Hexacarbonyl

Chromium hexacarbonyl has been prepared by the reaction of chromium (III) chloride with phenylmagnesium bromide in the presence of carbon monoxide. Unsatisfactory yields have been reported and difficulty experienced in repeating the synthesis. Unfortunately, no other methods for the preparation of this substance are recorded in the literature. 

The bomb is rocked for about 2% hours, or for about 2 hours after the contents reach room temperature longer periods are without effect on the yield of carbonyl. No heat is applied to the bomb and relatively little heat of reaction is observed under these conditions. 

Further purification of the carbonyl is effected by recrystallization from dry ether this is best accomplished by placing the crude product in the thimble of a Soxhlet extractor and extracting with dry ether. Pure chromium hexacarbonyl crystallizes on cooling it is filtered and washed as before. 

A completely odorless product is obtained by sublimation of the recrystallized carbonyl at 0.5 mm. or less, and at a bath temperature of 40 to 50° . the large, highly refractive crystals are collected in a receiver cooled with Dry Ice. The sublimation apparatus must have a short, wide bore connection between the hot and cold sections to prevent clogging with crystals. The loss of product in the crystallization and sublimation processes is slight several runs 

Chromium hexacarbonyl forms large, highly refractive crystals that can be sublimed in vacuum without change but decompose on heating above about 100°. The vapor pressure of chromium hexacarbonyl has been measured up to 125°. On exposure to light and air at room temperature 

Orthorhombic, highly refractive crystals sublimes at room temperature decomposes at 130°C explodes at 210°C.1 

Burns with luminous flame almost insoluble in water, ethanol, methanol soluble in ether, chloroform, and other organic solvents solutions and impure solid decompose in light.1 

Severe poison. May be fatal if inhaled, swallowed, or absorbed through skin. May cause irritation.2 LD50 (intravenous, mouse) 100 mg/kg.1 TLV-TWA 0.01 mg (Cr)/m3.3 Suspected to be animal and human carcinogen.4 

Wear nitrile rubber gloves, laboratory coat, and protection. To reduce risk of forming airborne dust, cover spill with a 1 1 1 mixture by weight of sodium carbonate or calcium carbonate, clay cat litter (bentonite), and sand. Scoop the solid into a container and transport to the fume hood. Slowly, while stirring, add the solid to household bleach (50 mL/g of chromium hexacarbonyl). Allow the solid to settle, decant the liquid to the drain with at least 50 times its volume of water. Dry and package the solid for disposal in accordance with local regulations.5,6 

Package Lots. Package securely, label, and send for burial in a site approved for disposal of poisonous wastes. 

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Other examples are iron pentacarbonyl, Fe(CO)s, and chromium hexacarbonyl, Cr(CO)(j, which have trigonal bipyramidal and octahedral configurations respectively. 

The O oxidation state is known in vanadium hexacarbonyl. V(CO)(,. a blue-green, sublimable solid. In the molecule VfCO), if each CO molecule is assumed to donate two electrons to the vanadium atom, the latter is still one electron short of the next noble gas configuration (krypton) the compound is therefore paramagnetic, and is easily reduced to form [VfCO, )]. giving it the... 

Preformed Carbocationic Intermediates. Propargyl cations stabilized by hexacarbonyl dicobalt have been used to effect Friedel-Crafts alkylation of electron-rich aromatics, such as anisole, /V, /V- dim ethyl a n il in e and 1,2,4,-trimethoxybenzene (24). Intramolecular reactions have been found to be regio and stereo-selective, and have been used ia the preparatioa of derivatives of 9JT- uoreaes and dibenzofurans (25). 

Various appHcations such as lubricant additives, dyes, pigments, and catalysts are under investigation. Tungsten can be deposited from tungsten hexacarbonyl, but carbide formation and gas-phase nucleation present serious problems (1,2). As a result, tungsten halides are the preferred starting material. 

Tungsten triiodide [15513-69-6] prepared by the action of iodine on tungsten hexacarbonyl in a sealed tube at 120°C (18). 

For example, in Ni(CO) nickel metal having 28 electrons coordinates four CO molecules to achieve a total of 36 electrons, the configuration of the inert gas krypton. Nearly every metal forming a carbonyl obeys the 18-electron rule. An exception is vanadium, forming a hexacarbonyl in which the number of electrons is 35. This carbonyl, which has a paramagnetism equivalent to one unpaired electron, however, readily adds one electron to form a closed valence shell complex containing the V(CO)(, anion. 

The neutral complexes of chromium, molybdenum, tungsten, and vanadium are six-coordinate and the CO molecules are arranged about the metal in an octahedral configuration as shown in stmcture (3). Vanadium carbonyl possesses an unpaired electron and would be expected to form a metal—metal bond. Steric hindrance may prevent dimerization. The other hexacarbonyls are diamagnetic. 

In equation 1, the Grignard reagent, C H MgBr, plays a dual role as reducing agent and the source of the arene compound (see Grignard reaction). The Cr(CO)g is recovered from an apparent phenyl chromium intermediate by the addition of water (19,20). Other routes to chromium hexacarbonyl are possible, and an excellent summary of chromium carbonyl and derivatives can be found in reference 2. The only access to the less stable Cr(—II) and Cr(—I) oxidation states is by reduction of Cr(CO)g. 

Olefin isomerization can be catalyzed by a number of catalysts such as molybdenum hexacarbonyl [13939-06-5] Mo(CO)g. This compound has also been found to catalyze the photopolymerization of vinyl monomers, the cyclization of olefins, the epoxidation of alkenes and peroxo species, the conversion of isocyanates to carbodiimides, etc. Rhodium carbonylhydrotris(triphenylphosphine) [17185-29-4] RhH(CO)(P(CgH )2)3, is a multifunctional catalyst which accelerates the isomerization and hydroformylation of alkenes. 

Isothlazoles react with hexacarbonyls M(CO)e to give N-coordlnate M(CO)s derivatives. 

Finally, the bimolecular cycloaddition of alkynes with 2-phenylazirines in the presence of molybdenum hexacarbonyl has been studied (79TL2983). The pyrrole derivatives (294) obtained appear to arise from an initial [2 + 2] cycloaddition followed by a ring opening reaction. 

In Chapter 3, we optimized the structure of chromium hexacarbonyl using two... 

CBS extrapolation 155, 278 CBS methods 10, 96, 155 cost vs. G2 methods 159 CBS-4 method 155 CBS-Q method 155 CCSD keywords 114 CH bond dissociation 186 charge xxxv, xlii, 15, 286 predicted atomic li charge distribution 20 Cheeseman 53 chlorine (atomic) 137, 159 chlorobenzene 165 chromium hexacarbonyl 52 Cioslowski 198 CIS keyword... 

Compounds containing M-C cr-bonds are frequently unstable and do not give rise to an extensive chemistry (p. 999). Vanadium forms a neutral (paramagnetic) hexacarbonyl which, though not very stable, contrasts with that of titanium in that it can at least be prepared in... 

The lithiated Cr(CO)3 derivatives of thiophene may react with organometal-lic species. Their interaction with hexacarbonyls of chromium and tungsten... 

The TT-complex 63 was obtained by the condensation of chromium hexacarbonyl with the thiophene a-derivative of dicarbonylironcyclopentadienyl 64 (76IZV153, 79IZV900). The presence of the electron-donor iron-containing substituent facilitates TT-coordination. 

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