On the Mechanism of Palladium-Catalyzed Aromatic C−H Oxidation

Powers, Dennis A.; Xiao, Di; Geibel, Matthias A. L.; Ritter, Tobias

doi:10.1021/ja1054274

Cited by 197 publications

(112 citation statements)

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“…[2] Two-electron redox processes are also well documented for binuclear gold complexes [3] as well as for gold/rhodium, [4] gold/iridium [5] and gold/platinum [6] heterobimetallic complexes. One of the common features displayed by all of these complexes relates to their ability to sustain two-electron redox chemistry without decomposition of the bimetallic core.…”

mentioning

confidence: 99%

Two‐Electron Redox Chemistry and Reversible Umpolung of a Gold–Antimony Bond

Wade

Gabbaı̈

2011

Angew Chem Int Ed

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Two-electron redox processes occurring at the core of dinuclear metal complexes are important because of their implication in a number of chemical transformations ranging from the photocatalytic production of dihydrogen [1] to the oxidative functionalization of CÀH bonds.[2] Two-electron redox processes are also well documented for binuclear gold complexes [3] as well as for gold/rhodium, [4] gold/iridium [5] and gold/platinum [6] heterobimetallic complexes. One of the common features displayed by all of these complexes relates to their ability to sustain two-electron redox chemistry without decomposition of the bimetallic core. As part of our interest in fundamental aspects of main-group chemistry, we have recently questioned whether similar processes could also be observed at the bimetallic core of main-group/transitionmetal complexes.Triarylstibines are soft s-donor ligands which have been incorporated in a variety of late transition-metal complexes. [7] They are also well known to undergo facile two-electron oxidation when exposed to oxidizing agents such as halogens.[8] While there is precedent for dialkylstibido transitionmetal compounds (type A) to undergo oxidative addition at the antimony center, [9] no analogous reactivity has been reported for stibine metal complexes of type B. With the discovery of main-group-based, two-electron redox platforms in mind, we have now decided to study the synthesis and oxidation of complexes of type B. Herein, we report the first incarnation of this idea in the case of a gold-antimony compound.To prevent dissociation of the gold-antimony bimetallic core upon oxidation, we chose to work with a stibine ligand whose interaction with the gold center would be supported by pendant donor ligands. These considerations led us to focus on the triphosphanylstibine ligand [(o-(Ph 2 P)C 6 H 4 ) 3 Sb] (referred to as L) [10] which was allowed to react with [AuCl(tht)] in CH 2 Cl 2 /acetone to produce 1-Cl as a pale yellow precipitate (Scheme 1). At À55 8C in CDCl 3 , the 31 P{ 1 H} NMR spectrum of 1-Cl displays two signals at d = + 39.5 and À7.4 ppm in a 2:1 intensity ratio thus suggesting that only two of the three phosphine arms of the ligand are coordinated to the gold atom. Upon elevation of the temperature, these two peaks coalesce into one signal at d = + 24.4 ppm indicating the onset of a rapid exchange. Line shape analysis of the 31 P{ 1 H} NMR spectra of 1-Cl over the À55 8C-+ 22 8C temperature range followed by an Eyring analysis afforded DH°= + 16.7 (AE 0.9) kcal mol À1 and DS°= + 16.6(AE3.8) cal mol À11 K À11 , suggesting a dissociative exchange of the phosphine arms. The ESI mass spectrum of this complex shows a peak at m/z 1101.1180 amu corresponding to the [LAu] + ion. A final clarification of the structure of this compound was derived from a single-crystal diffraction study which confirmed the coordination of two of the phosphorus atoms to the gold chloride fragment (Figure 1).[11] Inspection of the P-Au-P and P-Au-Cl angles (AE = 359.468) shows that these prim...

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confidence: 99%

Two‐Electron Redox Chemistry and Reversible Umpolung of a Gold–Antimony Bond

Wade

Gabbaı̈

2011

Angew Chem Int Ed

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“…Interested readers are directed to these references. 154,155 Furthermore, in these studies, mixed Pd(III) Cl/OAc dimers were implicated as competent catalytic intermediates in the oxidative C−H chlorination process, a proposal (supported by experimental evidence) which adds another element of complexity to the overall mechanistic scenario.…”

Section: Carbon−halogen Reductive Elimination From Pd(iii) Complexesmentioning

confidence: 66%

Modern Transition-Metal-Catalyzed Carbon–Halogen Bond Formation

2016

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The high utility of halogenated organic compounds has prompted the development of a vast number of transformations which install the carbon-halogen motif. Traditional routes to these building blocks have commonly involved multiple steps, harsh reaction conditions, and the use of stoichiometric and/or toxic reagents. In this regard, using transition metals to catalyze the synthesis of organohalides has become a mature field in itself, and applying these technologies has allowed for a decrease in the production of waste, higher levels of regio- and stereoselectivity, and the ability to produce enantioenriched target compounds. Furthermore, transition metals offer the distinct advantage of possessing a diverse spectrum of mechanistic possibilities which translate to the capability to apply new substrate classes and afford novel and difficult-to-access structures. This Review provides comprehensive coverage of modern transition metal-catalyzed syntheses of organohalides via a diverse array of mechanisms. Attention is given to the seminal stoichiometric organometallic studies which led to the corresponding catalytic processes being realized. By breaking this field down into the synthesis of aryl, vinyl, and alkyl halides, it becomes clear which methods have surfaced as most favored for each individual class. In general, a pronounced shift toward the use of C-H bonds as key functional groups, in addition to methods which proceed by catalytic, radical-based mechanisms has occurred. Although always evolving, this field appears to be heading in the direction of using starting materials with a significantly lower degree of prefunctionalization in addition to less expensive and abundant metal catalysts.

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“…Although there are more functional relationships between compressive strength σ and porosity P, the Balshin relation [10] seems to be quite fundamental. Compared with the classical Powers relation [11] σ = σ 0 · χ 3 χ gel−space ratio (6) the Balshin relation looks like an equivalent formula to that of Powers since the gel-space ratio χ may be expressed as χ ≈ (1 − P). However, due to the general fitting parameter , the Balshin formula might be considered a bit more general.…”

Section: Resultsmentioning

confidence: 99%

Roughness and fractality of fracture surfaces as indicators of mechanical quantities of porous solids

Ficker

Martišek

2011

Open Physics

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The 3D profile surface parameter H and fractal dimension D were tested as indicators of mechanical properties inferred from fracture surfaces of porous solids. High porous hydrated cement pastes were used as prototypes of porous materials. Both the profile parameter H and the fractal dimension D showed capability to assess compressive strength from the fracture surfaces of hydrated pastes. From a practical point of view the 3D profile parameter H seems to be more convenient as an indicator of mechanical properties, as its values suffer much less from statistical scatter than those of fractal dimensions.

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On the Mechanism of Palladium-Catalyzed Aromatic C−H Oxidation

Cited by 197 publications

References 102 publications

Two‐Electron Redox Chemistry and Reversible Umpolung of a Gold–Antimony Bond

Two‐Electron Redox Chemistry and Reversible Umpolung of a Gold–Antimony Bond

Modern Transition-Metal-Catalyzed Carbon–Halogen Bond Formation

Roughness and fractality of fracture surfaces as indicators of mechanical quantities of porous solids

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