Chemistry of Heavier Group 14 Base-Stabilized Heterovinylidenes

This review covers the synthesis, structures, and reactivity of heavier group 14 base-stabilized heterovinylidenes featuring a >C=E: bond (E = Si, Ge, Sn, Pb). The supporting ligands used in the synthesis of these base-stabilized heterovinylidenes are mainly bulky and bear electron-donating substituents which are essential in coordinating to the metal centers for stabilization. These isolated, thermally stable heavier group 14 metal analogues of vinylidene have been structurally characterized. The structural study of bis(germavinylidene) ((Me₃SiN=PPh₂)₂C=Ge→Ge=C(PPh₂=NSiMe₃)₂) had shown that the Ge-C distances of 1.905(8) and 1.908(7) Å found in the complex are consistent with a Ge-C double bond. The reactivity studies of these heterovinylidenes have been mainly focused on germavinylidenes and stannavinylidenes, as silavinylidenes and plumbavinylidenes are unstable reactive intermediates. The reactivity of bis(germavinylidene), including 1,2-additions, cycloadditions, oxidative additions, ligand-transfer reactions, and Lewis base properties, are described. The reactions of stannavinylidene with various reagents are also described. The results of the reactions of 1,3-diplumbacyclobutane with chalcogens suggested the existence of plumbavinylidene in the solution state. Selected X-ray structures of these base-stabilized heterovinylidenes are shown.