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 Cu4M2 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 Cu6Na2-based compound 2 exhibits high catalytic activity towards the oxidation of (i) hydrocarbons by H2O2 activated with HNO3, 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.
Bibliographical noteFunding Information:
This work was performed within the framework of the Program of Fundamental Research of the Russian Federation. Reg. No. 122040500068-0. Elemental and GC analyses were performed with the financial support from the Ministry of Education and Science of the Russian Federation using equipment from the Center for molecular composition studies of INEOS RAS. D.G. acknowledges RUDN University Scientific Projects Grant System, project No. 025239-2-174, the ISF (Israel Science Foundation) Grant No. 370/20 and Esther K. and M. Mark Watkins Chair for Synthetic Organic Chemistry.
This research was funded by the Russian Science Foundation, grant number 22-13-00252.
© 2022 by the authors.
- 8-hydroxyquinoline ligands
- alkyl hydroperoxide
- cage-like compounds
- coordination polymers
- half-sandwich units
- oxidative catalysis