Reactivity of a σ,σ,σ,σ-Tetraradical: The 2,4,6-Tridehydropyridine Radical Cation

Abstract

The 2,4,6-tridehydropyridine radical cation, an analogue of the elusive 1,2,3,5-tetradehydrobenzene, was generated in the gas phase and its reactivity examined. Surprisingly, the tetraradical was found not to undergo radical reactions. This behavior is rationalized by resonance structures hindering fast radical reactions. This makes the cation highly electrophilic, and it rapidly reacts with many nucleophiles by quenching the N-C ortho-benzyne moiety, thereby generating a relatively unreactive meta-benzyne analogue.

Spin–Spin Coupling Between Two meta‐Benzyne Moieties In a Quinolinium Tetraradical Cation Increases Their Reactivities

“…The analogous tri‐ and tetraradicals containing meta ‐benzyne moieties should be even more interesting due to their complex electronic structures, which have inspired some theoretical studies on the triradicals . However, due to extreme difficulties in studying these species experimentally, the reactivity of only three such triradicals (2,4,6‐tridehydro‐, 3‐hydroxy‐2,4,6‐tridehydro‐, and 3‐cyano‐2,4,6‐tridehydropyridinium cations) and one tetraradical (2,4,6‐tridehydropyridine radical cation) has been studied thus far and only in the gas phase . Unlike the triradicals, the tetraradical was found not to undergo radical reactions .…”

“…However, due to extreme difficulties in studying these species experimentally, the reactivity of only three such triradicals (2,4,6‐tridehydro‐, 3‐hydroxy‐2,4,6‐tridehydro‐, and 3‐cyano‐2,4,6‐tridehydropyridinium cations) and one tetraradical (2,4,6‐tridehydropyridine radical cation) has been studied thus far and only in the gas phase . Unlike the triradicals, the tetraradical was found not to undergo radical reactions . Due to resonance, this tetraradical is best described as a highly electrophilic carbocation with a delocalized, and therefore unreactive, meta ‐benzyne moiety.…”

Properties and Reactivity of Gaseous Distonic Radical Ions with Aryl Radical Sites

“…314 The reactivity of 93 and 95 indicates the presence of three radical sites as they abstract an iodine atom and HI from allyl iodide molecules. The main reactions observed for 93 and 95 with cyclohexane, allyl iodide and dimethyl disulfide were hydride abstraction, C 3 H 5 group abstraction and electron transfer, respectively.…”

“…311–314 However, the reported reactivity studies are limited only to five different tridehydropyridinium cations. 311–314 This limited amount of data may not be sufficient to make definite conclusions on what factors control the reactivity of these reactive species. However, possible reactivity controlling factors are discussed below.…”

“…The first reactivity study on such a tetraradical, the 1,2,4,6-tetradehydropyridinium cation 102 (Chart 11; a derivative of benzdiyne 101 ), was reported recently. 314 Tetraradical 102 was generated in a dual-cell FT-ICR mass spectrometer by using previously described methodology, as shown in Scheme 32. 330 The precursor, 2,4,6- triiodopyridine, 311 was introduced into the mass spectrometer and chemically ionized with ionized deuterated acetone to form a deuterated precursor cation.…”