Electronic Structure and Magnetic Anisotropy of an Unsaturated Cyclopentadienyl Iron(I) Complex with 15 Valence Electrons.

The 15 valence-electron iron(I) complex [CpAr Fe(IiPr2 Me2 )] (1, CpAr =C5 (C6 H4 -4-Et)5 ; IiPr2 Me2 =1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) was synthesized in high yield from the FeII precursor [CpAr Fe(μ-Br)]2 . 57 Fe Mössbauer and EPR spectroscopic data, magnetic measurements, and ab initio ligand-field calculations indicate an S= 3/2 ground state with a large negative zero-field splitting. As a consequence, 1 features magnetic anisotropy with an effective spin-reversal barrier of Ueff =64 cm-1 . Moreover, 1 catalyzes the dehydrogenation of N,N-dimethylamine-borane, affording tetramethyl-1,3-diaza-2,4-diboretane under mild conditions.