ELECTRON SELF-EXCHANGE OF THE DICYCLOPENTADIENYLNICKEL(II,III) COUPLE IN DICHLOROMETHANE

Electron transfer has been observed between dicyclopentadienylnickel(II) (nickelocene) and dicyclopentadienylnickel(III) (nickelocenium) in dichloromethane by the nuclear magnetic resonance line broadening technique. The rate constant for this electron-self-exchange reaction is 2.1 × 108 M−1 s−1, extrapolated to 25 °C from lower temperatures. The enthalpy of activation is low at 6.9 ± 0.5 kJ/mol, and the entropy of activation is -63 ± 2 J/(mol•K). Attempts to measure the electron exchange in other solvents gave ambiguous NMR signals. The rate constant for electron self-exchange in decamethylnickelocene and decamethylnickelocenium was also observed and is estimated to be approximately an order of magnitude larger than for the unsubstituted complex. These results support recent interpretations of trends for electron-transfer reactions between metallocenes based upon changes in metal character of the highest occupied molecular orbital of the reductant. © 1990, American Chemical Society. All rights reserved.