Transition Metal Catalysis Research Articles

Recent Advances in C-O Bond Cleavage of Aryl, Vinyl, and Benzylic Ethers.

Transition metal-catalyzed cross-coupling with aryl halides has revolutionized the way of diversifying aromatic compounds. Aryl ethers are attractive alternatives to aromatic halides as coupling partners considering the accessibility and potential environmental benefits. The last two decades have witnessed a striking success in the field of C-O bond activation of aryl ethers, including the construction of C-C bond and C-X bond, as well as reductive deoxygenation. Here, we present a comprehensive review of C-O bond activation in the context of aryl, vinyl, and benzylic ethers. This review elaborates on the current state-of-the-art methods, categorized by different catalytic systems, including transition metal catalysis, photoredox catalysis, and other innovative approaches. The newly developed methods allow C-O bond activation under mild conditions with exceptional functional group tolerance, potentially enabling the late-stage functionalization of pharmaceuticals. The limitations and future perspectives of the methods are also presented.

Synthesis and redox catalysis of Carbodiphosphorane ligated stannylene.

Heavier group 14 carbene analogues, exhibiting transition-metal-like behavior, display remarkable capability for small molecule activation and coordination chemistry. However, their application in redox catalysis remains elusive. In this paper, we report the synthesis and isolation of a stannylene with carbodiphosphorane ligand. The nucleophilic reactivity at the divalent tin center is elucidated by computational and reactivity studies. Moreover, this stannylene exhibits catalytic activity in the hydrodefluorination reaction of fluoroarenes. Mechanistic investigations into the elementary steps confirm a SnII/SnIV redox cycle involving C-F oxidative addition, F/H ligand metathesis, and C-H reductive elimination. This low-valent SnII catalytic system resembles the classical transition metal catalysis. Notably, this represents metallomimetic redox catalysis utilizing carbene analogue with heavier group 14 element as a catalyst.

Natural Chiral Ligand Strategy: Metal-Catalyzed Reactions with Ligands Prepared from Amino Acids and Peptides

Amino acids and peptides are readily available biomolecules and can function as chiral ligands for transition metal catalysis. An example is the copper complex catalyzed 1,4-addition of dialkylzinc to acyclic enones, which employs peptide ligands. This review provides a dataset of amino acids and peptides reported in the literature proving to be effective ligands for metal-centered catalysts. Several parameters were highlighted, including amino acid combination, metal atoms, carboxyl and amino protecting groups, modification of natural amino acids, and the mechanism of catalysis. Along with analyzing physical-chemical properties, the SMILES representation for each amino acid and/or peptide was generated and made available online, providing an easy-to-use means of training machine learning models. This review offers an opportunity for the development of more efficient peptide ligands for enantioselective metal-centered catalysts. The available online dataset is a reliable manually curated table, it enables the benchmark for comparison of new terminal functional groups. Moreover, the review provides insight into the structures of the more successful peptide ligands and can be used as the foundation for the development of the next generation of peptide-based chiral ligands.

Activation of Alkenes via Chalcogen Bond: Chalcogen⋅⋅⋅π Bond Catalyzed the Diels‐Alder Reaction of 2‐Vinylindoles

AbstractChalcogen bond catalysis is a promising catalytic strategy, characterized by its environmental friendliness, relatively inexpensive cost, and similar reactivity to transition metal catalysis. Experimental results suggest that the S⋅⋅⋅π and Se⋅⋅⋅π bonds can efficiently drive the vinyl‐indole‐based Diels‐Alder reaction (Angew. Chem. Int. Ed. 2021, 60, 9395–9400). In this work, chalcogen bond catalysis in the Diels‐Alder reaction between 2‐vinylindoles is investigated based on density functional theory. For this reaction, the Te⋅⋅⋅π bond catalysis is as an alternative catalytic strategy. The Diels‐Alder reaction catalyzed by chalcogen bond is stepwise and involves two steps: the carbon–carbon bond formation process and the cyclization process. The cyclization process is the rate‐determining step. From the perspective of energy decomposition analysis, the electrostatic interaction is the main factor to cause Se⋅⋅⋅π bond catalysis, the polarization interaction is the main factor to cause Te⋅⋅⋅π bond catalysis. Additionally, this catalytic reaction involves the endo pathway and exo pathway. The Gibbs free energy barrier values of the endo pathway are lower than those of the exo pathway, which facilitates the formation of the endo product. This study will provide a valuable perspective on the application of chalcogen bond in the activation of alkenes.

