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Publication Detail
trans-Fe-II(H)(2)(diphosphine)(diamine) complexes as alternative catalysts for the asymmetric hydrogenation of ketones? A DFT study
  • Publication Type:
    Journal article
  • Publication Sub Type:
    Article
  • Authors:
    Chen HYT, Di Tommaso D, Hogarth G, Catlow CRA
  • Publisher:
    ROYAL SOC CHEMISTRY
  • Publication date:
    2011
  • Pagination:
    402, 412
  • Journal:
    DALTON T
  • Volume:
    40
  • Issue:
    2
  • Print ISSN:
    1477-9226
  • Language:
    EN
  • Keywords:
    LIGAND BIFUNCTIONAL CATALYSIS, AB-INITIO PSEUDOPOTENTIALS, EFFECTIVE CORE POTENTIALS, ENANTIOSELECTIVE HYDROGENATION, STEREOSELECTIVE HYDROGENATION, MOLECULAR CALCULATIONS, ADJUSTABLE-PARAMETERS, TRANSITION-ELEMENTS, CARBONYL-COMPOUNDS, PROCHIRAL KETONES
  • Addresses:
    Chen, HYT
    UCL
    Dept Chem
    London
    WC1E 6BT
    England
Abstract
New insights into the structural, electronic and catalytic properties of Fe complexes are provided by a density functional theory study of model as well as real [Fe-II(H)(2)(diphosphine)(diamine)] systems. Calculations conducted using several different functionals on the trans- and cis-isomers of [Fe-II(H)(2)(S-xylbinap)(S,S-dpen)] complexes show that, as with the [Ru-II(H)(2)(diphosphine)(diamine)] complexes, the trans-[Fe-II(H)(2)(diphosphine)(diamine)] complex is the more stable isomer. Analysis of the spin states of the trans-[Fe-II(H)(2)(diphosphine)(diamine)] complexes also shows that the singlet state is significantly more stable than the triplet and the quintet, as with the [Ru-II(H)(2)(diphosphine)(diamine)] complexes. Calculations of the catalytic cycle for the hydrogenation of ketones using two model trans-[M-II(H)(2)(PH3)(2)(en)] catalysts, where M = Ru and Fe, show that the mechanism of reaction as well as the activation energies are very similar, in particular: (i) the ketone/alcohol hydrogen transfer reaction occurs through the metal-ligand bifunctional mechanism, with energy barriers of 3.4 and 3.2 kcal mol(-1) for the Ru- and Fe-catalysed reactions, respectively; (ii) the heterolytic splitting of H-2 across the M(sic)N bond for the regeneration of the Ru and Fe catalysts has an activation barrier of 13.8 and 12.8 kcal mol(-1), respectively, and is expected to be the rate determining step for both catalytic systems. The reduction of acetophenone by trans-[M-II(H)(2)(S-xylbinap)(S,S-dpen)] complexes along two competitive reaction pathways, shows that the intermediates for the Fe catalytic system are similar to those responsible for the high enantioselectivity of (R)-alcohol in those proposed trans-[Ru-II(H)(2)(S-xylbinap)(S,S-dpen)] catalysed acetophenone hydrogenation reaction. Thus the high enantiomeric excess in the hydrogenation of acetophenone could, in principle, be achieved using Fe catalysts.
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