Et2Zn-mediated stoichiometric C(sp)-H silylation of 1-alkynes and chlorosilanes

A first example of an Et₂Zn mediated silylation of 1-aklynes is reported. A series of functional groups are tolerated in this reaction. Mechanistic studies support Zn alkynilides as intermediates in the reaction. This reaction protocol provides a practical method for the preparation of alkynylsilanes and expands the application of organometallic zinc in organic synthesis.     

Structure and spectroscopic properties of the dimeric copper(I) N‐heterocyclic carbene complex [Cu2(CNCt‐Bu)2](PF6)2

In recent years, the use of copper N‐heterocyclic carbene (NHC) complexes has expanded to fields besides catalysis, namely medicinal chemistry and luminescence applications. In the latter case, multinuclear copper NHC compounds have attracted interest, however, the number of these complexes in the literature is still quite limited. Bis[μ‐1,3‐bis(3‐tert‐butylimidazolin‐2‐yliden‐1‐yl)pyridine]‐1κ⁴C²,N:N,C^2′;2κ⁴C²,N:N,C^2′‐dicopper(I) bis(hexafluoridophosphate), [Cu₂(C₁₉H₂₅N₅)₂](PF₆)₂, is a dimeric copper(I) complex bridged by two CNC, i.e. bis(N‐heterocyclic carbene)pyridine, ligands. Each Cu^I atom is almost linearly coordinated by two NHC ligands and interactions are observed between the pyridine N atoms and the metal centres, while no cuprophilic interactions were observed. Very strong absorption bands are evident in the UV–Vis spectrum at 236 and 274 nm, and an emission band is observed at 450 nm. The reported complex is a new example of a multinuclear copper NHC complex and a member of a compound class which has only rarely been reported.     

Beitrag zur Kenntnis der Wärmeleitfähigkeit poröser Stoffe Teil II

Zusammenfassung Die in einem ersten Teil dieser Untersuchung erhaltenen Ergebnisse werden durch zusätzliche neue Versuche kontrolliert. Der Meßbereich wird auf Rohdichten von 9,5 kg/m³ erweitert; die notwendigen Versuchsdaten für reines Polystyrol werden experimentell neu ermittelt. Ein Vergleich mit den Meßwerten anderer Beobachter ergibt gute Übereinstimmung aller Daten, wenn gleichartige Versuchsbedingungen eingehalten wurden. Der Verlauf der gemessenen (effektiven) Wärmeleitfähigkeit von Polystyrolpartikel-Hartschaumplatten (Styropor) in Abhängigkeit von Rohdichte und Schichtdicke wird aufgezeigt und diskutiert. Zusätzliche Messungen der Absorptionsspektren von Polystyrol und Polystyrol-Schaumstoff ergänzen die Messung der Wärmeleitfähigkeit und mögen zur Klärung des Wärmetransportes in porösen Schaumstoffen beitragen.

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A contribution to the knowledge of heat conductivity of porous materials part II

The results obtained in the first part of this experimental research are controlled by new measurements. The range of apparent over-all density was enlarged till 9.5 kg/m³. The necessary dates for pure polystyrene were experimentally determined. A comparison with the results of other observers shows good agreement, if equal measuring conditions are given. The behaviour of the measured (effective) thermal conductivity of polystyrene foam as function of apparent over-all density and the thickness of the layer may be learned from several diagrams; these are discussed. Additional measurements of some optical absorption spectra of pure polystyrene and polystyrene foam follow the measurement of thermal conductivity; they may contribute to the clearing up of heat transfer through porous materials.

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Herrn Dr.-Ing. F. Stastny, Ludwigshafen/Rh. und der BASF haben wir für sehr entgegenkommende Lieferung der verschiedenartigen Proben zu danken, ferner Herrn Techn. Reg. Amtmann Jugel für sorgfältige Kontrollversuche.     

The Structure Functions of the Velocity and Temperature Fields from the Perspective of Dimensional Scaling

In this paper, dimensional scaling is used to describe the turbulence structure of the velocity and temperature fields in the inertial range and the far dissipation range as well as the intermediate transition range under locally isotropic conditions at sufficiently large Reynolds numbers. This kind of scaling is expressed in a strictly mathematical manner employing dimensional π -invariants analysis. It is shown that in the case of the asymptotic solutions for either the inertial range or the far dissipation range only one π number occurs that has to be considered as a non-dimensional universal constant. This π number may be determined theoretically or/and empirically. In the case of the transition range two π numbers occur. Consequently, a universal function is established that has to be derived theoretically or/and empirically, too. Here, Batchelor's [7] classical interpolation formula for the turbulence structure of the velocity field and the empirical one of Stolovitzky et al. [59], both may serve as universal functions, are compared with the results provided by numerical solutions of Kolmogorov′s [32] structure equation for the velocity field. It is shown that these interpolation formulae match not only the asymptotic solutions of the inertial range and the far dissipation range, respectively, but also these numerical results in an excellent manner. The former may be considered as necessary condition and the latter as sufficient condition. In the case of the temperature field results of the corresponding universal function are predicted using Yaglom's [63] structure equation. These results also match the corresponding asymptotic solutions of both the inertial range and the far dissipation range. However, in contrast to the case of the velocity field, the predicted universal function for the temperature field may notably overshoot its asymptotic solution for the inertial range. This overshooting occurs in the transition range and may be considered as an analogue to the so-called Hill ‘bump’ that usually occurs in the high-wave number portion of the temperature spectrum.     

Oliveridepsidones A–D,antioxidant depsidones from Garcinia oliveri

Four new prenylated depsidones, oliveridepsidones A–D, were isolated from the bark of Garcinia oliveri collected in Vietnam. Their structures were elucidated using mainly NMR techniques (¹H and ¹³C NMR, HMQC, HMBC and NOE experiments). Copyright © 2012 John Wiley & Sons, Ltd.     

The Prospect of Dimensionality in Porous Semiconductors

With the advent of silicon-based semiconductors, a plethora of previously unknown technologies became possible. The development of lightweight low-dimensional organic semiconductors followed soon after. However, the efficient charge/electron transfers enabled by the non-porous 3D structure of silicon is rather challenging to be realized by their (metal-)organic counterparts. Nevertheless, the demand for lighter, more efficient semiconductors is steadily increasing resulting in a growing interest in (metal-)organic semiconductors. These novel materials are faced with a variety of challenges originating from their chemical design, their packing and crystallinity. Although the effect of molecular design is quite well understood, the influence of dimensionality and the associated change in properties (porosity, packing, conjugation) is still an uncharted area in (metal-)organic semiconductors, yet highly important for their practical utilization. In this Minireview, an overview on the design and synthesis of porous semiconductors, with a particular emphasis on organic semiconductors, is presented and the influence of dimensionality is discussed.