scholarly journals N-Arylphenothiazines as strong donors for photoredox catalysis – pushing the frontiers of nucleophilic addition of alcohols to alkenes

2019 ◽  
Vol 15 ◽  
pp. 52-59 ◽  
Author(s):  
Fabienne Speck ◽  
David Rombach ◽  
Hans-Achim Wagenknecht
Keyword(s):  
Excited State ◽  
Nucleophilic Addition ◽  
Reduction Potential ◽  
Phenyl Group ◽  
Addition Product ◽  
Electrochemical Characteristics ◽  
Photoredox Catalysis ◽  
Reaction Conditions ◽  
State Reduction ◽  
Reducing Properties

A new range of N-phenylphenothiazine derivatives was synthesized as potential photoredox catalysts to broaden the substrate scope for the nucleophilic addition of methanol to styrenes through photoredox catalysis. These N-phenylphenothiazines differ by their electron-donating and electron-withdrawing substituents at the phenyl group, covering both, σ and π-type groups, in order to modulate their absorbance and electrochemical characteristics. Among the synthesized compounds, alkylaminylated N-phenylphenothiazines were identified to be highly suitable for photoredox catalysis. The dialkylamino substituents of these N-phenylphenothiazines shift the estimated excited state reduction potential up to −3.0 V (vs SCE). These highly reducing properties allow the addition of methanol to α-methylstyrene as less-activated substrate for this type of reaction. Without the help of an additive, the reaction conditions were optimized to achieve a quantitative yield for the Markovnivkov-type addition product after 20 h of irradiation.

scholarly journals Hydricity, electrochemistry, and excited-state chemistry of Ir complexes for CO2 reduction

2017 ◽  
Vol 198 ◽  
pp. 301-317 ◽  
Author(s):  
Gerald F. Manbeck ◽  
Komal Garg ◽  
Tomoe Shimoda ◽  
David J. Szalda ◽  
Mehmed Z. Ertem ◽  
...  
Keyword(s):  
Excited State ◽  
Dft Calculations ◽  
Density Functional ◽  
Reduction Potential ◽  
Co2 Reduction ◽  
Theoretical Data ◽  
Functional Theory ◽  
State Reduction ◽  
State Potential ◽  
Derivatives Of

We prepared electron-rich derivatives of [Ir(tpy)(ppy)Cl]+ with modification of the bidentate (ppy) or tridentate (tpy) ligands in an attempt to increase the reactivity for CO2 reduction and the ability to transfer hydrides (hydricity). Density functional theory (DFT) calculations reveal that complexes with dimethyl-substituted ppy have similar hydricities to the non-substituted parent complex, and photocatalytic CO2 reduction studies show selective CO formation. Substitution of tpy by bis(benzimidazole)-phenyl or -pyridine (L3 and L4, respectively) induces changes in the physical properties that are much more pronounced than from the addition of methyl groups to ppy. Theoretical data predict [Ir(L3)(ppy)(H)] as the strongest hydride donor among complexes studied in this work, but [Ir(L3)(ppy)(NCCH3)]+ cannot be reduced photochemically because the excited state reduction potential is only 0.52 V due to the negative ground state potential of −1.91 V. The excited state of [Ir(L4)(ppy)(NCCH3)]2+ is the strongest oxidant among complexes studied in this work and the singly-reduced species is formed readily upon photolysis in the presence of tertiary amines. Both [Ir(L3)(ppy)(NCCH3)]+ and [Ir(L4)(ppy)(NCCH3)]2+ exhibit electrocatalytic current for CO2 reduction. While a significantly greater overpotential is needed for the L3 complex, a small amount of formate (5–10%) generation in addition to CO was observed as predicted by the DFT calculations.

