Tuning the Catalytic Activity of a Pincer Complex of Rhodium(I) by Supramolecular and Redox Stimuli

We report the rhodium(I) complex [Rh(CNC−NDI)(CO)]⁺, in which CNC−NDI refers to a pincer-CNC ligand decorated with a naphthalenediimide moiety. Due to the presence of the planar CNC ligand and the naphthalenediimide moiety, the electronic nature of the complex can be modulated by means of supramolecular and redox stimuli, respectively. The metal complex shows a strong π–π-stacking interaction with coronene. This interaction has an impact on the electron-richness of the metal, as demonstrated by the shifting of the ν(CO) stretching band to a lower frequency. The addition of tetrabutylammonium fluoride facilitates the sequential one- and two-electron reduction of the NDI moiety of the ligand, thus resulting in a situation in which the ligand can increase its electron-donor strength in two levels. The nature of the interaction with the fluoride anion was studied computationally. The catalytic activity of the [Rh(CNC−NDI)(CO)]⁺ complex was tested in the cycloisomerization of alkynoic acids, where it is observed that the activity of the catalyst can be modulated between four levels of activity, which correspond to i) the use of the unmodified catalyst, ii) catalyst+coronene, iii) catalyst+2 equivalents of fluoride, and iv) catalyst+5 equivalents of fluoride.     

Supramolecular Control of the Oxidative Addition as a Way To Improve the Catalytic Efficiency of Pincer-Rhodium (I) Complexes

¹H NMR studies using a cationic complex with a pyridine-di-imidazolylidene pincer ligand of formula [Rh(CNC)(CO)]⁺ revealed that this compound showed high binding affinity with coronene in CH₂Cl₂. The interaction between coronene and the planar Rh^I complex is established by means of π-stacking interactions. This interaction has a strong impact on the electron-donating strength of the pincer CNC ligand, which is increased significantly, as demonstrated by the shifting of the ν(CO) stretching bands to lower frequencies. The addition of coronene increases the reaction rate of the nucleophilic attack of methyl iodide on the rhodium (I) pincer complex, and also has a positive effect on the performance of the complex as a catalyst in the cycloisomerization of 4-pentynoic acid. These findings highlight the importance of supramolecular interactions for tuning the reactivity and catalytic activity of square-planar metal complexes.     

Water-Soluble Ligands,Metal Complexes,and Catalysts: Synergism of Homogeneous and Heterogeneous Catalysis

Rapid developments in the field of catalysis are leading to an increased demand for tailor-made catalysts. Water-soluble complex catalysts, which are being intensively investigated at the present time, combine the advantages of homogeneous and heterogeneous catalysis: simple and complete separation of the product from the catalyst, high activity, and high selectivity. From the large number of available water-soluble ligands, the appropriate catalysts can be developed for many reactions. The industrial applications in the fields of hydrogenation and hydroformylation have already indicated the wide scope of this type of catalyst. In addition, the annual production of 300 000 tons of butyraldehyde through application of water-soluble rhodium complexes at Hoechst AG in Oberhausen, Germany, has demonstrated the industrial importance of the concept of complex-catalyzed reactions in aqueous two-phase systems. The efficient operation of catalytic processes increasingly requires the loss-free recycling of the noble metal catalyst, and this can be simply and economically realized in two-phase systems. Special applications in biochemical problems open up developments in the field of water-soluble transition metal complexes that far transcend the familiar kinds of homogeneous catalysis. In the near future, the investigation and application of metal complex catalysts that are compatible with the physiological, cheap, and environmentally friendly solvent, water, is likely to become a high priority in catalysis research.     

Highly Efficient Self-Assembly of Metallacages and Their Supramolecular Catalysis Behaviors in Microdroplets

Developing a new strategy to improve the self-assembly efficiency of functional assemblies in a confined space and construct hybrid functional materials is a significant and fascinating endeavor. Herein, we present a highly efficient strategy for achieving the supramolecular self-assembly of well-defined metallacages in microdroplets through continuous-flow microfluidic devices. The high efficiency and versatility of this approach are demonstrated by the generation of five representative metallacages in different solvents containing water, DMF, acetonitrile, and methanol in a few minutes with nearly quantitative yields, in contrast to the yields obtained with the hour-scale reaction time in a batch reactor. A ring-opening catalytic reaction of the metallacages was selected as a model reaction for exploring supramolecular catalysis in microdroplets, whereby the catalytic yield was enhanced by 2.22-fold compared to that of the same reaction in the batch reactor. This work illustrates a new promising approach for the self-assembly of supramolecular systems.     

