Synthesis and structural characterisation of bulky heptaaromatic (hetero)aryl o-substituted s-aryltetrazines. (28th August 2020)

• Record Type: Journal Article
• Authors: Mboyi, Clève D.; Daher, Ahmad; Khirzada, Neelab; Devillers, Charles H.; Cattey, Hélène; Fleurat-Lessard, Paul; Roger, Julien; Hierso, Jean-Cyrille
• Is Part Of: New journal of chemistry. Volume 44:Number 35(2020)
• Page Start: 15235
• Page End: 15243
• Publication Date: 2020-08-28
• Subjects: Chemistry -- Periodicals; Chimie -- Périodiques; 540
• DOI: 10.1039/d0nj02338h
• Languages: English
• ISSNs: 1144-0546

Abstract

Abstract : Hexaphenylbenzene analogs with an electron-poor tetrazine core are synthesized in two high-yield steps from diphenyl- s -tetrazine. Crystal packing of these unique non-planar heptaaromatics is analyzed in details. Abstract : An expedient two-step synthesis produces in good yield polyaromatic heptacyclic (hetero)arylated o -substituted s -aryltetrazines ( s -Tz) directly from diphenyl s -tetrazine. This methodology overcomes the steric limitations of classical Pinner-like syntheses encountered for o -functionalized s -Tz. A single step palladium-catalyzed N -directed C–H bond tetrahalogenation is followed by a Pd-catalyzed Suzuki (hetero)arylation that is achieved simultaneously on four sites. The single crystal X-ray diffraction structure of the resulting typical polyaromatic heptacyclic aromatic compound 3, 6-bis(2, 6-diphenyl)-1, 2, 4, 5-tetrazine (3 ) is analyzed, together with R -functionalized peripheral phenyl derivatives [ R = p-t -Bu (4 ), and m -OMe (10 )]. Generally, stacking interactions between aromatic rings can be considerably stronger if electron-depleted rings are combined with electron-rich ones. Thus, electron-poor heteroaromatic aryltetrazines are expected to interact with electron-rich phenyl aromatic rings from reduced π⋯π repulsion, rendering the formation of stacking networks more favorable. Herein, despite the presence of strongly electron-deficient heteroaromatic tetrazine cores, the disruption of planarity between the various aromatic rings involved precludes the expected stacking arrangement. Thus, packing organization is driven by weak hydrogen bonding with C–H⋯N short contacts (or C–H⋯O when possible). These new heptaaromatics, which incorporate for the first time an electron-attracting nitrogen-rich core are easily modifiable from cross-coupling reactions, and constitute a relevant structural and electronical alternative to the well-known and high value class of hexaphenylbenzenes.