Hydrogen deuterium isotope effect on exchange rates in η2 bond transition metal dihydrogen complexes revealed by 2H solid state NMR spectroscopy

F. Wehrmann, J. Albrecht, E. Gedat, G. J. Kubas, J. Eckert, H. H. Limbach, G. Buntkowsky

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A selectively η2-D2 labeled isotopomer of the complex W(PCy3)2 (CO)3) (η2-D2) has been synthesized and the 2H NMR spectra and spin lattice relaxation rates of this complex have been measured in the temperature regime of 50 K to 300 K. The spectra have been analyzed employing a model of a combination of homonuclear dipolar D-D interaction and deuterium quadrupolar interaction and a D-D distance of 0.89 ± 0.1 Å. The line width of the spectra exhibits a weak temperature dependence at temperatures above 150 K. This temperature dependence is interpreted as a slight decrease of the quadrupolar coupling with increasing temperature, which is an indication of a change of the M-D2 distance with changing temperatures. The spin lattice relaxation data of the complex exhibit pronounced deviations from a simple Arrhenius behavior at lower temperatures, indicating the presence of a quantum mechanical tunneling process. This process is analyzed in terms of a simple one-dimensional Bell tunnel model. A comparison with INS data from the H2 complex reveals a strong isotope effect of 2 × 103 for the exchange rates of the deuterons.

Original languageEnglish
Pages (from-to)2855-2861
Number of pages7
JournalJournal of Physical Chemistry A
Issue number12
StatePublished - Mar 28 2002


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