Chemoenzymatic Cascades Combining Biocatalysis and Transition Metal Catalysis for Asymmetric Synthesis

The combination of catalytic methods provides multiple advantages in organic synthesis, allowing access to diverse organic molecules in a straightforward manner. Merging metal and enzyme catalysis is currently receiving great attention due to the possibility to assemble metal catalysis in C−C coupling, olefin metathesis, hydration and other reactions with the exquisite stereospecificity displayed by enzymes. Thus, this minireview is organized based on the action of the metal species (Pd, Ru, Au, Ir, Fe…) in combination with different enzymes. Special attention will be paid to the design of sequential processes and concurrent cascades, presenting solutions such as the use of surfactants or compartmentalization strategies for those cases where incompatibilities could hamper the overall process.     

Nickel: An Element with Wide Application in Industrial Homogeneous Catalysis

The efficiency and future development of the chemical industry are closely linked to catalysis. It has been estimated, for example, that 60 to 70% of all industrial chemicals have involved the use of a catalyst at some point during their manufacture. In the past two decades the share of the market credited to homogeneous transition metal catalysis increasead to 10–15%. Besides cobalt, which is used mainly in hydroformylation reactions, nickel is the most frequently used metal. Many carbon–carbon bond formation reactions can be carried out with high selectivity if catalyzed by organonickel complexes. Such reactions include, inter alia, carbonylation reactions, cyclic and linear oligomerization and polymerization reactions of monoenes and dienes, and hydrocyanation reactions. It was Reppe and Wilke who pioneered and shaped the field of homogeneous nickel catalysis. Great impetus was also given to the development of organonickel chemistry by Wilke and his students. Research in this area has contributed immensely towards an understanding of the reactions involved in catalysis.—This review is primarily concerned with nickel-catalyzed reactions which are of interest both preparatively and industrially; some mechanistic aspects are also dealt with.     

过渡金属碳化物的研究进展

过渡金属碳化物作为一种催化新材料显示了其独特的性能,在石油馏份的HDS、HDN、加氢和脱氢反应、烃的异构化和芳构化、甲烷转化、F-T合成和电催化等反应中都表现出了优良的催化性能.本文综述了国内外关于钼、钨碳化物的制备方法以及在上述反应中的应用研究进展。     

Caught in Action: Visualizing Dynamic Nanostructures Within Supramolecular Systems Chemistry

Supramolecular systems chemistry has been an area of active research to develop nanomaterials with life-like functions. Progress in systems chemistry relies on our ability to probe the nanostructure formation in solution. Often visualizing the dynamics of nanostructures which transform over time is a formidable challenge. This necessitates a paradigm shift from dry sample imaging towards solution-based techniques. We review the application of state-of-the-art techniques for real-time, in situ visualization of dynamic self-assembly processes. We present how solution-based techniques namely optical super-resolution microscopy, solution-state atomic force microscopy, liquid-phase transmission electron microscopy, molecular dynamics simulations and other emerging techniques are revolutionizing our understanding of active and adaptive nanomaterials with life-like functions. This Review provides the visualization toolbox and futuristic vision to tap the potential of dynamic nanomaterials.     

Transition Metal Thiometalates: Properties and Significance in Complex and Bioinorganic Chemistry

In their highest oxidation states the early transition metals V, Nb, Ta, Mo, W, and Re form tetrahedral, strongly colored thioanions endowed with some remarkable properties. Thiometalates can be formed by solid-state reactions or in solution from the oxometalates. Poly-thiometalates with mixed valences can be produced by new types of intramolecular condensation-redox reactions from thioanions. The metal-sulfur bonds can react either nucleophilically or electrophilically, and in the case of the Mo–S bonds this is of biochemical interest. It is important to mention the applications of thiometalates as ligands in complex chemistry (generation of multi-metal complexes, versatile coordination behavior, unique electronic properties of the ligands), in which thiometalato complexes with a variety of electron populations can exist because of the marked electron delocalization. Apart from this, MoS has a significance in bioinorganic problems, e.g. the nitrogenase problem and Cu? Mo antagonism.     

