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).