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.