Cu(II)‐Azabis(oxazoline)‐Complexes Immobilized on Superparamagnetic Magnetite@Silica‐Nanoparticles: A Highly Selective and Recyclable Catalyst for the Kinetic Resolution of 1,2‐Diols

Abstract

Two different types of azide functionalized magnetite@silica nanoparticles are synthesized, which are ideally suited as inexpensive supports for catalysts and reagents as demonstrated with the grafting of copper(II)‐azabis(oxazoline) complexes via a copper(I) catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The potential of the immobilized complexes as catalysts is tested in the desymmetrization of racemic 1,2‐diols through asymmetric benzoylation. Compared to azabis(oxazolines) “clicked” to common polymeric supports such as MeOPEG or Merrifield resin, Fe3O4@SiO2 proves to be superior with respect to activity and selectivity, as exemplified by employing the catalysts in up to five runs with consistent high activity and selectivity. Recycling of the catalysts is achieved quantitatively by magnetic decantation.

Chiral periodic mesoporous copper(II) bis(oxazoline) phenylene–silica: A highly efficient and reusable asymmetric heterogeneous catalyst

“…Thus propylation of the carbon bridge yields a more enantioselective heterogeneous catalyst than the corresponding homogeneous catalyst. These results are comparable to the reported heterogeneous catalysts based on the Cu(II) aza-bis(oxazoline) supported onto poly(ethyleneglycol) [33] and magnetic nanoparticles coated with silica [34] and carbon [35]. Post-grafting the Cu(II) complex with trimethoxypropylsilane functionalized 1 onto periodic mesoporous phenylenesilica resulted in lower catalyst density at the surface of the material and thus in a less efficient heterogeneous catalyst with significantly lower selectivity, enantioselectivity and yield.…”

Xylanase Immobilized on Novel Multifunctional Hyperbranched Polyglycerol-Grafted Magnetic Nanoparticles: An Efficient and Robust Biocatalyst

“…The Fe 3 O 4 nanoparticles were prepared and coated with silica, according to the reported procedures. 48 In a glove box, containing N 2 atmosphere, a saturated solution of potassium methoxide in methanol (2 mL) was mixed with 0.100 g of silica coated magnetic nanoparticles (MNP). The mixture was sonicated in an ultrasonic bath for 30 min and stirred at room temperature for 1 h. Then it was refluxed at 80 • C for 2 h. At the end of the reaction, the magnetic nanoparticles were separated by a magnet, washed three times with dry methanol and dried in a vacuum oven at 60 • C. The glycidol (2 mL) was added slowly to these deprotonated nanoparticles at 100 • C and the mixture was stirred at 100 • C for 4 h. Then it was cooled and the contents were dissolved in methanol.…”

Click-chemistry for nanoparticle-modification

“…When the chiral ligands azabis(oxazoline) were conjugated onto these MNPs, the obtained NPs can be complexed with Cu(II) for benzoylation of hydrobenzoin. 98 This catalyst performed well in the asymmetric benzoylation with excellent selectivity, and maintained its high activity and selectivity for at least 3 runs. Meanwhile, organic radical (TEMPO) was grafted successfully on graphene-coated nanobeads with a magnetic cobalt core by using generally applicable CuAAC 'click'-chemistry as a recyclable catalyst.…”