Isotopic Exchange of Hydrogen in Aromatic Complexes of the TransitionMetals

Abstract

This paper examines and evaluates the data on the isotopic exchange of hydrogen in aromatic complexes of the transitionmetals. Results of the kinetic investigation of isotopic exchange of a series of metallocenes in acid media are given, and thesedata are compared with those on hydrogen exchange of benzenoid compounds, permitting the relative reactivity of the sandwichcompounds in electrophilic hydrogen exchange to be characterised. The isotopic exchange reactions of hydrogen areused to obtain quantitative data on the influence of electron-donating and electron-withdrawing substituents on the ferrocenesystem. A deep difference in the nature of the interaction of the substituents with the electron systems of ferrocene andbenzene has been established. The isotopic exchange of hydrogen in alkaline media is used to evaluate the acidic properties of aromatic complexes of thetransition metals and as a characteristic of the effect of the nature of the central metal atom on the reactivity of the aromaticligands. A combination of hydrogen isotopic exchange and proton magnetic resonance enables the partial rate of exchange of hydrogenatoms at different ligand positions to be determined and hence the quantitative evaluation of their relative reactivity. Alevelling of differences in the field of the orientating action of substituents in aromatic ligands π-bonded with the atoms of thetransition metals has been established. There is a bibliography of 87 references.