Mechanochemical access to NDI-bridged Janus di-NHC complexes for light-driven redox-responsive catalysis

We describe the mechanochemical synthesis of previously inaccessible NDI-bridged Janus di-N-heterocyclic carbene (di-NHC) rhodium and iridium binuclear complexes, overcoming oxidative degradation pathways associated with conventional solution-based methods. These systems exhibit strong electronic communication between the redox-active naphthalene diimide (NDI) core and the metal centers, enabling reversible access to three distinct electronic states, as supported by spectroscopic, electrochemical, and DFT studies. The rigid, electron-deficient NDI scaffold enforces well-defined metal–metal arrangements and imparts multistate electronic tunability, highlighting their potential as versatile platforms for redox-responsive catalysis and functional metallosupramolecular assemblies. The complexes undergo selective one-electron reduction either with cobaltocene or via visible-light irradiation in the presence of triethylamine, which acts as an efficient reductive quencher. Under these conditions, NEt3 delivers catalytic performance comparable to that of cobaltocene in the activation of the NDI-di-NHC-di-iridium(i) system for the cycloisomerization of 4-pentynoic acid, while offering practical advantages such as lower cost, air stability, and milder, more controlled reactivity.