Carbene Radicals in Transition-Metal-Catalyzed Reactions

ACS Catalysis, Journal Year: 2023, Volume and Issue: 13(8), P. 5428 - 5448

Published: April 6, 2023

Discovered as organometallic curiosities in the 1970s, carbene radicals have become a staple modern-day homogeneous catalysis. Carbene exhibit nucleophilic radical-type reactivity orthogonal to classical electrophilic diamagnetic Fischer carbenes. Their successful catalytic application has led synthesis of myriad carbo- and heterocycles, ranging from simple cyclopropanes more challenging eight-membered rings. The field matured employ densely functionalized chiral porphyrin-based platforms that high enantio-, regio-, stereoselectivity. Thus far focus largely been on cobalt-based systems, but interest growing for past few years expand other transition metals. This Perspective covers advances made since 2011 gives an overview coordination chemistry, reactivity, radical species using metal complexes catalysts.

Language: Английский

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Synthesis and Characterization of Donor–Acceptor Iron Porphyrin Carbenes and Their Reactivities in N–H Insertion and Related Three-Component Reaction

Journal of the American Chemical Society, Journal Year: 2023, Volume and Issue: 145(9), P. 4934 - 4939

Published: Feb. 22, 2023

Iron porphyrin carbenes (IPCs) have been extensively recognized as the reactive intermediates in various iron porphyrin-catalyzed carbene transfer reactions. While donor–acceptor diazo compounds frequently used for such transformations, structures and reactivities of IPCs are less explored. To date, no crystal IPC complexes reported, therefore, involvement intermediacy transformations lacks direct evidence. Here we report synthesis NMR characterization several from corresponding compounds. The X-ray structure an complex derived a morpholine-substituted amide was obtained. those were tested by N–H insertion reactions with aniline or morpholine well three-component reaction γ,δ-unsaturated α-keto ester based on electrophilic trapping ammonium ylide intermediate. Based these results, identified real

Language: Английский

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Overview of Transition Metal Catalyzed Multicomponent Reactions Based on Trapping of Allylic Electrophiles

ChemCatChem, Journal Year: 2024, Volume and Issue: 16(4)

Published: Jan. 11, 2024

Abstract Multicomponent reactions provide an excellent approach toward quaternary carbon centres utilizing convergent chemical in a highly selective manner under one‐pot conditions. The reactivity of substrates and metal catalysts is carefully controlled, precluding the formation side‐products. In this context, transition catalyzed onium ylides generated via diazo precursors nucleophiles with third component (an electrophile) have garnered significant attention. Using allylic precursor as electrophilic partner provides opportunities to construct all‐carbon centres. Furthermore, presence allyl fragment multicomponent product serves pivotal handle for carrying out subsequent modifications. Several recent studies employed Rh, Pd, dual Rh/Pd catalytic systems involving alkylation that proceed synergistic or relay pathway. Although not significantly successful, few cases, asymmetric induction achieved through chiral phosphoric acids phosphine ligands. Limited substrate catalyst scope underlying mechanistic complexities posed formidable challenges, slowing advancement reactions. This review details using readily available like compounds, carbonates, (R‐OH, R‐NH 2 , etc .) forming complex organic compounds. Our primary objective discuss issues may facilitate progress field.

Language: Английский

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Mechanism and stereoselectivity in metal and enzyme catalyzed carbene insertion into X–H and C(sp²)–H bonds

Chemical Society Reviews, Journal Year: 2024, Volume and Issue: 53(22), P. 11004 - 11044

Published: Jan. 1, 2024

This review provides a mechanistic overview of asymmetric Fe, Cu, Pd, Rh, Au and heme-based enzymes catalyzed carbene insertion reactions to construct C–X (X = O, N, S, etc. ) C–C bonds, focusing on the stereochemical models.

Language: Английский

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Metal-Associated Enols as Key Intermediates in Controlling Enantioselectivity in Carbene Insertion Reactions

Synlett, Journal Year: 2025, Volume and Issue: unknown

Published: March 11, 2025

Abstract Transition-metal-catalysed asymmetric carbene insertion reactions into various X–H bonds typically suffer from poor stereoselectivity. It has been proposed that the presence of metal-free intermediates leads to erosion selectivity. In current account, we discuss our recent efforts understand mechanism and stereochemical model Rh- Fe-catalysed indole phenol. Our detailed DFT calculations show all transformations adopt a common involving an enol intermediate, further tautomerisation which is key stereodetermining step. To account for enantioinduction, propose novel metal-associated species can be solving challenges in reactions. The geometry metal–enol complex interaction between chiral metal prochiral play important roles driving reaction toward particular stereoisomer. 1 Introduction 2 Rh-Catalysed Carbene Insertion Indole 3 Fe-Catalysed C–H Functionalisation 4 O–H 5 Conclusion

Language: Английский

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A combined experimental and computational study reveals a crossover between conventional cross-coupling and carbene insertion pathways in a Pd catalyzed C(sp²)–H insertion

