Stable Germenolates and Germenes with Exocyclic Structures

The first germenolates with exocyclic structures [(Me3Si)2Ge­(Si2Me4)2GeC­(R)­O]−K+ (5a: R = Mes; 5b: o-Tol; 5c: 1-Ad) were synthesized by the reaction of the corresponding cyclic acylgermanes with KOtBu. 5a–c could be isolated by crystallization. The remarkable thermal stability of 5a–c 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 5a–c are best described as acyl germyl anions in solution and in the solid state as well. The reactivity of 5a–c versus chlorosilanes parallels that observed for the structurally related silenolates. The aryl-substituted compounds 5a,b, thus, reacted with ClSiMe3 to give the exocyclic germenes (Me3Si)2Ge­(Si2Me4)2GeC­(OSiMe3)­R (6a: R = Mes; 6b: o-Tol), while the alkyl-substituted species 5c 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 5a–c and 6a.