The reaction of an iridium PNP complex with parahydrogen facilitates polarisation transfer without chemical change

Abstract

The pincer complex [(C5H3N(CH2P(tBu)2)2)Ir(H)2(py)]BF4 is shown to be active for signal amplification by reversible exchange.

Achieving High 1H Nuclear Hyperpolarization Levels with Long Lifetimes in a Range of Tuberculosis Drug Scaffolds

“…In order to improve on the hyperpolarization level, a series of deuterated derivatives of 1 and 3 were prepared by the palladium‐catalysed reduction of the corresponding heteroaryl chlorides under D 2 , followed by transesterification or amidation as shown in Scheme . Full synthetic procedures and characterization data are presented in the Supporting Information.…”

Signal Amplification by Reversible Exchange (SABRE): From Discovery to Diagnosis

“…Likewise,i ft hese interactions are too weak, then the active SABRE catalyst can become unstable,l eading to rapid depletion of p-H 2, [14] inefficient polarization transfer, [13c] or, at worst, the catalystsd ecomposition. If these binding interactions are too strong and become irreversible,t hen efficient polarization is suppressed as the necessary p-H 2 addition is stopped.…”

“…[18] Despite there being over 10 commercially available NHC ligands for the SABRE polarization of pyridine, [18,19] to date [IrCl(COD)(IMes)] remains the most impressive mediator of polarization transfer.T his optimum activity is common across ar ange of heterocyclic motifs, although rare examples exist for which this is not the case. [22] Other SABRE catalysts have been shown to undergo such non-hydrogenative transfer of polarization including the bidentate NHC-phenolate (1), [23] an iridium PNP-pincer (2), [14] and an iridium cyclooctene complex (3) [24] shown in Figure 2. [19] This reflects the complexity of the SABRE transfer step,although recently the p-accepting ability parameter [21] has been shown to offer better insight into how the NHC ligand influences the rate of pyridine exchange.…”

“…If these binding interactions are too strong and become irreversible,t hen efficient polarization is suppressed as the necessary p-H 2 addition is stopped. Likewise,i ft hese interactions are too weak, then the active SABRE catalyst can become unstable,l eading to rapid depletion of p-H 2, [14] inefficient polarization transfer, [13c] or, at worst, the catalystsd ecomposition. As such, the development of metal complexes that mediate reversible exchange on an appropriate timescale has received much attention.…”

“…[19] This reflects the complexity of the SABRE transfer step,although recently the p-accepting ability parameter [21] has been shown to offer better insight into how the NHC ligand influences the rate of pyridine exchange. [22] Other SABRE catalysts have been shown to undergo such non-hydrogenative transfer of polarization including the bidentate NHC-phenolate (1), [23] an iridium PNP-pincer (2), [14] and an iridium cyclooctene complex (3) [24] shown in Figure 2. However,signal gains were reduced when compared to [IrCl(COD)(IMes)].…”