Redox-Switchable Naphthalenediimide–NHC Iridium Complexes for Switchable Catalysis in Aniline Methylation with Methanol

We report the synthesis and characterization of rhodium and iridium complexes featuring a naphthalene-diimide (NDI)-functionalized N-heterocyclic carbene (NHC) ligand, in which the NDI unit is directly attached through an imide nitrogen. Electrochemical and spectroelectrochemical studies reveal that one- and two-electron reductions of the NDI moiety moderately enhance the electron-donating ability of the ligand, albeit to a lesser extent than in analogues where the NDI is fused to the carbene backbone. Catalytic investigations demonstrate that the iridium complexes efficiently promote the N-methylation of anilines with methanol via a borrowing-hydrogen pathway, outperforming the rhodium analogue. One-electron reduction of the NDI-NHC ligand leads to reversible deactivation of the catalyst, providing direct evidence for redox-switchable control of catalytic activity. Kinetic analyses and substrate studies indicate that imine reduction, rather than methanol dehydrogenation, constitutes the rate-determining step. These findings highlight NDI-NHC ligands as versatile redox-responsive platforms for fine-tuning electronic properties and catalytic performance in hydrgen-borrowing transformations.