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ABSTRACT: In order to exploit the different textural properties of Laponite and MCM-41, specifically in terms of their external versus
internal surface areas, in the covalent anchoring of a chiral Mn(III) salen complex, these materials were functionalized with 3-aminopropyltriethoxysilane (APTES), subsequently activated with sodium
ethoxide, and finally used to anchor the Jacobsen catalyst derivative C1. All the materials were characterized by nitrogen
elemental analysis, XPS, PXRD, nitrogen adsorption at −196°C, FTIR and for those with the immobilized complex, they were
additionally characterized by Mn AAS. The APTES anchored at the edges of the Laponite single crystals and inside the MCM-41
pores. Moreover, under the same preparative conditions, higher amount of APTES was anchored onto MCM-41 than onto Laponite,
which is due to the higher surface area of MCM-41 compared to Laponite, as well as to its more exposed SiO4 tetrahedra. Activation of the two organo-functionalized materials with sodium ethoxide originated anionic nitrogen groups
as deduced by the increase of surface sodium content of these materials and N1s binding energy changes, but led to a small
decrease in N bulk content as a result of some APTES leaching. Moreover, for MCM-41 some disruption of the silica framework
occurred as a consequence of the basic treatment, as suggested by XPS, PXRD, and nitrogen adsorption study. The APTES functionalized
Laponite and MCM-41 materials, as well as the activated analogs, were able to anchor C1 through axial coordination of the
metal centre to the grafted surface nitrogen atoms. APTES functionalized MCM-41 presented similar complex content to Laponite
analog, what points out for the fact that, at least for the bulky complex used in this work, there was no clear benefit in
using a material of high internal area; for the ethoxide activated analogs, Laponite showed the highest complex content of
all materials, but MCM-41 was able to anchor the lowest complex quantity, probably as a consequence of damaging effect caused
by the basic treatment within its porous structure.
Journal of Materials Science 04/2012; 44(11):2865-2875. · 2.02 Impact Factor
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ABSTRACT: a b s t r a c t A copper(II) chiral bis(oxazoline) homogeneous catalyst (CuBox) was anchored onto mesoporous materi-als using three procedures: method 1, first anchoring of the bis(oxazoline) functionalized with 3-iodopro-pyltrimethoxysilane onto hexagonal mesoporous silica, SBA-15 and silica gel and then copper(II) coordination; method 2, anchoring of the CuBox functionalized with 3-iodopropyltrimethoxysilane onto hexagonal mesoporous silica, SBA-15 and silica gel; and method 3, first anchoring onto silica gel of 3-iod-opropyltrimethoxysilane and then anchoring of the CuBox. In methods 1 and 3, the remaining free silanol groups of the silica materials were also capped using trimethylsilane groups. The bis(oxazoline) ligand was also encapsulated onto copper(II) exchanged zeolites NaY and NaUSY as a simpler strategy for the homogeneous catalyst immobilization, method 4. The materials were characterized by ICP–AES, elemen-tal analyzes, 13 C and 29 Si MAS NMR, FTIR, thermogravimetry and nitrogen adsorption at À196 °C. The materials were tested as heterogeneous catalysts in the benchmark reaction of cyclopropanation of sty-rene to check the effect of the immobilization strategy on the catalytic parameters as well as on their reutilization in several catalytic cycles.
Microporous and Mesoporous Materials 04/2012; · 3.29 Impact Factor
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ABSTRACT: A copper C2-symmetric bis(oxazoline), CuBox, was introduced in two forms of commercial Y zeolite: a sodium form (NaY) and an ultrastable form (NaUSY). CuBox was introduced by first partially exchanging the sodium cations of both zeolites for copper and then by refluxing the obtained materials with a solution of bis(oxazoline) (Box). Two different loadings were prepared for each form of zeolite. The materials were characterized by copper ICP-AES, elemental analysis, XPS, FTIR, TG, and nitrogen adsorption isotherms at −196 °C. Evidence for Box ligand location in the supercages of NaY and NaUSY zeolites and its coordination to the exchanged copper(II) was obtained by the several techniques used. The materials were all active in the cyclopropanation of styrene with ethyldiazoacetate at room temperature and diastereoselective toward trans cyclopropanes. Although the materials containing Box showed low enantioselectivities, their catalytic activities were higher than the parent copper exchanged zeolites, and did not decrease with reuse, at least during three consecutive cycles.
09/2011;
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ABSTRACT: Silylation of several materials where the surface area arises from the internal pores (MCM-41 and FSM-16) or is essentially external (silica gel, and clays) was performed using three organosilanes: (3-aminopropyl)triethoxysilane (APTES), 4-(triethoxysilyl)aniline (TESA) and (3-mercaptopropyl)trimethoxysilane (MPTS). The materials were characterized by nitrogen adsorption-desorption at -196 degrees C, powder XRD, XPS, bulk chemical analysis, FTIR and (29)Si and (13)C MAS NMR. For MCM-41 and FSM-16 the highest amounts of organosilane are obtained for APTES, while for the remaining materials the highest amounts are for MPTS; TESA always anchored with the lowest percentage. In terms of surface chemical analysis, TESA anchored with the highest contents irrespectively of the material, and the opposite is registered for MPTS. Comparison of bulk vs surface contents indicate that TESA is mainly anchored at the material external surface. Moreover, with N or S (surface and bulk) contents expressed per unit of surface area, MCM-41 and FSM-16 (internal porosity) show the lowest amounts of silane; the highest amounts of silane per unit of surface area are obtained for the clays. Grafting of the organosilanes to the surface hydroxyl groups was corroborated by FTIR and (29)Si and (13)C MAS NMR. Furthermore, NMR data suggested that TESA and APTES grafted mostly through a bidentate approach, whereas MPTS grafted by a monodentate mechanism.
