Pushing SmI₂ Reactions towards the Limit‐ Entropy Driven Reduction of a Benzene Ring

Abstract

In order to reduce a benzene ring, alkali metals or similar strong reducing agents are needed. We have found that SmI2, which is considered to be a relatively mild reagent, can also perform this task. This is achieved by attaching a side arm of either ethanolamine or ethylenediamine to a benzene ring. These side arms strongly coordinate to SmI2, holding it in close vicinity to the benzene ring. As a result, the probability of electron transfer from the SmI2 to the benzene ring is significantly increased. However, at the same time, this proximity also enhances the rate of the back electron transfer. In order to slow the rate of this step, small amounts of water and Et3N were added to the reaction mixture. The two typical products of the classical Birch reduction of benzene were obtained with a yield as high as 95 %. This method was also applied to the corresponding chlorobenzene and methylbenzoate where the reactions were much enhanced but functionality reduction prevailed over ring reduction. It is remarkable that going from a termolecular to a unimolecular reaction is more effective than excitation of the SmI2 around 600 nm which is equivalent to ca. 47 kcal/mol.

Tools and techniques for solution‐phase structural understanding of SmI2–additive complexes

“…Hoz group demonstrated proximity‐induced reduction of a benzene ring by SmI 2 /water/amine. [ 12 ] In this case, substrate, a benzene ring, functionalized with ethanolamine and ethylene diamine, forms complex with SmI 2 which led to change in absorption spectrum of SmI 2 . It should be mentioned here that there are inner sphere types of electron transfer (in case of any oxygen or nitrogen containing substrates) where substrate does not alter the UV‐visible spectrum of SmI 2 , presumably due to weak SmI 2 –substrate interaction.…”

Samarium Iodide Showcase: Unraveling the Mechanistic Puzzle

“…The efficacy of the proximity effect culminates in the reduction of benzene . The reduction of benzene is usually achieved by using strong reducing agents .…”

“…Visible spectra of SmI 2 as a function of BNO concentration. Reproduced with permission from ref . Copyright 2017 Wiley-VCH.…”

“…21 The efficacy of the proximity effect culminates in the reduction of benzene. 22 The reduction of benzene is usually achieved by using strong reducing agents. 23 In order to position the SmI 2 in the vicinity of the benzene ring, we used bidentate ligands (ethanolamine and ethylenediamine) as side arms on the benzene ring.…”