Epoxidation of cyclooctene using soluble or MCM-41-supported molybdenum tetracarbonyl–pyridylimine complexes as catalyst precursors

Recent Advances in Facile Liquid Phase Epoxidation of Light Olefins over Heterogeneous Molybdenum Catalysts

Molybdenum complexes are versatile and efficient for liquid phase olefin epoxidation reactions. Rational design of catalysts is critical to achieve high atom efficiency during epoxidation processes. Although liquid phase epoxidation has been a popular topic for decades, three key issues, (a) rational control of morphology of molybdenum nanoparticles, (b) manipulating metal-support interaction and (c) altering electronic configuration at molybdenum center remains unsolved in this area. Therefore, in this paper, we have critically revised recent research progress on heterogeneous molybdenum catalysts for facile liquid phase olefin epoxidation in terms of catalyst synthesis, surface characterization, catalytic performance and structure-function relationship. Furthermore, plausible reaction mechanisms will be systematically discussed with the aim to provide insights into fundamental understanding on novel epoxidation chemistry.

New Molybdenum(II) Complexes with α-Diimine Ligands: Synthesis, Structure, and Catalytic Activity in Olefin Epoxidation

Three new complexes [Mo(η³-C₃H₅)Br(CO)₂{ⁱPrN=C(R)C₅H₄N}], where R = H (IMP = N-isopropyl 2-iminomethylpyridine), Me, and Ph, were synthesized and characterized, and were fluxional in solution. The most interesting feature was the presence, in the crystal structure of the IMP derivative, of the two main isomers (allyl and carbonyls exo), namely the equatorial isomer with the Br trans to the allyl and the equatorial with the Br trans to one carbonyl, the position trans to the allyl being occupied by the imine nitrogen atom. For the R = Me complex, the less common axial isomer was observed in the crystal. These complexes were immobilized in MCM-41 (MCM), following functionalization of the diimine ligands with Si(OEt)₃, in order to study the catalytic activity in olefin epoxidation of similar complexes as homogeneous and heterogeneous catalysts. FTIR, ¹³C- and ²⁹Si-NMR, elemental analysis, and adsorption isotherms showed that the complexes were covalently bound to the MCM walls. The epoxidation activity was very good in both catalysts for the cis-cyclooctene and cis-hex-3-en-1-ol, but modest for the other substrates tested, and no relevant differences were found between the complexes and the Mo-containing materials as catalysts.

Functionalized nanoparticles as adjuvant to increase the cytotoxicity of metallodrugs toward tumor cells

Silica nanoparticles increasing the cytotoxicity of copper(ii) and zinc(ii) metallodrugs.

Molybdenum(0) tricarbonyl and tetracarbonyl complexes with a cationic pyrazolylpyridine ligand: synthesis, crystal structures and catalytic performance in olefin epoxidation

The synthesis of molybdenum(0) tricarbonyl and tetracarbonyl complexes of the form [Mo(CO)3(ptapzpy)Br] (1) and cis-[Mo(CO)4(ptapzpy)]Br (2) is reported, where ptapzpy = 2-(1-propyltrimethylammonium-3-pyrazolyl)pyridine. Preparation of these derivatives was accomplished either through thermal replacement of CO in Mo(CO)6 (for 1) or substitution under milder conditions of piperidine ligands in the precursor cis-[Mo(CO)4(pip)2] (for 2). The crystal structures of the ligand [ptapzpy]Br and complexes 1 and 2 were determined. Thermal treatment of 2 at 125-150 °C leads to mono decarbonylation and formation of 1. On the other hand, oxidative decarbonylation of 1 and 2 by reaction with tert-butylhydroperoxide (TBHP, 10 equiv.) gives a molybdenum oxide hybrid material formulated as [Mo3O9([ptapzpy]Br)2]·nH2O (3), which was characterised by FT-IR and Raman spectroscopy, thermogravimetric analysis, and 13C{1H} CP MAS NMR spectroscopy. Compounds 1-3 were effective (pre)catalysts for the epoxidation of cis-cyclooctene at 55 °C with aqueous H2O2 or TBHP (slightly better results were obtained with the former). The characterisation of the Mo-containing solids isolated after the catalytic reaction showed that poorly soluble β-octamolybdate salts, (L) x [Mo8O26], were formed from 1-3 with TBHP and from 1 with H2O2, while soluble oxoperoxo species were formed from 3 with H2O2. These findings helped to explain the different catalytic performances obtained.

The Beneficial Sinergy of MW Irradiation and Ionic Liquids in Catalysis of Organic Reactions

The quest for sustainable processes is becoming more and more important, with catalysis playing a major role in improving atom economy and reducing waste. Organic syntheses with less need of protecting/de-protecting steps are highly desirable. The combination of microwave irradiation, as energy source, with ionic liquids, as both solvents and catalysts, offered interesting solutions in recent years. The literature data of the last 15 years concerning selected reactions are presented, highlighting the importance of microwave (MW) technology coupled with ionic liquids.

An environmentally friendly route for grafting of molybdenum carbonyl onto a diaminosilane-modified SBA-15 molecular sieve and its catalytic behaviour in olefin epoxidation

Molybdenum carbonyl (Mo(CO)₆) grafted onto a diaminosiloxane functionalized SBA-15 surface and showed promising activity for epoxidation of olefins.

Synthesis and Properties of Ionogels Based on 1-vinyl-3-alkylimidazolium Tetrahalogenidoferrate (III) [VAIM][FeClnBr4-n] and PMMA

The paramagnetic ionic liquid (IL) 1-vinyl-3-alkylimidazolium tetrahalogenidoferrate (Ⅲ) [VAIM][FeClnBr4-n] (A= n-butyl, n-pentyl, n-hexyl; n=3,4 or 2, 3,4.) has been used in the synthesis of paramagnetic [VAIM][FeClnBr4-n]/PMMA ionogels. The thermal stability for the ionogels increases significantly compared with [VAIM][FeClnBr4-n] and PMMA. Magnetic susceptibility measurements were carried out in the temperature range 1.8 K–300 K. The Curie–Weiss temperature is -0.989 K, -0.669 K and -0.169 K, respectively as the alkyl chain to 3 position of imidazole ring elongate. The magnetic properties are similar to those reported for the pure IL and the self-made [VAIM][FeClnBr4-n] and are not influenced by the incorporation of paramagnetic [VAIM][FeClnBr4-n] into the PMMA matrix. The magnetic ionogel is thus an interesting material combining the mechanical properties of the polyer with the functionality of the magnetic IL, such as magnetism.