Understanding and Optimizing the Behavior of Al- and Ru-Based Catalysts for the Synthesis of Polyisobutenyl Succinic Anhydrides

Polyisobutenyl succinic anhydrides (PIBSAs) are an important class of chemicals in the automotive industry due to their wide use in lubricant and fuel formulations. However, the synthesis of these molecules takes place at elevated temperatures through the ene reaction between maleic anhydride (MAA) and polyisobutylene (PIB). Lewis acid catalysts (e.g., AlCl3) have been shown to facilitate PIBSA synthesis by lowering the activation energy of the reaction; however, the desorption of the final product (PIBSA) from the catalyst can be highly endergonic. Herein, we demonstrate ligand engineering strategies to optimize the performance of Al- and Ru-based catalysts by combining first-principles calculations with kinetic modeling. We discover that alkyl chlorides such as the EtAlCl2 retain relatively low activation barriers like AlCl3, while lowering the desorption energy of the final product (PIBSA). In addition, we address metal oxidation state and ligand effects on the ene reaction performance of Ru-based catalysts. We demonstrate that depending on the metal oxidation state and type of ligands there is a competition between concerted and stepwise mechanisms. We uncover a Ru(II) catalyst, RuCl2·2H2O, exhibiting enhanced activity but suffering from low stability. Overall, our work identifies catalysts of industrial importance that can reduce the energy input required for intensified processes and highlights challenges associated with catalyst performance