Synthesis, Structure, and Reactivity of Paramagnetic Iron(II) and Iron(III) Amidodiphosphine Complexes

The preparation and characterization of a series of divalent and trivalent iron complexes that incorporate the amidodiphosphine ligand N(SiMe2CH2PPh2)2 are reported. Mononuclear, tetrahedral complexes of the type FeX[N(SiMe2CH2PPh2)2], where X = Cl, Br, have been prepared; magnetic susceptibility studies indicate that these are high-spin d6 systems. The preparation of Fe(II) alkyls of the formula FeR[N(SiMe2CH2PPh2)2] was examined; small alkyl substituents such as R = Me or CH2Ph were found to be thermally unstable and, thus, not isolable; however, for R = CH2SiMe3 and CH(SiMe3)2, room-temperature stable, yellow, paramagnetic solids could be obtained. The reaction of FeCl[N(SiMe2CH2PPh2)2] with NaCp·DME generates the thermally stable, diamagnetic complex Fe(η5-C5H5)[N(SiMe2CH2PPh2)2]. The corresponding Fe(III) derivative FeX2[N(SiMe2CH2PPh2)2] could be prepared in high yield by direct reaction of the LiN(SiMe2CH2PPh2)2 ligand precursor with either FeCl3 or FeBr3. Variable-temperature magnetic susceptibility studies indicate that FeBr2[N(SiMe2CH2PPh2)2] is an example of a spin-admixed system (S = 3/2 and 5/2 spin states).