In situ photochemistry on a benchtop NMR spectrometer with pH2 hyperpolarisation

High-resolution benchtop NMR spectrometers are uniquely suited for reaction monitoring applications, owing to their portability and accessibility, but the low inherent sensitivity of the approach can limit the observation of low-concentration transient species. In this work, a hyperpolarisation technique called parahydrogen induced polarisation (PHIP) was employed to overcome this limitation and observe both thermal and photochemical reactivity.

The developed PHIP hyperpolarised reaction monitoring procedure enabled quantitative analysis of the oxidative addition of H2 to trans-[IrCl(CO)(PPh3)2], with a k2 rate constant of (0.89 ± 0.03) dm3 mol-1 s-1 showing excellent consistency with established literature. The method was validated against several key experimental parameters (including temperature and relaxation) to establish it as a robust route to accurately monitor reactions at low-field.

Through integration of low-cost ex situ and in situ photochemistry setups that utilise broadband UV sources, the photochemistry of metal dihydrides (M = Ir, Ru) was explored on a benchtop NMR spectrometer for the first time. Implementation of a photochemical pump - NMR probe method with the in situ photochemistry setup allowed observation of photochemistry on the micro-to-millisecond timescale enabling the observation of short-lived hyperpolarised cis-[Ru(H)2(dppe)2] (with a hyperpolarised T1 of (250 ± 20) ms). This setup was employed to detect coherent magnetic evolution of metal complexes formed from addition of parahydrogen which has only been observed previously using a laser within a high-field NMR setup. Magnetic evolution was observed for cis-[Ru(H)2(dppe)2], [Ru(H)2(CO)2(dpae)], [Ir(H)2(CO)(PPh3)2I] and [Ir(H)2(13CO)(PPh3)2I] indicating the viability of a low-cost, benchtop NMR alternative to currently established practices.