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

Abstract

The 15 valence-electron iron(I) complex [Cp Fe(IiPr Me )] (1, Cp =C (C H -4-Et) ; IiPr Me =1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene) was synthesized in high yield from the Fe precursor [Cp Fe(μ-Br)] . 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 =64 cm . Moreover, 1 catalyzes the dehydrogenation of N,N-dimethylamine-borane, affording tetramethyl-1,3-diaza-2,4-diboretane under mild conditions.

Iron(II) High‐Spin and Low‐Spin Complexes from Pentaisopropylcyclopentadienyliron(II) Bis(trimethylsilyl)amide

“…The construction of a Cole–Cole diagram (see the Supporting Information) and a thorough analysis of the frequency‐dependent ac data between 2 and 12 K taking into account direct, Raman, and Orbach relaxation mechanisms revealed an energy barrier of U eff = 113 cm –1 and a characteristic relaxation time of τ 0 = 4.8 × 10 –10 s (Figure , bottom). The energy barrier is similar to the value of 143 K (100 cm –1 ), which was found for the heteroleptic aryl–iron(II) cyclopentadienyl complex [ 5 CpFeAr] and somewhat higher than for a recently published cyclopentadienyl iron(I) complex (64 cm –1 ) . The energy barriers of homoleptic two‐coordinate iron(II) complexes vary from 43 to 181 cm –1 depending on the ligands and on deviations from linear coordination geometry …”

Single Ion Magnets from 3d to 5f: Developments and Strategies

“…The high barrier of 16 seems to add value to the strategy of setting an Fe I ion in a linear coordination environment. However, the energy barriers of the following reported linear Fe I complexes [K(18‐crown‐6)][Fe I {N(TMS) 2 } 2 ] ( 17 ), [K(crypt‐222)][Fe I {N(TMS) 2 } 2 ] ( 18 ), [(cAAC) 2 Fe I ][B(C 6 F 5 ) 4 ] ( 19 , cAAC=cyclic alkyl(amino) carbene,) 1 [79] and an axially coordinated complex [Cp Ar Fe I (I i Pr 2 Me 2 )] ( 20 , Ar=C 6 H 4 ‐4‐Et, I i Pr 2 Me 2 =1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene) are around 20–64 cm −1 which are several times lower than that of 16 . Surprisingly, the barrier of the trigonal planar analogue of 19 † , [(cAAC) 2 Fe I Cl] ( 21 ) † [79] , is even slightly higher than the linear 19 † .…”

Sites of Electron Transfer Reactivity in Organometallic Compounds

“…, [20] reducible arenes ArH/ArH •-, [23] oligocarbon chains -C≡C-C≡C-/[-C=C=C=C-] 2-, [24] or carbenes CR 2 /CR 2…”

“…Out of the common organic (C‐bonded) ligands there are several which offer electron transfer potential, even though there is mostly one favored oxidation state (here in boldface, see also Scheme ). Well known examples include oxidizable alkyl substituents R 3 C – /R 3 C · (and related aryl or hydride groups), η 5 ‐R 5 C 5 – /η 5 ‐R 5 C 5 · , reducible arenes ArH /ArH · – , oligocarbon chains –C≡C–C≡C–/[–C=C=C=C–] 2– , or carbenes CR 2 /CR 2 · – …”