Palanquin-Like Cu4Na4 Silsesquioxane Synthesis (via Oxidation of 1,1-bis(Diphenylphosphino)methane), Structure and Catalytic Activity in Alkane or Alcohol Oxidation with Peroxides

Abstract

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 HO • and tert-BuO • which attack the C-H bonds of the substrate.

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

“…As shown above, the low selectivity of the oxidative effect of X species, which is close to the selectivity found for reactions involving hydroxyl radicals, and this indicates that hydroxyl radicals are generated in the catalytic systems studied in the present work. Similar results (a decrease in the relative reactivity of the oxidizing species for cyclohexane in comparison with acetonitrile) were obtained earlier by us in clarifying the nature of the oxidizing species during the catalysis of the decomposition of hydrogen peroxide on the complex palanquin-like Cu 4 Na 4 silsesquioxane [41] as well as using aluminum nitrate [85].…”

Recent Advances in Copper Catalyzed Alcohol Oxidation in Homogeneous Medium

“…Remarkably, cinnamaldehyde (85% yield, TOF 14.2 min −1 ) was the only product detected, clearly revealing the preference of 13 to oxidize the alcohol function. An extension of this study to the preparation of further copper complexes with the above types of ligands was reported by the same authors in 2017 [19] (Figure 4 (15) were tested as catalysts for the oxidation of primary and secondary alcohols. A good catalytic activity for the neat and additive-free MW-assisted oxidation of the aliphatic cyclohexanol (up to 90% yield of cyclohexanone) after 30 min of low power MW irradiation (entries 9 and 12, Table 2) was achieved by these dinuclear Cu(II) compounds.…”

“…In 2017, Shul pin and coworkers [14] applied the hexanuclear Cu(II)-based phenylsilsesquioxane complex [(PhSiO 1.5 ) 10 (CuO) 6 (HO 0.5 ) 2 (C 12 H 8 N 2 ) 2 ] (5) as catalyst for the oxidation of 1-phenylethanol with tert-butyl hydroperoxide (TBHP, 70% aq. solution) in acetonitrile, at 50 • C and in presence of HNO 3 , leading to 94% yield of acetophenone (TON = 600) after 14 h. Moreover, the cage-like (6), obtained very recently [15] by self-assembly synthesis, has also shown to be a very good catalyst for the oxidation of alcohols in acetonitrile solution: 1-phenylethanol was oxidized by TBHP to acetophenone in an almost quantitative yield. In addition, complexes bearing cyclic germsesquioxanes [PhGeO 1,5 ] 5 and phenanthrolines, namely [(PhGeO 1.5 ) 10 (CuO) 6 (HO 0.5 ) 2 (C 12 H 8 N 2 ) 2 ](H 2 O) 2 (7), exhibited high activity as pre-catalysts in homogeneous oxidations of cyclohexanol, 2-heptanol or 1-phenylethanol to the corresponding ketones, leading to yields up to 94% [16].…”

Oxidation of Organic Compounds with Peroxides Catalyzed by Polynuclear Metal Compounds

“…Such an increase in regioselectivity can be explained by the fact that oxidation in the case of complex 18 occurs in the cavities formed by bulky ligands surrounding the reaction centers of the catalyst molecule. As in the case of iron ions, a large number of works have been devoted to silsesquioxane complexes with copper and their use in catalytic oxidation [73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88]. A few structures of the catalysts used in the most recent years are shown in Figures 12-15.…”

“…Germanium-based sesquioxane copper complex exhibits an extremely high nuclearity (Cu42Ge24Na4) and unusual encapsulation features. This compound is a very active catalyst in the oxidation of al- Not only silsesquioxane complexes, but germsesquioxanes, which are precatalysts in the oxidation of organic compounds, were obtained and described [86][87][88]. An example of structure of such catalysts is given in Figure 15.…”