Large Polyhedral Oligomeric Silsesquioxane Cages: The Isolation of Functionalized POSS with an Unprecedented Si<sub>18</sub>O<sub>27</sub> Core
Mathilde Laird, Niklas J. Herrmann, Naseem A. Ramsahye, Cédric Totée, Carole Carcel, Masafumi Unno, John R. Bartlett, Michel Wong Chi Man
Abstract
Abstract The synthesis of organo‐functionalized polyhedral oligomeric silsesquioxanes (POSS, (R‐SiO 1.5 ) n , T n ) is an area of significant activity. To date, T 14 is the largest such cage synthesized and isolated as a single isomer. Herein, we report an unprecedented, single‐isomer styryl‐functionalized T 18 POSS. Unambiguously identified among nine possible isomers by multinuclear solution NMR ( 1 H, 13 C, and 29 Si), MALDI‐MS, FTIR, and computational studies, this is the largest single‐isomer functionalized T n compound isolated to date. A ring‐strain model was developed to correlate the 29 Si resonances with the number of 6‐, 5‐, and/or 4‐Si‐atom rings that each non‐equivalent Si atom is part of. The model successfully predicts the speciation of non‐equivalent Si atoms in other families of T n compounds, demonstrating its general applicability for assigning 29 Si resonances to Si atoms in cage silsesquioxanes and providing a useful tool for predicting Si‐atom environments.