Visiting Scholars: 2018

Farewell, Sascha Grotjahn and Kilian Mueller! Safe travels back to Regensburg

Uphill Catalysis
Electron Transfer Mediated Cross-Couplings
C-F Functionalization

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Uphill Catalysis

The dogma of catalysis which is that it lowers energy barriers but does not change the thermodynamics of reactions and therefore only thermodynamically favorable reactions need to be considered.  This is absolutely true, but it is not the end of the story.  A necessary prerequisite for this dogma to apply is the principle of microscopic reversibility.  Photochemical excitation promotes a substrate to a high energy surface from which all subsequent steps are thermodynamically downhill and essentially irreversible.  This opens the door to driving reactions in an overall endergonic direction, obtaining high selectivities when there is little energetic difference between isomers, or altering the normal since of a molecules physical properties.  Arguably, this strategy has been largely underappreciated in synthetic chemistry.  We are actively attempting to utilize this strategy to develop useful synthetic chemistry.  For representative publications, see below.


A. Singh, C.J. Fennell andJ. D. Weaver,"Photocatalyst size controls electron and energy transfer: selectable E/Z isomersynthesis via C–F alkenylation" Chem. Sci.,2016, DOI:10.1039/C6SC02422J.

This work contributes to both the photocatalytic C-F functionalizion efforts as well as the photocatalytic uphill isomerization work.  The products of electron transfer lead to a styrenoid that can then undergo photocatalytic isomerization.  In order to be able to control the olefin geometry outcome we needed to better understand the features that control the two mechanistic pathways.  We found that the photocatalyst volume, and not so much its emisive energy, made a dramatic difference in the rate of isomerization.Furthermore, we showed that this was true of other photocatalytic reactions in which energy transfer was involved and even that two types of photocatalysts could be employed simultaneously to accomplish both electron transfer and isomerization to a

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 Singh, K.; Staig, S.; Weaver, J.D. "Facile Synthesis of Z-alkenes via Uphill Catalysis" J. Am. Chem. Soc., 2014, 136, 5275.

In this work we show that catalytic Ir(ppy)3 can be used with visible light to drive the isomerization of trans styrene motifs towards the cis-motif.  We provided mechanistic evidence which suggests that the photocatalyst is acting as a selective sensitizer to the trans-alkene. 

This paper was highlighted as an item of interest in Organic Process Research and Development. Org. Process Res. Dev. 2014, 10.1021/op500154t.  

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