Oxidative 1,2-Difunctionalization of Ethylene via Gold-Catalyzed Oxyarylation

Oxidative 1,2-Difunctionalization of Ethylene via Gold-Catalyzed Oxyarylation
Matthew J. Harper†, Edward J. Emmett, John F. Bower , and Christopher A. Russell

School of Chemistry, University of Bristol, Bristol BS8 1TS, United Kingdom
Syngenta, Jealott’s Hill International Research Centre, Bracknell, Berkshire RG42 6EY, United Kingdom

Link:J. Am. Chem. Soc., 2017, 139 (36), pp 12386–12389

DOI: 10.1021/jacs.7b06668
Publication Date (Web): August 22, 2017



Abstract



Under the conditions of oxidative gold catalysis, exposure of ethylene to aryl silanes and alcohols generates products of 1,2-oxyarylation. This provides a rare example of a process that allows catalytic differential 1,2-difunctionalization of this feedstock chemical.

Iron-Catalyzed C−H Bond Activation

Iron-Catalyzed C−H Bond Activation

Shang, R.; Ilies, L.; Nakamura, E.
University of Tokyo

Chem. Rev. ASAP (http://pubs.acs.org/doi/pdf/10.1021/acs.chemrev.6b00772)
DOI: 10.1021/acs.chemrev.6b00772

Abstract:
Catalytic C−H bond activation, which was an elusive subject of chemicalresearch until the 1990s, has now become a standard synthetic method for the formation of new C−C and C−heteroatom bonds. The synthetic potential of C−H activation was first described for ruthenium catalysis and is now widely exploited by the use of various precious metals. Driven by the increasing interest in chemical utilization of ubiquitous metals that are abundant and nontoxic, iron catalysis has become a rapidly growing area of research, and iron-catalyzed C−H activation has been most actively explored in recent years. In this review, we summarize the development of stoichiometric C−H activation, which has a long history, and catalytic C−H functionalization, which emerged about 10 years ago. We focus in this review on reactions that take place via reactive organoiron intermediates, and we excluded those that use iron as a Lewis acid or radical initiator. The contents of this review are categorized by the type of C−H bond cleaved and the type of bond formed thereafter, and it covers the reactions of simple substrates and substrates possessing a directing group that anchors the catalyst to the substrate, providing an overview of iron-mediated and iron-catalyzed C−H activation reported in the literature by October 2016.

TOC:

Remote site-selective C–H activation directed by a catalytic bifunctional template

Department of Chemistry, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, California 92037, USAZhipeng Zhang, Keita Tanaka & Jin-Quan Yu
Nature (2017) doi:10.1038/nature21418

http://www.nature.com/nature/journal/vaop/ncurrent/full/nature21418.html

Abstract

In chemical syntheses, the activation of carbon–hydrogen (C–H) bonds converts them directly into carbon–carbon or carbon–heteroatom bonds without requiring any prior functionalization. C–H activation can thus substantially reduce the number of steps involved in a synthesis. A single specific C–H bond in a substrate can be activated by using a ‘directing’ (usually a functional) group to obtain the desired product selectively1–5. The applicability of such a C–H activation reaction can be severely curtailed by the distance of the C–H bond in question from the directing group, and by the shape of the substrate, but several approaches have been developed to overcome these limitations6–12. In one such approach, an understanding of the distal and geometric relationships between the functional groups and C–H bonds of a substrate has been exploited to achieve meta-selective C–H activation by using a covalently attached, U-shaped template13–17. However, stoichiometric installation of this template has not been feasible in the absence of an appropriate functional group on which to attach it. Here we report the design of a catalytic, bifunctional nitrile template that binds a heterocyclic substrate via a reversible coordination instead of a covalent linkage. The two metal centres coordinated to this template have different roles: one reversibly anchors substrates near the catalyst, and the other cleaves remote C–H bonds. Using this strategy, we demonstrate remote, site-selective C–H olefination of heterocyclic substrates that do not have the necessary functional groups for covalently attaching templates.

