Polyhedral Oligomeric Silsesquioxane (POSS) Chemistry

Polyhedral oligomeric silsesquioxanes (POSS) have long served as more than a hybrid organic-inorganic filler for polymers. Their partially condensed silanol forms present a rigid, oxygen-rich pocket that closely resembles a fragment of amorphous silica, and this pocket is an excellent ligand for metal ions of nearly every part of the periodic table. Single-crystal X-ray diffraction has been the decisive tool for confirming what these metal-POSS assemblies actually look like, since spectroscopic and computational evidence alone can rarely distinguish between competing cage topologies. This review surveys recent crystallographically confirmed metal-POSS complexes, organized by the metal center, and closes with a synthesis of the structural trends that emerge once the diffraction data are compared side by side.

中文版本 / Chinese version: POSS 二氟硼光催化剂：硫醚选择性氧化制亚砜 | 日本語版 / Japanese version: 日本語 The publication titled “Polyhedral oligomeric silsesquioxane difluoroboron complexes as cooperative octo-site catalysts for the photooxidation of sulfides to sulfoxides” by Mateusz Janeta and Sławomir Szafert, published in Inorganic Chemistry Frontiers on April 17, 2025, presents a study on the development of novel metal-free photocatalysts. These catalysts are based on polyhedral oligomeric silsesquioxanes (POSS) functionalized with difluoroboron complexes. Scheme 1. Synthesis of POSS-sal-BF 2 , POSS- tert -BF 2 , and POSS-npht-BF 2 . Isolated yields in parentheses.

The publication titled “Zinc Imine Polyhedral Oligomeric Silsesquioxane as a Quattro-Site Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Low-Pressure CO 2 ” by Mateusz Janeta et al., published in Chemistry – A European Journal in 2020, describes the first structurally characterized polyhedral oligomeric silsesquioxane (POSS) that anchors more than one metal cation through its organic side arms. The tetranuclear zinc imine-POSS complex Zn 4 @POSS-1 converts styrene oxide into styrene carbonate with 96% conversion in four hours at only 1 atm of CO 2 , eliminating the high carbon dioxide pressures that normally accompany this transformation. The four zinc centers act cooperatively rather than independently, and the catalyst tolerates five consecutive runs with conversion falling only from 99% to 90%.

Three studies, one published in Chemical Science in 2017 and two published in Chemistry – A European Journal and Journal of Catalysis in 2015, together define what a single reactive vertex on a silsesquioxane cage makes possible. The first two concern monofunctionalized POSS self-assembly, in which a platinum(II) terpyridine chromophore and a metal-free porphyrin, each carried by one cage, give solvent-switchable nanorings, nanoplates, vesicles and ordered sheets. The third turns the same architecture toward catalysis, where a cage-supported palladium center couples an aryl bromide with phenylboronic acid at a turnover number of 2.5 × 10 4 . Read together, the three papers show that one reactive arm is enough to program both morphology and catalytic behavior.