MoO2Cl2 as a novel catalyst for Friedel–Crafts acylation and sulfonylation

Chloroaluminate Ionic Liquid Immobilized on Magnetic Nanoparticles as a Heterogeneous Lewis Acidic Catalyst for the Friedel-Crafts Sulfonylation of Aromatic Compounds

Chloroaluminate ionic liquid bound on magnetic nanoparticles (Fe₃O₄@O₂Si[PrMIM]Cl·AlCl₃) was prepared and used as a heterogenous Lewis acidic catalyst for the Friedel–Crafts sulfonylation of aromatic compounds with sulfonyl chlorides or p-toluenesulfonic anhydride. The catalyst’s stability, efficiency, easy recovery, and high recyclability without considerable loss of catalytic capability after four recycles were evidence of its advantages. Furthermore, the stoichiometry, wide substrate scope, short reaction time, high yield of sulfones, and solvent-free reaction condition also made this procedure practical, ecofriendly, and economical.

Enantioselective hydrosilylation of unsaturated carbon-heteroatom bonds (C[double bond, length as m-dash]N, C[double bond, length as m-dash]O) catalyzed by [Ru-S] complexes: a theoretical study

A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium(ii) thiolate catalyst [Ru–S] ([L*-Ru(SDmp)]⁺[BAr₄^F]⁻) with a chiral monodentate phosphine ligand is carried out in this work. We elucidate all the pathways leading to the main products or by products mediated by the [Ru–S] complex in order to have deep understanding of the chemoselectivity and enantioselectivity. The DFT (Density Functional Theory) calculations show that the reaction mechanism including: (1) Si–H bond cleavage by the dual activity of Ru–S bond; (2) the generation of a sulfur-stabilized silane cation; (3) the electrophilic attack of silane cation to NC/OC; (4) hydrogen transfer from Ru to carbon cation. The hydrosilylation products are found to be the final products rather than the dehydrogenative ones, which is consistent with the experimental results. The dehydrogenative silylation reaction pathways which give N- or O-silylated enamine/enol ether are reversible according to our calculations. The computational results also show that the electrophilic attack of silicon to NC/OC is the rate-determining step and the ee value can be improved significantly with more bulky model phosphine ligand based on the same calculation methods.

A detailed theoretical study on the mechanism of enanthioselective hydrosilylation of imines and ketones catalyzed by the ruthenium(ii) thiolate catalyst with a chiral monodentate phosphine ligand is carried out in this work.

New insights into hydrosilylation of unsaturated carbon-heteroatom (C═O, C═N) bonds by rhenium(V)-dioxo complexes

The hydrosilylation of unsaturated carbon-heteroatom (C═O, C═N) bonds catalyzed by high-valent rhenium(V)-dioxo complex ReO2I(PPh3)2 (1) were studied computationally to determine the underlying mechanism. Our calculations revealed that the ionic outer-sphere pathway in which the organic substrate attacks the Si center in an η(1)-silane rhenium adduct to prompt the heterolytic cleavage of the Si-H bond is the most energetically favorable process for rhenium(V)-dioxo complex 1 catalyzed hydrosilylation of imines. The activation energy of the turnover-limiting step was calculated to be 22.8 kcal/mol with phenylmethanimine. This value is energetically more favorable than the [2 + 2] addition pathway by as much as 10.0 kcal/mol. Moreover, the ionic outer-sphere pathway competes with the [2 + 2] addition mechanism for rhenium(V)-dioxo complex 1 catalyzing the hydrosilylation of carbonyl compounds. Furthermore, the electron-donating group on the organic substrates would induce a better activity favoring the ionic outer-sphere mechanistic pathway. These findings highlight the unique features of high-valent transition-metal complexes as Lewis acids in activating the Si-H bond and catalyzing the reduction reactions.

Friedel-Crafts acylation of arenes with carboxylic acids using polystyrene-supported aluminum triflate

Cross-linked polystyrene-supported aluminum triflate (Ps- Al(OTf)3) has been shown to be a mild, efficient, and chemoselective heterogeneous Lewis acid catalyst for the acylation of aromatic compounds. The catalyst can be easily prepared from cheap starting materials, is stable (as a bench top catalyst) and is reusable.