Merging Visible Light Photoredox Catalysis with Metal Catalyzed C–H Activations: On the Role of Oxygen and Superoxide Ions as Oxidants

http://pubs.acs.org/doi/abs/10.1021/acs.accounts.6b00275
David C. Fabry† and Magnus Rueping*‡
† Institute of Organic Chemistry, RWTH-Aachen University, Landoltweg 1, 52072 Aachen, Germany
‡ King Abdullah University of Science and Technology (KAUST), KAUST Catalysis Center (KCC), Thuwal, 23955-6900Saudi Arabia
Acc. Chem. Res., 2016, 49 (9), pp 1969–1979
DOI: 10.1021/acs.accounts.6b00275
Publication Date (Web): August 24, 2016


Abstract 

The development of efficient catalytic systems for direct aromatic C–H bond functionalization is a long-desired goal of chemists, because these protocols provide environmental friendly and waste-reducing alternatives to classical methodologies for C–C and C–heteroatom bond formation. A key challenge for these transformations is the reoxidation of the in situ generated metal hydride or low-valent metal complexes of the primary catalytic bond forming cycle. To complete the catalytic cycle and to regenerate the C–H activation catalyst, (super)stoichiometric amounts of Cu(II) or Ag(I) salts have often been applied. Recently, “greener” approaches have been developed by applying molecular oxygen in combination with Cu(II) salts, internal oxidants that are cleaved during the reaction, or solvents or additives enabling the metal hydride reoxidation. All these approaches improved the environmental friendliness but have not overcome the obstacles associated with the overall limited functional group and substrate tolerance. Hence, catalytic processes that do not feature the unfavorable aspects described above and provide products in a streamlined as well as economically and ecologically advantageous manner would be desirable.


In this context, we decided to examine visible light photoredox catalysis as a new alternative to conventionally applied regeneration/oxidation procedures. This Account summarizes our recent advances in this expanding area and will highlight the new concept of merging distinct redox catalytic processes for C–H functionalizations through the application of visible light photoredox catalysis. Photoredox catalysis can be considered as catalytic electron-donating or -accepting processes, making use of visible-light absorbing homogeneous and heterogeneous metal-based catalysts, as well as organic dye sensitizers or polymers. As a consequence, photoredox catalysis is, in principle, an ideal tool for the recycling of any given metal catalyst via a coupled electron transfer (ET) process.


Here we describe our first successful endeavors to address the above challenges by combining visible light photoredox catalysis with different ruthenium, rhodium, or palladium catalyzed C–H activations. Since only small amounts of the oxidant are generated and are immediately consumed in these transformations, side reactions of substrates or products can be avoided. Thus, usually oxidant-sensible substrates can be used, which makes these methods highly suitable for complex molecular structure syntheses. Moreover, mechanistic studies shed light on new reaction pathways, intermediates, and in situ generated species. The successful development of our dual catalysis concept, consisting of combined visible light photoredox catalysis and metal catalyzed C–H functionalization, provides many new opportunities for further explorations in the field of C–H functionalization.

Catalytic Mechanism and Efficiency of Methane Oxidation by Hg(II) in Sulfuric Acid and Comparison to Radical Initiated Conditions

Catalytic Mechanism and Efficiency of Methane Oxidation by Hg(II) in Sulfuric Acid and Comparison to Radical Initiated Conditions

Jack T. Fuller, III, Steven Butler, Deepa Devarajan, Austin Jacobs, Brian G. Hashiguchi, Michael M. Konnick, William A. Goddard, III, Jason Gonzales, Roy A. Periana, and Daniel H. Ess

ACS Catal. 2016, 6, 4312-4322
http://pubs.acs.org/doi/pdf/10.1021/acscatal.6b00226

TOC: 


Abstract: 

