Abstract
Sila-molecules have recently attracted attention due to their promising applications in medical and industrial fields. Compared with all-carbon parent compounds, the different covalent ...radius and electronegativity of silicon from carbon generally endow the corresponding sila-analogs with unique biological activity and physicochemical properties. Vinylsilanes feature both silyl-hyperconjugation effect and versatile reactivities, developing vinylsilane-based Smiles rearrangement will therefore provide an efficient platform to assemble complex silacycles. Here we report a practical Ir(III)-catalyzed cycloaromatization of
ortho
-alkynylaryl vinylsilanes with arylsulfonyl azides for delivering naphthyl-fused benzosiloles under visible-light photoredox conditions. The combination of experiments and density functional theory (DFT) energy profiles reveals the reaction mechanism involving α-silyl radical Smiles rearrangement.
Unreactive C-H bond activation is a new horizon for frustrated Lewis pair (FLP) chemistry. This study provides a systematic assessment of the catalytic reactivity of recently reported intra-molecular ...FLPs on the activation of typical inert C-H bonds, including 1-methylpyrrole, methane, benzyl, propylene, and benzene, in terms of density functional theory (DFT) calculations. The reactivity of FLPs is evaluated according to the calculated reaction thermodynamic and energy barriers of C-H bond activation processes in the framework of concerted C-H activation mechanisms. As for 1-methylpyrrole, 14 types of N-B-based and 15 types of P-B-based FLPs are proposed to be active. Although none of the evaluated FLPs are able to catalyze the C-H activation of methane, benzyl, or propylene, four types of N-B-based FLPs are suggested to be capable of catalyzing the activation of benzene. Moreover, the influence of the strength of Lewis acid (LA) and Lewis base (LB), and the differences between the influences of LA and LB on the catalytic reactivity of FLPs, are also discussed briefly. This systematic assessment of the catalytic activity of FLPs should provide valuable guidelines to aid the development of efficient FLP-based metal-free catalysts for C-H bond activation.
Lithium carbenoids are important reagents in organic synthesis. Systemic DFT calculations have been carried out to reveal the influence of hetero-aggregation states on the reactivity of lithium ...carbenoid reagents. The results indicate that the cyclopropanation reaction could be accelerated dramatically by hetero-aggregated lithium carbenoids with a halogen or oxygen as an α-heteroatom. The origin of the enhancement could attribute to the novel structural character of the hetero-aggregated lithium carbenoids. These intriguing finding predicts that it is practical to control a wide range of SN2-type organometallic reactions by using aggregated lithium carbenoids with other economical and convenient compounds.
The effects of the hetero-aggregation revealed here provide a new concept of the SN2-type reaction control by employing hetero-aggregation with other economical and convenient compounds. Display omitted
•The effects of the hetero-aggregation on the reactivity of lithium carbenoid are revealed.•The SN2-type reaction could be controlled by hetero-aggregation.•The enhancement origins from the novel structure of the hetero-aggregation systems.
Chlorine atoms initiated oxidation reactions are significant for the removal of typical volatile organic compounds (VOCs) in the atmosphere. The intrinsic mechanisms of CH
2
=CHCOOH + Cl reaction ...have been carried out at the CCSD(T)/cc-pVTZ//M06-2X/6-311++G(d,p) level. There are hydrogen abstraction and C-addition pathways on potential energy surfaces. By analyses, the addition intermediates of IM1(ClCH
2
CHCOOH) and IM2(CH
2
CHClCOOH) are found to be dominant. The secondary reactions of IM1 and IM2 have been discussed in the presence of O
3
, O
2
, NO, and NO
2
. And we have also investigated the degradation mechanisms of ClCH
2
CHO
2
COOH with NO, NO
2
, and self-reaction. Moreover, the atmospheric kinetics has been calculated by the variable reaction coordinate transition–state theory (VRC-TST). As a result, the rate constants show negative temperature and positive pressure dependence. The atmospheric lifetime and global warming potentials of acrylic acid have been calculated. Overall, the current study elucidates a new mechanism for the atmospheric reaction of chlorine atoms with acrylic acid.
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•Selectivity of catalysts depends on catalysts acidity and basicity.•Acidic catalyst prefers dehydration while basic catalysts tend to promote dehydrogenation.•Solvent- and ...catalyst-free self-oxidation was an important for selective dehydrogenation.
Catalytic dehydration and dehydrogenation reactions of ethanol have been investigated systematically using the ab initio quantum chemistry methods The catalysts include water, hydrogen peroxide, formic acid, phosphoric acid, hydrogen fluoride, ammonia, and ethanol itself. Moreover, a few clusters of water and ethanol were considered to simulate the catalytic mechanisms in supercritical water and supercritical ethanol. The barriers for both dehydration and dehydrogenation can be reduced significantly in the presence of the catalysts. It is revealed that the selectivity of the catalytic dehydration and dehydrogenation depends on the acidity and basicity of the catalysts and the sizes of the clusters. The acidic catalyst prefers dehydration while the basic catalysts tend to promote dehydrogenation more effectively. The calculated water-dimer catalysis mechanism supports the experimental results of the selective oxidation of ethanol in the supercritical water. It is suggested that the solvent- and catalyst-free self-oxidation of the supercritical ethanol could be an important mechanism for the selective dehydrogenation of ethanol on the theoretical point of view.
