Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 134, Issue 30, Pages 12693-12699Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja304067k
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Funding
- U.S. Army Research Laboratory [W911NF-09-1-0446]
- National Science Foundation [CHE-0645563]
- Robert A. Welch Foundation [F-1621]
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A 4,5-dithienylimidazolium salt was found to undergo electrocyclic isomerization upon exposure to UV radiation (lambda(irr) = 313 nm) under neutral and basic conditions; subsequent exposure to visible light reversed the reaction. Under ambient light and in the presence of base, the imidazolium species catalyzed transesterifications as well as amidations in a manner similar to those of previously reported N-heterocyclic carbene precatalysts. However, upon UV irradiation to effect the aforementioned photocyclization, the rate of the transesterification reaction between vinyl acetate and allyl alcohol was significantly attenuated (k(vis/UV) = 12.5), as was the rate of the condensation of ethyl acetate with aminoethanol (k(vis/UV) = 100). The rates of these reactions were successfully toggled between fast and slow states by alternating exposure to visible and UV light, respectively, thus demonstrating a rare example of a photoswitchable catalyst that operates via photomodulation of its electronic structure.
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