Modelling the active sites of heterogeneous titanium-centred epoxidation catalysts with soluble silsesquioxane analogues

Klunduk, Marek C.; Martin, Caroline M.; Shephard, Douglas S.; Johnson, Brian F. G.; Maschmeyer, Thomas; Thomas, John Meurig

doi:10.1039/a703642f

Cited by 137 publications

(104 citation statements)

References 22 publications

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“…This indicated that channel-type aluminium-free pores were required for irreversible adsorption. (Tang et al 2006) (1a) and {[(c-C 6 H 11 ) 7 Si 8 O 9 ]Ti (O i Pr)} n (1b), respectively (figure 5; Maschmeyer et al 1997). Nuclear magnetic resonance (NMR) studies show that these compounds are in equilibrium between the four-coordinate monomer (1 M ) and a five-coordinate dimer (1 D ) with a relative monomer-dimer ratio of ca 2 : 1.…”

Section: (A) Half-sandwich Complexes Of Titanium(iv) Silsesquioxanesmentioning

confidence: 99%

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Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

et al. 2012

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We discuss herein selected examples of metal complexes of polyhedral oligosilsesquioxanes (POSSs) as models of single-site heterogeneous surface catalysts. The utility of these compounds as such models is illustrated when employed as analogues of single-site titanium species supported on a silica surface. Deep insights into structure-functionality relationships can be gained. In particular, it was possible to probe the relationship between accessibility of the reactive centre and turnover frequencies in a manner that is impossible for a purely heterogeneous catalyst. We also report that the partially dehydroxylated SiO 2 surface alone is an effective radical polymerization initiation catalyst. This surface reactivity is modelled by the solution reactions between the olefin substrate and two POSSs, the completely condensed triganol prism, Si 6 Cy 6 O 9 (a6b0, Cy = Cyclohexyl, C 6 H 11 ), and the incompletely condensed partial cube, Si 7 Cy 7 O 9 (OH) 3 (a7b3). The former, with six-membered Si 3 O 3 rings, is a catalyst. The latter, without this feature, is not. Similar reactivity discrimination is observed in the gas phase reactions of these POSSs with the olefin substrate, examined using atmospheric pressure chemical ionization-and collision-induced decomposition spectroscopies. Silsesquioxane a6b0, containing Si 3 O 3 rings, reacts with the olefin, forming grafted olefin monomers and dimers, while this reactivity is not observed with silsesquioxane a7b3.

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Section: (A) Half-sandwich Complexes Of Titanium(iv) Silsesquioxanesmentioning

confidence: 99%

“…(a) Synthesis of the titanasilsesquioxanes (1) and (2) (redrawn from Maschmeyer et al (1997)). (b) Crystal structure of (2b).…”

Section: (A) Half-sandwich Complexes Of Titanium(iv) Silsesquioxanesmentioning

confidence: 99%

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

et al. 2012

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“…In particular, a stability against chemical or mechanical impact is desirable for coatings in a wide range of morphologies. For instance, permeation barriers rely on compact pin-hole free coatings [6] whereas surfaces for heterogeneous catalysis require hierarchically nano-structured films with large surface area and their catalysts centered in chemically stable matrices [7,8]. The importance of hybrid materials production from molecular precursors leads to investigation of organosilicates from complex precursors.…”

Section: Introductionmentioning

confidence: 99%

Tetrakis(trimethylsilyloxy)silane for nanostructured SiO2-like films deposited by PECVD at atmospheric pressure

Schäfer

Hnilica

Šperka

et al. 2016

Surface and Coatings Technology

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a b s t r a c t a r t i c l e i n f oPlasma enhanced chemical vapor deposition (PECVD) from tetrakis(trimethylsilyloxy)silane (TTMS) has been studied at atmospheric pressure. TTMS has been chosen because of its unique 3D structure with potential to form nano-structured organosilicon polymers. Despite the widespread surveying of various silicon-organic molecules for PECVD, the use of TTMS in AP-PECVD has not been investigated deeper yet. PECVDs have been performed with two different plasma jets. While they are alike regarding the geometry and injection of TTMS, they differ in input power and excitation frequency. The radiofrequency plasma jet operates at lower power densities as compared to the microwave plasma jet. Despite this all the deposited films exhibit similar chemical properties resembling that of silicon dioxide (Si:O = 1:2) with carbon content below 5%. The films demonstrate a broad variety of morphologies from compact smooth films to nano-dendritic 3D structures depending on the particular process.

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“…Other Ti-containing POSS, 1b and 2 (see Scheme 2), showed similar activities (entries 3 and 4). The activities of Ti-containing POSS as homogeneous catalysts for the epoxidation by organic peroxides have been previously reported [16][17][18][19][20][21][22][23]. Silica-tethered 1a showed a catalytic activity similar to that of 1a, indicating that 1a was tethered without a loss of activity (entry 5).…”

Section: Methodsmentioning

confidence: 84%

“…In particular, the catalytic activities of Ti-containing POSS for the epoxidation of alkenes have been examined [16][17][18][19][20][21][22][23]. In addition to their activities as homogeneous catalysts, their application to heterogeneous catalysis using metal-containing POSS as precursors has been examined [10,13,15,[24][25][26][27][28][29][30][31].…”

Section: Introductionmentioning

confidence: 99%

Ti-bridged silsesquioxanes as precursors of silica-supported titanium oxide catalysts for the epoxidation of cyclooctene

Sakugawa

Wada

Inoue

2010

Journal of Catalysis

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ABSTRACT:Silica-supported titanium oxide catalysts were prepared by the controlled calcination of Ti-bridged polyhedral oligomeric silsesquioxanes (POSS) bearing four Si-O-Ti bonds, Ti[(c-C 5 H 9 ) 7 Si 7 O 11 (OSiMe 2 R)] 2 (1a; R = vinyl, 1b; R = methyl) and Ti[(c-C 5 H 9 ) 8 Si 8 O 13 )] 2 (2), supported on various silicas, and these catalysts showed excellent activities for the epoxidation of cyclooctene by t BuOOH as an oxidant to selectively give cyclooctene oxide in high yields. On the other hand, catalysts prepared using a corner-capped-type Ti-containing POSS, CpTi[(c-C 5 H 9 ) 7 Si 7 O 12 ] (3, Cp = cyclopentadienyl), or tetraisopropoxytitanium (4) showed lower activities. The 2 catalysts prepared from Ti-bridged POSS can be easily separated from the reaction mixture and reused without a significant loss of activity. These catalysts were also applicable for the epoxidation of limonene. A spectroscopic study revealed that calcination of Ti-bridged POSS supported on silica gave isolated tetrahedral Ti(IV) species, which would be responsible for the high activity, while calcination of silicasupported 3 or 4 gave aggregated surface titanium oxide species.

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Modelling the active sites of heterogeneous titanium-centred epoxidation catalysts with soluble silsesquioxane analogues

Cited by 137 publications

References 22 publications

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

Silsesquioxanes as molecular analogues of single-site heterogeneous catalysts

Tetrakis(trimethylsilyloxy)silane for nanostructured SiO2-like films deposited by PECVD at atmospheric pressure

Ti-bridged silsesquioxanes as precursors of silica-supported titanium oxide catalysts for the epoxidation of cyclooctene

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