Synthesis of Stable Dianionic Cyclic Silenolates and Germenolates

Abstract

In this contribution a convenient synthetic method to obtain the previously unknown dianionic cyclic silenolates and germenolates is described. These dianions 2a , b and 4a , b are easily accessible via a one-pot synthetic protocol in high yields. Their structural properties were analyzed by a combination of NMR, single-crystal X-ray crystallography, and DFT quantum mechanical calculations. Moreover, the reactivity of 2a , b and 4a , b with selected examples of electrophiles was investigated. 2a and 4a were reacted with ClSi i Pr 3 to give new examples of polysilanes and polygermanes with exocyclic double bonds. The reaction of 2b with ClSiMe 2 SiMe 2 Cl led to the formation of the acyl bicyclo[2.2.2]octasilane 6 . Moreover, the reaction of 2a , b and 4a , b with MeI, as an example of a carbon-centered electrophile, led to selective alkylation reactions at the negatively charged silicon and germanium atoms. The corresponding methylated structures 9a , b and 10a , b were formed in nearly quantitative yields. The competitive reactivity of the silyl and silenolate anion toward 1 equiv of ClSiMe 3 showed that the outcome of the reaction was strongly influenced by the substituent at the carbonyl moiety. 2a reacted with 1 equiv of ClSiMe 3 to give the corresponding cyclic silenolate S 1 a , which demonstrated that the silyl anion is more nucleophilic than the silenolate with attached aromatic groups. 2b , on the other hand, reacted with 1 equiv of ClSiMe 3 to give the bicyclic compound 11 via an intramolecular sila-Peterson alkenation reaction. These findings clearly showed that the alkyl-substituted silenolate is more nucleophilic than the silyl anion. This paper demonstrates that 2a , b and 4a , b have the potential to be used as unique building blocks for complex polysilane and polygermane frameworks.

Stable four‐membered cyclosilylenes at theoretical levels

“…[26][27][28] Many experimental and theoretical investigations have been conducted on the possible existence of carbon-free cyclic structures such as boron-nitrogen [29][30][31][32][33] and nitrogen- 34 and silicon-based molecules. 35 Cyclopolysilanes (SiR 2 ) n are known to be stable heterocycles, [36][37][38] which are prepared through the dehalogenation of (diorgano)dichlorosilanes (Wurtz coupling) and electrochemical reduction. 39 Cyclopolysilanes were first synthesized by Kipping in 1921.…”