Methyl methacrylate polymerization at samarium(II)-grafted MCM-41

Samarium- and Ytterbium-Grafted Periodic Mesoporous Silica for Carbon Dioxide Capture and Conversion

Immobilized coordination compounds of Lewis acidic metals are powerful catalytic components of systems for the cycloaddition of CO2 to epoxides that do not require sophisticated coordination frameworks to harness the metal center and modulate its activity. Surface organometallic chemistry (SOMC) is a valuable methodology to prepare well-defined and site-isolated surface complexes and coordination compounds on metal oxides, with ligand environments easily adjustable to a targeted catalytic reaction. In this work, the SOMC methodology is applied to prepare SmII, YbII, and SmIII alkoxide surface complexes on periodic mesoporous (organo)silica of distinct pore symmetry/size for application in the CO2 cycloaddition reaction. The surface complexes are readily accessible by the grafting of the bis(trimethylsilyl)amide precursors LnII[N(SiMe3)2]2(THF)2 (Ln = Sm, Yb) and SmIII[N(SiMe3)2]3, followed by ligand exchange with alcohols (ethanol and neopentanol). The use of periodic mesoporous supports led to hybrid materials with relatively high surface areas and pore sizes, affording good performance in CO2 capture and in the cycloaddition of CO2 to epoxides under mild conditions (60-80 °C, 1-10 bar). In terms of catalytic performance, recyclability, and low amount of added nucleophile TBAX (X = Br, I), the most active materials prepared in this work compare well to a variety of previously reported SOMC-derived surface complexes and to other heterogeneous Lewis acids displaying more elaborate ligand environments.

Synthesis of Polymer-Mesoporous Silica Nanocomposites

Polymer nanocomposites show unique properties combining the advantages of the inorganic nanofillers and the organic polymers. The mesoporous silica nanofillers have received much attention due to their ordered structure, high surface area and ease for functionalization of the nanopores. To accommodate macromolecules, the nanopores lead to unusually intimate interactions between the polymer and the inorganic phase, and some unusual properties can be observed, when compared with nonporous fillers. Whereas many review articles have been devoted to polymer/nonporous nanofiller nanocomposites, few review articles focus on polymer/mesoporous silica nanocomposites. This review summarizes the recent development in the methods for synthesizing polymer/mesoporous silica nanocomposites based on the papers published from 1998 to 2009, and some unique properties of these composites are also described.

Organometallic chemistry on periodic mesoporous organosilicas: generation of surface-confined zinc and yttrium centres

Periodic mesoporous ethylenesilicas with hexagonal P6mm and cubic Fm3m/Pm3n symmetry were prepared by using divalent surfactant C(16-3-1) and binary surfactant mixtures C(18-3-1) and C18TABr as structure-directing agents, respectively, under basic conditions. A tetramethyldisilazane-based surface silylation was carried out under mild conditions affording hybrid materials SiHMe2@PMO[MCM-41], SiHMe2@PMO[KIT-5] and SiHMe2@PMO[SBA-1], corresponding to silanol group populations of ca. 1.46, 0.67 and 1.63 mmol g(-1), respectively. New molecular zinc precursor compounds Zn[N(SiHMe2)2]2 and EtZn(OSiHtBu2) were synthesized via salt metathesis and alkane elimination procedures from ZnCl2 and LiN[SiH(CH3)2]2, HOSiHtBu2 and ZnEt2, respectively. Organozinc and organoyttrium complexes were reacted with the surface silanol groups according to a heterogeneously performed silylamide route, aswell as an alkane elimination reaction, yielding Zn[N(SiHMe2)2]@PMO[MCM-41], Zn[N(SiHMe2)2]@PMO[KIT-5], Zn[N(SiHMe2)2]@PMO[SBA-1], Zn[N(SiMe3)2]@PMO[MCM-41], Zn[N(SiMe3)2]@PMO[KIT-5], Zn[N(SiMe3)2]@PMO[SBA-1], Y[N(SiHMe2)2]x(THF)y@PMO[MCM-41], Y[N(SiHMe2)2]x(THF)y@PMO[KIT-5], Y[N(SiHMe2)2]x(THF)y@PMO[SBA-1] and Zn(OSiHtBu2)@PMO[MCM-41]. The metal loading mainly depended on the surface silanol group population, size and shape of metal-coordinated ligand, and reaction time as shown for Zn contents in the range of 4.2 to 10.6 wt%. In addition, a preferred N(SiHMe2)2/OC6H2tBu2-2,6-Me-4 ligand exchangeability was found for the large yttrium surface centres. The parent and functionalized materials were characterized by powder X-ray diffraction, elemental analysis, N2 physisorption, FTIR, 13C CP and 1H MAS NMR spectroscopy.

Silica-supported lanthanide silylamides for methyl methacrylate polymerisation: controlled grafting induces controlled reactivity

Lanthanide silylamides were grafted onto non-porous silica dehydroxylated at various temperatures, and the surface species nature and relative distribution were correlated with MMA polymerisation activity and selectivity.