Synthesis of Azo Dyes from Mesoionic Carbenes and Nitrous Oxide

Abstract

Covalent adducts of imidazole-based mesoionic carbenes and nitrous oxide (N O, "laughing gas") can be converted into azo dyes by reaction with arenes in the presence of AlCl or HCl. The azo coupling can be achieved with electron-rich aromatic compounds such as mesitylene, trimethoxybenzene, azulene, or dibenzo-18-crown-6. The latter coupling reaction allows for the easy preparation of a colorimetric sensor for potassium or sodium ions. As a putative intermediate of the reaction with acid, we were able to isolate and structurally characterize a rare diazohydroxide. Using imidazolium compounds with two N O groups, it was possible to prepare amine-substituted azo dyes or dyes with two azoarene groups attached to the heterocycle. A triazole-based mesoionic carbene was also found to form a stable covalent adduct with N O. The adduct could be used to prepare novel azo triazolium dyes in good yields.

Tuning the π‐Accepting Properties of Mesoionic Carbenes: A Combined Computational and Experimental Study

“…Over the last decade, MICs have been used extensively as ligands for transition and main group metal complexes [3–10] . Furthermore, MICs were employed for small molecule activation, [3–10,13–17] and as metal‐free catalysts for polymerization reactions [3–10,18–20] . The electronic properties of mesoionic imidazolylidenes have been examined experimentally [21–27] and theoretically [28–31] .…”

“…[ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 ] Over the last decade, MICs have been used extensively as ligands for transition and main group metal complexes. [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 ] Furthermore, MICs were employed for small molecule activation,[ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 13 , 14 , 15 , 16 , 17 ] and as metal‐free catalysts for polymerization reactions. [ 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 18 , 19 , 20 ] The electronic properties of mesoionic imidazolylidenes have been examined experimentally[ 21 , 22 , 23 , 24 , 25 , 26 , 27 ] and theoretically.…”

Synthesis of Organic Super-Electron-Donors by Reaction of Nitrous Oxide with N-Heterocyclic Olefins

“…A condensation reaction with remaining NHO then provides the dimers 1-3. Presumably, the condensation reaction is initiated by N-O bond rupture of the diazohydroxide B, 12 forming either a vinyl diazonium compound or a diazoalkene. 13 Scheme 2.…”

“…Analysis of 1 and 3 by single-crystal X-ray crystallography showed that azo-bridged NHO dimers had formed (for details, see the Supporting Information (SI)). The formation of these dimers can be rationalized by assuming that the reactions proceed via zwitterionic NHO–N 2 O adducts of type A (Scheme ), which can tautomerize to the diazohydroxides B . A condensation reaction with remaining NHO then provides the dimers 1 – 3 .…”

Lewis Acid‐Mediated One‐Electron Reduction of Nitrous Oxide

“…Our results suggest that activation of N 2 O by strong Lewis acids holds promise in exploring its utility as an oxidant. Activation by Lewis acids is a much less studied area compared to the nucleophilic activation/fixation of N 2 O,–,, and at the same time bears relevance to the enzymatic reduction of N 2 O …”