The development of heteroatom-doped carbons with fascinating hierarchical porosity is of great significance for the improvement of catalytic properties of carbon catalysts. In this work, we report a ...boron and nitrogen codoped hollow mesoporous carbon (denoted as BN/HMC) via a simple synthesis route by direct pyrolysis of phenylboronic acid/melamine/ZIF-8 precursors. Thanks to their high specific surface area, unique hollow mesoporous nanoarchitecture, rich defects, and boron and nitrogen codoping, the obtained BN/HMC-0.05 can be employed as a high-efficiency carbon-based catalyst for the reduction of 4-nitrophenol. Theoretical calculations reveal that the B and N codoping in a carbon matrix are essential for the adsorption and activation of 4-nitrophenol. The present work might pave a new way in construction of metal-free carbon catalysts with both heteroatom doping and hierarchical porosity for various applications.
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•Distinct difference between the lone-pair-driven MLC and the tautomerism-driven MLC for catalytic hydrogenation.•The driving force of the tautomerism-driven MLC is of key importance ...for selectivity.•Theoretical guidelines for the design of lone-pair-driven MLC and the tautomerism-driven MLC catalysts for selective hydrogenation.
Metal-ligand cooperation (MLC) is an important strategy in transition-metal (TM) catalysis. Tautomerism-driven MLC has recently been emerging as a novel type of catalyst design strategy. However, the difference between the conventional lone-pair-driven MLC and tautomerism-driven MLC in mechanism and selectivity remains unclear. Herein, a DFT study was performed to unveil the difference between them in the (iPrPHNN)Mn catalyzed selective hydrogenation of amide. The double deprotonated (iPrPHNN)Mn could lead to an active species with two functional sites, i.e., the N site and the C site, which would promote the lone-pair-driven MLC and the tautomerism-driven MLC for the catalytic hydrogenation, respectively. Systematic investigation of the full catalytic cycles, including hemiaminal formation, hydrogenation of amide, and the generation of alcohol and amine, reveals that the addition of H2 onto amide prefers the lone-pair-driven MLC mechanism assisted by a proton shuttle. Then, the formed hemiaminal intermediate would competitively undergo the C-O bond cleavage to the secondary amine product or the C-N bond cleavage to the primary amine and alcohol products. Both the C-N bond cleavage and the C-O bond cleavage prefer the tautomerism-driven MLC, with the free energy barrier of the former being lower than that of the latter by around 12 kcal/mol. In the tautomerism-driven MLC mechanism, the lone-pair electrons on the innocent amido would increase the electron density of the metal center, which would lead to an easier electron transfer from the Mn center to the substrate, causing the favorable cleavage of the C-N bond. In the following hydrogenation step, the generation of aldehyde to alcohol or the hydrogenation of imine to amine can occur via either the lone-pair-driven MLC or the tautomerism-driven MLC. The driving force of the tautomerism-driven MLC is of key importance for selectivity. The results of the lone-pair-driven MLC and the tautomerism-driven MLC mechanisms in selectivity would be helpful for the design of MLC catalysis.
An unusual cobalt(III)-catalyzed cross-coupling/cyclization of aryl C–H bonds of N-nitrosoanilines with α-diazo-β-ketoesters has been achieved. This protocol features a unique combination of Csp2-H ...activation/Wolff rearrangement process, allowing for the rapid assembly of quaternary 2-oxindoles. The empirical evidence and density functional theory (DFT) calculations reveal the trapping process of transient acceptor ketene intermediates by cobalt metallocycles.
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•High performing hollow CuO-NiCo2O4 catalysts for NH3BH3 methanolysis were prepared.•TOF for the hollow CuO-NiCo2O4 in NH3BH3 methanolysis is up to 23.2 min−1.•The Co center in ...CuO-NiCo2O4 is recognized as active sites by DFT calculations.•Synergistic effect between CuO and NiCo2O4 results from the electrons migration.
Rational construction of cost-efficient catalysts with high activity and durability for hydrogen production from ammonia borane (AB) methanolysis is highly desirable but remains a substantial challenge. In this work, we constructed a series of non-noble-metal based hollow CuO-NiCo2O4 nanospheres composite, in which the CuO-NiCo2O4-0.8 nanospheres exhibit robust catalytic activity with a high turnover frequency (TOF) of 23.2 molH2 molcat.−1 min−1 towards AB methanolysis. Systemic experimental and computational studies reveal the promotion of activity results from the synergistic effect between CuO and NiCo2O4. It is revealed the combination of CuO with NiCo2O4 caused the electrons migration among Cu, Ni and Co sites and the change of d-band centers of catalyst, thus enhancing the adsorption process of CH3OH and AB molecules on catalyst and subsequently promoting the catalytic activity. Moreover, the Co center in CuO-NiCo2O4 composite is recognized as active sites by DFT calculations. Mechanistically, the rate determining step is the dissociation of OH bond in CH3OH, which is confirmed by kinetic isotopic effect experiment. A plausible mechanism of methanolytic dehydrogenation of AB on CuO-NiCo2O4 was proposed based on experiment and DFT calculations. These findings should shed light on the rational construction of cost-efficient catalysts with high performance for hydrogen production from AB methanolysis.
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