Influence de l’énergie interne sur la réactivité de l’ion Fe(CO)2+ avec le diméthyléther, étudiée dans un spectromètre de masse FT–ICR

Mechanism of C−O Activation in Dimethoxyethane Cationic Iron Complexes

The fragmentation mechanism of iron complexes bearing a bidentate ligand, dimethoxyethane (CH(3)OCH(2)CH(2)OCH(3), labeled as DXE) has been investigated by means of FT-ICR mass spectrometry (ion-molecule reactions) and infrared multiphoton dissociation spectroscopy. Two possible reaction mechanisms were envisioned for the Fe(DXE)(+) + DXE reaction, leading to the formation of the Fe(CH(2)O)(DXE)(+) ion. The two mechanisms differ in the nature of the neutral molecules formed: CH(3)OC(2)H(5) or CH(2)=CH(2) + CH(3)OH. The combination of ion-molecule reactions, thermochemistry considerations, and IRMPD spectra leads us to suggest that the mechanism involves successive elimination of the neutrals CH(2)=CH(2) and CH(3)OH, the first step of the mechanism being the insertion of the iron atom in the O-C(central) bond.

Accurate measurement of the relative bond energies of CO and H2O ligands in Fe+ mono- and bis-ligated complexes

The systems Fe(H(2)O)(n) (+)/CO[bond]H(2)O and Fe(CO)(n) (+)/CO[bond]H(2)O (n = 1 and 2) were investigated in a triple cell Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer. Using mixtures of CO with a very small amount of water, the ligand exchange equilibrium was reached, allowing experimental determination of the relevant equilibrium constants and free energies of reaction. Quantum chemical calculations at the B3LYP level of theory on the reactant and product species allowed us to determine the entropic terms and to derive the relative bond energies of CO and H(2)O in the mono- and bis-ligated complexes. For n = 1, H(2)O is more strongly bound to Fe(+) than CO by 4.1 +/- 1.6 kJ x mol(-1) at 298 K. For n = 2, at the same temperature, H(2)O is more strongly bound than CO to (H(2)O)Fe(+) by 7.6 +/- 1.6 kJ x mol(-1), and to (CO)Fe(+) by more than 20.1 kJ x mol(-1).