João L. Ferreira da Silva

Decavanadates: a building-block for supramolecular assemblies

Abstract A donor–acceptor intermolecular interaction survey was performed for compounds containing the [H n V 10 O 28 ] 6– n anion, based on a Cambridge Structural Database search and on X-ray data examples in recent literature. Our aim was to systematize the supramolecular motifs present in the solid-state structures in order to understand the key factors determining the crystal packing of decavanadates and to develop a base for a methodology to construct new arrays. We were able to find four different main motifs: monomers, dimers, 1D and 2D arrays that were systematically analysed. The supramolecular assemblies found seem to depend both in the degree and site of protonation of the decavanadates, as well as on the size and shape of solvent and cation molecules.

Synthesis and characterisation of Ti, Cr, Mo and W bis(fluorene) complexes

Abstract The new η 6 -bisfluorene complexes of Ti, Cr, Mo, and W were prepared using the Metal Vapour Synthesis (MVS) technique and characterised by spectroscopic methods. The reactivity displayed by fluorene using MVS is different than for other ligands with acidic hydrogens: cyclopentadiene produces the same η 5 complexes that can be obtained by more conventional synthesis, while indene (where acidic hydrogens coexist with an aromatic ring) originates both η 5 or/and η 6 complexes, sometimes as an isomeric mixture (Mo and W). In the present case of fluorene, only η 6 complexes were isolated by MVS. In order to explain this reactivity the stability of Mo and W η 5 and η 6 metal complexes with fluorene, indene and cyclopentadiene is interpreted using Molecular Orbital Calculations by determining the corresponding Overlap Populations. These calculations are also used to explain the chemical shifts observed in the 1 H NMR spectra of the bisfluorene complexes of group 6 metals in terms of p z electronic density.

Oxidation of 2-hydroxynevirapine, a phenolic metabolite of the anti-HIV drug nevirapine: evidence for an unusual pyridine ring contraction.

Nevirapine (NVP) is an anti-HIV drug associated with severe hepatotoxicity and skin rashes, which raises concerns about its chronic administration. There is increasing evidence that metabolic activation to reactive electrophiles capable of reacting with bionucleophiles is likely to be involved in the initiation of these toxic responses. Phase I NVP metabolism involves oxidation of the 4-methyl substituent and the formation of phenolic derivatives that are conceivably capable of undergoing further metabolic oxidation to electrophilic quinoid species prone to react with bionucleophiles. The covalent adducts thus formed might be at the genesis of toxic responses. As part of a program aimed at evaluating the possible contribution of quinoid derivatives of Phase I phenolic NVP metabolites to the toxic responses elicited by the parent drug, we have investigated the oxidation of 2-hydroxy-NVP with dipotassium nitroso-disulfonate (Frémy’s salt), mimicking the one-electron oxidation involved in enzyme-mediated metabolic oxidations. We report herein the isolation and full structural characterization of a 1H-pyrrole-2,5-dione derivative as a major product, stemming from an unusual pyridine ring contraction.

Zirconium indenylamido complexes: synthesis and reactivity: Crystal structure of [Zr(Ind)2(NC3H6)2]

Abstract Reactions of [ZrInd(NMe2)3] (1) with Me3SiCl afforded [ZrInd(NMe2)2Cl] (2), [ZrInd(NMe2)Cl2] (3) and [ZrIndCl3]n (4) in high yields (≥90%). [ZrIndCl3(dme)] (5) was obtained either from 4 and dme or by a one-pot reaction from [ZrInd(NMe2)3], Me3SiCl and dme. Treatment of [ZrInd(NMe2)2Cl] with LiMe gave [ZrInd(NMe2)2Me] (6), and in similar reaction conditions [ZrInd2Me2] (10) was obtained from [ZrInd(NMe2)Cl2]. Whereas the reaction of 2 with LiN(H)tBu produced {[ZrInd(NMe2)2[N(H)tBu]} (7), the addition of LiN(H)tBu to [TiInd(NMe2)2Cl] afforded [Ti(NMe2)2(μ-NtBu)]2 (9) in quantitative yield. {TiInd(NMe2)2[N(H)tBu]} was identified by NMR as an intermediate in the synthesis of 9, and two isomeric forms corresponding to the parallel (8a) and perpendicular (8b) orientations of the indenyl and N(H)tBu ligands were characterised. The addition of an excess of azetidine to 1 gave [ZrInd2(NC3H6)2] (11), the molecular structure of which was determined by X-ray crystallography. Preliminary studies showed that 3–methylaluminoxane (MAO) polymerises ethylene and propylene, whereas [TiInd(NMe2)Cl2], 12–MAO, only polymerises ethylene.

Exploring mechanochemistry to turn organic bio-relevant molecules into metal-organic frameworks: a short review

Mechanochemistry is a powerful and environmentally friendly synthetic technique successfully employed in different fields of synthetic chemistry. Application spans from organic to inorganic chemistry including the synthesis of coordination compounds. Metal-organic frameworks (MOFs) are a class of compounds with numerous applications, from which we highlight herein their application in the pharmaceutical field (BioMOFs), whose importance has been growing and is now assuming a relevant and promising domain. The need to find cleaner, greener and more energy and material-efficient synthetic procedures led to the use of mechanochemistry into the synthesis of BioMOFs.

Chlorobis(dimethylamido)(η5-2,5-dimethylpyrrolyl)titanium(IV), [Ti(NMe2)2(DMP)Cl]

The structure of the title compound, [Ti(C2H6N)2(C6H8N)Cl], displays a eta5-coordination mode for the pyrrolyl ring, confirmed by the values of the slip parameter [0.073 (9) A] and the fold angle [4.6 (6) degrees ]. This coordination is confirmed by NMR data, which point to the involvement of the complex in a fluxional process in solution above 285 K, passing through an intermediate involving simultaneously a metal-azaallyl and a metal-olefin bond.

New Nitrogen Compounds Coupled to Phenolic Units with Antioxidant and Antifungal Activities: Synthesis and Structure–Activity Relationship

A selection of 1-amino-2-arylidenamine-1,2-(dicyano)ethenes 3 was synthesized and cyclized to 2-aryl-4,5-dicyano-1H-imidazoles 4 upon reflux in ethyl acetate/acetonitrile, in the presence of manganese dioxide. These compounds were tested for their antioxidant capacity by cyclic voltammetry, 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and deoxyribose degradation assays. The minimum inhibitory concentration of all compounds was evaluated against two yeast species, Saccharomyces cerevisiae and Candida albicans. Their toxicity was tested in mammal fibroblasts. Among the synthesised compounds, two presented dual antioxidant/antifungal activity without toxic effects in fibroblasts. The new compounds synthesized in this work are potential biochemical tools and/or therapeutic drugs.