Armando Cabrera

Stable preformed chiral palladium catalysts for the one-pot asymmetric reductive amination of ketones.

The application of air stable preformed [(R)-BINAP]PdBr2, [(S)-BINAP]PdBr2, [(R)-Tol-BINAP]PdBr2, and [(S,S)-CHIRAPHOS]PdBr2 complexes in the one-pot asymmetric reductive amination of various carbonyl compounds, leading to chiral amines in very good yields with high enantioselectivities (<99% ee), is reported.

Constituents of zaluzania species—II : Structures of zaluzanin C and Zaluzanin D

Abstract Zaluzanin C a constituent of Zaluzania augusta (Lag.) Schultz, Bip. and Z. triloba Pers has been shown to be a guaianolide with structure Ia. Zaluzanin D another constituent of Z. triloba was identified as acetylzaluzanin C (Ib). The eudesmanolide ivalin (XI) was also isolated from Z. triloba .

Perspectives of antimony compounds in oncology

AbstractAntimony, a natural element that has been used as a drug for over more than 100 years, has remarkable therapeutic efficacy in patients with acute promyelocytic leukemia. This review focuses on recent advances in developing antimony anticancer agents with an emphasis on antimony coordination complexes, Sb (III) and Sb (V). These complexes, which include many organometallic complexes, may provide a broader spectrum of antitumoral activity. They were compared with classical platinum anticancer drugs. The review covers the literature data published up to 2007. A number of antimonials with different antitumoral activities are known and have diverse applications, even though little research has been done on their possibilities. It might be feasible to develop more specific and effective inhibitors for phosphatase-targeted, anticancer therapeutics through the screening of sodium stibogluconate (SSG) and potassium antimonyltartrate-related compounds, which are comprised of antimony conjugated to different organic moieties. For example, SSG appears to be a better inhibitor than suramin which is a compound known for its antineoplastic activity against several types of cancers.

Tertiary stibines containing aromatic heterocycles and their silver complexes: synthesis and X-ray structures

Abstract The work presents the synthesis of tertiary stibines containing heterocyclic aromatic groups of general formula (2-C4H3X)3Sb where X=S (1), O (2) or NMe (3). These stibines were brominated to give corresponding dibromide and were complexed with silver(I) nitrate. The stibines, dibromides and their silver complexes were characterized by elemental analyses, IR, UV, mass, 1H, 13C, COSY, HETCOR NMR spectroscopy. Molecular structures of (2-C4H3S)3Sb (1); (2-C4H3S)3SbBr2 (4) and {Ag[(2-C4H3S)3Sb]2}NO3 (6) were determined by X-ray spectroscopy. This is the first X-ray crystallographic report on stibines containing heterocyclic aromatic groups and their silver complexes. The stibine (1) is pyramidal while its dibromide has trigonal bipyramidal structure. The silver complex (6) has a polymeric nature with NO3− acting as a bridging ligand.

Trans Influence of Triphenylstibine: Crystal Structures of cis‐[PtBr2(SbPh3)2], trans‐[PtBr(Ph)(SbPh3)2], [NMe4][PtBr3(SbPh3)], and cis‐[PtBr2(SbPh3)(PPh3)]

The work reports the unexpected reaction of diphenyldibromo antimonates (III) with PtCl2 and cis-[PtCl2(PPh3)2]. The reaction gives triphenylstibine containing PtII complexes viz. cis-[PtBr2(SbPh3)2] (1), trans-[[PtBr(Ph)(SbPh3)2] (2), [NMe4][PtBr3(SbPh3)] (3), and cis-[PtBr2(PPh3)(SbPh3)] (4). All the complexes were characterised by elemental analyses, IR, Raman, 195Pt NMR, FAB mass spectroscopy and X-ray crystallography. A plausible mechanism via the phenyl migration is proposed for the formation of these complexes. The average Pt–Br distance in 1 is 2.456(2) A, in 2 2.496 A(trans to Ph) while in 3 it is 2.476 A (trans to Sb) implying a comparable trans influence of Ph3Sb and Ph3P. Transeinflus von Triphenylantimon: Die Kristallstrukturen von cis-[PtBr2(SbPh3)2], trans-[PtBr(Ph)(SbPh3)2], [NMe4][PtBr3(SbPh3)] und cis-[PtBr2(SbPh3)(PPh3)] Es wird uber die unerwartete Reaktion von [Ph2SbBr2]– mit PtCl2 und cis-[PtCl2(PPh3)2] berichtet, die die Platin(II)-Komplexe cis-[PtBr2(SbPh3)2] (1), trans-[[PtBr(Ph)(SbPh3)2] (2), [NMe4][PtBr3(SbPh3)] (3) und cis-[PtBr2(PPh3)(SbPh3)] (4) ergibt. Die Komplexe werden durch Elementaranalyse, IR, Raman, 195Pt-NMR, FAB-Massenspektrometrie und Rontgenstrukturanalyse charakterisiert. Fur die Bildung der Komplexe wird ein Reaktionsmechanismus durch Ligandenaustausch vorgeschlagen. Der mittlere Pt–Br-Abstand betragt in 1: 2,456 A, in 2: 2,496 A (trans zu Ph), in 3: 2,476 A (trans zu Sb), was auf einen ahnlichen Transeinflus von Ph3Sb und Ph3P hinweist.

