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 [(PhSiO1.5 )8 (LnO1.5 )4 (O)(NO2.5 )6 (EtOH)2 (MeCN)2 ] (where Cat+ =Et4 N+ , PPh4 P+ and Ln3+ =Eu3+ , Tb3+ and (Ph4 P)4 [(PhSiO1.5 )8 (TbO1.5 )4 (O)2 (NO2.5 )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.

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

A new "bicycle helmet"-like copper(ii),sodiumphenylsilsesquioxane Ph12Si12O12(OH)(O-)11Cu5Na(bipy)3(H2O) exhibited high catalytic efficiency in two homogeneous reactions: (i) functionalization of C-H compounds; (ii) formation of benzamides from alcohols.

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

Unusual high-cluster (Cu9) cage phenylsilsesquioxanes were obtained via complexation of in situ CuII,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.

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

The first Ni(ii)-based metallagermaniumsesquioxane cage compound [(PhGeO1.5)10(NiO)4(NaO0.5)2] presents a sandwich-like structure where two germsesquioxane cages are linked through an {NiO}4 core and exhibits slow dynamics of the magnetization.

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) O2- 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).

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 [PhSiO1.5]5 siloxanolate ligands to form a skewed sandwich architecture with the composition [(PhSiO1.5)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.

Herein, the effect of replacement of the surrounding solvent and/or the partial substitution of sodium ions in the cage-like copper, sodium phenylsilsesquioxane [(PhSiO1.5)12(CuO)4(NaO0.5)4(n-BuOH)6] 1 with a globular structure was investigated; the synthesis of ten new derivatives of complex 1 was performed, and their crystal structures were determined. Solvate replacement of n-butanol in 1 with dimethyl sulfoxide, acetonitrile, 1,4-dioxane/EtOH, and 1,4-dioxane/PhCN afforded the complexes [(PhSiO1.5)12(CuO)4(NaO0.5)4(DMSO)8] (2), [(PhSiO1.5)12(CuO)4(NaO0.5)4(MeCN)6(H2O)2]·2MeCN (3), [(PhSiO1.5)12(CuO)4(NaO0.5)4(C4H8O2)(EtOH)4]·0.5EtOH (4), and [(PhSiO1.5)12(CuO)4(NaO0.5)4(C4H8O2)4(H2O)3]·2PhCN·2C4H8O2·H2O (5). In an aqueous solution of EtOH, a rearrangement reaction occurred instead of substitution, which resulted in a new complex, [(PhSiO1.5)10(CuO)2(NaO0.5)2(H2O)6] (6), with a cooling tower molecular structure. Transmetalation reactions of 1 with KCl or CsF resulted in the formation of the trimetallic complexes [(PhSiO1.5)12(CuO)4(NaO0.5)2(KO0.5)2(DMF)6] (7), [(PhSiO1.5)12(CuO)4(NaO0.5)(CsO0.5)3(DMF)4(DMSO)(H2O)]·1.5DMF (8), [(PhSiO1.5)12(CuO)4(NaO0.5)2(CsO0.5)2(DMF)8]·0.5H2O (9), and [(PhSiO1.5)12(CuO)4(NaO0.5)3(CsO0.5)(DMF)4] (10). The replacement of sodium ions of 1 by the bulky non-metallic cation PhMe3N+ upon the interaction of 1 with PhMe3NCl in a MeCN medium afforded the complex (PhNMe3)2[(PhSiO1.5)12(CuO)4(NaO0.5)2(O)(MeCN)4]·4MeCN (11). X-ray analysis confirmed the successful replacement of terminal butanol molecules in all complexes and the stability of the globular cage of the parent complex under the reaction conditions, with the exceptions of complexes 6 and 9 that underwent an unprecedented reorganization of cage metallasilsesquioxane (CLMS) units into the cooling tower and sandwich-like cages, respectively. The stability of the cage during substitution reactions provides the first experimental evidence that polynuclear cage metallasilsesquioxanes can act as building blocks for the construction of coordination polymers, opening new ways for the synthesis of hybrid CLMS-based frameworks. In particular, the compounds 4, 6, 7, 9, and 10 are one-dimensional coordination polymers, and 5 and 8 are two-dimensional coordination polymers with a square lattice topology. A magnetism study of the coordination polymer compounds 5, 6, 8, and 9 showed antiferromagnetic behavior between copper centers.

Unusual Tri-, Hexa-, and Nonanuclear Cu(II) Cage Methylsilsesquioxanes: Synthesis, Structures, and Catalytic Activity in Oxidations with Peroxides.

