Carbon–boron triple bond formed for the first time in a neutral novel molecule

Researchers have synthesised a triple bond between carbon and boron for the first time. This discovery could help chemists better understand chemical bonds and inspire other researchers to synthesise compounds that might seem improbable.

There are four elements on the periodic table that can form triple bonds due to their shared chemistry – boron, carbon, nitrogen and oxygen. There are confirmed triple bonds between all possible combinations of the four elements such as carbon monoxide, as well as homonuclear molecules such as nitrogen gas, but there has yet to be a stable triple bond between carbon and boron despite a diverse range of compounds containing B=C double bonds.

Chemists from Julius-Maximilians-Universität (JMU), Germany have now succeeded in synthesising a molecule with a boron-carbon triple bond, which they coined boryne, that is an orange solid at room temperature – as an uncoordinated neutral molecule. They began with a brominated boron compound stabilised using carbon-containing ligands, which they then reduced and stabilised, finding the right balance of steric and electronic factors to allow for the isolation of boryne as a metastable species. The researchers then carried out preliminary characterisation and initial reactivity studies of the new molecule to establish its chemical properties.

The molecule has the boron atom in a linear arrangement between two carbon atoms, one of which it shares a triple bond with. Boron is only bonded to two atoms leading to a strong electron deficiency as well as angular strain in the C–B–C unit, meaning a very special set of conditions is required to make it, which explains why it’s taken so long for scientists to create the molecule. The team conducted quantum calculations to gain further insight into the electronic structure of boryne and results were in good agreement with experimental data – the bonding is consistent with a true triple bond (one σ and two π bonds). The compound was also found to react in various ways including rearranging upon heating, binding to CO and forming a complex with copper.

The new molecule demonstrated interesting reactivity, so the team are now concentrating their efforts on exploring this. They hope that further research could lead to new chemical synthesis tools advancing understanding of chemical bonding theory.