Issue 7, 2015

Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen

Abstract

The reaction of [Ir(IMes)(COD)Cl], [IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene, COD = 1,5-cyclooctadiene] with pyridazine (pdz) and phthalazine (phth) results in the formation of [Ir(COD)(IMes)(pdz)]Cl and [Ir(COD)(IMes)(phth)]Cl. These two complexes are shown by nuclear magnetic resonance (NMR) studies to undergo a haptotropic shift which interchanges pairs of protons within the bound ligands. When these complexes are exposed to hydrogen, they react to form [Ir(H)2(COD)(IMes)(pdz)]Cl and [Ir(H)2(COD)(IMes)(phth)]Cl, respectively, which ultimately convert to [Ir(H)2(IMes)(pdz)3]Cl and [Ir(H)2(IMes)(phth)3]Cl, as the COD is hydrogenated to form cyclooctane. These two dihydride complexes are shown, by NMR, to undergo both full N-heterocycle dissociation and a haptotropic shift, the rates of which are affected by both steric interactions and free ligand pKa values. The use of these complexes as catalysts in the transfer of polarisation from para-hydrogen to pyridazine and phthalazine via signal amplification by reversible exchange (SABRE) is explored. The possible future use of drugs which contain pyridazine and phthalazine motifs as in vivo or clinical magnetic resonance imaging probes is demonstrated; a range of NMR and phantom-based MRI measurements are reported.

Graphical abstract: Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen

Supplementary files

Article information

Article type
Edge Article
Submitted
02 Mar 2015
Accepted
27 Apr 2015
First published
28 Apr 2015
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2015,6, 3981-3993

Author version available

Investigating pyridazine and phthalazine exchange in a series of iridium complexes in order to define their role in the catalytic transfer of magnetisation from para-hydrogen

K. M. Appleby, R. E. Mewis, A. M. Olaru, G. G. R. Green, I. J. S. Fairlamb and S. B. Duckett, Chem. Sci., 2015, 6, 3981 DOI: 10.1039/C5SC00756A

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