13C NMR spectra of metal σ‐cyclopentadienyls

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Abstract
Proton decoupled 13C NMR spectra have been measured for the cyclopentadienyl compounds C5H5Si(CH3)nCl3−n(n = 1, 2, 3), C5H5Ge(CH3)3, CH3C5H4Ge(CH3)3, C5H5Sn(CH3)3, σ‐C5H5Fe(CO)2‐π‐C5H5 and C5H5HgCH3. A fast metallotropic rearrangement occurring in the compounds causes the spectra to be temperature dependent for the Si, Ge, Sn and Fe derivatives. For the derivatives of silicon or germanium, the olefinic signals are unsymmetrically broadened by the 1,2‐shift at lower migration rates. Line widths of the ring carbon signals have been measured to give an estimate for the activation parameters of the rearrangement in C5H5Ge(CH3)3 (Ea = 10·7 ± 0·9 kcal/mole, ΔG‡ = 13·4 ± 0·9 kcal/mole) and C5H5Sn(CH3)3 (Ea = 6·8 ± 0·7 kcal/mole, ΔG‡ = 7·1 ± 0·7 kcal/mole). At room temperature, the spectrum of C5H5HgCH3 displays just one narrow signal responsible for the cyclopentadienyl ligand. The spectrum of CH3C5H4Ge(CH3)3 at –30° demonstrates that two isomers containing methyl in the vinylic position are present, the ratio being ca. 2:1. The 13C spectra of the vinylic isomers have been analysed in the case of C5H5Si(CH3)nCl3−n.