Chromium oxide addition compounds

Chromium (VI) oxide, addition compounds with pyridine and 3-and 4-picoline, 4 94, 95 analysis of, 4 95... 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

In an alternative oxidation, addition of chromium trioxide to hexamethyldisilox-ane (HMDSO) 7 gives bis(trimethylsilyl)chromate 2065, which is stabilized by addition of Si02 and which oxidizes primary or secondary alcohols such as 2066 or 2968, in CH2CI2, to their corresponding carbonyl compounds 2067 or 2069, in high yields [207] (Scheme 12.62). 

Although all of the above elements catalyze hydrogenation, only platinum, palladium, rhodium, ruthenium and nickel are currently used. In addition some other elements and compounds were found useful for catalytic hydrogenation copper (to a very limited extent), oxides of copper and zinc combined with chromium oxide, rhenium heptoxide, heptasulfide and heptaselen-ide, and sulfides of cobalt, molybdenum and tungsten. 

We could show that the modification of transition metal alkoxides is a versatile tool to adjust the reactivity of precursors for the needs in lyotropic crystalline templating processes. In case of high surfactant concentrations where the liquid crystalline template is formed prior to the addition of the precursor the use of a modifier may become unnecessary. The synthesis of nanostructured rhenium dioxide and the utilization of MTO as precursor for this purpose clearly shows that in some cases the use of unusual specialized compounds is imperative. First promising results in the synthesis of nanostructured chromium oxide surfactant composites have been displayed although hydrolysis of the precursor seems to be still uncompleted within the nanostructure. The possibility of tailoring the d-values in a desired way besides the synthesis of certain particle morphologies encourages for further work in the future. 

Bis(2,4-pentanedionato)oxovana-dium(IV), 5 113-115 Bis(8-quinolinolato)dioxouranium-(VI), and its addition compound with 8-quinolinol, 4 101 Jrans-Bis (thiocyanato)bis (ethylene-diamine)chromium(III) thiocyanate, 2 200, 202 Bis(triphenylgermyl)oxide, 5 78 Bis[tris(2,4-pen tanediono)titanium-(IV) jhexachlorotitanate(I V), 2 119... 

Pyridine and picoline addition compounds of chromium (VI) oxide, synthesis 33 Biurea, synthesis 8 Urazine, synthesis 9 Carbohydrazide, synthesis 10... 

Abstraction, reductive coupling, electron transfer, bond activation, oxidative addition, n-complexation, disproportionation and metal cluster formation are some of the reactions that occur when metal atoms interact with organic polymers and small molecules. Examples of these reactions are provided from the literature on the organometallic chemistry of free atoms and coordination-deficient molecules. Past uses of model compound studies to understand the early stages of chromium metallization on polyimide are critiqued. New evidence for reactions of chromium atoms with compounds related to polyimides is given. 

In the nickel(ll)-catalyzed NHK reaction, the first step is the reduction of Ni " to Ni that inserts into the halogen-carbon bond via an oxidative addition. The organonickel species transmetallates with Cr " to form the organochromium(lll) nucleophile, which then reacts with the carbonyl compound. To make the process environmentally benign, a chromium-catalyzed version was developed where a chlorosilane was used as an additive to silylate the chromium alkoxide species in order to release the metal salt from the product. The released Cr " is reduced to Cr " with manganese powder. 

As already shown in Scheme 120, both chromium and molybdenum compounds were used for phenolic oxidation. In addition, inexpensive chromium reagents such as Cr02Cl2 and Na2Cr207 2H20 have been used for the conversion of alkylphenols to the corresponding alkylquinones (30-84%) . However, they are scarcely used for phenolic oxidation. 

Chromium Doping. Additions of chromium compounds can be used to produce very fine metal powder grades (<0.5 pm). Chromium oxide is formed during reduction and acts as a grain refiner. Such powders are subsequently carburized to ultrafine WC. Special precautions have to be taken because of the high pyrophoricity of the metal powder. 

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