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Issue 2, 2016
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N-Heterocyclic carbene adducts to [Cp′FeI]2: synthesis and molecular and electronic structure

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Abstract

Addition of N-heterocyclic carbenes (L = 1,3-di-tert-butylimidazol-2-ylidene (ItBu), 1,3-di-iso-propyl-4,5-dimethylimidazol-2-yildene (IiPr2Me2), 1,3-mesitylimidazol-2-yildene (IMes) and 1,3-di-(2,6-di-isopropylphenyl)imidazol-2-yildene (IPr)) to the iron half-sandwich complex [Cp′FeI]2 (Cp′ = η5-1,2,4-(Me3C)3C5H2, 1) forms the neutral, 16VE adducts [Cp′FeI(L)] (2–5) in moderate to excellent yields. These complexes were structurally characterised. The NHC ligand binds strongly to the Fe(II) atom, so that no exchange is observed on the NMR and chemical time scale. Fe(II) atoms in the starting material 1 adopt a high-spin configuration (S = 2) and are weakly antiferromagnetically coupled at low temperatures. Furthermore, in contrast to previous reports on related [(η5-C5Me5)FeCl(NHC)] systems, in which the Fe(II) atoms assume an intermediate spin (S = 1), no spin state change occurs upon coordination of the NHC ligand; the Fe(II) atoms in complexes 2–5 retain their high-spin state (S = 2) as shown by solid state magnetic susceptibility and zero-field 57Fe Mössbauer spectroscopy investigations. Density functional theory (DFT) studies at the B3LYP level of theory also agree with a well separated S = 2 ground state for compounds 2–5. Surprisingly for Fe(II) high-spin systems, compounds 1–5 exhibit slow paramagnetic relaxation in their Mössbauer spectra; this can be traced to spin–spin and spin–lattice relaxation processes with unusually large spin–lattice relaxation barriers. A structural model is proposed that associates these processes with crystal packing effects.

Graphical abstract: N-Heterocyclic carbene adducts to [Cp′FeI]2: synthesis and molecular and electronic structure

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Supplementary files

Article information


Submitted
02 Nov 2015
Accepted
01 Dec 2015
First published
14 Dec 2015

This article is Open Access

Inorg. Chem. Front., 2016,3, 250-262
Article type
Research Article

N-Heterocyclic carbene adducts to [Cp′FeI]2: synthesis and molecular and electronic structure

M. Reiners, D. Baabe, K. Harms, M. Maekawa, C. G. Daniliuc, M. Freytag, P. G. Jones and M. D. Walter, Inorg. Chem. Front., 2016, 3, 250
DOI: 10.1039/C5QI00235D

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