Adrián Peña-Hueso

Coordination chemistry of a bis(benzimidazole) disulfide: eleven membered chelate ring in cobalt(II), zinc(II) and cadmium(II) halide compounds; oxidative disulfide cleavage when coordinated to nickel(II)

Herein we report the synthesis, structural and spectroscopic characterization of coordination compounds with bis[2-(1H-benzimidazol-2-yl)phenyl]disulfide [bis-(2phSbz)] (1) and cobalt(II), zinc(II) and cadmium(II) halides (2-7). Their X-ray diffraction analyses showed that the metal ions present similar distorted tetrahedral structures, with the disulfide ligand coordinated through the imidazolic nitrogen atoms, forming a twisted eleven membered chelate ring. Structures of nickel(II) compounds 8 and 9, showed that the disulfide bond in the ligand was cleaved forming six membered chelates. In 8, the two ligands are sulfides, however in 9 one of them was oxidized to a sulfone. In both compounds the nickel(II) has a distorted square planar geometry and the sulfur atoms are in cis positions. The oxidation reaction of bis-(2phSbz) was performed in KMnO4/NaOH, giving the 2-(1H,3H-benzimidazolium-2-yl)-benzene sulfonate (10). The solid state structure of compounds 2-5 and 7-10 was determined by X-ray diffraction analyses.

1,4-Dialkyl-1,4-diazabutadienes: their reactions with aluminum and indium halides

Reactions of 1,4-bis[(S) methylbenzyl]-1,4-diazabutadiene (1), 1,4-bis[(R) 1′-chlorobutan-2′-yl]-1,4-diazabutadiene (2), 1,4-bis[(S,S) 1′-chloro-1′-phenyl-propan-2′-yl]-1,4-diazabutadiene (3), and 1,4-di-tert-butyl-1,4-diazabutadiene (4) with aluminum and indium halides were performed. Reaction of 1,4-diazabutadienes 1–4 with two equivalents of aluminum halides in toluene afforded ionic aluminum coordination compounds (5–10) which in THF solution are transformed into 1,3-dialkyl-2-methaneiminealkyl imidazolium heterocycles (11–14) by condensation of two 1,4-diazabutadienes and elimination of amine hydrochloride. Equimolar reactions of 1–4 with InCl3 in dry acetonitrile at −78 °C afforded the neutral and diamagnetic InCl3 coordination compounds (15–18), which are stable in the solid state under dry conditions, but in THF solution are slowly transformed into the corresponding 1,3-dialkyl-imidazolium heterocycles 19–22. The X-ray diffraction analyses of compounds 2, 3, 10, 11, 14 and 17 are described. Quantum mechanical calculations were performed in order to find the minimum energy conformers of 1,4-diazabutadienes, 1,3-dialkyl-2-methaneiminealkyl imidazolium and 1,3-dialkyl-imidazolium derivatives as well as the aluminum and indium coordination compounds.

N-(2-Aminophenyl)maleamic acid

The title compound [also called (Z)-3-(2-aminophenylcarbamoyl)propenoic acid], C10H10N2O3, is a non-planar amidated maleic acid derivative, with the mean planes through the 2-aminophenyl and maleamic acid groups inclined at an angle of 43.08 (10) . Symmetry-related molecules are linked by intermolecular N—H N hydrogen bonds, forming centrosymmetric amine–amide dimers. The dimers are linked by N—H O and C—H O hydrogen bonds and weak N— H and – interactions [C-to-centroid distance 3.510 (3) A] into a three-dimensional network.

Stereochemistry of optically active nickel(II) and cobalt(II) coordination compounds derived from N-acetyl aminoalcohols

Herein, we report the stereoselective synthesis and stereochemical analysis of nickel(II) and cobalt(II) coordination compounds derived from N-acetyl-(−)-ephedrine 1(−) and N-acetyl-(+)-ephedrine 1(+), N-acetyl-(+)-pseudoephedrine 2(+) and N-acetyl-(−)-phenylephrine 3(−). Two ligands are coordinated to the metal ion in a tridentate mode giving place to optically active coordination compounds ML2, in a fac octahedral geometry. In all cases, the coordination to the metal ion occurs through the nitrogen atom, the OH group and the deprotonated carboxylic group, forming two five-membered rings. The coordination compounds are characterized in the solid state by UV-Vis-NIR reflectance spectra, IR, X-ray crystallography and magnetic susceptibility measurements. The metal becomes a stereogenic center and, for each ligand, coordination to the metal ion produces two new stereogenic nitrogen and oxygen. Different modes of ligand bonding are present, the fac all-trans, which originates from the fact that the two new stereogenic atoms in each ligand present opposite configurations (mirror effect), as a consequence the bonded ligands are diasteromeric and the complexes have C1 symmetry. The second bonding mode is the fac–cis, which results in the new stereogenic centers acquiring the same configuration; the two bonded ligands are stereochemically identical, producing a complex with C2 symmetry. The use of enantiomeric ligands 1(−) and 1(+) produces separately and stereoselectively the corresponding enantiomeric metallic complexes which are crystallized pure, whereas the use of a racemate of compound 1 produces a different isomer where the metal has a different configuration. Complexes prepared with N-acetyl-ephedrines are diasteromers of those obtained from N-acetyl-pseudoephedrine. The phenylephrine complexes show that the acquired N-configuration is independent of the substitution of the nitrogen vicinal carbon atom and depends only of the cis or trans ligand coordination mode. Analysis of the conformation of the aminoalcohol rings shows that, in all compounds, the phenyl groups are in the equatorial position determining the conformation of the chelates.