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

Abstract

Ten copper-based cage silsesquioxanes were prepared via convenient self-assembly synthesis employing halides of different quaternary ammonium cations, namely, Me4NBr, Et4NBr, PhMe3NCl, BzMe3NCl, and BzEt3NCl. This approach led to cages of similar Cu4M2 nuclearity (M = Rb, K, or Na). Sandwich-like structures of all compounds were established by single-crystal X-ray diffraction studies using synchrotron radiation. In all products, anionic cages are based on two cyclic silsesquioxane [Ph6Si6O12] ligands, coordinating to a central hexagonal CuII 4M2 motif with a 2M6-1 topology. The complexes include two charge balancers, namely, quaternary N-cations located at the external (crown ether-like) positions to cage fragments. Selected compounds were tested as homogeneous multicopper(II) catalysts in a series of model reactions, such as the mild oxidation and carboxylation of alkanes, including inert gaseous C2–C4 saturated hydrocarbons. This study extends the types of synthetic approaches and family of ionic metallasilsesquioxanes with promising structural features and catalytic properties.

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.…”

“…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.…”

Cagelike Manganesesilsesquioxane Complexes: Synthesis via an Acetone Approach, Structure, and Catalytic Activity for Toluene Oxidation

“…Among these, CLMSs’ derivatives were investigated in the design of molecular magnets (including examples of single-molecule magnet or spin glass behaviors) − and objects with photophysical properties (e.g., CLMS-based luminescent thermometers). − In turn, several functional coordination polymers, − ceramics, , anodes, , fungicides, and flame retardants were successfully developed on the basis of CLMSs. CLMSs are widely applied as homo- and heterogeneous catalysts as well as components of catalytic systems. ,− Among recent reports, CLMSs’ activity in (i) deacetalization/deketalization-Knoevenagel reactions, (ii) Chan–Evans–Lam couplings, (iii) Baeyer–Villiger reactions, (iv) CO 2 valorization, , and (v) carboxylations should be mentioned. Intriguingly, despite detailed investigations of Mn complexes in catalysis, , the very first example of catalytically active Mn–CLMSs has been reported by some of us very recently for the oxidative amidation conditions .…”

“…CLMSs are widely applied as homo-and heterogeneous catalysts as well as components of catalytic systems. 28,33−39 Among recent reports, CLMSs' activity in (i) deacetalization/deketalization-Knoevenagel reactions, 40 (ii) Chan−Evans−Lam couplings, 41 (iii) Baeyer−Villiger reactions, 42 (iv) CO 2 valorization, 31,43 and (v) carboxylations 44 should be mentioned. Intriguingly, despite detailed investigations of Mn complexes in catalysis, 45,46 the very first example of catalytically active Mn−CLMSs has been reported by some of us very recently for the oxidative amidation conditions.…”

“…A choice of fruitful synthetic solutions for the self-assembly of CLMS complexes remains a challenging task. Numerous articles confirm the opportunity for transformation of simple RSi(OR') 3 reagents into complicated CLMS structures [14][15][16][17][18][20][21][22][23][24][25][26][41][42][43][44]86,87 via the intermediate alkaline hydrolysis stage. 88,89 In this context, recent positive results witnessed a successful approach to a large family (14 examples) of copper-based CLMSs via the use of acetone as a key solvate.…”