Ethylene-bis(indenyl) catalytic complexes: Efficient synthesis, introduction of the active metal species and immobilization.

摘要

With more than 80% of industrial chemical processes incorporating a catalytic reaction, catalysis has emerged as a leading technology for improving the efficiency and minimizing chemical waste. Furthermore, in spite of the recent advances in homogeneous and bio-catalysis, heterogeneous catalysis remains the preferred method for industrial processes, due to the advantages, such as easy catalyst removal and recycling. Heterogeneous catalysts, however, are typically less active and selective than their homogeneous counterparts. Therefore, in recent years considerable effort has been devoted to developing methods for immobilizing homogeneous catalysts onto heterogeneous supports.; The primary goal of this work is to develop a strategy for immobilizing chiral homogeneous catalysts, making them more attractive for industrial processes. For this project, chiral ansa-ethylene-bis(eta-tetrahydroindenyl)-metal complexes (EBTHI-MX2) have been chosen, due to their high activity and selectivity for enantioselective reactions including various reduction and polymerization reactions. The key aspect of this catalyst is the diverse activity toward a wide range of substrates and reactions, as well as the strong metal-ligand interaction that should minimize metal leaching.; A comprehensive strategy divided the project into three phases; ligand development, metalation and immobilization. Since the homogeneous catalyst or the symmetrical ligand cannot be directly functionalized, a novel strategy was developed to introduce various tethers to the cyclohexane backbone and the ethylene bridge. Incorporation of oxirane ring-opening chemistry and a Suzuki coupling reaction helped to create an efficient and universal strategy for the introduction of various functional anchors to the EBI ligand. 1-[2'-(3H-inden-1''-yl)ethyl]-5-(4'''-vinylphenyl)-3H-indene offered the most promise and was therefore used for immobilization and metalation studies. Immobilization focused on anchoring the ligand to a well-defined silicon wafer surface and functionalized silica particles using a novel UV-hydrosilylation and thioesterification reaction. High Resolution FTIR analysis was used to characterize both surfaces. After an exhaustive effort to metalate the vinyl-phenyl tethered-EBI ligand with titanium or zirconium, it was determined that the tether inhibits the introduction of the metal. Our findings were confirmed through collaborations with experts in metallocene chemistry and catalysis. In conclusion, several recommendations were provided to improve the development of functional tethers and minimizing the influence on the metalation reaction.