Germanium joins in

Following tin and silicon, the germanium analogues of carboranes add to the line up of group 14 boron compounds.

Credit: © 2009 Wiley

Carboranes are highly symmetric clusters of boron and carbon that can have a wide range of compositions and shapes. Icosahedral ortho-carborane was first made in 1963, by reacting decaborane with acetylene. Analogues of the carboranes, containing other group 14 elements (silicon, tin and so on), were harder to synthesize because the equivalent triply bonded compounds — to be used in place of acetylene — do not exist. So it took until 1990 and 2006, respectively, for the silicon and tin analogues to be synthesized.

Now, Lars Wesemann and colleagues from the University of Tübingen have bridged the gap between silicon and tin by making a germanium analogue, or digermaborane¹. They obtained a dimer of Ge₂B₁₀H₁₀ by reacting germanium dibromide with decaborane at room temperature. They separated the dimer by reductively cleaving the germanium–germanium bond with NaH, which resulted in a product that was relatively stable, much more so than the tin analogue.

The two germanium atoms are bonded to each other (ortho), and the product could not be isomerized to the para or meta isomers — that is, with germanium atoms only bonded to boron atoms — by heating to reflux in toluene. Similar to the other members of the family, alkylating the germaboranes was relatively straightforward using alkyl halides. As expected from similar compounds, the alkyl groups added to the germanium atoms in the cluster, rather than the boron atoms.