Long-lived states to sustain SABRE hyperpolarised magnetisation

More than 4% net 1H-polarisation is created, in seconds, that is detectable for over 2 minutes.

For the 'flow' type experiments, we used 3 ml of sample volumes whilst maintaining the same relative concentrations.

General
Distilled water was employed where detailed. Brine refers to a saturated aqueous solution of NaCl. THF was freshly distilled from sodium and benzophenone ketyl or dried using a Grubbs solvent purification system. Petrol refers to the fraction of petroleum ether boiling in the range 40-60 C. All reactions were carried out under O 2 -free Ar or N 2 using oven-dried and/or flame-dried glassware.
Flash column chromatography was carried out using Fluka Chemie GmbH silica (220-440 mesh). Reverse-phase flash column chromatography was carried out using a Biotage Isolera with a SNAP-C 18 -12g cartridge eluting with H 2 O-MeCN containing 0.1% NH 4 OH. Thin layer chromatography was carried out using Merck F 254 aluminium-backed silica plates. 1 H (400 MHz) and 13 C (100.6 MHz) NMR spectra were recorded on a Bruker-400 instrument with an internal deuterium lock. Chemical shifts are quoted as parts per million and referenced to CHCl 3 ( H 7.27), (CH 3 ) 2 SO ( H 2.54), CDCl 3 ( C 77.0) or (CD 3 ) 2 SO ( C 40.45). 13 C NMR spectra were recorded with broadband proton decoupling. 13 C NMR spectra were assigned using DEPT experiments. Coupling constants (J) are quoted in Hertz. Electrospray high and low resolution mass spectra were recorded on a Bruker Daltronics microOTOF spectrometer.

Figure S4: (a) Full scale 1 H NMR spectra of 3 after SABRE at 65 G; (b) SABRE-LLS detection after 1 s of spin-lock; (c) thermally realised NMR spectrum. Spectra include resonances from IMes, COD and hydride sites. Inset figures show magnified resonances for the two substrate spins in each cases.
The Fig. S2, S3 and S4 display identical measurements in the three substrates. Enhancement factors are reported in the next section.

Effect of polarisation transfer field on SABRE enhancements
Field dependence studies of the level of SABRE were completed in an automated 'flow' system, which permits repeated hyperpolarisation of samples at a constant and accurate field. The fields were varied from 0 to 150 G in increments of 10 G. The 'flow' system offers highly stable experimental condition both inside and outside of the NMR magnet and hence the results obtained are highly reproducible.
The corresponding values are detailed pictorially in Fig. S5, S6 and S7 for the three substrates in two different concentrations.