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.

Theoretical Description of Triplet Silylenes Evolved from H2Si═Si

“…The answer is in the low ability of heavier group 14 elements to form hybrid orbitals. They prefer the (ns) 2 (np) 2 valence electron configuration, which leads to the divalent singlet ground state H 2 M (M = Si, Ge, Sn, Pb) . While methylene (H 2 C) has a triplet ground state with a singlet–triplet energy separation (Δ E S-T = E T – E S ) of −9.0 kcal/mol, the ground state of silylene (H 2 Si) is a singlet that lies 19–23 kcal/mol lower than its corresponding triplet state .…”

Reactions of a Zn(i) complex with group 14 azides – formation of zinc azide and zinc hexazene complexes

“…Metal-to-metal bonds in clusters and molecules are of fundamental interest in natural science. 1 Since the pioneering work in the mid-1960s, 2 main group metal complexes containing group 2, 3 13, 4 14, 5 and 15 metals 6 as well as transition metal complexes with multiple bonding including quintuple bonding 7 have received steadily growing interest. Two major stabilizing strategies have been developed, i.e.…”

“…9 Aside from their synthesis, the reactivity of such metal complexes has received increasing interest. 10 Since the landmark discovery of [Z 5 -Cp* 2 Zn 2 ] (Cp* = C 5 Me 5 ) by Carmona et al in 2004 11 roughly 25 compounds containing Zn in the formal oxidation state +I have been structurally characterized 12 and their chemical reactivity has been investigated. Lewis acid-base reactions, protonation reactions, 13 oxidative addition reactions of PhCCPh and alkyl halides 14 as well as reactions with transition metal complexes were reported.…”

Diazinylcarbenes and Their Heavier Analogues at DFT: An Intramolecular Stabilization of Singlet Si and Ge Divalent Centers

“…Table shows the geometrical parameters of the heteroarylsilylenes and germylenes. In silylenes and germylenes, because of the size difference between the ns and np orbitals, the ability to form hybrid orbitals is low, and the nonhybrid ns 2 np 2 electronic configurations are preferred in the order of Ge > Si . As a result, the divalent angle ∠C ring –M–H of silylenes and germylenes is reduced compared to the carbene analogues (Table ).…”

“…In silylenes and germylenes, because of the size difference between the ns and np orbitals, the ability to form hybrid orbitals is low, and the nonhybrid ns 2 np 2 electronic configurations are preferred in the order of Ge > Si. 39 As a result, the divalent angle ∠C ring −M−H of silylenes and germylenes is reduced compared to the carbene analogues (Table 4). On the other hand, σ-electron-donating substituents make the divalent angle larger since these substituents would make the ns orbital large enough to be mixed with the np orbital, which leads to partially hybridized orbitals.…”