239134-17-9Relevant academic research and scientific papers
Synthesis, redox chemistry, molecular and electronic structure of some cyclopentadienylcobalt pentafulvene complexes
Wadepohl, Hubert,Paffen, Franz-Josef,Pritzkow, Hans
, p. 391 - 403 (2007/10/03)
The pentafulvene complexes [(C5R5)Co(C6H4R′R″)] 3d (R = H, R′ = Me, R″ = Ph), 3f (R = H, R′ = Ph, R″ = C6H4NO2-4), 3g (R = H, R′ = R″ = SMe) and 9 (R = Me, R′ = R″ = Ph) were prepared from the respective fulvenes and [(C5R5)Co(C2H4)2] 8a,b. Protonation of 3 occurs at the fulvene C-α to give substituted cobaltocenium cations. The crystal and molecular structures of 3g, 9 and of the protonation product [3e + H]+ (R = R′ = Ph) were determined. In the neutral complexes the non-planar fulvene ligands are essentially η4-coordinated with short uncoordinated exocyclic carbon-carbon double bonds. In contrast, the protonated species exhibit n5-coordinated planar five-membered rings. Using cyclic voltammetry, the complexes 3e,f and 9 were shown to reversibly undergo one-electron oxidation and reduction reactions to give the cations [3e]+, [3f]+, [9]+ and anions [3e]-, [3f]-, [9]-. Complex 3g also forms an anion [3g]-, but oxidation is irreversible. The X-band ESR spectra of [3e]-, [3e]+ and of [9]-, [9]+ were recorded. In marked contrast to the cations, the anion radicals exhibit considerable anisotropy of the g and A tensors. d-Electron spin densities ρd = 0.5 for the radical anions were derived from a detailed analysis and simulation of the ESR spectra. Using extended Hueckel and Fenske-Hall MO calculations for the model complex [(C5H5)Co(C5H4CH2)] 3h, the ESR and electrochemical properties were explained by the different metal participation in the HOMO (= SOMO of the cation radicals) and LUMO (= SOMO of the anion radicals).
