Elizabeth Gómez

New perspectives for boronic esters in macrocyclic chemistry

In the present contribution a tetrameric macrocyclic compound derived from 2,6-pyridinedimethanol and 3-nitrophenyl boronic acid, as well as 10 new dimeric boronates prepared from 2-salicylideneaminoethanol and different aryl boronic acids such as a 2-methylphenyl-, 3-methylphenyl-, 4-methylphenyl-, 3-methoxyphenyl-, 4-methoxyphenyl-, 3-chlorophenyl-, 4-chlorophenyl-, 3-nitrophenyl-, 3-trifluoromethylphenyl- and 4-fluorophenylboronic acid are described. The tetrameric and three of the dimeric structures have been analyzed by X-ray crystallography, and a series of parameters such as bond length, bond angles, deviation of the boron atom from the boronate mean plane and intermolecular interactions are discussed.

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.

Synthesis and structure of pentacoordinated monoorganosilane derivatives of pyridine ligands

Abstract The reaction of 2,6-disubstituted pyridines with bis(dimethylamine)dimethylsilane, dichlorophenylmethylsilane and dichlorodiphenylsilane yielded the monomeric silanes: 2,6-pyridinebis(1,1-di- p -bromophenylmethoxy)dimethylsilane ( 9a ), 2,6-pyridinebis(1,1-di- p - tert -butylphenylmethoxy)dimethylsilane ( 9b ), 2,6-pyridinebis(1,1-diphenylethoxy)methylphenylsilane ( 12a ) and 2,6-pyridinebis(1,1-adamantylethoxy)diphenylsilane ( 12b ). The 29 Si-NMR data for these compounds confirmed the presence of N→Si bonds and the variable temperature NMR study of 12a and 12b showed the existence of a fluxional behavior for the 2,6-diethoxypyridine derivatives, additionally the X-ray diffraction study of 9a showed that in this compound the silicon atom adopts a square pyramidal geometry. Moreover, 1,3,10,12-tetraoxo-2,11-(dimethylsilylene)[5.5]paracyclophane ( 10 ) was synthesized from 1,4-benzenedimethanol and its structure established by X-ray crystallographic analysis showing that the aromatic rings are not perfectly eclipsed.

Multinuclear NMR and X-ray diffraction study of pentacoordinated siloxane structures derived of pyridine diols

Abstract Synthesis and characterization of hypervalent pentacoordinated organosilicon complexes obtained from the reaction of disubstituted pyridine ligands with dichlorodiphenylsilane, dichloromethylphenylsilane and bis(dimethylamino)dimethylsilane are reported. The monomeric complexes obtained were characterized by mass spectrometry and multinuclear NMR spectroscopy; additionally their structures were established by X-ray diffraction analysis. The structural parameters indicated Si–N interaction with pentacoordinated geometries displaced towards trigonal bipyramid (TBP); the 29 Si-NMR data for these compounds are in agreement with the presence of N→Si bond. In addition to a variable temperature 1 H-NMR study was carried out showing a dynamic behavior for these compounds.

Synthesis of new homochiral 2,3-dialkylpiperazines derived from (R)-(−)-phenylglycinol

Abstract The synthesis of four new 2,3-dialkylpiperazines in yields of 70–99% using (R)-(−)-phenylglycinol as a chiral inductor is described. The synthesis involved reduction of the oxazino–oxazine type derivatives obtained by condensation of glyoxal and phenylglycinol to give hydroxyethylenediamine precursors which were further condensed with glyoxal, butanedione and 1-phenyl-1,2-propanedione and then reduced to provide the corresponding piperazines. The stereochemical outcome is determined by the configuration of the bisoxazolidine precursors, which is in turn dictated by steric effects exerted by the substituents on the five membered ring. The structures of five derivatives were established by X-ray analysis.

