Synthesis and structural characterisation of bulky heptaaromatic (hetero)arylo-substituteds-aryltetrazines

An expedient two-step synthesis produces in good yield polyaromatic heptacyclic (hetero)arylatedo-substituteds-aryltetrazines (s-Tz) directly from diphenyls-tetrazine. This methodology overcomes the steric limitations of classical Pinner-like syntheses encountered foro-functionalizeds-Tz. A single step palladium-catalyzedN-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 withR-functionalized peripheral phenyl derivatives [R=p-t-Bu (4), andm-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 pi MIDLINE HORIZONTAL ELLIPSIS pi 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-HMIDLINE HORIZONTAL ELLIPSISN short contacts (or C-HMIDLINE HORIZONTAL ELLIPSISO 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.