Chromium carbonyl hydrogenation

Chromium carbonyl hydrogen complexes, preparation and characteristics, 5, 206 Chromium complexes... 

Erankel, E. (1970) Conversion of polyunsaturates in vegetable oils to cis Monounsaturates by homogeneous hydrogenation catalyzed with chromium carbonyls./.Am. Oil Chem. Soc., 47, 11-14. 

Another subject of dispute was the mechanism of the photochemical, chromium carbonyl catalyzed hydrogenation of dienes /42/. The question here was whether the catalytic reaction is started by the dissociation of CO (Equation 42) or by the dissociation of the coordinated diene (Equation 43) /42, 43/. 

An interesting example is the stereoselective reduction of a cyclopentadienone derivative with a chromium carbonyl itself without hydrogen (equation 13)32. 

A recent synthesis of this building block has been published by Eastham et al. in 2006 (48). Their key step is a Dotz benzannulation reaction and is shown in Scheme 2.10. The bromohydrin 66 was formed from dihydrofuran (50). Cobalt-mediated cyclization, followed by ozonolysis with reductive work-up yielded 68 after hydrazine formation. Reductive removal of the hydrazine function, followed by chromium-carbonyl formation gave the Dotz reaction precursor 69. This reacted with an alkyne in the Dotz reaction, and was then oxidized and hydrogenated 70). Pyrolysis gave the protected alcohol and the remaining free alcohol was protected as a triflate (—> 71). Reductive removal of the triflate and deprotection of the silyl ether yielded the desired 33 in 1.2% overall yield. 

There is also evidence for the intermediacy of alkene chromium carbonyl complexes in alkene hydrogenation. An example are the intermediacy of tranj,rrchromium tetracarbonyl in the photocatalytic hydrogenation of tronj,tra/tf-2,4-hexadiene. Substituted chromium tricarbonyl complexes that have ligands that can be replaced by alkenes also act as homogeneous... 

Norton has thoroughly investigated half-sandwich chromium carbonyl derivatives, inspired by literature reports of a radical pathway for the hydrogenation of certain unsaturated substrates by low-valent hydride complexes (Figure 28), that is, anthracene/HCo (CO)4, a-methylstyrene/HMt L (Mf L = Mn (CO)s, or CpM (CO)3 with M = Mo or W ), and styrene/HCo (CO)4. Note that the initial equilibrium corresponds to the p-H atom transfer process in CCT and that all above-mentioned substrates lead to highly stabilized radicals. 

Acetylene works Acrylates works Aldehyde works Aluminum works Amines works Ammonia works Anhydride works Arsenic works Asbestos works Benzene works Beryllium works Bisulfate works Bromine works Cadmium works Carbon disulfide works Carbonyl works Caustic soda works Cement works Ceramic works Chemical fertilizer works Chlorine works Chromium works Copper works Di-isocyanate works Electricity works Fiber works Fluorine works Gas liquor works Gas and coke works Hydrochloric acid works Hydrofluoric acid works Hydrogen cyanide works Incineration works Iron works and steel works... 

The MOCVD of chromium is based on the decomposition of dicumene chromium, (C9Hj2)2Cr, at 320-545°C.[ ]f ] However, the reaction tends to incorporate carbon or hydrogen in the deposit. It can also be deposited by the decomposition of its carbonyl which is made by dissolvingthe halide in an organic solvent such as tetrahydrofuran with CO at 200-300 atm and at temperatures up to 300°C in the presence of a reducing agent such as an electropositive metal (Na, Al, or Mg), trialkylaluminum, and others. 

Eastman-Halcon A process for making acetic anhydride from syngas. The basic process is the carbonylation of methyl acetate. Methanol is made directly from the carbon monoxide and hydrogen of syngas. Acetic acid is a byproduct of the cellulose acetate manufacture for which the acetic anhydride is needed. The carbonylation is catalyzed by rhodium chloride and chromium hexacarbonyl. 

Hydrogen transfer reactions from an alcohol to a ketone (typically acetone) to produce a carbonyl compound (the so-caUed Oppenauer-type oxidation ) can be performed under mild and low-toxicity conditions, and with high selectivity when compared to conventional methods for oxidation using chromium and manganese reagents. While the traditional Oppenauer oxidation using aluminum alkoxide is accompanied by various side reactions, several transition-metal-catalyzed Oppenauer-type oxidations have been reported recently [27-29]. However, most of these are limited to the oxidation of secondary alcohols to ketones. 

The M(C0)6 (M = Cr, Mo, W) stable carbonyls have been used to prepare metal supported catalysts of elements of group 6 that have been used as catalysts in several reactions, such as metathesis, water-gas shift, CO hydrogenation and olefin hydrogenation and polymerization [15-24]. Table 8.2 compiles several examples in which M(CO)s (M = Cr, Mo, W) compounds are used as an alternative for preparing chromium-molybdenum or tungsten-based catalysts. 

---