Organoiron chemistry
[1][2] Organoiron compounds are relevant in organic synthesis as reagents such as iron pentacarbonyl, diiron nonacarbonyl and disodium tetracarbonylferrate.
The highly nucleophilic anionic reagent can be alkylated and carbonylated to give the acyl derivatives that undergo protonolysis to afford aldehydes:[4] Similar iron acyls can be accessed by treating iron pentacarbonyl with organolithium compounds: In this case, the carbanion attacks a CO ligand.
Iron carbonyls are potential protective groups for dienes, shielding them from hydrogenations and Diels-Alder reactions.
The affinity of the Fe(CO)3 unit for conjugated dienes is manifested in the ability of iron carbonyls catalyse the isomerisations of 1,5-cyclooctadiene to 1,3-cyclooctadiene.
Cyclohexadiene complexes undergo hydride abstraction to give cyclohexadienyl cations, which add nucleophiles.
[8][9] The enone complex (benzylideneacetone)iron tricarbonyl serves as a source of the Fe(CO)3 subunit and is employed to prepare other derivatives.
[10] Stable iron-containing complexes with and without CO ligands are known for a wide variety of polyunsaturated hydrocarbons, e.g. cycloheptatriene, azulene, and bullvalene.
[18] Reduction of Fp2 with sodium gives "NaFp", containing a potent nucleophile and precursor to many derivatives of the type CpFe(CO)2R.
[20] The Fp+ fragment is Lewis acidic and readily forms complexes with ethers, amines, pyridine, etc., as well as alkenes and alkynes in the η2 coordination mode.
[22] Fp-R compounds are prochiral, and studies have exploited the chiral derivatives CpFe(PPh3)(CO)acyl.
[24] Similarly, allenyl(cyclopentadienyliron) dicarbonyl complexes exhibit reactivity analogous to main group allenylmetal species and serve as nucleophilic propargyl synthons.
[25] Complexes of the type Fe2(SR)2(CO)6 and Fe2(PR2)2(CO)6 form, usually by the reaction of thiols and secondary phosphines with iron carbonyls.
Organoiron(III) porphyrin complexes, including alkyl and aryl derivatives, are also numerous.
[34] Ferrocene is also known to undergo protonation at the iron center with HF/AlCl3 or HF/PF5 to give the formally Fe(IV) hydride complex, [Cp2FeH]+[PF6]–.
