Structural fluctuation of disilanyl double-pillared bisheteroarenes.

Silacyclophanes possessing two disilanyl pillars were synthesized from tricyclic heteroarenes in one-pot synthetic procedures. The step-like anti structures of three congeners bearing two heteroarene units were revealed in single crystals by X-ray crystallographic analysis. Depending on the structures of aromatic units, torsion angles at the disilanyl pillars altered to maintain the overall step-like molecular structures. The structure, however, fluctuated between anti and syn conformers in a solution phase despite the presence of eight methyl groups on the ring periphery. The analysis of the coalescence temperature with NMR spectroscopy showed the fundamental energetics of the dynamics. The subtle structural differences affected the dynamic behavior of the silacyclophanes.