Metal-Catalyzed Oxidations of C–H to C–N Bonds

Zalatan, David N.; Bois, J. Du

doi:10.1007/128_2009_19

Cited by 275 publications

(131 citation statements)

References 149 publications

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“…A series of dirhodium species were chosen as catalysts for the desired transformation owing to their success in various types of C−N bond formation via outer-sphere pathway. 12 In a reaction of 2-phenylpyridine with ptoluenesulfonyl azide, we observed that some dimeric rhodium-(II) species indeed catalyzed the regioselective C(sp 2 )−H amidation. However, the efficiency of the Rh(II)-catalyzed amidation was found to be rather low to afford only unsatisfactory product yields (Scheme 4a).…”

Section: Rh(iii)-catalyzed C−h Amination Usingmentioning

confidence: 96%

Transition-Metal-Catalyzed C–N Bond Forming Reactions Using Organic Azides as the Nitrogen Source: A Journey for the Mild and Versatile C–H Amination

2015

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Owing to the prevalence of nitrogen-containing compounds in functional materials, natural products and important pharmaceutical agents, chemists have actively searched for the development of efficient and selective methodologies allowing for the facile construction of carbon-nitrogen bonds. While metal-catalyzed C-N cross-coupling reactions have been established as one of the most general protocols for C-N bond formation, these methods require starting materials equipped with functional groups such as (hetero)aryl halides or their equivalents, thus generating stoichiometric amounts of halide salts as byproducts. To address this aspect, a transition-metal-catalyzed direct C-H amination approach has emerged as a step- and atom-economical alternative to the conventional C-N cross-coupling reactions. However, despite the significant recent advances in metal-mediated direct C-H amination reactions, most available procedures need harsh conditions requiring stoichiometric external oxidants. In this context, we were curious to see whether a transition-metal-catalyzed mild C-H amination protocol could be achieved using organic azides as the amino source. We envisaged that a dual role of organic azides as an environmentally benign amino source and also as an internal oxidant via N-N2 bond cleavage would be key to develop efficient C-H amination reactions employing azides. An additional advantage of this approach was anticipated: that a sole byproduct is molecular nitrogen (N2) under the perspective catalytic conditions. This Account mainly describes our research efforts on the development of rhodium- and iridium-catalyzed direct C-H amination reactions with organic azides. Under our initially optimized Rh(III)-catalyzed amination conditions, not only sulfonyl azides but also aryl- and alkyl azides could be utilized as facile amino sources in reaction with various types of C(sp(2))-H bonds bearing such directing groups as pyridine, amide, or ketoxime. More recently, a new catalyst system using Ir(III) species was developed for the direct C-H amidation of arenes and alkenes with acyl azides under exceptionally mild conditions. As a natural extension, amidation of primary C(sp(3))-H bonds could also be realized on the basis of the superior activity of the Cp*Ir(III) catalyst. Mechanistic investigations revealed that a catalytic cycle is operated mainly in three stages: (i) chelation-assisted metallacycle formation via C-H bond cleavage; (ii) C-N bond formation through the in situ generation of a metal-nitrenoid intermediate followed by the insertion of an imido moiety to the metal carbon bond; (iii) product release via protodemetalation with the concomitant catalyst regeneration. In addition, this Account also summarizes the recent advances in the ruthenium- and cobalt-catalyzed amination reactions using organic azides, developed by our own and other groups. Comparative studies on the relative performance of those catalytic systems are briefly described.

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Section: Rh(iii)-catalyzed C−h Amination Usingmentioning

confidence: 96%

Transition-Metal-Catalyzed C–N Bond Forming Reactions Using Organic Azides as the Nitrogen Source: A Journey for the Mild and Versatile C–H Amination

2015

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“…5–9 Many of the methods that have been developed are either intramolecular (requiring that a nitrogen source already be present in the same molecule as the targeted C–H bond) or utilize directing groups (also requiring the presence of specific functionality in the starting material). An elegant yet more elusive transformation is the intermolecular C–H amination of unfunctionalized hydrocarbons; such a reaction provides a dramatically simplifying and convergent disconnection for the synthesis of amines from alkanes (Fig.…”

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confidence: 99%

Enantioselective, intermolecular benzylic C–H amination catalysed by an engineered iron-haem enzyme

et al. 2017

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C–H bonds are ubiquitous structural units of organic molecules; while these bonds are generally considered to be chemically inert, the recent emergence of methods for C–H functionalization promises to transform the way synthetic chemistry is performed. The intermolecular amination of C–H bonds represents a particularly desirable and challenging transformation for which no efficient, highly selective, and renewable catalysts exist. Here we report the directed evolution of an iron-containing enzymatic catalyst, based on a cytochrome P450 monooxygenase, for the highly enantioselective, intermolecular amination of benzylic C–H bonds. The biocatalyst is capable of up to 1,300 turnovers, exhibits excellent enantioselectivities, and provides access to valuable benzylic amines. Iron complexes are generally poor catalysts for C–H amination: in this catalyst, the enzyme’s protein framework confers activity on an otherwise unreactive iron-heme cofactor.

