Jean Ollivier

Influence of steric crowding at the heteroatom on the metathesis of functionalized olefins : the polymerization of alkylthiocyclooctenes catalyzed by a metallacyclic aryloxo(chloro)neopentylidenetungsten complex

Abstract The ring-opening metathesis polymerization of various alkylthiocyclooctenes was successfully carried out in the presence of a metallacyclic aryloxo (chloro)neopentylidenetungsten complex. The polymerization rates depend strongly on the steric crowding of the alkylthio substituent which confirms that coordination of the heteroatom to the metal is one of the important factors that govern the rate of the metathesis of this type of functionalized olefin.

Catalytic hydrodesulphurization of terpenes

Abstract Sodium-doped CozMo catalysts were used at 200–280°C and 1 atm to desulphurize terpene fractions containing α- and β-pinene and Δ 3 -carene. The best results were obtained with special procedures for sodium addition. The surface acidity and isomerizing activity of the catalysts were controlled throughout their preparation by ammonia thermodesorption and certain probe reactions. The presence of thiophenic compounds and, to a lesser extent, the competitive adsorption of terpenes and sulphur-containing molecules can limit the desulphurization.

Sulfochloration of trifluoromethane: theoretical study of the trifluoromethane sulfonyl radical

Abstract In relation with the photochemical mechanism of sulfochloration of trifluoromethane ab initio (SCF+CI) calculations were performed on CF 3 SO 2 • and CH 3 SO 2 • radicals. With optimization of all geometrical parameters the exothermicity of the formati reactions CF 3 • +SO 2 →CF 3 SO 2 • and CH 3 • +SO 2 →CH 3 SO 2 • were evaluated. For CH 3 SO 2 • a experimental data; the low exothermicity calculated for CF 3 SO 2 • indicates a dissociation stability clearly reduced in comparison with that for CH 3 SO 2 • .

Ab initio CI study of the laser radiation effect on pyrolysis of 1,2-dichloroethane

Abstract Electronic spectra of 1,2-dichloroethane and the 1,2-dichloroethyl radical have been calculated with ab initio CI methods in order to propose a theoretical interpretation for the well known effect of laser radiation on the pyrolysis of 1,2-dichloroethane. According to this work, the 1,2-dichloroethyl radical produced by thermal pyrolysis is the most probable candidate for the absorption of 308 nm laser radiation used in experimental studies. Consequently, we also present a theoetical study of the CCl bond breaking process in the first excited state of the 1,2-dichloroethyl radical, leading to the formation of vinyl chloride and atomic chlorine. No potential barrier appears along the calculated dissociation pathway. Moreover the broad energy excess of the products formed enable us to propose an interpretation for the beneficial effect of laser radiation on the pyrolysis of 1,2-dichloroethane.

Olefin Metathesis: A New Tool in the Synthesis of Organic Sulfur Compounds

Abstract The metathesis of acyclic or cyclic olefinic sulfides is successfully achieved by using a chloroaryloxide neopentylidene complex of tungsten as catalyst. This reaction constitutes a new route to the synthesis of various olefins, dienes or unsaturated polymers containing one or more S atoms.

Ab initio CI study of hydrogen abstraction from hydrogen and methyl sulphide by ketone triplet excited state

Abstract In order to interpret the radical mechanism of the initiation of the photosulphydration reaction of terminal olefins we studied and compared hydrogen abstraction reactions from H 2 S, CH 3 SH and CH 4 by formaldehyde in triplet state. The fully optimised transition states and the potential energy curves were determined on a constrained reactive pathway maintaining a plane of symmetry for the entire system throughout the reaction. All theoretical results were obtained by using ab initio calculations including correlation effects evaluated at MP2 level on multireference states. The most noteworthy feature of this study is the ordering of the potential barriers: 23.4 kJ mol −1 for CH 3 SH, 41.4 kJ mol −1 for H 2 S and 81.1 kJ mol − for CH 4 . Correlatively we show that the hydrogen abstraction reaction on thiols is essentially a reversible process.

Ab initio study of the nucleophilic addition of the hydrosulfide anion HS− to formaldehyde

Abstract Nucleophilic addition of hydrosulfide ion to formaldehyde has been investigated by ab initio quantum mechanical methods. Contrary to the system HO − +H 2 CO, our study reveals that no minimum exists for the tetrahedral structure of the adduct of HS − and H 2 CO on the potential surface. Orbital interaction analysis allows one to understand the different behaviors of HO − and HS − towards H 2 CO. Moreover it appears that in the case of HS − the only reactive pathway involves simultaneous proton transfer and carbon sulfur bond formation leading to the formation of the H 2 C(S, OH) − species.

Reaction of amino radicals with olefins: Theoretical aspects

Abstract The role of photocatalysts in improving the photochemical synthesis of fatty amines has been examined. Ab initio SCF and CI calculations for the addition of the aminyl radical NH 2 • to ethylene are reported. In contrast with previous theoretical results a low activation energy and a rather small exothermicity were determined. Thus an explanation for the known inactivity of amino radicals in addition reactions can be found in the possibility of a retroaddition. The calculations indicate that the role of photocatalysts could be explained by a significant stabilization of the addition photoproduct blocking the reversibility of the process. The involvement of the photocatalyst with the primary photoproduct NH 2 • should also be considered in view of a significant increase in the exothermicity observed.