Overcoming the Limitations of Transition-Metal Catalysis in the Chemoenzymatic Dynamic Kinetic Resolution (DKR) of Atropisomeric Bisnaphthols

Overcoming the Limitations of Transition-Metal Catalysis in the Chemoenzymatic Dynamic Kinetic Resolution (DKR) of Atropisomeric Bisnaphthols

Selective Hydroboration of C-C Single Bonds without Transition-Metal Catalysis.

Selective hydroboration of C-C single bonds presents a fundamental challenge in the chemical industry. Previously, only catalytic systems utilizing precious metals Ir and Rh, in conjunction with N- and P- ligands, could achieve this, ensuring bond cleavage and selectivity. In sharp contrast, we discovered an unprecedented and general transition-metal-free system for the hydroboration of C-C single bonds. This methodology is transition-metal and ligand-free and surpasses the transition-metal systems regarding chemo- and regioselectivities, substrate versatility, or yields. In addition, our system tolerates various functional groups such as Ar-X (X=halides), heterocyclic rings, ketones, esters, amides, nitro, nitriles, and C=C double bonds, which are typically susceptible to hydroboration in the presence of transition metals. As a result, a diverse range of γ-boronated amines with varied structures and functions has been readily obtained. Experimental mechanistic studies, density functional theory (DFT), and intrinsic bond orbital (IBO) calculations unveiled a hydroborane-promoted C-C bond cleavage and hydride-shift reaction pathway. The carbonyl group of the amide suppresses dehydrogenation between the free N-H and hydroborane. The lone pair on the nitrogen of the amide facilitates the cleavage of C-C bonds in cyclopropanes.

Hybrid Metal Catalysts as Valuable Tools in Organic Synthesis: An Overview of the Recent Advances in Asymmetric C─C Bond Formation Reactions.

Carbon-carbon bond formation represents a key reaction in organic synthesis, resulting in paramount importance for constructing the carbon backbone of organic molecules. However, traditional metal-based catalysis, despite its advantages, often struggles with issues related to efficiency, selectivity, and sustainability. On the other hand, while biocatalysis offers superior selectivity due to an extraordinary recognition process of the substrate, the scope of its applicable reactions remains somewhat limited. In this context, Artificial Metalloenzymes (ArMs) and Metallo Peptides (MPs) offer a promising and not fully explored solution, merging the two fields of transition metal catalysis and biotransformations, by inserting a catalytically active metal cofactor into a customizable protein scaffold or coordinating the metal ion directly to a short and tunable amino acid (Aa) sequence, respectively. As a result, these hybrid catalysts have gained attention as valuable tools for challenging catalytic transformations, providing systems with new-to-nature properties in organic synthesis. This review offers an overview of recent advances in the development of ArMs and MPs, focusing on their application in the asymmetric carbon-carbon bond-forming reactions, such as carbene insertion, Michael additions, Friedel-Crafts and cross-coupling reactions, and cyclopropanation, underscoring the versatility of these systems in synthesizing biologically relevant compounds.

Recent Developments in Copper-Catalyzed Annulations for Synthesis of Spirooxindoles.

Spirooxindoles represent a special scaffold for pharmaceuticals and natural products, and significant advancements have been achieved in their synthesis in recent years. Among these, transition metal catalysis, particularly copper catalysis, has emerged as an efficient and reliable method for the synthesis of spirooxindoles. Based on different reaction types, two distinct substrate types have been summarized and classified by us for constructing spirooxindole scaffolds via intramolecular and intermolecular annulations. This review outlines the latest advancements in copper-catalyzed cyclization reactions for synthesizing spirooxindoles and provides detailed insights into the types of annulation reactions and their possible reaction mechanisms.

Transition Metal-Catalyzed C-H Activation/Functionalization of 8-Methylquinolines.

