Chemoselective Alkene Hydrosilylation Catalyzed by Nickel Pincer Complexes

Chemoselective hydrosilylation of functionalized alkenes is difficult to achieve using base‐metal catalysts. Reported herein is that well‐defined bis(amino)amide nickel pincer complexes are efficient catalysts for anti‐Markovnikov hydrosilylation of terminal alkenes with turnover frequencies of up to 83 000 per hour and turnover numbers of up to 10 000. Alkenes containing amino, ester, amido, ketone, and formyl groups are selectively hydrosilylated. A slight modification of reaction conditions allows tandem isomerization/hydrosilylation reactions of internal alkenes using these nickel catalysts.     

Co-continuity interval in immiscible polymer blends by dynamic mechanical spectroscopy in the molten and solid state

The work focuses on the detection of the co-continuity window in immiscible polymer blends. The purpose of the paper is to describe how rheological techniques can help to evaluate the composition range of the co-continuous morphology through the study of a particular system: PEO/PVDF-HFP. First, the blends were characterized by selective dissolution experiments and SEM observations. Then the ability of dynamic mechanical spectroscopy to detect the co-continuity was investigated in the melt and in the solid state. The evolution of the storage modulus of molten blends with their composition at a constant low frequency gives information about the co-continuity interval, especially as far as the onset of the continuity of the PEO phase is concerned. Then the immiscibility of the polymers and the continuity of PVDF-HFP as a function of blend composition have been highlighted by means of dynamic mechanical spectrometry below the melting point of PVDF-HFP. Comparison with results from classical methods shows fair agreement.This paper was presented at the first Annual European Rheology Conference (AERC) held in Guimarães, Portugal, September 11-13, 2003.     

Multiscale Approach to the Study of the Electronic Properties of Two Thiophene Curcuminoid Molecules

We studied the electronic and conductance properties of two thiophene–curcuminoid molecules, 2‐thphCCM ( 1 ) and 3‐thphCCM ( 2 ), in which the only structural difference is the position of the sulfur atoms in the thiophene terminal groups. We used electrochemical techniques as well as UV/Vis absorption studies to obtain the values of the HOMO–LUMO band gap energies, showing that molecule 1 has lower values than 2 . Theoretical calculations show the same trend. Self‐assembled monolayers (SAMs) of these molecules were studied by using electrochemistry, showing that the interaction with gold reduces drastically the HOMO–LUMO gap in both molecules to almost the same value. Single‐molecule conductance measurements show that molecule 2 has two different conductance values, whereas molecule 1 exhibits only one. Based on theoretical calculations, we conclude that the lowest conductance value, similar in both molecules, corresponds to a van der Waals interaction between the thiophene ring and the electrodes. The one order of magnitude higher conductance value for molecule 2 corresponds to a coordinate (dative covalent) interaction between the sulfur atoms and the gold electrodes.     

Trichloroethylene Combustion in a Submerged Thermal Plasma: Results and Chemical Kinetics Model

This work deals with incineration of organic liquid wastes using an oxygen thermal plasma jet, submerged in water. The results presented here concern incineration of trichloroethylene (TCE). During a trial run, the CO₂ and CO content in the exhaust gas is continuously measured; samples taken periodically from the solution are analyzed by appropriate methods: total organic carbon and chlorine content are measured. Process efficiency during tests with a few L/h of TCE is given by the mineralization rate. The trapping rate of chlorine as HCl is near 100 %. The TCE destruction and removal efficiency, measured by MS/GC, is better than 99.9999 %. A simplified kinetic model of gas quenching was constructed from a single-phase plug-flow reactor model taking into account 14 species and 34 reactions. It satisfies the requirements of heat balance and major components analysis, and reveals the major role of the OH radical on the concentrations of CO as well as HCl and/or Cl₂ in the off-gas stream.     

Gold-catalyzed intramolecular hydroarylation of olefins. Scope evaluation and preliminary mechanistic studies

We report a gold-catalyzed intramolecular hydroarylation of unactivated olefins using a combination of AuCl₃/AgOTf as the catalytic system affording dihydrobenzopyrans, tetralins and tetrahydroquinolines in good yields. For our preliminary mechanistic studies, we have investigated the kinetic isotope effects with deuterated arene compounds and found that this catalytic hydroarylation is consistent with an electrophilic aromatic substitution process.     

γ-Lactam-containing peptidomimetics

Protected diaminoalcohols obtained through allyl addition to α-amino acid-derived imines and subsequent hydroboration were used for the preparation of pyrrolidinones and pyrrolidines. Pyrrolidinones were synthesized with moderate yields by oxidation of the hydroxy function with tetrapropylammonium perruthenate/N-methylmorpholine-N-oxide and concomitant cyclization while pyrrolidines were synthesized in good yields by tosylation of the hydroxy group and subsequent intramolecular nucleophilic substitution. Thus accessible substrates were transferred into peptidomimetics by attachment of amino acid moieties at both termini using conventional peptide coupling strategies. Molecular mechanics optimizations suggest that these substrates preferentially adopt a turn conformation.     

A fluorinated selenide linker for solid-phase synthesis of n-pentenyl glycosides

[reaction: see text] A fluorine-labeled selenide linker for installing terminal isolated olefins has been synthesized in high overall yield. The resin-bound linker could be glycosylated both with glycosyl trichloroacetimidates and glycosyl fluorides. The linker did not decompose after oxidation with tBuOOH but underwent beta-elimination when it was subjected to heat. This allowed the released n-pentenyl glycoside 15 to be isolated in excellent yield and purity after filtration.