Journal of Colloid and Interface Science 04/2010; 344(2):603-10. · 3.07 Impact Factor
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ABSTRACT: The Jacobsen catalyst derivative, (R,R)-[Mn(3,5-dtButsalhd)]ClO4–CAT 2, was immobilized through axial coordination of the metal center onto a Laponite, MCM-41 and FSM-16 functionalized with
3-aminopropyltriethoxysilane. The catalytic activity of the Mn-based materials was screened for the enantioselective epoxidation
of three olefins: styrene, α-methylstyrene and 6-CN-2,2′-dimethychromene, using m-CPBA/NMO as oxidant, and the results were
compared with the corresponding homogenous complex (CAT 2) and with the Jacobsen’s catalyst, (R,R)-[Mn(3,5-dtButsalhd)Cl]–CAT 1. The results indicate that under comparable condition, the Laponite-based materials show both,
higher epoxide yield and enantiomeric excess (ee%) compared to MCM-41 and FSM-16-based materials. The best ee% value was obtained
for the substrate 6-CN-2,2′-dimethylchromene (64%) which is very close to that obtained with CAT 2 (67%) in homogeneous phase;
for the two regular mesoporous materials (MCM-41 and FSM-16) the catalytic results were more favorable for the FSM-16 samples.
Catalysis Letters 04/2009; 129(3):367-375. · 2.24 Impact Factor
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04/2008: pages 267 - 307; , ISBN: 9780470403709
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ABSTRACT: The parent clays laponite (Lap) and K10-montmorillonite (K10) and those functionalised with (3-aminopropyl)triethoxysilane (APTES) were used as supports to immobilise vanadyl(IV) acetylacetonate ([VO(acac)2]). All the materials were characterised by elemental analysis, XRD, TG-DSC, nitrogen adsorption isotherms at −196 °C and IR spectroscopy. The K10-based materials were also characterised by XPS.
In the case of K10-based materials, higher vanadium content was obtained for the APTES-functionalised K10, showing that the clay functionalisation enhanced the complex anchorage. In Lap-based materials the opposite tendency was observed, with a higher vanadium loading being obtained for direct complex immobilisation onto the parent clay. This is probably due to clay particles aggregation (resultant from the delaminated nature of Lap) provoked by functionalisation with APTES. Furthermore, FTIR data pointed out that in the amine-functionalised clays, the VO(IV) complex was anchored by Schiff condensation between the carbonyl groups of the acetylacetonate ligand and the amine groups from the grafted APTES, whereas the direct immobilisation of the complex onto the parents clays took place mostly through covalent bonding between the metal centre and the clay surface hydroxyl groups.
The [VO(acac)2]-based materials were tested in the epoxidation of geraniol using t-BuOOH as oxygen source and reused several times repeatedly. The [VO(acac)2]APTES@K10 material was the most efficient and stable catalyst upon reuse (5 cycles), among the four materials tested, with a substrate conversion and 2,3-epoxygeraniol regioselectivity comparable to the homogeneous phase reaction; the organofunctionalisation of K10 was also quite advantageous in the catalytic reaction since it passivated some active sites of the K10 support. In the case of Lap-based materials, the [VO(acac)2]@Lap was more catalytically efficient than [VO(acac)2]APTES@Lap.
Journal of Molecular Catalysis A Chemical 03/2008; 283(1-2):5-14. · 2.95 Impact Factor
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ABSTRACT: Copper (II) acetylacetonate was immobilised directly onto two clays, laponite (Lap) and K10-montmorillonite (K10), and after their amine functionalisation with (3-aminopropyl)triethoxysilane (APTES). All the materials were characterised by nitrogen adsorption isotherms at -196 degrees C, elemental analysis, TG-DSC, XRD, and IR spectroscopy. The K10-based materials were also characterised by XPS. The APTES-functionalised K10 showed higher copper loading than K10, indicating that the clay functionalisation enhanced the complex immobilisation; on the contrary, in Lap-based materials higher metal content was obtained by direct complex anchoring, probably due to the delaminated nature of Lap which induced the particles aggregation on functionalisation with APTES. All the results pointed out that the Cu complex was anchored onto the amine-functionalised clays by Schiff condensation between the amine groups of anchored APTES and the carbonyl groups of the acetylacetonate ligand, whereas direct immobilisation proceeded mostly through interaction between the metal centre and the clay surface hydroxyl groups.
