Nitrogen ligands in two-dimensional covalent organic frameworks for metal catalysis

We introduced bipyridine ligands into a series of two‐dimensional （2D） covalent organic frame‐works （COFs） using 2,2’‐bipyridine‐5,5’‐dicarbaldehyde （2,2’‐BPyDCA） as a component in the mixed building blocks. The framework of the COFs was formed by the linkage of imine groups. The ligand content in the COFs was synthetically tuned by the content of 2,2’‐BPyDCA, and thus the amount of metal, palladium（II） acetate, bonded to the nitrogen ligands could be manipulated. Both the bipyri‐dine ligands and imine groups can coordinate with Pd（II） ions, but the loading position can be var‐ied, with one ligand favoring binding in the space between adjacent COFs’ layers and the other lig‐and favoring binding within the pores of the COFs. The Pd（II）‐loaded COFs exhibited good catalytic activity for the Heck reaction.

Metal-mediated catalysis in the gas phase: A review

This review summarizes a variety of experimentally identified gas‐phase catalytic cycles,all of which are mediated by atomic metal ions,bare metal clusters,metal oxide clusters or metal complexes.Emphasis is placed on the latest advances in the unique catalytic reactivity of cluster‐confined single noble metal atoms.The cycles discussed in this paper cover a wide range of inorganic and organic molecules.The use of start‐of‐the‐art mass spectrometric instrumentation in conjunction with quantum chemistry calculations is also reported,as these techniques have determined the mechanistic details of the elementary steps of such catalytic cycles.The important role of gas‐phase data in guiding the rational design of better‐performing catalysts in related condensed phase reactions is also examined.In particular,this review focuses on the following three topics:(1)the catalytic oxidation of carbon monoxide,(2)the catalytic functionalization of methane,and(3)catalytic decarboxylation.

Palladacyclic N-heterocyclic carbene precatalysts for transition metal catalysis

Palladacycles remain a challenging and significant research field in organic chemistry and have emerged as a type of powerful and versatile precatalysts or key active intermediates for transition metal catalysis.These achievements in this area are correlated to the design and development of useful ancillary ligands,such as N-heterocyclic carbenes(NHCs),which not only stabilize the actual catalytic active species facilitating the transformations,but also provide additional control over the selectivity of reactions.In this context,NHCs-ligated palladacycles(NHCP_(dcycles))with different electronic and steric properties have been synthesized and applied as green precatalysts(high stability and activity,low catalyst loading and mild reaction conditions)to accelerate transition metalcatalyzed reactions.Therefore,this review focuses mainly on the strategy of NHC-Pd_(cycles) design and catalytic results obtained from representative transition metal catalysis,such as Suzuki-Miyaura,Heck-Mizoroki and Sonogashira cross-coupling reactions,Buchwald-Hartwig amination,carbonylation as well as arylation.At last,the current limitations and potential trends for further development of NHC-Pdcycles are also highlighted.

Modern information technologies in construction of kinetic models for reactions of metal complex catalysis

For detailed study of complex chemical reactions mechanisms experiment is conducted for selected private reactions. This causes a problem of kinetic parameters getting--the same set of rate constants must describe both public and private reaction stages, and also a general mechanism. In this paper, solution of this problem for a reaction of olefins hydroalumination is proposed. To optimize the computational process a methodology of parallelization is elaborated. On the base of parallel computations, a kinetic model for the reaction assigned is constructed, and on its base, the physical and chemical conclusions about reaction mechanism are done.

Nitrogen-Doped Hierarchical Heterostructured Aerophobic MoS_(x)/Ni_(3)S_(2)Nanowires by One-pot Synthesis:System Engineering and Synergistic Effect in Electrocatalysis of Hydrogen Evolution Reaction

Non-noble metal electrocatalysis has witnessed rapid and profound performance improvements owing to the emergence of advanced nanosynthetic techniques.Integration of these nanotechniques can lead to synergistic performance enhancement,but such system-engineering strategies are difficult to achieve because of the lack of effective synthesis method.We hereby demonstrate an integrated approach that combines most of the existing nanotechniques in a facile one-pot synthesis.Material characterization reveals that the product shows key features intended by techniques including morphological,structural,doping,heterointerface,and surface wetting engineering.The as-obtained nitrogen-doped hierarchical heterostructured MoS_(x)/Ni_(3)S_(2)nanowires show an overpotential that is only50 mV higher than commercial Pt/C for hydrogen evolution reaction over current densities from 10 to 150 mA cm^(-2).Correlations between the adopted nanotechniques and the electrochemical reaction rates are established by evaluating the impacts of individual techniques on the activation energy,pre-exponential factor,and transfer coefficient.This indepth analysis provides a full account of the synergistic effects and the overall improvement in electrocatalytic performance of hydrogen evolution reaction.This work manifests a generic strategy for multipurpose material design in non-noble metal electrocatalysis.

