A Family of Hexacopper Phenylsilsesquioxane/Acetate Complexes: Synthesis, Solvent-Controlled Cage Structures, and Catalytic Activity

Convenient self-assembly synthesis of copper(II) complexes via double (phenylsilsesquioxane and acetate) ligation allows to isolate a family of impressive sandwich-like cage compounds. An intriguing feature of these complexes is the difference in the structure of a pair of silsesquioxane ligands despite identical (Cu6) nuclearity and number (four) of acetate fragments. Formation of particular combination of silsesquioxane ligands (cyclic/cyclic vs condensed/condensed vs cyclic/condensed) was found to be dependent on the synthesis/crystallization media. A combination of Si4-cyclic and Si6-condensed silsesquioxane ligands is a brand new feature of cage metallasilsesquioxanes. A representative Cu6-complex (4) (with cyclic silsesquioxanes) exhibited high catalytic activity in the oxidation of alkanes and alcohols with peroxides. Maximum yield of the products of cyclohexane oxidation attained 30 %. The compound 4 was also tested as catalyst in the Baeyer-Villiger oxidation of cyclohexanone by m-chloroperoxybenzoic acid: maximum yields of 88 % and 100 % of ϵ-caprolactone were achieved upon conventional heating at 50 °C for 4 h and MW irradiation at 70 or 80 °C during 30 min, respectively. It was also possible to obtain the lactone (up to 16 % yield) directly from the cyclohexane via a tandem oxidation/Baeyer-Villiger oxidation reaction using the same oxidant.

A Family of Cagelike Mn-Silsesquioxane/Bathophenanthroline Complexes: Synthesis, Structure, and Catalytic and Antifungal Activity

This study reports a novel family of cage manganesesilsesquioxanes prepared via complexation with bathophenanthroline (4,7-diphenyl-1,10-phenanthroline). The resulting Mn4-, Mn6Li2-, and Mn4Na-compounds exhibit several unprecedented cage metallasilsesquioxane structural features, including intriguing self-assembly of silsesquioxane ligands. Complexes were tested in vitro for fungicidal activity against seven classes of phytopathogenic fungi. The representative Mn4Na-complex acts as a catalyst in the cycloaddition of CO2 to epoxides under solvent-free conditions to form cyclic carbonates in good yields.

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

A small family of nonanuclear Cu5Cs4-based phenylsilsesquioxanes 1-2 were prepared by a convenient self-assembly approach and characterized by X-ray diffraction studies. The compounds 1 and 2 show some unprecedented structural features such as the presence of a [Ph14Si14O28]14- silsesquioxane ligand and a CuII5CsI4 nuclearity in which the metal cations occupy unusual positions within the cluster. Copper ions are "wrapped" into a silsesquioxane matrix, while cesium ions are located in external positions. This resulted in cesium-involved aggregation of coordination polymer structures. Both compounds 1 and 2 realize specific metallocene (cesium-phenyl) linkage between neighboring cages. Compound 2 is evaluated as a catalyst in the Baeyer-Villiger (B-V) oxidation of cyclohexanone and tandem cyclohexane oxidation/B-V oxidation of cyclohexanone with m-chloroperoxybenzoic acid (mCPBA) as an oxidant, in an aqueous acetonitrile medium, and HNO3 as the promoter. A quantitative yield of ε-caprolactone was achieved under conventional heating at 50 °C for 4 h or MW irradiation for 30 min (for cyclohexanone as substrate); 17 and 19% yields of lactone upon MW irradiation at 80 °C for 30 min and heating at 50 °C for 4 h, respectively (for cyclohexane as a substrate), were achieved. Complex 2 was evaluated as a catalyst for the oxidation of alkanes to alkyl hydroperoxides and alcohols to ketones with peroxides at 60 °C in acetonitrile. The maximum yield of cyclohexane oxidation products was 30%. Complex 2 exhibits high activity in the oxidation of alcohols.

Silane-Bearing Borasilsesquioxanes: Synthetic Protocol and Unsuspected Redistribution Reactions

The presented work is a continuation of research on the reactivity of unsaturated borasilsesquioxanes under the conditions of common organometallic transformations. The catalytic hydrosilylation reaction with silanes, siloxanes and silsesquioxanes in presence of platinum catalyst was explored. The majority of the products were obtained in high yields (>90 %) and their structures were confirmed and characterized by spectroscopy and spectrometry, i. e. NMR and MALDI-TOF-MS. The most significant segment of the work is research on the spontaneous redistribution reaction of the alkoxy group from silane to borane moiety occurring in the obtained products, not being limited to the heterosilsesquioxane chemistry, however. The products were confirmed using GC-MS, ESI-MS methods and B3LYP exchange-correlation, in order to ascertain formation of the silicon-boron hybrid molecule.

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

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.

Multinuclear rhodium complexes supported by tetra-tert-butoxy disiloxide ligand: Synthesis, structure, and reactivity

Rhodium siloxide complexes have been used as homogeneous catalysts and model compounds for silica-supported metal catalysts. However, rhodium complexes with multidentate siloxide ligands have rarely been prepared. In this study,...