Chromium complexes carbonyl hydride

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

Chromium carbene complexes, 82 Chromium carbonyl, 51 Chromium(II) chloride, 84 Chromium(III) chloride-Lithium aluminum hydride, 84 Chromium(VI) oxide, 338... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

The oxidation of substituted dicarbonyl complexes of chromium(I) featuring the bidentate ligands dppm and dppe has been examined. Chromium(O) starting materials, Cr(CO)2(dppm)2 and Cr(CO)2(dppe)2, both with cis carbonyl configurations, were oxidized to trans cations [Cr(CO)2(dppm)2]+ and [Cr(CO)2(dppe)2]" chemical and electrochemical methods were employed. Chemical oxidation of the dppm compound proved more facile than that of the dppe analogue this had been predicted on the basis of electrochemical studies. The dicarbonyl hydride, [Cr (CO)2(dppm)2H]+, was isolated from the oxidation reaction of [Cr(CO)2(dppm)2] with O2/HCIO4, while the same reaction conditions oxidized the neutral dppe complex to the cation. 

The absolute configurations of the product alcohols of acyclic ketone reductions can be reliably predicted for many oxidoreductases by using the Prelog rule (Scheme 6). More complex models are required for cyclic ketones, as will be seen later. For a given substrate, oxidoreductases are usually available that deliver hydride equivalents from opposite enantiotopic faces. This can be exploited to produce either alcohol enantiomer at will, as noted in Scheme 7 by the reduction of (13) to either (R)- or (S)-(14). Organometallic ketones can also be reduced with enantiotopic specificity. This is demonstrated by the conversions (Scheme 8) of the ferrocenyl and chromium carbonyl ketones (15) (16) and (17)... 

Cholestanone, 497 5a-Cholestanone, 475 A -Cholestene, 497 A -Cholestene-3d,5a-diol, 110 A -Cholestene-3/3,5(3-diol, 110 Cholesteryl benzoate, 110 Chromenes, 235-236 A -Chromens, 407 Chromic acid-Silica gel, 110 Chromic anhydride-3,5-Dimethylpyrazole complex, 110 Chromium carbonyl, 110 Chromium(III) chloride-Lithium aluminum hydride, 110-112 Chromyl chloride, 112 ... 

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