Chromium substituted dicarbonyl

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 intermediate cyclooctene complex appears to be more reactive with respect to CS coordination and more sensitive to oxidation when the arene ring bears electron-withdrawing groups (e.g., C02CH3). Dicarbonyl(methyl rj6-benzoate)-thiocarbonyl)chromium is air stable in the solid state and reasonably stable in solution.9 The infrared spectrum exhibits metal carbonyl absorptions at 1980 and 1935 cm"1 and a metal thiocarbonyl stretch at 1215 cm"1 (Nujol) (these occur at 1978, 1932, and 1912 cm"1 in CH2C12 solution).10 Irradiation of the compound in the presence of phosphite or phosphine leads to slow substitution of CO by these ligands, whereas the CS ligand remains inert to substitution. The crystal structure has been published."... 

Certain other 1,3-dicarbonyl chelates were brominated with difficulty or not at all. For example, the trifluoro- and hexafluoroacetylacetonates (VI, R = CF3, R = CH3, and R = R = CF3) were not brominated under a variety of vigorous conditions. However, in the case of the chromium chelates of 1-phenyl-1,3-butanedione and dibenzoylmethane (VI, R = C( Hr), R = CH5, and R = R = C(iHr)), reaction with N-bromosuccinimide (NBS) was successful. That the electron density at the central carbon of the chelate ring is an important factor in the success or failure of these electrophilic substitutions is evident from the fact that the bis-(ethylenediamine)-2,4-pentanedionocobalt(III) cation cannot be brominated even under vigorous conditions. 

Photoreactions of [Cr(CO)3( /6-C7H8)] (41) with 6-mono- and 6,6-disub-stituted pentafulvenes (59a-59f) preferentially yield dicarbonyl complexes with substituted tj3 5-2-cyloheptadienylene-2-cyclopentadienylidenemethane chelate ligands (82,83). In the course of the reaction, C-6 of the fulvene forms a C—C bond to C-l of the 1,3,5-cycloheptatriene ligand, and one CO ligand is displaced. This reaction is of the same type as the formation of the f/3 5-[ 1 -(3-butene-1,2-diyl)-7-isopropylidenecycloheptadienyl] complexes 47c, 47e and 47t. The fulvene unit is transformed into a monosubstituted cyclo-pentadienyl entity, / -coordinated to the chromium, with the 1,3,5-cyclo-... 

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