Rubén A. Toscano

Structural studies of three isomeric forms of heterocyclic N(4)-substituted thiosemicarbazones and two nickel(II) complexes

Abstract Three structural forms have been isolated among four 2-formyl- and 2-acetylpyridine N(4)-substituted thiosemicarbazones reported. 2-Formylpyridine N(4)-methylthiosemicarbazone and 2-acetylpyridine N(4)-ethylthiosemicarbazone both exist as nonhydrogen bonding E isomers. 2-Formylpyridine 3-azabicyclo[3.2.2]nonylthiosemicarbazone crystallies as a hydrogen bondung Z isomer. The yellow 2-acetylpyridine 3-hexamethyleneiminylthiosemicarbazone crystallized with a bifurcated hydrogen bonding arrangement in which the N(3) hydrogen is formally positioned at N(2), making it tautomeric to the other two forms. Structures of four-coordinate nickel(II) complexes containing the monoanions of 2-formylpyridine 3-azabicyclo[3.2.2]nonylthiosemicarbazone and acetylpyrazine 3-hexamethyleneiminylthiosemicarbazone are included.

Copper(II) complexes of 2-benzoylpyridine 4N-substituted thiosemicarbazones

Abstract 2-Benzoylpyridine 4 N-substituted thiosemicarbazones commonly coordinate as neutral tridentate ligands to give five coordinate [Cu(HL)Cl 2 ] complexes when prepared in boiling isopropanol. However, when prepared in boiling ethanol, the anion (loss of the 3 N-hydrogen) coordinates as a tridentate ligand to give [CuLCl] complexes. Representative crystal structures of both stoichiometries have been determined. Spectral characterization of both the 2-benzoylpyridine 4 N-substituted thiosemicarbazones and their copper(II) complexes includes IR, UV-vis, EPR and NMR studies. Growth inhibition studies of the thiosemicarbazones and their complexes were performed against two human pathogenic fungi.

The structures of some ortho-hydroxy Schiff base ligands

Abstract Nine ortho-hydroxy Schiff base ligands, (1)–(9), were synthesized and characterized by chemical analysis, mass spectrometry, 1H and 13C NMR spectroscopy. The crystal and molecular structures of compounds (1), (3), (5), (7), (8) and (9) were determined. The solid state X-ray diffraction studies show that compounds (5) and (8) are in the keto–amine tautomeric form, while (1), (3), (7) and (9) are found as phenol–imine tautomers. Moreover, studies in the solution phase by 1H and 13C NMR spectroscopy indicate that compounds (2), (5) and (8) are found as keto–amine tautomers, while (1), (3), (4), (6), (7) and (9) are found as phenol–imine tautomers. Furthermore, ab initio calculations at the HF/6-31G∗ level with full optimization of geometry, performed for both tautomers of (1) and (5), agree with the observed behavior in solution and solid state of these compounds.

Synthetic and spectroscopic investigations of N(4)-substituted isatin thiosemicarbazones and their copper(II) complexes

Abstract A series of N(4)-substituted thiosemicarbazones of isatin were synthesized and their copper(II) complexes prepared from copper(II) chloride. X-ray crystal structures of two of the thiosemicarbazones, isatin 3-(hexamethylenimylthiosemicarbazone) and isatin 3-(N(4)-ethylthiosemicarbazone), have been solved and are compared with a previously published structure of isatin 3-(N(4)- p -tolythiosemicarbazone). The coordination chemistry of the copper(II) complexes of these and other isatin thiosemicarbazones is reported and discussed.

Structural and spectral studies of a heterocyclic N(4)-substituted bis(thiosemicarbazone), H22,6Achexim·H2O, its heptacoordinated tin(IV) complex [Bu2Sn(2,6Achexim)], and its binuclear zinc(II) complex [Zn(2,6Achexim)]2

Abstract The multidentate ligand, 2,6-diacetylpyridine bis(3-hexamethyleneiminylthiosemicarbazone) monohydrate, H22,6Achexim·H2O, crystallizes with one thiosemicarbazone moiety in an intramolecular hydrogen bonded, bifurcated E′ form. The other thiosemicarbazone moiety is E and is not involved in intramolecular hydrogen bonding, but is involved in hydrogen bonding with the hydrate water molecule. The dianion (loss of N3a and N3b hydrogens) of H22,6Achexim acts as a pentadentate ligand, 2,6Achexim, in a planar conformation to a central tin(IV) ion, and as a bridging tetradentate ligand with the two thiosemicarbazone moieties of 2,6Achexim coordinating to different zinc atoms. The tin(IV) is heptacoordinate in a distorted pentagonal dipyramidal configuration, with the five SNNNS donor atoms of 2,6Achexim in the pentagonal plane and the two n-butyl groups in the axial positions. The binuclear zinc complex has two equivalent tetrahedral zinc centers, with the pyridyl nitrogens of the two ligands not coordinated.

