title: trans-Fe(II)(H)2(diphosphine)(diamine) complexes as alternative catalysts for the asymmetric hydrogenation of ketones? A DFT study.
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)(PH(3))(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[partial double bond, bottom dashed]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.
authors.affiliation: Kathleen Lonsdale Building, Department of Chemistry, University College London, Gower Street, London, United Kingdom WC1E 6BT.
authors.forename: Hsin-Yi Tiffany
authors.initials: HY
authors.lastname: Chen
authors.forename: Devis
authors.initials: D
authors.lastname: Di Tommaso
authors.forename: Graeme
authors.initials: G
authors.lastname: Hogarth
authors.forename: C Richard A
authors.initials: CR
authors.lastname: Catlow
mesh_terms: D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003959:Diamines / Q000737:chemistry*; D006865:Hydrogenation; D007501:Iron / Q000737:chemistry*; D007536:Isomerism; D007659:Ketones / Q000737:chemistry*; D008968:Molecular Conformation; D010720:Phosphines / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry; D013816:Thermodynamics
chemical_list: D056831:Coordination Complexes; D003959:Diamines; D007659:Ketones; D010720:Phosphines; D012428:Ruthenium; D007501:Iron; C044646:phosphine