Synthesis and electronic structure of permethylindenyl complexes of iron and cobalt

Abstract

Fe(eta(5)-C9Me7)2 and Co(eta(5)-C9Me7)2 have been prepared by treatment of either FeCl2.xTHF (x congruent-to 2) or Co(acac)2 with LiInd* (Ind* = eta(5)-C9Me7) in THF. The cyclic voltammograms of both Fe(eta(5)-C9Me7)2 and Co(eta(5)-C9Me7)2 indicate that they are redox active with one-electron oxidations at E1/2 = -0.32 and -1.05 V vs SCE, respectively; both complexes exhibit second oxidations at E1/2 = 1.28 and 1.21 V vs SCE, respectively. The 17-electron and 18-electron cations [Fe(eta(5)-C9Me7)2]+PF6- and [Co(eta(5)-C9Me7)2]+PF6- were isolated by treatment of the neutral complexes with either [Fe(eta(5)-C5H5)2]+PF6- (for Fe) or NH4PF6 (for Co). Gas-phase UV photoelectron spectroscopy experiments on both Fe(eta(5)-C9Me7)2 and Co(eta(5)-C9Me7)2 show that the permethylindenyl ligand gives rise to lower first ionization energy (correlating with a more negative E1/2 value) than the Cp* (Cp* = eta(5)-C5Me5) ligand for Fe, while in the Co analogue the reverse is found. EPR and magnetic susceptibility experiments on [Fe(eta(5)-C9Me7)2]+PF6- and Co(eta(5)-C9Me7)2 both in solution and the solid state yield magnetic moments of 2.09-mu(B) for {Fe(eta(5)-C9Me7)2}+PF6- and 1.59-mu(B) for Co(eta(5)-C9Me7)2.