Miguel A. Salvadó

A new chiral glycine synthon. Synthesis, x-ray structure of (−).(2S,4R)-2-ethoxycarbonyl-4-phenyl-1,3-oxazolidine and diastereoselective nucleophilic ring opening to (R)-ethyl α-amino carboxylates.

Abstract Condensation of (R)-N-benzyl-2-phenylglycinol 1 with the methyl hemiacetal of ethyl glyoxylate leads to (2S,4R)-2-ethoxycarbonyl-4-phenyl-1,3-oxazolidine 2 as the major product, obtained as a pure enantiomer after column chromatography. Compound 2 is stereoselectively cleaved by dialkylzinc reagents, prepared from alkylmagnesium iodides and ZnCl 2 , with moderate to good d.e.ś (72–94 %). These compounds, after separation by column chromatography and debenzylation by hydrogenolysis in the presence of 10% Pd on carbon, lead to enantiomerically pure ethyl α-amino carboxylates with good chemical yields.

Layered acid arsenates α-M(HAsO4)2·H2O (M=Ti, Sn, Pb): synthesis optimization and crystal structures

Abstract The syntheses of α-M(HAsO 4 ) 2 ·H 2 O (M=Ti, Sn and Pb) have been optimized to prepare crystalline single phase materials. The crystal structures of M=Sn, Pb have been refined using X-ray powder diffraction data by the Rietveld method. A combined X-ray and neutron powder data refinement for M=Ti has allowed to obtain a very detailed picture of the structure including the hydrogen-bonding network. The results have been compared with those of the phosphates analogs. In addition, detailed characterization of the samples has been carried out by IR spectroscopy, thermal analysis and powder thermodiffractometry.

A study on the aminomercuration-nucleophilic demercuration of --1,5-cyclooctadiene; stereoselective synthesis of 2,6-disubstituted-9-aza bicyclo[3.3.1]nonanes

Abstract The aminomercuration of cis - cis -1,5-Cyclooctadiene with a series of mercury(II) salts followed by nucleophilic displacement of mercury by aromatic amines, water and nitrate ion has been studied. As a result, bicyclic triamines, aminoalcohols and nitrate esters have been obtained respectively in clean processes which occur under total stereoelectronic control by involvement of a tricyclic aziridium ion to afford a single stereoisomer in each case. The influence of the counter ion and the basicity of the amine on the tandem aminomercuration-demercuration is discussed.

An expeditious stereoselective synthesis of functionalized seven-membered carbocycles by reaction of 2-aminobuta-1,3-dienes with vinylchromium fischer type carbenes

The reaction between 2-aminobuta-1,3-dienes and pentacarbonyl-[1-methoxy-frans-3-(2-furyl)-prop-2-enylidene]-chromium(0) takes place at room temperature leading with total regio- and stereo-selectivity to functionalized seven-membered carbocycles with good yields.

Neo-clerodane diterpenoids from aerial parts of Linaria saxatilis var. Glutinosa

Abstract From the less polar fractions of the aerial parts of L. saxatilis var.glutinosa, one new neo-clerodane diterpenoid, highly oxygenated at the side chain, was isolated in addition to several known compounds. The structure of the new compound was established by a combination of 1H and 13C NMR spectral data analysis, while the assignment of the absolute stereochemistry of the side chain was performed by X-ray crystallographic analysis. Varied spectroscopic studies and several chemical correlations were used to confirm the structures of the remaining compounds.

Synthesis and electrochemical studies of new ferrocene-labelled dinuclear rhodium(II) complexes. Crystal structures of [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]Fe(C5H5)}2(HO2CMe)2] and [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]2Fe}(HO2CMe)]·CH2Cl2

