Intramolecularly Stabilized Heavier Tetrylenes: From Monodentate to Bidentate Ligands

Intramolecularly stabilized heavier tetrylenes (HTs) are group 14 metalylenes featuring at least one intramolecular DE interaction between a two-electron-donor group (D) and the group 14 atom (E = Si, Ge, Sn or Pb). With regard to their coordination chemistry, they normally bind to transition metals as monodentate ligands through the lone electron pair of their E atom; however, the donor group D initially involved in their internal stabilization can sometimes migrate from the E atom to the transition metal. This ring-expansion process transforms the original monodentate (E-1) ligand into a bidentate one (E-2,D) and enhances the stability of the resulting complex. This review collects and discusses the hitherto known reactions involving this ligand transformation, also shedding light on the factors that make it possible.