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)(norbornadiene)(THP)(2)](+)[BF(4)](-) catalyst utilizes the monodentate phosphine ligand tris(hydroxymethyl)phosphine (THP). The monodentate PHIP catalyst is less susceptible to oxygenation by air and THP ligand and 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% (13)C polarization for the parahydrogen addition product, 2-hydroxyethyl 1-(13)C-propionate-d(2,3,3) (HEP), with a (13)C T(1) relaxation of 108 seconds 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.