The derivatives of isosilabenzene and isogermabenzene with metal vinylidene bonds have been achieved from phantom species to stable compounds for the first time. The relative stability of these isomers has been elucidated by experimental observations and DFT calculations.

Comprehensive Summary

Metalla-isosilabenzenes and metalla-isogermabenzenes have been successfully synthesized by the formal [5+1]-cycloaddition of diethynylsilane or diethynylgermane with simple metal complexes. This is the first example of a heavier Group 14 metalla-isobenzene isomer bearing a cumulative double bond motif within a metallacycle. These novel complexes were fully characterized by NMR spectroscopy and single-crystal X-ray diffraction analysis. The stabilization of the cyclic metal-vinylidene complexes has been analyzed using density functional theory (DFT) calculations. When the metalla-isosilabenzenes bearing Si—H bond were treated with the trityl salt as a hydride scavenger, the formation of silylium cation was observed spectroscopically. Both of metalla-isosilabenzenes and metalla-isogermabenzenes can readily undergo migratory insertion reactions to furnish siloles or germoles.