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

A. Harthun, K. Woelk, J. Bargon, and A. Weigt, Tetrahedron 51, 11199-11206 (1995).

• Homogeneous hydrogenation of norbornadiene with enriched parahydrogen (p-H₂) and phosphonic ester phosphine rhodium complexes is detected using in situ NMR spectroscopy. The obtained polarization spectra remain unchanged during the catalysis in THF-d₈ as a solvent but change with time when the hydrogenation is executed in acetone-d₆.

• The observed phenomenon is attributed to a change of the phase correlation of the transferred parahydrogen nuclei via nuclear singlet-triplet (S/T₀) mixing during the reaction.

• Simultaneously, ³¹P spectra change indicating a change in the nature of the original rhodium complex when the hydrogenation is carried out in acetone-d₆.

K. Woelk, October 20, 1998