Building up Strain in One Step: Synthesis of an Edge‐Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion

Abstract

The exhaustive trichlorosilylation of hexachloro‐1,3‐butadiene was achieved in one step by using a mixture of Si2Cl6 and [nBu4N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu4N]2[1] was isolated in 36 % yield after recrystallization. The negative charges of [1]2− are mainly delocalized across its two carbanionic (Cl3Si)2C termini (α‐effect of silicon) such that the central bond possesses largely C=C double‐bond character. Upon treatment with 4 equiv of HCl, [1]2− is converted into neutral 1,2,3,4‐tetrakis(trichlorosilyl)but‐2‐ene, 3. The Cl− acceptor AlCl3, induces a twofold ring‐closure reaction of [1]2− to form a six‐membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X‐ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.

The power of trichlorosilylation: isolable trisilylated allyl anions, allyl radicals, and allenyl anions

“…The third 13 C NMR signal possessed a chemical shift value of 50.3 ppm, which is close to the value of the signal of the carbanionic centers in [C] 2-(50.2 ppm). 15 However, the total numbers of NMR signals were not consiste nt with a [C3(SiCl3)5]anion either of average C2v or Cs symmetry. We also noted smaller 29 Si resonances characteristic of chloride diadducts of perchlorinated cyclohexasilane s (e.g.…”

“…10 While a plethora of efficient routes to monosilylated allyl systems have been elaborated so far, 11 higher silylated derivatives are still difficult to access, which is unfortunate since geminal disilyl compounds in particular can be involved in numerous synthetically useful transformation s. 12 We have recently disclosed that the inexpensive chlorin ate d hydrocarbons CCl4, Cl2C=CCl2, and Cl2C=C(Cl)-C(Cl)=CCl2 can be straightforwardly converted to the exhaustive ly trichlorosilylated anions [A] --[C] 2upon treatment with Si2Cl6 in the presence of [nBu4N]Cl (Scheme 1). [13][14][15] The actual active silylation reagent, the silanide [SiCl3] -, [16][17][18] is generated by Cl -induced heterolysis of the disilane. [SiCl3]can either react as a nucleophile in a carbophilic or chlorophilic attack (abstract io n of a chloronium ion to form SiCl4 and a carbanion), or behave as a Cl --stabilize d dichlorosilyle ne [SiCl2•Cl] -.…”

“…13,16,18,19 The primary products, [A] --[C] 2-, have been further transformed into a variety of other multiply trichlorosilylated compounds with geminally and/or vicinally positioned SiCl3 substitue nts ([A•GaCl3] --E; Scheme 1). [13][14][15] An SiCl3 group differs from the more abundant SiMe3 group in a number of ways: (i) The Si-Cl bonds offer the possibility of extensive derivatizations, such as transformation to Si-H bonds, alkylation, or hydrolysis to (oligo)siloxanes. (ii) SiCl3 substituents are the better  acceptors and have a greater ability to stabilize adjacent carbanions ( effect).…”

Building up Strain in One Step: Synthesis of an Edge‐Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion

“…Forschungsartikel nounced a-effect of their SiCl 3 substituents.U nder inert conditions,[ 1] 2À is stable over days in THF solution and months in the solid state.Y et, it readily reacts with Brønsted (HOTf)a nd Lewis (AlCl 3 )a cids to furnish silacyclobutenes, such as the edge-fused six-membered double silacyclobutene 4.Especially the rich follow-up chemistry of the strained C=C double bond of the carbonaceous analogue I of 4,w hich encompasses cycloadditions,carbometallations,skeletal rearrangements,a nd radical reactions, [48] make us optimistic that also compound 4 will shape up as av ersatile platform of further transformations in the future. [49]…”

Selective One‐Pot Syntheses of Mixed Silicon‐Germanium Heteroadamantane Clusters

“…[15,16] The analogous reaction with Me 2 GeCl 2 led to the double silylation product Me 2 Ge(SiCl 3 ) 2 . Recently, our group succeeded in synthesizing germanide [C] À from GeCl 4 and the alternative trichlorosilylation system Si 2 Cl 6 / Cl À , [17][18][19][20] which disproportionates into SiCl 4 and the actual reactive intermediate [SiCl 3 ] À ; treatment of [C] À with AlCl 3 gave the neo-Si 4 Ge species [D]. [21] Herein, we describe reactions of Me 2 GeCl 2 with the Si 2 Cl 6 / Cl À system and show that, in striking contrast to du Mont's results with the Benkeser reagent, three structurally defined Si x Ge y heteroadamantanes, [0], [1], and [2], become accessible in good yields, which can be regarded as long-sought model systems of Si x Ge y alloys (see Figure 2 for the molecular structures and an explanation of the numbering scheme).…”