Iridium Cyclooctene Complex That Forms a Hyperpolarization Transfer Catalyst before Converting to a Binuclear C-H Bond Activation Product Responsible for Hydrogen Isotope Exchange

[IrCl(COE)(2)](2) (1) reacts with pyridine (py) and H-2 to form crystallographically characterized IrCl(H)(2)(COE)(py)(2) (2). 2 undergoes py loss to form 16 electron IrCI(H)(2)(COE)(py) (3), with equivalent hydride ligands. When this reaction is studied with parahydrogen, 1 efficiently achieves hyperpolarization of free py (and nicotinamide, nicotine, 5-aminopyrimidine, and 3,5-lutudine) via signal amplification by reversible exchange (SABRE) and hence reflects a simple and readily available precatayst for this process. 2 reacts further over 48 h at 298 K to form crystallographically characterized (Cl) (H) (py)(mu-Cl)(mu-H)(kappa-mu-NC5H4)Ir(H)(py)(2) (4). This dimer is active in the hydrogen isotope exchange process that is used in radiopharmaceutical preparations. Furthermore, while [Ir(H)(2)(COE)(py)(3)]PF6 (6) forms upon the addition of AgPF6 to 2, its stability precludes its efficient involvement in SABRE.