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 d(6) 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(eta(5)-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-admired system (S = 3/2 and 5/2 spin states).