Benzo-fused Tri[8]annulenes as Molecular Models of Cubic Graphite

Cyclotrimerization of 9,10-dibromo-9,10-dihydrodibenzo[3,4:7,8]cycloocta[1,2-l]phenanthrene with potassium tert-butoxide in the presence of a transition-metal catalyst afforded two polycyclic aromatic hydrocarbon stereoisomers consisting of three cyclooctatetraene (COT) moieties connected via a central benzene ring. Both isomeric tri[8]annulenes were obtained selectively through the choice of the catalyst: The alpha,alpha,alpha-form (Ru catalyst) displayed a threefold symmetrywith the COT subunits forming the side walls of a (chiral) molecular cup. In the thermodynamically more stable alpha,alpha,beta-isomer (Pd catalyst), one of the three boat-shaped COTs was flipped over and faced the opposite molecular hemisphere with respect to the central benzene ring as evidenced by crystal structure analysis. Both title compounds are small segments of cubic graphite, an elusive carbon allotrope.

Automated summary

The cyclotrimerization of 9,10-dibromo-9,10-dihydrodibenzo[3,4:7,8]cycloocta[1,2-l]phenanthrene with potassium tert-butoxide in the presence of a transition-metal catalyst yielded two polycyclic aromatic hydrocarbon stereoisomers consisting of three cyclooctatetraene (COT) moieties connected via a central benzene ring. The isomers were selectively obtained through the choice of catalyst, with the Ru catalyst displaying threefold symmetry and the Pd catalyst showing thermodynamic stability. The resulting compounds are small segments of cubic graphite, an elusive carbon allotrope.