Iron-Catalyzed hydrogen Induced Polarization.

hydrogen induced polarization (PHIP) can address the low sensitivity problem intrinsic to nuclear magnetic resonance spectroscopy. Using a catalyst capable of reacting with 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 hydrogen to hyperpolarize olefins. Complexes of the form (CCC)Fe(H)(L)(N) (L = Py (Py = pyridine), PMe, PPh) were synthesized from the reaction of the parent complexes (CCC)FeMes(L) (Mes = mesityl) with H. The isolated low-spin iron(II) hydride compounds were characterized via multinuclear NMR spectroscopy, infrared spectroscopy, and single crystal X-ray diffraction. (CCC)Fe(H)(Py)(N) is competent in the hydrogenation of olefins and demonstrated high activity toward the hydrogenation of monosubstituted terminal olefins. Reactions with -H 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.