Three types of unusual cagelike copper(II) methylsilsesquioxanes, namely, nona- [(MeSiO1.5)18(CuO)9] 1, hexa- [(MeSiO1.5)10(HO0.5)2(CuO)6(C12H8N2)2(MeSiO1.5)10(HO0.5)1.33(CH3COO0.5)0.67(CuO)6(C12H8N2)2] 2, [(MeSiO1.5)10(CuO)6(MeO0.5)2(C10H8N2)2] 3, and trinuclear [(MeSiO1.5)8(CuO)3(C10H8N2)2] 4, were obtained in 44%, 27%, 20%, and 16% yields, respectively. Nuclearity and structural fashion of products was controlled by the choice of solvent system and ligand, specifically assisting the assembling of cage. Structures of 1-4 were determined by single-crystal X-ray diffraction analysis. Compounds 1 and 4 are the first cage metallasilsesquioxanes, containing nine and three Cu ions, respectively. Product 1 is the first observation of nonanuclear metallasilsesquioxane ever. Unique architecture of 4 represents early unknown type of molecular geometry, based on two condensed pentamembered siloxane cycles. Topological analysis of metal clusters in products 1-4 is provided. Complex 1 efficiently catalyzes oxidation of alcohols with tert-butylhydroperoxide TBHP to ketones or alkanes with H2O2 to alkyl hydroperoxides in acetonitrile.

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 FeIII 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.

Novel Cage-Like Hexanuclear Nickel(II) Silsesquioxane. Synthesis, Structure, and Catalytic Activity in Oxidations with Peroxides.

New hexanuclear nickel(II) silsesquioxane [(PhSiO1.5)12(NiO)6(NaCl)] (1) was synthesized as its dioxane-benzonitrile-water complex (PhSiO1,5)12(NiO)6(NaCl)(C4H8O2)13(PhCN)2(H2O)2 and studied by X-ray and topological analysis. The compound exhibits cylinder-like type of molecular architecture and represents very rare case of polyhedral complexation of metallasilsesquioxane with benzonitrile. Complex 1 exhibited catalytic activity in activation of such small molecules as light alkanes and alcohols. Namely, oxidation of alcohols with tert-butylhydroperoxide and alkanes with meta-chloroperoxybenzoic acid. The oxidation of methylcyclohexane gave rise to the isomeric ketones and unusual distribution of alcohol isomers.

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

Fine-tuning of the reaction between alkali metal siloxanolate [PhSi(O)ONa]n and [Ni(NH3)6]Cl2 allowed us to design new hexa- [(PhSiO1,5)12(NiO)6(H2O)(DMSO)9] () and pentanuclear [(PhSiO1,5)10(NiO)5(NaOH)(DMF)7] () cage-like silsesquioxanes. Their specific structures were studied by single crystal X-ray diffraction and topological analyses. Compound is the first example of a pentanuclear "cylinder"-like metallasilsesquioxane. Magnetic property investigations demonstrate the presence of a slow relaxation of the magnetization, induced by spin glass-like behavior in both cases.

Heterometallic Na6Co3 Phenylsilsesquioxane Exhibiting Slow Dynamic Behavior in its Magnetization.

A heterometallic phenylsilsesquioxane [(PhSiO1,5)22(CoO)3(NaO0.5)6]⋅(EtOH)6⋅(H2O) 1 cage architecture of Co(II) ions in a triangular topology exhibits a slow dynamic behavior in its magnetization, induced by the freezing of the spins of individual molecules.

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.

Solvent-controlled synthesis of tetranuclear cage-like copper(II) silsesquioxanes. Remarkable features of the cage structures and their high catalytic activity in oxidation with peroxides.

Two principally different in their molecular architecture isomeric tetranuclear copper(ii) silsesquioxanes, "Globule"-like compound [(PhSiO1.5)12(CuO)4(NaO0.5)4] (1) and "Sandwich"-like derivative [(PhSiO1.5)6(CuO)4(NaO0.5)4(PhSiO1.5)6] (2), were synthesized by the partial cleavage of polymeric copper(ii) silsesquioxane [(PhSiO1.5)2(CuO)]n by tetraphenylcyclotetrasiloxanolate. The route leading to the formation of either 1 or 2 entirely depends on the nature and composition of the solvent used for this reaction. Thus, the process in an ethanol-1-butanol solution gives compound 1. When a 1,4-dioxane-methanol mixture was used, compound 2 was prepared. The structures and unusual crystal packing of the cages were confirmed by the X-ray studies. It has been found that the reaction of benzene with H2O2 in acetonitrile solution at 50 °C catalyzed by 1 requires addition of trifluoroacetic acid (TFA) in low concentration and gives phenol with a turnover number (TON) of 250 after 3 h. The initial reaction rate W0 linearly depends on the concentration of catalyst 2. The oxidation of 1-phenylethanol to acetophenone with hydrogen peroxide catalyzed by complex 1 in the presence of TFA is not efficient. In contrast, 1 exhibited excellent activity in the oxidation with tert-butyl hydroperoxide (TBHP) in the absence of any acid (the yield of acetophenone was close to the quantitative, TON attained 475 after 2 h). A kinetic study of this reaction led to the conclusion that the process occurs with the participation of radicals tert-BuO˙ produced in the Cu-promoted decomposition of TBHP. The mode of dependence of W0 on the initial concentration of TBHP indicates the formation of an intermediate adduct between the catalyst 1 and TBHP (characterized by the equilibrium constant K1≈ 2 M(-1) for the conditions of conducted experiments) followed by subsequent decomposition of the adduct (k2≈ 0.2 s(-1)) to generate an intermediate species tert-BuO˙ which induces the alcohol oxidation.