Hexacarbonyl Chromium

It is used as a catalyst for polymerization and isomerization of olefins. It is also used as an additive to gasoline, to increase the octane number. 

White crystalline solid sublimes at room temperature decomposes at 130°C (266°F) vapor pressure 1 torr at 48°C (118°F) (Merck 

1989) insoluble in water and alcohol soluble in most other organic solvents. 

Chromium hexacarbonyl is a highly toxic substance by all routes of exposure. The toxic effects are similar to those of molybdenum and tungsten carbonyls. The symptoms are headache, dizziness, nausea, vomiting, and fever. The oral LD50 in mice is 150 mg/kg and in rats 230 mg/kg. The intravenous LD50 in mice is 30 mg/kg. As a hexavalent compound of chromium, it is a carcinogenic substance. 

It explodes when heated at 210°C (410°F). Its ethereal solution is susceptible to explode after prolonged storage. 

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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. 

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. 

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... 

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. 

Reaction of chromium hexacarbonyl with the derivative of tryptophan yields 99 (R = Me), which is hydrolyzed to 99 (R = H) and transformed into 99 (R = C6H4N02) when treated with p-nitrophenol and dicyclohexylcarbodiimide [82JOM(240)163],... 

If the reaction temperature is raised to 430 K and the carbon monoxide pressure to 3 atm, coordination of the metal atom in the rearranged product occurs via the phosphorus site, as in 159 (M = Cr, Mo, W) [84JOM(263)55]. Along with this product (M = W) at 420 K, formation of the dimer of 5-phenyl-3,4-dimethyl-2//-phosphole, 160 (the a complex), is possible as a consequence of [4 - - 2] cycloaddition reactions. Chromium hexacarbonyl in turn forms phospholido-bridged TiyP)-coordinatedcomplex 161. At 420 K in excess 2,3-dimethylbutadiene, a transformation 162 163 takes place (82JA4484). 

Chromium carbene complexes like 13, which are called Fischer carbene complexes, can conveniently be prepared from chromium hexacarbonyl 11 and an organolithium compound 12, followed by an O-alkylation step ... 

The unsaturated substituent in the carbene complex 1 often is aromatic or heteroaromatic, but can also be olefinic. The reaction conditions of the Dotz procedure are mild various functional groups are tolerated. Yields are often high. The use of chromium hexacarbonyl is disadvantageous, since this compound is considered to be carcinogenic however to date it cannot be replaced by a less toxic compound. Of particular interest is the benzo-anellation procedure for the synthesis of anthra-cyclinones, which are potentially cytostatic agents. ... 

Other miscellaneous imines that underwent photoreaction with chromium alkoxycarbenes include iminodithiocarbonates [33],the mono-N-phenylimine of benzil and the bis-JV-phenyl imine of acetoin [20]. By preparing the chromium carbene complex from 13CO-labeled chromium hexacarbonyl, /J-lactams with two adjacent 13C labels were synthesized [34]. 

Optically active (—)-(8R)-methylcanadine was stereoselectively synthesized through selective monocomplexation of (—)-canadine (26) to chromium tricarbonyl (240). Heating of chromium hexacarbonyl with 26 effected regioselective complexation of the D ring to give the diastereomeric complexes, which were treated with n-butyllithium and trimethylsilyl chloride to give the 11-trimethylsilyl derivative 475 (Scheme 97). Methylation of this complex with methyl iodide gave stereoselectively the 8-methyl derivative 476 by preferential alkylation from the opposite face to the bulky chromium... 

The time resolved spectra produced on excimer laser photolysis of Mn2(CO)io are shown in figure 6. Note that as in the case of iron pentacarbonyl and chromium hexacarbonyl photolysis, there is a distinct increase in the amplitude of the lower frequency absorption bands as the photolysis energy increases. By comparison with the frequency of matrix isolated and solution phase Mn(C0)5, the band at -1996 cm l is assigned to the gas phase Mn(C0)5 radical [33]. This... 

The second alternative assumed that chromium hexacarbonyl reacts with hydroxyl ions to give a formate complex, without any preceding dissociation (Equation 41) /40/. 

Caution All operations should be conducted in a well-ventilated hood with breathing protection. The chromium carbene complex generally is contaminated with the very volatile and toxic chromium hexacarbonyl, which is also generated as a by-product of the reaction. 

The chromium complex degrades into chromium hexacarbonyl and an intractable green chromium tar. The addition of silica gel prior to solvent removal adsorbs this material before it can form a tar. 

The binary metal carbonyls are named by giving the name of the metal followed by the name carbonyl, with the number of carbonyl groups indicated by the appropriate prefix. For example, Ni(CO)4 is nickel tetracarbonyl, whereas Cr(CO)6 is chromium hexacarbonyl. If more than one metal atom is present, the number is indicated by a prefix. Thus, Co2(CO)8 is dicobalt octacarbonyl, and Fe2(CO)9 has the name diiron nonacarbonyl. 

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. 

To derive the chromium-benzene bond dissociation enthalpy, the values of several stepwise bond dissociation enthalpies in chromium hexacarbonyl are... 

Although we ignore the values for some of the six stepwise Cr-CO bond dissociation enthalpies in chromium hexacarbonyl, their sum is equal (equation 5.16) to the enthalpy of reaction 5.15, which is calculated as 641.7 4.8 kJ mol-1 (at 298.15 K) from the well-known standard enthalpies of formation of all the species involved [16,17,31],... 

To avoid the formation of the metallic mirror and thus the adsorption process, Connor, Skinner, and Virmani used the microcalorimeter to examine the iodination of chromium hexacarbonyl at 514 K ... 

We can now proceed to the final step before obtaining the standard enthalpy of formation of chromium hexacarbonyl. The enthalpy of reaction 9.18 at 298.15 K is related to Ar77°(9.18) by... 

A. W. Adamson, A. Vogler, H. Kunkely, R. Wachter. Photocalorimetry. Enthalpies of Photolysis of trans-Azobenzene, Ferrioxalate and Cobaltioxalate Ions, Chromium Hexacarbonyl, and Dirhenium Decacarbonyl. J. Am. Chem. Soc. 1978, 100, 1298-1300. 

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