Q. about the Cossee-Arlman mechanism in alkene polymerization

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SUMMARY

The discussion centers on the Cossee-Arlman mechanism in alkene polymerization, specifically involving titanium tetrachloride (TiCl4) and triethylaluminum. The process begins with triethylaluminum alkylating TiCl4 to form polymeric titanium trichloride (TiCl3). When ethene coordinates with the alkylated TiCl3, it occupies a vacant site, leading to a decrease in the oxidation state of titanium from +4, facilitating the catalytic cycle. This coordination is crucial for the olefin insertion step, which generates another vacant site on the titanium atom for further reactions.

PREREQUISITES
  • Understanding of the Cossee-Arlman mechanism in polymer chemistry
  • Familiarity with titanium chemistry, specifically TiCl4 and TiCl3
  • Knowledge of alkylation processes involving triethylaluminum
  • Basic principles of oxidation states in transition metals
NEXT STEPS
  • Research the detailed steps of the Cossee-Arlman mechanism in alkene polymerization
  • Study the role of transition metal oxidation states in catalysis
  • Explore the properties and applications of triethylaluminum in organic synthesis
  • Investigate the formation and stability of intermediates in coordination chemistry
USEFUL FOR

Chemists, polymer scientists, and students studying catalysis and polymerization mechanisms will benefit from this discussion.

anthemrider22
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Starting out with TiCl4 and triethylaluminum, I understand how the triethylaluminum alkylates the TiCl4 and creates a polymeric TiCl3, but then an ethene molecule coordinates with a vacant site on the alkylated TiCl3? I thought titanium's highest oxidation state was +4?
 
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That's what makes it catalytic. It let's go again.


However... think about this. What would happen to the oxidation state of Ti+4 if you added electron density to it (in the form of a double bond)? Would it go up or down?
 
The oxidation state would go down right? When the ethene molecule coordinates with the alkylated TiCl3 does it occupy an empty d orbital on the titanium atom? I suppose that would create an unstable intermediate and open the door for the olefin insertion step to create another vacant site on the titanium atom. Thank you for your help.
 
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