: 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

The development of clean sustainable energy technologies has been significantly promoted by advances in electrocatalysts, especially for low‐dimensional metallic nanomaterials (LDMNs), which have distinctive structural, physiochemical, and electronic properties, including a highly active surface area, efficient electron transfer, and rich surface unsaturated atoms. Recent advances have also revealed that surface engineering, interface engineering, and strain engineering for LDMNs can readily lead to increased surface active centers, strong synergistic effects, and electronic modulation, thus providing new approaches that greatly promote the electrocatalytic performance. In this review, the recent progress in LDMNs is highlighted in the context of their potential as electrocatalysts with superb performance for advanced electrocatalytic reactions. The latest achievements in their structural design, controllable synthesis, mechanistic understanding, and avenues for performance enhancement are illustrated. Strategies for controlled synthesis of high‐quality LDMNs and discussed, and to boost the future development of LDMNs for energy‐related conversion technology, future perspectives and potential challenges are also proposed.

Low-Dimensional Metallic Nanomaterials for Advanced Electrocatalysis

Metal carbene plays a vital role in modern organic synthesis. The neutral divalent carbon of metal carbene renders it an active intermediate throughout a range of reactions. In experiments, diverse metal carbene-related transformation reactions have been established, including transition-metal-catalyzed cross-coupling reactions using N-heterocyclic carbenes as ligands, metal carbene insertion into σ bonds, cyclopropanations, ylide formation, and so forth. The remarkable progress achieved in synthetic chemistry, in turn, has increased the demand for mechanistic studies of carbene chemistry. A thorough understanding of reaction mechanisms can extend the application scope of metal carbene compounds and inspire the rational design of new carbene transformation reactions.Density functional theory (DFT) calculations have been performed in our group to gain more mechanistic insights into metal carbene-related reactions. This account focuses on computational studies of transition-metal-catalyzed carbene transformation reactions with nucleophiles. The generation of metal carbene or metal-ligated free carbene and subsequent carbene transformation pathways is discussed. According to our mechanistic studies of carbene transformation with nucleophiles, three generalized reaction models are summarized, including the intramolecular migratory insertion of metal carbene, intermolecular nucleophilic addition toward metal carbene, and outer-sphere nucleophilic addition to the metal-ligated free carbene.In general, the intermolecular nucleophilic addition mechanism is commonly proposed since metal carbene has an electrophilic carbene carbon. From a mechanistic point of view, the intramolecular migratory insertion mechanism is also widely used because metal carbene insertion into σ bonds formally occurs through this mechanism. An outer-sphere nucleophilic addition mechanism is proposed for reactions that form a metal-ligated free carbene complex instead of the commonly proposed metal carbene. The metal-ligated free carbene complex contains a naked carbene carbon that is not coordinated with the metal center. In this case, a transition-metal catalyst is used only as a Lewis acid, and nucleophilic addition occurs directly at the free carbene carbon. Our computational results suggested that outer-sphere nucleophilic addition is a facile step because metal ligation could stabilize the transition state as well as the generated intermediate. The intramolecular migratory insertion mechanism also has a low energy barrier due to the lack of an entropy penalty. Carbene formation from carbene precursors is usually the rate-determining step, except in intermolecular nucleophilic addition, and the reactivity of nucleophiles has a significant influence on the overall reaction rate. We can also envision that the weak nucleophilicity of nucleophiles would suppress outer-sphere nucleophilic addition. These computational studies showcase the characteristics of three carbene transformation models, and we hope that it will spur the development of mechanistic studies of carbene chemistry.

Recent Advances in Theoretical Studies on Transition-Metal-Catalyzed Carbene Transformations.

Generally, N-heterocyclic carbene (NHC) complexed with carbonyl compounds would transform into several important active intermediates, ie, enolates, Breslow intermediates, or acylazolium intermediates, which act as either a nucleophile (Nu) or an electrophile (E) to react with the other E/Nu partner Hence, the key to predicting the origin of chemoselectivity is to compute the activity (ie, electrophilic index ω for E and nucleophilic index N for Nu) and stability of the intermediates and products, which are suggested in a general mechanistic map of these reactions To support this point, we selected and studied different cases of the NHC-catalyzed reactions of carbonyl compounds in the presence of a base and/or an oxidant, in which multiple possible pathways involving acylazolium, enolate, Breslow, and α,β-unsaturated acylazolium intermediates were proposed and a novel index ω + N of the E and Nu partners was employed to exactly predict the energy barrier of the chemoselective step in theory This work provides a guide for determining the general principle behind organocatalytic reactions with various chemoselectivities, and suggests a general application of the reaction index in predicting the chemoselectivity of the nucleophilic and electrophilic reactions

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Prediction of NHC-catalyzed chemoselective functionalizations of carbonyl compounds: a general mechanistic map.

Recent advances in nitrene chemistry from acyclic precursors are reviewed in this paper. Early developments in nitrene chemistry predominantly focused on exploiting new nitrene precursors and inventing new types of nitrene-based transformations. Organic azides, iminoiodinanes (even in situ generated iminoiodinanes), amines, and amide N–O compounds have all been reported as efficient acyclic nitrene precursors. Nitrene-based transformations mainly include C–H amination/amidation, aziridination, addition to unsaturated bonds, sulfimidation, etc. In many cases, asymmetric versions of C–H amination/amidation, aziridination and sulfimidation have been demonstrated. In this review, a particular emphasis is placed on reactions of nitrene with unsaturated bonds and reactions using amide N–O compounds as nitrene precursors. It can be seen that the reactivity of nitrene species can be controlled by the metal centre, ligand, type of nitrene precursor, and reaction system.

