Reactivity of a Methylene-Bridged 1,3-Bis(germylene) in Dynamic Equilibrium with Its Dimer

We report the properties and reactivity of an unprecedented methylene-bridged 1,3-bis(germylene) derivative. In the solid state, it undergoes dimerization to afford a 1,2,4,5-tetragermacyclohexa-1,4-diene derivative (Ge₄CHD). Moreover, theoretical calculations on Ge₄CHD reveal σ*-π interactions between the two π orbitals (Ge═Ge) and the CH σ* orbital. This interaction is confirmed by a significant red shift in the solid-state UV-vis spectrum. In contrast to the behavior in the solid state, the Ge₄CHD derivative dissociates in solution into a methylene-bridged 1,3-bis(germylene) derivative. The resultant 1,3-bis(germylene) derivative reacted with S₈ to form a novel cage compound containing three S and two Ge atoms. On the other hand, in the reaction with triphenylphosphine sulfide, the in situ generated 2-thia-1,3-digermabicyclo[1.1.0]butane derivative activated the benzene solvent, leading to the formation of a [2 + 2] cycloaddition product. Additionally, the 1,3-bis(germylene) derivative reacted with 4-dimethylaminopyridine (DMAP) to form a three-membered ring. Its structural parameters and the results of theoretical calculations indicated the zwitterionic character.