Structural characterization of open, half-open, and closed ferrocenes in solution by 57Fe and 13C NMR spectroscopy

Abstract

Substituted open, half-open and closed ferrocene derivatives have been characterized by 13C and 57Fe NMR spectroscopy. Unsymmetrical substitution of the open pentadienyl moiety, as in (2,3-dimethyl-C 5H 5), leads to the presence of two diastereoisomers, as confirmed by variable temperature 13C NMR spectra or directly by 57Fe NMR spectroscopy at T = 300 K. On going from the corresponding closed via the half-open to the open ferrocenes there is a deshielding of the iron nucleus by about 700 and 1100 ppm. This can be rationalized in terms of the 1/Δ E dependence of the paramagnetic shielding term.