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Bis(diisopropylphosphino)pyridine Iron Dicarbonyl, Dihydride, and Silyl Hydride Complexes

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posted on 04.09.2006, 00:00 authored by Ryan J. Trovitch, Emil Lobkovsky, Paul J. Chirik
Treatment of the bis(diisopropylphosphino)pyridine iron dichloride, (iPrPNP)FeCl2 (iPrPNP = 2,6-(iPr2PCH2)2(C5H3N)), with 2 equiv of NaBEt3H under an atmosphere of dinitrogen furnished the diamagnetic iron(II) dihydride dinitrogen complex, (iPrPNP)FeH2(N2). Addition of 1 equiv of PhSiH3 to (iPrPNP)FeH2(N2) resulted in exclusive substitution of the hydride trans to the pyridine to yield the silyl hydride dinitrogen compound, (iPrPNP)FeH(SiH2Ph)N2, which has been characterized by X-ray diffraction. The solid-state structure established a distorted octahedral geometry where the hydride ligand distorts toward the iron silyl. Both (iPrPNP)FeH2(N2) and (iPrPNP)FeH(SiH2Ph)N2 form η2-dihydrogen complexes upon exposure to H2. The iron hydrides and the η2-H2 ligands are in rapid exchange in solution, consistent with the previously reported “cis” effect, arising from a dipole/induced dipole interaction between the two ligands. Taken together, the spectroscopic, structural, and reactivity studies highlight the relative electron-donating ability of this pincer ligand as compared to the redox-active aryl-substituted bis(imino)pyridines.