To initiate the hydrogenation reaction, the NMR tube was heated in a hot water bath at 80°C for 30 s which melted the sample and raised the internal pressure to 9.6 bar, then shaken vigorously for 10 s. The NMR tube was opened to release the parahydrogen pressure and immediately placed in a magnetic shield (Aspect Imaging, Shoham, Israel) for the application of a magnetic field cycle. Magnetic fields were applied using a solenoid coil controlled by a Keysight Technologies 33220A 20 MHz waveform generator (Keysight Technologies, Santa Rosa, U.S.). The field was initially set at 1.5 mT, dropped to 50 nT in less than 1 ms, then increased adiabatically to 3.7 µT in 4 s (see Fig. ). The sample was then removed from the shield for NMR experiments.