Synthesis and characterization of two cyclic organosiloxanes by multinuclear NMR spectroscopy and X-ray crystallography

Abstract 1,3-[2′,6′-Pyridinebis(methyleneoxy)]-1,3-bis(diphenyl)cyclodisiloxane ( 9 ) and 2,6-pyridinebis(1,1-diphenylethoxy)diphenylsilane ( 11 ) were obtained from 2,6-pyridinediol derivatives with dichlorodiphenylsilane. An N→Si interaction is present in 2,6-pyridinebis(1,1-diphenylethoxy)diphenylsilane, which also shows fluxional behavior. The activation energy of 13.2 kcal mol −1 for 11 was obtained for the intramolecular exchange between the phenyl groups from a variable-temperature 1 H-NMR study. The compounds were characterized by 1 H-, 13 C- and 29 Si-NMR and their structures were established by X-ray crystallographic studies.

A new oxo-bridged borate derived from dimeric boron complexes

Reaction of 2-salicylideneamino hydroxyethane (H2SAE) with B(NMe2)3, B(OH)3 and C6F5B(OH)2 leads to the dimeric boron compounds [B(SAE)(NMe2)]2 (2), [B(SAE)(OH)]2 (3) and [B(SAE)(C6F5)]2 (4) in moderate to good yields. Compound 2 hydrolyses slowly at room temperature (r.t.) to give the dimeric oxo-bridged boron compound m-oxo-[B(SAE)]2 (5). Dehydration of 3 or hydrolysis of 4 with elimination of the aryl group conduced to the same derivative. The X-ray crystallographic analysis confirmed the molecular structure for compound 5.

Facile Synthesis of Aminoalcohols by Ring Opening of Epoxides Under Solvent Free Conditions

Abstract The convenient cleavage of symmetrical and unsymmetrical epoxides with either aromatic or aliphatic amine under solvent free conditions is reported. The reactions were carried out in a sealed ampoule at 90°C to give regioselectively the corresponding β‐amino alcohol in one pot in high yields.

Diorganotin (IV) Heptacoordinated Complexes Containing Pentadentate [N3O2] Ligands Derived From 5-Substituted-Salicylaldehydes and Diethylenetriamine: Synthesis, Characterization, and Molecular Structure

A series of heptacoordinated tin(IV) mononuclear complexes [(R′)2Sn(5-X-saldien)] (X = H, OCH3, NO2) were synthesized by reaction of dimethyl-, di-n-butyl-, di-n-octyl-, and diphenyltin (IV) oxides with the pentadentate Schiff base ligands saldienH2, 5-MeO-saldienH2, and 5-NO2-saldienH2. All of the complexes were characterized by IR, mass spectrometry, and 1H, 13C, and 119Sn NMR spectroscopies, and the spectra display chemical shifts corresponding to a seven-coordinated tin environment. The crystal structures of complexes 2a, 2d, and 4b were determined by X-ray diffraction. The complexes are isostructural and the tin atoms exhibit pentagonal-bipyramidal geometries with the methyl, n-butyl, and phenyl groups occupying the axial positions and the donor atoms from the ligand occupying the equatorial positions. A fluxional behavior was also observed that involves a dissociation-association mechanism of the N-Sn bonds.

Synthetic, Spectroscopic, Crystallographic, and Biological Studies of Seven-Coordinated Diorganotin(iv) Complexes Derived from Schiff Bases and Pyridinic Carboxylic Acids

The synthesis and characterisation of diorganotin(iv) monomeric derivatives of pyridine Schiff bases and pyridinic carboxylic acids are reported. All complexes were characterised by mass spectrometry, elemental analyses, IR spectra, and multinuclear NMR analyses. Among them, complexes 5a, 5d, 5e, 5g, and 6a were also confirmed by X-ray crystallography diffraction analyses, which led to establishing that the tin atom is seven-coordinated and has a distorted pentagonal–bipyramidal coordination environment in the solid state and also revealed that both ligands occupy the equatorial positions and the organic substituents the axial positions. The antioxidant activity of the synthetic derivatives towards 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) as well as the thiobarbituric acid reactive substances (TBARS) assay were determined, and were compared with standard antioxidants, showing a dose-dependent activity in both cases. A prominent response was obtained depending on the substituent. The anti-inflammatory activity was also evaluated on a 12-O-tetradecanoylphorbol-13-acetate (TPA) model of induced acute inflammation. The results of the biological tests are discussed in terms of structural characteristics.