Investigation of protonation and rotational isomerization of 6-dimethylaminofulventungsten tricarbonyl in acidic media by dynamic 1H NMR spectroscopy

Abstract

Rotational isomerization of 6-dimethylaminofulventungsten tricarbonyl in media of various acidities has been studied by dynamic 1H NMR spectroscopy, and the kinetic parameters of the rotation about the C(6)N bond have been determined. The rate of rotation about this bond increases in weakly acidic media and decreases in strongly acidic solutions with respect to that in the parent complex. This dependence indicates that the complex has dual reactivity in protonation, i.e. in weakly acidic media the protonation involves the nitrogen atom, and in highly acidic solutions the tungsten atom. On increasing the acidity of the medium the ammonium form of the complex is converted into the W-protonated complex. A study of deuterium exchange in acidic media has shown that the H or D atom attached to the W atom may be readily exchange for the deuteron (or the proton, respectively) of the acid, while the H atoms of the cyclopentadienyl ring do not undergo deuterium exchange under the conditions investigated. Protonation involving the Cp ring of the complex was not observed.