Organoiron chemistry

Organoiron chemistry is the chemistry of iron compounds containing a carbon-to-iron chemical bond. Organoiron compounds are relevant in organic synthesis as reagents such as iron pentacarbonyl, diiron nonacarbonyl and disodium tetracarbonylferrate. While iron adopts oxidation states from Fe(−II) through to Fe(VII), Fe(IV) is the highest established oxidation state for organoiron species. Although iron is generally less active in many catalytic applications, it is less expensive and "greener" than other metals. Organoiron compounds feature a wide range of ligands that support the Fe-C bond; as with other organometals, these supporting ligands prominently include phosphines, carbon monoxide, and cyclopentadienyl, but hard ligands such as amines are employed as well. Important iron carbonyls are the three neutral binary carbonyls, iron pentacarbonyl, diiron nonacarbonyl, and triiron dodecacarbonyl. One or more carbonyl ligands in these compounds can be replaced by a variety of other ligands including alkenes and phosphines. An iron(-II) complex, disodium tetracarbonylferrate (Na2[Fe(CO)4]), also known as "Collman's Reagent," is prepared by reducing iron pentacarbonyl with metallic sodium. The highly nucleophilic anionic reagent can be alkylated and carbonylated to give the acyl derivatives that undergo protonolysis to afford aldehydes: LiFe(CO)4(C(O)R) + H+ → RCHO (+ iron containing products) Similar iron acyls can be accessed by treating iron pentacarbonyl with organolithium compounds: ArLi + Fe(CO)5 → LiFe(CO)4C(O)R In this case, the carbanion attacks a CO ligand. In a complementary reaction, Collman's reagent can be used to convert acyl chlorides to aldehydes. Similar reactions can be achieved with [HFe(CO)4]− salts. Iron pentacarbonyl reacts photochemically with alkenes to give Fe(CO)4(alkene). Iron diene complexes are usually prepared from Fe(CO)5 or Fe2(CO)9. Derivatives are known for common dienes like cyclohexadiene, norbornadiene and cyclooctadiene, but even cyclobutadiene can be stabilized.