Dicarbonyl iron anion

In iron reactions where the reagent was equivalent to C, described in Section 8.9.A, the iron moiety was used as an auxiliary. Iron can also stabilize cations, which then react with nucleophiles to generate new carbon-carbon bonds. 08 xhese cations are formed as iron-alkene complexes, usually by reaction of cyclo-pentadienyl dicarbonyl ferrate anion (478) with an allylic halide such as 3-chloro-2-methyl-l-propene. The... 

The starting materials for these complexes are dicarbonyl(cyclopentadienyl)-iron chloride (Fischer and Moser, 1970) and the dicarbonylcyclopentadienyl-iron anion [as the sodium salt (Green and Nagy. 1963)], both obtainable from tetracarbonyl (di-Tr-cyclopentadienyl)diiron which is available commercially. The reaction is carried out in tetrahydrofuran (THF). Equation (1) demonstrates the ease of manipulation of these substances in the preparation of an olefin complex from an epoxide. The tetrafluoroborate salt precipitates from ether. This reaction is also useful as a means of reducing expoxides stereospecifically to olefins with retention of configuration. The olefin is readily liberated from the complex by treatment with sodium iodide in acetone at room temperature for 15 min (Giering et ai, 1972). 

Treating pentacarbonyliron with dicyclopentadiene affords the dicarbonyl (ri -cyclopentadienyl)iron dimer [Cp(CO)2pe]2. Reduction of the latter with sodium amalgam provides the nucleophilic dicarbonyl(r -cyclopentadienyl)iron anion [Cp(CO)2Fe]. Allylic halides or tosylates can be reacted with this Fe(0) complex to afford ri -allyl-Fp-iron complexes (Fp = Fe(CO)2Cp, Scheme... 

In a similar manner, Jt-allyl complexes of manganese, iron, and molybdenum carbonyls have been obtained from the corresponding metal carbonyl halides [5], In the case of the reaction of dicarbonyl(r 5-cyclopentadienyl)molybdenum bromide with allyl bromide, the c-allyl derivative is obtained in 75% yield in dichloromethane, but the Jt-allyl complex is the sole product (95%), when the reaction is conducted in a watenbenzene two-phase system. Similar solvent effects are observed in the corresponding reaction of the iron compound. As with the cobalt tetracarbonyl anion, it is... 

Tetracarbonyl(trifluoromethyl)iron(II) iodide reacts with C-C bond formation to give per-fluoroethene. Tetracarbonyl(perfluorohexyl)iron(II) iodide gives several products, but no per-fluorohexene resulting from /1-elimination has been found.148 However, reductive defluorination of perfluoro(methylcyclohexane) has been reported with dicarbonyl(ty5-cyclopcn-tadienyl)iron(III).212 The defluorination is accompanied by substitution of fluorine with the cyclopentadienyl anion and proton abstraction from the solvent, the latter is well known in the chemistry of fluoroaromatics with the cyclopentadienyl anion. 

The cyclopentadienyliron dicarbonyl anion was reacted with an optically active chlorosilane giving rise to an optically active iron complex58 (equation 8) which was isolated in 98% optical purity. On the basis of the known stereochemistry of nucleophilic displacement of chlorine nucleofuge, the reaction was assumed to occur with inversion of configuration at silicon. 

The solution is cooled in an ice bath and is stirred rapidly as 9.65 g (0.107 mole) of l-chloro-2-methyl-l-propene (isobutenyl chloride) [Aldrich] is added over a period of 5 min. The reaction can be followed by observing the changes in the IR spectrum of the solution. The carbonyl absorption bands characteristic of the anion are replaced by those typical of the product at 1998 and 1950 cm. Upon completion of the addition of l-chloro-2-methyl-l-propene, stirring at 0" is continued for 1 hr to ensure completion of the reaction. The resulting solution of dicarbonyl (Ti -cyclopentadienyl)(2-methyl-l-propenyI-KC )iron may be used directly without purification. Alternatively, the product can be isolated and purified by removing solvent under reduced pressure, followed by chromatogra(>Ay of the residue on 300 g of neutral activity III alumina. The column is made up in anhydrous diethyl ether, and after dissolving the crude product in petroleum ether, elution under N2 is carried out with this solvent. The product may 6e further purified by short-path distillation at pressures less than 10 mm (pot temperature less than 40°). It is then sufficiently pure to be stored at -20° for... 

Cationic olefin complexes of dicarbonyl(> -cyclopentadienyl) iron have been of wide interest in syntheses for a number of years. These complexes, generally isolated as their tetrafluoroborate or hexafluorophosphate salts, have been prepared by the reaction of Fe(f -CsHs)(CO)2Br with simple olefins in the presence of Lewis acid catalysts, by protonation of allyl ligands in Fe(t/ -CsHjXCO)2[(allyl)KC ] complexes, or by treatment of these with cationic electrophiles, by hydride abstraction from Fe(f) -CsHjXCO)2(alkyI) complexes, through reaction of epoxides with Fe(fi -CsHjXCO)2 anion followed by protonation, or by thermally induced ligand exchange between [Fe( i -CjHsXCO)2(ij -2-methyH-propene)][BF4] " or [Fe( -C,HsXCO)2(tetrahydrofuran)][BF4] and excess olefin. 

Alternatively, acyliron complexes can be obtained in a two-step sequence either from dicarbonyl(cyclopentadienyl)ferrates or from dicarbonyl(cyclopentadienyl)iron halides via alkyl-Fp complexes. The first method makes use of the nucleophilicity of [CpFe(CO)2] anions. Their reaction with alkyl halides provides alkyl-Fp complexes that, upon treatment with phosphanes or phosphites, undergo a migratory insertion of a carbonyl ligand into the metal-alkyl bond leading to an acyliron complex (Scheme 4-38). " ... 

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