Zur Synthese einiger Siliciumstickstoffverbindungen

The preparation of 1-dimethylamino-hexamethyldisilazane, tridecamethyltetrasilazane and hexadecamethylpentasilazane is described. All the compounds are colourless liquids.     

Reaktionen der Siliciumtetrahalogenide mit 2,2′-Dipyridyl und mit 1,10-Phenanthrolin

Zusammenfassung In den Systemen Siliciumtetrahalogenid/2,2-Dipyridyl und Siliciumtetrahalogenid/1,10-Phenanthrolin bilden sich unter Wärmeentwicklung weiße bis leicht getönte röntgenkristalline Additionsverbindungen des Typs Hlg₄Si(dipy) bzw. Hlg₄Si(phen) mit SiHlg₄=SiCl₄, SiHCl₃ und SiBr₄. Mit SiJ₄ waren analog die gelben Verbindungen J₄Si(dipy) und J₄Si(phen)₂ zu erhalten. Methylchlorsilane reagieren mit den beiden Heterocyclen nicht. Pyrazin setzte sich nur mit SiJ₄ um, offensichtlich zu gelbem J₄Si(pyz)₄.

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The reaction of silicon tetrahalides (SiCl₄, SiHCl₃, SiBr₄) with 2.2-dipyridyl and 1.10-phenanthroline respectively results in white, or only slightly coloured crystalline addition compounds of the composition X₄Si(dipy) and X₄Si(phen), whereas SiI₄ formed the yellow compounds I₄Si(dipy) and I₄Si(phen)₂ and, with pyrazine, the yellow I₄Si(pyz)₄. Methylchlorosilanes did not react.

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Ausführliche Darstellung eines Diskussionsvortrages beim 1. Dresdener Symposium für Siliciumchemie, Mai 1958. Vgl. hierzu.

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65. Mitt.:U. Wannagat, K. Hensen undP. Petesch, Mh. Chem.98, 1407 (1967).

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Zugleich 5. Mitt. über Verbindungen von Nichtmetallhalogeniden mit Pyridin und seinen Homologen; 4. Mitt. siehe.

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Mit Auszügen aus der DiplomarbeitP. Petesch, T. H. Aachen 1958, und den DissertationenF. Vielberg, T. H. Aachen 1956, sowieK. Hensen, T. H. Aachen 1962.     

Surface-Modified Carbon Materials for CO2 Electroreduction

The electrochemical reduction of CO₂ to produce sustainable fuels and chemicals has attracted great attention in recent years. It is shown that surface-modified carbons catalyze the CO₂RR. This study reports a strategy to modify the surface of commercially available carbon materials by adding oxygen and nitrogen surface groups without modifying its graphitic structure. Clear differences in CO₂RR activity, selectivity and the turnover frequency between the surface-modified carbons were observed, and these differences were ascribed to the nature of the surface groups chemistry and the point of zero charge (PZC). The results show that nitrogen-containing surface groups are highly selective towards the formation of CO from the electroreduction of CO₂ in comparison with the oxygen-containing surface groups, and the carbon without surface groups. This demonstrates that the selectivity of carbon for CO₂RR can be rationally tuned by simply altering the surface chemistry via surface functionalization.     

Efficient tandem synthesis of methyl esters and imines by using versatile hydrotalcite-supported gold nanoparticles

Efficient basic hydrotalcite (HT)-supported gold nanoparticle (AuNP) catalysts have been developed for the aerobic oxidative tandem synthesis of methyl esters and imines from primary alcohols catalyzed under mild and soluble-base-free conditions. The catalytic performance can be fine-tuned for these cascade reactions by simple adjustment of the Mg/Al atomic ratio of the HT support. The one-pot synthesis of methyl esters benefits from high basicity (Mg/Al=5), whereas moderate basicity greatly improves imine selectivity (Mg/Al=2). These catalysts outperform previously reported AuNP catalysts by far. Kinetic studies show a cooperative enhancement between AuNP and the surface basic sites, which not only benefits the oxidation of the starting alcohol but also the subsequent steps of the tandem reactions. To the best of our knowledge, this is the first time that straightforward control of the composition of the support has been shown to yield optimum AuNP catalysts for different tandem reactions.     

Efficient Tandem Synthesis of Methyl Esters and Imines by Using Versatile Hydrotalcite‐Supported Gold Nanoparticles

Efficient basic hydrotalcite (HT)‐supported gold nanoparticle (AuNP) catalysts have been developed for the aerobic oxidative tandem synthesis of methyl esters and imines from primary alcohols catalyzed under mild and soluble‐base‐free conditions. The catalytic performance can be fine‐tuned for these cascade reactions by simple adjustment of the Mg/Al atomic ratio of the HT support. The one‐pot synthesis of methyl esters benefits from high basicity (Mg/Al=5), whereas moderate basicity greatly improves imine selectivity (Mg/Al=2). These catalysts outperform previously reported AuNP catalysts by far. Kinetic studies show a cooperative enhancement between AuNP and the surface basic sites, which not only benefits the oxidation of the starting alcohol but also the subsequent steps of the tandem reactions. To the best of our knowledge, this is the first time that straightforward control of the composition of the support has been shown to yield optimum AuNP catalysts for different tandem reactions.     

New Cu-based catalysts supported on TiO2 films for Ullmann S(N)Ar-type C-O coupling reactions

New routes for the preparation of highly active TiO(2)-supported Cu and CuZn catalysts have been developed for C-O coupling reactions. Slurries of a titania precursor were dip-coated onto glass beads to obtain either structured mesoporous or non-porous titania thin films. The Cu and CuZn nanoparticles, synthesized using a reduction by solvent method, were deposited onto calcined films to obtain a Cu loading of 2 wt%. The catalysts were characterized by inductively coupled plasma (ICP) spectroscopy, temperature-programmed oxidation/reduction (TPO/TPR) techniques, (63)Cu nuclear magnetic resonance (NMR) spectroscopy, X-ray diffraction (XRD), scanning and transmission electron microscopy (S/TEM-EDX) and X-ray photo-electron spectroscopy (XPS). The activity and stability of the catalysts obtained have been studied in the C-O Ullmann coupling of 4-chloropyridine and potassium phenolate. The titania-supported nanoparticles retained catalyst activity for up to 12 h. However, catalyst deactivation was observed for longer operation times due to oxidation of the Cu nanoparticles. The oxidation rate could be significantly reduced over the CuZn/TiO(2) catalytic films due to the presence of Zn. The 4-phenoxypyridine yield was 64% on the Cu/nonporous TiO(2) at 120 °C. The highest product yield of 84% was obtained on the Cu/mesoporous TiO(2) at 140 °C, corresponding to an initial reaction rate of 104 mmol g(cat) (-1) s(-1). The activation energy on the Cu/mesoporous TiO(2) catalyst was found to be (144±5) kJ mol(-1), which is close to the value obtained for the reaction over unsupported CuZn nanoparticles (123±3 kJ mol(-1)) and almost twice the value observed over the catalysts deposited onto the non-porous TiO(2) support (75±2 kJ mol(-1)).