Iron-Catalyzed Para hydrogen Induced Polarization.

Para hydrogen induced polarization (PHIP) can address the low sensitivity problem intrinsic to nuclear magnetic resonance spectroscopy. Using a catalyst capable of reacting with para hydrogen and substrate in either a hydrogenative or nonhydrogenative manner can result in signal enhancement of the substrate. This work describes the development of a rare example of an iron catalyst capable of reacting with para hydrogen to hyperpolarize olefins. Complexes of the form ( Mes CCC)Fe(H)(L)(N 2 ) (L = Py (Py = pyridine), PMe 3 , PPh 3 ) were synthesized from the reaction of the parent complexes ( Mes CCC)FeMes(L) (Mes = mesityl) with H 2 . The isolated low-spin iron(II) hydride compounds were characterized via multinuclear NMR spectroscopy, infrared spectroscopy, and single crystal X-ray diffraction. ( Mes CCC)Fe(H)(Py)(N 2 ) is competent in the hydrogenation of olefins and demonstrated high activity toward the hydrogenation of monosubstituted terminal olefins. Reactions with p -H 2 resulted in the first PHIP effect mediated by iron which requires diamagnetism throughout the reaction sequence. This work represents the development of a new PHIP catalyst featuring iron, unlocking potential to develop more PHIP catalysts based on first-row transition metals.