Harnessing asymmetric N-heterocyclic carbene ligands to optimise SABRE hyperpolarisation.

The catalytic signal amplification by reversible exchange process has become widely used for the hyperpolarisation of small molecules to improve their magnetic resonance detectability. It harnesses the latent polarisation of hydrogen, and involves the formation of a labile metal complex that often contains an N-heterocyclic carbene (NHC) ligand ( [Ir(H)(NHC)(pyridine)]Cl), which act as a polarisation transfer catalyst. Unfortunately, if the target molecule is too bulky, binding to the catalyst is poor and the hyperpolarisation yield is therefore low.