH showed the immediate replacement of GSH by chelating DMPS, underlining the importance of dithiols as detoxifying agent.

Synthesis and temperature-dependent NMR studies of monomeric and dimeric tris(dialkylamido)alanes.

After an introductory overview of all currently known tris(dialkylamido)alanes with the formula [Al(NR2)3]n (n = 1, 2), a simplified synthetic method based on the usage of is presented. The simplification results from the fact that the ether adduct can already be obtained during the necessary synthesis of the alane moiety and that the use of trimethylamine is no longer required. Current conflicts regarding the experimental data of tris(diethylamido)alane and their interpretation have been resolved by means of single crystal structure analysis. The N-methylpiperazine derivative was described for the first time and characterised by various analytical methods. In temperature-dependent NMR measurements ranging from -35 °C to 90 °C coalescence phenomena of 13C and 1H NMR signals of tris(N-methylpiperazino)alane as well as thermal migration of 1H NMR signals of tris(diethylamido)alane were observed.

Disilanes with Pentacoordinate Si Atoms by Carbon Dioxide Insertion into Aminodisilanes: Syntheses, Molecular Structures, and Dynamic Behavior.

The insertion of carbon dioxide into the Si-N bonds of aminodisilanes ((RR'N) n Me3-n Si)2 affords carbamoyloxydisilanes ((RR'NC(O)O) n Me3-n Si)2. Some of the obtained insertion products feature pentacoordinate silicon atoms in the solid state and in solution, with two carbamoyloxy moieties bridging the Si-Si bond. The aminodisilanes and their insertion products were extensively analyzed, including single-crystal X-ray structure analyses. The temperature dependence of the higher coordination was investigated using variable temperature NMR experiments.

Bis-(triphenylphosphane) Aluminum Hydride: A Simple Way to Provide, Store, and Use Non-Polymerized Alane for Synthesis.

AlH3 (PPh3 )2 was synthesized as a stable solid being the first known 1 : 2 alane arylphosphane adduct. Although only weakly intra-molecularly coordinated, it displays as a molecular crystal significant inertness against atmospheric humidity and oxygen due to strong steric screening of the alane unit. The compound readily dissociates PPh3 in solution allowing for its use as a Lewis acidic reducing agent. These features lead to an easy to store, easy to use reducing agent that may enable the quantitative investigation of aluminum hydride chemistry including reduction, complexation and hydroalumination reactions. The structure contains two non-equivalent penta-coordinated aluminum centers that despite long Al-P distances of ca. 2.7 Šdisplay unusually high quadrupolar coupling constants CQ of 25.1 and 26.5 in 27 Al solid state NMR measurements. The product was also tested as a reducing agent on a small set of selected compounds with various functional groups.

Ylenes in the M(II)→Si(IV) (M=Si, Ge, Sn) coordination mode.

The reaction of the methimazolyl (mt, i.e., 2-mercapto-1-methylimidazolide) substituted silane Si(mt)(4) with SnCl(2) and GeCl(2) in dioxane affords the paddlewheel-shaped complexes [ClSi(µ-mt)(4)MCl] (M=Sn (1) and Ge (2), respectively). These compounds represent the first crystallographically characterized hexacoordinate silicon complexes comprising a Sn or Ge atom in the Si coordination sphere. An attempt to synthesize the related silicon compound 3 [ClSi(µ-mt)(4)SiCl] instead afforded the trisilane [ClSi(µ-mt)(4)Si-SiCl(3)] (3a), which provides the first crystallographic evidence for the feasibility of oligosilanes with adjacent hexacoordinate Si atoms. One of the hexacoordinate Si atoms of 3a features the unprecedented (Si(2)S(4))Si skeleton. Natural bonding orbital (NBO) analyses of compounds 1, 2, 3a (and the target compound 3) revealed characteristics of M(II)→Si(IV) (for 2 and 3) or M(I)→Si(IV) (for 3a) dative bonding in the systems with M=Si and Ge, whereas compound 1 exhibits a covalent Sn(III)-Si(III) bond.