Synthesis and characterization of vanadium-containing silsesquioxanes

Feher, Frank J.; Walzer, John F.

doi:10.1021/ic00008a005

Cited by 144 publications

(118 citation statements)

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“…A decrease in the TISP temperature elicited a dramatic loss in mass spectral signal. Likewise, under our experimental conditions, complex 11 yielded a predominant signal corresponding to its [M À CH 3 …”

Section: Resultsmentioning

confidence: 59%

“…The partial dimerization of complex 12 was reported to be enthalpically favored (DH°= À6.02 AE 0.27 kcal/mol) with a large negative entropy for dimerization of DS°= À17.1 AE 0.2 eu. 3,4 We were unable to obtain conclusive data on the existence of the dimer using APCI-or TISP-MS. It is conceivable that the dimer of 12 dissociates during the droplet formation and ion evaporation processes (i.e.…”

Section: Resultsmentioning

confidence: 93%

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Mass spectrometric characterization of polyhedral oligosilsesquioxanes and heterosilsesquioxanes

Bakhtiar

Feher

1999

Rapid Commun. Mass Spectrom.

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The term 'silsesquioxane' refers to structures with an even number of silicon atoms (i.e. [RSiO 3/2 ] n with n = even integer) and extended network solids (i.e. [RSiO 3/2 ]) which can achieve the idealized empirical formula for silsesquioxanes, (RSiO 3/2 ) ? . In order to avoid confusion, it is often useful to distinguish between 'fully condensed' and 'incompletely condensed' silisesquioxane frameworks. A fully condensed silsesquioxane has an empirical formula of [RSiO 3/2 ] n , whereas an incompletely condensed silsesquioxane possesses reactive Si-OH groups. A host of heterosilsesquioxanes including main-group, transitionmetal and lanthanide metallasilsesquioxanes are also available via functionalization of incompletely condensed silsesquioxanes. Recent applications include soluble models for silica-supported catalysts, and precursors to hybrid inorganic/organic materials. 1-14 For these reasons metallasilsesquioxanes generated from the coordination of incompletely condensed silsesquioxanes to high-valent transition metals have emerged as useful solution-state models for silica-supported catalysts.15 A wide range of silsesquioxanes can be prepared via the hydrolytic condensation reactions of trifunctional organosilicon monomers, as presented in Scheme 1.Herein, using mass spectrometry, we present evidence on the generation and characterization of a selected group of silsesquioxanes in neat hexane or n-hexane/ethanol (i.e. 90:10, v/v). The results in this study indicate that atmospheric pressure chemical ionization (APCI) and turbo ionspray (TISP) mass spectrometry (MS) could be useful Scheme 1.

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Section: Resultsmentioning

confidence: 59%

Section: Resultsmentioning

confidence: 93%

Mass spectrometric characterization of polyhedral oligosilsesquioxanes and heterosilsesquioxanes

Bakhtiar

Feher

1999

Rapid Commun. Mass Spectrom.

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“…The construction of molecular models for metal-oxo surface sites requires ligands that are capable of mimicking the environments that metaloxo moieties experience on oxidic support or bulk materials, and for the modeling of silica supports in particular silsesquioxanebased ligands have established themselves. [5,6] Silsesquioxanes in general exhibit one-dimensionally extended or cage structures that are saturated by organic residues. Some of these, for example, the structure of the octamer R T 8 , resembles skeletal frameworks found in crystalline forms of silica, and silsesquioxanes in general are therefore discussed as molecular sections of silica.…”

Section: Introductionmentioning

confidence: 99%

“…[5][6][7] A second ligand system that is often employed for the more general modeling of an oxidic coordination platform are calixarenes, [10] and in the context of the above-mentioned supported oxovanadium catalysts employed for ODH processes, we have recently reported the results of structure-function analyses performed for calixarene-based model compounds with respect to the ODH of alcohols. [3,11] Furthermore we have utilized oxovanadium silsesquioxane complexes as spectroscopic models.…”

Section: Introductionmentioning

confidence: 99%

From Surface‐Inspired Oxovanadium Silsesquioxane Models to Active Catalysts for the Oxidation of Alcohols with O₂—The Cinnamic Acid/Metavanadate System

