Germanium gets chiral

Like carbon and silicon, germanium’s lighter brethren on the periodic table, the metalloid can bond to four different groups, forming a chiral, tetrahedral molecule. Researchers at Nankai University led by Qi-Lin Zhou have devised a way to make these rare germanium compounds, reporting dozens of molecules with stereocenters of that element (J. Am. Chem. Soc. 2024, DOI: 10.1021/jacs.3c14386).

Although Zhou’s group prepared a variety of heteroatom chiral compounds in the past, including those of silicon, phosphorus, and boron, chiral germanium compounds have remained elusive; just one example had ever been reported. So “curiosity was our main driving force,” Zhou says.

Germanium’s slipperiness can be partly attributed to its larger size and empty 3d orbitals, which have a penchant to bond to five or six groups rather than the four found at tetrahedral stereocenters. Also, because germanium’s bonds with organic groups are often weaker than lighter heteroatoms’, the groups are more likely to pop off and on in solution, scrambling their arrangement and making it hard to capture a set stereochemistry.

To make the new compounds, the researchers designed a chiral rhodium-based catalyst and used it to react a carbene with a germanium molecule sporting two germanium-hydrogen bonds. At room temperature and pressure, the carbene inserted itself into one of the Ge–H bonds, creating a new chiral compound.

The researchers used the reaction to prepare dozens of different molecules. By simply lengthening the reaction time, the researchers scaled up the preparation of one compound from tens of milligrams to more than a gram. They also managed to further react the remaining Ge–H bond in that compound without disrupting the compound’s stereochemistry.

The researchers plan to fully investigate the properties of these chiral germanium compounds, Zhou says. The metalloid has semiconducting properties, which makes him hopeful that its compounds could lead to novel materials for semiconductor or electronic applications, he says.