Makume Boitumelo F, Holzapfel Cedric W, Maumela Munaka C, Willemse J Alexander, van den Berg Jan A
Department of Chemical Sciences, University of Johannesburg, Kingsway Campus, Aucklandpark, 2006, Johannesburg, South Africa.
Group Technology, Sasol South Africa, 1 Klasie Havenga road, 1947, Sasolburg, South Africa.
Chempluschem. 2020 Oct;85(10):2308-2315. doi: 10.1002/cplu.202000553.
The effect of ethylene tetramerisation ligand structures on 1-octene selectivity is well studied. However, by-product formation is less understood. In this work, a range of PNP ligand structures are correlated with the full product selectivity and with catalyst activity. As steric bulk on the N-substituent increases, the product selectivity shifts from >10 % to < 3% of both C6 cyclics and C16+ by-products. 1-Octene peaks at ca. 70%. Thereafter, only 1-hexene increases. Similar selectivity changes were observed for ortho-Ph-substituted PNP ligands. The C10-14 selectivity was less affected by the ligand structure. The ligand effect on the changes in selectivity is explained mechanistically. Lastly, an increase in ligand steric bulk was found to improve catalyst activity and reduce polymer formation by an order of magnitude. It is proposed that steric bulk promotes formation of cationic catalytic species which are responsible for selective ethylene oligomerisation.
乙烯四聚配体结构对1-辛烯选择性的影响已得到充分研究。然而，副产物的形成却鲜为人知。在这项工作中，一系列PNP配体结构与完整的产物选择性以及催化剂活性相关联。随着N-取代基上空间位阻的增加，产物选择性从C6环状物和C16 +副产物的> 10％转变为<3％。1-辛烯在约70％处达到峰值。此后，只有1-己烯增加。对于邻位苯基取代的PNP配体，观察到类似的选择性变化。C10 - 14选择性受配体结构的影响较小。从机理上解释了配体对选择性变化的影响。最后，发现配体空间位阻的增加可提高催化剂活性并将聚合物形成减少一个数量级。有人提出，空间位阻促进了负责选择性乙烯齐聚的阳离子催化物种的形成。
