A heterometallic phenylsilsesquioxane [(PhSiO1,5)22(CoO)3(NaO0.5)6]⋅(EtOH)6⋅(H2O) was synthesized via one-pot procedure and structurally characterized. Its “Spider Web” cage architecture of CoII ions in a triangular topology exhibits a slow dynamic behavior in its magnetization, induced by the freezing of the spins of individual molecules.

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] (1) and pentanuclear [(PhSiO1,5)10(NiO)5(NaOH)(DMF)7] (2) cage-like silsesquioxanes. Their specific structures were studied by single crystal X-ray diffraction and topological analyses. Compound 2 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.

The exotic “Asian Lantern” heterometallic cage silsesquioxane [(PhSiO1.5)20(FeO1.5)6(NaO0.5)8(n-BuOH)9.6(C7H8)] (I) was obtained and characterized by X-ray diffraction, EXAFS, topological analyses and DFT calculation. The magnetic property investigations revealed that it shows an unusual spin glass-like behavior induced by a particular triangular arrangement of Fe(III) ions. Cyclohexane and other alkanes as well as benzene can be oxidized to the corresponding alkyl hydroperoxides and phenol, respectively, by hydrogen peroxide in air in the presence of catalytic amounts of complex I and nitric acid. The I-catalyzed reaction of cyclohexane, c-C6H12, with H216O2 in an atmosphere of 18O2 gave a mixture of labeled and non-labeled cyclohexyl hydroperoxides, c-C6H11–16O–16OH and c-C6H11–18O–18OH, respectively, with an 18O incorporation level of ca. 12%. Compound I also revealed high efficiency in the oxidative amidation of alcohols into amides: in the presence of complex I, only 500 ppm of iron was allowed to reach TON and TOF values of 1660 and 92 h−1.

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.

The novel “cylinder”-like cobalt(ii) phenylsilsesquioxane [(PhSiO1.5)10(CoO)5(NaOH)] was obtained and characterized. This unusual pentanuclear “cylinder” shape is due to specific self-assembly involving the coordination of metallasilsesquioxane units in the presence of charged (Na+ and OH−) moieties used as a template. The combined effect of an unusual odd-membered ring arrangement of Co(II) ions in the cage architecture with a high spin value and spin–orbit coupling of Co(II) induces the appearance of a spin glass-like behavior induced by a spin frustration in each molecule. Additionally, complex efficiently (yield 62%) catalyzes stereoselective (trans/cis ratio = 0.04) dimethylcyclohexanes’ oxidation with m-CPBA and 1-phenylethanol's oxidation (yield 99%) with TBHP.

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 {Fe6O19} 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.

The review describes catalytic properties of a unique class of metal complexes—polycyclic cage-like metallasilsesquioxanes. Article is composed in retrospective manner and reflects the progress of the investigations in the field: from classic applications to recently discovered perspectives of cage-like metallasilsesquioxanes in catalysis of oxidation of С–H compounds.

Tri-, hexa-, and nonacopper(II)methylsilsesquioxanes were synthesized from simple alkoxysilane. Fascinating structures of products were determined by XRD, which witness the observation of the first cage metallasilsesquioxanes, containing nine and three Cu ions. Nonacopper product is the first instance of nonanuclear metallasilsesquioxane ever. Unique architecture of trinuclear complex represents unprecedented “Knight’s Helmet” type of molecular geometry. Complex 1 catalyzes oxidation of either alcohols with TBHP to ketones or alkanes with H2O2 to alkyl hydroperoxides in acetonitrile.

Two types of heterometallic (Fe(III),Na) silsesquioxanes—[Ph5Si5O10]2[Ph10Si10O21]Fe6(O2‒)2Na7(H3O+)(MeOH)2(MeCN)4.5.1.25(MeCN), I, and [Ph5Si5O10]2[Ph4Si4O8]2Fe6Na6(O2‒)3(MeCN)8.5(H2O)8.44, II — were obtained and characterized. X-ray studies established distinctive structures of both products, with pair of Fe(III)-O-based triangles surrounded by siloxanolate ligands, giving fascinating cage architectures. Complex II proved to be catalytically active in the formation of amides from alcohols and amines, and thus becoming a rare example of metallasilsesquioxanes performing homogeneous catalysis. Benzene, cyclohexane, and other alkanes, as well as alcohols, can be oxidized in acetonitrile solution to phenol—the corresponding alkyl hydroperoxides and ketones, respectively—by hydrogen peroxide in air in the presence of catalytic amounts of complex II and trifluoroacetic acid. Thus, the cyclohexane oxidation at 20 °C gave oxygenates in very high yield of alkanes (48% based on alkane). The kinetic behaviour of the system indicates that the mechanism includes the formation of hydroxyl radicals generated from hydrogen peroxide in its interaction with di-iron species. The latter are formed via monomerization of starting hexairon complex with further dimerization of the monomers.

