Bonding and structure of disilenes and related unsaturated group-14 element compounds

Abstract

Structure and properties of silicon-silicon doubly bonded compounds (disilenes) are shown to be remarkably different from those of alkenes. X-Ray structural analysis of a series of acyclic tetrakis(trialkylsilyl)disilenes has shown that the geometry of these disilenes is quite flexible, and planar, twist or trans-bent depending on the bulkiness and shape of the trialkylsilyl substituents. Thermal and photochemical interconversion between a cyclotetrasilene and the corresponding bicyclo[1.1.0]tetrasilane occurs via either 1,2-silyl migration or a concerted electrocyclic reaction depending on the ring substituents without intermediacy of the corresponding tetrasila-1,3-diene. Theoretical and spectroscopic studies of a stable spiropentasiladiene have revealed a unique feature of the spiroconjugation in this system. Starting with a stable dialkylsilylene, a number of elaborated disilenes including trisilaallene and its germanium congeners are synthesized. Unlike carbon allenes, the trisilaallene has remarkably bent and fluxional geometry, suggesting the importance of the π-σ* orbital mixing. 14-Electron three-coordinate disilene-palladium complexes are found to have much stronger π-complex character than related 16-electron tetracoordinate complexes.

Dynamic Complexation of Copper(I) Chloride by Carbene‐Stabilized Disilicon

“…The side‐on coordination of the L:SiSi:L (L:=:C[N(Me)CH] 2 ) fragment to CuCl in 2′‐Me only results in a slight elongation of the silicon–silicon distance (to 2.295 Å from 2.2294(11) Å in 1 ) 10. Indeed, the 2.295 Å silicon–silicon bond length in 2′‐Me is similar to those reported for disilene–transition‐metal π complexes 23. Interestingly, 2 only gave a singlet 29 Si NMR resonance.…”

“…[10] Indeed, the 2.295 silicon-silicon bond length in 2'-Me is similar to those reported for disilene-transition-metal p complexes. [23] Interestingly, 2 only gave a singlet 29 Si NMR resonance. This, coupled with the fact that two carbene ligands are chemically equivalent in both 1 H and 13 C NMR spectra of 2, suggests that in solution, 2 may exist in the C 2 symmetric p-complex isomer form or rapidly equilibrate at room temperature, very likely via a p-complex intermediate ( Figure 5).…”

Functional Disilenes in Synthesis

“…The interconverison among the Si 4 R 6 valence isomers 4 and 70 was demonstrated with labeling experiments using cyclotetrasilene 4 , that is partially substituted with t Bu(CD 3 ) 2 Si groups, showing that the interconversion between 4 and 70 occurs through a 1,3‐cyclobutanediyl‐like diradical intermediate, formed by the 1,2‐silyl migration of 4 …”

“…In the latter case, the migration of a silyl substituent is plausibly the key to the formation of a proposed bis(silylene) intermediate. Upon irradiation, isomerization of cyclotetrasilene 4 takes place—presumably through 1,2‐silyl migration to 1,3‐diradical intermediate 83— to afford the bicyclo[1.1.0]tetrasilane 70 (Scheme ) …”

Synthesis and Characterization of N-Heterocyclic Carbene-Coordinated Silicon Compounds Bearing a Fused-Ring Bulky Eind Group

“…Over many years, a number of unsaturated silicon compounds have been successfully obtained by virtue of the complexation of metal ions and/or coordination of ligands (mainly Lewis bases) in addition to steric protection with bulky substituents [1][2][3][4][5][6][7][8][9][10][11]. Among them, the coordination chemistry of highly-reactive halosilylenes, i.e., halogen-substituted divalent Si(II) species, have attracted a lot of attention as potentially useful precursors for the construction of a wide range of silicon-containing compounds [12][13][14][15][16][17].…”