A mechanistic analysis of the Rh-catalyzed intramolecular C–H amination reaction

Fiori, Kristin Williams; Espino, Christine G.; Brodsky, Benjamin H.; Bois, J. Du

doi:10.1016/j.tet.2008.11.073

Cited by 227 publications

(183 citation statements)

References 64 publications

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“…+ is low, its appearance is consistent with the catalytic pathway that we and others have postulated for the C-H amination process (7)(8)(9). Many of the ionic species detected in this study have been proposed previously based on bulk solution mechanistic data.…”

Section: S1c) Although the Intensity Of [7+na]supporting

confidence: 90%

“…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). Studies of the reaction mechanism suggest the generation of a one-electron oxidized form of the catalyst, [Rh 2 (esp) 2 …”

mentioning

confidence: 99%

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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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Section: S1c) Although the Intensity Of [7+na]supporting

confidence: 90%

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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“…Linear correlations are consistent with cationic charge stabilization in the transition state and typically observed in concerted amination chemistry with Rh 2 -carboxylate catalysts. 4 The lack of correlation with our catalyst led us to consider the incorporation of a spin delocalization parameter, s c JJ , developed by Jiang and coworkers. 23 The log k R vs. Octahedral (porphyrinato)Ru-(|r c JJ /r mb | aziridination ¼ 0.5) 24 and tetrahedral (trispyrazolylborate)Cu-based (|r c JJ /r mb | aziridination ¼…”

Section: B Mechanism Of Benzylic Amination and Aziridination Reactionsmentioning

confidence: 99%

Iron-mediated intermolecular N-group transfer chemistry with olefinic substrates

et al. 2014

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“…Importantly, radical clock experiments provided no evidence for the involvement of radicals in these intramolecular reactions. [17] In contrast to the intramolecular reactions described above, catalytic intermolecular reactions are mechanistically more complex, though they have a greater potential utility in synthesis. In 2004, the Du Bois group made a major breakthrough in intermolecular C À H amination through the introduction of the new catalyst [Rh 2 A C H T U N G T R E N N U N G (esp) 2 ] (1) (Scheme 1); its robustness is believed to be due to the chelating dicarboxylate ligand, esp, which disfavors ligand dissociation.…”

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confidence: 99%

Evidence for a One‐Electron Mechanistic Regime in Dirhodium‐Catalyzed Intermolecular CH Amination

Kornecki

Berry

2011

Chemistry A European J

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Swift and energy efficient conversion of chemical feedstocks to pharmaceuticals and agrochemicals requires the development of new methods to add nitrogen functionality to unfunctionalized organic substrates. Dirhodium-catalyzed insertion of nitrene species into C-H bonds is a promising new method, the main drawback of which is the currently limited understanding of the catalytic mechanism. Herein, cyclic voltammetry and controlled potential electrolysis measurements have enabled us to solve many of the mechanistic mysteries of intermolecular C-H amination catalyzed by [Rh(2)(esp)(2)] (esp=α,α,α',α'-tetramethyl-1,3-benzenedipropanoate). The primary result is that, in addition to a simple nitrene-transfer mechanism that dominates the early stages of the reaction, another mechanism is available that relies on sequential proton-coupled electron transfer steps. Whereas the nitrene-transfer mechanism requires the use of expensive, atom-inefficient oxidants, we show that simple one-electron oxidants such as Ce(4+) may be used to achieve catalytic C-H amination via the one-electron mechanistic regime.

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A mechanistic analysis of the Rh-catalyzed intramolecular C–H amination reaction

Cited by 227 publications

References 64 publications

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

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

Iron-mediated intermolecular N-group transfer chemistry with olefinic substrates

Evidence for a One‐Electron Mechanistic Regime in Dirhodium‐Catalyzed Intermolecular CH Amination

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