Synthesis and Properties of the First Stable Germabenzene

The first stable germabenzene (1a) bearing an efficient steric protection group, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl, was successfully synthesized by the reaction of the corresponding chlorogermane (4) with lithium diisopropylamide in THF. The molecular structure and aromaticity of 1a were
discussed on the basis of its NMR, UV−vis, and Raman spectra, X-ray crystallographic analysis, and
theoretical calculations. All 1H and 13C NMR chemical shifts of the germabenzene ring of 1a were in good
agreement with those calculated. UV−vis and Raman spectra of 1a showed patterns similar to those of
benzene, suggesting the structural similarity between germabenzene and benzene. X-ray crystallographic
analysis of 1a revealed that the germabenzene ring was almost planar, indicating the delocalization of
π-electrons. Theoretical calculations (NICS(1) and ASEisom) also indicated the ring current effects and
aromatic stabilization of the germabenzene. While germabenzene 1a reacted as a Ge−C double-bond
compound (germene) with mesitonitrile oxide and 2,3-dimethyl-1,3-butadiene, 1a also reacted as a
1-germabuta-1,3-diene with C−C double- and triple-bond compounds. Furthermore, 1a reacted with water
and MeOH to give both 1, 2- and 1, 4-adducts.