Antonio Costa

Counterintuitive interaction of anions with benzene derivatives

Abstract Ab initio calculations were carried out on complexes between 1,3,5-trinitrobenzene (TNB) and anions, where the anion is positioned over the ring along the C 3 axis. This study combines crystallographic and computational evidences to demonstrate an attractive interaction between the anion and the π-cloud of TNB. This interaction is rationalized based on the important role of the quadrupole moment of TNB and the anion-induced polarization. In addition, this study has been extended to 1,3,5-trifluorobenzene (TFB), which possesses a very small quadrupole moment. As a result, minimum energy complexes have been found between TFB and both anions and cations due to the stabilization obtained from the ion-induced polarization.

Anion–π interactions: must the aromatic ring be electron deficient?

The favorable interaction of anions with the π-cloud of aromatic derivatives has been studied theoretically using ab initio calculations and confirmed by X-ray data retrieved from the Cambridge Structural Database.

A theoretical study of aromaticity in squaramide complexes with anions

Abstract A systematic estimation of aromaticity in squaramide complexes with anions has been studied using structural and magnetic criteria. Results based on Nucleus Independent Chemical Shift (NICS) predict that squaramide is less aromatic than its complexes with several anions. We had previously observed the same behavior in squaramide complexes with cations. This bifunctionality can be used to design ditopic receptors. In fact a 1:1:1 complex between squaramide and both ammonium cation and formiate anion is more aromatic than any of the other two 1:1 squaramide-cation/anion complexes.

Grafted squaramide monoamine nanoparticles as simple systems for sulfate recognition in pure water

New simple systems formed by a chain containing a squaramide function and a quaternised amine group attached to boehmite or silica-coated boehmite nanoparticles are able to discriminate anions in pure water.

OPLS all-atom force field for squaramides and squaric acid

Abstract The OPLS all-atom (AA) force field has been expanded to include squaramides and squaric acid. A complete set of stretching–bending, all-atom torsional and non-bonded parameters has been calculated. Starting from reported non-bonded parameters of amides, parameters were fitted to reproduce results from ab initio (MP2/6- 31 G ∗ ) calculations on squaramides and squaric acid. Their application in the solution phase was tested by determining rotational barriers and cis/trans ratios of several squaramides in CHCl 3 via Monte Carlo statistical mechanics simulations and comparing them with experimental ones determined by NMR experiments.

A novel degradative strategy for the synthesis of p-quinones.

Abstract p-Hydroxybenzylalcohols undergo Fremys salt promoted degradative oxidation to give the corresponding p-benzoquinones. A novel strategy for the synthesis of p-benzoquinones based on the regioselective metalation of 2-methoxy-4-methoxymethyl phenols is presented.

Predicting experimental complexation-induced changes in 1H NMR chemical shift for complexes between metalloporphyrins and ligands using the Ab initio/GIAO-HF methodology

Abstract Ab initio calculations were carried out on several metalloporphyrins complexed to several ligands. The experimental spectra of metalloporphyrin–ligand complexes show large upfield shifts for the ligand proton signals compared to the free ligand. These shifts are caused by the proximity of the porphyrin π-system. The 1 H NMR chemical shifts of these complexes were computed via ab initio calculations using the GIAO method at several levels of theory and the obtained values agree satisfactorily with experimental results.

Unsaturated carboxylic acid dienolates. Reaction with substituted cyclohexanones and unsubstituted cycloalkanones. Regio- and stereo-selectivity

Regio- and stereo-selectivities for the reaction of lithium dienolates derived from crotonic and dimethylacrylic acids with substituted cyclohexanones (4)–(6) are found to depend on reaction time and temperature. α-Adducts resulting from equatorial attack predominate after a short time at –70 °C, but axial approach and γ-addition are favoured by longer reaction time and higher temperature. Inversion of axial/equatorial stereoselectivity is observed for some cyclohexanones. For unsubstituted cycloalkanones, regioselectivity is dependent on ring size. This effect can be explained on the basis of Browns ‘I-strain’ rationalization. For C5—C12ketones, γ-adducts are found when reactions are carried out above room temperature, but at 0 °C, C5, C6 and C12 cycloalkanones yield α-isomers whereas mesocyclic ketones afford γ- isomers.

Dienediolates from unsaturated carboxylic acids: Michael addition of dilithium buta-1,3-diene-1,1-diolate (from crotonic acid) to unsaturated ketones

Conjugate addition of the lithium dienediolate derived from crotonic acid to several α,β-unsaturated ketones gave 7-oxocarboxylic acids. Styrl ketones (2a–g) afforded mixtures of 1,4-α- and 1,4-γ-adducts, in proportions depending on the bulk of the substituents attached to the carbonyl group. The reaction with the styryl ketones occurs through a tandem 1,2-addition–oxy-Cope rearrangement mechanism. On the other hand, α- and β-methyl styryl phenones (2h and i) afforded 1,4-γ-products through 1,2-addition with subsequent retro-aldol and Michael-type addition.

Macrocyclic Tetraimines: Synthesis and Reversible Uptake of Diethyl Phthalate by a Porous Macrocycle

The imine bond has attracted much attention for the synthesis of macrocycles used to construct porous materials. In the present article, we report on the synthesis of two series of isomeric macrocyclic tetraimines based on bis-alkynylbenzene diamines. Under heterogeneous solid-liquid conditions the condensation of the diamines with isophthalaldehyde or terephthaldehyde afforded mainly the corresponding [2 + 2] adducts. Among the eight macrocycles studied, only the macrocycle 1 has a porous structure. The article describes not only the synthesis of these macrocycles but also the encountered difficulties during their preparation. Finally, we expand the use of 1a as a porous solid support by studying its reversible and preferential liquid-solid adsorption properties for diethyl phthalate in front of other commercial phthalates.