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 dilsopropylamide in THF. The molecular structure and aromaticity of la were discussed on the basis of its NMR, UV-vis, and Raman spectra, X-ray crystallographic analysis, and theoretical calculations. All H-1 and C-13 NMR chemical shifts of the germabenzene ring of la were in good agreement with those calculated. UV-vis and Raman spectra of la showed patterns similar to those of benzene, suggesting the structural similarity between germabenzene and benzene. X-ray crystallographic analysis of la revealed that the germabenzene ring was almost planar, indicating the delocalization of pi-electrons. Theoretical calculations (NICS(1) and ASE(isom)) also indicated the ring current effects and aromatic stabilization of the germabenzene. While germabenzene la 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, la reacted with water and MeOH to give both 1, 2- and 1, 4-adducts.