Luo Lubin, Younker Jarod M, Zabula Alexander V
ExxonMobil Technology and Engineering Company, Baytown, TX 77520, USA.
Science. 2024 Jun 28;384(6703):1424-1428. doi: 10.1126/science.adm7305. Epub 2024 Jun 27.
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 [AlO(CH)][Al(CH)] featuring two trimethylaluminum units, Al(CH), coordinated to two unsaturated aluminum sites. Our structural data are consistent with the hypothesis that the active sites bear coordinated Al(CH) and provide [Al(CH)] for precatalyst activation. Quantum chemical calculations revealed the most preferred sites for [Al(CH)] 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.
甲基铝氧烷（MAO）被用作商业聚烯烃百万吨级生产的预催化剂活化剂，但其精确结构和相关活化机制在40多年来一直是一个基础研究难题。我们在此报告一种活性MAO组分的晶体学表征，其揭示了一种离散的二维片状簇[AlO(CH)][Al(CH)]，其具有两个三甲基铝单元Al(CH)，与两个不饱和铝位点配位。我们的结构数据与活性位点带有配位Al(CH)并为预催化剂活化提供[Al(CH)]的假设一致。量子化学计算揭示了[Al(CH)]夺取的最优选位点（吉布斯自由能变化为每摩尔0.0千卡）。用结晶MAO活化的茂金属进行的烯烃聚合试验显示出比使用商业MAO更高的活性。
