Isotopic Exchange of Hydrogen in Aromatic Complexes of the Transition Metals

This paper examines and evaluates the data on the isotopic exchange of hydrogen in aromatic complexes of the transition metals. Results of the kinetic investigation of isotopic exchange of a series of metallocenes in acid media are given, and these data are compared with those on hydrogen exchange of benzenoid compounds, permitting the relative reactivity of the sandwich compounds in electrophilic hydrogen exchange to be characterised. The isotopic exchange reactions of hydrogen are used to obtain quantitative data on the influence of electron-donating and electron-withdrawing substituents on the ferrocene system. A deep difference in the nature of the interaction of the substituents with the electron systems of ferrocene and benzene has been established.
The isotopic exchange of hydrogen in alkaline media is used to evaluate the acidic properties of aromatic complexes of the transition metals and as a characteristic of the effect of the nature of the central metal atom on the reactivity of the aromatic ligands.
A combination of hydrogen isotopic exchange and proton magnetic resonance enables the partial rate of exchange of hydrogen atoms at different ligand positions to be determined and hence the quantitative evaluation of their relative reactivity. A levelling of differences in the field of the orientating action of substituents in aromatic ligands π-bonded with the atoms of the transition metals has been established.
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