Search

Two novel disilenes of type ABSi＝SiAB bearing N-heterocyclic imino (A = NItBu) and trialkylsilyl (B = SitBu31, B = SitBu2Me 2) groups are reported. The reduced steric demand in 2 results in a highly stable, nonetheless flexible system, wherefore (E/Z) isomerization is observed from room temperature up to 90 °C. The proposed isomerization mechanism proceeds via monomeric silylenes in line with experimental results. Despite enhanced stability, disilene 2 retains high reactivity in the activation of small molecules, including H2. The rare example of a disilene radical cation 7 is isolated and shows reversible redox behavior. White phosphorous (P4) selectively reacts with 2 to give the unique cage-compound 8. Selective thermal rearrangement of 2 at higher temperatures yields the A2Si＝SiB2-type disilene 9 (A = NItBu, B = SitBu2Me), which bears characteristics of a zwitterionic and a dative central Si–Si bond. The proposed mechanism proceeds via an initial NHI migration followed by silyl migration. [ABSTRACT FROM AUTHOR]

Conventional industrial crosslinking of silicones is usually done by the well-established tin-catalysed condensation, platinum-catalysed addition or peroxide curing. We report the first application of highly reactive multifunctional silylenes as universal crosslinkers for catalyst-free curing of standard industrial silicones. The reactive silylene species is generated by thermal decomposition of stable silacyclopropane precursors and reacts with various functionalities of silicone building blocks in an addition reaction. Alternatively, the multifunctional silacyclopropanes can be ring-opened by nucleophilic compounds like siloxanols, which can also be employed for network formation with standard nucleophilic siloxanes. These new crosslinking methods are not dependent on non-recoverable Pt- or toxic Sn-catalysts and enable the production of clean, extractable-free elastomers. We describe the synthesis of multifunctional siliranes as model compounds and their application in silicone curing. [ABSTRACT FROM AUTHOR]

Due to their outstanding reactivity, acyclic silylenes have emerged as attractive organosilicon alternatives for transition metal complexes on the way to metal-free catalysis. However, exploration of their reactivity is still in its infancy, as only a few derivatives of this unique compound class have been isolated so far. Here, we present the results of an extensive reactivity investigation of the previously reported acyclic iminosiloxysilylene 1. Divalent silylene 1 proved to be a versatile building block for a plethora of novel organosilicon compounds. Thus, not only the activation of the rather challenging targets NH3 and P4 could be achieved, but also the conversion into a reactive donor-free silaimine, which itself turned out to be a useful reagent for small molecule activation. In addition, 1 served as an excellent precursor for gaining access to donor-stabilized heavier carbonyl compounds. Our results thus provide further insights into the chemistry of low-valent silicon at the interface between carbon and transition metals. [ABSTRACT FROM AUTHOR]

Heavier analogues of silaacylium ions 2–4 ([m-TerSiE(NHC)2]Cl; m-Ter = 2,6-Mes2C6H3; Mes = 2,4,6-Me3C6H2; 2 (E = S), 3 (E = Se), 4 (E = Te)) were synthesized by the reaction of the NHC-stabilized silyliumylidene cation 1 with elemental chalcogens. Fascinating regeneration of 1 from the reaction of 2–4 with AuI was achieved, as successful recovery of a parent Si(ii) species from a silachalcogen Si(iv) compound. Furthermore, unique chalcogen exchange reactions from 4 → 3 → 2 were observed in line with the calculated silicon–chalcogen bond energies. [ABSTRACT FROM AUTHOR]