Homogeneous Hydrogenation of Norbornadiene with Parahydrogen and Phosphonic Ester Phosphine Rhodium Complexes Studied by in situ NMR Spectroscopy

Homogeneous hydrogenation of norbornadiene with enriched parahydrogen (p-H ₂ ) and phosphonic ester phosphine rhodium complexes is detected using in situ NMR spectroscopy The obtained polarization spectra remain unchanged during the catalysis in thf-d ₈ as a solvent but change with time when the hydrogenation is executed in acetone-d ₆ . The observed phenomenon is attributed to a change of the phase correlation of the transferred parahydrogen nuclei via nuclear singlet-triplet (S/T ₀ ) mixing during the reaction. Simultaneously, ³¹ P NMR spectra change indicating a change in the nature of the original rhodium complex when the hydrogenation is carried out in acetone-d ₆ .