Unveiling the full reaction path of the Suzuki-Miyaura cross-coupling in a single-molecule junction.

Conventional analytic techniques that measure ensemble averages and static disorder provide essential knowledge of the reaction mechanisms of organic and organometallic reactions. However, single-molecule junctions enable the in situ, label-free and non-destructive sensing of molecular reaction processes at the single-event level with an excellent temporal resolution. Here we deciphered the mechanism of Pd-catalysed Suzuki–Miyaura coupling by means of a high-resolution single-molecule platform. Through molecular engineering, we covalently integrated a single molecule Pd catalyst into nanogapped graphene point electrodes. We detected sequential electrical signals that originated from oxidative addition/ligand exchange, pretransmetallation, transmetallation and reductive elimination in a periodic pattern. Our analysis shows that the transmetallation is the rate-determining step of the catalytic cycle and clarifies the controversial transmetallation mechanism. Furthermore, we determined the kinetic and thermodynamic constants of each elementary step and the overall catalytic timescale of this Suzuki–Miyaura coupling. Our work establishes the single-molecule platform as a detection technology for catalytic organochemistry that can monitor transition-metal-catalysed reactions in real time. Although conventional analytical techniques can measure ensemble averages, single-molecule junctions can sense molecular reaction processes at the single-event level. The integration of a single-molecule Pd catalyst into a gapped graphene junction enables the electrical detection of a full catalytic cycle of the Suzuki–Miyaura coupling and clarifies the controversial transmetallation mechanism.