MAGNETIC NON-EQUIVALENCE OF METHYLENE PROTONS IN METALLOCENES (CYMANTRENS .8. FEREOCENE DERIVATIVES .43.)

The NMR spectra of about 20 derivatives of cymantrene and ferrocene were found to show magnetic non-equivalence (MNÄ) of methylene protons. This phenomenon, in ferrocenes hitherto observed only in the spectra of α-disubstituted compounds, occurs in cymantrenes also in some β-disubstituted derivatives. Recording of low temperature NMR spectra (at-60°C) of several compounds provided additional information as to different conformational mobilities in ferrocenes and cymantrenes. Compounds containing C=O groups show particularly large differences in the chemical shifts of methylene protons. The possibilities of employing MNÄ for problems of preferred conformations and for structural assignments of isomers are discussed. © 1969 Springer-Verlag.