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.

二锗炔与环辛四烯（cyclooctatetraene, COT）反应，得到两种异构体产物。其中动力学产物为二价锗反三明治结构，该产物由Ge≡Ge键完全断裂并形成π配位的COT环生成。该动力学产物在室温溶液中历经5天发生异构化，得到热力学产物四环二烯二锗烷；此热力学产物中，单键连接的Ge-Ge基团插入到了COT碳环的一条C=C双键内。动力学研究测得其活化焓（ΔH‡）与活化熵（ΔS‡）分别为14.9千卡每摩尔与−6.2卡每摩尔每开尔文。将该热力学产物的晶体在约120 ℃下加热，可干净地再生得到初始的反三明治异构体。