Hyperpolarisation through reversible interactions with parahydrogen

Lloyd, Lyrelle S.; Asghar, Aziz; Burns, Michael J.; Charlton, Adrian; Coombes, Steven; Cowley, Michael J.; Dear, Gordon J.; Duckett, Simon B.; Genov, Georgi R.; Green, Gary G. R.; Highton, Louise A. R.; Hooper, Alexander J. J.; Khan, Majid; Khazal, Iman G.; Lewis, Richard. J.; Mewis, Ryan E.; Roberts, Andrew D.; Ruddlesden, Amy J.

Abstract

We describe here how the complexes Ir(COD)(NHC)Cl [NHC = IMes, SIMes, IPr, SIPr, ICy, IMe and ImMe2NPri2] provide significant insight into the catalytic process that underpins the hyperpolarization method signal amplification by reversible exchange (SABRE). These complexes react with pyridine and H2 to produce [Ir(H)2(NHC)(py)3]Cl which undergo ligand exchange on a timescale commensurate with good catalytic activity for the signal amplification by reversible exchange effect. This activity results from hydride ligand magnetic inequivalence and is highly dependent on the NHC. Variable temperature and kinetic studies demonstrate that rates of ligand loss which lie between 0.1 and 0.5 s−1 are ideal for catalysis. A role for the solvent complex [Ir(H)2(MeOH)(NHC)(py)2]Cl, which contains chemically inequivalent hydride ligands is revealed in the ligand exchange pathway. By optimisation of the conditions and NHC, a 5500-fold total pyridine signal enhancement is revealed when the NHC is IMes. Both T1-reduction effects and HD exchange with the solvent are probed and shown to link to catalyst efficiency. The resulting signal enhancements suggest future in vivo MRI measurements under physiological conditions using this catalytic effect will be possible.

Citation

Lloyd, L. S., Asghar, A., Burns, M. J., Charlton, A., Coombes, S., Cowley, M. J., …Ruddlesden, A. J. (2014). Hyperpolarisation through reversible interactions with parahydrogen. Catalysis science & technology, 4(10), 3544-3554. https://doi.org/10.1039/c4cy00464g

• Journal Article Type: Article
• Acceptance Date: Jul 11, 2014
• Online Publication Date: Jul 11, 2014
• Publication Date: Oct 1, 2014
• Deposit Date: Apr 9, 2019
• Journal: Catalysis Science and Technology
• Print ISSN: 2044-4753
• Electronic ISSN: 2044-4761
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 4
• Issue: 10
• Pages: 3544-3554
• DOI: https://doi.org/10.1039/c4cy00464g
• Public URL: https://hull-repository.worktribe.com/output/1563135
• Publisher URL: https://pubs.rsc.org/en/content/articlelanding/2014/cy/c4cy00464g
• Additional Information: : This document is CrossCheck deposited; : Supplementary Information; : The Royal Society of Chemistry has an exclusive publication licence for this journal; OPEN ACCESS: The accepted version of this article will be made freely available after a 12 month embargo period; : Received 11 April 2014; Accepted 11 July 2014; Accepted Manuscript published 11 July 2014; Advance Article published 4 August 2014; Version of Record published 8 September 2014