Stable Germenolates and Germenes with Exocyclic Structures

The first germenolates with exocyclic structures [(Me₃Si)₂Ge­(Si₂Me₄)₂GeC­(R)­O]⁻K⁺ (<b>5a</b>: R = Mes; <b>5b</b>: <i>o</i>-Tol; <b>5c</b>: 1-Ad) were synthesized by the reaction of the corresponding cyclic acylgermanes with KO<i>t</i>Bu. <b>5a</b>–<b>c</b> could be isolated by crystallization. The remarkable thermal stability of <b>5a</b>–<b>c</b> even at room temperature allowed full characterization by NMR and UV–vis spectroscopy and by single-crystal X-ray crystallography. Spectroscopic and structural features in combination with DFT quantum mechanical calculations indicated that <b>5a</b>–<b>c</b> are best described as acyl germyl anions in solution and in the solid state as well. The reactivity of <b>5a</b>–<b>c</b> versus chlorosilanes parallels that observed for the structurally related silenolates. The aryl-substituted compounds <b>5a</b>,<b>b</b>, thus, reacted with ClSiMe₃ to give the exocyclic germenes (Me₃Si)₂Ge­(Si₂Me₄)₂GeC­(OSiMe₃)­R (<b>6a</b>: R = Mes; <b>6b</b>: <i>o</i>-Tol), while the alkyl-substituted species <b>5c</b> afforded the Ge-silylated cyclic acylgermane. TDDFT calculations were used to assign the UV–vis absorption spectra and to gain more insight into the electronic nature of <b>5a</b>–<b>c</b> and <b>6a</b>.