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.