Bis(diisopropylphosphino)pyridine iron dicarbonyl, dihydride, and silyl hydride complexes

Treatment of the bis(diisopropylphosphino) pyridine iron dichloride, ((PNP)-P-iPr)FeCl2 ((PNP)-P-iPr = 2,6-((Pr2PCH2)-Pr-i)(2)(C5H3N)), with 2 equiv of NaBEt3H under an atmosphere of dinitrogen furnished the diamagnetic iron(II) dihydride dinitrogen complex, ((PNP)-P-iPr)FeH2(N-2). Addition of 1 equiv of PhSiH3 to ((PNP)-P-iPr)FeH2(N-2) resulted in exclusive substitution of the hydride trans to the pyridine to yield the silyl hydride dinitrogen compound, ((PNP)-P-iPr)FeH(SiH2Ph)N-2, 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 ((PNP)-P-iPr)FeH2(N-2) and ((PNP)-P-iPr)FeH(SiH2Ph)N-2 form eta(2)-dihydrogen complexes upon exposure to H-2. The iron hydrides and the eta(2)-H-2 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.