Search results for "SELECTIVITY"

Cyclic metal(oid) clusters control platinum-catalysed hydrosilylation reactions : from soluble to zeolite and MOF catalysts

2020

The Pt-catalysed addition of silanes to functional groups such as alkenes, alkynes, carbonyls and alcohols, i.e. the hydrosilylation reaction, is a fundamental transformation in industrial and academic chemistry, often claimed as the most important application of Pt catalysts in solution. However, the exact nature of the Pt active species and its mechanism of action is not well understood yet, particularly regarding regioselectivity. Here, experimental and computational studies together with an ad hoc graphical method show that the hydroaddition of alkynes proceeds through Pt-Si-H clusters of 3-5 atoms (metal(oid) association) in parts per million amounts (ppm), which decrease the energy of…

Palladium on Charcoal as a Catalyst for Stoichiometric Chemo- and Stereoselective Hydrosilylations and Hydrogenations with Triethylsilane

2014

Stoichiometric quantities of triethylsilane in the presence of activated Pd/C as the catalyst can be used to effect chemo-, regio-, and stereoselective hydrosilylation and transfer hydrogenation reactions. α,β-Unsaturated aldehydes and ketones are selectively hydrosilylated to give the corresponding enol silanes or transfer hydrogenated to give the saturated carbonyl compounds in the presence of other reducible functional groups.

Chemoselektive mono- und disilyletherbildung aus tertiären und sekundären silanen

1985

Abstract Tertiary and secondary silanes are O-selective. With alcohols the corresponding silyl ethers are formed. Cesium fluoride/imidazole (CsF/Im) is a better activating system than CsF alone. Primary OH groups are silylated remarkably faster under CsF/Im activation than secondary OH groups. Tertiary alcohols do not react. Primary OH groups are selectively protected also in the presence of secondary OH groups by silanes with bulky ligands such as triisopropylsilane ((i-Pr) 3 SiH ( 4 )). Ketones are neither reduced to silyl ethers nor transformed to silylenol ethers under the conditions employed. Secondary silanes form monosilyl ethers by amine activation; with CsF the formation of disilyl…

Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent‐ and Metal‐Free Anodic Cross‐Coupling Reaction

2016

The oxidative cross-coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2'-biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent-free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale-up and inherently safe. The implementation of O-silyl-protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2…

ChemInform Abstract: Selective Synthesis of Partially Protected Nonsymmetric Biphenols by Reagent- and Metal-Free Anodic Cross-Coupling Reaction.

2016

The oxidative cross-coupling of aromatic substrates without the necessity of leaving groups or catalysts is described. The selective formation of partially protected nonsymmetric 2,2'-biphenols via electroorganic synthesis was accomplished with a high yield of isolated product. Since electric current is employed as the terminal oxidant, the reaction is reagent-free; no reagent waste is generated as only electrons are involved. The reaction is conducted in an undivided cell, and is suitable for scale-up and inherently safe. The implementation of O-silyl-protected phenols in this transformation results in both significantly enhanced yields and higher selectivity for the desired nonsymmetric 2…

Molecular Selectivity of CH 4 –C 2 H 6 Mixed Hydrates: A GCMC Study

2021

International audience; In this paper, we report the first grand canonical Monte Carlo simulation study aiming at characterizing the competitive trapping of CH4 and C2H6 molecules into clathrate hydrates under temperature conditions typical of those encountered at the surface of Titan. Various compositions of the fluid in contact with the clathrate phase have been considered in the simulations, including pure methane, pure ethane, and mixed fluids made of various methane/ethane ratios. The trapping isotherms obtained from the simulations clearly show that ethane molecules can be enclathrated at lower pressures than methane molecules. In addition, they provide evidence that the methane molec…

2020

Abstract Challenge is a key motivation for videogame play. But what kind of challenge types videogames include, and which of them players prefer? This article helps to answer the above questions by developing and validating Videogame Challenge Inventory (CHA), a psychometrically sound measurement for investigating players’ challenge preferences in videogames. Based on a review of literature, we developed a 38-item version of CHA that was included in a social media user survey (N = 813). An exploratory factor analysis (EFA) revealed a latent structure of five challenge types: Physical, Analytical, Socioemotional, Insight, and Foresight. CHA was amended in another EFA with USA-based survey da…

Socioemotional Wealth and Networking in the Internationalisation of Family SMEs

2021

In internationalisation processes, international expansion exposes family SMEs to external networking and the risks such expansion entails, and perceived threats to their socioemotional wealth (SEW) might restrain their willingness to take these actions. However, very few studies measure SEW and associate it with internationalisation. Considering SEW preservation’s prominence in family SMEs and SMEs’ heavy dependence on networking during internationalisation, we hypothesise that SEW preservation has a negative association and networking has a positive association with the family SMEs’ degree of internationalisation (DOI). We reconstruct four SEW constructs that carry significance for family…

The temporal dimension in the understanding of maternal sensitivity in caregiver-infant interactions: The 'Early Mother-Child Interaction Coding Syst…

2021

Abstract Caregiver-child interaction is known to play a central role in children’s socioemotional development, yet the diversity of measures commonly used to evaluate it call into question the nature of the construct being assessed. Contingency within caregiver-child interactions has been identified as a key dyadic process that requires taking a temporal perspective to evaluating interactions. The Early Mother-Child Interaction Coding System is a psychometrically sound measure that sequentially code the flow of interactive and non-interactive behaviours within a caregiver-infant system. Its use of the framework of nonlinear dynamical systems (NDS) expands our understanding of contingent car…

Modification of the Selectivity Properties of Tubular Ceramic Membranes after Alkaline Treatment

2017

International audience; This work focuses on the selectivity modification of ceramic membranes after a mild alkaline treatment. Filtration of pure saltwater solutions was carried out with commercial titania membranes before and after the treatment. After treatment, the rejection of NaF significantly decreased, while the rejection of NaCl and NaBr increased. Additionally, NaI and Na 2 SO 4 remained close to zero. Pore size and electrical charge being almost unchanged, only significant modifications in the dielectric effects can explain this modification of selectivity. Therefore, the surface chemistry and the interaction (nature and magnitude) with the solvent and with the species present in…