Syntheses, Structures, and Reactions of Heptacoordinate Trihalogermanes Bearing a Triarylmethyl-Type Tetradentate Ligand

Trichloro[tris(3-tert-butyl-6-methoxyphenyl)methyl]germane (3), containing a tetradentate ligand with
three methoxy groups as coordinating sites, was synthesized by the reaction of the corresponding
(triarylmethyl)lithium species with tetrachlorogermane. In contrast to the case for the previously reported
trichlorosilane analogue, 3 slowly decomposed during column chromatography on silica gel, although it
was quite stable against moisture. The corresponding trifluoro-, tribromo-, and triiodogermanes 4−6
were prepared from the trichlorogermane 3. X-ray crystallographic analyses of 3−6 showed heptacoordinate
structures with interatomic distances between the oxygen atom and the central germanium atom shorter
than the sum of van der Waals radii. By systematic comparisons of these intramolecular interactions
based on the interatomic distances, it was found that they strongly depend on the Lewis acidity of the
trihalogenated germanium atom. An Atoms-in-Molecules (AIM) analysis of the model compound 4‘, in
which three tert-butyl groups of trifluorogermane 4 were omitted, showed the existence of weak and
ionic bonding between oxygen and germanium atoms. Reactions of these trihalogermanes with aqueous
NaOH, LiAlH4, and BX3 were also investigated. Alkaline hydrolysis of trihalogermanes resulted in the
cleavage of the carbon−germanium bond. LiAlH4 also caused the same kind of bond cleavage, together
with nucleophilic attack on the germanium atom, giving the trihydrogermane 8. Reaction of the
trihalogermanes with trihaloboranes was found to be an efficient procedure to give other trihalogermanes
through a halogen exchange reaction.