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

## TL;DR

Scientists created a new iridium complex that can switch its catalytic activity on and off through redox changes, improving the methylation of anilines with methanol.

## Contribution

The novelty lies in the redox-switchable NDI-NHC iridium complexes that enable controlled catalytic activity in aniline methylation.

## Key findings

- Iridium complexes outperform rhodium analogues in N-methylation of anilines via a borrowing-hydrogen pathway.
- Reduction of the NDI-NHC ligand reversibly deactivates the catalyst, demonstrating redox-switchable control.
- Imine reduction is identified as the rate-determining step, not methanol dehydrogenation.

## Abstract

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.