Structure of methylaluminoxane (MAO): Extractable [Al(CH<sub>3</sub>)<sub>2</sub>]<sup>+</sup> for precatalyst activation.
basic_science · Level V
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- Record sourced from PubMed, PMID 38935705.
- Also identified by DOI 10.1126/science.adm7305.
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Abstract
Methylaluminoxane (MAO) is used as a precatalyst activator for million ton-scale production of commercial polyolefins, but its precise structure and associated activation mechanisms have been a fundamental research puzzle for more than 40 years. We report here the crystallographic characterization of an active MAO component, which reveals a discrete two-dimensional sheet cluster [Al<sub>33</sub>O<sub>26</sub>(CH<sub>3</sub>)<sub>47</sub>][Al(CH<sub>3</sub>)<sub>3</sub>]<sub>2</sub> featuring two trimethylaluminum units, Al(CH<sub>3</sub>)<sub>3</sub>, coordinated to two unsaturated aluminum sites. Our structural data are consistent with the hypothesis that the active sites bear coordinated Al(CH<sub>3</sub>)<sub>3</sub> and provide [Al(CH<sub>3</sub>)<sub>2</sub>]<sup>+</sup> for precatalyst activation. Quantum chemical calculations revealed the most preferred sites for [Al(CH<sub>3</sub>)<sub>2</sub>]<sup>+</sup> abstraction (a change in Gibbs free energy of 0.0 kilocalories per mole). Olefin polymerization tests on metallocenes activated with the crystallized MAO show higher activities than with the commercial MAO.