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Asymmetric Arylation of Ketones with Chiral NHC Modified Fe3O4/Pd Nanoparticles
K. V. S. Ranganath, J. Kloesges, A. H. Schäfer, F. Glorius*
Westfälische Wilhelms-Universität Münster and Nano Analytics GmbH, Münster, Germany
21 December 2010 (online)
Chiral N-heterocyclic carbene modified Fe3O4/palladium nanoparticles (Fe3O4/Pd NPs-L) were prepared by impregnation of K2[PdCl4] to Fe3O4 nanoparticles in the presence of NaBH4 followed by treatment with L˙HBF4 and NaOt-Bu (eq. 1). The asymmetric α-arylation of 1a with bromo- or chlorobenzene proceeded in the presence of Fe3O4/Pd NPs-L and NaOt-Bu to give 2a in 72 or 56% yield with 48 or 60% ee (eq. 2). The chiral nanoparticles were also generated in situ by mixing Fe3O4/Pd NPs, L˙HBF4 and NaOt-Bu to achieve the asymmetric α-arylation of ketones (eq. 3, 11 examples; 56-91% yield with 33-85% ee).