Solvent responsive catalyst improves NMR sensitivity via efficient magnetisation transfer† †Electronic supplementary information (ESI) available: Experimental details; synthesis and characterisation of compounds, SABRE experiments, kinetic data, activation parameters, UV-vis data. The underlying research data for this paper is available in accordance with EPSRC open data policy from DOI: 10.15124/cdaf969f-ba47-401e-876b-512c0cece55c. See DOI: 10.1039/c6cc03185d Click here for additional data file.

A bidentate iridium carbene complex, Ir(κC,O-L1)(COD), has been synthesised which contains a strongly electron donating carbene ligand that is functionalised by a cis-spanning phenolate group. This complex acts as a precursor to effective magnetisation transfer catalysts which form after reaction with H2 and a suitable two electron donor. In solvents such as benzene, containing pyridine, they are exemplified by neutral, chiral Ir(H)2(κC,O-L1)(py)2 with inequivalent hydride ligands and Ir-O bond retention, whilst in methanol, Ir-O bond cleavage leads to zwitterionic [Ir(H)2(κC,O(-)-L1)(py)3](+), with chemically equivalent hydride ligands. The active catalyst's form is therefore solvent dependent. Both these complexes break the magnetic symmetry of the hydride ligands and are active in the catalytic transfer of polarisation from parahydrogen to a loosely bound ligand. Test results on pyridine, nicotinaldehyde and nicotine reveal up to ≈1.2% single spin proton polarisation levels in their (1)H NMR signals which compare to the normal 0.003% level at 9.4 Tesla. These results exemplify how rational catalyst design yields a solvent dependent catalyst with good SABRE activity.