Reaction of a digermyne with cyclooctaietraene (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 pi-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 (Delta H-double dagger) and entropy (Delta S-double dagger) of 14.9 kcal mol(-1) and -6.2 cal mol(-1) K-1 respectively. Heating crystals of the thermodynamic product at ca. 120 degrees C cleanly regenerated the original inverse sandwich isomer.