Spin-Forbidden Excitation Enables Infrared Photoredox Catalysis

2020 ◽  
Author(s):  
Tomislav Rovis ◽  
Benjamin D. Ravetz ◽  
Nicholas E. S. Tay ◽  
Candice Joe ◽  
Melda Sezen-Edmonds ◽  
...  
Keyword(s):  
Excited State ◽  
Ground State ◽  
Intersystem Crossing ◽  
Photoredox Catalysis ◽  
Infrared Irradiation ◽  
Triplet Excitation ◽  
New Family ◽  
Ir Light

We describe a new family of catalysts that undergo direct ground state singlet to excited state triplet excitation with IR light, leading to photoredox catalysis without the energy waste associated with intersystem crossing. The finding allows a mole scale reaction in batch using infrared irradiation.

Synthesis of 4-arylethyl-6-arylpyrimidine-2-thiols through aza-Michael addition/nucleophilic addition/aromatization tandem reactions

2018 ◽  
Vol 24 (1) ◽  
pp. 23-26
Author(s):  
Zheng Li ◽  
Wenli Song ◽  
Jiaojiao He ◽  
Yan Du ◽  
Jingya Yang
Keyword(s):  
Efficient Method ◽  
Michael Addition ◽  
Nucleophilic Addition ◽  
Tandem Reactions ◽  
Reaction Conditions ◽  
High Yields ◽  
Work Up

Abstract An efficient method for the synthesis of the title compounds by reactions of divinyl ketones with thiourea is described. This protocol has the advantages of high yields, mild reaction conditions and simple work-up procedure.

Synthesis of the Novel Thienopyrimidine-Based S-Glycoside Analogues via Nucleophilic Addition/Cyclization/Glycosylation Reactions

2013 ◽  
Vol 781-784 ◽  
pp. 999-1002
Author(s):  
Qiu Hong Dai ◽  
Kun Zou ◽  
Ming Guo Liu ◽  
Lin Luo ◽  
Nian Yu Huang
Keyword(s):  
Elemental Analysis ◽  
Nucleophilic Addition ◽  
The Novel ◽  
Reaction Conditions ◽  
Biological Screening ◽  
Structural Motifs ◽  
Efficient Approach

The title compounds thienopyrimidine-basedS-glycoside analogues were synthesized through the nucleophilic addition/cyclization/glycosylation reactions in good yields from easily accessible starting materials under mild reaction conditions. All of compounds were characterized by NMR, MS, IR and elemental analysis. The efficient approach allowed the facial synthesis of small libraries of thienopyrimidine-basedS-glycoside analogues with different structural motifs for biological screening.

scholarly journals 46 Species-specificity in metmyoglobin reduction

2019 ◽  
Vol 97 (Supplement_1) ◽  
pp. 83-84
Author(s):  
Emily Bechtold ◽  
Surendranath Suman ◽  
Smita Mohanty ◽  
Suman Mazumder ◽  
Sadagopan Krishnan ◽  
...  
Keyword(s):  
Reduction Potential ◽  
Species Specificity ◽  
Oxidation Reduction ◽  
Oxidation Reduction Potential ◽  
Sarcoplasmic Protein ◽  
Reducing Activity ◽  
Mechanistic Basis ◽  
Species Specific ◽  
Reducing Properties

