Iron hydrido carbonyl anion

It is deduced from infrared data (206) that iron pentacarbonyl reacts with bromine at — 80° C to form the cationic halogeno carbonyl [Fe(CO)sBr]+Br (206), and the covalent Br—CO—Fe(CO)4Br. From similar infrared data, however, it is concluded that the product is a seven-coordinate non-ionic complex Fe(CO)5Br2 (76) The reaction of Os(CO)3(PPh3)2 with hydrogen chloride produces a cationic hydrido carbonyl, which may be isolated, although it readily reverts to a neutral dichloride by attack of the associated chloride anion (52). 

A more favorable synthesis of salts of the iron, cobalt and nickel carbonyl anions, which were initially prepared by disproportionation reactions of Fe(CO)5, Co2(CO)8, and Ni(CO)4 with pyridine and other amines, was found by treatment of the neutral carbonyls with alkali in aqueous or alcoholic solutions. Careful studies by Hieber revealed that Fe(CO)5 as well as Fe3(CO)12 reacted with exactly four equivalents of hydroxide ions to give the corresponding dianionic iron carbonylates (Scheme 4.4). These dianions are relatively strong bases and readily accept a proton from a water molecule to give the monoanionic hydrido carbonylates [I IFe(CO)4] and [HFe3(CO)n], respectively [36]. The related carbonylates of cobalt and manganese, [Co(CO)4] and [Mn(CO)5], were obtained by a similar way as [Fe(CO)4]2 [25]. With regard to the mechanism of Hieber s Basenreaktion , the most plausible explanation is based on an initial nucleophilic attack by the hydroxide ion at the carbon atom of a CO... 

In addition to the electron-precise 48e hydrido cluster anion 2, the 47e-radical anion, [Fe3(CO)nl 3, is regarded as a key intermediate in reductive transformation of nitroaromatics to anilines or their carbonylated derivatives. The radical 3 is formed via a redox disproportionation reaction upon treatment of 1 with halide (Cl, Br, I ) or pseudohalide (NCO ) in THF in contrast to the reactions of the Ru and Os derivatives, which afford the diamagnetic substituted anions, [M3(CO)io(/t-X)] Treatment of iron carbonyls such as 1 with trimethylamine iV-oxidc or... 

The reductive dehalogenation of haloalkanes has also been achieved in high yield using polymer supported hydridoiron tetracarbonyl anion (Table 11.15). In reactions where the structure of the alkyl group is such that anionic cleavage is not favoured, carbonylation of the intermediate alkyl(hydrido)iron complex produces an aldehyde (see Chapter 8) [3]. 

The reaction of sodium hydroxide with iron pentacarbonyl results in a nucleophilic attack by a hydroxide ion on the carbonyl group to give a metal carboxyHc add complex. Upon further action with sodium hydroxide, the carboxyHc add gives up carbon dioxide to form a hydrido anion. The protonation of this anion results in the formation of iron tet-racarbonyl hydride (Fleiber base) as... 

Similar to reactions with arsenic selenide anions described in the previous section, pentacarbonyliron or the hydrido-iron tetracarbonyl anion react with arsenic tellurides to produce complex iron carbonyl-bound tellurium arsenic anions (Scheme 85). Unlike the selenium analogs, the isolated complex for Te does not exhibit Fe-As bonds. 

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