8-Methylquinoline is regarded as an ideal substrate to participate in diversely C(sp3)-H functionalization reactions. The presence of the chelating nitrogen atom enables 8-methylquinoline to easily form cyclometallated complexes with various transition metals, leading to the selective synthesis of functionalized quinolines. Considering the great importance of quinoline cores in medicinal chemistry, in this review article, we have covered the publications related to the C-H activation and functionalization of 8-methylquinoline under transition metal catalysis during the last decade.

In Situ Generation of Quinoliziniums for Dual Visible Light‐Induced Gold(III)‐Catalyzed Alkynylation and Peptide Modification

AbstractA new approach of dual visible light‐induced gold(III)‐catalyzed alkynylation and its application in selective modification of alkyne‐linked peptides has been developed. The bis‐cyclometalated gold(III) complex exhibited dual roles of (1) in situ generation of quinolizinium‐based photosensitizer (λem=500 – 594 nm) and (2) alkynylation of iminium ions. Under optimized conditions, alkynylated products were afforded in good yields up to 73 %. The application of this strategy in selective modification of alkyne‐linked peptides gave modified peptides in up to 67 % conversion. Our dual visible light/gold(III) catalysis exemplifies the potential of merging photocatalysis and transition metal catalysis to develop novel bioconjugation.

Pd-, Cu-, and Ni-Catalyzed Reactions: A Comprehensive Review of the Efficient Approaches towards the Synthesis of Antibacterial Molecules.

A strong synthetic tool for many naturally occurring chemicals, polymers, and pharmaceutical substances is transition metal-catalyzed synthesis. A serious concern to human health is the emergence of bacterial resistance to a broad spectrum of antibacterial medications. The synthesis of chemical molecules that are potential antibacterial candidates is underway. The main contributions to medicine are found to be effective in transition metal catalysis and heterocyclic chemistry. This review underlines the use of heterocycles and certain effective transition metals (Pd, Cu, and Ni) as catalysts in chemical methods for the synthesis of antibacterial compounds. Pharmaceutical chemists might opt for clinical exploration of these techniques due to their potential.

Synthesis of Biheteroaryls by Pd-Catalyzed Homocoupling of Heteroaryl Bromides.

Symmetrical biheteroaryl compounds, such as bypyridines and bipyrazoles, are important ligands in transition-metal catalysis. They also serve as synthetic precursors of photo catalysts/sensitizers, bioactive agents, and energetic materials. To facilitate the concise synthesis of these useful structures, an efficient Pd-catalyzed homocoupling of heteroaryl bromides has been successfully established using the electron-rich and sterically hindered monophosphorus ligand BIDIME. The coupling protocol features a tandem Miyaura borylation/Suzuki coupling sequence and exhibits unprecedented tolerance of a wide range of heteroaryl bromides, providing a series of symmetrical biheteroaryls in moderate to good yields. Notably, the use of the corresponding polymeric ligand, PolyBIDIME, enabled the recycling of a palladium catalyst, demonstrating the potential of the homocoupling in practical applications.

At the Speed of Light: Recent Advances on Photocatalyzed Generation and Applications of Iminyl Radicals Promoted by Visible-light

: Nitrogen-positioned radicals are chemical entities that have a lengthier history than carbon ones and their high reactivity makes them invaluable. But, despite its power, much of its chemistry is still uncharted. Currently, developed methodologies to access nitrogen-positioned radicals, such as transition metal catalysis or visible-light photoredox methods through a single-electron transfer process, avoiding the use of harmful or toxic reagents, excess raw materials, solvents as well as pre-functionalization steps or extensive synthetic routes are in continuous progress. This revision aims to depict the recent advances in the field of iminyl-radicals’ syntheses, a special class of radicals placed on nitrogen, catalyzed by transition metals or photoredox techniques for the construction of C-N bonds and their synthetic applications. This work serves as a comprehensive guide for the scope of synthetic applications that this kind of radicals could have.

