section_path: Chemistry and compounds/Organometallic compounds
section_name: Organometallic compounds
paragraph_text: Organometallic compounds
  
  Organoiron chemistry is the study of organometallic compounds of iron, where carbon atoms are covalently bound to the metal atom. They are many and varied, including cyanide complexes, carbonyl complexes, sandwich and half-sandwich compounds.
  
  Prussian blue or "ferric ferrocyanide", Fe, is an old and well-known iron-cyanide complex, extensively used as pigment and in several other applications. Its formation can be used as a simple wet chemistry test to distinguish between aqueous solutions of Fe and Fe as they react (respectively) with potassium ferricyanide and potassium ferrocyanide to form Prussian blue.
  
  Another old example of an organoiron compound is iron pentacarbonyl, Fe(CO), in which a neutral iron atom is bound to the carbon atoms of five carbon monoxide molecules. The compound can be used to make carbonyl iron powder, a highly reactive form of metallic iron. Thermolysis of iron pentacarbonyl gives triiron dodecacarbonyl, Fe (CO), a complex with a cluster of three iron atoms at its core. Collman's reagent, disodium tetracarbonylferrate, is a useful reagent for organic chemistry; it contains iron in the −2 oxidation state. Cyclopentadienyliron dicarbonyl dimer contains iron in the rare +1 oxidation state.
  
  A landmark in this field was the discovery in 1951 of the remarkably stable sandwich compound ferrocene Fe(C H), by Pauson and Kealy and independently by Miller and colleagues, whose surprising molecular structure was determined only a year later by Woodward and Wilkinson and Fischer. Ferrocene is still one of the most important tools and models in this class.
  
  Iron-centered organometallic species are used as catalysts. The Knölker complex, for example, is a transfer hydrogenation catalyst for ketones.