Summary
A Nature study reports a rhodium-catalysed method that inserts a carbon atom into biphenylene frameworks to form spirocyclic structures. The approach activates carbon–carbon single bonds and uses N-isocyanoiminophosphorane as a carbon-atom equivalent.
A rhodium-catalysed reaction can insert a carbon atom into carbon–carbon single bonds in biphenylene compounds, producing spirocyclic molecules, according to research published in Nature on 14 October 2026. The study uses N-isocyanoiminophosphorane, or PINC, as an atomic carbon equivalent and reports formation of four new carbon–carbon bonds at the resulting spiro centre.
In a spirocyclic molecule, two rings share one carbon atom. Their ring structures sit in an orthogonal arrangement, giving the molecule a rigid three-dimensional shape. These frameworks occur in natural products and are also used in the design of optoelectronic and hole-transport materials and ligands for coordination complexes.
Inserting a carbon atom into single bonds
Carbon-atom-transfer reactions have generally made use of the reactivity of π bonds, found in double and triple bonds. By contrast, controlled insertion of a carbon atom into a carbon–carbon σ bond—a single bond—has been difficult. The reported method addresses that challenge by using rhodium catalysis to activate bonds in biphenylene substrates in sequence, then build the spiro structure around the transferred carbon atom.
PINC serves as the source of that carbon in the reaction; the description identifies it as an atomic carbon equivalent. The result is a way to join molecular components through a newly formed shared carbon centre, rather than relying only on transformations at π bonds.
The researchers report both homo- and cross-spirofusion of biphenylenes. They also describe extending the approach to reactions that combine σ- and π-bond activation. Together, these reaction types broaden the reported method beyond a single route to spirocyclic structures.
The work establishes a synthetic strategy for constructing complex molecular frameworks through carbon–carbon σ-bond activation. Its significance is methodological: spirocyclic motifs are useful across several areas of chemistry and materials design, and the study adds a way to assemble them using a transferred carbon atom as the central link. The Nature page identifies this as an early version of peer-reviewed, accepted research that may receive further edits before the final Version of Record.