Editing Ferrocene (section)

==History==
===Discovery===
Ferrocene was [[Role of chance in scientific discoveries|discovered by accident]] twice. The first known synthesis may have been made in the late 1940s by unknown researchers at [[Union Carbide]], who tried to pass hot cyclopentadiene vapor through an iron pipe. The vapor reacted with the pipe wall, creating a "yellow sludge" that clogged the pipe. Years later, a sample of the sludge that had been saved was obtained and analyzed by Eugene O. Brimm, shortly after reading Kealy and Pauson's article, and was found to consist of ferrocene.<ref name=werner2012/><ref name = Pauson2001 />

The second time was around 1950, when Samuel A. Miller, John A. Tebboth, and John F. Tremaine, researchers at [[BOC (company)|British Oxygen]], were attempting to synthesize amines from hydrocarbons and [[nitrogen]] in a modification of the [[Haber process]]. When they tried to react cyclopentadiene with nitrogen at 300&nbsp;°C, at atmospheric pressure, they were disappointed to see the hydrocarbon react with some source of iron, yielding ferrocene. While they too observed its remarkable stability, they put the observation aside and did not publish it until after Pauson reported his findings.<ref name=werner2012/><ref name=miller/><ref name=laszloRmon/> Kealy and Pauson were later provided with a sample by Miller ''et al.'', who confirmed that the products were the same compound.<ref name = Pauson2001 />

In 1951, [[Peter L. Pauson]] and [[Thomas J. Kealy]] at [[Duquesne University]] attempted to prepare [[fulvalene]] ({{chem2|(C5H4)2}}) by oxidative dimerization of [[cyclopentadiene]] ({{chem2|C5H6}}). To that end, they reacted the [[Grignard reagent|Grignard]] compound [[cyclopentadienyl magnesium bromide]] in [[diethyl ether]] with [[iron(III) chloride|ferric chloride]] as an oxidizer.<ref name=werner2012/> However, instead of the expected fulvalene, they obtained a light orange powder of "remarkable stability", with the formula {{chem2|C10H10Fe}}.<ref name = Pauson2001 /><ref name=pauson/>

===Determining the structure===
[[File:Ferrocene kealy.svg|thumb|left|Pauson and Kealy's original (incorrect) notion of ferrocene's molecular structure.<ref name=pauson/>]]
Pauson and Kealy conjectured that the compound had two cyclopentadienyl groups, each with a single covalent bond from the saturated carbon atom to the iron atom.<ref name=werner2012/> However, that structure was inconsistent with then-existing bonding models and did not explain the unexpected stability of the compound, and chemists struggled to find the correct structure.<ref name=laszloRmon/><ref name=federman/>

The structure was deduced and reported independently by three groups in 1952.<ref name=werner2008/> [[Robert Burns Woodward]], [[Geoffrey Wilkinson]], et al. observed that the compound was diamagnetic and nonpolar.<ref name="wilk52" />  A few months later they described its reactions as being typical of aromatic compounds such as [[benzene]].<ref>{{Cite journal |last1=Woodward |first1=R. B. |last2=Rosenblum |first2=M. |last3=Whiting |first3=M. C. |date=1952-06-02 |title=A New Aromatic System |url=https://pubs.acs.org/doi/abs/10.1021/ja01133a543 |journal=Journal of the American Chemical Society |language=en |volume=74 |issue=13 |pages=3458–3459 |doi=10.1021/ja01133a543 |issn=0002-7863}}</ref> The name ferrocene was coined by Mark Whiting, a postdoc with Woodward.<ref>{{Cite web |last=Sutton |first=Mike |date=2023-09-27 |title=Fifty years since the ferrocene furore |url=https://www.chemistryworld.com/features/fifty-years-since-the-ferrocene-furore/4018098.article |access-date=2024-11-02 |website=Chemistry World |language=en}}</ref> [[Ernst Otto Fischer]] and Wolfgang Pfab also noted ferrocene's diamagneticity and high symmetry. They also synthesize [[nickelocene]] and [[cobaltocene]] and confirmed they had the same structure.<ref name="fischer" /> Fischer described the structure as ''Doppelkegelstruktur'' ("double-cone structure"), although the term "sandwich" came to be preferred by British and American chemists.<ref name="okuda" /> Philip Frank Eiland and Raymond Pepinsky confirmed the structure through [[X-ray crystallography]] and later by [[Nuclear magnetic resonance|NMR]] spectroscopy.<ref name="laszloRmon" /><ref name="eiland52" /><ref name="dunitz53" /><ref name="dunitz56" />

The "sandwich" structure of ferrocene was shockingly novel and led to intensive theoretical studies. Application of [[molecular orbital theory]] with the assumption of a Fe<sup>2+</sup> centre between two [[cyclopentadienide]] anions {{chem2|C5H5(-)}} resulted in the successful [[Dewar–Chatt–Duncanson model]], allowing correct prediction of the geometry of the molecule as well as explaining its remarkable stability.<ref name=mingos/><ref name=mehr/>

===Impact===
The discovery of ferrocene was considered so significant that Wilkinson and Fischer shared the 1973 [[Nobel Prize in Chemistry]] "for their pioneering work, performed independently, on the chemistry of the organometallic, called [[sandwich compound]]s".<ref>{{Cite web |url= http://nobelprize.org/nobel_prizes/chemistry/laureates/1973/ |title= The Nobel Prize in Chemistry 1973 |publisher= [[Nobel Foundation]] |access-date= 12 September 2010}}</ref>