Chromium, organo-compounds

Chromium (III) chloride forms adducts with a variety of donor ligands. The tetrahydrofuran complex CrCl3-3THF, which is obtained as violet crystals by action of a little zinc on CrCl3 in THF, is a particularly useful material for the preparation of other chromium compounds such as carbonyls or organo compounds, as it is soluble in organic solvents. 

Neutral Solvated Mono(Organo)chromium(III) Compounds... 

Table 2 Homoleptic tetra(organo)chromium(IV) compounds...

Titanium, vanadium or chromium oxides activated with chlorine-free organo-aluminum compounds, triethyl- or triisobutyl aluminum, have also been used as catalysts [285],... 

The present volume describes 1166 selenium, 489 tellurium, 90 chromium, and 8 platinum compounds. It is the first time that the organo-derivatives of these four elements have been collectively reviewed in detail. 

Other chromium catalysts for ethylene polymerization employ chromo-cene [246] and bis(triphenylsilyl) chromate [247] deposited on silica-alumina. The catalyst support is essential for high activity at moderate ethylene pressures (200—600 p.s.i.). The former catalyst is activated further by organo-aluminium compounds. Polymerization rates are proportional to ethylene pressure and molecular weight is lowered by raising the temperature or with hydrogen (0.1—0.5 mole fraction) in the monomer feed wide molecular weight distributions were observed. 

The generation of alkynylchr(xnium reagents and their addition to carbonyl compounds has been studied by Takai and cow( ers. The chemoselectivity of these reagents resembles that of other organo-chromium(ni) reagents. Preparation of alkynylchromiums can be accomplished by treatment of haloalkynes with chromium(II) chloride in DMF. Representative addition reactions of alkynylchromiums are offered in equations (75) to (79). 

The bio-availabilities of these elements through the gastrointestinal tract vary markedly. Molybdenum, iodine, fluorine, and arsenic are apparently highly bio-available, whereas medium uptake occurs with haem iron, cobalt, zinc, chromium in the presence of a glucose tolerance factor, selenium, either as selenate or as organo selenium compounds, whereas only low bio-availability is experienced with non-haem iron,... 

The data of Table 55 show how the polymer composition varied with activation temperature. Such observations have been reported from this and other laboratories for catalysts made with several different organo-chromium compounds [301,640,644,654], and most recently by Bade et al. [311], who used chromium allyl to make their catalyst. Presumably, the calcination temperature of the silica resulted in the formation of two very different species. Cr(DMPD)2 reacted with silica treated at 250 and at 400 °C to yield di-attached or coordinated species, whereas it reacted differently with silica treated at 600 °C, because on that support only a single oxide attachment can form. Clearly, the higher OH group population has a major effect on the behavior of the site. 

Slurry processes may use a combination of organo-aluminum and organo-magnesium compounds with titanium tetrachloride. Phillips-type catalysts (supported chromium compounds) are also used. Pressures and temperatures are moderate. 

Gmelin s Handbuch der anorganischen Cliemie, 8th edn., Main Suppl. Vol. 3, Organo-metallic Compounds of Chromium, Verlag Cliemie, 1971. 

Of these three types of poly (organo) chromate anions, only the hexaorgano species tolerates a variety of ligand types bound to chromium. Hexamethylchromate has been reported,as well as an unusual spirocyclic compound, Li3[Cr(l,4-C4Hg)3] (Et20)2.s. Notable polyaryls... 

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