Comparative chemistry of unsaturated compounds of Group 14 elements

Abstract

Structures and reactions of a stable dialkylsilylene and various cyclic and acyclic disilenes, which we have recently synthesized, are discussed in detail. The stable silylene was found to be well protected sterically from dimerization but least perturbed electronically as evidenced by UV-vis and NMR spectroscopy. Persilylated acyclic and cyclic disilenes have shown interesting features in the Si=Si bond distances, electronic spectra, and reactions, due to the remarkable electronic and steric effects of trialkylsilyl substituents. Detailed theoretical calculations for the addition of water to disilene has shown that the intramolecular antiaddition pathway is rationalized using the orbital symmetry rule. The reactions of disilenes with haloalkanes were judged to proceed via the rate-determining halogen abstraction of disilenes from haloalkanes. The biradical character of disilenes may be related to the small π bond energy.

A Molecular Silicon Cluster with a “Naked” Vertex Atom

“…Reductive dehalogenation of a divalent species in the presence of GeCl 2 had proven successful for the preparation of the germanium cluster Ge 6 R 2 as reported by Power and co‐workers 6c. Unfortunately, the instability of divalent silicon compounds renders such an approach unsuitable 11. On the other hand, the recently reported disilenides, analogues of vinyl anions, should be good precursors for multiply unsaturated silicon π systems, which could subsequently rearrange to yield the desired partially substituted clusters owing to the low stability of SiSi double bonds.…”

Ein molekularer Siliciumcluster mit einem “nackten” Gerüstatom

“…[11] Andererseits sollten die unlängst beschriebenen Disilenide, Analoga von Vinylanionen, gute Ausgangsverbindungen für mehrfach ungesättigte p-Systeme von Silicium sein, die sich ihrerseits wegen der Labilität der Si = Si-Bindungen leicht zu den anvisierten, teilsubstituierten Clustern umlagern sollten. [17] Um die Natur der Wechselwirkungen aufzuklären, die zu den extremen Verzerrungen in 3 führen, wurden DFTRechnungen auf B3LYP/6-31G(d,p)-Niveau am H-substituierten Grundkörper 3 u durchgeführt.…”

Designing the Backbone of Hexasilabenzene Derivatives with a High Unimolecular Kinetic Stability

“…It is known that Si−Si π bonds are not as stable as C−C π bonds. This makes it difficult to synthesize compounds having Si−Si multiple bonds, and hence, considerable efforts have been made to design and synthesize such compounds . One of the most challenging synthetic targets in this field would be hexasilabenzene.…”

“…This makes it difficult to synthesize compounds havingS i ÀSi multiple bonds, and hence,c onsiderable effortsh ave been made to design and synthesize such compounds. [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] Oneo ft he most challenging synthetic targets in this field would be hexasilabenzene. It was shown theoretically that the monocyclic (SiH) 6 takes an on-planar chair-type geometry at its local minimum (MIN) on the potential energy surface( PES).…”