Abstract Myoglobin is the primary sarcoplasmic protein responsible for meat color. Previous research has reported that myoglobin oxidation is species-specific. Metmyoglobin reducing activity is an inherent property to limit myoglobin oxidation. However, limited research has determined species specificity in metmyoglobin reducing properties. The objective of current study was to compare metmyoglobin reducing properties of eight different species such as beef, porcine, bison, deer, emu, equine, goat, and sheep in vitro. Myoglobin was isolated from eight different species via ammonium sulfate precipitation. The pH of the myoglobin was adjusted by passing through a column pre-calibrated with 50 mM phosphate buffer at pH 5.6. All species myoglobin were converted to metmyoglobin, and the metmyoglobin reduction was determined by two different approaches, non-enzymatic metmyoglobin reducing activity (NMRA) and oxidation-reduction potential (ORP). In the first method, NADH (electron donor), EDTA, and methylene blue (electron carrier), were added in a cuvette and increase in absorbance at 582 nm was monitored using a UV-Vis spectrophotometer. In the second method, the ability of the heme to get reduced was determined using an RedoxSys analyzer, in which electron was directly transferred to heme. The NMRA and ORP experiments were replicated five times. The data were analyzed using the Mixed Procedure of SAS, with species as the fixed effect. There were species-specific differences (P < 0.05) in NMRA and ORP. Bovine myoglobin had the greatest (P < 0.05) NMRA compared with sheep, equine, goat, deer, bison, pork, and emu. There were no differences (P > 0.05) in NMRA among equine, goat, deer, bison, pork, and emu. ORP studies indicated that beef and porcine myoglobins had the greatest ability to get reduced (P < 0.05) compared with other species. Hence, use of different techniques and approaches will help to elucidate the mechanistic basis of metmyoglobin reduction.

The influence of phenylethynyl linkers on the photo-physical properties of metal-free porphyrins

2000 ◽  
Vol 04 (07) ◽  
pp. 669-683 ◽  
Author(s):  
GARY A. BAKER ◽  
FRANK V. BRIGHT ◽  
MICHAEL R. DETTY ◽  
SIDDHARTH PANDEY ◽  
COREY E. STILTS ◽  
...  
Keyword(s):  
Excited State ◽  
Radiative Decay ◽  
Phenyl Group ◽  
Quantum Yields ◽  
Fluorescence Lifetimes ◽  
Strongly Coupled ◽  
Metal Free ◽  
Fluorescence Quantum Yields ◽  
Porphyrin Core ◽  
Absorbance Spectra

Series of 5,10,15,20-tetraarylporphyrins 1 and 5,10,15,20-tetrakis[4-(arylethynyl)phenyl]porphyrins 2 were prepared via condensation of pyrrole with the appropriate benzaldehyde or 4-(arylethynyl)benzaldehyde derivative (3). Condensation of meso-phenyldipyrromethane with mixtures of benzaldehyde and 4-(trimethylsilyl-ethynyl)benzaldehyde gave a separable mixture of mono- (6), bis- (both cis-7 and trans-8) and tris[4-(trimethylsilylethynyl)phenyl]porphyrin (9). Following removal of the trimethylsilyl groups of 6–9, the 4-ethynylphenyl groups of 11–14 were coupled to 1-iodo-3,5-di(trifluoromethyl)benzene with Pd ( OAc )2 to give 15–18 bearing one, two (both cis- and trans-) and three 4-[bis-3,5-(trifluoromethyl)phenylethynyl]phenyl groups respectively. Coupling of 11 and 1-iodo-4-nitrobenzene with Pd ( OAc )2 gave porphyrin 19 with one 4-(4-nitrophenylethynyl)phenyl group. Porphyrin 24 with a p-quinone linked to the porphyrin core via a phenylethynyl group was prepared via similar chemistry. The absorbance spectra, emission maxima, excited-state fluorescence lifetimes, quantum yields of fluorescence, rates of fluorescence and rates of non-radiative decay were measured for each of the porphyrins. Absorbance spectra and emission maxima were nearly identical for all the porphyrins of this study, which suggests that the aryl groups and 4-(arylethynyl)phenyl groups are not strongly coupled to the porphyrin core in these metal-free compounds. Fluorescence quantum yields and rates of radiative decay were larger for porphyrins bearing 4-(arylethynyl)phenyl groups, while excited-state fluorescence lifetimes were somewhat shorter. These effects were additive for each additional 4-(arylethynyl)phenyl group.

scholarly journals Photoredox-Catalyzed Intermolecular Radical Addition to Allenamides: A Complementary Approach to Conjugated N-Acyliminium Formation.

