Primary 2/1H isotope shift
Secondary 2H isotope shift
2H signal narrowing
Analytical Chemistry and Spectroscopy
Wiley InterScience Backfile Collection 1832-2000
Chemistry and Pharmacology
1H and 2H NMR spectra were recorded for the paramagnetic metallocenes Cp2M (M = V, Cr, Mn, Co, Ni). For Cp2V, Cp2Cr, Cp2Mn and Cp2Ni, a signal narrowing factor of 36-37 is observed on going from Cp2M-h10 to Cp2M-d10, which is close to simple theoretical predictions. Additional quadrupolar relaxation leads to a factor of 27 for cobaltocene. The enhanced resolution of the 2H NMR spectra makes it possible to observe isotopomeric cobaltocenes with signals showing a secondary isotope shift of 0.71 ppm. In Cp2 Co-d9 and -d8, the residual 1H atoms lead to a splitting of the 2H NMR signals, which is traced to the lifting of an orbital degeneracy due to the perturbation of the ligand π-system by the lighter isotope. Primary isotope shifts of 2.33, 1.24, and 1.45 ppm are found for the pairs Cp2Mn-d10/h10, Cp2Co-d10/h10 and Cp2Ni-d10/h10. They reflect a change in the electron spin distribution after complete deuteriation.
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