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

2021 ◽  
Author(s):  
Roel Epping ◽  
Mees Hoeksma ◽  
Eduard Bobylev ◽  
Simon Mathew ◽  
Bas de Bruin
Keyword(s):  
Radical Intermediate ◽  
Radical Intermediates ◽  
Ligand Modification ◽  
Catalytic Application ◽  
Square Planar ◽  
Carbene Transfer ◽  
Cyclic Compounds ◽  
Catalytic Cycles ◽  
Iodonium Ylides

Abstract Square-planar cobalt(II)-systems have emerged as powerful carbene transfer catalysts for the synthesis of numerous (hetero)cyclic compounds via cobalt(III)-carbene radical intermediates. Spectroscopic detection and characterization of reactive carbene radical intermediates is limited to a few scattered experiments, centering around mono-substituted carbenes. Here, we reveal the unique formation of disubstituted cobalt(III)-carbene radicals derived from a cobalt(II)-porphyrin complex and acceptor–acceptor λ3-iodaneylidenes (iodonium ylides) as carbene precursors and their catalytic application. Particularly noteworthy is the fact that iodonium ylides generate novel bis-carbenoid species via reversible ligand modification of the paramagnetic [Co(TPP)]-catalyst. Two interconnected catalytic cycles are involved in the overall mechanism, with a mono-carbene radical and an unprecedented N-enolate-carbene radical intermediate at the heart of each respective cycle. Notably, N-enolate formation is not a deactivation pathway, and both the N-enolate and carbene radical moieties can be transferred to styrene. The findings are supported by extensive experimental and computational studies.

Electrochemical and spectroscopic characterization of a dicobalt macrocyclic Pacman complex in the catalysis of the oxygen reduction reaction in acid media

2013 ◽  
Vol 17 (04) ◽  
pp. 252-258 ◽  
Author(s):  
Qinggang He ◽  
Xiao Cheng ◽  
Ying Wang ◽  
Ruimin Qiao ◽  
Wanli Yang ◽  
...  
Keyword(s):  
Oxygen Reduction Reaction ◽  
Oxygen Reduction ◽  
Reaction Pathway ◽  
Spectroscopic Characterization ◽  
Reduction Reaction ◽  
Acid Media ◽  
Crystal Fields ◽  
Mononuclear Cobalt ◽  
X Ray Absorption

The dicobalt complex [ Co2(L2) ] of a Schiff-base pyrrole macrocycle adopts a Pacman structure in solution and the solid state and shows much greater catalytic activity and selectivity for the four-electron oxygen reduction reaction (ORR) than the mononuclear cobalt phthalocyanine (CoPc) counterpart. Soft X-ray absorption spectroscopy (XAS) shows that the Co center in Co2(L2) is of the same valence as mononuclear CoPc . However, the former complex shows higher unoccupied Co 3d density which is believed to be beneficial for electron transfers. Furthermore, the XAS data suggests that the crystal fields for Co2(L2) and CoPc are different, and that an interaction remains between two Co atoms in Co2(L2) . DFT calculations imply that the sterically hindered, cofacial structure of the dicobalt complex is critical for the operation of the four-electron reaction pathway during the ORR.

Spectroscopic characterization of a Ni-organic radical intermediate in the aerobic oxidation of methanol catalyzed by a Ni(II)(polyoximate) complex

2008 ◽  
Vol 361 (4) ◽  
pp. 947-955 ◽  
Author(s):  
Sara E. Edison ◽  
Sean D. Conklin ◽  
Necati Kaval ◽  
Lionel E. Cheruzel ◽  
Jeanette A. Krause ◽  
...  
Keyword(s):  
Aerobic Oxidation ◽  
Spectroscopic Characterization ◽  
Organic Radical ◽  
Radical Intermediate ◽  
Oxidation Of Methanol

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

NMR Spectroscopic Characterization of a β-(1,4)-Glycosidase along Its Reaction Pathway:  Stabilization upon Formation of the Glycosyl−Enzyme Intermediate†

Biochemistry ◽  
2007 ◽  
Vol 46 (7) ◽  
pp. 1759-1770 ◽  
Author(s):  
David K. Y. Poon ◽  
Martin L. Ludwiczek ◽  
Mario Schubert ◽  
Emily M. Kwan ◽  
Stephen G. Withers ◽  
...  
Keyword(s):  
Reaction Pathway ◽  
Spectroscopic Characterization ◽  
Enzyme Intermediate

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.

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