Asymmetric Hydrosilation of Aromatic Ketones Catalyzed by CuFe2O4 Nanoparticles

CuFe2O4 nanoparticles were synthesized by coprecipitation, sol. gel and solvothermal methods, respectively. The asymmetric hydrosilation of aromatic ketones was catalyzed by CuFe2O4 nanoparticles, employing (R). BINAP[2,2'-bis(diphenylphosphino)-1,1'-binaphthalene] as chiral ligand and polymethylhydrosiloxane as hydrosilating reagent. The results showed that compared to the others, the CuFe2O4 nanoparticles prepared by solvothermal method had spherical shape, small size, better dispersion, uniform distribution and excellent catalytic activities. Meanwhile, it was found that the catalytic activity of the CuFe2O4 nanoparticles was significantly improved with the addition of t-BuOK and t-BuOH. An efficient heterogeneous catalytic system CuFe2O4/t-BuOK/t-BuOH was finally obtained. Under room temperature and air atmosphere, the conversion of the aromatic ketones and the enantiomeric excesses of the (R)-1-arylethanols were up to 99% and 92%, respectively, with the heterogeneous catalytic system. It was also confirmed that the electronic effect and steric hindrance of the groups on the aromatic ring distinctly affected the results of hydrosilation. And a possible mechanism was presented to explain the influence of some key factors on the reaction. Furthermore, it was demonstrated that the CuFe2O4 nanocatalyst could be easily separated from reaction system under an external magnetic field. And after recycling for four times, the catalyst could also have a high catalytic activity for the asymmetric hydrosilation.