Unravelling nitrene chemistry from acyclic precursors: recent advances and challenges

Computational advances aiding mechanistic understanding of silver-catalyzed carbene/nitrene/silylene transfer reactions

Density functional theory calculations were performed to reveal the mechanisms of Pd‐catalyzed cascade carbocyclization‐borylation and arylation reactions. The computational results indicate that the reactions start with allylic C−H cleavage through concerted metalation‐deprotonation and an intramolecular exo‐type allene insertion to form a six‐membered carbocycle intermediate. The regioselectivity of insertion could be explained by frontier molecular orbital theory and natural population analysis calculation. In the absence of extra nucleophiles, η1/η3‐isomerization followed by acetate‐assisted deprotonation could yield polyene product. When nucleophile was added to the reaction system, transmetalation and subsequent reductive elimination could give the exo‐substituted triene as major product. Meanwhile, η1/η3‐isomerization, transmetalation, and reductive elimination could afford the endo‐isomer as side product. The regioselectivity of further functionalization is controlled by the competition of transmetalation and η1/η3‐isomerization. The computational results show that both exo‐ and endo‐boronation product could be observed when bis(pinacolato)diboron is added as nucleophile. However, only exo‐phenylation product is observed when phenylboronic acid is used as nucleophile because of the high free‐energy barrier for reductive elimination from aryl η3‐allylic palladium.

Mechanistic Insight into Palladium‐Catalyzed Carbocyclization‐Functionalization of Bisallene: A Computational Study

For C-H alkenylation of aryl-substituted diarylisoxazoles, one mode is N-directed C-H alkenylation and the other is C-H alkenylation in the isoxazole ring. In this study, selective C-H alkenylations of 3,5-diarylisoxazoles have been investigated theoretically with the aid of density functional theory (DFT) calculations. With Cp*RhIII as the catalyst, the N-directed C-H alkenylation is preferred as a result of the stronger interaction energy caused by the nitrogen-directing effect. With Pd(OAc)2 as the catalyst and Ag2CO3 as the cocatalyst, their combination switches the regioselectivity to the C-H alkenylation in the isoxazole ring. The strong structural distortion involved in the competing N-directed olefin insertion transition state was found to suppress N-directed C-H alkenylation. With Pd(OAc)2 as the catalyst and Cu(OTf)2 as the cocatalyst, the N-directed C-H alkenylation becomes preferred due to the strong coordination of the nitrogen atom to the copper center. In particular, the structural and mechanistic information involved in the above two heterodimetallic Pd/Ag and Pd/Cu catalytic systems will help toward understanding and designing novel relevant heterodimetallic-catalyzed reactions.

Distinct Roles of Ag(I) and Cu(II) as Cocatalysts in Achieving Positional-Selective C-H Alkenylation of Isoxazoles: A Theoretical Investigation.

Density functional theory calculations were performed to study the competing pathways of rhodacycle intermediates generated in Rh(III)-catalyzed annulations of 2-alkenyl phenols and 2-alkenyl anilides with alkynes. The results show that the multiple pathways of eight-membered rhodacycles can be subtly tuned to give specific cyclic products. The seven-membered oxacyclic and spirocyclic products from 2-alkenyl phenols are formed by favoring the pathway of dissociating the Rh-O bond of O-contained rhodacycles, which are followed by antarafacial nucleophilic attack. The indoline product from 2-alkenyl anilides is generated through the pathway of intramolecular olefin migratory insertion of the N-contained rhodacycle.

Multiple Reaction Pathways of Eight-Membered Rhodacycles in Rh-Catalyzed Annulations of 2-Alkenyl Phenols/Anilides with Alkynes.

Polycyclic compounds having biological activities can be modified by employing different substituents. Substituent-dependent generation of tricyclic frameworks by the rhodium-catalyzed cycloisomerization of homopropargyl allene-alkynes was investigated by using density functional theory calculations. A mechanistic study revealed that all the three reactions, A (Z = Me, X = tBu), B (Z = Me, X = Me), and C (Z = H, X = Me), underwent initial oxidative cyclization, from which the divergent cycloisomerization was triggered when different substituents were employed. It was found from our calculations that reactions A and B underwent alkyne insertion into the Rh-C(sp2) bond and resulted in a key metal carbenoid intermediate. From the metal carbenoid species, reaction A bearing a more hindered tert-butyl group prefers 1,2-hydrogen migration to produce a 6/5/4 tricyclic product, while reaction B bearing a less hindered methyl group prefers 1,2-carbon migration leading to ring expansion and producing a 6/5/5 tricyclic product. The origins of the distinct selectivity were disclosed, which are beneficial for the development of novel related reactions. For reaction C (Z=H, Z=H or Z=H, Z=Me), the β-hydrogen elimination was found to be favored over the alkyne insertion into the Rh-C(sp2) bond and thus the monocyclic product is delivered. The E/Z effects involved in the above two cases were also discussed.

Substituent-dependent generation of tricyclic frameworks by the rhodium-catalyzed cycloisomerization of homopropargyl allene-alkynes: a theoretical study.

Jing Zhang

Papers

Computational advances aiding mechanistic understanding of silver-catalyzed carbene/nitrene/silylene transfer reactions

Mechanistic Insight into Palladium‐Catalyzed Carbocyclization‐Functionalization of Bisallene: A Computational Study

Distinct Roles of Ag(I) and Cu(II) as Cocatalysts in Achieving Positional-Selective C-H Alkenylation of Isoxazoles: A Theoretical Investigation.

Multiple Reaction Pathways of Eight-Membered Rhodacycles in Rh-Catalyzed Annulations of 2-Alkenyl Phenols/Anilides with Alkynes.

Substituent-dependent generation of tricyclic frameworks by the rhodium-catalyzed cycloisomerization of homopropargyl allene-alkynes: a theoretical study.