Substituent effects on homolytic versus heterolytic photocleavage of (1-naphthylmethyl)trimethylammonium chlorides

1987 ◽  
Vol 65 (7) ◽  
pp. 1599-1607 ◽  
Author(s):  
B. Foster ◽  
B. Gaillard ◽  
N. Mathur ◽  
A. L. Pincock ◽  
J. A. Pincock ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Charge Distribution ◽  
Rate Constants ◽  
Bond Cleavage ◽  
Substituent Effects ◽  
Hydrogen Atom Transfer ◽  
Singlet Excited State ◽  
State Rate

Singlet excited state rate constants have been measured for both the heterolytic and homolytic photocleavage of 3- and 4-methoxy and 3- and 4-cyano (1-naphthylmethyl)trimethylammonium chlorides, 6–10. The results are interpreted in terms of the meta effect or changes in charge distribution upon excitation and the competition between bond cleavage, electron transfer, and hydrogen atom transfer in the contact pairs resulting from the two types of cleavage.

scholarly journals Light-driven deracemization enabled by excited-state electron transfer

Science ◽  
2019 ◽  
Vol 366 (6463) ◽  
pp. 364-369 ◽  
Author(s):  
Nick Y. Shin ◽  
Jonathan M. Ryss ◽  
Xin Zhang ◽  
Scott J. Miller ◽  
Robert R. Knowles
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Visible Light ◽  
Asymmetric Synthesis ◽  
Hydrogen Atom Transfer ◽  
Product Distributions ◽  
Reaction Proceeds ◽  
Molecular Catalysts ◽  
Distinct Approach

Deracemization is an attractive strategy for asymmetric synthesis, but intrinsic energetic challenges have limited its development. Here, we report a deracemization method in which amine derivatives undergo spontaneous optical enrichment upon exposure to visible light in the presence of three distinct molecular catalysts. Initiated by an excited-state iridium chromophore, this reaction proceeds through a sequence of favorable electron, proton, and hydrogen-atom transfer steps that serve to break and reform a stereogenic C–H bond. The enantioselectivity in these reactions is jointly determined by two independent stereoselective steps that occur in sequence within the catalytic cycle, giving rise to a composite selectivity that is higher than that of either step individually. These reactions represent a distinct approach to creating out-of-equilibrium product distributions between substrate enantiomers using excited-state redox events.

Light-Driven Deracemization Enabled by Excited-State Electron Transfer

2019 ◽  
Author(s):  
Nick Shin ◽  
Jonathan Ryss ◽  
Xin Zhang ◽  
Scott Miller ◽  
Robert Knowles
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Visible Light ◽  
Hydrogen Atom Transfer ◽  
Catalytic Cycle ◽  
Product Distributions ◽  
Reaction Proceeds ◽  
New Strategy ◽  
Molecular Catalysts

A new strategy for catalytic deracemization is presented, wherein amine derivatives undergo spontaneous optical enrichment upon exposure to visible light in the presence of three distinct molecular catalysts. Initiated by an excited-state iridium chromophore, this reaction proceeds <i>via </i>a sequence of favorable electron, proton, and hydrogen atom transfer steps that serve to break and reform a stereogenic C–H bond. The enantioselectivity in these reactions is jointly determined by two independent stereoselective steps that occur in sequence within the catalytic cycle, giving rise to a composite selectivity that is higher than that of either step individually. These reactions represent a distinct and potentially general approach to creating out-of-equilibrium product distributions between substrate enantiomers using excited-state redox events.

scholarly journals Reactivity of hydropersulfides toward the hydroxyl radical unraveled: disulfide bond cleavage, hydrogen atom transfer, and proton-coupled electron transfer

2018 ◽  
Vol 20 (7) ◽  
pp. 4793-4804 ◽  
Author(s):  
Josep M. Anglada ◽  
Ramon Crehuet ◽  
Sarju Adhikari ◽  
Joseph S. Francisco ◽  
Yu Xia
Keyword(s):  
Electron Transfer ◽  
Hydrogen Atom ◽  
Hydroxyl Radical ◽  
Disulfide Bond ◽  
Bond Cleavage ◽  
Hydrogen Abstraction ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Oh Radical ◽  
Proton Coupled Electron Transfer

Hydropersulfides (RSSH) are highly reactive towards OH radical, and depending on the nature of R substitute, a selective OH substitution with S–S bond cleavage competes with the hydrogen abstraction by the radical.

scholarly journals Evaluation of excited state bond weakening for ammonia synthesis from a manganese nitride: stepwise proton coupled electron transfer is preferred over hydrogen atom transfer

2019 ◽  
Vol 55 (39) ◽  
pp. 5595-5598 ◽  
Author(s):  
Florian Loose ◽  
Dian Wang ◽  
Lei Tian ◽  
Gregory D. Scholes ◽  
Robert R. Knowles ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Visible Light ◽  
Driving Force ◽  
Ammonia Synthesis ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Proton Coupled Electron Transfer ◽  
Manganese Nitride

Concepts for the thermodynamically challenging synthesis of weak N–H bonds by photoinduced proton coupled electron transfer are explored. By harvesting visible light as driving force, ammonia synthesis was achieved and mechanistically elucidated.

Light-Driven Deracemization Enabled by Excited-State Electron Transfer

2019 ◽  
Author(s):  
Nick Shin ◽  
Jonathan Ryss ◽  
Xin Zhang ◽  
Scott Miller ◽  
Robert Knowles
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Visible Light ◽  
Hydrogen Atom Transfer ◽  
Catalytic Cycle ◽  
Product Distributions ◽  
Reaction Proceeds ◽  
New Strategy ◽  
Molecular Catalysts

A new strategy for catalytic deracemization is presented, wherein amine derivatives undergo spontaneous optical enrichment upon exposure to visible light in the presence of three distinct molecular catalysts. Initiated by an excited-state iridium chromophore, this reaction proceeds <i>via </i>a sequence of favorable electron, proton, and hydrogen atom transfer steps that serve to break and reform a stereogenic C–H bond. The enantioselectivity in these reactions is jointly determined by two independent stereoselective steps that occur in sequence within the catalytic cycle, giving rise to a composite selectivity that is higher than that of either step individually. These reactions represent a distinct and potentially general approach to creating out-of-equilibrium product distributions between substrate enantiomers using excited-state redox events.

Photo-induced proton coupled electron transfer from a benzophenone ‘antenna’ to an isoindoline nitroxide

RSC Advances ◽  
2015 ◽  
Vol 5 (116) ◽  
pp. 95598-95603 ◽  
Author(s):  
Jason C. Morris ◽  
Liam A. Walsh ◽  
Brunell A. Gomes ◽  
Didier Gigmes ◽  
Kathryn E. Fairfull-Smith ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Energy Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Transfer Process ◽  
Energy Transfer Process ◽  
Hydrogen Atom Transfer ◽  
Atom Transfer ◽  
Proton Coupled Electron Transfer

When exposed to light, a novel nitroxide-benzophenone hybrid will undergo an energy transfer process whereby the nitroxide enters an excited state which induces an efficient hydrogen atom transfer from unactivated alkanes.

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