Cesium Carbonate-Catalyzed Oxidation of Substituted Phenylsilanes for the Efficient Synthesis of Polyhedral Oligomeric Silsesquioxanes.

Cesium carbonate-catalyzed oxidation of substituted phenylsilanes (ArSiH3) in N, N-dimethylformamide (DMF) at room temperature for the efficient synthesis of polyhedral oligomeric silsesquioxanes (POSS) was described. This protocol allowed the rapid and selective access to several types of new POSS cages in modest to good yields under nonaqueous conditions. Depending on the bulkiness of the substituents on the phenyl rings, hexa- (T6), octa- (T8), and dodecaphenylsilsesquioxanes (T12) can be selectively obtained. With the more bulky 2-(2',4',6'-trimethylphenyl)phenyl group, the cyclic tetrasiloxane (D4) bearing four hydroxyl groups was isolated. Mechanism studies disclosed that the initial step involved the Cs2CO3-catalyzed hydrosilylation of DMF with a hydrosilane to generate a siloxymethylamine intermediate followed by the dehydrocarbonative cross-coupling of the hydrosilane with the siloxymethylamine.