Editing Metallocene (section)

==History==
[[File:Ferrocene.svg|thumb|120px|Ferrocene]]
The first metallocene to be classified was [[ferrocene]], and was discovered simultaneously in 1951 by Kealy and Pauson,<ref name="Pauson_Kealy"/> and Miller et al.<ref name="Miller_S.A.">{{cite journal|last1= Miller|first1= S. A.|last2= Tebboth|first2= J. A.|last3= Tremaine|first3= J. F.|journal= [[J. Chem. Soc.]]|date= 1952|volume=1952|pages= 632–635|title= 114. Dicyclopentadienyliron|doi= 10.1039/JR9520000632}}</ref> Kealy and Pauson were attempting to synthesize [[fulvalene]] through the oxidation of a [[cyclopentadienyl anion|cyclopentadienyl]] salt with anhydrous FeCl<sub>3</sub> but obtained instead the substance C<sub>10</sub>H<sub>10</sub>Fe<ref name="Pauson_Kealy">{{cite journal |last1= Kealy|first1=T. J.|last2= Pauson|first2= P. L. |title= A New Type of Organo-Iron Compound |journal= [[Nature (journal)|Nature]] |year= 1951 |volume= 168 |pages= 1039 |doi= 10.1038/1681039b0 |issue=4285|bibcode= 1951Natur.168.1039K|s2cid=4181383}}</ref> At the same time, Miller ''et al'' reported the same iron product from a reaction of [[cyclopentadiene]] with iron in the presence of aluminum, potassium, or molybdenum oxides.<ref name="Miller_S.A."/> The structure of "C<sub>10</sub>H<sub>10</sub>Fe" was determined by [[Geoffrey Wilkinson]] et al.<ref name="Wilkinson_G."/> and by [[Ernst Otto Fischer]] et al.<ref>{{cite journal|last1= Fischer|first1= E. O.|author-link1= Ernst Otto Fischer|last2= Pfab|first2= W.|trans-title=On the crystal structure of the di-cyclopentadienyl compounds of divalent iron, cobalt and nickel|title= Zur Kristallstruktur der Di-Cyclopentadienyl-Verbindungen des zweiwertigen Eisens, Kobalts und Nickels|journal= [[Z. Naturforsch. B]]|year= 1952|volume=7|issue= 7|pages= 377–379|doi=10.1515/znb-1952-0701|doi-access= free}}</ref> These two were awarded the [[Nobel Prize in Chemistry]] in 1973 for their work on sandwich compounds, including the structural determination of ferrocene.<ref name="Wilkinson_G.">{{cite journal|last1= Wilkinson|first1= G.|last2= Rosenblum|first2= M.|last3= Whiting|first3= M. C.|last4= Woodward|first4= R. B.|author-link1= Geoffrey Wilkinson|author-link4= Robert Burns Woodward|title= The Structure of Iron Bis-Cyclopentadienyl|journal= [[J. Am. Chem. Soc.]]|year= 1952|volume= 74|pages= 2125–2126|doi= 10.1021/ja01128a527|issue= 8}}</ref> They determined that the carbon atoms of the cyclopentadienyl (Cp) [[ligand]] contributed equally to the bonding and that bonding occurred due to the metal {{nowrap|[[d-orbital]]s}} and the {{nowrap|π-[[electron]]s}} in the {{nowrap|[[p-orbital]]s}} of the Cp ligands. This complex is now known as ferrocene, and the group of [[transition metal]] dicyclopentadienyl compounds is known as metallocenes. Metallocenes have the general formula {{nowrap|[(''η''<sup>5</sup>-C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>M].}} Fischer et al. first prepared the ferrocene derivatives involving Co and Ni. Often derived from substituted derivatives of [[cyclopentadienide]], metallocenes of many elements have been prepared.<ref>{{cite journal |last1= Chirik |first1= Paul J. |year= 2010 |title= Group 4 Transition Metal Sandwich Complexes: Still Fresh after Almost 60 Years |journal= Organometallics |volume= 29 |issue= 7|pages= 1500–1517 |doi= 10.1021/om100016p}}</ref>

One of the very earliest commercial manufacturers of metallocenes was Arapahoe Chemicals in Boulder, Colorado<ref>.{{Cite journal|last=ARAPAHOE CHEMICALS, INC|title=Arapahoe Chemicals, Inc|date=1962-11-01|journal=Analytical Chemistry|volume=34|issue=12|pages=122A|doi=10.1021/ac60192a828|issn=0003-2700}}</ref>