Editing Ziegler–Natta catalyst (section)

===Homogeneous catalysts===
A second class of Ziegler–Natta catalysts are soluble in the reaction medium. Traditionally such homogeneous catalysts were derived from [[metallocene]]s, but the structures of active catalysts have been significantly broadened to include nitrogen-based ligands.
[[File:VersifyCats.png|thumb|A post-metallocene catalyst developed at [[Dow Chemical]].<ref name=Klosin>{{cite journal |author1=Klosin, J.|author2=Fontaine, P. P.|author3=Figueroa, R. |title=Development of Group Iv Molecular Catalysts for High Temperature Ethylene-Α-Olefin Copolymerization Reactions|journal=Accounts of Chemical Research|year=2015|volume=48|issue=7 |pages=2004–2016|doi=10.1021/acs.accounts.5b00065|pmid=26151395|doi-access=free}}</ref>]]

====Metallocene catalysts====
{{main|Kaminsky catalyst}}
These catalysts are metallocenes together with a cocatalyst, typically MAO, −[O−Al(CH<sub>3</sub>)]<sub>''n''</sub>−. The idealized metallocene catalysts have the composition [[Cyclopentadienyl|Cp]]<sub>2</sub>MCl<sub>2</sub> (M = Ti, [[zirconium|Zr]], [[hafnium|Hf]]) such as [[titanocene dichloride]]. Typically, the organic ligands are derivatives of [[cyclopentadienyl]]. In some complexes, the two [[cyclopentadiene]] (Cp) rings are linked with bridges, like −CH<sub>2</sub>−CH<sub>2</sub>− or >SiPh<sub>2</sub>. Depending on the type of their cyclopentadienyl ligands, for example by using an [[Ansa-metallocene|''ansa''-bridge]], metallocene catalysts can produce either isotactic or syndiotactic polymers of propylene and other 1-alkenes.<ref name="ref1"/><ref name="ref2"/><ref>{{cite book|last=Bochmann|first=M. |title=Organometallics 1, Complexes with Transition Metal-Carbon σ-Bonds |publisher=Oxford University Press|location=New York |date=1994| pages=69–71|isbn=9780198558132}}</ref><ref>{{cite journal |first1=H. G. |last1=Alt |first2=A. |last2=Koppl |title=Effect of the Nature of Metallocene Complexes of Group IV Metals on Their Performance in Catalytic Ethylene and Propylene Polymerization |year=2000 |journal=[[Chem. Rev.]] |volume=100 |issue=4 |pages=1205–1222 |doi=10.1021/cr9804700 |pmid=11749264}}</ref>

====Non-metallocene catalysts====
{{main|Post-metallocene catalyst}}
Ziegler–Natta catalysts of the third class, non-metallocene catalysts, use a variety of complexes of various metals, ranging from scandium to lanthanoid and actinoid metals, and a large variety of ligands containing [[oxygen]] (O<sub>2</sub>), [[nitrogen]] (N<sub>2</sub>), [[phosphorus]] (P), and [[sulfur]] (S). The complexes are activated using MAO, as is done for metallocene catalysts.

Most Ziegler–Natta catalysts and all the alkylaluminium cocatalysts are unstable in air, and the alkylaluminium compounds are [[pyrophoric]]. The catalysts, therefore, are always prepared and handled under an inert atmosphere.