Successive reactions of iron carbonyl cations with H2O: influence of a buffer gas on ligand substitution rate

The kinetics of the successive ligand substitutions in the Fe(CO)n+/H2O systems (n=1–5) are studied using a triple cell Fourier Transform Ion Cyclotron Resonance spectrometer. For n=3 and 4, substitution of the last ligand is not observed and the terminal substitution products are Fe(CO)(H2O)n−1+; a second channel in which two CO are simultaneously replaced by a H2O molecule is also observed. The internal energy of the Fe(CO)n+ ions has no significant effect on the reactivity. In the Fe(CO)2+/H2O system, the second substitution shows a marked negative dependence with the energy of the reacting Fe(CO)(H2O)+ ions, as confirmed by a quantitative study of the effect of a variable argon pressure in the reaction cell.