“…At 180 K, the onset to a decoalescence, evidenced by a saddle point in the resonance, was observed at 6.81 ppm for 2a. An estimation of the Gibbs free energy for this sigmatropic migration in 2a, based on these data, provides 37 ± 1 kJ/mol, which is higher than for Me 3 Sn(g 1 -C 5 H 5 ), 29.7 ± 2.9 kJ/mol [19]. One might expect that the coordination of Me 2 N-group to tin would increase the ionic character of Sn-Cp bond (trans effect), thus leading to the decrease in energy barrier.…”