Targeted attachment of functional groups at Ge₉ clusters via silylation reactions

Molecules with low-valent Ge atoms are generally synthesized from organohalogen germanes as precursors. The Zintl phase K₄Ge₉ provides reactive building blocks for a targeted synthesis of germanium-rich molecules. The silylation of Ge9 clusters with chlorosilanes ClSiR₂R', that carry unsaturated olefin groups R' leads to the introduction of olefinic side chains of variable lengths allowing for further reactions. The compounds K[Ge₉{Si(SiMe₃)₃}₂(SiPh₂R')] (R' = -CH[double bond, length as m-dash]CH₂ (1); -(CH₂)₃CH[double bond, length as m-dash]CH₂ (2)) carry one such functionality, whereas K[Ge₉(SiPh₂R')₃] (3 and 4) offer the possibility for an interconnection of clusters due to three functional groups on the Ge₉ core. XPS measurements show that the silylated clusters are much more air-stable than the unsubstituted, bare cluster units.