From a Cyclotrisilane to a Cyclotriplumbane:  Low Coordination and Multiple Bonding in Group 14 Chemistry

Abstract

In less than three decades the chemistry of low-coordinated compounds of the heavier elements of group 14 has made unforeseen and unprecedented advances. In the meantime not only have homonuclear double bonds been realized between all elements of this group but also the first examples of compounds analogous to the alkynes have been isolated. Similarly, syntheses of molecules containing heteronuclear bonds have been achieved. Analogues of the allenes as well as the first example of a spiropentasiladiene are of particular interest. The present short review covers mainly work done in the author's laboratories together with other relevant reports from the literature. It begins with the synthesis of hexa-tert-butylcyclotrisilane, which is cleaved photochemically into a short-lived silylene and a marginally stable disilene; in subsequent reactions both of these species can undergo cycloadditions to furnish a broad palette of mostly novel ring systems. Furthermore, the first molecules with conjugated SiSi, GeC, and GeGe double bonds have been obtained and their reactivities examined. The isolation of the first diplumbenes and a cyclotriplumbane exhibiting an unusual bonding situation as the first homocyclic compound of lead constitute a provisional end of these developments.

Recent Advances in the N-Heterocyclic Carbene-Supported Chemistry of Silicon

“…For example, C-C multiple bonding is a prominent feature of organic chemistry, whereas the formation of stable multiple bonds between silicon requires steric protection of the weaker and more reactive Si-E π-bonds (E ¼ element) in the form of bulky substituents at silicon ( [2][3][4][5][6]; for a recent report of a stable Ge¼O double bond, see [7]). Despite numerous efforts to prepare compounds with Si-Si multiple bonds in the condensed phase, this goal was only achieved in 1981 when West reported the landmark synthesis of Mes 2 Si¼SiMes 2 (Mes ¼ 2,4,6-Me 3 C 6 H 2 ) [8].…”

Structure and bonding of MCB5H7 and its sandwiched dimer CB5H6M–MCB5H6 (M=Si, Ge, Sn): Isomer stability and preference for slip distorted structure

“…Recently, Power et al [34][35][36][37][38][39][40][41] described the compounds RE"ER (E = Ge-Pb) comprising of bulky aryl ligands. These compounds have trans-bend geometries with bond orders less than three.…”

Steric effects on the dialkyl substituted X2C2Si silylenes: A theoretical study

“…Shortly later, Masamune et al reported not only on the first examples of the cyclotrisilanes, cyclotrigermanes, and cyclotristannanes but also on their photochemical or thermal ring cleavages to afford disilenes, digermenes, and one, although not isolable, distannene [21][22][23]. These results appear to suggest that the chemistry of multiple bonds between the heavier elements of group 14 has been more or less completely unknown [24]. However, the recent successful isolation of a trisilaallene [25], together with the more well-known tristannaallene [26], shows that the potential for novel compounds is by no means exhausted.…”