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

The 15 valence‐electron iron(I) complex [Cp Ar Fe(IiPr 2 Me 2 )] ( 1 , Cp Ar =C 5 (C 6 H 4 ‐4‐Et) 5 ; IiPr 2 Me 2 =1,3‐diisopropyl‐4,5‐dimethylimidazolin‐2‐ylidene) was synthesized in high yield from the Fe II precursor [Cp Ar 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 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.