(2,3-Bis(methylen)bicycIo[2.2.2]octan)zirconocen: Synthese, Struktur und elektrochemische Reduktion/(2,3-Bis(methylene)bicyclo[2.2.2]octane)zirconocene: Synthesis, Structure, and Electrochemical Reduction
Photolysis of diphenylzirconocene and 2,3-bis(methylene)bicyclo[2.2.2]octane in toluene at -25 °C yields biphenyl and (2,3-bis(methylene)bicyclo[2.2.2]octane)zirconocene (lg) (67.5% isolated yield).1g exhibits dynamic NMR spectra indicating rapid alternation of diene faces coordinated to zirconium (ring-flip mechanism). This degenerate intramolecular rearrangement is characterized by an extremely low activation barrier (⊿G≠-131°C = 7.1 ± 0.3 kcal/mol). 1g crystallizes in space group P1̄with a = 7.215(1) Å, b = 9.654(1) Å, c = 11.831(1) Å, α = 94.97(1)°, β = 91.81(1)°, and γ = 103.22(1)°. The X-ray structure determination reveals a pronounced metal alkyl character of the (diene)ZrCp2 moiety. Accordingly, 1g is easily reduced electrochemically to give a Zr(III) radical anion (7) observed by esr (g = 1.990; a(H) = 2.976 G; a(Zr) = 18.36 G).