Functionalization of Fe3O4 magnetic nanoparticles for organocatalytic Michael reactions

(S)-alpha,alpha-Diphenylprolinol trimethylsilyl ether supported onto well-defined (5.7 +/- 1.1 nm) superparamagnetic Fe3O4 nanoparticles was used as a highly active, magnetically recoverable and reusable catalyst for the asymmetric, organocatalytic Michael addition of propanal to nitroolefins leading to high enantioselectivities. The assembly of the catalytic functional nanoparticles involves two successive steps: (i) introduction of a 3-azidopropyl unit through the formation of Si-O bonds, and (ii) integration of the organocatalytic unit by means of a copper-catalysed alkyne-azide cycloaddition reaction leading to a 1,2,3-triazole linker. Neither the process of nanoparticle assembly nor its catalytic use in dichloromethane solution provokes particle growth or agglomeration, this behaviour being key for the observation of high catalytic activity and for recyclability.