A Novel Family of Cage-like (CuLi, CuNa, CuK)-phenylsilsesquioxane Complexes with 8-Hydroxyquinoline Ligands: Synthesis, Structure, and Catalytic Activity

Abstract

The first examples of metallasilsesquioxane complexes, including ligands of the 8-hydroxyquinoline family 1–9, were synthesized, and their structures were established by single crystal X-ray diffraction using synchrotron radiation. Compounds 1–9 tend to form a type of sandwich-like cage of Cu4M2 nuclearity (M = Li, Na, K). Each complex includes two cisoid pentameric silsesquioxane ligands and two 8-hydroxyquinoline ligands. The latter coordinates the copper ions and corresponding alkaline metal ions (via the deprotonated oxygen site). A characteristic (size) of the alkaline metal ion and a variation of characteristics of nitrogen ligands (8-hydroxyquinoline vs. 5-chloro-8-hydroxyquinoline vs. 5,7-dibromo-8-hydroxyquinoline vs. 5,7-diiodo-8-hydroxyquinoline) are highly influential for the formation of the supramolecular structure of the complexes 3a, 5, and 7–9. The Cu6Na2-based compound 2 exhibits high catalytic activity towards the oxidation of (i) hydrocarbons by H2O2 activated with HNO3, and (ii) alcohols by tert-butyl hydroperoxide. Studies of kinetics and their selectivity has led us to conclude that it is the hydroxyl radicals that play a crucial role in this process.

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

“…It is known that variations of the nature of alkaline metal ions strongly influence the structural features of phenylsurrounded CLMSs, especially in the context of supramolecular aggregation observed for large-sized ions (K, Rb, Cs) [ 16 , 23 , 25 , 47 , 60 ]. For the method of synthesis of methylsurrounded Cu-CLMSs, a universal approach that included alkaline hydrolysis [ 61 , 62 , 63 ] of MeSi(OMe) 3 assisted by the action of corresponding hydroxide MOH (M = Na, K, Rb, or Cs), was chosen.…”

“…Among recent results we could mention activity in CO 2 cycloaddition [ 43 ], Chan-Evans-Lam coupling [ 44 ], biomass transformations [ 45 ], and oxidative amidation [ 46 ]. Considering the significant potential of copper-based CLMSs as catalysts [ 47 , 48 , 49 , 50 ], we were interested in designing new types of these compounds. Numerous results pointed out the significant influence of the nature of the substituent at the silicon center on molecular geometry of arising CLMSs, e.g., for nickel-based (phenyl- [ 51 , 52 , 53 , 54 ] vs. 4-vinylbenzyl-substituted [ 55 ] CLMSs), titanium-based ( t -Bu vs. (2,6- i Pr 2 C 6 H 3 )N(SiMe 3 )-substituted [ 56 , 57 ] CLMSs), aluminum-based (cyclopentyl [ 58 ] vs. cyclohexyl-substituted [ 59 ] CLMSs) compounds.…”

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

“…Scheme shows the synthesis of the clusters 1 and 2 by combining alkaline hydrolysis of RSi­(OMe) 3 , and subsequent exchange reaction between the intermediate [PhSi­(O)­O – ] x siloxanolates and copper dichloride. Taking in mind (i) a well-known feature of alkaline metal ions to locate at external positions to the metallasilsesquioxane cage, ,,,,,− ,,,,− as well as (ii) an ability of siloxane ligands to coordinate metal centers in crown ether fashion, , we expected additional effects in cage formation in the case of leaving a part of alkaline metal ions non replaced by copper ones. Theoretically, the largest alkaline metal ion should provide the biggest impact on both cage formation and intercage connectivity.…”

Cagelike Rb2-, K2-, and Na2-Tetracopper(II) Silsesquioxanes with Quaternary Ammonium Cations: Synthesis, Structures, and Catalytic Activity

“…This points at a potentially general tendency of quaternary ammonium cation-containing CLMSs to avoid supramolecular aggregation. Considering that the potassium ions are also reported as mediators for supramolecular aggregation of CLMSs, ,,− in the next stage we performed some parallel reactions focusing on the insertion of ammonium cations into CuRb- and CuK-phenylsilsesquioxanes (Scheme ). The reactions carried out for three other types of quaternary ammonium reagents (PhMe 3 NCl and Et 4 NBr for Rb-CLMSs, Me 4 NBr for K-CLMS) lead to the corresponding complexes [(PhMe 3 N) 2 Rb 2 Cu 4 (Ph 6 Si 6 O 12 ) 2 (H 2 O) 2.5 ]·2EtOH ( 2 ), [(Et 4 N) 2 Rb 2 Cu 4 (Ph 6 Si 6 O 12 ) 2 (H 2 O) 2.5 ]·2EtOH ( 3 ), and [(Me 4 N) 2 K 2 Cu 4 (Ph 6 Si 6 O 12 ) 2 (EtOH) 4 ]·[(Me 4 N) 2 K 2 Cu 4 (Ph 6 Si 6 O 12 ) 2 (EtOH) 1.5 ] ( 4 ).…”