Catalysis by design: Well-Defined Aluminum tetra-coordinated Surface Ligand for Catalytic applications

Abstract

The main target of this thesis is the design of a new aluminum-based surface ligand with low coordination and expected high acidity. These new supports will serve for the immobilization of different organometallic complexes with the surface organometallic chemistry (SOMC). The resulting molecular like species will be used for various catalytic applications including alkane metathesis, olefin metathesis and polymerization.

The first chapter is an introduction to the field of catalysis, more specifically, surface organometallic with a summary of its concept and the main examples cited for the immobilization of transition metal complexes on different oxide surfaces (silica, silica-alumina and alumina). This chapter presents, as well, an overview of the use of the aluminum alkyls compounds and their immobilization on a surface for the generation of various aluminum based surfaces.

The Second chapter details the reaction involving the grafting of the monomeric triisobutylaluminum on SBA-15700. The final structures and the mechanism involved were determined by various characterization techniques including FT-IR, 1H and 13C solid-state NMR, and DFT calculations. The reaction leads mainly to a bipodal [(≡Si-O-Si≡)(≡SiO)2AliBu] species with 3 differents types of alumium coordinations (AlIV, AlV and AlVI) along with 37% [≡Si-H] and 63% [≡Si-ibu]. The Third chapter describes the reaction of a highly dehydroxylated SBA-15 with a trimeric di-isobutyl aluminum hydride, [i-Bu2AlH]3 is investigated by both experiments and DFT calculations. The mechanism involves very different pathway comparing to the TIBA case where only AlIV-isobutyl were generated. Further β-H elimination leads to an well-defined AlIV hydride analog [(≡Si-O-Si≡)(≡SiO)2Al-H]. The later shows good activity in ethylene polymerization reaction with the formation of HDPE.

The Fourth Chapter deals with the immobilization of the 2nd generation Hoveyda-Grubbs (HGII) catalyst onto well-ordered 2D hexagonal (SBA15), and 3D fibrous (KCC-1) mesostructure silica containing tetra-coordinated [Al-H] sites. The resulting catalysts show high activity in the non-functionalized olefin metathesis of propene. The results clarified that the supported catalyst prepared using KCC-1 shows better performance than the one prepared using SBA-15 due to the diffusion effect; and exhibits much higher activity than the HG-II itself, in homogeneous phase.

The Fifth chapter of this thesis presents the formation of tetra-coordinated [(≡Si–O–Si≡)(≡Si– O)2Al–OH], through [Al-H] oxidation using N2O. The synthesis was detailed and the grafted species were fully characterized. This new site will serve as anchoring site for the immobilization of the tungsten based complexes. Its activity was evaluated in the propane metathesis reactions, where a TON of 800 was obtaine, which is the highest value obtained for a SOMC monometallic catalyst.

Finally, the last chapter will present the thesis conclusion including most of the ongoing applications related to the use of those new surfaces.