Isolation of cationic and neutral (allenylidene)(carbene) and bis(allenylidene)gold complexes.

The one-electron reduction of a cationic (allenylidene)[cyclic(alkyl) (amino)carbene]gold(i) complex leads to the corresponding neutral, paramagnetic, formally gold(0) complex. DFT calculations reveal that the spin density of this highly robust coinage metal complex is mainly located on the allenylidene fragment, with only 1.8 and 3.1% on the gold center and the CAAC ligand, respectively. In addition, the first homoleptic bis(allenylidene)gold(i) complex has been prepared and fully characterized

L’ABF à l’école des lettres

Depuis six ans, Philippe Apeloig développe l’identité de l’ABF. Il s’efforce de la mettre en phase avec la promotion d’une conception moderne des bibliothèques qui sont devenues des espaces modulables accueillant des activités multiples et des lieux d’expérimentation

A Convenient Preparation of Organofluorosilanes. A Possible Involvement of Tetracoordinated Siliconium Ion Pairs

Organofluorosilanes and their complexes with weakly coordinating fluorine con- taining salts are frequently used in mechanistic studies of organosilicon compounds.1 Examples include studies of nucleophilic attack at silicon2 and attempts to generate silicenium ions of type R3Si+.3’4 Silyl fluorides are also used in key steps in the synthesis of sterically hindered tetraalkylsilanes5’6 or of highly congested trialkylsilyl halides (chlorides, bromides and iodides).6’7 In view of these important applications, it is surprising that until very recently the available synthetic methods for preparing silyl fluorides were limited and used quite inconvenient chemicals, procedures and reaction conditions. Thus, organofluorosilanes were prepared by the treatment of the corresponding silyl halides with anhydrous hydrofluoric acid,8 antimony trifluoride,9 or zinc fluoride.7,10 Only one report in the older literature indicated that triphenylfluorosilane can be prepared under much milder conditions, i.e., by the reaction of the corresponding chloride with sodium fluoroborate in acetone at room temperature.11 The lack of simple straightforward methods for preparing silyl fluorides is especially intriguing in view of the fact that the Si-F bond is the strongest known bond to silicon, and consequently fluorosilanes are expected to exhibit high thermodynamic stability.12 Progress towards a more simple synthesis of fluorosilanes was made in recent years. Bassindale and Stout noted that the reaction of Me3SiCl with silver tetrafluoroborate yields trimethylfluorosilane138 (not trimethylsilyl tetrafluoroborate as previously suggested).136 Della and Tsanaktidis reported in 1988 that silyl triflates react at 25-70 °C with potassium fluoride in DMF in the presence of 18-crown-6 to produce the corresponding silyl fluorides.1

PLIF Measurements of Nitric Oxide and Hydroxyl Radicals Distributions in Swirled Stratified Premixed Flames

Environmental and economic concerns have pushed aeronautical authorities to set stringent environmental regulations on fuel consumption, noise production, and pollutant emission. Engine manufacturers are developing novel staged injection concepts to ensure their respect. The injection staging creates a fuel-air mixture stratification involving new combustion processes not fully understood. This paper presents the experimental investigation of NO production for known swirled and / or stratified lean premixed flames. The fuel staging parameter defined as the stratification ratio is studied for values of 1, 2, and 3, while the swirl fractions are 0, 25 and 33%, changing the flowfield from non-swirling cond itions to high swirl numbers (up to 0.55). The implementation of simultaneous OH- and NOPLIF imaging techniques is achieved using high energy pulsed laser systems, able, for instance, to deliver 30 mJ/ pulse around the 226-nm UV wavelength for NO excitation. OH-PLIF is used to characterize the flame structure through the commonly extracted curvature, and also through the measurement of the flame thickness. These results show to be more accurate than thickness obtained from temperature profiles measured by Raman/ Rayleigh laser diagnostics. NO-PLIF is used to quantify the pollutant concentration. To this end, preliminary work was done to select the Q1 (29.5) transition as it the least temperature dependent excitation scheme with high fluorescence levels. After realizing a specific calibration of the NO-PLIF technique, the stud ied flames presented concentrations ranging from traces (20 ppm) to high levels (230 ppm). Further analysis of these results reveals that for high stratification ratios the prompt NO is favored and is responsible for the elevated level of NO pollutant

Ab-initio-MO-Studie Methyl- und Phenyl-substituierter Allenyl-Kationen

An den Methyl- und Phenyl-substituierten Allenyl-Kationen 3 - 12 (Tab. 1) wurden ab-initio-MO-Berechnungen unter Verwendung des STO-3G Basissatzes durchgeführt. Die berechneten Bindungslängen und Ladungsverteilungen zeigen Delokalisierung der positiven Ladung an, wie in Formel 1 gezeigt. Mit Hilfe isodesmischer Reaktionen werden Stabilisierungsenergien von Substituenten in 1- und 3-Position ermittelt. Diese Werte ermöglichen in Kombination mit der experimentell bekannten Bildungswärme des Stammkörpers 2 die Bestimmung von H sämtlicher Allenyl-Kationen 3 - 12. Der Vergleich dieser Daten mit einigen experimentell bestimmten Bildungswärmen zeigt Übereinstimmung innerhalb von 2 kcal/mol. Es werden Voraussagen für das Reaktionsverhalten gegenüber n-Nucleophilen und -Systemen gemacht

A theoretical study of nitrososilane and six isomers of SiH3NO

Article on a theoretical study of nitrososilane and six isomers of SiH2NO