: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Nanozymes Inspired by Natural Enzymes

Visible-light-induced deoxygenative C2-sulfonylation of quinoline N-oxides with sulfinic acids

A series of pincer-type compounds possessing an N-heterocyclic carbene precursor and a carboxyl group as proton transfer agent were synthesized and used as organocatalysts for the cycloaddition of epoxides with CO2 In this context, we have demonstrated the high activity of these one-component organocatalysts in the CO2 transformation to cyclic carbonates under ambient conditions (room temperature, 1 bar of CO2) The catalytic potential of these multifunctional organocatalysts on challenging internal epoxides is particularly deserving of mention because organocatalysts that are able to mediate the cycloaddition reaction of internal epoxides with CO2 under mild conditions remain scarce The intramolecular synergistic activation mechanism was elucidated by control experiments and DFT calculations

Cooperative Multifunctional Organocatalysts for Ambient Conversion of Carbon Dioxide into Cyclic Carbonates

The past several decades have witnessed the fast-growing field of plasmonics, which localize and concentrate incident light at the nanoscale and provide a source of light, heat and energetic carriers. Plasmonic nanostructures, which are able to harvest and convert the abundant sunlight to drive chemical reactions, have shown great prospects in heterogeneous photocatalysis. To maximize solar energy utilization, the rational design and precise manipulation of plasmonic nanostructures are, therefore, essential to obtain their strong light–matter interaction. In this review, we focus on the very recent advances in harnessing single-active plasmonic nanocatalysts (i.e., plasmonic materials as the only photo- and catalytic-active species), involving noble metals and doped-semiconductors, for enhanced photocatalytic reactions with visible light.

Harnessing single-active plasmonic nanostructures for enhanced photocatalysis under visible light

First-principles quantum mechanical/molecular mechanical (QM/MM)-free energy calculations have been performed to uncover how uricase catalyzes metabolic reactions of uric acid (UA), demonstrating that the entire reaction process of UA in uricase consists of two stages—oxidation followed by hydration. The oxidation consists of four steps: (1) chemical transformation from 8-hydroxyxythine to an anionic radical via a proton transfer along with an electron transfer, which is different from the previously proposed electron-transfer mechanism that involves a dianion intermediate (UA2–) during the catalytic reaction process; (2) proton transfer to the O2– anion (radical); (3) diradical recombination to form a peroxo intermediate; (4) dissociation of H2O2 to generate the dehydrourate. Hydration, for the most favorable pathway, is initiated by the nucleophilic attack of a water molecule on dehydrourate, along with a concerted proton transfer through residue Thr69 in the catalytic site. According to the calculated ...

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Catalytic Mechanisms for Cofactor-Free Oxidase-Catalyzed Reactions: Reaction Pathways of Uricase-Catalyzed Oxidation and Hydration of Uric Acid.

The possible mechanisms and the origin of the stereoselectivity of the N-heterocyclic carbene (NHC)-catalyzed [3 + 4] annulation reaction of 2-bromoenal with N-Ts hydrazone have been investigated using density functional theory (DFT). The general mechanism of NHC-catalyzed debromination of 2-bromoenals has been uncovered in theory for the first time. Our calculated results indicate that the C–C bond formation involved in the stepwise [3 + 4] process is the rate- and stereoselectivity-determining step, and the SR-isomer is the predominant product, which is consistent with the experiment. Non-covalent interaction (NCI) analysis discovers that the strong C–H⋯O and C–H⋯π interactions should be the key for controlling the stereoselectivity in the reaction. The local reactivity index analysis shows that the reaction prefers to proceed via the [3 + 4] annulation reaction rather than the [3 + 2] annulation reaction. It is noteworthy that further analysis indicates that the main role of the NHC in this kind of reaction is to activate the C–Br bond, which is different from the umpolung role in the NHC-catalyzed annulation reactions of enals.

