ELECTRON-TRANSFER REACTIONS OF METALLOCENES - INFLUENCE OF METAL OXIDATION-STATE ON STRUCTURE AND REACTIVITY

: Vacuum- and low-temperature electrochemical techniques have been used to characterize the redox pathways of Cp2V (Cp = η5-cyclopentadienyl), Cp2Cr, Cp2Ni, Cp2VCl2, and CpNi(η3-C5H7). The pure metallocenes show an electrontransfer series of three or four members. The nickelocene anion, a d9,21-electron species, was shown to be a reduction intermediate, stable in DMF at-60 °C, and CpN(η3-C5H7) was but a minor product of the bulk reduction of nickelocene. The heterogeneous electron-transfer rate was abnormally slow for the nickelocene reduction, suggesting that a structural distortion and/ or a change in solvation occurs to relieve the high metal electron density. Vanadocene was oxidized in two one-electron steps, only the first of which was reversible. It is unlikely that there are gross changes in structure in going from vanadocene to the vanadocene cation, but the irreversibility of the second oxidation suggests the formation of Cp2V(THF)22+for the d1species. © 1979, American Chemical Society. All rights reserved.