Restricted Rotation of an Unsubstituted η⁵‐Cyclopentadienyl Group in Solution Demonstrated by ¹³C NMR Spectroscopy

Abstract

The barrier ΔG ≠ for the rotation of the Cp ring in 1 has been estimated from 13C-NMR spectra to be 34.2 ± 1.5 kJmol−1 at −90 °C. The other sterically very bulky ligands may be the reason for the rotation about the CpM bond in 1 and 2 being so strongly hindered that it is slow on the NMR time scale below ca. −100 °C. When the styrene ligand in 1 is replaced by an ethylene ligand the Cp-13C-NMR signal does not change significantly up to −95 °C.