Iridium(III) Hydrido N-Heterocyclic Carbene–Phosphine Complexes as Catalysts in Magnetization Transfer Reactions

• DOI: 10.1021/ic401783c
• Publication Date: 2013-11-11T15:45:13Z
• Authors: Marianna Fekete; Oliver Bayfield; Simon B. Duckett; Sam Hart; Ryan E. Mewis; Natalie Pridmore; Peter J. Rayner; Adrian Whitwood
• Keywords: IMes; Transfer hydrogenation

The hyperpolarization (HP) method signal amplification by reversible exchange (SABRE) uses para-hydrogen to sensitize substrate detection NMR. catalyst systems [Ir(H)2(IMes)(MeCN)2(R)]BF4 and [Ir(H)2(IMes)(py)2(R)]BF4 [py = pyridine; R PCy3 or PPh3; IMes 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene], which contain both an electron-donating N-heterocyclic carbene a phosphine, are used here catalyze SABRE. They react with acetonitrile pyridine produce [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4 [Ir(H)2(NCMe)(py)(IMes)(PCy3)]BF4, complexes that undergo ligand on time scale commensurate observation of the SABRE effect, is illustrated HP. In this study, required symmetry breaking underpins provided for use chemical inequivalence rather than previously reported magnetic inequivalence. As consequence, we show sphere polarization transfer itself becomes hyperpolarized hence high-sensitivity number reaction intermediates possible. These species include [Ir(H)2(NCMe)(py)(IMes)(PPh3)]BF4, [Ir(H)2(MeOH)(py)(IMes)(PPh3)]BF4, [Ir(H)2(NCMe)(py)2(PPh3)]BF4. Studies also described employ deuterium-labeled substrates CD3CN C5D5N, labeled ligands P(C6D5)3 IMes-d22, demonstrate dramatically improved levels HP can be achieved as consequence reducing proton dilution wastage. By combination these studies experiments in field experienced sample at point varied, confirmation resonance assignments achieved. Furthermore, when [Ir(H)2(pyridine-h5)(pyridine-d5)(IMes)(PPh3)]BF4 examined, its hydride signals shown become visible through para-hydrogen-induced