Synthesis, Structures, and Thermal Properties of Symmetric and Janus "Lantern Cage" Siloxanes

Symmetric and asymmetric (Janus-type) new "lantern cage" siloxanes (PhSiO_1.5 )₄ (Me₂ SiO)₄ (RSiO_1.5 )₄ (R=Ph or iBu) were synthesized through reaction of all-cis-[PhSi(OSiMe₂ Br)O]₄ with all-cis-[RSi(OH)O]₄ (R=Ph or iBu). These precursors were obtained by facile two or three-step reactions from commercially available compounds. The spectroscopic properties of the resulting products were fully characterized and they showed high thermal stability and sublimation without decomposition. The crystal structures clearly indicated that the internal vacancy volumes of the lantern cages are considerably larger than that of octaphenylsilsesquioxane (PhSiO_1.5 )₈ . DFT calculations of the lantern cage showed a distinctly different electronic state from that of octasilsesquioxane. These results suggest that lantern cage siloxanes have a characteristic "field" in the molecule.