Synthesis of Zintl Triads Comprising Extended Conjugated π-Electronic Systems: [RGe₉–CH═CH–CH═CH–Ge₉R]^4– (R = −CH═CH₂, −C(CH₃)═CH–CH═N(CH₂)₂NH₂)

Abstract

Triads with extended conjugated π-electronic systems between polyhedral cage molecules possess promising electronic properties. In contrast to the known fullerene-bridge-fullerene triads, fewer synthetic procedures are known for the related homoatomic deltahedral cage molecules of the heavier homologues of carbon. The synthesis of the organo-Zintl triads [RGe₉-CH═CH-CH═CH-Ge₉R]^4- with R = -CH═CH₂ (R₁), -C(CH₃)═CH-CH═N(CH₂)₂NH₂ ((2Z,4E)-7-amino-5-azahepta-2,4-dien-2-yl) (R₂) is reported, in which the deltahedral Ge₉ cages carry an additional functional group, allowing for further connections. Both anionic cage entities bear a butadiene-1,4-diyl bridge which is formed by reacting the Zintl ion [Ge₉]^4- with 1,4-bis(trimethylsilyl)butadiyne in ethylenediamine. The organic tethers can be attached by nucleophilic attack of the Ge₉ clusters at the bis(trimethylsilyl)acetylene and (3Z/3E)-7-amino-1-(trimethylsilyl)-5-azahepta-3-en-1-yne, respectively, in ethylenediamine, and the products cis/trans-[R₁Ge₉-CH═CH-CH═CH-Ge₉R₁]^4- and cis/cis-[R₂Ge₉-CH═CH-CH═CH-Ge₉R₂]^4- have been isolated as [A(2,2,2-crypt)]⁺ salts with A = K, Rb, respectively. Crystals containing the novel anions [RGe₉-CH═CH-CH═CH-Ge₉R]^4- have been structurally characterized by X-ray diffraction methods, and the compounds have been investigated by ¹H and ¹³C NMR as well as by Raman spectroscopy. The cis/cis configurational isomer of [R₁Ge₉-CH═CH-CH═CH-Ge₉R₁]^4- was characterized by means of NMR spectroscopy. Via in situ NMR measurements, we shed some light on the formation of the Zintl triads [RGe₉-CH═CH-CH═CH-Ge₉R]^4- bearing supplemental organic tethers.