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“…mass spectrometry | transient intermediates | C-H oxidation | catalysis C atalytic methods for selective C-H oxidation rely on the exquisite choreography of a series of ligand substitution and redox events (1,2) and in some instances, the controlled generation of a hyperreactive electrophile (3)(4)(5). The Du Bois laboratory has developed an amination protocol that uses the catalyst bis [rhodium(α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid)], hereafter designated as Rh 2 (esp) 2 , to promote both intra-and intermolecular oxidation reactions (1,2).…”

mentioning

confidence: 99%

“…The Du Bois laboratory has developed an amination protocol that uses the catalyst bis [rhodium(α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid)], hereafter designated as Rh 2 (esp) 2 , to promote both intra-and intermolecular oxidation reactions (1,2). Indirect evidence has implicated a reactive Rh-nitrene intermediate that oxidizes saturated C-H bonds through a concerted asynchronous two-electron insertion event (6)(7)(8)(9)(10).…”

mentioning

confidence: 99%

Capturing fleeting intermediates in a catalytic C–H amination reaction cycle

Perry

Cahill

Roizen

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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We have applied an ambient ionization technique, desorption electrospray ionization MS, to identify transient reactive species of an archetypal C-H amination reaction catalyzed by a dirhodium tetracarboxylate complex. Using this analytical method, we have detected previously proposed short-lived reaction intermediates, including two nitrenoid complexes that differ in oxidation state. Our findings suggest that an Rh-nitrene oxidant can react with hydrocarbon substrates through a hydrogen atom abstraction pathway and raise the intriguing possibility that two catalytic C-H amination pathways may be operative in a typical bulk solution reaction. As highlighted by these results, desorption electrospray ionization MS should have broad applicability for the mechanistic study of catalytic processes.mass spectrometry | transient intermediates | C-H oxidation | catalysis C atalytic methods for selective C-H oxidation rely on the exquisite choreography of a series of ligand substitution and redox events (1, 2) and in some instances, the controlled generation of a hyperreactive electrophile (3-5). The Du Bois laboratory has developed an amination protocol that uses the catalyst bis [rhodium(α,α,α′,α′-tetramethyl-1,3-benzenedipropionic acid)], hereafter designated as Rh 2 (esp) 2 , to promote both intra-and intermolecular oxidation reactions (1, 2). Indirect evidence has implicated a reactive Rh-nitrene intermediate that oxidizes saturated C-H bonds through a concerted asynchronous two-electron insertion event (6-10). Studies of the reaction mechanism suggest the generation of a one-electron oxidized form of the catalyst, [Rh 2 (esp) 2 ]+ , which appears to result from reaction of the nitrenoid oxidant (4, 5, 11). The fast rates of the on-and off-path steps in this catalytic process and the transient nature of the reactive Rh-nitrene have confounded direct detection of many of the proposed reaction intermediates.A preponderance of experimental and theoretical data (7-10, 12, 13) supports the mechanism for Rh-catalyzed C-H amination depicted in Fig. 1. Sulfamate 2 and iodine oxidant 3 condense to form iminoiodinane 4 (14, 15). The iminoiodinane is a ligand for Rh 2 (esp) 2 , which react to generate [Rh 2 (esp) 2 ]•PhINSO 2 OR 5; subsequent loss of iodobenzene (PhI) furnishes nitrenoid 6. Oxidation of adamantane by 6 gives the sulfonamide product 7 and regenerates the dirhodium catalyst 1. The structures of intermediates 5 and 6 were postulated through analogy to carbenoid intermediates in reactions of dirhodium catalysts with diazo compounds, and to the best of our knowledge, have not been observed spectroscopically (6-10, 12, 13). In our experience, the oxidation of substrate by Rh-nitrene 6 seems to correlate with competitive formation of a mixed-valent (Rh 2+ /Rh 3+ ) dimer 8 that visibly colors the reaction solution red. Previous studies show that this red species is generated when Rh 2 (esp) 2 1, sulfamate 2, and oxidant 3 are mixed in solution (e.g., 0.3 mM 1 in chlorobenzene) (4,5,11). In this report, we provide direct...

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Metal-Catalyzed Oxidations of C–H to C–N Bonds

Cited by 275 publications

References 149 publications

Transition-Metal-Catalyzed C–N Bond Forming Reactions Using Organic Azides as the Nitrogen Source: A Journey for the Mild and Versatile C–H Amination

Transition-Metal-Catalyzed C–N Bond Forming Reactions Using Organic Azides as the Nitrogen Source: A Journey for the Mild and Versatile C–H Amination

Enantioselective, intermolecular benzylic C–H amination catalysed by an engineered iron-haem enzyme

Capturing fleeting intermediates in a catalytic C–H amination reaction cycle

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