Methane conversion to methyl bisulfate by HgII(SO4) in sulfuric acid is an example of fast and selective alkane oxidation catalysis. Dichotomous mechanisms involving C−H activation and electron transfer have been proposed based on experiments. Radical oxidation pathways have also been proposed for some reaction conditions. HgII is also of significant interest because as a d10 transition metal it is similar to d10 main-group metals that also oxidize alkanes. Density- functional calculations are presented that use both implicit and a mixture of implicit/explicit solvent models for the complete HgII catalytic cycle of methane oxidation to methyl bisulfate. These calculations are consistent with experiment and reveal that methane is functionalized to methyl bisulfate by a C−H activation and reductive metal alkyl functionalization mechanism. This reaction pathway is lower in energy than both electron transfer and proton-coupled electron transfer pathways. After methane C−H functionalization, catalysis is completed by conversion of the proposed resting state, [HgI(HSO4)]2, into Hg0 followed by Hg0 to HgII oxidation induced by SO3 from dehydration of sulfuric acid. This catalytic cycle is efficient because in sulfuric acid the HgII/Hg0 potential results in a moderate free energy barrier for oxidation (∼40 kcal/mol) and HgII is electrophilic enough to induce barriers of <40 kcal/mol for C−H activation and reductive metal alkyl functionalization. Comparison of HgII to TlIII shows that while C−H activation and reductive metal alkyl functionalization have reasonable barriers for TlIII, the oxidation of TlI to TlIII has a significantly larger barrier than Hg0 to HgII oxidation and therefore TlIII is not catalytic in sulfuric acid. Comparison of HgII to CdII and ZnII reveals that while M0 to MII oxidation and C−H activation are feasible for these first-row and second-row transition metals, reductive metal alkyl functionalization barriers are very large and catalysis is not feasible. Calculations are also presented that outline the mechanism and energy landscape for radical-initiated (K2S2O8) methane oxidation to methanesulfonic acid in sulfuric acid. 

Mild metal-catalyzed C–H activation: examples and concepts

Mild metal-catalyzed C–H activation: examples and concepts

T. Gensch, M. N. Hopkinson, F. Glorius, and J. Wencel-Delord

Chem. Soc. Rev.

Abstract:

Organic reactions that involve the direct functionalization of non-activated C–H bonds represent an attractive class of transformations which maximize atom- and step-economy, and simplify chemical synthesis. Due to the high stability of C–H bonds, these processes, however, have most often required harsh reaction conditions, which has drastically limited their use as tools for the synthesis of complex organic molecules. Following the increased understanding of mechanistic aspects of C–H activation gained over recent years, great strides have been taken to design and develop new protocols that proceed efficiently under mild conditions and duly benefit from improved functional group tolerance and selectivity. In this review, we present the current state of the art in this field and detail C–H activation transformations reported since 2011 that proceed either at or below ambient temperature, in the absence of strongly acidic or basic additives or without strong oxidants. Furthermore, by identifying and discussing the major strategies that have led to these improvements, we hope that this review will serve as a useful conceptual overview and inspire the next generation of mild C–H transformations.

A steric tethering approach enables palladium-catalysed C–H activation of primary amino alcohols

Jonas Calleja, Daniel Pla, Timothy W. Gorman, Victoriano Domingo, Benjamin Haffemayer, & Matthew J. Gaunt

 

Nature Chemistry 7, 1009–1016  (2015)  doi:10.1038/nchem.2367    Received 27 May 2015             Accepted    02 September 2015     Published online 02 November 2015

Abstract      

Aliphatic primary amines are a class of chemical feedstock essential to the synthesis of higher-order nitrogen-containing molecules, commonly found in biologically active compounds and pharmaceutical agents. New methods for the construction of complex amines remain a continuous challenge to synthetic chemists. Here, we outline a general palladium-catalysed strategy for the functionalization of aliphatic C–H bonds within amino alcohols, an important class of small molecule. Central to this strategy is the temporary conversion of catalytically incompatible primary amino alcohols into hindered secondary amines that are capable of undergoing a sterically promoted palladium-catalysed C–H activation. Furthermore, a hydrogen bond between amine and catalyst intensifies interactions around the palladium and orients the aliphatic amine substituents in an ideal geometry for C–H activation. This catalytic method directly transforms simple, easily accessible amines into highly substituted, functionally concentrated and structurally diverse products, and can streamline the synthesis of biologically important amine-containing molecules.

