Por favor, use este identificador para citar o enlazar a este item:
http://hdl.handle.net/10261/37560
COMPARTIR / EXPORTAR:
SHARE CORE BASE | |
Visualizar otros formatos: MARC | Dublin Core | RDF | ORE | MODS | METS | DIDL | DATACITE | |
Título: | Low-Temperature NMR Studies of Zn Tautomerism and Hindered Rotations in Solid Zincocene Derivatives |
Autor: | López del Amo, Juan Miguel; Buntkowsky, Gerd; Limbach, Hans-Heinrich; Resa, Irene CSIC; Fernández, Rafael CSIC; Carmona, Ernesto CSIC ORCID | Palabras clave: | NMR Decamethylzincocene Iminoacyl Low-temperature Zincocene |
Fecha de publicación: | 27-mar-2008 | Editor: | American Chemical Society | Citación: | Journal of Physical Chemistry A 112(16): 3557-3565 (2008) | Resumen: | Using a combination of NMR methods we have detected and studied fluxional motions in the slip-sandwich structure of solid decamethylzincocene (I, [(eta5-C5Me5)Zn(eta1-C5Me5)]). For comparison, we have also studied the solid iminoacyl derivative [(eta5-C5Me5)Zn(eta1-C(NXyl)C5Me5)] (II). The variable temperature 13C CPMAS NMR spectra of I indicate fast rotations of both Cp* rings in the molecule down to 156 K as well as the presence of an order-disorder phase transition around 210 K. The disorder is shown to be dynamic arising from a fast combined Zn tautomerism and eta1/eta5 reorganization of the Cp* rings between two degenerate states A and B related by a molecular inversion. In the ordered phase, the degeneracy of A and B is lifted; that is, the two rings X and Y are inequivalent, where X exhibits a larger fraction of time in the eta5 state than Y. However, the interconversion is still fast and characterized by a reaction enthalpy of DeltaH = 2.4 kJ mol-1 and a reaction entropy of DeltaS = 4.9 J K-1 mol-1. In order to obtain quantitative kinetic information, variable temperature 2H NMR experiments were performed on static samples of I-d6 and II-d6 between 300 and 100 K, where in each ring one CH3 is replaced by one CD3 group. For II-d6, the 2H NMR line shapes indicate fast CD3 group rotations and a fast "eta5 rotation", corresponding to 72 degrees rotational jumps of the eta5 coordinated Cp* ring. The latter motion becomes slow around 130 K. By line shape analysis, an activation energy of the eta5 rotation of about 21 kJ mol-1 was obtained. 2H NMR line shapes analysis of I-d6 indicates fast CD3 group rotations at all temperatures. Moreover, between 100 and 150 K, a transition from the slow to the fast exchange regime is observed for the 5-fold rotational jumps of both Cp* rings, exhibiting an activation energy of 18 kJ mol-1. This value was corroborated by 2H NMR relaxometry from which additionally the activation energies 6.3 kJ mol-1 and 11.2 kJ mol-1 for the CD3 rotation and the molecular inversion process were determined. | Descripción: | 9 páginas, 10 figuras, 2 tablas, 1 esquema. | Versión del editor: | http://dx.doi.org/10.1021/jp711504g | URI: | http://hdl.handle.net/10261/37560 | DOI: | 10.1021/jp711504g | ISSN: | 1089-5639 |
Aparece en las colecciones: | (IIQ) Artículos |
Mostrar el registro completo
CORE Recommender
SCOPUSTM
Citations
6
checked on 04-may-2024
WEB OF SCIENCETM
Citations
2
checked on 27-feb-2024
Page view(s)
312
checked on 06-may-2024
Google ScholarTM
Check
Altmetric
Altmetric
NOTA: Los ítems de Digital.CSIC están protegidos por copyright, con todos los derechos reservados, a menos que se indique lo contrario.