On the reactivity of naphthalene and biphenyl dianions: tying up loose ends concerning an S_N 2-ET dichotomy in alkylation reactions

Abstract

Naphthalene and biphenyl dianions are interesting compounds that can be obtained by double reduction of the corresponding arenes in solution with certain alkali metals. These dianions are highly reactive and rather elusive species with very high laying and highly delocalized electrons. They share many aspects of the reactivity of the alkali metal they originated from and consequently behave primarily as strong electron transfer (ET) reagents. We report here kinetic evidence for a different type of reactivity in their alkylation reactions with alkyl fluorides. By using cyclopropylmethyl fluoride (c‐C3H5CH2F) as a very fast radical probe, we were able to settle that this alkylation does not involve the classical electron transfer reaction followed by radical coupling between diffusing radicals, but supports the alternative SN2 concerted mechanism, discerning thus this mechanistic SN2‐ET dichotomy. Copyright © 2015 John Wiley & Sons, Ltd.

Mechanistic and Synthetic Studies of Biaryl Birch Reductions

“…The alkylation of biphenyl dianion 1 2– (Scheme 4) under ammonia-free conditions proceeds via an S N 2 mechanism. 25 With ammonia, protonated monoanions 4 – (Scheme 4) react with alkyl halides presumably via an S N 2 mechanism as well. The Rabideau group investigated the Birch reduction of methyl-substituted biphenyls and trapped intermediates with MeBr.…”

Seed-mediated synthesis of monodisperse plasmonic magnesium nanoparticles

“…This is due to the formation of a dianion of naphthalene (Li 2 Napht), as obtained by Smid when excess Li reacts with naphthalene in THF. 26 This highly reduced species has a reduction potential 0.2–0.3 eV more negative than the radical anion, 27 and substantially impacts the formation of organoLi compounds with catalytic amounts of arene. 28 However, the role of the dianion in Mg NP synthesis has not been previously described.…”