Chemistry of palladium phosphinite (PPh(2)(OR)) and phosphonite (P(OPh)(2)(OH)) complexes: catalytic activity in methoxycarbonylation and Heck coupling reactions

The new phosphinite and phosphonite complexes (1-8) are very efficient catalysts for the methoxycarbonylation of iodobenzene and Heck cross-coupling of bromobenzene with butyl acrylate. High catalytic activity of these complexes can be explained by their in situ transformations during the reaction, stimulated by the presence of water, acid (HCl) or base (NEt(3)). Hydrolysis of phosphinite palladium complexes of the form trans-PdCl(2)[PPh(2)(OR)](2) (R = C(6)F(5), 2, (t)Bu 3, or O-menthyl 4) results in the formation of the dimeric complex [mu-ClPd(PPh(2)OH)(PPh(2)O)](2) 5, which is deprotonated by NEt(3), producing a polymeric complex of formula [Pd(P(O)PPh(2))(2)](n) 8. The reverse reaction, protonolysis of 8 with HCl, leads back to 5 and the monomeric complex 5a. The phosphinite complex PdCl(2)[PPh(2)(OBu)](2)1 with a more lipophilic ligand, PPh(2)(OBu), does not undergo hydrolysis under the same conditions. In the reaction of PdCl(2)(cod) with P(OPh)(2)(OH), the new dimer [mu-ClPd(P(OPh)(2)OH)(P(OPh)(2)O)](2) 6 was obtained, whereas reaction of Pd(OAc)(2) with P(OPh)(2)(OH) leads to the polymeric complex [Pd[P(O)(OPh)(2)](2)](n) 7. Protonolysis of 7 with HCl results in the formation of 6.     

Cis-coordination of the chromate anions in helical Co/Ni block-type polymeric systems. Structural and spectroscopic characteristics of catena(μ-CrO4-O,O′)[Co(HIm)3H2O] and catena(μ-CrO4-O,O′)[Co0.43Ni0.57(HIm)3H2O]

Two polymeric complexes: catena(μ-CrO₄-O,O′)[Co(HIm)₃H₂O] (1) and catena(μ-CrO₄-O,O′)[Co_0.43Ni_0.57(HIm)₃H₂O] (2) (where HIm=imidazole) with a cis-bridging coordination mode of the CrO₄ ²⁻ anion have been synthesized and characterized by X-ray and spectroscopic methods. These crystals were isolated from nine systems of varying reagent molar ratios and three excluding anions: Cl⁻, NO₃ ⁻ and SO₄ ²⁻ exclusively as mer [M(HIm)₃O₃]-type isomers. The unit cell of these isostructural complexes (monoclinic crystal system P2₁ /n) contains two independent helixes, left- and right handed, stabilized by intrahelical and interhelical hydrogen bonding and π–π interaction between pairs of the imidazole rings from neighbouring helixes. The Raman spectra at 77 K of 1 and 2 deconvoluted into lorentzian components revealed the block-type polymeric structure of the complexes. Moreover, the solution studies at millimolar concentrations of 1 and 2 indicated their complete decomposition in water. Four K electronic spectral analysis of the crystals (band deconvolution into gaussian components) enhanced with the data obtained in the polarized light allowed for assignment of the bands to the respective d–d transition (D_4h symmetry). It was found that the metallic centres are independently absorbing species, which supports the suggestion of a block-type structure of the polymers. The respective crystal field parameters for Co and Ni were calculated.     

Glucofuranose derivatives as a library for designing and investigating low molecular mass organogelators

We designed and synthesized a class of saccharide-based gelators having three free OH groups in the glucofuranose fragment. The gelating abilities of fourteen compounds were examined to systematically study the influence of the hydrophobic fragment connected to the C2′ carbon. Also the correlation between the saccharide crystal structure and its gelating properties was examined, showing limited usefulness in this particular case. SEM observations were carried out in order to investigate the hierarchical structure of xerogels and changes depending on different gel concentration.     

Fine tuning the structure of the Cu2+ complex with the prion protein chicken repeat by proline isomerization

The interaction between the single hexarepeat unit of chicken prion protein [ChPrP(54-59)] and Cu(II) was investigated by NMR, finding different coordination modes for the trans/trans and cis/trans isomers.     

Nature of the chemical bond between metal atoms and oxide surfaces: new evidences from spin density studies of K atoms on alkaline earth oxides

We have studied the interaction of K atoms with the surface of polycrystalline alkaline-earth metal oxides (MgO, CaO, SrO) by means of CW- and Pulsed-EPR, UV-Vis-NIR spectroscopies and DFT cluster model calculations. The K adsorption site is proposed to be an anionic reverse corner formed at the intersection of two steps, where K binds by more than 1 eV, resulting in thermally stable species up to about 400 K. The bonding has small covalent and large polarization contributions, and the K atom remains neutral, with one unpaired electron in the valence shell. The interaction results in strong modifications of the K electronic wave function which are directly reflected by the hyperfine coupling constant, (K)a(iso). This is found to be a very efficient "probe" to measure the degree of metal-oxide interaction which directly depends on the substrate basicity. These results provide an original and general model of the early stages of the metal-support interaction in the case of ionic oxides.     

Brucine and two solvates

The crystal structures of brucine (2,3‐di­methoxy­strychnidin‐10‐one), C₂₃H₂₆N₂O₄, brucine acetone solvate, C₂₃H₂₆N₂O₄·C₃H₆O, and brucine 2‐propanol solvate dihydrate, C₂₃H₂₆N₂O₄·C₃H₇O·2H₂O, have been determined. Crystals of brucine and its 2‐propanol solvate dihydrate exhibit similar monolayer sheet packing, whereas crystals of the acetone solvate adopt a different mode of packing, as brucine pillars. The solvent appears to control the brucine self‐assembly on the basis of common donor–acceptor properties of the surfaces.     

Dynamische interpretation von infrarotspektren

(Dynamic Interpretation of Infrared Spectra) Results of investigation of an algorithm, based on a novel static-dynamic method, for interpretation of infrared spectra are presented. The IRSCAN-D algorithm can recognize 103 infrared-active substructures comprising C, H, N, O, S, halogen, P and Si atoms. The results indicate that the algorithm is efficient; roughly 97% of the substructures are correctly ascribed, with a surprisingly low number (60%) of false recognition.     

Diaza crown ethers bearing heterocyclic ligating groups on nitrogen atoms and their complexing properties with divalent inorganic cations

Two nitrogen-substituted 4,13-diaza-I8-crown-6 compounds, bearing 2-methylquinolyl and 2-methylquinolyl-1-oxide groups, have been prepared. Ionophore-cation selectivities with a range of inorganic divalent cations have been investigated by means of membrane techniques, demonstrating their high selectivity for the Hg(II) cation.     

Guest Editor's Note: Clifford Algebras and Their Applications

The history and immediate future of the International Conferences on Clifford Algebras and Their Applications. Seven topical sessions in Ixtapa. Dirac operator: cross relations. Polemic guide: signature change, quasigroups, pseudotwistors. Clifford cogebra, coconnection and Dirac operator for Clifford cogebra.