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).

The Fe III catalysed Michael reaction of b-oxo esters 1 with methyl vinyl ketone (2a) and methyl acrylate (2b) as acceptors is investigated. The proposed mechanism, based on experimental results, is supported for the first time by ab initio calculations. Thereby different Fe III complexes 4, derived from the catalyst and 1, with either neutral (H 2 O) or anionic (a second diketonate 1) coligands are considered and their stabilities calculated. Ligand exchange in 4 by acceptors 2 gives intermediates 5 and subsequent C Ã/C bond formation affords complexes 6. Both 5 and 6 are found to be minima on the potential hypersurface and a pathway from 5 to 6 via transition states 7 could be identified. For the reaction of 4a (L 0/H 2 O) with 2a, b no reactivity difference was found. The anionic coligand, however, causes a significant change in the reaction profile: due to the higher reaction barrier for the C Ã/C coupling for 2b (5d to 6d) compared to 2a (5f to 6f) a fast subsequent reaction and thus, catalytic turnover is inhibited. #

Three α‐cyclopropyl β‐dicarbonyl compounds have been used as probes for α‐radicals as electrophilic reaction intermediates in a cerium‐catalyzed α‐hydroxylation reaction with molecular oxygen. Since the cyclopropyl group did not ring‐open to products with a butenyl moiety, but was retained in the products, a localized unpaired electron at the α position can be excluded during the course of the reaction. The α‐cyclopropyl‐substituted substrates were prepared by aldol or Claisen reactions. Other substrates with α‐methyl, α‐isopropyl, and α‐tert‐butyl substituents were prepared and converted under the α‐hydroxylation conditions in order to estimate steric influences on the yield of the reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

The reaction of TCNE and TCNQ zwitterionic benzoquinonemonoimine derivatives under basic conditions resulted in HCN elimination to give a tricyanoethenyl derivative - which forms a π-complex with Pd(0)--or a stable malodinitrile salt, respectively. In the latter case, chemoselective C-alkylation was observed whereas oxidation led to dimerization by C-C coupling.