New Cu4Na4- and Cu5-Based Phenylsilsesquioxanes. Synthesis via Complexation with 1,10-Phenanthroline, Structures and High Catalytic Activity in Alkane Oxidations with Peroxides in Acetonitrile

Abstract

Self-assembly of copper(II)phenylsilsesquioxane assisted by the use of 1,10-phenanthroline (phen) results in isolation of two unusual cage-like compounds: (PhSiO1,5)12(CuO)4(NaO0.5)4(phen)4 1 and (PhSiO1,5)6(PhSiO1,5)7(HO0.5)2(CuO)5(O0.25)2(phen)3 2. X-Ray diffraction study revealed extraordinaire molecular architectures of both products. Namely, complex 1 includes single cyclic (PhSiO1,5)12 silsesquioxane ligand. Four sodium ions of 1 are additionally ligated by 1,10-phenanthrolines. In turn, “sodium-less” complex 2 represents coordination of 1,10-phenanthrolines to copper ions. Two silsesquioxane ligands of 2 are: (i) noncondensed cubane of a rare Si6-type and (ii) unprecedented Si7-based ligand including two HOSiO1.5 fragments. These silanol units were formed due to removal of phenyl groups from silicon atoms, observed in mild conditions. The presence of phenanthroline ligands in products 1 and 2 favored the π–π stacking interactions between neighboring cages. Noticeable that in the case of 1 all four phenanthrolines participated in such supramolecular organization, unlike to complex 2 where one of the three phenanthrolines is not “supramolecularly active”. Complexes 1 and 2 were found to be very efficient precatalysts in oxidations with hydroperoxides. A new method for the determination of the participation of hydroxyl radicals has been developed.

Metal Complexes Containing Redox-Active Ligands in Oxidation of Hydrocarbons and Alcohols: A Review

“…A method was developed and used by Shul'pin (see Figure 1) [25][26][27][28][29][30][31]. In this method, the samples of reaction solutions obtained in the alkane oxidation with a peroxide are analyzed twice, i.e., before and after the addition of the excess of solid PPh 3 .…”

“…This may be explained by the reduction of the formed cyclohexyl hydroperoxide to give the corresponding alcohol. An example is presented in Figure 2 [30,31]. This method (i.e., a comparison of the cyclohexanol and cyclohexanone concentrations before and after treating with PPh 3 ) allows us to calculate the real concentrations, not only of the alkyl hydroperoxide, but also of the alcohols and ketones present in the solution at a given moment.…”

“…[31]. Figure) in MeCN at 50 • C. The concentrations of cyclohexanone and cyclohexanol were determined before (graph A) and (graph B) after reduction of the aliquots with solid PPh 3 (according to the Shul'pin method [26][27][28][29][30][31]). The Figure 2 is adapted from Ref.…”

“…In order to determine the kinetic characteristics of the oxidizing species X generated by the catalytic system studied in this work, the dependence of the alkane oxidation rate on its initial concentration was studied (see, for example, Figure 2) [30,31]. The nature of the dependence corresponds to the assumption of the competitive interaction of the oxidizing species X with acetonitrile and cyclohexane (RH):…”

“…In recent years, Bilyachenko and co-workers have proposed a new convenient route to metallasilsesquioxanes and synthesized a series of complexes containing various transition metal ions (iron, copper, cobalt, and nickel). These compounds have been used as efficient catalysts in hydrogen peroxide oxidations of hydrocarbons and alcohols [30,31, (see an example in Figure 2; see also Reviews [108,109]). The activity of such catalysts was especially high if their molecules contained amines and olygoamines (pyridine, dipyridyl, phenanthroline, etc.).…”