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The crucial need for quality refined sugar has led to the development of advanced adsorbents, with a focus on the decolorization of remelt syrup. In this study, (3-chloro-2-hydroxypropyl) trimethylammonium chloride and polyethyleneimine co-modified pomelo peel cellulose-derived aerogel (CP-PPA) was fabricated, and synthetic melanoidins were used as model colorants of remelt syrup to evaluate the validity and practicality of CP-PPA for eliminating colored impurities. Integrating abundant amine-functionalized groups (quaternary ammonium and protonated amine) within the pomelo peel-derived aerogel directionally captured electronegative melanoidins via electrostatic interactions. Furthermore, the active sites, types, and relative strength of the weak interactions between CP-PPA and melanoidins were determined using density functional theory simulations. CP-PPA exhibited an excellent equilibration adsorbing capacity for capturing melanoidins of 749.51 mg/g, and a removal efficiency of 93.69 %. Additionally, the adsorption mechanism was thoroughly examined in an effort to improve the economy of the sugar refinement industry. [Display omitted] • Pomelo peel was exploited to make cost-effective and non-toxic aerogel. • Well-developed porous network-like CP-PPA was prepared and characterized. • The absorption mechanism was deciphered by the phenomenological models. • The possible donor–acceptor adsorption relationship was vividly presented. [ABSTRACT FROM AUTHOR]

Graphical abstract Theoretical advances on the mechanistic study of Ag-catalyzed carbene/nitrene/silylene transfer reactions were summarized in this review, which could be considered to involve two major steps: Ag–carbene/nitrene/silylene complex formation and the subsequent transformation of these complexes. Highlights • DFT studies on the mechanism of Ag-catalyzed group transfer reactions are summarized. • The mechanism consists of Ag–carbene/nitrene/silylene formation and transformation. • The mechanism is related to the electronic behaviors of Ag–carbene/nitrene/silylene. Abstract Carbene and its isoelectronic species nitrene and silylene, have long been considered reactive intermediates in organic synthesis. Ag-catalyzed carbene/nitrene/silylene transfer reactions have emerged as an important topic because they have made remarkable progress in organic synthesis. A series of theoretical investigations on the mechanism of these reactions is important to ensure their thorough understanding and aid design of new synthetic methodologies. Here, a mechanistic overview of Ag-catalyzed carbene/nitrene/silylene transfer reactions is given, which can be separated into two major steps including Ag–carbene/nitrene/silylene complex formation and the subsequent transformation of these complexes. Theoretical studies revealed that Ag–carbene and Ag–silylene complexes can be considered as typical Fischer-type complexes, in which the carbene/silylene moiety behaves as both a sp σ donor and p π acceptor. Conversely, the triplet Ag–nitrene complexes are usually more stable than the singlet ones because of the higher electronegativity of nitrogen than those of carbon and silicon. Density functional theory calculations have indicated that the triplet state of an Ag–nitrene complex has two unpaired electrons that are mainly localized on nitrogen. In this review, theoretical studies on the generation of Ag–carbene/nitrene/silylene complexes are systematically summarized. Moreover, the nucleophilic functionalization of Ag–carbene/nitrene/silylene complexes with halogen, hydroxyl, carbonyl, alkane, or arene groups are also considered theoretically. We believe that the mechanistic details discussed here will be of great importance for rational design of desired catalytic cycles and reactions. [ABSTRACT FROM AUTHOR]

Density functional theory calculations were performed to study the counterion effect and directing group effect in rhodium mediated concerted metalation deprotonation type C H bond activation of arenes. The use of different carboxylates as counterions results in changes to the activation energies over a narrow range. These changes are mainly attributed to the opposing effects of alkalinity and nucleophilicity of the substituted groups. The effects of directing groups were also considered. By introducing directing groups, the C H bond activation energy is greatly reduced. Our results show that different directing groups have similar effects and activation energies. [ABSTRACT FROM AUTHOR]

