Metal Chromium Complexes

Chromium complexes of long-chain fatty acids are exceUent water repeUents which are also used for their food-release properties in certain packaging appHcations. The presence of chromium has raised environmental concerns, despite the fact that the metal is in the trivalent rather than in the highly toxic hexavalent state. This material is available as Qudon (DuPont). 

These siUca-supported catalysts demonstrate the close connections between catalysis in solutions and catalysis on surfaces, but they are not industrial catalysts. However, siUca is used as a support for chromium complexes, formed either from chromocene or chromium salts, that are industrial catalysts for polymerization of a-olefins (64,65). Supported chromium complex catalysts are used on an enormous scale in the manufacture of linear polyethylene in the Unipol and Phillips processes (see Olefin polymers). The exact stmctures of the surface species are still not known, but it is evident that there is a close analogy linking soluble and supported metal complex catalysts for olefin polymerization. 

An example of a 1 1 metal dye complex is shown in Figure 5a. The net charge on the molecule is derived from the plus three charge on chromium,... 

Methylthiophene is metallated in the 5-position whereas 3-methoxy-, 3-methylthio-, 3-carboxy- and 3-bromo-thiophenes are metallated in the 2-position (80TL5051). Lithiation of tricarbonyl(i7 -N-protected indole)chromium complexes occurs initially at C-2. If this position is trimethylsilylated, subsequent lithiation is at C-7 with minor amounts at C-4 (81CC1260). Tricarbonyl(Tj -l-triisopropylsilylindole)chromium(0) is selectively lithiated at C-4 by n-butyllithium-TMEDA. This offers an attractive intermediate for the preparation of 4-substituted indoles by reaction with electrophiles and deprotection by irradiation (82CC467). 

Chromium lignosulfonates are the biggest contributions to heavy metals in drilling fluids. Although studies have shown minimal environmental impact, substitutes exist that can result in lower chromium levels in muds. The less used chromium lignites (trivalent chromium complexes) are similar in character and performance with less chromium. Nonchromium substitutes are effective in many situations. Typical total chromium levels in muds are 100-1000 mg/1. 

The reactions which take place when the mixed etch primer is applied to a metal are complex. Part of the phosphoric acid reacts with the zinc tetroxychromate pigment to form chromic acid, zinc phospliates and zinc chromates of lower basicity. The phosphoric acid also attacks the metal surface and forms on it a thin chromate-sealed phosphate film. Chromic acid is reduced by the alcohols in the presence of phosphoric acid to form chromium phosphate and aldehydes. It is believed that part of the chromium phosphate then reacts with the resin to form an insoluble complex. Excess zinc tetroxy chromate, and perhaps some more soluble less basic zinc chromes, remain to function as normal chromate pigments, i.e. to impart chromate to water penetrating the film during exposure. Although the primer film is hard... 

Entries where the oxidation state of a metal has been specified occur after all the entries for the unspecified oxidation state, and the same or similar entries may occur under both types of heading. Thus cyanide appears under Chromium complexes, Chromium(O) complexes, Chromium(I) complexes, etc. More specific entries, such as Chromium, hexacyano-, may also occur. Similar ligands may also occur in different entries. Thus a carboxylic acid-metal complex may occur under Carboxylic acid complexes, under entries for specific carboxylic acids, and under the specific metal. Coordination complexes may also be listed in the Cumulative Formula Index. 

Pyrazolone, l(4-bromophenyl)-3-methyl-4-(2-methyl-6-carboxyphenylazo)-chromium complex geometrical isomerism, 6, 69 5-Pyrazolone, o-carboxyarylazo-metal complexes geometrical isomerism, 6,68... 

A transmetalation of the styrylcarbene chromium complex 62 in the presence of stoichiometric amounts of [Ni(cod)2] to give the nickel carbene intermediate 63 was applied to the synthesis of Cr(CO)3-coordinated cycloheptatriene 64 upon reaction with terminal alkynes [57] (Scheme 37). The formation of pen-tacarbonyl(acetonitrile)chromium is expected to facilitate the metal exchange. 

Cyanides, including metal-cyanide complexes Drug residues Chromium, cadmium, lead, mercury, nickel. dissolve material used in sealing a site... 

Good non-colored negative charging CCAs have been obtained by making non-colored analogues of the 2 1 chromium complex azo dyes. This is achieved by making the metal complex of an aromatic ortho-hydroxy carboxylic acid. Typical examples are the chromium, aluminum, and zinc complexes of di-tert-butyl salicylic acid, e.g., BONTRON E-8136 41 (53) and BON-acid36,41,42 e.g., BONTRON E-82 (54). 

Cycloaddition of the carbene chromium complexes 97 with CO incorporation provides a versatile method for naphthol synthesis, in which the metallacy-clic intermediates 99 are involved [47]. An alternative entry to 101 is achieved by metal carbonyl-catalyzed rearrangement of the cyclopropenes 98 via the same metalla-cyclobutenes 99 and vinylketene complexes 100 [52], Mo(CO)6 shows a higher activity than Cr(CO)6 and W(CO)6. The vinylketene complex 103 is formed by the regioselective ring cleavage of 1,3,3-trimethylcyelopropene 102 with an excess of Fe2(CO)9 [53]. (Scheme 35 and 36)... 

In spite of the fact that silver(i) X-heterocyclic carbene complexes were widely employed as carbene-transfer reagents for the synthesis of other transition metal carbene complexes, their synthesis could also be achieved by the reaction of silver salts with relatively more labile carbene metal complexes, albeit rare. Complexes 71a-71c were reported to be synthesized from the reaction of the corresponding pentacarbonyl(carbene)chromium(i) complexes with silver(i) hexafluorophosphate in CDC13 under inert atmosphere (Scheme 17).117... 

Whether [6]radialenes have a potential as novel ligands for metal complexes remains to be seen. A first example of a successful complexation is provided by 150, which reacts with tris(acetonitrile)tricarbonylchromium in dioxane at room temperature to give the ortho-xylylene chromium complex 175 in excellent yield (83%) (equation 23)105. 

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. 

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