| Sumario: | The isotopomeric complexes trans-W(Cmesityl)[(C(H,D))PCHCHP(C(H,D))](H,D) 1-4 were prepared. 2 (W(C)(dmpe)D) was used to study the Deuterium Quadrupole Coupling Constant (DQCC) and the ionicity of the W-D bond (DQCC = 34.1 kHz; ionicity 85%). 1 (W(C)(dmpe)H) shows several dynamic exchange processes in solution, such as H/H, H/ortho-Me, and H/H exchanges observed by NMR in combination with deuterium labeling studies and double label crossover experiments. Except for the H/H, these reactions comprise elementary steps, which also appear along the isomerization pathway of 1 into (2,3,5-trimethylphenylcarbyne)(dmpe)WH (5) at 60 °C. 5 was characterized by an X-ray diffraction study. In the solid state only an H/Me exchange process prevails appearing at higher temperatures, which was identified by NMR and by Quasielastic Neutron Scattering. The latter also provided an activation barrier of 5 kcal/mol and a "jump width" for the moving H nucleus in agreement with the H⋯Me distance of the X-ray diffraction study of 1.
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