http://www.nature.com/nchem/journal/v7/n12/full/nchem.2367.html

Recent developments in the preparation of N-heterocycles using Pd-catalyzed C-H activation

Recent developments in the preparation of N-heterocycles using Pd-catalyzed C-H activation
http://www.sciencedirect.com/science/article/pii/S0022328X15301935

Tanveer Mahamad Ali Shaikha, Fung-E. Honga

doi:10.1016/j.jorganchem.2015.10.022

Journal of Organometallic Chemistry, In Press, Accepted Manuscript

Abstract: The direct and selective activation of C-H bonds for the synthesis of N-heterocycles (C-N bonds) is an important areain modern synthetic chemistry due to its wide application in both in academics and industry. These compounds are frequently found as backbones in bioactive molecules and fine chemicals and are often used as organocatalysts or as auxiliary ligands in transition metal complexes assisted catalyses. Various kinds of palladium-containing complexes as active catalysts in the C(sp3)-H or C(sp2)-H bond activation have attracted increasing attention because of their accessibility and catalytic efficiencies. This review summarizes the recent developments in this area which employs Pd0-PdIV as versatile catalyst precursors to the syntheses of N-heterocycles. The N-heterocycles, including five- and six-membered rings, are described separately. Furthermore, some of the asymmetric C-H bond activation and mechanistic aspects of these catalytic reactions are discussed. 

Contrasting Mechanisms and Reactivity of Tl(III), Hg(II), and Co(III) for Alkane C−H Functionalization

http://pubs.acs.org/doi/abs/10.1021/acs.organomet.5b00849

Organometallics ASAP

Contrasting Mechanisms and Reactivity of Tl(III), Hg(II), and Co(III) for Alkane C−H Functionalization

Samantha J. Gustafson,† Jack T. Fuller, III,† Deepa Devarajan,† Justin Snyder,† Roy A. Periana,‡ Brian G. Hashiguchi,‡ Michael M. Konnick,‡ and Daniel H. Ess*,† 

† Department of Chemistry and Biochemistry, Brigham Young University, Provo, Utah 84602, United States 

‡ Department of Chemistry, The Scripps Research Institute, Jupiter, Florida 33458, United States

Abstract: Activation and functionalization of alkane C–H bonds has historically been dominated by transition-metal complexes. Light alkanes can also be partially oxidized by sixth-row main-group compounds, such as Tl^III(TFA)₃ (TFA = trifluoroacetate). Here we present density-functional calculations which demonstrate that Tl^III(TFA)₃ oxidizes alkanes by closed-shell C–H activation and Tl–alkyl functionalization mechanisms. The discovery of a C–H activation pathway is surprising, because Tl^III often oxidizes arene C–H bonds through an electron transfer mechanism and the transition-metal complex Co^III(TFA)₃, with similar oxidation state and ligand coordination, oxidizes alkanes via an open-shell radical mechanism. Comparison of Tl^III(TFA)₃to the transition-metal analogue Ir^III(TFA)₃ reveals that key to Tl^III oxidation of alkanes is a moderate barrier for C–H bond activation that is lower in energy than open-shell pathways and a subsequent metal–alkyl functionalization reaction step with a very low barrier. Our calculations suggest that the high-spin ground state of Co^III(TFA)₃ provides a low-energy open-shell decarboxylation pathway that leads to radical oxidation of alkanes, which is not available for the d¹⁰ Tl^III(TFA)₃ complex. The C–H activation pathway and transition state model provide a straightforward explanation for why Tl^III(TFA)₃ promotes alkane C–H bond activation but Hg^II(TFA)₂ does not.