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

The 15 valence-electron iron(I) complex [Cp^ArFe(IiPr₂Me₂)] (1, Cp^Ar=C₅(C₆H₄-4-Et)₅; IiPr₂Me₂=1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) was synthesized in high yield from the Fe^II precursor [Cp^ArFe(μ-Br)]₂. ⁵⁷Fe 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 U_eff=64 cm⁻¹. Moreover, 1 catalyzes the dehydrogenation of N,N-dimethylamine–borane, affording tetramethyl-1,3-diaza-2,4-diboretane under mild conditions.