• Density functional theoretical (DFT) calculations were performed to reveal the mechanism for nickel-catalyzed hydroaminomethylation reaction of alkyne with imine. • An alternative Ni(I) mechanism, without a redox reaction, was proposed by DFT calculations. The mechanism based on these calculations is favorable compared with the previously proposed redox Ni(0)-Ni(II) pathway. • AIM analysis shows that the dissociation of the amine ligand to provide a vacancy would lead to a higher free-energy barrier for the Ni(0)-Ni(II) pathway. Herein, we report a theoretical investigation on the nickel-catalyzed hydroaminomethylation reaction of alkyne with imine. In this work, an alternative Ni(I) mechanism, without a redox reaction, was proposed by DFT calculations. The mechanism based on these calculations is favorable compared with the previously proposed redox Ni(0)-Ni(II) pathway. A Ni(I)-amino complex is considered to be the active species, which can be obtained from hydrogen transfer between an imine-coordinated Ni(0) complex and an amine. A Meerwein-Ponndorf type hydride transfer takes place between an amino group and a coordinated alkyne. Then an imine insertion affords Ni(I)-allylamino. Proton transfer with the approaching imine yields the hydroaminomethylation product and regenerates the Ni(I)-amino active species. Throughout the catalytic cycle, the oxidative state of Ni remains at +1. Furthermore, AIM analysis shows that the dissociation of the amine ligand to provide a vacancy would lead to a higher free-energy barrier for the Ni(0)-Ni(II) pathway. An alternative Ni(I) mechanism, without a redox reaction, was proposed by DFT calculations. [Display omitted] [ABSTRACT FROM AUTHOR]

Ir-catalysis has been widely adopted in hydrogenation reactions for the transformation of unsaturated molecules to the corresponding saturated ones. We reviewed herein the DFT studies on mechanism of Ir-catalyzed homogeneous hydrogenations with respect to various hydrogen sources. Moreover, the stereochemistry and substituent effects in the Ir-catalyzed hydrogenations are considered. • Mechanistic studies towards Ir-mediated hydrogenation were summarized in this review. • General catalytic cycles given by theoretical studies are involved in each example. • Mechanism discussions are classified according to the substrates. • The understanding of mechanism would be helpful for further design new Ir-catalysis. Ir catalysis is widely used in hydrogenation reactions to transform unsaturated molecules to the corresponding saturated molecules. Understanding the reaction mechanism is helpful for design of new Ir-catalyzed hydrogenation reactions, as well as for controlling the regio/stereoselectivity. Density functional theory is a powerful tool for mechanistic study of organometallic catalysis, and it has been widely used to reveal the reaction pathways in this research area. With the development of computational methods, much progress has recently been made in mechanistic study of Ir-catalyzed hydrogenation reactions. Herein, we present a review of theoretical studies of the mechanism of Ir-catalyzed homogeneous hydrogenation. A redox pathway is commonly proposed for hydrogenation of non-polar unsaturated bonds, which involves oxidative addition of a hydrogen molecule to afford a high valence Ir hydride complex, insertion of an unsaturated bond into the Ir–H bond, and reductive elimination. Alternatively, the dihydrogen molecule can undergo a heterolysis reaction to provide a formal hydride ion and a proton. Subsequent nucleophilic and electrophilic attack can then also achieve hydrogenation of the polar unsaturated bond. In this review, the studies of the mechanism of Ir-catalyzed hydrogenation are classified according to the type of substrate: olefins, carbonyls, and imines. In each category, the reactions are discussed with respect to the various hydrogen sources. The stereochemistry and substituent effect in Ir-catalyzed hydrogenation are also considered. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mechanism and origin of selectivities of NHC-catalyzed hydroacylation-Stetter reaction has been systematically studied. • The role of NHC has been disclosed by using global reactivity index analysis. • ELF and IRC analyses are performed to clarify the bonding modes of hydroacylation and Stetter reaction. The regioselectivity of hydroacylation mediated by transition metal and organocatalyst has been and continues to be one of the most challenging questions in the synthesis field. To explore the possible mechanisms and origin of the regio-/enantioselectivity, the density functional theory (DFT) calculations were performed for studying intramolecular hydroacylation-Stetter reaction of alkynyl bisbenzaldehyde catalyzed by N-heterocyclic carbene (NHC). Computational results show that the hydroacylation process was the rate-determining step and irreversible. Four different stereoisomers (RR, RS, SR, and SS) were considered and the lowest energy mode agreed with the reported enantioselectivity in experiment. Global reaction index (GRI) analysis showed that NHC catalyst can convert alkynyl bisbenzaldehyde electrophilic carbonyl carbon into nucleophilicity to initiate the reaction. Moreover, electron localization function (ELF) and intrinsic reaction coordinate (IRC) analyses were performed to characterize the manner difference between the process of hydroacylation and Stetter reaction. [ABSTRACT FROM AUTHOR]