Clay-mediated cyclooligomerization of olefin oxides: a one-pot route to crown ethers

The catalytic synthesis of substituted 1,3-dioxolanes, 1,4-dioxanes, 9-crown-3, 12-crown-4 and 15-crown-5 ethers, from alkyl oxiranes and a montmorillonite type clay is discussed.

Synthesis and characterization of some arene hydrido-complexes [Ru(η6-arene)(EPh3)2H]+ (η6-arene=benzene, p-cymene or hexamethylbenzene; E=P, As or Sb). Crystal structure of [Ru(η6-C6H6)(PPh3)2H]BF4

[{Ru( η 6 -arene)Cl 2 } 2 ] ( η 6 -arene=benzene, p-cymene or hexamethylbenzene) reacts with EPh 3 (E=P, As or Sb) in methanol to give monomeric cationic arene hydrido complexes [Ru( η 6 -arene)(EPh 3 ) 2 H] + in presence of AgBF 4 or AgPF 6 . However, reactions in presence of triphenylphosphine also yield a symmetrically bridged tris ( μ -methoxy) complex [(PPh 3 ) 3 Ru( μ -OMe) 3 Ru(PPh 3 ) 3 ] + . The crystal structure of [Ru( η 6 -C 6 H 6 )(PPh 3 ) 2 H]BF 4 has been determined. Crystal data, monolinic system, space group P2 1/n , a =14.792 (2) A; b =14.351 (1) A; c =17.661 (2) A; β =102.25 (1)° and Z =4. Crystal structure determination reveals the distortion of the Ru(PPh 3 ) 2 H + unit in the cation [Ru( η 6 -C 6 H 6 )(PPh 3 ) 2 H] + .

1,3-dioxolane formation with a montmorillonite-type clay catalyst

Abstract The coupling reaction of oxiranes with carbonyl compounds to produce 1,3-dioxolanes was promoted by catalytic amounts of a bentonitic clay. The product yield was found to be dependent on the catalyst, the reaction temperature and the reagent concentrations. A kinetic study performed with acetone and ethylene oxide showed a first-order dependence in both reagents. Other experiments made with different epoxides, carbonyl compounds and catalysts are also discussed.

Cyclic and linear oligomerization reaction of 3,4,5-trimethoxybenzyl alcohol with a bentonite-clay

Abstract The catalytic induction and structures of cyclic and linear oligomers from 3,4,5-trimethoxybenzyl alcohol with a bentonite clay as catalyst are discussed.

Catalytic hydrocyanation of α-ketoalkynes by Ni(CN)2/CO/KCN system in alkaline aqueous media: Identification of the active species

Abstract 5-Hydroxy-3-pyrrolin-2-ones are regioselectively synthesized in a good yield under very mild conditions by tetracyanonickelate (0) ion catalyzed hydrocyanation of α-ketoalkynes, in the absence of hydrogen cyanide. The catalyst is prepared in situ in a basic aqueous medium by reduction of Ni(CN) 2 with CO in the excess of KCN. From the IR spectroscopy studies and by evaluation of catalytic activity of some cyanonickelates it is proposed that [Ni(CN) 4 ] −4 anion is the active species in the process. A possible mechanism is suggested for the conversion of nickel cyanide to [Ni(CN) 4 ] −4 . The effect of the reaction variables, e.g.: reaction time, temperature, absorption of carbon monoxide, the concentration of potassium cyanide, water, substrate, and sodium hydroxide were also examined.