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- Title
Reversed Electron Apportionment in Mesolytic Cleavage: The Reduction of Benzyl Halides by SmI<sub>2</sub>.
- Authors
Yitzhaki, Offir; Hoz, Shmaryahu
- Abstract
The paradigm that the cleavage of the radical anion of benzyl halides occurs in such a way that the negative charge ends up on the departing halide leaving behind a benzyl radical is well rooted in chemistry. By studying the kinetics of the reaction of substituted benzylbromides and chlorides with SmI2 in THF it was found that substrates para-substituted with electron-withdrawing groups (CN and CO2Me), which are capable of forming hydrogen bonds with a proton donor and coordinating to samarium cation, react in a reversed electron apportionment mode. Namely, the halide departs as a radical. This conclusion is based on the found convex Hammett plots, element effects, proton donor effects, and the effect of tosylate (OTs) as a leaving group. The latter does not tend to tolerate radical character on the oxygen atom. In the presence of a proton donor, the tolyl derivatives were the sole product, whereas in its absence, the coupling dimer was obtained by a SN2 reaction of the benzyl anion on the neutral substrate. The data also suggest that for the para-CN and CO2Me derivatives in the presence of a proton donor, the first electron transfer is coupled with the proton transfer.
- Subjects
BENZYL halides; SAMARIUM iodide; SCISSION (Chemistry); TRANSITION state theory (Chemistry); CHARGE exchange
- Publication
Chemistry - A European Journal, 2015, Vol 21, Issue 25, p9242
- ISSN
0947-6539
- Publication type
Article
- DOI
10.1002/chem.201500519