Chromium carbon dioxide complex

The question of the compatibility of metals and alloys with carbon and carbonaceous gases has assumed considerable importance in connection with the development of the gas-cooled nuclear reactor in which graphite is used as a moderator and a constituent of the fuel element, and carbon dioxide as the coolant. Tests of up to 1 000 h on a series of metals and nickel-containing alloys under pressure contact with graphite at 1 010°C" showed that only copper was more resistant than nickel to diffusion of carbon and that the high-nickel alloys were superior to those of lower nickel content. The more complex nickel-chromium alloys containing titanium, niobium and aluminium were better than the basic nickel-chromium materials. 

Merlic demonstrated the direct, non-photochemical insertion of carbon monoxide from acylamino chromium carbene complexes 14 to afford a presumed chromium-complexed ketene 15 <00JA7398>. This presumed metal-complexed ketene leads to a munchnone 16 or munchnone complex which undergo dipolar cycloaddition with alkynes to yield the pyrroles 17 upon loss of carbon dioxide. 

Abstract This chapter focuses on well-defined metal complexes that serve as homogeneous catalysts for the production of polycarbonates from epoxides or oxetanes and carbon dioxide. Emphasis is placed on the use of salen metal complexes, mainly derived from the transition metals chromium and cobalt, in the presence of onium salts as catalysts for the coupling of carbon dioxide with these cyclic ethers. Special considerations are given to the mechanistic pathways involved in these processes for the production of these important polymeric materials. 

Diarene metals generally decompose under conditions of normal electrophilic substitution, but dibenzene chromium can be metalated with amyl sodium in alkanes, and subsequent reaction with carbon dioxide and dimethyl sulfate results in a complex mixture of mono-, di-, and poly-substituted dibenzene chromium methyl esters. It is interesting that these polysubstituted compounds are homoannular in contrast to the corresponding ferrocene compounds. In view of the scanty evidence and ease of oxidation, it is impossible to conclude whether the diarene metals are less aromatic than the dicyclopentadienyl metals as predicted by simple theory (Sec. III.A). 

Simple carboxylates of chromium(III) find industrial application as catalysts for the polymerization of to-alkenes854,855 and in the preparation of chrome-tanning solutions.856,857 There seems to be no simple carbonate of chromium(III). Compounds formed on the surface of Cr203, sometimes formulated Cr2(C03)3- H20, are best viewed as carbon dioxide adsorbed on the oxide.858 Carboxylate complexes of chromium(III) will now be considered in terms of the various ligand types. 

The paramagnetic chromium complex, Cr(o-CH2C6H4NMe2)3, was found to insert qne C02 molecule to afford a chelating carboxylate group (95,96). (PhCH2)2Mn was also found to give a chelated carboxylate complex on reaction with carbon dioxide (97). 

Dibenzoic acid chromium is reported as produced when the mixture formed in the preparation of dibenzene chromium by the Grignard reaction is treated with carbon dioxide (227). Substitution reactions for the hydrogen atoms in the rings of the complex, such as are known to occur readily for ferrocene, do not occur in this case (90). 

A general method of preparation of the zero valent metal trifluorophosphines is by ligand replacement. Under high PF3 pressure, for example, the chromium or molybdenum compound can be prepared from the dibenzene derivatives (8.175). Carbon dioxide is also displaced under high pressure (8.176), although the reaction is reversible. Under some conditions, partial replacement can be effected to produce complexes of type M(CO) j (PFslx-... 

Cr, Mo and W - The chromium complex [CMt -C2H4)(CO)s] has been isolated as a stable solid for die first time by the photolysis of [Cr(CO)6] in supercritical ethene at room temperature using a miniature flow reactor. Bis-ethene compounds of the type trans [M(C2H4)2(P-P)(PMe3)2] (M = Mo, P-P = dmpe, depe, dmpm M = W, P-P = dmpe, depe) have been reported and the interdependence between the electron density at the metal and the C-chemical shift of the coordinated ethene established. The reaction of carbon dioxide with some of... 

---