Heteronuclear heavy alkenes E=E′ (E, E′ = group 14 elements):: Germasilenes, silastannenes, germastannenes...: Next stop?

Recent advances in the chemistry of stable heteronuclear heavy alkenes >Edouble bondE'< (E, E' group 14 elements) are reviewed, covering silenes (>Sidouble bondC<), germenes (>Gedouble bondC<), stannenes (>Sndouble bondC<), germasilenes (>Gedouble bondSi<), silastannenes (>Sidouble bondSn<), and germastannenes (>Gedouble bondSn<). Their unique structures, bonding modes, and reactivities have been shown to be different from those of the homonuclear species, primarily due to the polarity of the >Edouble bondE'< bond resulting from the difference in the electronegativities of the doubly bonded atoms.