Giovanni Predieri

Conformational behaviour and E/Z isomerization of N-acyl and N-aroylhydrazones

Abstract The stereochemical behaviour of N -acyl and N -aroylhydrazones of aromatic aldehydes, of pyruvates and of acetone, in polar and less polar solvents, has been studied by HPLC and by NMR techniques. Z/E Geometrical isomers and cis / trans amide conformers have been found for N -acylhydrazones, while for N -aroylhydrazones only geometrical isomers were detected. Energy barriers of isomers are reported, and solvent effects are discussed with regard to hydrogen bond interactions.

Aroylhydrazones as chelating agents: d10-metal complexes of pyridine-2-carbaldehyde salicyloylhydrazone and x-ray structure of the zinc derivative

Abstract The title organic ligands (Hsip) gave, by reaction with d10-metal acetates, complexes of the type M(sip)2 (M = Zn, Cd, Hg), in which the ligand behaved as terdentate, producing a distorted octahedral environment around the metal. The 1H and 13C chemical shifts found for these complexes in DMSO are compared with the corresponding ones of the free ligand. The crystal structure of the zinc derivative has been determined from diffractometer data to R = 0.072 for 1086 independent reflections. Crystals are monoclinic, space group C2/c, with unit-cell dimensions a = 18.193(2), b = 24.532(6), c = 11.535(2) A,β = 103.71(1)° and Z = 8. Coordination occurs through the carbonyl oxygens (Zn−O = 2.10, 2.16(1) A), the azomethine nitrogens (Zn−N = 2.04, 2.07(1) A) and the pyridine nitrogen s(Zn−N = 2.24, 2.26(1) A).

Influence of the preparation method on the thiophene HDS activity of silica supported CoMo catalysts

Abstract The effect of the preparation method of CoMo/SiO2 catalysts with and without sodium ions, on the hydrodesulfurization (HDS) of thiophene was investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and N2 physisorption (BET). The samples were prepared by total sol–gel route, by classic wetness impregnation and by co-impregnation, in the presence of nitrilotriacetic acid (NTA), of commercial and sol–gel prepared silica. The influence of sodium ions added to the sol mixture and to the silica before the impregnation with Co and Mo salt solution, was also considered. The presence of sodium favoured the phase transition of amorphous silica to cristobalite with consequent reduction of the surface area and of the catalytic activity. The catalysts prepared by the sol–gel method exhibited better metal oxide dispersion but lower catalytic activity. On the contrary the catalysts supported on home-made sol–gel silica were quite active in spite of the lower surface areas and the low metal dispersion. Addition of NTA to the impregnation solution yielded better performing catalysts.

Mixed-oxide catalysts involving V, Nb and Si obtained by a non-hydrolytic sol-gel route : preparation and catalytic behaviour in oxydative dehydrogenation of propane

Abstract One-step non-hydrolytic condensation reactions, starting from VO(O i Pr) 3 and NbCl 5 , have been used for the first time to prepare Nb-V oxide catalysts. Different materials containing the NbVO 5 phase at different purity levels have been obtained, after thermal treatments, depending on the experimental conditions. The synthetic procedure has also been applied to prepare ternary Nb-V-Si oxide systems. From preliminary catalytic reaction studies it appears that the catalysts so prepared are promising with respect to their interesting performances in the oxidative dehydrogenation (ODH) of propane. It has also been found that α-Sb 2 O 4 , physically blended with the Nb-V oxide materials, could act as an appropriate promoter to improve the catalytic performances of these systems.

The Reactivity of HRu3(CO)9C2BUt. The Synthesis and crystal structure of (PPH3)AuRu3(CO)9C2BUt, a new ruthenium-gold cluster

Abstract The (PPh 3 )AuRu 3 (CO) 9 C 3 Bu t complex has been obtained by reacting (PPh 3 )AuCl with the anionic complex [Ru 3 (CO) 9 C 2 Bu t ] − , prepared from the hydride HRu 3 (CO) 9 C 2 Bu t with a new procedure. The crystal structure of this heterometallic complex, as acetone solvate, has been determined by X-ray methods: it crystallizes in the orthorhombic space group F dd2, with 16 molecules in a unit cell of dimensions a = 33.64(2), b = 48.38(2), c = 9.23(1) A. The structure has been solved from diffractometer data by direct and Patterson methods, and refined by full-matrix least-squares to R = 0.068 for 1628 observed reflections. The complex consists of a AuRu 3 cluster in a butterfly arrangement with the Au atom on a wingtip. The Au atom of the Au(PPh 3 ) group bridges one side of the ruthenium triangle and practically substitutes the hydride ligand of the HRu 3 (CO) 9 C 2 -Bu t complex, maintaining the basic features of the Ru 3 (CO) 9 C 2 Bu t framework virtually unchange.

Synthesis and characterization of organotin hexacyanoferrates

Abstract The synthesis and structural characterization by IR, ESR, 119 Sn and 57 Fe Mossbauer spectroscopy, X-ray powder diffraction, and TG and DSC methods of a new series of organotin hexacyanoferrates are reported.

