scholarly journals Spectroscopic characterization of photoaccumulated radical anions: a litmus test to evaluate the efficiency of photoinduced electron transfer (PET) processes

2013 ◽  
Vol 9 ◽  
pp. 800-808 ◽  
Author(s):  
Maurizio Fagnoni ◽  
Stefano Protti ◽  
Davide Ravelli ◽  
Angelo Albini
Keyword(s):  
Electron Transfer ◽  
Spectroscopic Characterization ◽  
Secondary Amines ◽  
Radical Anions ◽  
Radical Intermediates ◽  
Ipso Substitution ◽  
Back Electron Transfer ◽  
Anthracene Derivatives ◽  
Litmus Test

Steady-state irradiation in neat acetonitrile of some aromatic nitriles, imides and esters (10−5–10−3 M solution) in the presence of tertiary amines allowed the accumulation of the corresponding radical anions, up to quantitative yield for polysubstituted benzenes and partially with naphthalene and anthracene derivatives. The condition for such an accumulation was that the donor radical cation underwent further evolution that precluded back electron transfer and any chemical reaction with the radical anion. In fact, no accumulation occurred with 1,4-diazabicyclo[2.2.2]octane (DABCO), for which this condition is not possible. The radical anions were produced from benzene polyesters too, but decomposition began early. Ipso substitution was one of the paths with secondary amines and the only reaction with tetrabutylstannane. The results fully support the previously proposed mechanism for electron transfer (ET) mediated photochemical alkylation of aromatic acceptors via radical ions and radical intermediates.

Combined spectroscopic characterization of electron transfer at hybrid CuPcF16/GaAs semiconductor interfaces

2008 ◽  
Vol 19 (42) ◽  
pp. 424010 ◽  
Author(s):  
Juan Cabanillas-Gonzalez ◽  
Hans-Joachim Egelhaaf ◽  
Alberto Brambilla ◽  
Paolo Sessi ◽  
Lamberto Duò ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Spectroscopic Characterization ◽  
Semiconductor Interfaces

Spectroscopic characterization of 2,6-dimethoxyphenol radical intermediates in the Coriolopsis gallica laccase-mediator system

2014 ◽  
Vol 107 ◽  
pp. 100-105 ◽  
Author(s):  
Andrea Martorana ◽  
Rafael Vazquez-Duhalt ◽  
Sergio A. Aguila ◽  
Riccardo Basosi ◽  
Maria Camilla Baratto
Keyword(s):  
Spectroscopic Characterization ◽  
Radical Intermediates ◽  
Mediator System ◽  
Laccase Mediator System

scholarly journals [Co(TPP)]–Catalyzed Carbene Transfer from Acceptor–Acceptor Iodonium Ylides via N-enolate Carbene Radicals

2021 ◽  
Author(s):  
Roel F.J. Epping ◽  
Mees M. Hoeksma ◽  
Eduard O. Bobylev ◽  
Simon Mathew ◽  
Bas de Bruin
Keyword(s):  
Catalyst Deactivation ◽  
Reaction Pathway ◽  
Spectroscopic Characterization ◽  
Radical Intermediate ◽  
Radical Intermediates ◽  
Key Species ◽  
Carbene Transfer ◽  
Cyclic Compounds ◽  
Iodonium Ylides

<b>Abstract: </b>Square-planar cobalt(II)-systems have emerged as powerful carbene transfer catalysts for the synthesis of a variety of (hetero)cyclic compounds via redox non-innocent Co(III)-carbene radical intermediates. Spectroscopic detection and characterization of these reactive carbene radical intermediates has thus far been limited to a few scattered experiments, in part due to the fact that most studies have focused on mono-substituted carbene precursors. In this work, we demonstrate the unique formation of disubstituted cobalt(III)-carbene radicals in reactions between a cobalt(II)-porphyrin com-plex with acceptor-acceptor iodaneylidenes (iodonium ylides) as the carbene precursors. We report detailed spectroscopic characterization of the resulting reactive carbene radical species, and their application in styrene cyclopropanation. In particular, we demonstrate that iodonium ylides generate novel bis-carbenoid species leading to reversible substrate-promoted ligand modification of the commercially available [Co(TPP)]-catalyst. Two interconnected catalytic cycles are involved in the overall catalytic reaction with a mono-terminal carbene radical and an unprecedented N-enolate-carbene radical intermediate as the respective key species for the mono- and bis-carbene cycles. Notably, N-enolate formation is not a catalyst deactivation pathway, and both the N-enolate and the carbene radical moieties can be transferred as carbene units to styrene. The studies provide a detailed picture of the new [Co(TPP)]-catalyzed carbene transfer reactions from iodonium ylides. The findings are supported by detailed and unequivocal characterization of the reactive N-enolate & carbene radical intermediates and their deactivation products (EPR, UV-Vis, HR-MS, NMR, in-situ ATR-FT-IR, SC-XRD), Hammett analysis, mechanistic control experiments, DFT reaction pathway profiling and NEVPT2-CASSCF electronic structure calculations.<br>

scholarly journals Stepwise N–H bond formation from N2-derived iron nitride, imide and amide intermediates to ammonia

