Utilisation of water soluble iridium catalysts for signal amplification by reversible exchange

Abstract

The catalytic hyperpolarisation of pyridine, 3-hydroxypyridine and oxazole by the Signal Amplification By Reversible Exchange (SABRE) process is achieved by a series of water soluble iridium phosphine and N-heterocyclic carbene dihydride complexes. While the efficiency of the SABRE process in methanol-d₄ solution or ethanol-d₆ solution is high, with over 400-fold ¹H polarisation of pyridine being produced by [Ir(H)₂(NCMe)(py)(IMes)(monosulfonated-triphenylphosphine)]BF₄, changing to a D₂O or a D₂O–ethanol solvent mixture leads to dramatically reduced activity which is rationalised in terms of low H₂ solubility.