DFT studies on the distinct mechanisms of C–H activation and oxidation reactions mediated by mononuclear- and binuclear-palladium

Zhang, Lulu; Zhang, Lei; Li, Shi-Jun; Fang, De‐Cai

doi:10.1039/c8dt00236c

Cited by 14 publications

(10 citation statements)

References 101 publications

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“…Since the attempted step involves charge separation, the distance scans were repeated with PCM/MeCN, and the results were the same, as well as with the dimer I2 instead of I1 . This is in contrast to the computational result for the oxidative chlorination of Pd(2-phenylpyridine) 2 by NCS . However, if NBS had been first ligated to the Pd atom ( via oxygen atom) by the substitution of MeCN, the bromine transfer became possible.…”

Section: Mechanistic Studysupporting

confidence: 61%

“…This is in contrast to the computational result for the oxidative chlorination of Pd(2phenylpyridine) 2 by NCS. 28 However, if NBS had been first ligated to the Pd atom (via oxygen atom) by the substitution of MeCN, the bromine transfer became possible. Another oxidation route was discovered by scanning the distance between the Pd atom and the center of the N−Br bond in NBS.…”

Section: ■ Mechanistic Studymentioning

confidence: 99%

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Mechanistic Study of the Mechanochemical Pd^II-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods

et al. 2022

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The mechanism of mechanochemical Pd II -catalyzed selective bromination of the carbon−hydrogen bond in azobenzene by N-bromosuccinimide (NBS) was investigated using in situ timeresolved Raman spectroscopy and quantum-chemical (density functional theory, DFT) calculations. Raman monitoring of the reactions in the presence of different amounts of Pd(OAc) 2 , ptoluenesulfonic acid (TsOH), and acetonitrile (MeCN) as solid and liquid additives provided direct evidence that the formation of the carbon−halogen bond in the solid state proceeds from catalytically active cyclopalladated intermediates that are monomeric in the presence of MeCN or dimeric without MeCN. The reaction pathway via the monomeric palladacycle is more efficient than the pathway via the dimeric palladacycle for the bromination of azobenzene, offering better yields and faster reactions. Both reaction routes require the presence of TsOH, which is involved in the formation of the active Pd II catalysts and palladacyclic intermediates, as well as in the activation of NBS. Four possible reaction mechanisms for the bromination of cyclopalladated azobenzene were investigated by DFT modeling. Three mechanistic pathways include (i) oxidative addition of the Br to Pd atom and (ii) reductive elimination by the 1,2-displacement of Br to the carbon atom. In one pathway, the transfer of Br to Pd occurs only after the initial displacement of the neutral ligand by NBS. In another, the Pd atom is inserted directly into the N−Br bond of NBS, and in the last one, Br + migrates spontaneously from the protonated NBS to Pd. In all three cases, the subsequent elimination step is remarkably lower in energy. In the fourth mechanism, Br + migrates from free NBS directly to the activated carbon, simultaneously with the Pd−C bond breaking. Besides NBS, the hydrogen bond complex NBS•••TsOH was also considered as the bromine source. None of the considered mechanisms can be definitely rejected on the basis of experimental findings and the current modeling level, and more than one could be operative depending on the reaction conditions.

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Section: Mechanistic Studysupporting

confidence: 61%

Section: ■ Mechanistic Studymentioning

confidence: 99%

Mechanistic Study of the Mechanochemical Pd^II-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods

et al. 2022

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“…While catalysis by Pd was initially understood as mononuclear Pd 0/II cycles, along with Pd IV intermediates, metal–metal bonded Pd III dimers have been isolated and proposed to play a key role in C–X and C–C bond formations. − Bimetallic cooperativity was suggested to lower the barriers for oxidation of organometallic Pd II precursors and accelerate the subsequent reductive elimination from Pd III dimers. , Furthermore, Pd III intermediates of various structures have also been invoked in other types of reactions such as aerobic hydroxylation, radical C–C coupling, and halogen addition to alkenes. , However, the structures of high-valent Pd intermediates in catalytic transformations often remain elusive because of their high reactivity and propensity to undergo rapid reductive elimination. Furthermore, the structure of high-valent Pd intermediates and their mechanism of formation are strongly dependent on many factors, including the supporting ligands, type of oxidant, and solvent. − Thus, expanding the palette of structurally characterized high-valent Pd catalytic intermediates and elucidating the structural factors that contribute to their formation would enable more systematic access to their rich oxidation reactivity.…”

