| Abstract
| - Iron(II) dihydride and silyl hydride complexes bearing a bis(phosphino)pyridine pincer ligand have been prepared and evaluated in catalytic hydrogenation and hydrosilation reactions. The electronic structure and reactivity of these compounds are compared to bis(imino)pyridine-ligated iron compounds where the terdentate chelate engages in redox chemistry with the metal center.
- 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 dinitrogencomplex, (iPrPNP)FeH2(N2). Addition of 1 equiv of PhSiH3 to (iPrPNP)FeH2(N2) resulted in exclusive substitution ofthe hydride trans to the pyridine to yield the silyl hydride dinitrogen compound, (iPrPNP)FeH(SiH2Ph)N2, which hasbeen characterized by X-ray diffraction. The solid-state structure established a distorted octahedral geometry wherethe hydride ligand distorts toward the iron silyl. Both (iPrPNP)FeH2(N2) and (iPrPNP)FeH(SiH2Ph)N2 form η2-dihydrogencomplexes upon exposure to H2. The iron hydrides and the η2-H2 ligands are in rapid exchange in solution, consistentwith 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 ofthis pincer ligand as compared to the redox-active aryl-substituted bis(imino)pyridines.
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