Editing Metallocene (section)

==Synthesis==

Three main routes are normally employed in the formation of these types of compounds:<ref name="Metallocenes">{{cite book|last=Long|first=N. J.|title=Metallocenes: Introduction to Sandwich Complexes|year=1998|isbn=978-0632041626|publisher=[[Wiley-Blackwell]]|location=London}}</ref>

===Using a metal salt and cyclopentadienyl reagents===
Sodium cyclopentadienide (NaCp) is the preferred reagent for these types of reactions. It is most easily obtained by the reaction of molten sodium and dicyclopentadiene.<ref>{{cite journal |last1= Panda |first1= T. K. |last2= Gamer |first2= M. T. |last3= Roesky |first3= P. W. |year= 2003 |title= An Improved Synthesis of Sodium and Potassium Cyclopentadienide |journal= Organometallics |volume= 22 |issue= 4|page= 877 |doi= 10.1021/om0207865}}</ref> Traditionally, the starting point is the cracking of [[dicyclopentadiene]], the dimer of cyclopentadiene. Cyclopentadiene is deprotonated by strong bases or alkali metals.

:MCl<sub>2</sub> + 2&nbsp;NaC<sub>5</sub>H<sub>5</sub> → (C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>M + 2&nbsp;NaCl {{space|10}} (M = V, Cr, Mn, Fe, Co; solvent = THF, DME, NH<sub>3</sub>)

:CrCl<sub>3</sub> + 3&nbsp;NaC<sub>5</sub>H<sub>5</sub> → [(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>Cr] + {{1/2}}&nbsp;"C<sub>10</sub>H<sub>10</sub>" + 3&nbsp;NaCl

NaCp acts as a reducing agent and a ligand in this reaction.

===Using a metal and cyclopentadiene===
This technique provides using metal atoms in the gas phase rather than the solid metal. The highly reactive atoms or molecules are generated at a high temperature under vacuum and brought together with chosen reactants on a cold surface.
:M + C<sub>5</sub>H<sub>6</sub> → MC<sub>5</sub>H<sub>5</sub> + {{1/2}}&nbsp;H<sub>2</sub> {{space|10}} (M = Li, Na, K)
:M + 2&nbsp;C<sub>5</sub>H<sub>6</sub> → [(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub>M] + H<sub>2</sub> {{space|10}} (M = Mg, Fe)

===Using cyclopentadienyl reagents===
A variety of reagents have been developed that transfer Cp to metals. Once popular was [[thallium cyclopentadienide]]. It reacts with metal halides to give thallium chloride, which is poorly soluble, and the [[cyclopentadienyl complex]]. Trialkyl[[tin]] derivatives of Cp<sup>−</sup> have also been used.

Many other methods have been developed. [[Chromocene]] can be prepared from [[chromium hexacarbonyl]] by direct reaction with cyclopentadiene in the presence of [[diethylamine]]; in this case, the formal deprotonation of the cyclopentadiene is followed by [[redox|reduction]] of the resulting protons to [[hydrogen]] gas, facilitating the [[oxidation]] of the metal centre.<ref>{{cite journal|last1= Fischer|first1= E. O.|author-link1= Ernst Otto Fischer|last2= Hafner|first2= W.|year= 1955|title= Cyclopentadienyl-Chrom-Tricarbonyl-Wasserstoff|trans-title=Cyclopentadienylchromium tricarbonyl hydride|journal= [[Z. Naturforsch. B]]|volume= 10|issue= 3|pages= 140–143|language= de|doi=10.1515/znb-1955-0303|s2cid= 209650632|doi-access= free}}</ref>

:Cr(CO)<sub>6</sub> + 2&nbsp;C<sub>5</sub>H<sub>6</sub> → Cr(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> + 6&nbsp;CO + H<sub>2</sub>

Metallocenes generally have high thermal stability. Ferrocene can be sublimed in air at over 100&nbsp;°C with no decomposition; metallocenes are generally purified in the laboratory by vacuum [[sublimation (chemistry)|sublimation]]. Industrially, sublimation is not practical so metallocenes are isolated by crystallization or produced as part of a hydrocarbon solution. For Group IV metallocenes, donor solvents like ether or THF are distinctly undesirable for polyolefin catalysis.  Charge-neutral metallocenes are soluble in common organic solvents. Alkyl substitution on the metallocene increases the solubility in hydrocarbon solvents.