Group 14 Multiple Bonding

Abstract Multiply bonded compounds between heavier group 14 elements cannot exist as monomers under normal conditions owing to their inherent high reactivity, that is, they readily undergo oligomerization, oxidation, hydrolysis, and so on. The bulkiness of substituents on the reactive sites shows a great effect on the stabilization of such highly reactive compounds. Since the synthesis and isolation of the first stable disilene, Mes 2 SiSiMes 2 (Mes = mesityl), by R. West et al. in 1981, the idea of kinetic stabilization using bulky substituents have led to the successful isolation of several types of unsaturated compounds of group 14 elements, such as heavy alkenes (double bonds between heavier group 14 elements), heavy ketones (heavier group 14–16 double bonds), heavy imines (heavier group 14–15 double bonds), heavy aromatics (aromatic systems containing heavier group 14 elements), heavy butadienes , and triply bonded systems containing heavier group 14 elements, and so on. Now, unsaturated compounds containing heavier group 14 elements are no more imaginary species but are those of real existence even in the case of lead, the heaviest group 14 element, when they are appropriately protected by bulky substituents. The synthesis and properties of the kinetically stabilized unsaturated compounds containing heavier group 14 elements will be described in this section. Although a number of multiple bondings between heavier group 14 elements and transition metal elements have been reported so far, only unsaturated compounds containing main group elements should be considered here from the viewpoint of comparisons with carbon chemistry.