Catalyzed Oxidation/Dehydrogenation Reactions In Green Solvents

This work included the design, characterization and catalytic application of the soluble metal salt/nanoparticles coordinated/stabilized by the functionalized-poly(ethylene glycol) molecules. Firstly, the palladium nanoparticles catalysts were demonstrated for aerobic oxidation of alcohols in poly(ethylene glycol) and aqueous phase; the relationship between the catalytic performance of Pd nanoparticles and its properties was investigated in detailed. Second, an environmentally benign water-soluble Pd(II) complex was developed as a catalyst for the selective aerobic oxidation of styrene to benzaldehyde in high selectivity without any additives in the aqueous phase. Finally, PVP-stabilized ruthenium nanoparticles with [BMMIM]OAc as an additive were utilized as an efficient and reusable catalyst for the oxidant-free dehydrogenation of alcohols in water.(1) The bidentate nitrogen ligand-functionalized-PEG played an important role in stabilizing and immobilizing catalytically active palladium(0) and Pd(?) species. Pd species stabilized by the functionalized PEG showed superior stability, and could be reused several times in the oxidation of alcohols or olefins without losing catalytic activities. The excellent stability attributed to the strong electronic interaction between the bidentate nitrogen ligand and Pd species.(2) The particle size and surface properties of the generated palladium nanoparticles can be controlled by varying the amount of protective ligand and the kinds of reducing agents and its properties played very important roles in affecting catalytic performance. The particle size decreased with increasing the amount of the functionalized PEG. The surface composition of the nanoparticles can also be tuned by adopting appropriate reducing agents in the preparation of nanoparticles. By relating catalytic activity to the properties of Pd nanoparticles, we found that the metallic palladium was the active species for benzyl alcohol oxidation in the present system, moreover, the catalytic performance depended strongly on the properties (size and oxidation state) of Pd nanoparticles.(3) Selective oxidation of styrene to benzaldehyde was carried out in aqueous phase by using a green and water-soluble palladium(?) complex as a catalyst under neutral, chloride and base-free conditions. The water-soluble Pd(?) complex was proved to be stable and highly catalytically active under the present conditions. In particular, the catalyst was easily recovered and could be reused at least twelve times without significant decrease in catalytic performance. UV-Vis spectra indicated that Pd(?) complex might serve as the true catalytically active species in the present system and the reaction mechanism different from Wacker Oxidation was proposed.(4) The oxidant-free dehydrogenation of alcohols was developed in water for the first time. The Ru nanoparticles were active for the reaction under N2 atmosphere at reflux conditions for 24 h, giving benzaldehyde in 99% yield together with the generation of H2, where RuCl3 exhibited lower catalytic activity for benzyl alcohol dehydrogenation under the same reaction conditions. The base additive played an important role in effecting catalytic activies. The catalyst could be reused six times without losing catalytic activities, but showed poor activities in the dehydrogenation of aliphatic alcohols.(5) The several catalytic system designed were green, and these results will also contribute to the development of efficient and environmentally friendly catalysts for various organic reactions.