Ales Styskalik

Non-aqueous template-assisted synthesis of mesoporous nanocrystalline silicon orthophosphate

The first synthesis of mesoporous nanocrystalline silicon orthophosphate Si5P6O25 is presented. The synthetic procedure is based on the non-hydrolytic sol–gel reaction in the presence of Pluronic P123 template and subsequent calcination in air. The condensation of silicon acetate, Si(OAc)4, and tris(trimethylsilyl)phosphate, OP(OSiMe3)3 (TTP), in non-aqueous solvents driven by elimination of trimethylsilyl acetate provides a homogeneous network with a high content of Si–O–P bonds and SiO6 moieties. After burning out the template, mesoporous silicon orthophosphate was obtained with surface areas up to 128 m2 g−1 and pore sizes around 20 nm. The nanocrystalline Si5P6O25 phase forms relatively easily (500 °C, 4 h) in comparison with other synthetic routes. All samples were characterized by SEM, TEM, elemental analysis, TGA, nitrogen adsorption, SAXS, 1H, 13C, 29Si, and 31P solid-state NMR spectroscopy, and powder XRD. These xerogels showed superior catalytic activity and selectivity in methylstyrene dimerization.

Novel non-hydrolytic templated sol–gel synthesis of mesoporous aluminosilicates and their use as aminolysis catalysts

A novel non-hydrolytic sol–gel (NHSG) synthesis of mesoporous aluminosilicate xerogels is presented. The polycondensation between silicon acetate, Si(OAc)4, and tris(dimethylamido)alane, Al(NMe2)3, leads to homogeneous aluminosilicate xerogels containing Si–O–Al linkages through dimethylacetamide elimination. The addition of Pluronic P123 and F127 templates provides stiff gels that are, after calcination at 500 °C, converted to stable mesoporous xerogels with a high surface area (>600 m2 g−1) and wormhole-type pores (d = 5.9 nm). The xerogels exhibit high catalytic activity in aminolysis of styrene oxide (82% conversion) with the turnover frequency up to 100.

Control of micro/mesoporosity in non-hydrolytic hybrid silicophosphate xerogels

Non-hydrolytic sol–gel reactions of acetoxysilanes with trimethylsilyl esters of phosphoric and phosphonic acids produce cross-linked matrices containing homogeneous dispersions of silicon and phosphoryl groups connected together by networks of Si–O–P(O) linkages. These polycondensation reactions proceed cleanly and under mild conditions for a wide variety of precursor silanes RnSi(OAc)4−n (R = alkyl, aryl; n = 1, 2) and phosphoryl compounds RP(O)(OSiMe3)2 (R = alkyl, aryl) to provide hybrid xerogels, the final properties of which are a sensitive function of the organic substituents and the Si : P ratio of the precursors. The reactions of bridged acetoxysilanes (AcO)3Si–X–Si(OAc)3 and phosphoryl reagents (Me3SiO)2P(O)–X–P(O)(OSiMe3)2 have also been investigated and found to produce gels that exhibit large surface areas (up to 700 m2 g−1). The presence of SiO6 structural units in bridged-phosphoryl xerogels is related to their microporosity while the absence of such moieties in bridged-acetoxysilane networks is congruent with significant mesoporosity. Several important parameters are identified which can be used to tailor the properties of these hybrid matrices such that gels with specific polarity, porosity and surface area can be targeted at the time of synthesis.

Mesoporous SnO2–SiO2 and Sn–silica–carbon nanocomposites by novel non-hydrolytic templated sol–gel synthesis

A novel non-hydrolytic sol–gel (NHSG) synthesis of mesoporous tin silicate xerogels is presented. The polycondensation between silicon tetraacetate, Si(OAc)4, and tetrakis(diethylamido)tin, Sn(NEt2)4, resulting in acetamide elimination leads to tin silicate xerogels containing Si–O–Sn linkages. The addition of Pluronic P123 or F127 templates provides homogeneous stiff gels that are, after template removal by calcination at 500 °C in air, converted to stable mesoporous silica xerogels with large surface areas (476 m2 g−1) and dispersed SnO2 nanoparticles (6–7 nm). Heat treatment of the as-prepared tin silicate gels in an inert N2 atmosphere leads to reduction and transformation to Sn nanoparticles (70–150 nm) embedded in a silica–carbon matrix. The composition and morphology of the xerogels, volatile reaction byproducts, and thermal transformations were followed by elemental analyses, IR spectroscopy, thermal analysis TG-DSC, nitrogen adsorption measurements, solid-state NMR spectroscopy, DRUV-vis spectroscopy, electron microscopy, and HT powder XRD. The SnO2–SiO2 xerogels were tested as potential catalysts for aminolysis of styrene oxide with aniline and for the Meerwein–Ponndorf–Verley reduction of 4-tert-butylcyclohexanone. The resulting reaction systems displayed good activity and selectivity.

Surface reactivity of non-hydrolytic silicophosphate xerogels: a simple method to create Brønsted or Lewis acid sites on porous supports

Non-hydrolytic sol-gel reactions of silicon acetates with trimethylsilyl (TMS) esters of phosphoric and phosphonic acids produce cross-linked matrices containing homogeneous dispersions of silicate and phosphoryl groups connected together by networks of Si-O-P(QO) linkages. The condensation degrees reach 80 to 90%. Residual organic groups (10 to 20%) were reacted with a variety of compounds (H2O, Me3SiOSiMe3, POCl3, SiCl4, AlMe3, Al(NMe2)(3), and AlCl3) in order to enrich the surface of these porous matrices with Bronsted (RP-OH) and Lewis (tetracoordinated Al) acid functional groups. The differences in the reactivity of RSi-OAc and RP-OSiMe3 groups were utilized for the selective modification at the silicon and phosphorus atoms. The reaction procedures were optimized and significantly porous silicophosphate materials with a high content of either hydroxyl groups or four-coordinated aluminium species were obtained. The activity and selectivity of prepared samples as catalysts for the dimerization of a-methylstyrene were tested. Excellent activities and moderate to very high selectivities were achieved suggesting the potential use of silicophosphate xerogels in heterogeneous catalysis.

New Adamantane-like Silicophosphate Cage and Its Reactivity toward Tris(pentafluorophenyl)borane

The condensation reaction between Ph2Si(OC(O)CH3)2 and OP(OSiMe3)3 leads to elimination of CH3C(O)OSiMe3 and the formation of the new silicophosphate cage molecule Ph12Si6P4O16 (1) with an adamantane-like core possessing four terminal P═O moieties and six O-SiPh2-O bridging groups. Compound 1 was further reacted with the Lewis acid B(C6F5)3. We observed adduct formation by coordination through the P═O→B bonds and isolated and structurally characterized two new molecules. In the first of them, the adamantane-like cage is preserved and three phosphoryl oxygen atoms coordinate to boranes, forming Ph12Si6O16P4·3B(C6F5)3 (2); the remaining P═O group is inverted toward the cage center pointing along a C3 molecular axis. The molecule is chiral, and the compound 2 crystallizes as a conglomerate of homochiral crystals. Enantiomers 2M and 2P were both structurally characterized. The second adduct resulted from an unexpected reorganization of the Si-O-P linkages in the adamantane cage during the reaction of 1 with 4 equiv of B(C6F5)3. The bis-adduct Ph6Si3O8P2·2B(C6F5)3 (3) was formed with an inorganic core representing half of the parent molecule 1.