Department of Chemistry, University of Eastern Finland, P.O. Box 111, FI-80101 Joensuu, Finland.
Chemistry. 2013 May 27;19(22):7133-42. doi: 10.1002/chem.201204450. Epub 2013 Apr 9.
Herein, we introduce an approach for the computational screening of stoichiometric reactions between trimethylaluminum (TMA) and water. The thermodynamic products of these reactions are methylaluminoxanes (MAOs) with different compositions, which have the general formula (AlOMe)n(AlMe3 )m, in which n describes the degree of oligomerization and m is the number of associated TMA molecules. These reaction products were thoroughly explored up to n=4, thus demonstrating the thermodynamically preferable association of up to four AlMe3 molecules, that is, TMA molecules in their monomeric form. The relative Lewis acidities of the Al sites in these MAOs were systematically explored and we found that the associated TMA molecules were a key ingredient for co-catalytic activity in olefin-polymerization catalysis. This conclusion was supported by computational studies on catalyst activation, which revealed an exergonic insertion of ethene into the metallocene/MAO complex.
在此，我们介绍了一种用于计算筛选三甲基铝（TMA）与水之间计量反应的方法。这些反应的热力学产物是具有不同组成的甲基铝氧烷（MAO），其通式为（AlOMe）n（AlMe3）m，其中 n 描述了齐聚度，m 是缔合的 TMA 分子数。这些反应产物被深入研究至 n=4，从而证明了最多四个 AlMe3 分子的热力学有利缔合，即单体形式的 TMA 分子。我们系统地研究了这些 MAO 中 Al 位的相对路易斯酸度，发现缔合的 TMA 分子是烯烃聚合催化中助催化活性的关键因素。这一结论得到了催化剂活化的计算研究的支持，该研究揭示了乙烯在茂金属/MAO 配合物中的插入是放热的。