Advances in Transition-Metal Catalysis and Organocatalysis Approaches towards Asymmetric Synthesis of β-Amino Acid Derivatives

AbstractThe stereoselective synthesis of β-amino acids has attracted major attention among the synthetic community in recent years. This review provides an overview of the important advances in chiral β-amino acid synthesis over the past decade. It covers the development of enantioselective methods using transition-metal complexes or organocatalysts, mainly including catalytic asymmetric hydrogenation, the Mannich reaction, multicomponent reactions of diazo compounds, and conjugate addition. Additionally, the asymmetric synthesis of optically active β-amino acids by other approaches are also summarized.1 Introduction2 Strategies towards the Asymmetric Synthesis of β-Amino Acids2.1 Hydrogenation2.2 Mannich Reaction2.3 Conjugate Addition2.4 Multicomponent Reactions2.5 Miscellaneous2.5.1 Synthesis of β-Amino Acids from Chiral Amines2.5.2 Synthesis of β-Amino Acids from Isoxazolidinones2.5.3 Synthesis of β-Amino Acids by Other Methodologies3 Summary and Outlook

Photoinduced Nickel-Catalyzed Homolytic C(sp3)-N Bond Activation of Isonitriles for Selective Carbo- and Hydro-Cyanation of Alkynes.

The exploration of strong chemical bonds as synthetic handles offers new disconnection strategies for the synthesis of functionalized molecules via transition metal catalysis. However, the slow oxidative addition rate of these covalent bonds to a transition metal center hampers their synthetic utility. Here, we report a C(sp3)-N bond activation strategy that bypasses thermodynamically challenging 2e- or 1e- oxidative addition via a distinct pathway in nickel catalysis. This strategy leverages a previously unknown activation pathway of photoinduced inner-sphere charge transfer of low-valent nickel(isonitriles), triggering a C(sp3)-N bond cleavage distal to the metal-ligand interaction to deliver nickel(cyanide) and versatile alkyl radicals. Utilizing this catalytic strategy, the selective intermolecular 1,2-carbocyanation reaction of alkynes with alkyl isonitriles as both alkylating and cyanating agents can be achieved, delivering a wide array of trisubstituted alkenyl nitriles with excellent atom-economy, regio-, and stereoselectivity under mild conditions. Furthermore, Markovnikov-selective hydrocyanation of aliphatic alkynes can be accomplished through the synergistic action of a photocatalyst utilizing isonitriles as the cyanation agents. Mechanistic investigations support the photogeneration of low-valent Ni(isonitrile) complexes that undergo photochemical homolysis of the C(sp3)-N bond to engage catalytic cyanation with alkynes.

1,5-Diaza-3,7-diphosphacyclooctanes (P2N2): An Underappreciated Ligand Class for Nickel- and Palladium-Catalyzed Heck-Type Cross-Couplings

Abstract1,5-Diaza-3,7-diphosphacyclooctane (P2N2) scaffolds represent a readily accessible, tunable ligand class for transition metals. However, despite their prevalence in areas such as electrocatalysis and coordination chemistry, P2N2 ligands have been rarely used to make catalysts for organic synthesis. Research into Mizoroki–Heck-type aldehyde, alcohol, and alkene arylation reactions has revealed that the P2N2 family outperforms many commonly used phosphines. This Synpacts article summarizes our work and provides a broad overview on the preparation and application of P2N2 ligands in organic synthesis. It also serves to highlight how a simple, modular class of ligands can solve contemporary challenges with transition-metal catalysis, including novel reactivity and exceptional regioselectivity.

Merging Organocatalysis with 1,2-Boronate Rearrangement: A Lewis Base-Catalyzed Asymmetric Multicomponent Reaction.

Catalytic asymmetric multicomponent 1,2-boronate rearrangements provide a practical approach for synthesizing highly valuable enantioenriched boronic esters. When applied to alkenyl or heteroaryl boronates, these reactions have relied mainly on transition-metal catalysis. Herein, we present an organocatalytic, Lewis base-catalyzed asymmetric multicomponent 1,2-boronate rearrangement, involving indoles, boronic esters, and Morita-Baylis-Hillman carbonates, leading to enantioenriched, highly substituted indole and indoline derivatives. Using cinchona alkaloid-based catalysts, high selectivity has been achieved, enabling expansion of the chemical space around pharmaceutically relevant indole and indoline derivatives.

