Synthesis and structural characterisation of bulky heptaaromatic (hetero)aryl o -substituted s -aryltetrazines

• Published in: New journal of chemistry Vol. 44; no. 35; pp. 15235 - 15243
• Main Authors: Mboyi, Clève D., Daher, Ahmad, Khirzada, Neelab, Devillers, Charles H., Cattey, Hélène, Fleurat-Lessard, Paul, Roger, Julien, Hierso, Jean-Cyrille
• Format: Journal Article
• Language: English
• Published: Cambridge Royal Society of Chemistry 01.01.2020; Royal Society of Chemistry [1987-....]
• Subjects: Aromatic compounds; Bonding strength; Chemical reactions; Chemical Sciences; Coupling (molecular); Cross coupling; Crystal structure; Crystallography; Electrons; Hydrogen bonding; Hydrogen bonds; Molecular interactions; Nitrogen; NMR; Nuclear magnetic resonance; Organic chemistry; Palladium; Single crystals; Stacking; Substitutes; Synthesis
• ISSN: 1144-0546; 1369-9261
• DOI: 10.1039/D0NJ02338H

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.