Synthesis and Characteristics of Iridium Complexes Bearing N-Heterocyclic Nitrenium Cationic Ligands

N-Heterocyclic nitrenium cations are isostructural and isoelectronic analogues of the ubiquitous N-heterocyclic carbene. We present the first examples of coordination of nitrenium ions to the Ir(I) and Ir(III) metal centers. This work includes rare complexes with cation-cation interactions between a positively charged ligand and an iridium ion. These species represent the first example of iridium complexes bearing any cationic ligand of group 15 elements analogous to the Arduengo carbene. These nitrenium-based monocationic and even dicationic Ir(I) complexes can smoothly oxidatively activate H₂ at room temperature and ambient pressure. Utilizing our system, we were able to observe an Ir-dihydrogen σ-complex, which undergoes oxidative addition to yield a well-defined Ir(III) dihydride. Comparative studies of the analogous Rh(I)-nitrenium species, which exhibit reversible dihydrogen activation, are presented. New Ir complexes were fully characterized by multinuclear nuclear magnetic resonance (including ¹⁵N labeling) and X-ray crystallography.