François Volatron

Solvent-free preparation of amides from acids and primary amines under microwave irradiation

Synthesis of amides via pyrolysis of the salts obtained by mixing neat primary amines and carboxylic acids were realized under solvent-free conditions within short times and appreciable yields under microwave activation. The evident specific non-thermal microwave effects are attributed to polarity increase during the course of the reaction, due to development of a dipole in the transition state.

A Square‐Planar Dinickel(II) Complex with a Noninnocent Dinucleating Oxamate Ligand: Evidence for a Ligand Radical Species

The new bimetallic nickel(II) compound (PPh4)4[Ni2(2)]·6H2O (3), where H8[2] stands for N,N′,N′′,N′′′-1,2,4,5-benzene-tetrayltetrakis(oxamic acid), has been synthesized and its crystal structure determined by single-crystal X-ray diffraction. The structure of 3 consists of [Ni2(η4:η4-2)]4– anions, tetraphenylphosphonium cations, and water molecules. Facile one-electron oxidation of the square-planar diamagnetic dinickel(II) complex [Ni2(η4:η4-2)]4– generates the metallo-radical species [Ni2(η4:η4-2·+)]3– with characteristic intra-ligand π-cation radical transitions in the visible region (475–550 nm) as well as a typical quasi-isotropic EPR signal at g ≈ 2.0.

Is the hypervalent radical SiH5 a stable species? An ab initio study

Abstract Ab initio calculations have been performed at various levels on the SiH 5 hypervalent radical in D 3h and C 4v symmetry. Optimization at UHF and UMP2 are presented for these structures and show that both of them are neither stable nor metastable species. The calculation of a potential energy surface at the CASSCF level confirms the transition state nature of the radical in its D 3h geometry.

Qualitative valence bond analysis of (10-S-4) sulfuranes and (9-S-3) sulfuranyl radicals

Abstract Valence-bond (VB) correlation diagrams are used for the analysis of sulfur hypervalent compounds. It is shown that the stability of (10-S-4) sulfuranes is closely related to the electronegativity of the apical substituents. Moreover, it is predicted that an antisymmetrical bond stretch of apical bonds is easier with less-electronegative substituents. The electronic structure of (9-S-3) sulfuranyl radicals is analyzed by means of ab initio calculations. VB correlation diagrams are then used to discuss the factors which favor the σ or π nature of these radicals. Qualitative arguments are developed for predicting the possible metastability of these radicals.

An ab initio SCF+CI study of the SH3 and SF3 radicals

Abstract The symmetric sulfuranyl radicals SH3 and SF3 are studied by means of ab initio SCF + CI calculations. All geometries are optimized at the UHF level using analytical gradients. SH3 is found to be a transition state corresponding to a hydrogen exchange reaction, whereas SF3 is stable with respect to decomposition to SF2 + F.

Ab initio study of the (SO2)(SO2− dimer: structures involving a two-electron SO bond

The structure of the (SO 2 ) 2 − dimer involving one or two S O bonds has been investigated by means of ab initio calculations at the PUMP4/6–31 + G * / /UMP2/6–31 + G * level. Two minima with one S O bond are found; their formation energies are in reasonable agreement with experimental data. Two bifurcated structures with two equal S O bonds are characterized as transition states. They allow oxygen exchange in each of the S O bound minima. The possible structure of the dimer is discussed in comparison with our previous results in which a S S bound dimer was found.

Ab initio study of the electronic structure of the (SO2)(SO−2) dimer. A one-electron SS bond formation?

Abstract The strucutre of the (SO 2 )(SO − 2 ) anion with a SS linkage is studied by means of ab initio calculations at the PUMP4/6–31+G*//UMP2/6–31+G* level. The trans structure is found to be a minimum on the potential energy surface and is mainly characterized by a long (286 pm) one-electron SS bond. The theoretical dimerization enthalpy is in agreement with experiment. Moreover, this structure in which the unpaired electron is used to bind the sulfur atoms might well explain the smaller enthalpy variations associated with further addition of SO 2 molecules.

Theoretical models for activation of CO2 towards hydration (CO2 + H2O → H2CO3) by cationic binding sites

Abstract Theoretical models are studied which illustrate how the hydration reaction CO 2 + H 2 O → H 2 CO 3 can be catalysed by one or two cationic binding sites (NH 4 + ). In the latter, the arrangement of the two bindings sites is held during the course of the reaction, simulating a rigid molecular receptor. Two different arrangements of the binding sites are studied, and their relative abilities to lower the activation energy of the hydration reaction are studied.

Ab initio study of the rotational energy barrier in carbonylylide

The rotational energy barrier in carbonylylide CH2OCH2 is studied using RHF CI calculations. Depending on the size of the CI and the basis set (STO-3G and 4–31G), values in the range 13–17 kcalmol are found. At this level of calculation, the mid-point of the isomerization process can be mainly described by the diradical rather than the zwitterion.

Ab initio study of the hydration complexes of HCO−3

Abstract Ab initio SCF-MO calculations have been performed on the first three hydrates of CHO − 3 using minimal (STO-3G) and extended (4-31G) basis sets. The influence of diffuse functions (STO-3G* and 4-31G* basis sets), and the magnitude of the basis set superposition error (BSSE) have also been tested in few monohydrate complex calculations. Except for minimal basis set calculations, the computed hydration energy (Δ E 0,1 ) associated with the first hydration step is in rather good agreement with the experimental value if the BSSE is taken into account. We also present the structures and the energies of the most stable di- and trihydrated complexes computed with the 4-31G basis set. Our results are discussed with a view to a study of the aqueous-phase reaction: CO 2 (aq) + OH − (aq) → HCO − 3 (aq).