Dioxomolybdenum(VI)-Modified Mesoporous MCM-41 and MCM-48 Materials for the Catalytic Epoxidation of Olefins

Syntheses and catalytic activities of new metallodendritic catalysts

Metallodendritic catalysts showed high selectivity in the epoxidation of olefins even after being used for at least five cycles.

Periodic mesoporous organosilicas with bis(8-quinolinolato) dioxomolybdenum(VI) inside the channel walls

Novel periodic mesostructured organometallic silicas of MCM-41 type bearing homogeneously distributed bis(8-quinolinolato)dioxomolybdenum(VI) inside the channel walls (denoted as MoO(2)Q(2)@PMO-x) are synthesized via a convenient one-pot method and examined as catalysts in the epoxidation of cyclooctene. The ordered mesoporous structures as well as the organometallic groups incorporated into the framework are fully determined by comprehensive characterization techniques such as XRD, TEM, N(2) adsorption/desorption, SEM, FT-IR, UV-vis spectroscopy, solid-state NMR, ICP-AES, XPS and TG/DSC. MoO(2)Q(2)@PMO-6% catalyst exhibits higher activity for the epoxidation of cyclooctene with tert-butyl hydroperoxide than other MoO(2)Q(2)@PMO materials and its homogeneous or randomly grafted analogue.

Convenient ultrasound-mediated synthesis of 1,4-diazabutadienes under solvent-free conditions

An ultrasound-assisted preparation of 1,4-diazabutadienes via smooth condensation of diketones with amines under solvent-free conditions is described. The generality of this method was examined by the synthesized N,N'-diaryl- and N,N'-dialkyl-1,4-diazabutadiene derivatives. In addition to experimental simplicity, the main advantages of the procedure are mild conditions, short reaction time (2-15 min) and high yields (71-98%).

Vibrational Study on the Local Structure of Post-Synthesis and Hybrid Mesoporous Materials: Are There Fundamental Distinctions?

Organic-inorganic mesoporous materials of the MCM-41 type are important materials that can be prepared by either post-synthesis or one-pot synthesis procedures. A complete control of the characteristics at a local level is of the utmost importance in view of the applications of such materials. However, there are not many studies relating such features with synthetic approaches. In this work, we prepared samples by post-synthesis derivatization of materials from Si-based MCM-41, with bidentate nitrogen ligands bearing one or two silylated arms, and by one-pot synthesis of organic-inorganic hybrid materials. The bulk properties of the two kinds of materials were comparable. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy and Raman spectroscopy were used to investigate the local environment, namely, the number of OH groups and distribution of SiO(4) units (large and small ring units). Hydrophilicity correlates with both the type of organic moiety used (mono- or disilylated), as well as with the synthetic procedure. The same vibrational studies showed how the structure in the channels changes as a function of pressure, reflecting the low mechanical stability of the mesoporous materials.

Immobilization of Oxomolybdenum Species in a Layered Double Hydroxide Pillared by 2,2‘-Bipyridine-5,5‘-dicarboxylate Anions

A Zn,Al layered double hydroxide (LDH) with Zn/Al = 1.45 and containing nitrate anions was prepared by coprecipitation and characterized by powder X-ray diffraction, Zn K-edge extended X-ray absorption fine structure spectroscopy (EXAFS), thermogravimetric analysis, FTIR and FT Raman spectroscopy, and (27)Al MAS NMR spectroscopy. Three Zn...O and four Zn...M (M = Zn, Al) shells could be fitted to the low-temperature (40 K) EXAFS spectrum, in accordance with a model for an ordered cationic sheet. The nitrate anions were easily exchanged by 2,2'-bipyridine-5,5'-dicarboxylate anions, resulting in an increase in the basal spacing from 9 to 18 A. The basal spacing of the pillared derivative indicates that the anions are arranged with their longest dimension nearly perpendicular to the host layers. This material exhibits a high encapsulating ability, as evidenced by its interaction with a dichloromethane solution of the dioxomolybdenum(VI) complex MoO(2)Cl(2)(THF)(2). A material with a metal loading of 11.2 wt % was obtained. Molybdenum K-edge EXAFS analysis could not substantiate the formation of a supported complex of the type MoO(2)Cl(2)(N-N) but instead indicated the formation of unidentate-bridged entities of the type [O(2)Mo-O-MoO(2)] with a metal-metal separation of 3.29 A. The molybdenum-containing LDH was active as a catalyst for the liquid-phase epoxidation of cis-cyclooctene, 1-octene, and trans-2-octene using tert-butyl hydroperoxide as the oxygen source, yielding the corresponding epoxides as the only products. For reactions carried out with no additional solvent (other than n-decane) or in the presence of 1,2-dichloroethane, the solid catalyst could be recycled with no major loss of activity. Other tests confirmed that the systems functioned as true heterogeneous catalysts.

Heterogenisation of CpMo(CO)3Cl on mesoporous materials and its application as olefin epoxidation catalyst

CpMo(CO)(3)Cl reacts with the hydroxyl (Si-OH or Si-OH-Al) functionalities of mesoporous molecular sieves such as MCM-41, MCM-48 and its aluminium analogues during grafting. XRD, N(2) adsorption-desorption, BET surface area analysis and TEM show the resulting samples as being well ordered and maintaining a uniform pore size. FT-IR spectra, elemental analysis, (13)C and (29)Si CP MAS NMR spectra confirm the successful grafting. In the presence of excess TBHP the materials show high activity in cyclooctene epoxidation and good stability.