Kinetic and Energetic Analysis of the Free Electron Transfer

Baidak, Aliaksandr; Naumov, Sergej; Brede, O.

doi:10.1021/jp8053982

Cited by 6 publications

(6 citation statements)

References 32 publications

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“…The tritylium species [Ph 3 C] + , which undergoes a swift decomposition in the gas phase, is in solution a well-known stable multifaceted Lewis acidic cation . It may act not only as a hydride and/or a halide abstraction agent but also as a one-electron oxidant (Ph 3 C • /Ph 3 C + couple) in the ground state as well as in the excited state and may be involved also in the hydride abstraction process as reported by Mandon, Astruc, et al Quite interestingly, to the best of our knowledge there has been no mention of any major drawbacks related to the oxidative properties of the tritylium as an “activator”, i.e. as a halido ligand “remover”, in transition-metal-mediated homogeneous catalysis.…”

Section: Resultsmentioning

confidence: 99%

Fate of Cobaltacycles in Cp*Co-Mediated C–H Bond Functionalization Catalysis: Cobaltacycles May Collapse upon Oxidation via Co(IV) Species

Deraedt

Cornaton

et al. 2021

Organometallics

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Recent reports have identified Cp*Co-based complexes as powerful catalysts for aromatic C-H bond activation under oxidative conditions. However, little is known about the speciation of Cp*Co species during catalysis. We now show that key intermediates, Cp*Co(III) metallacycles derived from 2-phenylpyridine (phpy-H), react swiftly in solution with one-electron oxidants to irreversibly collapse by a cyclocondensation of the organic ligands to afford cationic alkaloids in yields of >70 %. Low temperature EPR analysis of a mixture of cobaltacycle with the tritylium cation reveals the signatures of trityl and Co(IV)-centred radicals. Electrochemical analyses show that the oxidation of these cobaltacycles is irreversible and gives rise to several products in various amounts, among which the most salient ones are a cationic alkaloid resulting from the cyclocondensation of the phpy and Cp* ligands, and the dimeric cation {[Cp*Co] 2 (-I) 3 } + . DFT investigations of relevant noncovalent interactions using QTAIMbased NCI plots and Intrinsic Bond Strength Index suggest a ligand-dependent predisposition by "NCI-coding" for the Co(IV)templated cyclocondensation, the computed reaction network energy profile for which supports the key roles of a short lived Co(IV) metallacycle and of a range of triplet state organocobalt intermediates. These data are provided free of charge by the joint Cambridge Crystallographic Data Centre and Fachinformationszentrum Karlsruhe Access Structures service www.ccdc.cam.ac.uk/structures. Full experimental procedures and details, voltammograms, EPR, Mass and NMR spectra, energies and Cartesian coordinates, high resolution NCI figures. This material is available free of charge via the Internet at http://pubs.acs.org.

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Section: Resultsmentioning

confidence: 99%

Fate of Cobaltacycles in Cp*Co-Mediated C–H Bond Functionalization Catalysis: Cobaltacycles May Collapse upon Oxidation via Co(IV) Species

Deraedt

Cornaton

et al. 2021

Organometallics

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“…9. 43 Although none of the conformations of Fig. 9 really stand for the sterically preferred structures, the Figure visualizes extremes in the electron distribution in the ground state.…”

Section: Benzylsilanesmentioning

confidence: 97%

“…For the example of the sulfide Np-S-CPh 3 the usual FET reaction scheme should be adapted (reaction (12)). 43 In this reaction sequence it is assumed that the unusual dissociation products are formed by the prompt dissociation of the twisted radical cation. The observed species are given in bold type.…”

Section: Benzylsilanesmentioning

confidence: 99%

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Free electron transfer—relations between molecule dynamics and reaction kinetics

Brede¹,

Naumov²

2010

Chem. Soc. Rev.

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Electron transfer in non-polar media (alkanes, alkyl chlorides) exhibits some essential peculiarities. For instance the reaction of hetero-substituted aromatics with parent solvent radical cations results in the parallel formation of metastable donor radical cations and fragmentation products, in comparable amounts. The fragmentation products originate from a dissociative donor radical cation which decays extremely rapidly, i.e., in a few femtoseconds. This phenomenon is explained in terms of intramolecular dynamic motions which cause changes of the electron density (pi- and n-orbitals) in dependence on the deformation angle between the substituents and the aromatic ring. Hence femtosecond dynamics is reflected in the nanosecond time range and can be observed with real-time spectroscopy. Therefore, the process is named free electron transfer (FET) which corresponds to an unhindered electron jump occurring in the first approach of the reactants. This dynamic controlled process is compared with the classical electron transfer theories which are based on equilibrium kinetics. From the FET mechanism some new aspects for chemical reaction kinetics can be derived (critical review, 69 references).

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“…In the mesolysis of 1,1,1,2-Ph 4 E •+ , formation of Ph 3 C + with absorption peak at 415 nm and benzyl radical was observed (Supporting Information Figure S4). , The k meso for 1,1,1,2-Ph 4 E •+ was ten folds larger than that for 1,1,2,2-Ph 4 E •+ . This is consistent with the BDE of 1,1,1,2-Ph 4 E •+ smaller than that of 1,1,2,2-Ph 4 E •+ due to steric hindrance of triphenylmethyl chromophore.…”

Section: Resultsmentioning

confidence: 98%

Mesolysis of Radical Anions of Tetra-, Penta-, and Hexaphenylethanes

2012

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A central carbon–carbon (C–C) σ bond dissociation of polyphenylethane radical anions (Ph(n)E•-, n = 3–6), mesolysis, was investigated by the transient absorption measurement during pulse radiolysis of Ph(n)E in 2-methyltetrahydrofuran. The charge resonance (CR) band of 1,1,2,2-tetraphenylethane radical anion (1,1,2,2-Ph4E•-) was observed in the near-infrared region immediately after an electron pulse to be attributed to the intramolecular dimer radical anion. The CR band disappeared with simultaneous formation of two absorption bands at 330 and 460 nm corresponding to diphenylmethyl radical and diphenylmethyl anion, respectively, indicating the occurrence of the mesolysis in 1,1,2,2-Ph4E•-. During pulse radiolysis of 1,1,1,2,2,2-hexaphenylethane (Ph6E), an absorption band of triphenylmethyl radical was observed at 340 nm immediately after an electron pulse. It is suggested that one electron attachment to Ph6E is followed by the subsequent rapid C–C σ bond dissociation. Formation of intramolecular dimer radical anions in Ph(n)E•- such as 1,1,2-triphenylethane (Ph3E), 1,1,1,2-tetraphenylethane (1,1,1,2-Ph4E), and 1,1,1,2,2-pentaphenylethane (Ph5E) was also studied together with the subsequent mesolysis. The mesolysis of Ph(n)E•- is discussed in terms of charge delocalization in the intramolecular dimer radical anions and the central C–C σ bond as well as bond dissociation energy of the central C–C σ bond of Ph(n)E•-.

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Kinetic and Energetic Analysis of the Free Electron Transfer

Cited by 6 publications

References 32 publications

Fate of Cobaltacycles in Cp*Co-Mediated C–H Bond Functionalization Catalysis: Cobaltacycles May Collapse upon Oxidation via Co(IV) Species

Fate of Cobaltacycles in Cp*Co-Mediated C–H Bond Functionalization Catalysis: Cobaltacycles May Collapse upon Oxidation via Co(IV) Species

Free electron transfer—relations between molecule dynamics and reaction kinetics

Mesolysis of Radical Anions of Tetra-, Penta-, and Hexaphenylethanes

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