Reactivity studies, structural characterization, and thermolysis of cubic titanosiloxanes: Precursors to titanosilicate materials which catalyze olefin epoxidation

The cubic titanosiloxane [RSiO3Ti(OPri)](4) (R = 2,6-(Pr2C6H3NSiMe3)-C-i) (1) is found to be relatively inert in its attempted reactions with alcohols and other acidic hydrogen containing compounds. The reaction of 1 with silanol ((BuO)-O-t)(3)SiOH however proceeds over a period of approximately 3 months to result in the hydrolysis of ((BuO)-O-t)(3)SiOH and yield the transesterification product [RSiO3Ti(OBut)](4) (2) rather than the expected [RSiO3Ti(OSi(OBut)(3))](4). Products 1 and 2 have been characterized by elemental analysis, thermal analysis, and spectroscopic techniques (IR, EI-MS, and NMR). The solid-state structures of both 1 and 2 have been determined by single-crystal X-ray diffraction studies. Compounds 1 and 2 are isomorphous and crystallize in a cubic space group with a central cubic Ti4Si4O12 core. Solid state thermolysis of 1 was carried at 450, 600, 800, 900, 1000, and 1200 degreesC in air, and the resulting titanosilicate materials 1a-f were characterized by spectroscopic (IR and DR UV), powder XRD, and electron microscopic methods. While, the presence of Ti-O-Si linkages appears to be dominant in the samples prepared at lower temperatures (450-800 degreesC), phase separation of anatase and rutile forms of TiO2 occurs at temperatures above 900 degreesC as revealed by IR spectral and PXRD studies. The presence of octahedral titanium centers was observed by DR UV spectroscopy for the samples heated at higher temperatures. The use of new titanosilicate materials as catalysts for olefin epoxidation has been investigated. The titanosilicate materials produced at temperatures below 800 degreesC with a large number of Ti-O-Si linkages (or tetrahedral titanium centers) were found to be more active catalysts compared to the materials produced above 900 degreesC. The observed conversion in the epoxidation reactions was found to be somewhat low although the selectivity of the epoxide formation over the other possible oxidized products was found to be very good

A novel cyclic titanasiloxane derived from [Ph2Si(OH)](2)O: synthesis and crystal structure of [Cp*Ti(Cl)(OSiPh(2)OSiPh(2)OSiPk(2)O)]

Reaction of Cp*Ti(OAr)Cl-2 (Ar = 2,6-Me2C6H3) with dilithium salt of [Ph2Si(OH)](2)O in a 1:1 molar ratio in toluene at room temperature yields titanatrisiloxane ring compound [Cp*Ti(Cl)(OSiPh2OSiPh2OSiPh2O)] (1). Siloxane chain-expansion effect has been observed in the product formation, which is presumed to be a consequence of the ring strain in the titanadisiloxane system. Compound 1 has been characterized by microanalysis, IR, and NMR spectroscopic techniques. The molecular structure Of 1 determined by X-ray diffraction reveals that the central eight-membered TiSi3O4 siloxane-ring exists in an unusual butterfly-like conformation. (C) 2001

Metal containing new inorganic ring systems based on siloxane and phosphazane frameworks

High-Field P-31 NMR spectroscopy and single crystal X-ray diffraction studies have been used to study the ring opening and nucleophilic substitution reactions of the lambda (3)-cyclotriphosphazane [EtNPCl](3). The synthesis of the ring opened silicophosphonate [RSi(OH){OP(O)(H)(OH)}](2)O (R=(2,6-iPr(2)C(6)H(3))NSiMe3) (1) represents the first ever molecular silicophosphonate to be isolated bearing free reactive hydroxyl groups. The structure and conformation of the bulky aryloxide substituted lambda (3)-cyclotriphosphazane derivative [EtNP(OAr)](3) (Ar = 2,6-iPr(2)C(6)H(3)) (2) has also been investigated. Interaction of 2 with transition metal precursor complexes leads to the isolation of phosphazane metal complexes with different mode of co-ordination of 2. Further, the reaction of Cp*Ti(OAr)Cl-2 (Ar = 2,6-(CH3)(2)C6H3H) with O{SiPh2(OH)}(2) gave the eight-membered trititanosiloxane [Cp*Ti(Cl) (O(SiPh2O)(2)SiPh2O) (3). Siloxane chain expansion effects, presumed to be a consequence of ring strain, have been observed in the product. The presence of reactive Ti-Cl bond in 3 offers opportunities for its reaction chemistry to be explored

Carbon monoxide electrooxidation on Pt and PtRu modified zeolite X

Zeolite NaX was modified by Pt and Pt/Ru nanodispersed metallic clusters. This modification was achieved by zeolite impregnation with acetylacetonate salt/acetone solution, followed by acetone evaporation and thermal decomposition of organometallic complex. Samples characterization was performed by X-ray diffraction analysis, nitrogen adsorption-desorption measurements and Raman spectroscopy. The incorporation of metal into zeolite cavities induced the amorphisation of the zeolite framework on the local level. The mixture of modified zeolite and 10 wt% of carbon black, in a form of thin layer, was pasted to a glassy carbon surface by Nafion. Electrocatalytic properties of metal-modified zeolites were tested in CO electrooxidation reaction. The mutual influence between Pt and Ru atoms enhanced electroactivity of Pt/Ru-modified zeolite toward carbon monoxide electrooxidation. The behavior of untreated 13X zeolite was investigated under the same condition in order to asses the influence of the support. Gradual deactivation of 13X electrode occurred