Cu6- and Cu8-Cage Sil- and Germsesquioxanes: Synthetic and Structural Features, Oxidative Rearrangements, and Catalytic Activity

This study reports intriguing features in the self-assembly of cage copper(II) silsesquioxanes in the presence of air. Despite the wide variation of solvates used, a series of prismatic hexanuclear Cu₆ cages (1-5) were assembled under mild conditions. In turn, syntheses at higher temperatures are accompanied by side reactions, leading to the oxidation of solvates (methanol, 1-butanol, and tetrahydrofuran). The oxidized solvent derivatives then specifically participate in the formation of copper silsesquioxane cages, allowing the isolation of several unusual Cu₈-based (6 and 7) and Cu₆-based (8) complexes. When 1,4-dioxane was applied as a reaction medium, deep rearrangements occurred (with a total elimination of silsesquioxane ligands), causing the formation of mononuclear copper(II) compounds bearing oxidized dioxane fragments (9 and 11) or a formate-driven 1D coordination polymer (10). Finally, a "directed" self-assembly of sil- and germsesquioxanes from copper acetate (or formate) resulted in the corresponding acetate (or formate) containing Cu₆ cages (12 and 13) that were isolated in high yields. The structures of all of the products 1-13 were established by single-crystal X-ray diffraction, mainly based on the use of synchrotron radiation. Moreover, the catalytic activity of compounds 12 and 13 was evaluated toward the mild homogeneous oxidation of C₅-C₈ cycloalkanes with hydrogen peroxide to form a mixture of the corresponding cyclic alcohols and ketones.

New Luminescent Tetranuclear Lanthanide-Based Silsesquioxane Cage-Like Architectures

Invited for the cover of this issue are Alexey N. Bilyachenko, Joulia Larionova and co-workers at the Russian Academy of Sciences, the Peoples' Friendship University of Russia, and University of Montpellier. The image depicts lanthanide-based cage-like silsesquioxanes exhibiting magnetic and luminescence properties that could constitute a particularly interesting new family related to multifunctional nanomaterials. Read the full text of the article at 10.1002/chem.202003351.

New Luminescent Tetranuclear Lanthanide-Based Silsesquioxane Cage-Like Architectures

The synthesis, structure, magnetic, and luminescence properties investigations of four new cage-like lanthanide-based silsesquioxanes (Cat)₂ [(PhSiO_1.5 )₈ (LnO_1.5 )₄ (O)(NO_2.5 )₆ (EtOH)₂ (MeCN)₂ ] (where Cat⁺ =Et₄ N⁺ , PPh₄ P⁺ and Ln³⁺ =Eu³⁺ , Tb³⁺ and (Ph₄ P)₄ [(PhSiO_1.5 )₈ (TbO_1.5 )₄ (O)₂ (NO_2.5 )₈ ]⋅10MeCN are reported. They present an unusual prism-like topology of cage architectures and lanthanide-characteristic emission, which makes them the first luminescent cage-like lanthanide silsesquioxanes. One of the Tb³⁺ -based cages presents a magnetic spin-flip transition.

Coordination Affinity of Cu(II)-Based Silsesquioxanes toward N,N-Ligands and Associated Skeletal Rearrangements: Cage and Ionic Products Exhibiting a High Catalytic Activity in Oxidation Reactions

An unusual skeletal rearrangement of piperazine into ethylenediamine has been observed for the first time as a result of an attempt to synthesize a piperazine-linked metal-organic framework (MOF) using cage Cu(II),Na-phenylsilsequixane as a potential building block. Instead of the expected "metallasilsesquioxane-based MOF", a Cu₆ complex 1 coordinated both by silsesquioxane and ethylenediamine ligands was isolated. An effort to reproduce this result via direct interaction of Cu-phenylsilsequioxane and ethylenediamine surprisingly afforded two other types of complexes, copper-sodium 2 and copper 3 ionic products. Cationic components in both products 2 and 3 are represented by (i) copper and sodium ions (in the case of 2) or (ii) copper ions exclusively (in the case of 3) coordinated by ethylenediamine ligands. Both complexes 2 and 3 include Si₆-based condensed silsesquioxane fragments serving as anionic components of the products. Symptomatically, the types of the Si₆-frameworks in 2 and 3 are drastically different. More specifically, the Si₆ unit in 2 is an unprecedented distorted silsesquioxane skeleton consisting of two condensed tetramembered rings. Structural features of compounds 1-3 were established by single crystal X-ray diffraction. Compound 2 was found to catalyze the oxidation of cyclohexane to cyclohexanol and cyclohexanone with H₂O₂ (a mixture of these products was obtained after adding PPh₃ to the reaction solution) as well as the transformation of cyclohexanol to cyclohexanone under the action of tert-butyl hydroperoxide.