Chemical Science, Journal Year: 2025, Volume and Issue: unknown

Published: Jan. 1, 2025

Computational (DFT and DLPNO-CCSD(T)) calculations along with experimental tools (deuterium labelling, kinetic studies using VTNA, ESI-HRMS UV) are used to probe the mechanism of a Pd(ii)-catalyzed enantioselective carbene insertion into C(sp2)-H indole. Using deuterium labelling studies, we demonstrate intermediacy metal-hydride species, which contrasts mechanistic routes for other transition metals (Rh, Fe, Au, Cu, etc.). Our VTNA study reveals order be one in both diazo indole, microkinetic modelling aligns well computationally predicted mechanism. The is further supported by detection most stable intermediate catalytic cycle ESI-HRMS. An investigation origin stereoselectivity DLPNO-CCSD(T) presents new paradigm, wherein stereocontrol arises during formation Pd itself as opposed proton transfer steps found all metal catalysts.

Language: Английский

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Unveiling the Importance of Catalyst Framework and Non Covalent Interactions in an Asymmetric Fe-Catalyzed O–H Insertion: Insights from Computational Tools

Chemical Communications, Journal Year: 2024, Volume and Issue: 60(75), P. 10322 - 10325

Published: Jan. 1, 2024

Fe-based catalysts as well enzymes typically yield low stereoselectivity for carbene insertion into X-H bonds. Here, we have utilized DFT methods to understand the mechanism and unusually high enantioselectivity in an Fe-spiroBox catalyzed reaction O-H bond of aliphatic alcohols. Our transition state model shows a unique binding intermediates chiral catalyst enabled by weak non covalent interactions that is absent other reactions.

Language: Английский

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Is Enol Always the Culprit? The Curious Case of High Enantioselectivity in a Chiral Rh(II) Complex Catalyzed Carbene Insertion Reaction

Chemistry - A European Journal, Journal Year: 2023, Volume and Issue: 29(66)

Published: Sept. 4, 2023

The mechanism of Rh2 (S-NTTL)4 catalyzed carbene insertion into C(3)-H indole is investigated using DFT methods. Since the commonly accepted enol cannot account for enantioinduction, a concerted oxocarbenium pathway was proposed in an earlier work model catalyst. However, after considering full catalytic system, this study finds that akin to other reactions, here, too, lower energy, which now naturally raises conundrum regarding mode chiral induction. Herein, new water promoted mechanistic involving metal-associated intermediate hydrogen bonding and stereochemical are solve puzzle. It shown how catalyst bowl-shaped structure along with substrate-catalyst binding crucial achieving high levels enantioselectivity. A stereodetermining water-assisted proton transfer confirmed through deuterium-labeling experiments. molecules held together by H-bonding interactions carboxylate ligands reminiscent enzyme catalysis. Although several previous studies have aimed at understanding metal origin stereoinduction especially complexes remains unclear, till date there no transition state can explain enantioselectivity such Rh complexes. currently underrepresented cycles may play role design. adopted metal-catalyzed X-H reactions diazoester, presented results not specific current reaction. Therefore, could provide direction otherwise difficult achieve single

Language: Английский

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Oxidized Bridged Carbenoids as Viable Intermediates in a Fe(III) Catalyzed C−H Insertion Reaction

Chemistry - A European Journal, Journal Year: 2023, Volume and Issue: 29(33)

Published: March 29, 2023

Abstract Fe catalyzed carbene insertion reactions present an efficient route for direct C−H functionalization. The use of Fe(III) in place the widely used Fe(II) presents several benefits. However, mechanistic understanding severely lags behind complexes. One major unsolved issues relates to formation bridged versus terminal metallocarbenes. Even though oxidized carbenoid complexes have been isolated and found be thermodynamically more stable, they are generally considered a dead end catalytic cycle. In current report, subsequent Fe(TPP)Cl C(sp 2 )−H investigated. Using DFT calculations, it is observed that both mono bis can participate Importantly, first time, pathway showing these species not catalysis presented. Their existence other might prevalent than what currently believed. study will important implications utilizing reactions, especially heme containing enzymes which necessarily need carried out under anaerobic/reducing conditions.

Language: Английский

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Investigating the Nature of the Onium Ylide and Michael Acceptor in a Rhodium(I)-Catalyzed Multicomponent Reaction

The Journal of Organic Chemistry, Journal Year: 2023, Volume and Issue: 88(14), P. 10040 - 10047

Published: July 3, 2023

We computationally study the mechanistic pathway for synthetically valuable cascading N-H functionalization followed by C-C bond-forming reaction. The impetus to such multicomponent reactions catalyzed Rh(I) arises from highly fluxional nature of onium ylide involved, which is often not amenable experimental detection. Our results throw light on an interesting paradigm where binding metal plays a crucial role. provides some much-needed insights expand scope these methodologies broader range asymmetric reactions.

Language: Английский

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