2016 ◽  
Vol 7 (9) ◽  
pp. 5736-5746 ◽  
Author(s):  
K. Cory MacLeod ◽  
Sean F. McWilliams ◽  
Brandon Q. Mercado ◽  
Patrick L. Holland
Keyword(s):  
Electron Transfer ◽  
Bond Formation ◽  
Iron Complexes ◽  
Spectroscopic Characterization ◽  
Iron Nitride ◽  
Proton Coupled Electron Transfer

The pathway from N2to NH3at low-coordinate iron complexes is shown through crystallographic and spectroscopic characterization of intermediates, including bridging nitride, imide, and amides. Proton-coupled electron transfer plays a key role in the transformations.

scholarly journals [Co(TPP)]–Catalyzed Carbene Transfer from Acceptor–Acceptor Iodonium Ylides via N-enolate Carbene Radicals

2021 ◽  
Author(s):  
Roel F.J. Epping ◽  
Mees M. Hoeksma ◽  
Eduard O. Bobylev ◽  
Simon Mathew ◽  
Bas de Bruin
Keyword(s):  
Catalyst Deactivation ◽  
Reaction Pathway ◽  
Spectroscopic Characterization ◽  
Radical Intermediate ◽  
Radical Intermediates ◽  
Key Species ◽  
Carbene Transfer ◽  
Cyclic Compounds ◽  
Iodonium Ylides

<b>Abstract: </b>Square-planar cobalt(II)-systems have emerged as powerful carbene transfer catalysts for the synthesis of a variety of (hetero)cyclic compounds via redox non-innocent Co(III)-carbene radical intermediates. Spectroscopic detection and characterization of these reactive carbene radical intermediates has thus far been limited to a few scattered experiments, in part due to the fact that most studies have focused on mono-substituted carbene precursors. In this work, we demonstrate the unique formation of disubstituted cobalt(III)-carbene radicals in reactions between a cobalt(II)-porphyrin com-plex with acceptor-acceptor iodaneylidenes (iodonium ylides) as the carbene precursors. We report detailed spectroscopic characterization of the resulting reactive carbene radical species, and their application in styrene cyclopropanation. In particular, we demonstrate that iodonium ylides generate novel bis-carbenoid species leading to reversible substrate-promoted ligand modification of the commercially available [Co(TPP)]-catalyst. Two interconnected catalytic cycles are involved in the overall catalytic reaction with a mono-terminal carbene radical and an unprecedented N-enolate-carbene radical intermediate as the respective key species for the mono- and bis-carbene cycles. Notably, N-enolate formation is not a catalyst deactivation pathway, and both the N-enolate and the carbene radical moieties can be transferred as carbene units to styrene. The studies provide a detailed picture of the new [Co(TPP)]-catalyzed carbene transfer reactions from iodonium ylides. The findings are supported by detailed and unequivocal characterization of the reactive N-enolate & carbene radical intermediates and their deactivation products (EPR, UV-Vis, HR-MS, NMR, in-situ ATR-FT-IR, SC-XRD), Hammett analysis, mechanistic control experiments, DFT reaction pathway profiling and NEVPT2-CASSCF electronic structure calculations.<br>

Zinc porphyrin-anthraquinonylimidazole supramolecular dyads

2020 ◽  
Vol 24 (05n07) ◽  
pp. 850-859
Author(s):  
Federica Sabuzi ◽  
Alessia Coletti ◽  
Valeria Conte ◽  
Barbara Floris ◽  
Pierluca Galloni
Keyword(s):  
Electron Transfer ◽  
Chain Length ◽  
Strong Correlation ◽  
Transient Absorption ◽  
Binding Constants ◽  
Spectroscopic Characterization ◽  
Zinc Ion ◽  
Transient Absorption Spectroscopy ◽  
Zinc Porphyrin

In this work, the synthesis and spectroscopic characterization of new zinc porphyrin-anthraquinone dyads is proposed. In particular, electron donor units based on zinc meso-tetraphenylporphyrin (ZnTPP) and zinc octaethylporphyrin (ZnOEP) have been coupled with differently substituted anthraquinones as acceptors. The quinone moiety was properly functionalized with imidazole, thus ensuring porphyrin complexation through zinc ion coordination. Accordingly, absorption and emission measurements demonstrated that the coordination occurred, and calculated binding constants were in the range 6.6 [Formula: see text] 10[Formula: see text]–3.9 [Formula: see text] 10[Formula: see text] M[Formula: see text]. Transient absorption spectroscopy for ZnTPP and ZnOEP dyads demonstrated that the electron transfer occurred, with the formation of the corresponding charge separated state, ZnTPP[Formula: see text]-AQ. Moreover, in ZnOEP complexes, a strong correlation between the chain length and flexibility with the charge separated state lifetime was observed.

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