Recent advances in annulations enabled by nucleophilic Lewis base/metal dual catalysis

Metal/nucleophilic Lewis base dual catalysis has been recognized as a reliable and promising strategy for finishing ideal organic synthesis over the past decades.The new strategy can usually achieve some chemical reactions that cannot be realized by the traditionally mono-catalytic system,dramatically expanding the synthetic utility of chemical transformations by leveraging additional activation modes.Thus considerable progress has been made in the synthesis of a wide range of heterocyclic and biologically active compounds by using the combination of diversely metal/nucleophilic Lewis base dual catalysts,including metal/phosphine,metal/N-heterocyclic carbene(NHC)and metal/tertiary amine dual catalysis systems.In this review,we describe a comprehensive and updated advance of metal/nucleophilic Lewis base dual catalytic annualtion reactions,meanwhile,the related mechanism and the application of these annulation strategies in natural product total synthesis will be highlighted in detail.

A review of enantioselective dual transition metal/photoredox catalysis

Transition metal catalysis is one of the most important tools to construct carbon-carbon and carbon-heteroatom bonds in modern organic synthesis. Visible-light photoredox catalysis has recently drawn considerable attention of the scientific community owing to its unique activation modes and significance for the green synthesis. The merger of photoredox catalysis with transition metal catalysts, termed metallaphotoredox catalysis, has become a popular strategy for expanding the synthetic utility of visiblelight photocatalysis. This strategy has led to the discovery of novel asymmetric transformations, which are unfeasible or not easily accessible by a single catalytic system. This contemporary area of organic chemistry holds promise for the development of economical and environmentally friendly methods for the asymmetric synthesis of chiral compounds. In this review, the advances in the enantioselective metallaphotoredox catalysis(EMPC) are summarized.

Synergism of Pt nanoparticles and iron oxide support for chemoselective hydrogenation of nitroarenes under mild conditions

An efficient and low-cost supported Pt catalyst for hydrogenation of niroarenes was prepared with colloid Pt precursors andα-Fe2O3 as a support.The catalyst with Pt content as low as 0.2 wt%exhibits high activities,chemoselectivities and stability in the hydrogenation of nitrobenzene and a variety of niroarenes.The conversion of nitrobenzene can reach 3170 molconv h^–1 molPt^–1 under mild conditions(30°C,5 bar),which is much higher than that of commercial Pt/C catalyst and many reported catalysts under similar reaction conditions.The spatial separation of the active sites for H2 dissociation and hydrogenation should be responsible for the high chemoselectivity,which decreases the contact possibility between the reducible groups of nitroarenes and Pt nanoparticles.The unique surface properties ofα-Fe2O3 play an important role in the reaction process.It provides active sites for hydrogen spillover and reactant adsorption,and ultimately completes the hydrogenation of the nitro group on the catalyst surface.

Mechanistic Applications of Nonlinear Effects in First-Row Transition-Metal Catalytic Systems

Knowledge of asymmetric catalytic reaction mechanism is very important for rational design and synthesis of new chiral catalysts or catalytic systems with high catalytic activity and stereoselectivity.The studies of nonlinear effect have attracted wide attentions as a simple and practical mechanistic tool to probe complex asymmetric catalytic reactions.

Recent advances in radical‐mediated transformations of 1,3‐dienes

1,3‐Dienes are a class of easily accessible and versatile feedstock chemicals that can participate in a wide range of reactions to facilitate the synthesis of various valuable allylic compounds.In the past decades,radical methodology has emerged as a powerful tool for organic synthesis by virtue of the fact that diverse highly reactive radical species can usually be generated under mild,neutral and controlled conditions,and allow for rapid generation of molecular complexity.In this review,we critically illustrate the recent advances in the field of radical‐mediated transformations of 1,3‐dienes based on the different radical precursors and working modes.Wherever possible,particular emphasis is also put on the related mechanistic studies and synthetic applications.

