Addition of H2-D2 mixtures to 2-butyne and norbornene catalyzed by solutions of chlorotris(triphenylphosphine)rhodium(I), hydridocarbonyltris(triphenylphosphine)rhodium(I), and hydridotetrakis(5-phenyl-5-H-dibenzophosphole)rhodium(I)

The use of H-2/D-2 mixtures in place of H-2 as a probe of the mechanisms of hydrogenation is explored using the catalyst precursors chlorotris(triphenylphosphine)rhodium(I) (II), hydridocarbonyltris(triphenylphosphine)rhodium(I) (II), and hydridotetrakis(5-phenyl-5-H-dibenzophosphole)rhodium (I) (III). Benzene solutions of these complexes catalyze the H-2-D-2 equilibration, the relative rates decreasing in the order III > II > I. The accepted mechanism of hydrogenation catalyzed by I does not accommodate the observed isotopic exchange, which is inhibited by added acids (trifluoroethanol, 1,3,4-trichlorophenol) and accelerated by small amounts of triethylamine; the formation of hydridotris(triphenylphosphine)rhodium(l) is implicated. The H-2 and D, added to an unsaturated hydrocarbon is randomized with complexes II and III as the catalyst, whereas the molecular identity of H-2 and D, is retained if the dihydrido is the catalyst.