Ohde

Limberg

2010

Chemistry A European J

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Silsesquioxane dioxovanadate(V) complexes were investigated with respect to their potential as a catalyst for the oxidative dehydrogenation of alcohols with O(2) as an oxidant. The turnover frequencies determined were comparatively low, but during the oxidation of cinnamic alcohol an increase in activity was observed in the course of the process, which was inspected more closely. It turned out that during the oxidation of cinnamic alcohol, not only was the aldehyde formed but also cinnamic acid, which in turn reacts with the silsesquioxane complex employed to give NBu(4)[O(2)V(O(2)CC(2)H(2)Ph)(2)], which can also be obtained from NBu(4)VO(3) and cinnamic acid and represents a far more active catalyst, not only for cinnamic alcohol but also for other activated alcohols and hydrocarbons. The rate-determining step of the conversion corresponds to an hydrogen-atom abstraction from the C-H units, as shown by the determination of the kinetic isotope effect in case of 9-hydroxyfluorene, and the reoxidation of the reduced catalyst proceeds via a peroxo intermediate, which is also capable of oxidizing one alcohol equivalent. Furthermore the influence of the organic residues at the carboxylate ligands on the catalyst performance was investigated, which showed that the activity increases with decreasing pK(s) value. Moreover, it was found that during the oxidation the catalyst slowly decomposes, but can be regenerated by addition of excessive carboxylic acid.

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“…F. J. Feher et al were the first to systematically explore the coordination chemistry of deprotonated H 3 R T 7 (Chart 1) -also with respect to vanadium(V) centres [10]. They were able to synthesize a mononuclear complex R I (with R = cyclo-hexyl), which crystallized in form of a dimeric version, R II, from solutions containing both complexes in equilibrium (see Chart 2).…”

Section: Chartmentioning

confidence: 99%

Progress in the Compilation of an Oxovanada‐Silsesquioxane Portfolio and Catalytic Activity of Organometallic Representatives in Ethylene Polymerisation

Ohde

Limberg

Schmidt

et al. 2010

Zeitschrift anorg allge chemie

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Employing various incompletely condensed silsesquioxanes as ligand precursors in reactions with simple oxovanadates a variety of oxovanadium silsequioxanes could be synthesized, that might be regarded as models for oxovanadium units on silica surfaces. These include a tetranuclear vanadium(IV) compound as well as two complexes where O 2 V + units are coordinated to two siloxide functions as part of a silsesquioxane framework. Moreover, compounds containing Cp*V(O) 2+ moieties were prepared, whose activities as polymerization procatalysts has been examined: They turned out to be moderately active for the polymerization of ethylene. All compounds were fully characterised, in case of the tetranuclear vanadium(IV) complex this also includes the investigation of magnetic behaviour. Moreover, for two complexes also the molecular structures could be determined with sufficient quality via XRD.

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Synthesis and characterization of vanadium-containing silsesquioxanes

Cited by 144 publications

References 1 publication

Mass spectrometric characterization of polyhedral oligosilsesquioxanes and heterosilsesquioxanes

Mass spectrometric characterization of polyhedral oligosilsesquioxanes and heterosilsesquioxanes

From Surface‐Inspired Oxovanadium Silsesquioxane Models to Active Catalysts for the Oxidation of Alcohols with O₂—The Cinnamic Acid/Metavanadate System

Progress in the Compilation of an Oxovanada‐Silsesquioxane Portfolio and Catalytic Activity of Organometallic Representatives in Ethylene Polymerisation

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Synthesis and characterization of vanadium-containing silsesquioxanes

Cited by 144 publications

References 1 publication

Mass spectrometric characterization of polyhedral oligosilsesquioxanes and heterosilsesquioxanes

Mass spectrometric characterization of polyhedral oligosilsesquioxanes and heterosilsesquioxanes

From Surface‐Inspired Oxovanadium Silsesquioxane Models to Active Catalysts for the Oxidation of Alcohols with O2—The Cinnamic Acid/Metavanadate System

Progress in the Compilation of an Oxovanada‐Silsesquioxane Portfolio and Catalytic Activity of Organometallic Representatives in Ethylene Polymerisation

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From Surface‐Inspired Oxovanadium Silsesquioxane Models to Active Catalysts for the Oxidation of Alcohols with O₂—The Cinnamic Acid/Metavanadate System