title: Investigations into the metal species of the homogeneous iron(III) catalyzed Michael addition reactions.
abstract: An investigation into the species formed in the first step of the solvent free homogeneous Michael reaction of alpha,beta-unsaturated ketones with 2-oxocyclopentanecarboxylate (1) is presented. This reaction is catalyzed by FeCl(3).6H(2)O (2) and Fe(ClO(4))(3).9H(2)O (3). EXAFS, XANES, Raman and UV-Vis studies were carried out to explain the experimentally found higher catalytic activity of Fe(ClO(4))(3).9H(2)O (3) compared to FeCl(3).6H(2)O (2). A very intense pre-edge peak is found for a 1.6 mol% solution of FeCl(3).6H(2)O (2) in 1, suggesting a tetrachloroferrate(III) compound to be present in this solution. This is proved by UV-Vis and Raman spectroscopy. The counterion of this anionic complex is an octahedral [Fe(III)(1-H)(2)(H2O2)](+) complex with two deprotonated 2-oxocyclopentanecarboxylate (1) as the chelating ligand, (1-H)(-), as suggested by the examination of the XANES region, the obtained coordination numbers from the EXAFS analysis and by UV-Vis and Raman spectroscopies. In summary, the anion-cation species [Fe(III)Cl(4)](-)[Fe(III)(-H)(2)(H2O2)](+) is formed with FeCl(3).6H(2)O (2), whereas in the case of Fe(ClO(4))(3).9H(2)O (3) XAFS, Raman and UV-Vis investigations suggest the presence of a complex of the form [Fe(III)(1-H)(2)(H2O2)](+)[ClO(4)](-). The obtained results are discussed to explain the reduced catalytic activity of FeCl(3).6H(2)O (2) in comparison to Fe(ClO(4))(3).9H(2)O (3).
authors.affiliation: Institut für Physikalische Chemie, Pfaffenwaldring 55, 70569 Stuttgart, Germany. m.bauer@ipc.uni-stutttart.de
authors.forename: Matthias
authors.initials: M
authors.lastname: Bauer
authors.forename: Thomas
authors.initials: T
authors.lastname: Kauf
authors.forename: Jens
authors.initials: J
authors.lastname: Christoffers
authors.forename: Helmut
authors.initials: H
authors.lastname: Bertagnolli
mesh_terms: D002384:Catalysis; D003517:Cyclopentanes / Q000138:chemical synthesis* / Q000737:chemistry; D004952:Esters / Q000138:chemical synthesis* / Q000737:chemistry; D005290:Ferric Compounds / Q000737:chemistry*; D007659:Ketones / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D013057:Spectrum Analysis / Q000379:methods; D013499:Surface Properties; D014965:X-Rays
chemical_list: D003517:Cyclopentanes; D004952:Esters; D005290:Ferric Compounds; D007659:Ketones; C506754:ethyl 2-oxocyclopentanecarboxylate