Chirality in Transition Metal Chemistry.Molecules,Supramolecular Assemblies and Materials. By Hani Amouri and Michel Gruselle.

John Wiley & Sons, Hoboken 2008. 260 pp., softcover € 47.90.—ISBN 978‐0470060544

     

Single-Site Carbon-Supported Metal-Oxo Complexes in Heterogeneous Catalysis: Structure,Reactivity, and Mechanism

When early transition metal complexes are molecularly grafted onto catalyst supports, well-defined, surface-bound species are created, which are highly active and selective single-site heterogeneous catalysts (SSHCs) for diverse chemical transformations. In this minireview, we analyze and summarize a less conventional type of SSHC in which molybdenum dioxo species are grafted onto unusual carbon-unsaturated scaffolds, such as activated carbon, reduced graphene oxide, and carbon nanohorns. The choice of earth-abundant, low-toxicity, versatile metal constituents, and various carbon supports illustrates “catalyst by design” principles and yields insights into new catalytic systems of both academic and technological interest. Here, we summarize experimental and computational investigations of the bonding, electronic structure, reaction scope, and mechanistic pathways of these unusual catalysts.     

Merging Manganese and Iminium Catalysis: Selective Hydroalkenylation of Unsaturated Aldehydes and Ketones

The use of synergistic catalytic strategy can usually circumvent the intrinsic limitations of one catalytic system. In this communication, we disclose a cooperative catalysis strategy of manganese and iminium catalysis to realize selective hydroalkenylation of unsaturated aldehydes and ketones. Its success stems from the LUMO activation of unsaturated carbonyl compounds with secondary amines as the organocatalyst and the synergistic HOMO activation of alkenylboronic acids with Mn₂(CO)₈Br₂. This protocol exhibits several synthetic advances, e.g., simple operation, good functional group compatibility and good regioselectivity. The theoretical calculation indicates the migratory insertion followed by demetallation-isomerization process is kinetically more favorable than Michael-like nucleophilic addition. The use of proline-derived organocatalyst can deliver the desired products in moderate enantioselectivity.     

Transition Metal Catalysis in the Baeyer–Villiger Oxidation of Ketones

Environmentally friendly oxidizing agents such as hydrogen peroxide or dioxygen can be used today in catalytic versions of the almost one century old Baeyer–Villiger oxidation with transition metal complexes as catalysts. On the right is a sketch of a possible mechanism for this reaction with a platinum catalyst in homogeneous solution.     

Integrating Computation,Experiment, and Machine Learning in the Design of Peptide-Based Supramolecular Materials and Systems

Interest in peptide-based supramolecular materials has grown extensively since the 1980s and the application of computational methods has paralleled this. These methods contribute to the understanding of experimental observations based on interactions and inform the design of new supramolecular systems. They are also used to virtually screen and navigate these very large design spaces. Increasingly, the use of artificial intelligence is employed to screen far more candidates than traditional methods. Based on a brief history of computational and experimentally integrated investigations of peptide structures, we explore recent impactful examples of computationally driven investigation into peptide self-assembly, focusing on recent advances in methodology development. It is clear that the integration between experiment and computation to understand and design new systems is becoming near seamless in this growing field.     

含铜过渡金属水滑石类化合物对苯酚过氧化氢羟化的催化作用

合成了一系列二元、三元过渡金属水滑石类化合物, 并经XRD、IR进行了表征.苯酚过氧化氢羟化结果表明, 含铜水滑石类化合物对该反应有较高的催化活性, 并初步提出了反应机理.     

Supramolecular Memristor Based on Bistable [2]Catenanes: Toward High-Density and Non-Volatile Memory Devices

The ever-increasing demand for data storage and neuromorphic computing calls for innovative, high-density solutions, such as resistive random-access memory (RRAM). However, the integration of resistive switching and rectification at the nanoscale remains a formidable challenge. In this study, we introduce a bistable [2]catenane-based supramolecular junction that simultaneously functions as a resistive switch and a diode. All supramolecular junctions are highly stable and reproducible over thousands of resistive switching cycles, because the nano-confinement of two mechanically interlocked rings can stabilize the radical states of pyridinium moieties under ambient conditions. The successful realization of supramolecular junctions in functionality with a thickness of approximately 2 nm presents a promising avenue for the development of molecule-scale based RRAM for a better solution to high density and energy efficiency.