51614-82-5Relevant academic research and scientific papers
Reactions of odd-electron cobaltacycles: Characterization of a persistent 17-electron anionic intermediate in electron-transfer-catalyzed (ETC) substitution reactions
Donovan-Merkert, Bernadette T.,Rieger, Philip H.,Geiger, William E.
, p. 3194 - 3200 (1999)
The cobaltafluorene complex Cp(PPh3)CoC12H8 (1) undergoes an electrochemically irreversible one-electron reduction in THF Cp,c = ca. -2.56 V vs ferrocene) with release of PPh3 to give a persistent 17-electron Co(II) monoanion, 2 , which was characterized by electrochemistry and by ESR spectroscopy. The unpaired spin density in 2- is highly delocalized, with the majority being located in the cyclopentadienyl ring rather than the cobaltacyclic fragment. Reoxidation of 2- in the presence of L (L = phosphines, phosphites) forms Cp(L)CoC12H8 in high yield. Slow electron-transfer-catalyzed (ETC) substitution processes are found when 1 is electrolyzed in the presence of P(OMe)3, with the efficiency of the catalysis being dependent on both the relative and absolute concentrations of 1 and P(OMe)S. The substitution reaction is accounted for by a model in which the anion 2- is in equilibrium with the 19-electron adducts [Cp(L)CoC12H8]-, where L = THF, PPh3, P(OMe)3. Further reduction of 2- is possible in a reversible one-electron reduction (E1/2 = -2.80 V) to an 18-electron dianion that is stable in solution. The dianion 22- was characterized by 1H NMR spectroscopy and shown to have C8 or higher symmetry.
