Photochemical Pump, Benchtop NMR Probe Spectroscopy for Reaction Monitoring With paraHydrogen

The ability to observe transient intermediates and determine precise kinetic parameters is fundamental to understanding catalysis. This study demonstrates a methodology for the in situ investigation of photochemical ligand exchange and oxidative addition using a benchtop NMR spectrometer equipped with a through-bore UV irradiation system. To overcome the inherent sensitivity limitations of benchtop NMR, parahydrogen-induced polarisation (PHIP) was employed, providing significant signal enhancements for hydride-containing products. Specifically, the addition of pH ${}_2$ to trans-[IrCl(CO)(PPh ${}_3$ ) ${}_2$ ], that proceeds over 10 min, was monitored yielding a second-order rate constant, 1.36 $\pm$ 0.02 M ${}^{-1}$ s ${}^{-1}$ . To resolve faster catalytic processes, pump-probe synchronisation between the UV pulse and NMR detection was implemented. A spin-lock pulse was also added to preserve the singlet state of the pH ${}_2$ -derived hydride ligands in the reaction products, enabling the observation of coherent magnetic oscillations after reaction in the corresponding 2D pump-probe NMR spectra. Following optimisation on diagnostic zero-quantum correlations for cis-[Ru(H) ${}_2$ (dppe) ${}_2$ ], a set of iodo-derivatives of Vaska's complex were explored. For these systems two photochemical pathways were effectively mapped, enabling the identification of several ligand-exchange products. These results establish that the combination of hyperpolarisation and synchronised in situ irradiation makes benchtop NMR a powerful tool for the study of reactivity.