High-Cluster (Cu9) Cage Silsesquioxanes: Synthesis, Structure, and Catalytic Activity

Unusual high-cluster (Cu₉) cage phenylsilsesquioxanes were obtained via complexation of in situ Cu^II,Na-silsesquioxane species formed with phenanthroline and neocuproine. In the first case, phenanthroline, acting as "a silent ligand" (not participating in the composition of the final product), favors the formation of an unprecedented cagelike phenylsilsesquioxane of Cu₉Na₆ nuclearity, 1. In the second case, neocuproine ligands withdraws two Cu ions from the metallasilsesquioxane matrix, producing two cationic fragments Cu⁺(neocuproine)₂. The remaining metallasilsesquioxane is rearranged into an anionic cage of Cu₉Na₄ nuclearity, finalizing the formation of a specific ionic complex, 2. The impressive molecular architecture of both types of complexes, e.g., the presence of different (cyclic/acyclic) types of silsesquioxane ligands, was established by single-crystal X-ray diffraction studies. Compound 1 was revealed to be highly active in the oxidative amidation of benzylic alcohol and the catalyst loading could be reduced down to 100 ppm of Cu. Catalytic studies of compound 1 demonstrated its high activity in hydroperoxidation of alkanes with H₂O₂ and oxidation of alcohols to ketones with tert-BuOOH.

Heptanuclear Fe5Cu2-Phenylgermsesquioxane containing 2,2'-Bipyridine: Synthesis, Structure, and Catalytic Activity in Oxidation of C-H Compounds

A new representative of an unusual family of metallagermaniumsesquioxanes, namely the heterometallic cagelike phenylgermsesquioxane (PhGeO₂)₁₂Cu₂Fe₅(O)OH(PhGe)₂O₅(bipy)₂ (2), was synthesized and structurally characterized. Fe(III) ions of the complex are coordinated by oxa ligands: (i) cyclic (PhGeO₂)₁₂ and acyclic (Ph₂Ge₂O₅) germoxanolates and (ii) O^2- and (iii) HO^- moieties. In turn, Cu(II) ions are coordinated by both oxa (germoxanolates) and aza ligands (2,2'-bipyridines). This "hetero-type" of ligation gives in sum an attractive pagoda-like molecular architecture of the complex 2. Product 2 showed a high catalytic activity in the oxidation of alkanes to the corresponding alkyl hydroperoxides (in yields up to 30%) and alcohols (in yields up to 100%) and in the oxidative formation of benzamides from alcohols (catalyst loading down to 0.4 mol % in Cu/Fe).

A new “bicycle helmet”-like copper(ii),sodiumphenylsilsesquioxane. Synthesis, structure and catalytic activity

Use of silsesquioxane and 2,2′-bipyridine leads to isolation of catalytically active “Bicycle Helmet” cage.

New Ni4Na2-phenylgermsesquioxane architecture: synthesis, structure and slow dynamic behaviour

The first Ni(ii)-based germaniumsesquioxane cage compound [(PhGeO_1.5)₁₀(NiO)₄(NaO_0.5)₂] presents a unique sandwich-like structure and exhibits slow dynamics of the magnetization.

Si10Cu6N4 Cage Hexacoppersilsesquioxanes Containing N Ligands: Synthesis, Structure, and High Catalytic Activity in Peroxide Oxidations

The synthesis, composition, and catalytic properties of a new family of hexanuclear Cu(II)-based phenylsilsesquioxanes are described here. Structural studies of 17 synthesized compounds revealed the general principle underlying their molecular topology: viz., a central metal oxide layer consisting of two Cu₃ trimers is coordinated by two cyclic [PhSiO_1.5]₅ siloxanolate ligands to form a skewed sandwich architecture with the composition [(PhSiO_1.5)₁₀(CuO)₆]²⁺. In addition to this O ligation by the siloxanolate rings, two opposite copper ions are additionally coordinated by the nitrogen atoms of corresponding N ligand(s), such as 2,2'-bipyridine (compounds 1-9), 1,10-phenanthroline (compounds 10-13), mixed 1,10-phenanthroline/2,2'-bipyridine (compound 14), or bathophenanthroline (compounds 15-17). Finally, the charge balance is maintained by two HO^- (compounds 1-7, 10-13, and 15-17), two H₃CO^- (compound 8), or two CH₃COO^- (compounds 9 and 14) anions. Complexes 1 and 10 exhibited a high activity in the oxidative amidation oxidation of alcohols. Compounds 1, 10, and 15 are very efficient homogeneous catalysts in the oxidation of alkanes and alcohols with peroxides.

