Iridium Cyclooctene Complex That Forms a HyperpolarizationTransfer Catalyst before Converting to a Binuclear C–H BondActivation Product Responsible for Hydrogen Isotope Exchange

摘要

[IrCl(COE)2]2 (>1) reacts with pyridine (py) and H2 to form crystallographically characterized IrCl(H)2(COE)(py)2 (>2). >2 undergoes py loss to form 16-electron IrCl(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)(μ-Cl)(μ-H)(κ-μ-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.