Dinuclear Iron(0) Complexes of N‑Heterocyclic
Carbenes
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Abstract
The
synthesis, structures, and reactivity of dinuclear Fe<sup>0</sup> complexes
of N-heterocyclic carbenes (NHCs, denoted as L) are reported.
The NHC adducts of ferric chloride (L)FeCl<sub>3</sub> were prepared
from the reactions of FeCl<sub>3</sub> with L in toluene. The reduction
of (L)FeCl<sub>3</sub> with KC<sub>8</sub> resulted in the formation
of the dinuclear Fe<sup>0</sup> complexes Fe<sub>2</sub>{μ-η<sup>1</sup>(C):η<sup>6</sup>(arene)-L}<sub>2</sub> (<b>2a</b>, L = 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes); <b>2b</b>, L = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr)),
in which NHC ligands bridge two iron atoms using one of the arene
rings as an η<sup>6</sup> ligand. Their magnetic properties
are different: <b>2a</b> is paramagnetic and <b>2b</b> is diamagnetic. The dinuclear complexes <b>2a</b>,<b>b</b> serve as precursors for monomeric (NHC)Fe<sup>0</sup> species, and
treatment of <b>2a</b>,<b>b</b> with 1 atm of CO led to
the formation of (L)Fe(CO)<sub>4</sub>. Complex <b>2a</b> was
found to react with 1-azidoadamantane, giving rise to the dinuclear
tetrazene complex (IMes)Fe(μ-NAd)<sub>2</sub>Fe(AdNNNNAd) (<b>4</b>)
