Synthesis and Properties of Iron(II) Hydride Complexes Containing the Tripodal Tetraphosphine Ligand P(CH₂CH₂PMe₂)₃

The preparation and characterization of iron(II) hydride complexes containing the tripodal tetraphosphine ligand tris[2-(dimethylphosphino)ethyl]phosphine, P(CH₂CH₂PMe₂)₃ (PP₃), 1, are reported. Dissolution of the chloro hydride complex FeHCl(PP₃), 2, in methanol affords an equilibrium mixture of 2 and the methoxy hydrido complex FeH(OMe)(PP₃), 3. Reaction of a methanol solution containing 2 and 3 with anionic or neutral ligands affords the corresponding hydrido complexes: reaction with NaBr affords FeHBr(PP₃), 4; reaction with NaI affords FeHI-(PP₃), 5; reaction with NaN₃ affords FeHN₃(PP₃), 6; reaction with CO affords [FeH(CO)(PP₃)]⁺, 8; reaction with N₂ affords [FeH(N₂)(PP₃)]⁺, 8; and reaction with PPh₃ affords [FeHPPh₃(PP₃)]⁺, 9. In some cases, further reaction of the product iron hydride complexes is observed. Reaction of FeHN₃(PP₃), 6, with NaN₃ for an extended period affords Fe(N₃)₂(PP₃), 10. On standing in solution, [FeH(N₂)(PP₃)]⁺, 8, is converted to the dinitrogen-bridged complex [FeH(PP₃)N≡NFeH(PP₃)]²⁺, 11. The carbonyl hydride complex 7 and the dinitrogen hydride complex 8 can be deprotonated to give the neutral iron(O) complexes Fe(CO)(PP₃), 12, and Fe(N₂)(PP₃), 13, respectively. The air-sensitive complexes 4-13 were characterized, by multinuclear NMR, IR, Raman, and mass spectroscopy and by elemental analysis.