Kaminského katalyzátor

Kaminského katalyzátor je soustava katalyzátorů používaná při polymerizaci alkenů.[1] Základem jsou metaloceny kovů 4. skupiny (Ti, Zr, Hf), které jsou aktivovány methylaluminoxanem (MAO). Objev tohoto systému, společně s dalšími objevy, odstartoval vývoj nové skupiny katalyzátorů, kteerý vedl k novému způsobu průmyslové výroby polyalkenů.[2]

Struktura Kaminského katalyzátoru v jeho (neaktivní) chloridové formě

Historie

Před objeven Kaminského katalyzátoru se jako heterogenní katalyzátory polymerizace alkenů používaly (a dosud se používají) chloridy titanu, aktivované většinou trimethylhliníkem. Kaminsky zjistil, že titanocen a jemu podobné komplexy by mohly mít podobné vlastnosti jako tyto Zieglerovy–Nattovy katalyzátory, ovšem s nižší aktivitou; následně si uvědomil, že by bylo možné jejich aktivitu zvýšit aktivací methylaluminoxanem. Methylaluminoxan alkyluje halogenid metalocenu a také způsobuje odštěpení aniontového ligandu (chloridu nebo methylu) za vzniku elektrofilního katalyzátoru.[1][3]

Ligandy

Kaminského objev velmi aktivních heterogenních katalyzátorů cedl k vývoji mnoha nových ligandů, jako jsou ansa metaloceny (Cs symetrické fluorenyl-Cp ligandy).[4] Tím bylo umožněno provádět velmi stereoselektivní (nebo stereomericky pravidelné) polymerizace α alkenů, přičemž některé z těchto reakcí se využívají i průmyslově.[2]

Je-li k polymerizaci propenu použit metalocen 1, tak vzniká ataktický polypropylen, zatímco při použití C2 symetrického metalocenu 2 a Cs symetrického metalocenu 3 se tvoří isotaktický, respektive syndiotaktický polymer.

Reference

V tomto článku byl použit překlad textu z článku Kaminsky catalyst na anglické Wikipedii.

  1. ↑ a b Walter Kaminsky. Highly Active Metallocene Catalysts For Olefin Polymerization. Journal of the Chemical Society, Dalton Transactions. 1998, s. 1413–1418. 
  2. ↑ a b J. Klosin; P. P. Fontaine; R. Figueroa. Development of Group Iv Molecular Catalysts for High Temperature Ethylene-Α-Olefin Copolymerization Reactions. Accounts of Chemical Research. 2015, s. 2004–2016. 
  3. ↑ E. Y.-X. Chen; T. J. Marks. Cocatalysts for Metal-Catalyzed Olefin Polymerization: Activators, Activation Processes, and Structure-Activity Relationships. Chemical Reviews. 2000, s. 1391–1434. PMID 11749269. 
  4. ↑ J. A. Ewen; R. L. Jones; A. Razavi; J. D. Ferrara. Syndiospecific propylene polymerizations with Group IVB metallocenes. Journal of the American Chemical Society. 1988, s. 6255–6256. 

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