Ph3PSe as a convenient synthon for one-step syntheses of Ph3P-substituted selenido carbonyl iron and ruthenium clusters. Crystal structures of Fe3(μ3-Se)(μ-CO)(CO)7(PPh3)2, M3(μ3-Se)2(CO)7(Pph3)2 (MFe or Ru) and Ru4(μ4-Se)2(μ-CO)2(CO)7(PPh3)2☆

Abstract Ph3PSe reacts in toluene with Fe3(CO)12 or Ru3(CO)12 affording a variety of Ph3P-substituted selenido carbonyl clusters. In the case of iron the reaction is unselective, six products (1–6) having been obtained belonging to three different families of clusters. Fe2(μ-Se2)(CO)6−nLn (two products, 3, 5, n = 1, 2), Fe3(μ3-Se)2(CO)9−nLn (three products, 1, 2, 4, n = 0–2) and Fe3(μ3-Se)(μ-CO)(CO)9−nLn (one product, 6, n = 2). In the case of ruthenium, under certain conditions, the reaction is quite selective giving the disubstituted trinuclear cluster Ru3(μ3-Se)2(CO)7(PPh3)2 (8) in very high yield (> 90%). Minor products are the mono- and trisubstituted analogous derivatives 7 and 10 and the tetraruthenium cluster Ru4(μ4-Se)2(μ-CO)2(CO)7(PPh3)2 (9). The crystal structures of the clusters 4, 6, 8 and 9 are described.

Self-assembly of polyoxoselenitopalladate nanostars [Pd15(μ3-SeO3)10(μ3-O)10Na]9− and their supramolecular pairing in the solid state

An anionic Pd₁₅-oxo-cluster [Pd₁₅(μ₃-SeO₃)₁₀(μ₃-O)₁₀Na]⁹⁻ has been synthesized. It is the result of an unprecedented self-assembly of Pd(2+) and Na(+) cations, SeO₃²⁻ and oxo anions. It has been found for the first time, that selenito groups can give rise to supramolecular interactions in the solid state with palladium atoms, through the selenium electron lone pairs.

Anchoring rhodium(I) on benzoylthiourea-functionalized silica xerogels. Production of recyclable hydroformylation catalysts and the crystal structure of the model compound [Rh(cod)(Hbztu)Cl]☆

Two benzoylthiourea-functionalized silica xerogels, 4.5SiO2 · SiO3/2(CH2)3NHC(S)NHC(O)Ph (XGbztu) and SiO3/2 (CH2)3NHC(S)NHC(O)Ph (XGbztu∗) have been prepared from (EtO)3Si(CH2)3NHC(S)NHC(O)Ph by the sol-gel process. They are able to bind rhodium(I) species giving the composite materials Rh/XGbztu and Rh/XGbztu∗, which are very active insoluble and recoverable catalysts for the hydroformylation of styrene. The anchored species undergo major changes during the catalytic cycles, particularly in the Rh/XGbztu system, whose iso/normal selectivity ratio gradually increaased in the first five runs. Futhermore, CH3(CH2)2NHC(S)NHC(O)Ph (HBztu) has been studied as a model of the surface binding function. The structure of [Rh(cod)(Hbztu)Cl]1, which represents a suitable molecular model for the anchored complexes, has been determined by X-ray diffraction.

Coordination behaviour of diphosphine and diarsine oxides in four organotin(IV) adducts

Abstract Four new molecular adducts of diphenyl- and triphenyl-tin(IV) nitrates with 1,2-bis(diphenylarsoryl)ethane (dpaoe), bis(diphenylphosphoryl)methane (dppom) and trans -1,2-bis(diphenylphosphoryl)ethylene (tdppoet) have been synthesised and characterized by infrared spectroscopy, and an X-ray diffraction study has been carried out on two of them, {SnPh 3 NO 3 } 2 dpaoe ( 1 ) and SnPh 2 (NO 3 ) 2 dppom ( 2 ). Both 1 and 2 crystallize in the triclinic space group P 1 , with unit-cell dimensions. 1 : a 12.810(8), b 11.938(6), c 10.394(4) A, α 97.92(4), β 90.00(5), γ 111.13(4)°, Z = 1, R = 0.0454; 2 : a 13.845(6), b 13.119(4), c 10.444(6) A, α 106.50(4), β 101.24(4), γ 91.33(4)°, Z = 2, R = 0.0504. The structure of 1 consists of binuclear monomeric units in which each tin atom is bound in a trigonal bipyramidal configuration to three phenyl rings in the equatorial plane and to the diarsine ligand and the nitrate group in the axial positions. In compound 2 the tin atom exhibits a pentagonal-bipyramidal coordination geometry with five oxygen atoms, two from the chelating dppom ligand and three from the two nitrate groups, around the pentagonal girdle, and the two phenyl groups at the apices of the bipyramid. The vibrational frequencies of the nitrate groups and of the diarsine and diphosphine ligands are discussed in the light of the X-ray results.