¹³C NMR spectra of metal σ‐cyclopentadienyls

Abstract

Abstract Proton decoupled 13 C NMR spectra have been measured for the cyclopentadienyl compounds C 5 H 5 Si(CH 3 ) n Cl 3− n ( n = 1, 2, 3), C 5 H 5 Ge(CH 3 ) 3 , CH 3 C 5 H 4 Ge(CH 3 ) 3 , C 5 H 5 Sn(CH 3 ) 3 , σ‐C 5 H 5 Fe(CO) 2 ‐π‐C 5 H 5 and C 5 H 5 HgCH 3 . 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 C 5 H 5 Ge(CH 3 ) 3 ( E a = 10·7 ± 0·9 kcal/mole, Δ G ‡ = 13·4 ± 0·9 kcal/mole) and C 5 H 5 Sn(CH 3 ) 3 ( E a = 6·8 ± 0·7 kcal/mole, Δ G ‡ = 7·1 ± 0·7 kcal/mole). At room temperature, the spectrum of C 5 H 5 HgCH 3 displays just one narrow signal responsible for the cyclopentadienyl ligand. The spectrum of CH 3 C 5 H 4 Ge(CH 3 ) 3 at –30° demonstrates that two isomers containing methyl in the vinylic position are present, the ratio being ca . 2:1. The 13 C spectra of the vinylic isomers have been analysed in the case of C 5 H 5 Si(CH 3 ) n Cl 3− n .