A Novel Family of Cage-like (CuLi, CuNa, CuK)-phenylsilsesquioxane Complexes with 8-Hydroxyquinoline Ligands: Synthesis, Structure, and Catalytic Activity.

The first examples of metallasilsesquioxane complexes, including ligands of the 8-hydroxyquinoline family 1 - 9 , were synthesized, and their structures were established by single crystal X-ray diffraction using synchrotron radiation. Compounds 1 - 9 tend to form a type of sandwich-like cage of Cu 4 M 2 nuclearity (M = Li, Na, K). Each complex includes two cisoid pentameric silsesquioxane ligands and two 8-hydroxyquinoline ligands. The latter coordinates the copper ions and corresponding alkaline metal ions (via the deprotonated oxygen site). A characteristic (size) of the alkaline metal ion and a variation of characteristics of nitrogen ligands (8-hydroxyquinoline vs. 5-chloro-8-hydroxyquinoline vs. 5,7-dibromo-8-hydroxyquinoline vs. 5,7-diiodo-8-hydroxyquinoline) are highly influential for the formation of the supramolecular structure of the complexes 3a , 5 , and 7 - 9 . The Cu 6 Na 2 -based compound 2 exhibits high catalytic activity towards the oxidation of ( i ) hydrocarbons by H 2 O 2 activated with HNO 3 , and ( ii ) alcohols by tert -butyl hydroperoxide. Studies of kinetics and their selectivity has led us to conclude that it is the hydroxyl radicals that play a crucial role in this process.