Biomimetic asymmetric catalysis

Enzymes are the core for biological transformations in nature.Their structures and functions have drawn enormous attention from biologists as well as chemists since last century.The large demand of bioactive molecules and the pursuit of efficiency and greenness of synthesis have spurred the rapid development of biomimetic chemistry in the past several decades.Biomimetic asymmetric catalysis,mimicking the structures and functions of enzymes,has been recognized as one of the most promising synthetic strategies for the synthesis of valuable chiral compounds.This review summarizes the evolution of asymmetric catalysis inspired by aldolases,vitamin B_(1)/B_(6)-dependent enzymes,NAD(P)H,flavin,hydrogenases,heme oxygenases,nonheme oxygenases,and dinuclear/multinuclear metalloenzymes in aspects of biomimetic design,catalyst development and related catalytic transformations.Those well-established synthetic approaches originating from biological reactions have demonstrated the unique prowess of biomimetic asymmetric catalysis in bridging the gap between bio-catalysis and chemical synthesis.

Valorization of carbon dioxide with alcohols

Utilizing CO_(2)for the production of bulky and valuable chemicals presents an attractive solution to address environmental and fossil energy crises.Among the various approaches,direct carboxylation of alcohols with CO_(2)stands out as an eco-friendly process capable of efficiently producing carboxylic acids in a sustainable manner.However,the high dissociation energy of the C–O bond poses a significant challenge in this process.Over the past few decades,several strategies have been developed to activate alcohols and establish efficient catalytic systems for carboxylation with CO_(2).Nevertheless,the sporadic nature of reported approaches makes it difficult to determine the most effective one.This perspective aims to provide an overview of the current state-of-the-art catalytic protocols for carboxylating alcohols with CO_(2),encompassing esterification,halogenation,and photocatalysis,while considering their respective advantages and limitations.We aim to discern the most promising avenues for future development in this field.The insights presented in this perspective will contribute to the advancement of efficient and sustainable carboxylation methods using CO_(2),leading to the production of valuable chemicals in future.

Elucidating ligand effects in rhodium(Ⅲ)-catalyzed arene-alkene coupling reactions

Rhodium(Ⅲ)-catalyzed C-H couplings of arenes with alkenes are among the most powerful methods for C-C bond formation.For these transformations,subtle manipulation of ancillary ligands can lead to dramatic changes in reactivity and selectivity.However,detailed mechanistic studies concerning the ligand effects are rare.In this study,we investigated the origin of ligand-controlled product-selectivity in rhodium(Ⅲ)-catalyzed C-H couplings of arenes with alkenes,using a series of well-defined[CpXRhⅢ]complexes that feature electronically or sterically distinct Cp^(X)(Cp(η^(5)-C_(5)H_(5)),Cp^(CF3)(η^(5)-C_(5)Me_(4)CF_(3))and Cp^(∗)(η^(5)-C_(5)Me_(5)))ligands.A combination of experimental and theoretical investigations showed that(i)rhodium hydride species containing the electron rich Cp^(∗)ligand can undergo reinsertion of the alkene,thereby allowing rhodium-walking,(ii)rhodium hydride species involving the electron-deficient Cp or Cp^(CF3) ligands prefer reductive elimination rather than alkene insertion.These findings offer valuable insights on future rational catalyst design for selective arene-alkene cross coupling reactions.

Advances in Dearomative Carboxylation of Aromatic Compounds with Carbon Dioxide

Dearomative carboxylation of aromatic compounds with carbon dioxide(CO_(2))could be utilized for the synthesis of cyclic carboxylative frameworks.The dearomative carboxylation exhibits advantages such as reconstitution molecular spatial structure,environmental friendliness,mild conditions,high yield,and high selectivity,and is of significant importance in pharmaceutical synthesis and natural product chemistry.The recent advancements in the dearomative carboxylation of aromatics with CO_(2) are summarized,including elucidation of the reaction characteristics and the scope of substrates via transition-metal catalysis,photoredox catalysis,and electropromoted chemistry.

Research Progress in Enantioselective Radical Desymmetrization Reactions

Enantioselective radical desymmetrization is a highly effective approach for rapidly creating enantioenriched molecules,introducing dramatically increased structural complexity from readily available prochiral or meso compound feedstocks.Two strategic modes have been developed for these reactions,which differ in the nature of the stereo-determining steps.The first category deals primarily with the stereoselective desymmetrization of closed-shell radical precursors or functional reagents,whereas the second category achieves desymmetrization by stereoselectively functionalizing open-shell radical species.This mini-review explores the research progress in this growing field,aiming to elucidate mechanistic scenarios related to stereochemical control.Additionally,it offers insights into the challenges and opportunities that lie ahead for further development.

