Polyhedral Oligomeric Silsesquioxane D_3h-(RSiO_1.5)₁₄

While smaller polyhedral oligomeric silsesquioxanes T_nR_n (POSS) are readily accessible or even commercially available, unambiguously authenticated larger systems (n>12) have barely been reported. Synthesis and isolation procedures are lengthy, and yields are often very low. Herein, we present the surprisingly straightforward and high-yielding access to the phenyl-substituted derivative of a so far only postulated second D_3h-symmetric T₁₄ isomer and with that the largest crystallographically characterized POSS cage with organic substituents. Treatment of the commercially available incompletely condensed T₇Ph₇(OH)₃ silsesquioxane with catalytic amounts of trifluoromethanesulfonic acid results in high yields of the T₁₄Ph₁₄ framework, which is isolated in crystalline form by a simple work-up. D_3h-T₁₄Ph₁₄ was analyzed by single crystal X-ray diffraction, multinuclear NMR spectroscopy and thermal analysis. The relative energies of all four theoretically possible T₁₄Ph₁₄ isomers were determined by optimization of the corresponding structure using DFT methods.