Journal of Colloid and Interface Science 01/2008; 316(2):570-9. · 3.07 Impact Factor
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ABSTRACT: Several pillared clays were prepared by using a polyalcohol (ethylene glycol or poly(vinyl alcohol)) or a poly(ethylene oxide) surfactant as an interlayer gallery template and an aluminum oligomer species as the pillaring agent. The use of polyalcohols or nonionic surfactants, such as Tergitol, gave materials which, in general, presented larger basal spacing than those found for the solids prepared by a similar procedure but without additives. The initial positive effect in the expansion of the clay interlayers was not totally retained after calcination of the materials; most probably, at the end, the basal spacing is still ruled by the intercalating aluminum species. The pillared clay with the largest basal spacing and specific surface area was used to encapsulate copper(II) complexes with pentadentate N3O2 Schiff base ligands derived from copper(II) acetylacetonate by in situ synthesis. The characterization made (X-ray diffraction, X-ray photoelectron spectroscopy, FTIR spectroscopy, chemical analysis, and low-temperature N2 adsorption) provided evidence that copper(II) complexes with pentadentate N3O2 Schiff base ligands were efficiently entrapped within the lower dimension pores of the pillared clay and that they interact strongly with the pillared clay matrix.
Langmuir 04/2004; 20(7):2861-6. · 4.19 Impact Factor
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Berichte der deutschen chemischen Gesellschaft 03/2004; 2004(10):2027 - 2035. · 2.94 Impact Factor
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ABSTRACT: Manganese(III) salen complexes bearing hydroxyl groups on the aldehyde moiety were grafted onto the surface of an air oxidised activated carbon. The resulting carbon materials were characterised by elemental analysis, X-ray photoelectron spectroscopy and N2 adsorption at 77 K. The catalytic activity of the novel manganese(III) salen based materials was tested in the epoxidation of styrene in acetonitrile, using iodosylbenzene as oxygen source, and compared with the corresponding homogeneous phase data. The heterogenised catalysts are chemoselective towards the styrene epoxide as their homogeneous counterparts, are resistant to leaching and can be re-used without loss of their catalytic activity.
Microporous and Mesoporous Materials.
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ABSTRACT: Vanadyl(IV) acetylacetonate ([VO(acac)2]) was grafted onto a hexagonal mesoporous silica (HMS) using three different methodologies: method A â direct complex immobilisation; method B â functionalisation of the HMS with 3-aminopropyltriethoxysilane (APTES) followed by the complex immobilisation; and method C â treatment of the APTES functionalised support prepared by method B with trimethylethoxysilane (TMS) to deactivate eventually unreacted surface silanol groups, followed by complex grafting.
Polyhedron. 28(5):994-1000.
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ABSTRACT: The hydroxyl functionalised manganese(III) salen complex, bearing a large π delocalisation, [Mn(4-HOsaldPh)Cl], was immobilised onto a commercial activated carbon and its air and acid oxidised forms using three different metal loadings. For all the materials the manganese contents were determined by ICP-AES and they were screened as heterogeneous catalysts in the epoxidation of styrene, using iodosylbenzene as oxygen source and acetonitrile as reaction media.All the heterogeneous catalysts were as chemoselective towards the styrene epoxide as the homogeneous counterpart, with the exception of the complex supported onto the acid oxidised activated carbon, which exhibited the lowest styrene epoxide selectivities, a consequence of its acidic oxygen surface groups; the highest styrene conversions and styrene epoxide yields were obtained for that complex immobilised onto the air oxidised activated carbon. Generally, an increase in styrene conversion and styrene epoxide selectivity with the manganese(III) complex loading onto all supports was observed. Upon reuse all the heterogeneous catalysts do not lose their styrene epoxide selectivity, but generally a slight decrease in the styrene epoxide yield is observed; catalyst aging studies done for one of the material prepared, [Mn(4-OHsaldPh)Cl]@C2_1%, revealed high stability and the same catalytic efficiency for almost 2 months.
Applied Catalysis A: General.
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ABSTRACT: A modified Jacobsen-type catalyst, possessing an hydroxyl group on the aldehyde fragment of the salen ligand, was anchored through cyanuric chloride onto: (i) an air oxidized activated carbon functionalized with 3-aminotriethoxysilane and (ii) a nitric acid activated carbon treated with thionyl chloride and functionalized with 1,8-diaminooctane. The new heterogeneous catalysts, as well as the precedent materials, were characterized by nitrogen elemental analysis, Mn ICP-AES, nitrogen adsorption at 77 K, TG-IR and XPS. The results showed that the amine derivatives, cyanuric chloride and the manganese(III) salen complex were sequentially anchored onto the two activated carbons (AC). These Mn based materials acted as active and enantioselective heterogeneous catalysts in the epoxidation of α-methylstyrene, using NaOCl as oxidant. The heterogenized complex showed higher catalytic activity than the homogeneous catalyst. The increase of distance of the manganese(III) salen complex to the carbon surface did not have a significant effect on the asymmetric inductions, which were lower than the homogeneous catalyst. Nevertheless, the catalyst bearing the shorter amine alkyl chain showed higher catalytic activity due to unique steric effects that prevent hindrances to diffusion of the substrates to the active catalytic sites.
Carbon.