Section: Introductionmentioning

confidence: 81%

Rapid Electrochemical Methane Functionalization Involves Pd–Pd Bonded Intermediates

et al. 2020

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High-valent Pd complexes are potent agents for the oxidative functionalization of inert C–H bonds, and it was previously shown that rapid electrocatalytic methane monofunctionalization could be achieved by electro-oxidation of PdII to a critical dinuclear PdIII intermediate in concentrated or fuming sulfuric acid. However, the structure of this highly reactive, unisolable intermediate, as well as the structural basis for its mechanism of electrochemical formation, remained elusive. Herein, we use X-ray absorption and Raman spectroscopies to assemble a structural model of the potent methane-activating intermediate as a PdIII dimer with a Pd–Pd bond and a 5-fold O atom coordination by HxSO4 (x–2) ligands at each Pd center. We further use EPR spectroscopy to identify a mixed-valent M–M bonded Pd2 II,III species as a key intermediate during the PdII-to-PdIII 2 oxidation. Combining EPR and electrochemical data, we quantify the free energy of Pd dimerization as <−4.5 kcal/mol for Pd2 II,III and <−9.1 kcal/mol for PdIII 2. The structural and thermochemical data suggest that the aggregate effect of metal–metal and axial metal–ligand bond formation drives the critical Pd dimerization reaction in between electrochemical oxidation steps. This work establishes a structural basis for the facile electrochemical oxidation of PdII to a M–M bonded PdIII dimer and provides a foundation for understanding its rapid methane functionalization reactivity.

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“…In the present study, our solution translational entropy model encoded in the THERMO program was used to compute more accurate entropic and free-energy data. Such a solution translational entropy model has previously been applied to Gibbs free-energy calculations in solution …”

Section: Computational Detailsmentioning

confidence: 99%

DFT Case Study on the Comparison of Ruthenium-Catalyzed C–H Allylation, C–H Alkenylation, and Hydroarylation

2022

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Density functional calculations at the B3LYP-D3+IDSCRF/TZP-DKH(-dfg) level of theory have been performed to understand the mechanism of ruthenium-catalyzed C–H allylation reported in the literature in depth. The plausible pathway consisted of four sequential processes, including C–H activation, migratory insertion, amide extrusion, and recovery of the catalyst, in which C–H activation was identified as the rate-determining step. The amide extrusion step could be promoted kinetically by trifluoroacetic acid since its mediation lowered the free-energy barrier from 32.1 to 12.2 kcal/mol. Additional calculations have been performed to explore other common pathways between arenes and alkenes, such as C–H alkenylation and hydroarylation. A comparison of the amide extrusion and β-H elimination steps established the following reactivity sequence of the leaving groups: protonated amide group > β-H group > unprotonated amide group. The suppression of hydroarylation was attributed to the sluggishness of the Ru–C protonation step as compared to the amide extrusion step. This study can unveil factors favoring the C–H allylation reaction.

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DFT studies on the distinct mechanisms of C–H activation and oxidation reactions mediated by mononuclear- and binuclear-palladium

Cited by 14 publications

References 101 publications

Mechanistic Study of the Mechanochemical Pd^II-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods

Mechanistic Study of the Mechanochemical Pd^II-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods

Rapid Electrochemical Methane Functionalization Involves Pd–Pd Bonded Intermediates

DFT Case Study on the Comparison of Ruthenium-Catalyzed C–H Allylation, C–H Alkenylation, and Hydroarylation

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DFT studies on the distinct mechanisms of C–H activation and oxidation reactions mediated by mononuclear- and binuclear-palladium

Cited by 14 publications

References 101 publications

Mechanistic Study of the Mechanochemical PdII-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods

Mechanistic Study of the Mechanochemical PdII-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods

Rapid Electrochemical Methane Functionalization Involves Pd–Pd Bonded Intermediates

DFT Case Study on the Comparison of Ruthenium-Catalyzed C–H Allylation, C–H Alkenylation, and Hydroarylation

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Mechanistic Study of the Mechanochemical Pd^II-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods

Mechanistic Study of the Mechanochemical Pd^II-Catalyzed Bromination of Aromatic C–H Bonds by Experimental and Computational Methods