Unusual Electrocyclic Rearrangements with Group 14 Element Compounds: Reversible Isomerization of a π-Aromatic Digermyl Complex with Carbon−Carbon and Germanium−Germanium Multiple Bond Cleavage

Reaction of a digermyne with cyclooctatetraene (cot) gave two isomeric products. A Ge(II) inverse sandwich is formed as the kinetic product, which was a result of complete GeGe bond cleavage and the formation of a π-bound cot ring. This isomerized in solution at room temperature over a period of 5 days to give the thermodynamic product, a tetracyclic diene-digermane, in which a single-bonded GeGe moiety has inserted into a CC bond of the cot carbocycle. Kinetic studies afforded an activation enthalpy (ΔH‡) and entropy (ΔS‡) of 14.9 kcal mol−1 and −6.2 cal mol−1 K−1 respectively. Heating crystals of the thermodynamic product at ca. 120 °C cleanly regenerated the original inverse sandwich isomer.