Dinuclear Iron(0) Complexes of N‑Heterocyclic Carbenes

The synthesis, structures, and reactivity of dinuclear Fe0 complexes of N-heterocyclic carbenes (NHCs, denoted as L) are reported. The NHC adducts of ferric chloride (L)­FeCl3 were prepared from the reactions of FeCl3 with L in toluene. The reduction of (L)­FeCl3 with KC8 resulted in the formation of the dinuclear Fe0 complexes Fe2{μ-η1(C):η6(arene)-L}2 (2a, L = 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes); 2b, 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 η6 ligand. Their magnetic properties are different: 2a is paramagnetic and 2b is diamagnetic. The dinuclear complexes 2a,b serve as precursors for monomeric (NHC)­Fe0 species, and treatment of 2a,b with 1 atm of CO led to the formation of (L)­Fe­(CO)4. Complex 2a was found to react with 1-azidoadamantane, giving rise to the dinuclear tetrazene complex (IMes)­Fe­(μ-NAd)2Fe­(AdNNNNAd) (4).