Vernetzungsreaktionen mit Estern der Orthotitansäure und anderen Metallalkoholaten

Schmidt, Fritz

doi:10.1002/ange.19520641906

Cited by 22 publications

(2 citation statements)

References 6 publications

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“…Titanium tetraalkoxides react with β‐diketones to give products formulated as (β‐diketonato)Ti(OR) 3 and (β‐diketonato) 2 Ti(OR) 2 1,2. For (bzac) 2 Ti(OEt) 2 , bzac = benzoylacetonato, an equilibrium mixture of the three possible octahedral cis stereoisomers is seen in CH 3 CN/H 2 O solution 3.…”

Section: Introductionmentioning

confidence: 99%

(4‐Acyl‐5‐pyrazolonato)titanium Derivatives: Oligomerization, Hydrolysis, Voltammetry, and DFT Study

et al. 2003

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Twenty 4‐acyl‐5‐pyrazolonato (Q) titanium derivatives of varied nuclearity have been synthesized from Ti(OR)4 or TiCl4 and characterized with spectroscopic methods (IR, NMR, ESI‐MS). While Ti−(β‐diketonato) cleavage is not seen in isolated solids, Ti−O(alkoxy) (or Ti−Cl) bonds cleave upon hydrolysis, leading to several structural forms, including oligomers. Ionic Q species with no Ti, i.e., obtained after Ti−Q cleavage, are seen for some Ti−Q derivatives by ESI‐MS, which also indicates a varied nuclearity for a given species, e.g., the isolated polynuclear [Q2Ti‐μ‐O]n has several “n” values. Mononuclear Ti complexes are obtained under rigorous anhydrous conditions. The cis structures of the mononuclear species (QT)2Ti(OCH3)2, QT = 3‐methyl‐4‐(neopentylcarbonyl)‐1‐phenylpyrazol‐5‐onato have been analyzed with DFT methods. A trans influence is a major driving force that accounts for several sets of Ti−O bonds. One of the cis stereoisomers is 56 kcal/mol higher in energy than the other two. In contrast, all (QT)2TiCl2 cis isomers show similar energies. Voltammetry of the mononuclear species (QT)2Ti(OnPr)2 and the antitumor tetranuclear compound [(QB)2Ti‐μ‐O]4, (QB = 4‐benzoyl‐3‐methyl‐1‐phenylpyrazol‐5‐onato) indicate that the TiIV is less prone to reduction to TiIII in the latter (Epc for the TiIV/TiIII couple is −1.71 V and −1.46 V versus Fc+/Fc, respectively). Potential antitumor compounds having a Ti/Q ratio of 1:1 do not disproportionate, unlike the equivalent acetylacetonato derivatives, and are water‐soluble. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)

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Section: Introductionmentioning

confidence: 99%

(4‐Acyl‐5‐pyrazolonato)titanium Derivatives: Oligomerization, Hydrolysis, Voltammetry, and DFT Study

et al. 2003

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“…Moreover, according to previous studies, two different forms of titanium precursors can be obtained, depending on the acac/Ti ratio used. The substitution of 1 and 2 acac molecules per titanium isopropoxide molecule leads to the formation of dimeric Ti 2 (acac) 2 (O i Pr) 6 (1) and monomeric Ti(acac) 2 (O i Pr) 2 (2), respectively (see Scheme ). , Since the reactivity of the modified titanium alkoxide in aqueous media decreases with the number of substituted acac, this could be an explanation for the increase of the titanium retention, as a function of that synthesis parameter . Indeed, under the acidic condition used here (pH 0.5), the hydrolysis of the isopropoxy groups of the alkoxide precursor could lead to the protonation of the titanium species thus increasing significantly their solubility.…”

Section: Resultsmentioning

confidence: 81%

Controlled Postgrafting of Titanium Chelates for Improved Synthesis of Ti-SBA-15 Epoxidation Catalysts

et al. 2010

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A new synthesis procedure that is based on the grafting of titanium alkoxide species chemically modified by acetylacetone (acac) on the surface of a P123/SBA-15 composite material is proposed to prepare Ti-SBA-15 catalysts and studied by a combination of elemental analysis, Fourier transform infrared spectroscopy (FTIR), solid-state 13 C (CP) NMR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), diffuse reflectance UV-vis (DR-UV-vis), and N 2 physisorption at -196 °C. In the absence of the acac chelates, the observed formation of anatase TiO 2 onto the surface of the material demonstrates that the coordinating ligand acts as an inhibitor for the crystallization of anatase. Furthermore, FTIR and 29 Si NMR results show that the chelated titanium alkoxide precursor interacts strongly with the silanol groups, which, in turn, greatly enhances the dispersion of the titanium species in the mesoporous silica matrix. Moreover, a decrease of the temperature applied for the postgrafting and an increase of both the acac/Ti ratio and pH are shown to favor the retention of titanium on the materials surface without affecting the titanium dispersion. According to the X-ray photoelectron spectroscopy (XPS) results, a maximal titanium content of 13.8% can be well-dispersed on the surface of the mesopores without formation of an excess on the external surface of the solids. However, the results of the DR-UV-vis analyses and the catalytic epoxidation of cyclohexene reveal that the maximal concentration of titanium species in tetrahedral coordination is obtained for materials with a Ti/Si ratio of 5.6%. Even if materials with higher titanium content do not show higher conversion of cyclohexene, they do exhibit remarkably low catalytic deactivation during the recycling tests. A higher hydrothermal stability is suggested as an explanation for the lower deactivation of Ti-SBA-15 at high titanium content.

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Metal Alkoxides

Bradley

1960

Progress in Inorganic Chemistry

108

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Vernetzungsreaktionen mit Estern der Orthotitansäure und anderen Metallalkoholaten

Abstract: oder vernickelte bzw. verchromte Formflichen verwandt werden. Neben der hohen Dauertemperaturbestlndigkeit von 1 9 0 0 und der v o l l i g e n U n b r e n n b a r k e i t liegt der Hauptwert des Polytrifluor-chlorlthylens in seiner hervor-

Cited by 22 publications

References 6 publications

(4‐Acyl‐5‐pyrazolonato)titanium Derivatives: Oligomerization, Hydrolysis, Voltammetry, and DFT Study

(4‐Acyl‐5‐pyrazolonato)titanium Derivatives: Oligomerization, Hydrolysis, Voltammetry, and DFT Study

Controlled Postgrafting of Titanium Chelates for Improved Synthesis of Ti-SBA-15 Epoxidation Catalysts

Metal Alkoxides

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