A new approach to the design of heterogeneous single-site enantioselective catalysts

We analyze the merits of an approach to the design of enantioselective catalysts that relies on constraining an anchored organometallic complex at the inner walls of mesoporous silica. Two distinct metal centers {Rh(I) and Pd(II)}, three distinct diamino ligands {(S)-(-)-2-aminomethyl-1-ethylpyrrolidine, (AMP), (S)-(+)-(2-pyrrolidinyl-methyl)pyrrolidine, (PMP), and (1R,2R)-(+)-1, 2-diphenylethylenediamine; (DED)}, two distinct methods of anchoring (a covalent and a noncovalent one), and two specific examples of enantioselective hydrogenation (the asymmetric hydrogenation of the C=C bond in E-alpha-phenylcinnamic acid and the asymmetric hydrogenation of the C=O bond in methyl benzoylformate) have been investigated. Values of enantiomeric excess (ee) ranging from a low of 66 to a high of 93 have been achieved by this approach. Moreover, the catalysts are robust and stand up well to recycling.