Tribenzotriquinacene Fused Dimers ("Fusodimers")-Synthesis and Host-Guest Properties

The synthesis and structural properties of two stereoisomeric tribenzotriquinacene (TBTQ) derivatives, syn-4 and anti-4, in which two rigid TBTQ bowls share a common benzene ring, are described. Owing to the orthogonal orientation of the three indane wings in each of the TBTQ units, four veratrole rings point either at right angles or parallel into the 3-space. In contrast to the convex-concave anti-isomer, the biconcave fusodimer syn-4 was found to host C₆₀ and C₇₀ fullerenes as 1:1 complexes both in solution and in the solid state, as shown by ¹H NMR spectroscopy and x-ray crystallography. Complexation-induced chemical shift (CIS) measurements gave similar binding constants, K_a = 382 (± 4) for syn-4⊂C₆₀ and K_a = 410 (± 8) M^{- 1} for syn-4⊂C₇₀. Structural details of the torsion and widening of the formally C_2v-symmetric host skeleton upon embedding of the fullerenes into the deep biconcave molecular surface of syn-4 were determined along with intermolecular peculiarities of the solid-state complexes.