HALO(PENTAMETHYLCYCLOPENTADIENYL)(1,2-BIS(DIPHENYLPHOSPHINO)ETHANE)IRON(III) AND ALKYL(PENTAMETHYLCYCLOPENTADIENYL)(1,2-BIS(DIPHENYLPHOSPHINO)ETHANE)IRON(III) 17-ELECTRON COMPLEXES - SYNTHESIS, NMR AND MAGNETIC-PROPERTIES, AND EHMO CALCULATIONS

Reaction of Fe(dppe)Cl2 (dppe = 1,2-bis(diphenylphosphino)ethane) with LiCp* (Cp* = eta-5-pentamethylcylopentadienyl) in THF yields Fe(Cp*)(dppe)Cl (1). The X-ray crystal structure of 1 shows that it crystallizes in the triclinic space group P1 with unit cell parameters a = 10.410(7) angstrom, b = 10.987(3) angstrom, c = 16.872 (4) angstrom, alpha = 80.43 (2)-degrees, beta = 94.28 (5)-degrees, gamma = 70.92 (5)-degrees, and Z = 2. The structure was solved and refined (5732 reflections) to the final residual values R = 0.37 and R(w) = 0.36. Compound 1 reacts with LiI and LiCH3 to afford respectively Fe(Cp*)(dppe)I (2) and Fe(Cp*)(dppe)CH3 (4). The hydride Fe-(Cp*)(dppe)H (3) can be obtained by reaction of 1 with LiAlH4 or by direct preparation in 50% yield from Cp*H and Fe(dppe)Cl2 reduced by a sonochemically (20 kHz) activated colloidal dispersion of potassium metal. The alkyl derivatives (Fe(Cp*)(dppe)R (R = CH3 (4) and CH2OCH3 (5)) are synthesized from FeCp*(CO)2R upon CO displacement by ultraviolet (UV) photolysis and trapping with dppe. Cyclic voltammetry (CV) reveals a reversible one-electron oxidation process for all these neutral iron(II) compounds including the hydride (3). Ferrocenium and trityl salts as well as molecular oxygen can be used to synthesize the halide and alkyl 17-electron [Fe(Cp*)(dppe)X]PF6 complexes in 90-95% yield. ESR, Mossbauer, and NMR experiments indicate that the Cp* ring and the alkyl or halide ligands contribute significantly to the delocalization of the odd electron. EHMO calculations on the [Fe(Cp)(PH3)2CH2OH].+ model are fully consistent with this finding: the singly occupied HOMO, of predominantly x2 - y2 character, is found to be 52% localized on the metal, 28% on Cp, and 15% on CH2OH. Magnetic susceptibility obeys the modified Curie-Weiss expression, and the important values of mu-B observed are attributed to an orbital contribution. The low and negative values observed for theta characterize these complexes as having short-distance dominant antiferromagnetic interactions.