Multimodal Reactivity of N–H Bonds in Triazanes and Isolation of a Triazinyl Radical

Abstract

The employment of nitrogen Lewis acids based on nitrenium cations has been increasingly featured in the fields of main group chemistry and catalysis. A formally reduced form of nitrenium D�cyclic triazanes E�are intriguing chemical compounds, the chemistry of which is completely unexplored. In this work, we reveal that N−H-triazanes exhibit unusual N−H bond properties; namely, they can serve as protons, hydrides, or hydrogen atom donors. This unique multimodal reactivity provides an N-cation, N-anion, or N-radical from the same species. It allowed us to isolate, for the first time, a stable naphto[1,2,3]triazinyl radical, which was fully characterized both computationally and experimentally, including its monomeric X-ray structure. Moreover, this radical can be prepared directly from the nitrenium cation by a single electron reduction (E = −0.46 V), and this process is reversible. We envision versatile uses of this radical in synthetic and materials chemistry.

Nitrenium ions as new versatile reagents for electrophilic amination

“…These unique properties of NHNs allowed us and others to demonstrate that NHNs can act as nitrogen-based Lewis acids, [29][30][31][32][33] activators of strong bonds through frustrated Lewis pair chemistry, 30,34 catalytic Lewis acids for several reactions, [35][36][37][38] photocatalysts [39][40][41] and a platform for stable nitrogen-based radicals. 42,43 Exploring this Lewis acidity, we previously demonstrated that NHN 1 reacts with phenyllithium or n-butyllithium to furnish cyclic triazanes 2 (Scheme 2b). 29 While such triazanes possess an unusual molecular structure bearing three saturated nitrogen atoms in row, their intriguing chemistry is previously unexplored.…”

“…These unique properties of NHNs allowed us and others to demonstrate that NHNs can act as nitrogen-based Lewis acids, 29–33 activators of strong bonds through frustrated Lewis pair chemistry, 30,34 catalytic Lewis acids for several reactions, 35–38 photocatalysts 39–41 and a platform for stable nitrogen-based radicals. 42,43…”

N-heterocyclic nitrenium charge transfer catalysis via inner-sphere electron transfer in concert with halogen-atom dissociation

“…Recent studies have demonstrated the effectiveness of NHNs as Lewis acid catalysts to activate lone-pair donor substrates. 4 We recently discovered that NHN salts could form a photoactive CTC with its counteranion or additional Lewis base. 5 Specifically, upon visible light irradiation, the formed CTC could undergo charge transfer to generate inaccessible neutral NHN aminyl radical species.…”

N-2,6-Di(isopropyl)phenyl-2-azaphenalenyl radical cations

“…Because the intriguing properties of 1 can be modulated by the functionalization of heteroatoms, the incorporation of nitrogen atoms into phenalenyls is also well-documented. 5 Among four monoazaphenalenyls, 2-azaphenalenyl 2 alone is known as an isoelectronic radical species of 1 . 6 Although the spin distribution of 2 is characterized by an electron spin resonance (ESR) spectrum in solution, little is known about its structural and electronic properties because of its high reactivity.…”