Functionalized alkynyl-chlorogermanes: Hydrometallation, Ge-Cl bond activation, Ge-H bond formation and chlorine-tert-butyl exchange via a transient germyl cation

Honacker C., Qu Z., Tannert J., Layh M., Hepp A., Grimme S., Uhl W.

Abstract

Treatment of alkynyl-arylchlorogermanes ArylnGe(Cl)(C≡C-tBu)3-n (n = 1, 2) with HMtBu2 (M = Al, Ga) yielded mixed Al or Ga alkenyl-alkynylchlorogermanes via hydrometallation reactions. Intramolecular interactions between the Lewis-basic Cl atoms and the Lewis-acidic Al or Ga atoms afforded MCGeCl heterocycles. The endocyclic M-Cl distances were significantly lengthened compared to the starting compounds and indicated Ge-Cl bond activation. Dual hydrometallation succeeded only with HGatBu2. One Ga atom of the product was involved in a Ga-Cl bond, while the second one had an interaction to a C-H bond of a phenyl group. In two cases treatment of chlorogermanes with two equivalents of HAltBu2 resulted in hydroalumination of one alkynyl group and formation of unprecedented Ge-H functionalized germanes, Aryl-Ge(H)(C≡C-tBu)[C(AltBu2)=C(H)-tBu] (Aryl = mesityl, triisopropylphenyl). The Al atoms of these compounds interacted with the α-C atoms of the alkynyl groups. Ph(Cl)Ge(C≡C-tBu)[C(AltBu2}=C(H)-tBu] reacted in an unusual Cl/tBu exchange to yield the tert-butylgermane Ph(tBu)Ge(C≡C-tBu)[C{Al(tBu)(Cl)}=C(H)-tBu]. Quantum chemical calculations suggested the formation of a germyl cation as a transient intermediate.