Palanquin-like Cu 4 Na 4 silsesquioxane synthesis (via oxidation of 1,1-bis(diphenylphosphino)methane), structure and catalytic activity in alkane or alcohol oxidation with peroxides

The self-assembly synthesis of copper-sodium phenylsilsesquioxane in the presence of 1,1-bis(diphenylphosphino)methane (dppm) results in an unprecedented cage-like product: [(PhSiO 1,5 ) 6 ] 2 [CuO] 4 [NaO 0.5 ] 4 [dppmO 2 ] 2 1. The most intriguing feature of the complex 1 is the presence of two oxidized dppm species that act as additional O-ligands for sodium ions. Two cyclic phenylsiloxanolate (PhSiO 1,5 ) 6 ligands coordinate in a sandwich manner with the copper(II)-containing layer of the cage. The structure of 1 was established by X-ray diffraction analysis. Complex 1 was shown to be a very good catalyst in the oxidation of alkanes and alcohols with hydrogen peroxide or tert-butyl hydroperoxide in acetonitrile solution. Thus, cyclohexane (CyH), was transformed into cyclohexyl hydroperoxide (CyOOH), which could be easily reduced by PPh 3 to afford stable cyclohexanol with a yield of 26% (turnover number (TON) = 240) based on the starting cyclohexane. 1-Phenylethanol was oxidized by tert-butyl hydroperoxide to give acetophenone in an almost quantitative yield. The selectivity parameters of the oxidation of normal and branched alkanes led to the conclusion that the peroxides H 2 O 2 and tert-BuOOH, under the action of compound (1), decompose to generate the radicals HȮ and tert-BuȮ which attack the C-H bonds of the substrate. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.