The ordered mesoporous silica MCM-41 was covalently grafted with (3-chloropropyl)trimethoxysilane. Chloro substitution by the anion [4-CH₂-4′-Me-2,2′-bipyridine]⁻ gave a ligand-silica containing ca. 0.3 mmol bipyridyl groups per gram. Powder X-ray diffraction and nitrogen adsorption–desorption analysis demonstrated that the textural characteristics of the support were preserved during the grafting experiments and that the channels remained accessible, despite sequential reductions in surface area, pore volume and pore size. The coupling reactions were monitored by ²⁹Si MAS NMR and ¹³C CP MAS NMR spectroscopy. Bipyridyl-functionalized MCM-41 exhibits a high encapsulating ability, as evidenced by its interaction with a dichloromethane solution of MoO₂Cl₂(THF)₂. A material with a metal loading of 8.3 mass% was obtained. Molybdenum K-edge EXAFS analysis could not substantiate the formation of a tethered complex of the type MoO₂Cl₂(N–N), but instead indicated the formation of unidentate-bridged entities of the type [O₂Mo–X–MoO₂] with a metal–metal separation of 3.28 Å. The molybdenum-containing MCM was active as a catalyst for the epoxidation of cyclooctene by tert-butyl hydroperoxide. However, this activity is due, at least in part, to leached molybdenum species in solution.

Increasing attention has been dedicated to the development of nanomaterials rendering green and sustainable processes, which avail in benign aqueous reaction media. Herein, we demonstrate the synthesis of a novel family of green nanomaterials, layered double hydroxide (LDH) nanoclusters, which are concentrated (98.7 g/L in aqueous solvent), stably-dispersed (transparent sol for >2 weeks), and catalytically-active colloids of nano LDHs (isotropic shape with the size of 7.8 nm by SAXS). LDH nanocluster is available as colloidal building blocks to give access to meso/macroporous LDH materials. Proof-of-concept applications revealed that the LDH nanocluster works as a solid basic catalyst and is separable from solvents of catalytic reactions, confirming the nature of nanocatalysts. The present work closely investigates the unique physical/chemical features of this colloid, the formation mechanism, and the capability as basic nanocatalysts in benign aqueous reaction systems.

The dioxomolybdenum(VI) complex [MoO₂Cl₂{p-tolyl(CH₃DAB)}] has been prepared in good yield by reaction of the solvent adduct MoO₂Cl₂(THF)₂ with one equivalent of the bidentate ligand N,N-p-tolyl-2,3-dimethyl-1,4-diazabutadiene. Treatment of the dichloro complex with the Grignard reagent CH₃MgCl gives the dimethyl derivative [MoO₂(CH₃)₂{p-tolyl(CH₃DAB)}]. The complexes are highly active and selective catalysts for the homogeneous epoxidation of cyclooctene using tert-butyl hydroperoxide (TBHP) as the oxidant. In both cases, the initial activity is ca. 175 mol mol⁻¹ _Mo h⁻¹ and cyclooctene oxide is obtained quantitatively within 4 h. It was possible to recover the dimethyl complex at the end of the reaction and reuse it in a second run with only a small decrease in activity. The complexes are also active and selective for the epoxidation of other olefins, such as 1-octene, 2-octene, cyclododecene and (R)-(+)-limonene, with TBHP. The catalytic production of cyclooctene oxide was investigated in detail, varying either the reaction temperature or the initial concentrations of substrate, oxidant and catalyst precursor. Kinetic studies show that the catalyst precursor–oxygen donor complex formation is first-order in TBHP and in the metal complex [MoO₂Cl₂{p-tolyl(CH₃DAB)}]. A specific rate of 3.2 mol⁻¹ dm³ s⁻¹ was found for catalyst formation at 25 °C. Activation parameters for this reaction have also been measured (ΔH^≠ = 48 ± 3 kJ mol⁻¹, ΔS^≠ = −112 ± 10 J mol⁻¹ K⁻¹).