Structure of methylaluminoxane (MAO): Extractable [Al(CH3)2]+ for precatalyst activation

• 成果类型: Article
• 署名作者: Luo, Lubin; Younker, Jarod M.; Zabula, Alexander V.
• 刊物名称: SCIENCE
• ISSN/ISSBN: 0036-13842
• DOI: 10.1126/science.adm7305
• 发表日期: 2024-06-28
• 页码: 1424-1428
• 关键词: ultrasoft pseudopotentials; olefin polymerization; tert-butylaluminum; trimethylaluminum; alkylalumoxanes; cocatalysts; functionals; prediction; catalysts; energies

摘要

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 [Al33O26(CH3)(47)][Al(CH3)(3)](2) featuring two trimethylaluminum units, Al(CH3)(3), coordinated to two unsaturated aluminum sites. Our structural data are consistent with the hypothesis that the active sites bear coordinated Al(CH3)(3) and provide [Al(CH3)(2)](+) for precatalyst activation. Quantum chemical calculations revealed the most preferred sites for [Al(CH3)(2)](+) 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.