Hexacoppergermsesquioxanes as complexes with N-ligands: Synthesis, structure and catalytic properties

Abstract

A simple and versatile strategy of synthesis of cage metallagermaniumsesquioxanes is demonstrated for isolation of Cu 6-based phenylgermsesquioxanes 1e6. Structure of newly synthesized coppergermsesquioxanes was established by single-crystal X-ray diffraction analysis. General principle of these cages' topology implies the presence of two linear Cu 3 fragments, coordinated by three pairs of ligands. These are: (i) cyclic germsesquioxanes [PhGeO 1,5 ] 5 , products 1e6, (ii) 1,10-phenanthrolines, (1, 3e5) or 2,2'bipyridines, (2, 6), (or and (iii) OX species (X ¼ H, 1e2, CH 3 , 3, H and C 2 H 5 O, 4, HCO, 5, CH 3 CO, 6). Appearance of non-expected species (formiate for 5, acetate for 6), resulted from corresponding alcohols used as reaction media, points at easyness of oxidation processes in the conditions of such selfassembling reactions. Catalytic tests showed high activity of complexes 1 and 2 as precatalysts in homogeneous oxidations of alkanes (cyclohexane, methylcyclohexane, n-heptane, cis-1,2dimethylcyclohexane with hydrogen peroxide in acetonitrile solution. Hydroxyl radicals take part in the reaction. The same complexes catalyze oxidation of alcohols (cyclohexanol, 2-heptanol, 1phenylethanol) to corresponding ketones with tert-butyl hydroperoxide in almost 100% yield. With the addition of various alkyl ammonium salts, complex 2 could also furnish corresponding amides in high yield.

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.).…”