Fifty Years of π‐Conjugated Triaz­enes

Abstract

This microreview describes synthetic methodologies, properties, and applications of π‐conjugated triazenes, derived from coupling of different N‐heterocyclic carbenes (NHCs), following reactions with diverse azides. Recently, promising results have been achieved by utilizing such triazenes in a variety of important organic transformations. These early accomplishments clearly emphasize the great potential of utilizing π‐conjugated triazenes in diverse fields of research. Specifically, synthesis of new organic molecules containing N‐heterocycles and azide moieties for applications into organic chemistry and material science are highlighted herein. In summary, this microreview encompasses fifty years of π‐conjugated triazenes (1965–2015) chemistry.

New Insights in Frustrated Lewis Pair Chemistry with Azides

“…[4,5] Organic azides are common organic molecules and are key buildingb locks in, for example, the Staudingerr eaction, which is the reaction of ap hosphine with an azide to form ap hosphazene after elimination of dinitrogen. [6] Interestingly,t he reaction between N-heterocyclic carbenes (NHCs) and azideso ffers the opportunity to trap reaction intermediates by an "interrupted Staudinger" reaction [7,8] forming the stabilized triazene moiety A (Figure 1) [9,10] that can be functionalized and gives access to highly colored donor-acceptor materials (B), which may find new applicationsi nn onlinear optics. [11] The analogous reaction with TMSÀN 3 (TMS:S iMe 3 ) leads to the facile eliminationo fd initrogen and formationo f the imidazolidin-2-imine derivative C,w hich can be viewed as aN HC-nitrene adduct.…”

π‐Conjugated Triazenes and Nitriles: Simple Photoinduced Synthesis of Anilides Using Mild and Metal‐Free Conditions

“…On the other hand, aromatic nitriles resulted in modest yields (i. e., 4 x 41%, 4 y 44%, and 4 aa 31%) to only traces (e. g., 4 ae ). These results can be rationalized by the lower nucleophilicity of aryl vs alkyl nitriles due to electron delocalization over the aromatic system . Nonetheless, it is also worth mentioning that in contrast to the experiments performed in benzonitrile as the solvent ( 4 x and 4 y ), the solids p ‐nitrobenzonitrile, p ‐(trifluoromethyl)benzonitrile, and anisonitrile were dissolved in 2 mL of dichloromethane (DCM) and subjected to the same reaction conditions (Scheme ).…”

“…These results can be rationalized by the lower nucleophilicity of aryl vs alkyl nitriles due to electron delocalization over the aromatic system. [27] Nonetheless, it is also worth mentioning that in contrast to the experiments performed in benzonitrile as the solvent (4 x and 4 y), the solids p-nitrobenzonitrile, p-(trifluoromethyl)benzonitrile, and anisonitrile were dissolved in 2 mL of dichloromethane (DCM) and subjected to the same reaction conditions (Scheme 4). Importantly, it was observed that the electron-rich anisonitrile was a suitable reagent to produce the expected adduct (4 aa) in 31%, due to its higher nucleophilicity.…”

Methylene: The Linker of Two Aromatic Iminium Salts

“…In 2014, our laboratory reported a straightforward method for the synthesis of nitrogen-enriched p-conjugated triazenes [6,7], (Fig.1). Due to the current scientific interest and known applications of p-conjugated triazenes, a review on the subject appeared in the literature in 2015 [8]. Figure 1 also shows two molecules with similar chemical structures that were reported last year and voted as top molecules of the year, due to their unique electronic and structure properties [9,10].…”