Three-Coordinate Iron(II) Expanded Ring N‑Heterocyclic Carbene Complexes
journal contributionposted on 14.04.2016 by Jay J. Dunsford, David J. Evans, Thomas Pugh, Sachin N. Shah, Nicholas F. Chilton, Michael J. Ingleson
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A sterically demanding seven-membered expanded ring N-heterocyclic carbene (NHC) ligand allows access to rare examples of three-coordinate iron(II)–NHC complexes incorporating only halide coligands of the general formula [Fe(NHC)X2] (NHC = 7-DiPP; X = Br (1) Cl (2)). Reducing the steric influence of the ancillary NHC ligand through modulation of the N-aryl substituents leads to either four- or three-coordinate complexes of the general formula [Fe(NHC)Br2(THF)] (3) or [Fe(NHC)Br2] (4) (NHC = 7-Mes), dependent upon the solvent of recrystallization. The further reduction of NHC steric influence results in four-coordinate geometries at iron in the form of the dimeric species [Fe(NHC)Br(μ-Br)]2 (5) or [Fe(NHC)Br2(THF)] (6) (NHC = SDiPP), again dependent upon the solvent of recrystallization. Compounds 1–6 have been analyzed by 1H NMR spectroscopy, X-ray crystallography, elemental microanalysis, Mössbauer spectroscopy (for 1 and 3–5), and Evans method magnetic susceptibility. In addition to these measurements the three-coordinate species 1 and 4 have been further analyzed by SQUID magnetometry and CASSCF calculations, which show significant magnetic anisotropy that is extremely sensitive to the coordination geometry.