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Solid hybrid catalysts for aromatic alkenylation and arylation via C-H activation

Book - Dissertation

Metal-catalyzed activation of C-H bonds has attracted much attention over the past decade for its potential to efficiently introduce complexity in organic molecules, without the need for prefunctionalization. However, even in the state-of-the-art systems, high noble metal loadings (5–10 mol %) are generally needed to achieve high yields, which impedes industrial implementation of this new synthetic strategy given the high costs associated with noble metals and the strict regulations regarding trace amounts of platinum-group metals in pharmaceutical products. In this PhD dissteration, solid hybrid catalysts for oxidative C-H activation reactions are presented, which combine the active site design of organometallic complexes with the stability and heterogeneity of solid catalysts.In the first part of this work, the synthesis and performance of Pd(II)-loaded Zr-MOFs as single-site solid hybrid catalysts for the oxidative coupling of arenes via C-H/C-H activation is described. Superior TONs compared to the analogous homogeneous system could be achieved with the optimal Pd(II)-loaded MOF-808 catalyst due to the isolation of the active sites on the MOF material, which prolongs catalyst lifetime. Another interesting C-H activation reaction is the oxidative C-H alkenylation of arenes, which was studied in the second part of this dissertation. A MOF-based heterogeneous single-site catalyst containing S,O-moieties was synthesized and characterized in-depth. The MOF-supported S,O-moieties increased the catalytic activity of Pd(II), ranking Pd@MOF-808-L1 among the most active heterogeneous catalysts ever reported for the non-directed oxidative C-H alkenylation of arenes. Futhermore, the structure of the isolated palladium active sites could be identified by X-ray absorption spectroscopy, and the applicability of this heterogeneous system was demonstrated by the gram-scale synthesis of industrially relevant products. The feasibility to perform an industrially-relevant oxidative C-H activation reaction on a pilot-scale using the Pd@MOF-808-L1 heterogeneous single-site catalyst was further investigated in the next part. The synthesis of MOF-808, the tailor-made L1 ligand, and the procedure to attach L1 on the Zr6-clusters of MOF-808 could successfully be upscaled to a kilogram-scale. Moreover, the active MOF-808-L1 catalyst support powder could be shaped into stable, well-accessible cylindrical pellets, ready to be used in an industrial pilot plant. In the last part, related mesoporous metal oxide-bisphosphonate materials containing S,O-binding sites that enhance the activity of Pd(II) for C-H activation reactions were developed. Significantly higher yields were obtained using highly porous metal oxide-bisphosphonate materials as supports compared to materials with lower porosities, such as conventional metal oxides, indicating that the high surface area facilitates the presence of isolated, well-accessible S,O-supported Pd(II) active sites.
Number of pages: 259
Publication year:2020