Search

Herein, we report the catalytic activity of a series of platinum(II) pre‐catalysts, bearing N‐heterocyclic carbene (NHC) ligands, in the alkene hydrosilylation reaction. Their structural and electronic properties are fully investigated using X‐ray diffraction analysis and nuclear magnetic resonance spectroscopy (NMR). Next, our study presents a structure‐activity relationship within this group of pre‐catalysts and gives mechanistic insights into the catalyst activation step. An exceptional catalytic performance of one of the complexes is observed, reaching a turnover number (TON) of 970 000 and a turnover frequency (TOF) of 40 417 h−1 at 1 ppm catalyst loading. Finally, an attractive solvent‐free and open‐to‐air alkene hydrosilylation protocol, featuring efficient platinum removal (reduction of residual Pt from 582 ppm to 5.8 ppm), is disclosed. [ABSTRACT FROM AUTHOR]

In the present study, we report the first silver-dependent enantiodivergent gold-catalysed reaction. The asymmetric intramolecular hydroamination of alkenes catalysed by the combination of a single chiral binuclear gold(I) chloride complex and silver perchlorate can afford both enantiomers of the products by a simple solvent change from toluene to methanol. Such an enantiodivergent reaction is strictly independent of the reaction temperature or of the nature of the catalyst anion and displays the same first-order kinetic rate law with respect to substrate concentration in both solvents. Beyond a simple solvent effect the enantioinversion is controlled by gold-silver chloride adducts which occur only in methanol and allow a dual activation of the reagent. While one single gold atom activates the alkene moiety, the other gold atom forms an oxophilic gold-silver chloride adduct which is likely to interact with the carbamate function. By comparison with toluene, which affords ( S)-enantiomer, this proximal and bimetallic activation would allow an opposite stereodifferentiation of the two diastereomeric intermediates during the final protodeauration step and lead therefore to the ( R)-enantiomer. [ABSTRACT FROM AUTHOR]

In the background is featured Ginkakuji (Silver Pavilion), a Zen temple along Kyoto′s eastern mountains (Higashiyama) in Japan. In the foreground is featured a chemistry sketch based on the Yin and Yang symbol. As many possible dualities (such as light and dark, fire and water…) are thought of as physical manifestations of the duality symbolised by Yin and Yang, parallels can be drawn with organic chemistry and the gold(I)‐catalysed asymmetric hydroamination of alkenes. An enantiodivergent reaction is possible depending on the presence of silver. Whereas a gold‐catalysed hydroamination reaction afforded (S)‐product in toluene, the use of methanol led to an enantioinversion and the generation of (R)‐product through solvation of silver and bimetallic activation of the amino‐alkene reagent. For more information see the Full Paper by F. Agbossou‐Niedercorn, C. Michon and co‐workers on page 10777 ff. [ABSTRACT FROM AUTHOR]

In this contribution, we study the conversion of a bio-sourced unsaturated fatty ester by cross-metathesis with nitrile-functionalized olefinic partners (acrylonitrile and crotonitrile). A switch from terminal to internal olefins leads to higher conversion. This is in part rationalized by involvement of a more stable ruthenium ethylidene species with crotonitrile. A new carbenic complex forms upon reaction with the nitrile-functionalized olefins, that is also catalytically active. [ABSTRACT FROM AUTHOR]