Some recent advances in transition-metal-catalyzed ortho SP^2 C–H functionalization using Ru, Rh, and Pd

In the past decade,transition-metal-catalyzed C–H functionalization by weak coordination has emerged as a practical and powerful tool to access many valuable chemicals.Two classes of weakly coordinating directing groups,commonly occurring functional groups,and easily removable auxiliaries,have been found to be efficient and practical for C–H activation reactions.This mini-review contains examples of recent research advances on transition-metal-catalyzed SP2 C–H functionalization via weak coordination,using Ru,Rh,and Pd.A number of weakly coordinating functional groups(e.g.,ketone,ester,carbamate,tertiary amide,ether,thioether,alcohol,and some others)are covered.As the field of transition-metal-catalyzed C–H functionalization continues to develop and more synthetically useful chemo-,regio-,and enantioselective reactions catalyzed by transition metal via weak coordination are discovered,this promising and attractive strategy will play a more important role in modern organic synthesis.

Chiral Imidazoline Ligands and Their Applications in Metal-Catalyzed Asymmetric Synthesis

As a structural analog of oxazoline,imidazoline(4,5-dihydroimidazole)has received much attention in the rational design of chiral ligands.The additional N-substituent provides broader space for fine-tuning of electronic and steric effects,and it offers a good handle for immobilizing onto solid supports.In the past decades,imidazoline ring has emerged as a powerful candidate for the design of chiral nitrogen-containing ligands,as well as a significant alternative for oxazoline ring.Various chiral imidazoline ligands have been designed and utilized in asymmetric organic reactions.These new catalysts can not only be applied in classical reactions,but also be employed to develop new organic reactions with high enantioselectivities.This review provides an overview of chiral imidazoline ligands.Their applications in asymmetric synthesis are also summarized.

Postassembly Modifications of Peptides via Metal-Catalyzed C–H Functionalization

The growing importance of peptides and proteins in therapeutic and biomedical applications has provided immense motivation toward the development of new ways to construct and transform peptide molecules.As in other areas of organic synthesis,C–H functionalization(CHF)chemistry could potentially exemplify disruptive technologies for peptide engineering.Over the past decade,the field has witnessed an exciting surge of reports of various metal-catalyzed CHF chemistry for postassembly modification of peptides and proteins.This review chronicles present advances in this research area up to June 2020.The content is organized based on the location of CHF on peptides:amino acid side chains(aromatic and nonaromatic),backbone,and appendant groups on peptide terminus.In addition to the reaction mechanisms of the metal-catalyzed CHF chemistry used in these peptide modification protocols,brief comments on the corresponding nonmetal-mediated strategies are included to provide readers a broad view of the current status of CHF-enabled peptide modification.

Transition Metal Catalyzed Enantioselective Borylative Cyclization Reactions

Due to the significance of corresponding products,enantioselective borylative cyclization reactions have been studied intensively in recent years.Many groups have developed efficient methods to transform unsaturated system into asymmetric cyclic organoboron compounds with the ring-size range from three-membered to six-membered in general.Notably,in some cases,fused rings which contain more than two contiguous chiral centers could be obtained by this kind of strategies.This review summarized and reviewed the recent advances in this field and classified these work according to the species of metal catalysts.

Transition metal-catalyzed conversion of aldehydes to ketones

Ketones are one of the most important classes of organic compounds, and widely present in various pharmacological compounds, biologically active molecules and functional materials. Over the past few decades, transition metal-catalyzed conversion of aldehydes has been found to be a powerful method.With the continuous development in recent years, it has become an efficient and uncomplicated strategy for constructing ketones. There are four major mechanisms for transition metal-catalyzed ketone synthesis from aldehyde:(1) carbonyl-Heck reaction, that is 1,2-insertion of organometal species to aldehydic C=O double bond,(2) direct insertion of transition metal catalysts to aldehydic C-H bond,(3) aldehyde as acyl radical,(4) aldehyde as carbon radical acceptor. This article summarizes related reports on the transformations of aldehydes to generate corresponding ketones under different reaction conditions.