Chalcogen‐Expanded Unsaturated Silicon Clusters: Thia‐, Selena‐, and Tellurasiliconoids

Abstract

Reactions of silylenes with heavier chalcogens (E) typically result in Si=E double bonds or their π‐addition products. In contrast, the oxidation of a silylene‐functionalized unsaturated silicon cluster (siliconoid) with Group 16 elements selectively yields cluster expanded siliconoids Si7E (E=S, Se, Te) fully preserving the unsaturated nature of the cluster scaffold as evident from the NMR signatures of the products. Mechanistic considerations by DFT calculations suggest the intermediacy of a Si6 siliconoid with exohedral Si=E functionality. The reaction thus may serve as model system for the oxidation of surface‐bonded silylenes at Si(100) by chalcogens and their diffusion into the silicon bulk.

[Cl@Si20H20]−: Parent Siladodecahedrane with Endohedral Chloride Ion

“…Most of the synthetically accessible molecular silicon cages, such as Fässler’s [R 2 Si 9 ] 2– anions, − Kyushin’s decasilahexa­hydrotriquinacene, Marschner’s decasilaadamantane, Scheschkewitz’s siliconoids, − or the above-mentioned silatetrahedranes and -cubanes present chemically rather innocent (bulky) organyl groups to their environments. Hydrogenated species are rare, and functionalized derivatives feature mainly low-valent, nucleophilic Si sites .…”

Gerüsterweiterung eines Silicoids um ein einzelnes Germaniumatom über isolierte Zwischenprodukte

“…Der Clusterkern von 4 [Li(dme) 2 ] weist ein Propellanmotiv auf, das durch die zweifache Verbindung der “Propellerblätter” verzerrt ist, ähnlich wie bei Si 7 Tip 5 Cp* und Si 7 Tip 5 Li [7c] . Dies führt zu einer sägebockartigen Koordinationsumgebung des Si5 mit einer quasi‐linearen Anordnung bezüglich Si6 und Si4 (Si6‐Si5‐Si4 in 4 [Li(dme) 2 ]: 173.52(3)°, Si6−Si5−Si4 in 4 Li⋅(NHC) 2 : 176.50(2)° vs. 173.77° für Si 7 Tip 5 Cp* und 162.705(4)° für Si 7 E) [7c, 11d] . Während die beiden basalen Gerüstatome des zentralen Dreieckmotivs, E1 und E2, sowie das formal anionische Gerüstatom E7 entweder von Silicium oder Germanium besetzt sind, ist Position 5 nur durch Silicium besetzt, was die Schlussfolgerungen aus den 29 Si NMR Daten bestätigt.…”

Molecular Silicon Clusters

“…Notably, the cluster cores of Si 7 E heterosiliconoids 96a−c (E = S, Se, Te), which are accessible by cluster expansion of the silylene substituted Si 6 siliconoid 91a with chalcogens (Scheme 52) 322 strongly resemble those of the Si 8 species 94 and 95 (Scheme 51).…”

“…Here too, only the two “naked” vertices are part of the base of the central triangle exhibit hemispheroidal coordination spheres, while the apex silicon atom appears to be distorted tetrahedrally coordinated in every case as indicated by negative Φ values (Table ). Expectedly, the 29 Si NMR resonances assignable to the “naked” silicon atoms in all eight-atomic clusters ( 94 , 95 , 96a – c ) appear in the high-field region and are comparable to what was observed for their homonuclear Si 7 counterparts 92 and 93 (Table ). Note that the amidinate-substituted silicon vertices in 96a – c give rise to 29 Si NMR resonances at δ = 33.5 ( 96a ), 26.6 ( 96b ), and 2.3 ppm ( 96c ), which is extraordinarily low-field shifted for pentacoordinate silicon centers.…”