Bis(2,4,6-tri-tert-butylphenyl)germylene Reinvestigated: Crystal Structure, Lewis Acid Catalyzed C−H Insertion, and Oxidation to an Unstable Germanone

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Abstract

Bis(2,4,6-tri-tert-butylphenyl)germylene (1), which had been reported to undergo an insertion of the germanium atom into a C−H bond of an o-tert-butyl group at room temperature, was found to be quite stable. Such a C−H insertion does occur in solution, forming germaindane 2, but only in the presence of a Lewis acid such as the starting material GeCl2. 1 can be stored unchanged at −30 °C for months; at 20 °C it decomposes within several weeks under release of 1,3,5-tri-tert-butylbenzene. Compound 1 was characterized by X-ray diffraction methods. The X-ray structure of 1 shows that the two aryl ligands have very different geometries: one aryl group is greatly distorted to give a “boat” form and the Ge atom is remote from any of the ring planes, while the second aryl group is only slightly deformed and the Ge atom lies in the ring plane. UV/vis spectra exhibit an intense absorption at 430 nm in solution and at 405 nm in the solid state, which represents an enormous hypsochromic shift compared to other germylenes with bulky aryl ligands. Oxidation of 1 with trimethylamine N-oxide leads to a germanone, which rearranges very rapidly by a C−H insertion process yielding the germaindanol 3.

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