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.