Iron complexes cyclopentadienyl dicarbonyl dimer

The commercially available (tj5-cyclopentadienyl)iron dicarbonyl dimer 1 is the source of the carbonyl(//5-cyclopentadienyl)iron(L) moiety. Reductive or oxidative cleavage of 1 provides reactive monomeric species that may be converted into iron-acyl complexes as described in the following sections (see also Houben-Weyl, Vol. 13/9a, p208). 

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... 

Any interconversion in a sample may give rise to temperature-dependent NMR spectra. For example, the 13C NMR spectrum of dimeric cyclopentadienyl iron dicarbonyl is temperature dependent [114]. This was attributed to intermolecular exchanges of carbonyls and interconversion between cis and trans complexes. 

The reaction of 1,2,3-triphenylcyclopropenylium ion 28 with sodium dicarbonyl(// -cyclopen-tadienyl)ferrate afforded the tr-complex, dicarbonyl(f -cyclopentadienyl)(l,2,3-triphenylcy-cloprop-2-enyl)iron (29), whose structure was determined by X-ray crystallography." Complex 29 was transformed into the original cyclopropenylium ion or its dimer by various reagents."... 

A solution of sodium dicarbonyl(cyclopentadienyl)ferrate prepared from the dicarbonyl(T] -cyclopentadienyl)iron dimer [Cp(CO)2pe]2 (4.11 g, 11.6 mmol) and sodium amalgam (2%, 35.3 g) in tetrahydrofuran (80 mL) is added slowly at -78 °C to a solution of 4-bromo-2//-chromene-3-carbaldehyde (5.5 g, 23 mmol) in tetrahydrohiran (70 mL). The mixture is stirred at -78 °C for 1 h and then allowed to warm to room temperature over a period of 1 h. The solvent is evaporated in vacuo, and the residue is dissolved in diethyl ether/acetone (1 1) and subsequently purified by column chromatography on silica gel. With petroleum ether/diethyl ether (2 1) tetracarbonyl(dicyclopentadienyl)diiron is separated, whereas with diethyl ether/acetone (1 1) the alkenyl-Fp complex is obtained. The solvent is evaporated and the yellow-brown solid is dissolved in dichloromethane (200 mL), dried (magnesium sulfate), and the solution concentrated in vacuo to yield the q -alkenyl-Fp complex as a yellow-brown, amorphous solid 6.9 g (89%). ... 

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