2019 ◽  
Author(s):  
Kayode Koleoso ◽  
Matthew Turner ◽  
Felix Plasser ◽  
Marc Kimber
Keyword(s):  
Nucleophilic Addition ◽  
Radical Addition ◽  
Photoredox Catalysis ◽  
Complementary Approach ◽  
Central Carbon ◽  
Electrophilic Activation

<div><div><div><p>An intermolecular radical addition, using photoredox catalysis, to allenamides is reported. This transformation synthesizes <i>N</i>-acyl-<i>N’</i>-aryl-<i>N</i>,<i>N’</i>-allylaminals, and proceeds by a conjugated <i>N</i>-acyliminium intermediate, that previously, has only been generated by electrophilic activation methods. The radical adds to the central carbon of the allene giving a conjugated <i>N</i>-acyliminium, that undergoes nucleophilic addition by arlyamines and alcohols.<b></b></p></div></div></div>

scholarly journals Hole-Mediated PhotoRedox Catalysis: Tris(p-Substituted)biarylaminium Radical Cations as Tunable, Precomplexing and Potent Photooxidants

2020 ◽  
Author(s):  
Shangze Wu ◽  
Jonas Zurauskas ◽  
Michal Domanski ◽  
Patrick Hitzfeld ◽  
Valeria Butera ◽  
...  
Keyword(s):  
Cyclic Voltammetry ◽  
Excited State ◽  
Excited States ◽  
Organic Molecules ◽  
Radical Cations ◽  
Single Electron Transfer ◽  
Photoredox Catalysis ◽  
Small Organic Molecules ◽  
Fundamental Limitations ◽  
Ion Species

<p>Electrochemically-mediated Photoredox Catalysis emerged as a powerful synthetic technique in recent years, overcoming fundamental limitations of electrochemistry and photoredox catalysis in the single electron transfer activation of small organic molecules. However, the mechanism of how photoexcited radical ion species with ultrashort (picosecond-order) lifetimes could ever undergo productive photochemistry has eluded synthetic chemists. We report tri(<i>para</i>-substituted)biarylamines as a tunable class of electroactivated photocatalysts that become superoxidants in their photoexcited states, even able to oxidize molecules (such as dichlorobenzene and trifluorotoluene) beyond the solvent window limits of cyclic voltammetry. Furthermore, we demonstrate that precomplexation not only permits the excited state photochemistry of tris(<i>para</i>-substituted)biarylaminium cations, but enables and rationalizes the surprising photochemistry of their <i>higher-order</i> doublet (D<i><sub>n</sub></i>) excited states.</p>

A study of photocyclization of O-alkyl N-(3-chloro-2-benzo[b]thienocarbonyl)monothiocarbamates

1986 ◽  
Vol 51 (9) ◽  
pp. 2002-2012 ◽  
Author(s):  
Peter Kutschy ◽  
Ján Imrich ◽  
Juraj Bernát ◽  
Pavol Kristian ◽  
Iveta Fedoriková
Keyword(s):  
Excited State ◽  
Complex Formation ◽  
Emission Spectra ◽  
Radical Mechanism ◽  
Singlet Excited State ◽  
Model Compounds ◽  
Reaction Conditions ◽  
Absorption And Emission ◽  
Absorption And Emission Spectra ◽  
High Yields

The O-alkyl N-(3-chloro-2-benzo[b]thienocarbonyl)monothiocarbamates prepared by the reaction of 2-isothiocyanatocarbonyl-3-chlorobenzo[b]thiophene with methanol, ethanol, 1-propanol, and 2-propanol are cyclized on irradiation with light of the wavelength above 300 nm to give high yields (80-90%) of 2-alkoxy-4H-benzo[b]thieno[2,3-e]-1,3-thiazin-4-one derivatives. From the absorption and emission spectra of the starting compounds as well as from a study of model compounds and influence of the reaction conditions it is presumed that the investigated intramolecular photosubstitution of chlorine by sulphur proceeds from the first singlet excited state (π, π*) by a radical mechanism through the phase of radical complex formation.

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