Family of Polynuclear Nickel Cagelike Phenylsilsesquioxanes; Features of Periodic Networks and Magnetic Properties

A new family of bi-, tetra-, penta-, and hexanickel cagelike phenylsilsesquioxanes 1-6 was obtained by self-assembly and transmetalation procedures. Their crystal structures were established by single-crystal X-ray analysis, and features of crystal packing relevant to the network formation were studied by a topological analysis. Compounds 1, 2, and 4 are isolated architectures, while 3, 5, and 6 present extended 1D and 3D networks. The investigation of magnetic properties revealed the presence of ferro- (1 and 3-5) or antiferromagnetic (2 and 6) interactions between Ni(II) ions, giving rise in the most cases (1, 2, and 4-6) to the presence of a slow relaxation of the magnetization, which can originate from the spin frustration.

Tuning linkage isomerism and magnetic properties of bi- and tri-metallic cage silsesquioxanes by cation and solvent effects

The ability of the polynuclear cage metallasilsesquioxane [(PhSiO_1.5)₁₂(CuO)₄(NaO_0.5)₄(n-BuOH)₈] with a globular structure to act as a stable building block of hybrid materials with respect to the substitution of sodium cations and terminal butanol molecules was confirmed.

Cage-like Fe,Na-Germsesquioxanes: Structure, Magnetism, and Catalytic Activity

A series of four unprecedented heterometallic metallagermsesquioxanes were synthesized. Their cage-like architectures have a unique type of molecular topology consisting of the hexairon oxo {Fe₆ O₁₉ } core surrounded in a triangular manner by three cyclic germoxanolates [PhGe(O)O]₅ . This structural organization induces antiferromagnetic interactions between the Fe^III ions through the oxygen atoms. Evaluated for this first time in catalysis, these compounds showed a high catalytic activity in the oxidation of alkanes and the oxidative formation of benzamides from alcohols.

A heterometallic (Fe6Na8) cage-like silsesquioxane: synthesis, structure, spin glass behavior and high catalytic activity

The exotic “Asian Lantern” heterometallic cage silsesquioxane [(PhSiO_1.5)₂₀(FeO_1.5)₆(NaO_0.5)₈(n-BuOH)_9.6(C₇H₈)] (I) was obtained and characterized by X-ray diffraction, EXAFS, topological analyses and DFT calculation.

Unusual penta- and hexanuclear Ni(ii)-based silsesquioxane polynuclear complexes

Cage-like Ni(ii)-silsesquioxanes demonstrate the presence of a slow relaxation of the magnetization, induced by spin glass-like behavior.

Correction: A heterometallic (Fe6Na8) cage-like silsesquioxane: synthesis, structure, spin glass behavior and high catalytic activity

Correction for ‘A heterometallic (Fe₆Na₈) cage-like silsesquioxane: synthesis, structure, spin glass behavior and high catalytic activity’ by Alexey N. Bilyachenko et al., RSC Adv., 2016, 6, 48165–48180.

Cage-like copper(II) silsesquioxanes: transmetalation reactions and structural, quantum chemical, and catalytic studies

The transmetalation of bimetallic copper-sodium silsesquioxane cages, namely, [(PhSiO1.5 )10 (CuO)2 (NaO0.5 )2 ] ("Cooling Tower"; 1), [(PhSiO1.5 )12 (CuO)4 (NaO0.5 )4 ] ("Globule"; 2), and [(PhSiO1.5 )6 (CuO)4 (NaO0.5 )4 (PhSiO1.5 )6 ] ("Sandwich"; 3), resulted in the generation of three types of hexanuclear cylinder-like copper silsesqui- oxanes, [(PhSiO1.5 )12 (CuO)6 (C4 H9 OH)2 (C2 H5 OH)6 ] (4), [(PhSiO1.5 )12 (CuO)6 (C4 H8 O2 )4 (PhCN)2 (MeOH)4 ] (5), and [(PhSiO1.5 )12 (CuO)6 (NaCl)(C4 H8 O2 )12 (H2 O)2 ] (6). The products show a prominent "solvating system-structure" dependency, as determined by X-ray diffraction. Topological analysis of cages 1-6 was also performed. In addition, DFT theory was used to examine the structures of the Cooling Tower and Cylinder compounds, as well as the spin density distributions. Compounds 1, 2, and 5 were applied as catalysts for the direct oxidation of alcohols and amines into the corresponding amides. Compound 6 is an excellent catalyst in the oxidation reactions of benzene and alcohols.

Alkane oxidation with peroxides catalyzed by cage-like copper(ii) silsesquioxanes

Copper(ii) silsesquioxanes [(PhSiO_1.5)₁₂(CuO)₄(NaO_0.5)₄] or [(PhSiO_1.5)₁₀(CuO)₂(NaO_0.5)₂] are catalysts for alkane oxidation with H₂O₂ort-BuOOH.