Solvent responsive catalyst improves NMR sensitivity via efficient magnetisation transfer

TY - JOUR

T1 - Solvent responsive catalyst improves NMR sensitivity via efficient magnetisation transfer

AU - Duckett, Simon

AU - Ruddlesden, Amy Jane

N1 - © The Royal Society of Chemistry 2016. This is an author-produced version of the published paper. Uploaded in accordance with the publisher’s self-archiving policy. Further copying may not be permitted; contact the publisher for details

PY - 2016/6/2

Y1 - 2016/6/2

N2 - 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 1H 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.

AB - 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 1H 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.

U2 - 10.1039/C6CC03185D

DO - 10.1039/C6CC03185D

M3 - Article

SN - 1359-7345

JO - Chemical communications

JF - Chemical communications

ER -