The reaction of diphenylphosphinoferrocene and 1,1′-bis(diphenylphosphino)ferrocene with [Rh2(O2CMe)4(MeOH)2](1:1 and 1:2 molar ratio respectively) yields the monoadducts [Rh2(O2CMe)4{(Ph2PC5H4)Fe(C5H5)}]1 and [{Rh2(O2CMe)4(MeOH)}2{(Ph2PC5H4)2Fe}]2. By thermal treatment of 1 in refluxing toluene–acetic acid (10:3) the monometallated product [Rh2(O2CMe)3{[(C6H4)PhP(C5H4)]Fe(C5H5)}(HO2CMe)2]3 was obtained in practically quantitative yield. Compound 3 reacts with [Fe(C5H5)(C5H4PPh2)](1:1 molar ratio) giving the adduct [Rh2(O2CMe)3{[(C6H4)PhP(C5H4)]Fe(C5H5)}{(Ph2PC5H4)Fe(C5H5)}]4, which reacts thermally in toluene–acetic acid (10:3) yielding the doubly metallated product [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]Fe(C5H5)}2(HO2CMe)2]5 as a mixture of conformational isomers. An X-ray determination of 5 has been carried out: space group Pbca(orthorhombic), a= 18.065(3), b= 20.606(4), c= 26.242(5)A, Z= 8, and R= 0.038. The crystal structure shows that the two metallated phosphines are in a head-to-tail configuration. Thermal treatment of a mixture of [Rh2(O2CMe)4(MeOH)2] and [Fe(C5H4PPh2)2](1:1 molar ratio) in acetic acid yields the compound [Rh2(O2CMe)2{[(C6H4)PhP(C5H4)]2Fe}(HO2CMe)]·CH2Cl26 after purification and crystallization from a CH2Cl2–hexane–acetic acid mixture. An X-ray diffraction investigation showed that this compound crystallizes in space group P21/c(monoclinic) with a= 12.735(4), b= 16.811(5), c= 20.161(8)A, β= 95.17(4)°, Z= 4 and R= 0.089. The two PPh2 fragments of the ferrocene ligand act as bridging orthometallated ligands in a head-to-head configuration. Two well defined oxidation processes were detected by cyclic voltammetry for all the complexes in CH2Cl2 solution: the first one, in the range 0.6–0.7 V, is due to the couple Fe2+–Fe3+ while the second one, in the range 0.9–1.32 V, is due to the couple Rh24+–Rh25+.

Hydrothermal synthesis and structural characterization of framework microporous mixed tin–zirconium silicates with the structure of umbite

Abstract A novel framework mixed tin–zirconium silicate, K2Sn0.25Zr0.75Si3O9·H2O (1), was synthesized under mild hydrothermal conditions. The unit cell is orthorhombic, a=10.260(2) A, b=13.272(2) A, c=7.174(1) A, space group P212121, Z=4. Isotypic with the mineral umbite, the structural formula may be written as K 2 ( Sn , Zr ){ uB ,1 ∞ 1 }[ 3 Si 3 O 9 ] . In a topotactical process, the K+ ions in compound 1 were replaced by Na+ ions, thus obtaining compound 2: Na2Sn0.25Zr0.75Si3O9·H2O (2), a=10.500(1) A, b=13.354(2) A, c=7.2731(9) A.

Synthesis and crystal structure of thorium bis(hydrogenphosphate) monohydrate.

Microcrystals of Th(HPO 4) 2.H 2O were hydrothermally obtained from a Th(NO 3) 4-CO(NH 2) 2-H 3PO 3-H 2O system ( T = 180 masculineC). The structure [orthorhombic, Pbca, a = 9.1968(2) A, b = 18.6382(2) A, c = 8.7871(2) A], unlike alpha-Zr(HPO 4) 2.H 2O-type layered compounds, consists of a three-dimensional framework with PO 4 tetrahedra coordinated to Th atoms. The water molecule is also coordinated to the Th atom and projected toward small channels running along the directions of the a and c axes. The ThO 6O(w) environment could be described as a highly distorted pentagonal bipyramid.

Structure and crystallization behavior of the (Ba,Sr)HAsO4·H2O solid-solution in aqueous environments

Abstract Crystals of different members of the (Ba,Sr)HAsO4·H2O solid solution have been synthesized, and the first structural studies indicate that they crystallize in the same space group, Pbca, with Z = 8. The unit-cell parameters are a = 7.436(2), b = 8.481(1), c = 14.348(6) Å, and a = 7.752(1), b = 8.759(1), c = 14.668(3) Å for the strontium and barium end-members, respectively. Both end-members have a layered structure with slices parallel to (001) linked by hydrogen bonds from the water molecules. These features are consistent with both the perfect cleavage on {001} and the morphological importance of this form in the crystals obtained. However, the two end-members are not isostructural and show differences in both the anionic hydrogen positions and number of hydrogen bonds. Complementary powder-diffraction measurements indicate that the cell parameters increase in a non-linear way with the barium content indicating that the solid solution is complete but could be non-ideal. Preliminary data suggest that barium partitions preferentially into the solid phase when crystallizing this solid solution from aqueous solutions.

Structural and magnetic phases of Fe(ND3)2PO4

Polycrystalline samples of Fe(ND3)2PO4 were prepared by means of a hydrothermal route and characterized using powder x-ray diffraction, scanning electron microscopy, chemical and thermal analysis, magnetic measurements, specific heat and neutron diffraction experiments. This material orders within an orthorhombic (Pnma space group) crystal structure at room temperature, but below 220 K the crystal structure changes towards a monoclinic P 21/n structure through a phase transition with almost no latent heat. Furthermore, the magnetic cell at 2 K is twice the size of the crystallographic cell observed at 80 K. The magnetic structure associated with the Fe(III) ions is thus commensurate with the crystal lattice having a propagation vector , the magnetic moments lying in the yz plane of the crystallographic cell.