Iridium and Ruthenium Complexes bearing Uracil-based N-heterocyclic Carbenes: Synthesis and Catalytic Activity in the Reduction of NAD +

The synthesis of iridium and ruthenium complexes bearing uracil-derived N-heterocyclic carbene (NHC) ligands is reported. The synthesis employs different synthetic pathways, yielding both abnormal (C5-bound) and normal (C2-bound) NHC isomers, with iridium demonstrating a strong preference for the abnormal coordination mode. The catalytic performance of these complexes was evaluated for the reduction of NAD + to NADH using formic acid as a proton source. The results show that the iridium complexes significantly outperform their ruthenium analogues. While the ruthenium complexes are largely inactive and show signs of instability, the iridium catalysts lead to higher turnover frequencies. These findings establish uracilbased iridium NHCs as effective organometallic catalysts for the selective reduction of NAD + .