Phytotoxic compounds from Esenbeckia yaxhoob

Abstract Investigation of the aerial parts of Esenbeckia yaxhoob Lundell (Rutaceae) led to the isolation of a new dammarane-type of triterpene which was characterized by spectral means as (24S)-24-methyl-dammara-20,25-diene-3β-yl-acetate. In addition, 2-tridecanone, asarinin, imperatorin, lupeol and hesperidin were obtained. (24S)-24-Methyl-dammara-20,25-diene-3β-yl-acetate, 2-tridecanone, asarinin and imperatorin caused significant inhibition of the radicle growth and\or germination of seedlings of Amaranthus hypochondriacus, Echinochloa crusgalli, Lactuca sativa and Lycopersicum esculentum. Also, it has been found that imperatorin inhibited ATP synthesis and both phosphorylating and uncoupled electron flow from H2O to K3[Fe(CN)6]. On the other hand, this coumarin stimulated the basal electron flow from H2O to K3[Fe(CN)6] and the activity of the light-activated Mg2-ATPase. These effects were measured in freshly lysed illuminated spinach chloroplasts and allowed to determine that imperatorin acts as an uncoupler and as a Hill reaction inhibitor.

Triphenyltelluronium derivatives of dithiophosphorus ligands: Crystal and molecular structure of [Ph3Te][S2PPh2] and [Ph3Te][(SPPh2)2N], displaying weak cation-anion Te…S secondary interactions

Abstract Triphenyltelluronium diphenylphosphinodithioate, [Ph 3 Te][S 2 PPh 2 ] ( 1 ) and tetraphenyldithioimidodiphosphinate, [Ph 3 Te][(SPPh 2 ) 2 N] ( 2 ), were obtained by metathesis reaction between Ph 3 TeCl and NH 4 [S 2 PPh 2 ] and K[(SPPh 2 ) 2 N], respectively, and were characterized by IR, MS and multinuclear NMR. The molecular structure of both compounds was investigated by X-ray diffractometry. The compounds are monomeric and predominantly ionic in the solid state. The Te…S interactomic distances (3.331 and 3.655 A in 1 , and 3.264 and 3.451 A in 2 indicate weak cation-anion secondary interactions. In both compounds the tellurium atom is five-coordinated, with distorted square-pyramidal geometry. The coordination polyhedron in 2 is less distorted due to the flexibility of the SPNPS system and the larger S…S bite of this ligand (4.276 A in 2 , vs 3.368 A in 1 ).

Highly diastereoselective alkylation, acylation and aldol condensation of cis- and trans-(N-acyloyl)hexahydrobenzoxazolidin-2-ones

Abstract The potential of hexahydrobenzoxazolidinones 1a – d as chiral auxiliaries was explored. N -Acylation of 1a – d , 2a – d and 3a – d was followed by methylation and benzylation via the corresponding sodium enolates generated by treatment with NaHMDS. Diastereoselectivities of 98% or higher were observed. The absolute configuration of the newly created stereogenic center was established by chemical correlation with 2-benzyl-1-propanol. The stereochemical results are congruent with addition to the electrophile from the less hindered face of a ( Z )-configured enolate, the sodium cation being coordinated by both carbonyl oxygens of the substrate. cis - and trans - N -Propionyl derivatives 2a – d were treated with Bu 2 BOTf/Et 3 N to give dialkylboron enolates 6a – d , which were then reacted with acetaldehyde and benzaldehyde. 1 H and 13 C NMR analyses showed the formation of a single diastereomeric aldol addition product, whose relative configuration was ascertained as syn from the measurement of the 3 J H(2′)/H(3′) coupling constants, and whose absolute configuration was determined by X-ray crystallographic analysis. The results are rationalized in terms of a Zimmerman–Traxler transition state, with a ( Z )-configured enolate where boron is coordinated to the aldehyde carbonyl rather than the oxazolidinone carbonyl. Substrate 2a was also reacted with acyl chlorides via the sodium enolate (NaHMDS). The effect of reaction conditions on O - versus C -acylation, as well as the influence of solvent and additives on diastereoselectivity, are discussed.

Clerodane and aromatic seco-clerodane diterpenoids from salvia rhyacophua.

Abstract The known clerodane diterpenes salviarin 1 and 6β-hydroxy-7,8-dehydrobacchatricunactin 2, were isolated from Salvia rhyacophila together with five new clerodane diterpenoids 3-6 and 12. The structures of diterpenes 3-6 were established on spectral evidence and chemical transformations. Rhyacophiline is an aromatic seco-clerodane diterpenoid whose structure 12 was established by spectral means and X-ray diffraction analysis.

Dimethyltin(IV) 2,6-disubstituted pyridine complexes

Abstract The synthesis and characterization of hypervalent pentacoordinated dimethyltin complexes obtained from the reaction of 2,6-disubstituted pyridine ligands with dichlorodimethyltin are reported. The complexes were characterized by mass spectrometry, 1H-, 13C- and 119Sn-NMR and Mossbauer spectroscopy, additionally the structures for two compounds were established by X-ray diffraction analysis. The structural parameters indicated pentacoordinated structures, which present Sn–N interaction and trigonal bipyramidal tin environment.