Complexes with chromium compounds

Bis(alkyl) complexes, with mercury, preparation, 2, 428 Bis(alkylidene)s, in Ru and Os half-sandwiches, 6, 583 Bis(alkylimido) complexes, with chromium(VI), 5, 346 Bis(rj2-alkyne)platinum(0) complexes, preparation, 8, 640 Bis(alkynyl) complexes in [5+2+l + l]-cycloadditions, 10, 643 with manganese, 5, 819 with mercury, preparation, 2, 426 mononuclear Ru and Os compounds, 6, 409 with platinum, 12, 125 with platinum(II), 8, 539 with titanium(IV), 4, 643 with zirconium, 4, 722... 

Bis(tj6-arene) complexes, with chromium hydrocarbon-substituted arenes, 5, 338 with peripheral heteroatoms, 5, 340 with ring integral heteroatoms, 5, 339 theoretical considerations, 5, 338 Bis(l,2-arenedithiolato) compounds, in mono-Cp Ti(IV) complexes, 4, 503-504... 

Cyclopentadienyl-ligated complexes, with chromium, 5, 380 Cyclopentadienyl-like compounds, lanthanide and Group 3 complexes, 4, 105... 

Polysulfanides, in Ru and Os half-sandwich complexes, 5-Gp and 7 5-indenyl compounds, 6, 496 Polysulfide rings, with germanium, 3, 742-743 Polysulfides, in Ru and Os half-sandwich complexes, rjS-Cp and ]5-indenyl compounds, 6, 496 Polysulfido nitrosyl complexes, with chromium, 5, 303 Polytetrafluoroethylene valves, in high vacuum lines, 1, 198 Polythiaether macrocyclic ligands, in hexaruthenium carbido clusters, 6, 1018-1019... 

Since reactions of Cr can often be conducted when the ring is substituted with potentially competing functional groups, it is surprising that no evidence for jt-complexes with ODA has been found in the surface studies of PMDA-ODA/Cr. We sought first to determine if ODA-like molecules would form isolable n-complexes with chromium. 4-phenoxyaniline and phenyl ether were selected for reaction with atomic Cr. In separate experiments each compound was co-condensed with thermally evaporated chromium in an evacuated spinning glass reactor, cooled to 77 K. 

Arylazo-3-pyrazolin-5-ones have been used as dyes. They form complexes with chromium which have good dyeing properties.1060 Miehaelis, Kotelmann and Drews984 report the reduction of 4-aryl-azo-3-pyrazolin-5-ones having no 1-substituent to pyrazoles by use of phosphorus pentasulfide (eq. 202). Reaction of such azo compounds... 

Fisher and Hafner [14] found the synthesis of Ti-aryl complexes with aromatic compounds, chromium chloride, aluminum chloride and aluminum metal in 1955 as shown in eq. (13.9). These mixture is heated to afford bisaryl cation, and bisaryl complexes are prepared by reduction with water soluble sodium dithionite (Na2S204). ( -(C6H6))2Cr is isolated as a dark brown material by sublimation by heating under a high vacuum [15]. 

The mechanisms of these reactions bear marked similarities, in spite of the differences in their reactivities and selectivities. Thus, in certain cases, a four-membered intermediate similar to the 1,2-oxaphosphetane intermediate in the Wittig reaction appears in the Peterson reaction as a pentacoordinate 1,2-oxasiletanide. Reactions of transition metal carbene complexes with carbonyl compounds also proceed through the formation of a four-membered oxametallacycle, which was recently found to be an intermediate of some McMurry reactions. Carbonyl olefination utilizing dimetallic species of zinc or chromium is somewhat similar to the Julia reaction in that they both involve the process of ) -elimination. 

Leather Tanning and Textiles. Although chromium (VT) compounds are the most important commercially, the bulk of the appHcations in the textile and tanning industries depend on the abiUty of Cr(III) to form stable complexes with proteins, ceUulosic materials, dyestuffs, and various synthetic polymers. The chemistry is complex and not well understood in many cases, but a common denominator is the coordinating abiUty of chromium (ITT) (see LEATHER Textiles). 

Chromium-containing wood preservatives and their chemical compositions are Hsted ia Table 13 (199). Chromium compounds have a triple function ia wood preservation (200). Most importantiy, after impregnation of the wood the Cr(VI) compounds used ia the formulations react with the wood extractives and the other preservative salts to produce relatively insoluble complexes from which preservative leaches only very slowly. This mechanism has been studied in the laboratory (201—206) and the field (207). Finally, although most of the chromium is reduced to chromium (ITT), there is probably some slight contribution of the chromium (VT) to the preservative value (208). 

Precipitation is often applied to the removal of most metals from wastewater including zinc, cadmium, chromium, copper, fluoride, lead, manganese, and mercury. Also, certain anionic species can be removed by precipitation, such as phosphate, sulfate, and fluoride. Note that in some cases, organic compounds may form organometallic complexes with metals, which could inhibit precipitation. Cyanide and other ions in the wastewater may also complex with metals, making treatment by precipitation less efficient. A cutaway view of a rapid sand filter that is most often used in a municipal treatment plant is illustrated in Figure 4. The design features of this filter have been relied upon for more than 60 years in municipal applications. 

Silylketenes in formation of (3-lactones and (3-lactams 98JCS(P1)2105. Syntheses of (3-lactams, (3-lactones, and 1,3- and 1,4-diazetidinediones by pho-tochemically induced cycloaddition reactions of chromium carbene complexes with imines, aldehydes, and azo compounds 97T4105. 

By a photochemically induced elimination of CO, a chromium carbene complex with a free coordination site is generated. That species can coordinate to an alkyne, to give the alkyne-chromium carbonyl complex 4. The next step is likely to be a cycloaddition reaction leading to a four-membered ring compound 5. A subsequent electrocyclic ring opening and the insertion of CO leads to the vinylketene complex 6 ... 

The fact that pentacarbonyl carbene complexes react with enynes in a chemo-selective and regiospecific way at the alkyne functionality was successfully applied in the total synthesis of vitamins of the Kj and K2 series [58]. Oxidation of the intermediate tricarbonyl(dihydrovitamin K) chromium complexes with silver oxide afforded the desired naphthoquinone-based vitamin K compounds 65. Compared to customary strategies, the benzannulation reaction proved to be superior as it avoids conditions favouring (E)/(Z)-isomerisation within the allylic side chain. The basic representative vitamin K3 (menadione) 66 was synthesised in a straightforward manner from pentacarbonyl carbene complex 1 and propyne (Scheme 38). 

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