Cagelike Octacopper Methylsilsesquioxanes: Self-Assembly in the Focus of Alkaline Metal Ion Influence—Synthesis, Structure, and Catalytic Activity

Abstract

A family of unusual octacopper cage methylsilsesquioxanes 1–4 were prepared and characterized. Features of their cagelike (prismatic) structure were established using X-ray diffraction studies. Effects of distortion of prismatic cages 1–4 due to variation of (i) additional alkaline metal ions (K, Rb, or Cs), (ii) combination of solvating ligands, and (iii) nature of encapsulating species were found. Opportunities for the design of supramolecular 1D extended structures were found. These opportunities are based on (i) formate linkers between copper centers (in the case of Cu8K2-based compound 2) or (ii) crown ether-like contacts between cesium ions and siloxane cycles (in the case of Cu8Cs2-based compound 4). Cu8Cs2-complex 4 was evaluated in the catalysis of alkanes and alcohols. Complex 4 exhibits high catalytic activity. The yield of cyclohexane oxidation products is 35%. The presence of nitric acid is necessary as a co-catalyst. The oxidation of alcohols with the participation of complex 4 as a catalyst and tert-butyl hydroperoxide as an oxidizer also proceeds in high yields of up to 98%.

Cage-like Cu5Cs4-Phenylsilsesquioxanes: Synthesis, Supramolecular Structures, and Catalytic Activity

“…As a consequence, unlike complex 1 , encapsulation in complex 2 results in the externally “naked” central copper ion of the arc-like fragment (the other four copper ions in both compounds are sterically shielded and have no possibility to coordinate an external ligand). The same “naked” effect was observed in Cu 8 - and Cu 9 -based methylsilsesquioxanes.…”

“…CLMSs are widely applied in homo- and heterogeneous catalyses. ,− Recent reports involve activity in (i) hydrogen production, (ii) Chan–Evans–Lam (CEL) couplings, (iii) the hydroboration of ketones, (iv) CO 2 valorization, (v) the synthesis of bio-derived ethers, and (vi) oxidative amidation . Separately, we would like to mention a well-known activity of transition metal complexes in catalysis of the oxidations of hydrocarbons and alcohols involving the functionalization of C–H bonds. − Furthermore, multicopper­(II) cores are among the most active oxidation catalysts. − ,− Recently, an implementation of the alkaline metal ions rubidium and cesium has been applied for the design of unusual types of catalytically active CLMS frameworks. ,, Being interested in both of these directions [(i) design of potential oxidative catalysts and (ii) investigation of the influence of large alkaline metal ions on CLMS structure formation], we have performed detailed studies on Cu,Cs-CLMSs’ self-assembly. Herein, we report the synthesis, structures, and catalytic activity of these cage-like Cu 5 Cs 4 -modified metallasilsesquioxanes.…”

A Family of Cagelike Mn-Silsesquioxane/Bathophenanthroline Complexes: Synthesis, Structure, and Catalytic and Antifungal Activity

“…Several recent reports point at a significant role of these metal centers on molecular and supramolecular structures of CLMSs. 14,21,23,79,80 In this context, we performed (Scheme 2) parallel reactions involving different alkali reagents (LiOH vs. NaOH). The stoichiometric ratio of reactants in these reactions was oriented on only partial replacement of alkaline metal ions by manganese centers.…”

“…The observation of acetate fragments is a consequence of spontaneous partial oxidation of ethanol solvates, which is in perfect accord with several earlier reports. 68,78,80,83,85,86 Finally, another unusual feature of complex 2 is the presence, along with acetone solvates, of two molecules of pentane. Despite recent results pointing at acetone ligands as a favorable choice for CLMS single crystal isolation, 79,80,87,88 we failed to crystallize complex 2 directly from the acetone solution.…”

“…68,78,80,83,85,86 Finally, another unusual feature of complex 2 is the presence, along with acetone solvates, of two molecules of pentane. Despite recent results pointing at acetone ligands as a favorable choice for CLMS single crystal isolation, 79,80,87,88 we failed to crystallize complex 2 directly from the acetone solution. To overcome this issue, following the popular tactics of crystallization, nonpolar pentane was layered over the polar acetone solution, which successfully gave single crystals of 2.…”