Synthesis of Silsesquioxane Derivatives via Hydrosilylation of Alkenes and Alkynes Catalyzed by Pt/XAD-4 in Supercritical CO 2

A new heterogeneous platinum catalyst on the styrene–divinylbenzene resin (Pt/XAD-4) was developed for the hydrosilylation of various functional alkenes (2b–f) and alkynes (2a–j) using high-molecular-weight silsesquioxanes (1a–d) and applied in supercritical CO2 (scCO2) as a reaction medium. The obtained Pt/XAD-4 catalyst is competitive to previous Pt heterogeneous systems in these transformations and provides possibilities for effective catalyst reuse. Comparing the processes in scCO2 to commonly used toluene showed that the catalyst was significantly more active and stable upon application of this green solvent. Extraction of the products with scCO2 allowed for simple catalyst recycling over up to 40 cycles without visible loss of its activity, providing much higher accumulative total turnover numbers (TTONs) of 2375 vs 739 in toluene. The present work represents the first example of effective reaction and separation of high-molecular-weight silsesquioxyl derivatives in scCO2, demonstrating the feasibility of synthesizing and isolating high-molecular-weight polyhedral oligomeric silsesquioxane (POSS) derivatives without the necessity of organic solvents.