Stereoselective Synthesis by Catalysts Supported on Magnetic Nanoferrites

The outstanding relevance of catalysis in stereoselective synthesis is established by the huge number of methodologies developed in order to obtain enantiopure molecules. Supporting enantiopure ligands onto magnetic nanoparticles (MNPs) constitutes a successful strategy in the field of stereoselective synthesis for several reasons. The high surface/mass ratio of the MNPs and the location of the catalytic moieties on the MNP surface does not impede mass transfer. Furthermore, The MNP-supported catalyst can be easily dispersed in and separated from the reaction mixture. Among the many types of MNPs, cubic ferrite MFe2O4 (M = Fe, Mn, Ni, Co, Cu) NPs are particularly suited since they are dispersible but insoluble in all solvents, chemically stable and usually inert. This chapter focuses on stereoselective organic reactions catalysed by MNP-supported chiral nanocatalysts affording enantiopure molecules. Rather than a comprehensive review of the field, the present chapter was shaped as a critical assessment of recent achievements. First, the structural and functional variety of the chiral MNP-supported catalysts are described with brief considerations about the nanocatalyst synthesis. The next section is devoted to the important and complex field of the characterization of MNP-supported chiral nanocatalysts where it is emphasised that the identity, mutual organization, and relative amount of all components of the MNP-supported chiral nanocatalysts need to be known to successfully rationalize the design and performance of catalysts. Thus, their characterization requires a large but rewarding effort. Finally, the stereoselective organic transformations achieved by using MNP-supported chiral nanocatalysts are reviewed according to the reaction type. The use of these nanocatalysts has grown into a successful methodology at the disposal of the organic chemist for the obtainment of small organic molecules in the enantiopure form. Emphasis was given on the comparison with the free or otherwise supported catalyst. The key points behind such success is that (i) all MNP-supported catalysts can be quickly and completely recovered by the application of an external magnet, and (ii) the catalytic performance is often good and sometimes rivals with well-established homogeneous catalysts. A successful asymmetric transformation involving a MNP-supported catalysts is actually the result of the understanding at a multidisciplinary level, involving organic chemistry, physical chemistry and nanoscience. The ongoing interest in this field makes us certain that in the near future an even wider variety of asymmetric organic reactions will be successfully carried out by this methodology.