Crystal Structures of Tetramesityl‐Substituted Tetracyclopenta[def,jkl,pqr,vwx]tetraphenylene

Abstract

Crystal structures of tetramesityl-substituted tetracyclopenta [def,jkl,pqr,vwx]tetraphenylene (TCPTP) derivative were determined for crystals containing different solvents, CHCl 3 , CH 2 Cl 2 , acetone, and benzene at different temperatures to discuss the conjugation modes in the antiaromatic system, i. e., whether it adopts a D 2h structure consisting of local aromatic sextets and quinodimethane substructures or a D 4h double annulenenoid structure. The structures of the TCPTP core in all crystals determined at 113 K or 93 K resemble those of the theoretical D 2h geometry, whereas the bond lengths at room temperature (293 K) adopt averaged values of the theoretical D 2h and D 4h geometries. These results are interpreted in terms of disorder of two perpendicularly oriented D 2h structures at room temperature and support the theoretical prediction which favours the D 2h geometry. The slightly different bond length distributions in the crystals are ascribed to the different space in the vicinity of the molecule which allows the molecule to adopt the two orientations in different occupancies.

Synthesis and Characterization of Dibenzothieno[a,f]pentalenes Enabling Large Antiaromaticity and Moderate Open-Shell Character through a Small Energy Barrier for Bond-Shift Valence Tautomerization

“…Therefore, a dynamic disorder between the two equivalent C s structures through the bond-shift valence tautomerization in the crystals of 6b should be most reasonable in the thermally averaged geometry of molecule B owing to an energy barrier small enough to reach a thermal equilibrium during the X-ray data collection. Although similar temperature-dependent structural variations were observed in some antiaromatic molecules, such as tetra- tert -butylcyclobutadiene and tetramesityl-substituted tetracyclopenta­[ def , jkl , pqr , vwx ]­tetraphenylene, determining the factor of averaging the structure has been controversial, whether static or dynamic disorder exists between two equivalent low-symmetric structures. In 6b , considering the identity of the observed C s -geometry of molecule B at 93 K with the theoretically optimized structure, the possibility of a static disorder is minimal.…”

“…On the other hand, for planar polycyclic antiaromatic systems, experimental understanding of the structure–property relationship derived from the PJTE is still in its infancy. It remains a considerable challenge due to the lack of a suitable molecular model to control the energy barrier given by PJTE. ,− …”

Tuning (Anti)Aromaticity: Variations on the [8]‐Circulene Framework

“…The aromatic signature of hetero [8]circulenes in particular has been investigated with a variety of computational models (HOMA, NICS, GIMIC, ACID). [1,[12][13][14][15][16] Previous models have indicated underlying aromatic/anti-aromatic signatures, but point-wise sampling methods, such as NICS (1), are known not to be adequate for understanding the detail and variability of currents in extended systems such as TO [8]C and its homologues. [13] A more fruitful approach is demonstrated by other work [17] in which current maps for neutral TO [8]C, and their origins in specific transitions were studied.…”

“…Aromaticity of polycyclic heteroatom‐doped systems challenges concepts based on monocyclic systems. The aromatic signature of hetero[8]circulenes in particular has been investigated with a variety of computational models (HOMA, NICS, GIMIC, ACID) [1,12–16] . Previous models have indicated underlying aromatic/anti‐aromatic signatures, but point‐wise sampling methods, such as NICS(1), are known not to be adequate for understanding the detail and variability of currents in extended systems such as TO[8]C and its homologues [13] .…”