Parahydrogen-Induced Polarization with a Rh-Based Monodentate Ligand in Water

Reported here is a water-soluble Rh(I)-based catalyst for performing parahydrogen-induced polarization (PHIP). The [Rh(I)(norbomadiene)(THP)(2)](+)[BF4](-) catalyst utilizes the monodentate phosphine ligand tris(hydroxymethyl)phosphine (THP). The monodentate PHIP catalyst is less susceptible to oxygenation by air and the THP ligand is significantly less expensive than bidentate water-soluble PHIP ligands. In situ PHIP detection with this monodentate Rh(I)-based catalyst in water yielded 12% C-13 polarization for the parahydrogen addition product, 2-hydroxyethyl 1-C-13-propionate-d(2,3,3) (HEP), with a C-13 T-1 relaxation of 108 s at 0.0475 T. PHIP polarization yields were high, reflecting efficient hydrogenation even under conditions of high content of the oxidized phosphine form of the THP ligand.