Insights into N-heterocyclic carbene-catalyzed [3 + 4] annulation reactions of 2-bromoenals with N-Ts hydrazones

In this work, the reaction mechanism, stereoselectivity, and chemoselectivity of oxidative α-fluorination of aliphatic aldehydes enabled by N-heterocyclic carbene catalysts have been investigated using a density functional theory (DFT) method. The computed outcomes reveal that the whole reaction includes several processes, i.e., formation of the Breslow intermediate, oxidative deprotonation to give the cation intermediate, deprotonation of the α-C(sp3)–H bond, α-fluorination, esterification by CyOH affording the α-fluoroester, and dissociation of the catalyst and the final product. According to the computational results, the fluorination process was identified to be the stereoselectivity-determining step. The addition on the different prochiral faces of the enolate intermediate results in the formation of a stereoselective fluorinated intermediate and the chiral center assigned to the α-carbon emerges during the fluorination process. Non-covalent interaction (NCI) analysis revealed the presence of relatively stronger non-covalent interactions (i.e. π–π stacking), which leads to the predominant position of the S-configurational reaction pathway. Moreover, the competing reaction pathways affording the by-products of aliphatic ester and difluorinated ester were calculated to be kinetically unfavorable. Furthermore, global reactivity index (GRI) analysis shows that NHC promotes the reaction by enhancing the nucleophilicity of the enolate intermediate and the electrophilicity of the monofluorinated intermediate. The obtained theoretical insights would be useful for rational design of the fluorination of aliphatic aldehydes with high selectivity under organocatalysis.

Computational study on NHC-catalyzed enantioselective and chemoselective fluorination of aliphatic aldehydes

Lewis base N-heterocyclic carbene (NHC)-catalyzed annulation is the subject of extensive interest in synthetic chemistry, but the reaction mechanisms, especially the unexpected chemoselectivity of some of these reactions, are poorly understood. In this work, a systematic theoretical calculation has been performed on NHC-catalyzed annulation between allenals and chalcone. Multiple possible reaction pathways (A-E) leading to three different products have been characterized. The calculated results reveal that NHC is more likely to initiate the reaction by nucleophilic attack on the center carbon atom of the allene group but not the carbonyl carbon atom in allenals leading to the Breslow intermediate, which is remarkably different from the other NHC-catalyzed annulations of unsaturated aldehydes with chalcones. The computed energy profiles demonstrate that the most energetically favorable pathway (A) results in polysubstituted pyranyl aldehydes, which reasonably explains the observed chemoselectivity in the experiment. The observed chemoselectivity is demonstrated to be thermodynamically but not kinetically controlled, and the stability of the Breslow intermediate is the key for the possibility of homoenolate pathway D and enolate pathway E. This work can improve our understanding of the multiple competing pathways for NHC-catalyzed annulation reactions of unsaturated aldehydes with chalcones and provide valuable insights for predicting the chemoselectivity for this kind of reaction.

Insights into the Unexpected Chemoselectivity for the N-Heterocyclic Carbene-Catalyzed Annulation Reaction of Allenals with Chalcones

Palladium (Pd)‐catalyzed intermolecular oxidative annulation represents as an attractive approach to regioselective synthesis of 2/3‐arylindoles, but the unexpected regioselectivity remains to be one of the most challenging questions in this field. Herein, we present a systematically theoretical study on the Pd‐catalyzed regioselective synthesis of 3‐arylindoles from N−Ts‐anilines and styrenes with the presence of oxidant, special ligand, and benzoquinone (BQ) additive. A refined mechanism, in which the single six‐membered ring CMD‐type transition state was involved in the C−H activation of styrenes, is obviously more energetically favorable than the proposed pathway associated with the [6‐6] palladacyclic transition state in the experimental report (Youn et al., Angew. Chem. Int. Ed. 2017, 56, 1–6). The preferred reaction pathway consists of N−H deprotonation, CMD‐type C−H bond activation of styrenes, carbopalladation, BQ‐assisted β‐C−H activation, α‐C−H bond activation, and reductive elimination. With BQ additive, the carbopalladation is the key step for controlling the regioselectivity, and the favorable Pd−O coordinating bond interaction between Pd and BQ as well as the less distortion degree of styrene in the C3‐regioselective transition state determine the observed regioselectivity. The obtained computational insights should be valuable for understanding and rational design of the transition metal‐catalyzed oxidative annulation reactions with special regioselectivity.

Yan Qiao

Papers

Catalytic Mechanisms for Cofactor-Free Oxidase-Catalyzed Reactions: Reaction Pathways of Uricase-Catalyzed Oxidation and Hydration of Uric Acid.

Insights into N-heterocyclic carbene-catalyzed [3 + 4] annulation reactions of 2-bromoenals with N-Ts hydrazones

Computational study on NHC-catalyzed enantioselective and chemoselective fluorination of aliphatic aldehydes

Insights into the Unexpected Chemoselectivity for the N-Heterocyclic Carbene-Catalyzed Annulation Reaction of Allenals with Chalcones

Insights into the Oxidative Palladium-Catalyzed Regioselective Synthesis of 3-Arylindoles from N−Ts-Anilines and Styrenes: A Computational Study