Ruthenium, Rhodium Or Palladium Nanoparticle Catalyzed Selective Hydrogenation And Hydroaminomethylation In The Thermoregulated Poly(Ethylene Glycol) Biphasic System

Soluble Ru, Rh and Pd nanoparticles were prepared by hydrogen reduction of the corresponding RuCl3·3H2O, RhCl3·3H2O or Na2PdCl4·xH2O in the presence of poly(ethylene glycol)(PEG). The thermoregulated PEG biphasic system composed of PEG-stabilized Ru, Rh or Pd nanoparticles and a mixture of toluene and n-heptane possesses the thermoregulated phase-transition property, that is, at room temperature, the lower PEG phase containing Ru, Rh or Pd nanoparticles was immiscible with the upper organic phase consisting of toluene and n-heptane. Interestingly, when the temperature was elevated gradually to the miscibility temperature of the system, the biphasic system merged into a single phase. Finally, by decreasing the temperature to room temperature again, the system recovered to the biphasic form. The product and the catalyst were collected easily from the organic and PEG phase, respectively. The recovered catalyst can be reused without further purification or activation. This methodology opens up a new avenue for recovery and recycling of soluble transition-metal nanoparticle catalysts, especially for noble transition-metal nanoparticle catalysts. In this dissertation, PEG-stabilized Ru, Rh or Pd nanoparticles were employed as catalysts for the selective hydrogenation of α,β-unsaturated aldehydes or ketones, alkynes and quinoline. Moreover, PEG-stabilized Rh nanoparticles were also investigated in the hydro-aminomethylation of olefins. The results were as follows:PEG4000-stabilized Pd nanoparticles were used as catalysts for the selective hydro-genation of α,β-unsaturated aldehydes or ketones. Under the optimized reaction conditions:t=7h, T=120℃, PH2=4MPa, cinnamaldehyde/Pd=1000(molar ratio), the conversion of cinnamaldehyde and the selectivity of hydrocinnamaldehyde were99%and98%, respectively. The catalyst could be reused for eight times without evident loss in activity or selectivity. The value of turnover number (TON) was8,642.Ru nanoparticles were used as catalysts for the selective hydrogenation of alkynes for the first time. For the PEG2000-stabilized Ru nanoparticle catalyzed selective hydrogenation of methyl propiolate, under the optimized reaction conditions:t=10h, T=100℃, PH2=2.0MPa, methyl propiolate/Ru=1000(molar ratio), the conversion of methyl propiolate and the selectivity of methyl acrylate were92%and97%, respectively. The catalyst could be reused for ten times without evident loss in activity or selectivity. The value of TON reached9,717.PEG4000-stabilized Rh nanoparticles were used as catalysts for quinoline. Under the optimized reaction conditions:t=3h, T=100℃, PH2=3MPa, quinoline/Rh=1000(molar ratio), the conversion of quinoline and the selectivity of1,2,3,4-tetrahydroquinoline were97%and99%, respectively. The catalyst could be reused for ten times without evident loss in activity or selectivity. The value of TON was10,592.Furthermore, PEG4000-stabilized Rh nanoparticles were employed as catalysts for the hydroaminomethylation of olefins. Under the optimized reaction conditions:t=4h, T=120℃, P=6MPa (CO/H2=1:1),1-octene/Rh=1000(molar ratio), the conversion of1-octene and the selectivity of amines were99%and90%, respectively. The catalyst could be reused for twenty times without evident loss in activity or selectivity. The value of TON was up to19,080, the highest TON reported so far in literatures.