Chemistry

Doing Better Caged

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Science  18 Apr 2014:
Vol. 344, Issue 6181, pp. 237
DOI: 10.1126/science.344.6181.237-a
CREDIT: J. M. FALKOWSKI ET AL., JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 136, 14 (1 APRIL 2014) © 2014 AMERICAN CHEMICAL SOCIETY

Asymmetric synthesis, which builds organic molecules with a preferred chirality, is often performed with homogeneous metal complexes bearing large chiral ligands that position reactants to produce the desired isomer. However, for catalyst recovery, heterogeneous catalysts are often more convenient, and the caged environment of metal-organic frameworks (MOFs) can also perform asymmetric catalysis if linkers based on chiral ligands are used. Falkowski et al. now report on MOF-based syntheses with one of most successful ligands for late-transition metals, Noyori's BINAP ligand, 2,2′-bis(diphenylphosphine)-1,1′-binaphthyl. They first synthesized a MOF where the structure-directing unit is a zirconium-based cluster [Zr6O4(OH)4] and the linkers are BINAP-derived dicarboxylic acids. They then introduced Ru or Rh by adding metal complexes and then HBr. Rotational disorder prevented assignment of the metal coordination by x-ray diffraction, but x-ray absorption fine-structure spectroscopy confirmed metal coordination to the two P atoms of BINAP. They obtained very high enantiomeric excesses for a variety of organic reactions, including the asymmetric addition of arylboronic acids to 2-cyclohexanone (where yields with a Rh catalyst were moderate to high) and asymmetric hydrogenation of β-ketoesters (where the yields with a Ru catalyst were quantitative).

J. Am. Chem. Soc. 10.1021/ja500090y (2014).

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