Polynuclear transition metal complexes in Si- or Ge-sesquioxane frameworks synthesized in recent years turned out to be efficient catalysts in oxidation of organic compounds with peroxides: H2O2, tert-butyl hydroperoxide (TBHP), meta-chloroperoxybenzoic acid (MCPBA). This brief review describes oxygenations by peroxides of alkanes to alkyl hydroperoxides, alcohols and ketones and benzene to phenol as well as oxidation of alcohols to the corresponding ketones. Some reactions with MCPBA occur stereoselectively. Important that these metallasesquioxane catalyst often exhibit activity much higher than efficiency demonstrated by simple inorganic salts and many other metal derivatives.

Herein, we describe an approach to cage metallasilsesquioxanes by self-assembly with 1,2-bis(diphenylphosphino)ethane as a key reactant. This approach allowed us to achieve a unique family of complexes that includes anionic tetra- and nonanuclear cage copper(II) sodium silsesquioxane and cationic copper(I) 1,2-bis(diphenylphosphino)ethane components. Additional representatives of this intriguing metallasilsesquioxane family (Cu9Na6 and Cu9Na3Cs3) were obtained through the replacement of the original ethanol-based reaction medium by DMSO. The fascinating structural peculiarities of all products were established by using XRD and topological studies. Initial tests for the application of the synthesized complexes as catalysts revealed their very high activity in the homogeneous oxidation of alkanes and alcohols to produce alkyl hydroperoxides, ketones, and amides.

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.

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.

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).

The deliberate synthesis of two types of prismatic cage-like metallasilsesquioxanes (hereinafter, referred to as CLMSs), viz., penta- and hexanuclear ones, is reported. It is shown that the size of the prismatic cage can be readily and reliably controlled by synthesis parameters. More specifically, the nuclearity shift from six, which is most common in CLMS chemistry (complexes 1–6, 8), to five, which is observed significantly more rarely, is achieved by applying pyridine as a key solvent/crystallization medium (complexes 7, 9–12). Structures of 1–12 were established by single-crystal X-ray diffraction. In sum, their composition could be described as [PhSiO1.5]12[CuO]6 (for hexanuclear products) or [RSiO1.5]10[MO]5 (R = Ph, Vin, M = Cu, Ni, Co for pentanuclear products). Compounds 7, 9–10 represent the rare examples of cage silsesquioxanes comprising pentagonal metalla-oxa rings of Cu(II) ions. The complex 10 is the very first observation of a co-crystal composed of different CLMS (i.e., two Co(II)5 and one Cu(II)5 prismatic cages). The compound 12 (Co5 cage with vinyl substituents at the silicon atoms) is the very first example of a pentanuclear CLMS-based coordination polymer. Complex 7 efficiently catalyzes oxidation of secondary alcohols to the corresponding ketones and alkanes to the corresponding alkyl hydroperoxides.

Two prismatic phenyl- (PhSiO1.5)14(CuO)7 (1, 29 % yield) and methyl- (MeSiO1.5)14(CuO)7 (2, 19 % yield) heptacoppersilsesquioxanes were obtained by the interaction of Cu,Na-based cage silsesquioxanes [(RSiO1.5)12(CuO)4(NaO0.5)4] (R = Ph, Me) with 4,4′-bipyridine and pyrazine, respectively, acting as “silent witness” ligands. Unusual molecular topologies of both compounds 1 and 2, which are the first representatives of cage silsesquioxanes with seven metal ions in their cores, were established by X-ray diffraction studies. Complex 1 was found to be an active precatalyst in the oxidation of alkanes and 1-phenylethanol to alkyl hydroperoxides and acetophenone, respectively. Alkanes were oxidized by hydrogen peroxide, and the alcohol was oxidized by tert-butyl hydroperoxide.

We herein report a study of Cu(II)-silsesquioxanes’ self-assembly in the presence of two possible template agents (acetonitrile and acetone). This results in the isolation of unusual high-nuclearity cluster CuII8 cage silsesquioxanes [(Ph8Si8O16)2Cu8(DMF)8][Ph8Si8O12]·2MeCN 1 and [(Me8Si8O16)2Cu8(Me2CO)4]2[MeCOO–]2[Na+]2·2(H2O)·3(Me2CO) 2. In the case of 1, acetonitrile indeed serves as a template being incorporated into the inner void of the prism-like cage of the crystalline product. To the contrary, in the case of complex 2, acetone molecules just play the role of external solvates. An inner void of the prism-like cage in 2 is occupied by sodium acetate groups. The latter, most likely, are produced via the mild oxidation of ethanol during the synthesis of 2. Finally, the sodium centers of these acetate groups caused an unprecedented “cage connectivity” (dimerization of two octacopper cage silsesquioxanes in 2).

