In situ NMR observation of mono- and binuclear rhodium dihydride complexes using parahydrogen-induced polarization

Starting from the binuclear complex [RhCl(NBD)](2) (NBD = 2,5-norbornadiene) in the presence of the phosphines L = PMe3, PMe2Ph, PMePh2, PEt3, PEt2Ph, PEtPh2, or P(n-butyl)(3), various mononuclear dihydrides of the type Rh(H)(2)ClL3, i.e., those of the homogeneous hydrogenation catalysts RhClL3, have been obtained upon addition of parahydrogen, and their H-1 NMR spectra have been investigated using parahydrogen-induced polarization (PHIP). Furthermore, the two binuclear complexes (H)(Cl)Rh(PMe3)(2)(mu -Cl)(mu -H)Rh(PMe3) and (H)(CI)Rh(PMe2Ph)(2)(mu -Cl)(mu -H)Rh(PMe2Ph) have been detected and characterized by means of this in situ NMR method. Analogous complexes with trifluoroacetate instead of chloride, i.e., Rh(H)(2)(CF3COO)L-3, have been generated in situ starting from Rh(NBD)(acac) in the presence of trifluoroacetic acid in combination with the phosphines L = PPh3, PEt2Ph, FEB, and P(n-butyl)(3), and their H-1 NMR parameters have been determined.