Synthesis of Stable Dianionic Cyclic Silenolates and Germenolates.

In this contribution a convenient synthetic method to obtain the previously unknown dianionic cyclic silenolates and germenolates is described. These dianions , and , are easily accessible 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 , and , with selected examples of electrophiles was investigated. and were reacted with ClSiPr to give new examples of polysilanes and polygermanes with exocyclic double bonds. The reaction of with ClSiMeSiMeCl led to the formation of the acyl bicyclo[2.2.2]octasilane . Moreover, the reaction of , and , 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 , and , were formed in nearly quantitative yields. The competitive reactivity of the silyl and silenolate anion toward 1 equiv of ClSiMe showed that the outcome of the reaction was strongly influenced by the substituent at the carbonyl moiety. reacted with 1 equiv of ClSiMe to give the corresponding cyclic silenolate , which demonstrated that the silyl anion is more nucleophilic than the silenolate with attached aromatic groups. , on the other hand, reacted with 1 equiv of ClSiMe to give the bicyclic compound 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 , and , have the potential to be used as unique building blocks for complex polysilane and polygermane frameworks.