Atomic decoration of MoS2 using Fe, Co or Ni for highly efficient and selective hydrodesulfurization

Hydrodesulfurization (HDS) is one of the most efficient processes for removing sulfur-containing molecules such as dibenzothiophene (DBT) from oil, whatever fossil based or bio-based. However, hydrodesulfurization using molybdenum sulfides (MoS2) as catalytic active centers and transition metals (X) as promoters is seriously challenged by the insufficient catalytic activity and selectivity because of the separate phases of sulfides, and sparse X-Mo-S active sites, leading to poor synergistic effect between the X promoter and MoS2 active centers. Herein, atomically doped MoS2 catalysts (denoted as XMo, X = Fe, Co or Ni) were synthesized by using polyoxometalate template-based synthetic strategy were proposed. The pre-organized Anderson-type POMs, [XMo6O24H6]n− (X = Fe, Co or Ni), acted as a pre-assembled molecular platform with intimate X-Mo interactions, ensure the uniform formation of X-Mo-S active sites after sulfuration. The promoter atoms, including Fe, Co and Ni, enhanced the efficiency of hydrodesulfurization of MoS2. Particularly, NiMo exhibits the highest HDS activity, while CoMo shows a moderate HDS activity with the highest DDS selectivity (∼85 %). Despite the lowest HDS activities, FeMo with the cheapest Fe promoter, shows good DDS selectivity (∼70 %). Further study reveal NiMo has the most laminated morphology and highest stacking slabs, resulting in the highest HDS activity. Benefiting from the Co(Fe)-Mo-S structure and abundant sulfur vacancy, CoMo and FeMo showed great enhancement in the DDS selectivity. Moreover, the DDS selectivity of these designed catalysts were supported energetically by first principle calculations. This research will expand on the ability to improve the HDS activities and DDS selectivity by precisely engineering catalytic active sites to achieve significant synergistic effect in atomic scale.

IPr# Complexes-Highly-Hindered, Sterically-Bulky Cu(I) and Ag(I) N-Heterocyclic Carbenes: Synthesis, Characterization, and Reactivity.

Metal-N-heterocyclic carbene (M-NHC) complexes are well-known as an important class of organometallic compounds widely used in transition-metal catalysis. Taking into account that the steric hindrance around the metal center is one of the major effects in M-NHC catalysis, the development of new, sterically hindered M-NHC complexes is an ongoing interest in this field of research. Herein, we report the synthesis and characterization of exceedingly sterically hindered, well-defined, air- and moisture-stable Cu(I) and Ag(I) complexes, [Cu(NHC)Cl] and [Ag(NHC)Cl], in the recently discovered IPr# family of ligands that hinge upon modular peralkylation of anilines. The complexes in both the BIAN and IPr families of ligands are reported. X-ray crystallographic analyses and computational studies were conducted to determine steric effects, Frontier molecular orbitals, and bond orders. The complexes were evaluated in the model hydroboration of the alkynes. We identified [Cu(BIAN-IPr#)Cl] and [Ag(BIAN-IPr#)Cl] as highly reactive catalysts with the reactivity outperforming the classical IPr and IPr*. Considering the attractive features of well-defined Cu(I)-NHC and Ag(I)-NHC complexes, this class of sterically bulky yet wingtip-flexible complexes will be of interest for catalytic processes in various areas of organic synthesis and catalysis.

Experimentally Assessing the Electronic Structure and Spin-State Energetics in MnFe Dimers Using 1s3p Resonant Inelastic X-ray Scattering.

The synergistic interaction between Mn and Fe centers is investigated via a comprehensive analysis of full 1s3p resonant inelastic X-ray scattering (RIXS) planes at both the Fe and Mn K-edges in a series of homo- and heterometallic molecular systems. Deconvolution of the experimental two-dimensional 1s3p RIXS maps provides insights into the modulation of metal-ligand covalency and variations in the metal multiplet structure induced by subtle electronic structural differences imposed by the presence of the second metal. These modulations in the electronic structure are key toward understanding the reactivity of biological systems with active sites that require heterometallic centers, including MnFe purple acid phosphatases and MnFe ribonucleotide reductases. Herein, we demonstrate the capabilities of 1s3p RIXS to provide information on the excited state energetics in both element- and spin-selective fashion. The contributing excited states are identified and isolated by their multiplicity and π- and σ-contributions, building a conceptual bridge between the electronic structures of metal centers and their reactivity. The ability of the presented 1s3p RIXS methodology to address fundamental questions in transition metal catalysis reactivity is highlighted.