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

Abstract

Treatment of alkynyl–arylchlorogermanes Aryl_nGe(Cl)(CC–^tBu)_3−n (n = 1, 2) with HM^tBu₂ (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 HGa^tBu₂. 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 HAl^tBu₂ resulted in hydroalumination of one alkynyl group and formation of unprecedented Ge–H functionalized germanes, Aryl–Ge(H)(CC–^tBu)[C(Al^tBu₂)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(CC–^tBu)[C(Al^tBu₂}C(H)–^tBu] reacted in an unusual Cl/^tBu exchange to yield the tert-butylgermane Ph(^tBu)Ge(CC–^tBu)[C{Al(^tBu)(Cl)}C(H)–^tBu]. Quantum chemical calculations suggested the formation of a germyl cation as a transient intermediate.