Hélène Mestdagh

Ultrasensitive spectroscopy of ionic reactive intermediates in the gas phase performed with the first coupling of an IR FEL with an FTICR-MS

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.

Activation of tetrabutylammonium hydrogen difluoride with pyridine: A mild and efficient procedure for nucleophilic fluorination

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.

Influence of the ligand on the gas-phase reactivity of iron complexes Fe(CX)+ (X = O, N, S, F2, Cl2)

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.

Gas phase ion chemistry: a comparative study of reaction of first row transition metal cations with 2-methyl propane

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 CH and CC bonds of 2-methylpropane and react further.

Gas-phase reactivity of ionic iron complexes: comparison with solution chemistry

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.

Successive reactions of iron carbonyl cations with dimethyl ether: direct cleavage versus rearrangement

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.

A technique for mass selective ion rejection in a quadrupole reaction chamber

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.

O-alkylation d'amides A l'aide de sels d'alkyldiphenylsulfonium

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%.

Une methode simple de synthese des phosphates terpeniques allyliques primaires et tertiaires

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.

Bonding in the CuCH4+ and FeCO+ cations

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.