Catalytic Deuteration of Amines in Water (D ₂ O) With Ir, Ru, and Rh Pentamethylcyclopentadienyl Dioxime Complexes

A new family of pentamethylcyclopentadienyl (C ₅ Me ₅ , Cp*) iridium(III), rhodium(III), and ruthenium(III) complexes bearing bidentate 1,2‐dioxime ligands was developed as a promising platform for aqueous‐phase catalysis. A modular series of piano‐stool complexes of general formula [MX(η ⁵ ‐Cp*)(κ ² N ‐dioxime)] ⁺ (M = Ir, Rh, Ru; X = Cl, I) was obtained in excellent yields from inexpensive and readily available dioximes. Spectroscopic and crystallographic analyses showed that dioxime coordination strongly affects the acid–base behavior and water solubility of the complexes, while D ₂ O speciation studies revealed sequential deprotonation equilibria (pK _a1  ≈ 3.3; pK _a2  ≈ 6.5–7.1) and halide lability, highlighting the dynamic behavior of these systems under catalytic conditions. The catalytic performance of the complexes was evaluated in amine H/D exchange using D ₂ O as both solvent and deuterium source. Iridium derivatives, particularly [IrCp*X(κ ² N ‐nioxime)] ⁺ (X = Cl, I), achieved >95% deuterium incorporation in pyrrolidine under optimized conditions. Cyclic, acyclic, and benzylic amines underwent efficient isotopic exchange, including incorporation at positions remote from the nitrogen, demonstrating broad but substrate‐dependent reactivity. These results identify Cp*Ir‐dioxime complexes as effective proton‐responsive catalysts for H/D exchange in water, and 1,2‐dioxime ligands provide a useful and tunable framework for the development of aqueous isotope‐exchange catalysis.