Solid‐state (CP‐MAS) ²⁹Si‐, ¹¹⁹Sn and ²⁰⁷Pb nuclear magnetic resonance study of bis(pentamethylcyclopentadienyl)‐silicon, ‐tin and ‐lead

Abstract

Abstract Solid‐state CP‐MAS 29 Si‐, 119 Sn‐ and 207 Pb NMR spectra of bis(pentamethylcyclopentadienyl)‐silicon (1) ‐tin (2) and ‐lead (3) were measured. The spectra reflect the gross structural features, known from x‐ray analyses for 1–3. In 1a, which has a parallel arrangement of the Me 5 C 5 rings, the 29 Si nuclear shielding is found to be 20.2 ppm higher than that of the bent structure in 1b. The assignment is supported by the relative intensities of the 29 Si resonances and by the analyses of the spinning sideband patterns. The δ 29 Si value of 1 in solution is close to that of 1b, suggesting that the bent structure is preferred in solution. The comparison of the solution‐ and solid‐state δ values shows that the η 5 ‐bonding of the cyclopentadienyl rings is retained in solution. Attempts to analyse the spinning sideband pattern of 2 by the usual methods failed, which may be explained by the presence of molecular reorientation in the solid state which occurs at room temperature at a rate affecting the 119 Sn shielding tensor.