Brand new cage-like Ni(II)-based germosesquioxane architecture has been obtained via self-assembly reaction starting from PhGe(OMe)3. Product presents an early unknown skewed sandwich molecular structure with a cubane-like core of Ni(II) centers and perpendicular orientation of each two molecules in the crystal packing. This compound exhibits the slow dynamics of the magnetization and particularly the spin glass behavior of a complex origin.

A series of three unprecedented heterometallic copper(II) sodium silsesquioxanes were isolated (i) via the unusual rearrangement process during synthesis of coordination polymers or (ii) via the self-assembly reaction using 2,2′-bipyridine. The unique type of these products’ molecular topology consists of an unusual fusion of two sandwich-like components (each including five copper and one sodium sites) via a central copper ion. These compounds correspond to the highest nuclearity among Cu(II)-based cage silsesquioxanes reported to date.

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.

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.

Unprecedented germanium-based sesquioxane exhibits an extremely high nuclearity (Cu42Ge24Na4) and unusual encapsulation features. The compound demonstrated a high catalytic activity in the oxidative amidation of alcohols, with cost-effective catalyst loading down to 400 ppm of copper, and in the oxidation of cyclohexane and other alkanes with H2O2 in acetonitrile in the presence of nitric acid. Selectivity parameters and the mode of dependence of initial cyclohexane oxidation rate on initial concentration of the hydrocarbon indicate that the reaction occurs with the participation of hydroxyl radicals and alkyl hydroperoxides are formed as the main primary product. Alcohols have been transformed into the corresponding ketones by the catalytic oxidation with tert-butyl hydroperoxide.

Different types of germanium-based metal compounds are reviewed. Features of different synthetic approaches are discussed. Role of organic ligands in germanium metal complexes formation is presented. Potential applications (as magnetic, porous and catalytic materials) are reviewed.

A simple and versatile strategy of synthesis of cage metallagermaniumsesquioxanes is demonstrated for isolation of Cu6-based phenylgermsesquioxanes 1–6. Structure of newly synthesized coppergermsesquioxanes was established by single-crystal X-ray diffraction analysis. General principle of these cages' topology implies the presence of two linear Cu3 fragments, coordinated by three pairs of ligands. These are: (i) cyclic germsesquioxanes [PhGeO1,5]5, products 1–6, (ii) 1,10-phenanthrolines, (1, 3–5) or 2,2’-bipyridines, (2, 6), (or and (iii) OX species (X = H, 1–2, CH3, 3, H and C2H5O, 4, HCO, 5, CH3CO, 6). Appearance of non-expected species (formiate for 5, acetate for 6), resulted from corresponding alcohols used as reaction media, points at easyness of oxidation processes in the conditions of such self-assembling reactions. Catalytic tests showed high activity of complexes 1 and 2 as precatalysts in homogeneous oxidations of alkanes (cyclohexane, methylcyclohexane, n-heptane, cis-1,2-dimethylcyclohexane with hydrogen peroxide in acetonitrile solution. Hydroxyl radicals take part in the reaction. The same complexes catalyze oxidation of alcohols (cyclohexanol, 2-heptanol, 1-phenylethanol) to corresponding ketones with tert-butyl hydroperoxide in almost 100% yield. With the addition of various alkyl ammonium salts, complex 2 could also furnish corresponding amides in high yield.

The self-assembly synthesis of copper-sodium phenylsilsesquioxane in the presence of 1,1-bis(diphenylphosphino)methane (dppm) results in an unprecedented cage-like product: [(PhSiO1,5)6]2[CuO]4[NaO0.5]4[dppmO2]2 1. The most intriguing feature of the complex 1 is the presence of two oxidized dppm species that act as additional O-ligands for sodium ions. Two cyclic phenylsiloxanolate (PhSiO1,5)6 ligands coordinate in a sandwich manner with the copper(II)-containing layer of the cage. The structure of 1 was established by X-ray diffraction analysis. Complex 1 was shown to be a very good catalyst in the oxidation of alkanes and alcohols with hydrogen peroxide or tert-butyl hydroperoxide in acetonitrile solution. Thus, cyclohexane (CyH), was transformed into cyclohexyl hydroperoxide (CyOOH), which could be easily reduced by PPh3 to afford stable cyclohexanol with a yield of 26% (turnover number (TON) = 240) based on the starting cyclohexane. 1-Phenylethanol was oxidized by tert-butyl hydroperoxide to give acetophenone in an almost quantitative yield. The selectivity parameters of the oxidation of normal and branched alkanes led to the conclusion that the peroxides H2O2 and tert-BuOOH, under the action of compound (1), decompose to generate the radicals HO. and tert-BuO. which attack the C-H bonds of the substrate.