Bond-stretch isomerism in 2-chalcogen-trimetallabicyclo[1.1.0]butane derivatives

Electronic and steric factors that control the bond-stretch isomerism phenomenon in 2-chalcogen-trimetallabicyclo[1.1.0]butane systems have been investigated using quantum chemical calculations. Beside the short-bond and long-bond extremes we found and characterized a third, stable conformer with significantly elongated central bond and anti arrangement of the bridgehead substituents. Electronic structures of the isomers have been described and interpreted in details within the framework of MO theory. Germanium analogues of trisilirene have been predicted to also react with sulphur to form the corresponding 2-thia-trimetallabicyclo[1.1.0]butane analogues. The systematic analysis of the relative stability dependence on the ring composition as well as the bridgehead substituents revealed that the hitherto unknown anti isomer is a promising synthetic target in germanium bridged bicyclo compounds with bridgehead substituents containing carbon contact atom.