Hélène Mestdagh
University of Paris-Sud
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Featured researches published by Hélène Mestdagh.
international free electron laser conference | 2003
Philippe Maı̂tre; Sophie Le Caër; Aude Simon; William Jones; Joël Lemaire; Hélène Mestdagh; Michel Heninger; G. Mauclaire; Pierre Boissel; R. Prazeres; F. Glotin; J.M. Ortega
First example of coupling a Fourier Transform Ion Cyclotron Resonance Mass Spectrometer (FTICR-MS) with an infrared Free Electron Laser (FEL) is presented. This experimental setup is ideally suited for the direct structural characterization of reactive polyatomic ions. Ultrasensitive measurements of the infrared vibrational spectrum of ionic reactive intermediate selectively prepared is allowed by the association of the high peak power of the FEL, its wide tunability, and the flexibility of FTICR-MS, where several mass selections and ion-molecule reactions can be combined. These possibilities are demonstrated in the case of Fe + complexes where two photofragmentation pathways compete. The resulting infrared spectrum is in excellent agreement, both with respect to the position and to the relative intensities of the infrared transitions, with predicted by ab initio electronic structure calculations. r 2003 Elsevier Science B.V. All rights reserved.
Tetrahedron Letters | 1998
Khadija Moughamir; Aziz Atmani; Hélène Mestdagh; Christian Rolando; Charlette Francesch
Abstract The nucleophilic fluorination of alkyl iodides, bromides and tosylates and of α-bromo- or α-chloroketones is smoothly effected by tetrabutylammonium hydrogen difluoride in the presence of pyridine, in dioxane or THF, with good or satisfying substitution-to-elimination ratio.
Tetrahedron Letters | 1997
Laure Capron; Hélène Mestdagh; Christian Rolando
Abstract Ion-molecule reactivities of different one-carbon ligand complexes Fe(CX) + with oxygen and allyl chloride appeared strongly dependent on the nature and binding energy of the ligand. With oxygen ligand oxidation occurred for X = O, S. With allyl chloride the only case of the Fe(CS) + complex.
Tetrahedron Letters | 1986
Hélène Mestdagh; Nicole Morin; Christian Rolando
Abstract The gas phase reactivity of first row transition metal cations with 2-methylpropane was investigated using a triple quadrupole mass spectrometer. This reactivity is very variable depending on the nature of the metal : Ti + and V + give mainly the multiple collision product M(C 8 H 14 ) + whereas Cr + , Mn + , Cu + and Zn + (reported to be unreactive under other conditions) aaa I or 2 C 4 H 10 units ; Fe + , Co + , Ni + cleave CH and CC bonds of 2-methylpropane and react further.
Coordination Chemistry Reviews | 1998
Laure Capron; Hélène Mestdagh; Christian Rolando
Abstract After a brief survey of experimental methods and a summary of bond energies of iron complexes, the gas-phase reactivity of ionic iron complexes is reviewed according to ligands. Complexes bearing one strongly bound ligand such as FeCH + 3 , FeCH + 2 and FeO + are very reactive, in a quite different way from Fe + , and may participate in catalytic cycles in the gas phase. The presence of additional L ligands modulates their reactivity. The L ligands may also act as leaving groups, allowing oxidative addition, or be directly involved in bond-forming reactions. An increase of the number of ligands generally favors solution-like reactivity.
Physical Chemistry Chemical Physics | 2002
Sophie Le Caër; Michel Heninger; Pascal Pernot; Hélène Mestdagh
The reaction kinetics of electron impact ionization generated Fe(CO)n+ cations with dimethyl ether (DME) is investigated using a triple-cell Fourier Transform Ion Cyclotron Resonance spectrometer. The primary reaction is rapid substitution of CO by DME. One-step substitution of two CO ligands by one DME molecule also occurs for n = 3–4, and for unrelaxed Fe(CO)2+ ions. Successive substitutions in the Fe(CO)4+/DME system lead mainly to Fe(CO)(DME)2+, in which the last CO remains unsubstituted. This ion is slowly converted to Fe(CO)(DME)3+ and Fe(DME)2+. The latter reaction implies formation of neutral CH3COOCH3 resulting from iron-promoted CO insertion reaction. Further reaction of Fe(DME)+ with DME involves the cleavage of a C–O bond according to two channels, either direct CH3˙ loss or more exothermic CH4 loss, implying a molecular rearrangement. The branching ratio is strongly energy-dependent: the latter channel is observed only for Fe(DME)+ ions having a very low energy content.
International Journal of Mass Spectrometry and Ion Processes | 1989
J.Throck Watson; Daniel Jaouen; Hélène Mestdagh; Christian Rolando
Abstract Ions can be selectively rejected from the r.f.-only collision cell of a tandem quadrupole mass spectrometer, using an auxiliary r.f. field tuned into their characteristic transverse frequency. The efficiency of this method was studied on a mixture of Fe(CO) + n ions ( n = 0–5, m/z 54–196) confined (0.5 ms) in the collision cell. Optimization of r.f. power allowed almost complete rejection of the 56 Fe + ion (at an intensity equal to 2.5% of its initial value) with no distortion of other Fe(CO) + n ions, and with only a slight intensity decrease of the minor isotope, the 54 Fe + ion (at an intensity equal to 75% of its initial value). The rejection efficiency was also determined as a function of the frequency of the auxiliary r.f. field. The rejection technique was applied to reaction mechanism elucidation in the case of the reaction between Fe + ions and allyl chloride. Upon rejection of one of the product ions (C 3 H + 5 , m/z 41), a large intensity decrease was also observed for some other product ions (e.g. C 6 H + 9 , m/z 81; C 6 H + 7 , m/z 79), indicating that these ions are produced from further reactions of the rejected ion.
Tetrahedron | 1983
Marc Julia; Hélène Mestdagh
Resume O-Alkylation of amides and ureas was easily accomplished with alkyldiphenylsulphonium salts. These alkylating agents are readily available, often crystalline, and non-hygroscopic. They are somewhat less powerful than oxonium salts but are not limited to methyl and ethyl groups. The following order of reactivities was observed: PhCH 2 S + Ph 2 > EtS + Ph 2 ≈ Et 2 SO 4 > MeS + Ph 2 . Benzylation proceeded under very mild conditions (room temperature). The counterion and solvent have no significant influence on the reaction rate. Sulphonium salts where the leaving group is a dialkyl sulphide are much less active as alkylating agents. New alkoxymethyleneiminium salts have been prepared in this way in yields above 70%.
Tetrahedron | 1986
Marc Julia; Hélène Mestdagh; Christian Rolando
Abstract Alkylation of tetrabutylammonium dihydrogenophosphate by terpenic allylic sulphonium salts give the corresponding primary terpenic allylic phosphates in fair to moderate yields, without complex procedures of purification. The catalysis of the reaction by cuprous ion leads to the isolation of tertiary allylic phosphates.
Journal of Molecular Structure-theochem | 1992
G. Berthier; Renzo Cimiraglia; Abdelali Daoudi; Hélène Mestdagh; Christian Rolando; Michèle Suard
Abstract The electronic structures and geometrical parameters of the CuCH 4 + and FeCO + adducts as observed in mass spectroscopy experiments for instance, were determined by means of ab initio LCGO-SCF and perturbation CI calculations. These cations are predicted to be stable complexes in which the bonding between metal and ligand is mainly due to electrostatic factors, in accordance with previous results for the great majority of ML + complexes.