Design and Characterization of Phosphine Iron Hydrides: Toward Hydrogen-Producing Catalysts.

Diamagnetic iron chloro compounds [(PPh2NPh2)FeCp*Cl] [1Cl] and [(PCy2NPh2)FeCp*Cl] [2Cl] and the corresponding hydrido complexes [(PPh2NPh2)FeCp*H] [1H] and [(PCy2NPh2)FeCp*H] [2H] have been synthesized and characterized by NMR spectroscopy, electrochemical studies, electronic absorption, and 57Fe Mossbauer spectroscopy (PPh2NPh2 = 1,3,5,7-tetraphenyl-1,5-diphospha-3,7-diazacyclooctane, PCy2NPh2 = 1,5-dicyclohexyl-3,7-diphenyl-1,5-diphospha-3,7-diazacyclooctane, Cp* = pentamethylcyclopentadienyl). Molecular structures of [2Cl], [1H], and [2H], derived from single-crystal X-ray diffraction, revealed that these compounds have a typical piano-stool geometry. The results show that the electronic properties of the hydrido complexes are strongly influenced by the substituents at the phosphorus donor atoms of the PR2NPh2 ligand, whereas those of the chloro complexes are less affected. These results illustrate that the hydride is a strong-field ligand, as compared to chloride, and thus leads to a significant deg...