N-heterocyclic carbene (NHC) adducts of iron dichloride, (IMes) 2 FeCl 2 (1a; IMes = 1,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene) and (IEtPh*) 2 FeCl 2 (1b; IEtPh* = 1,3-bis((R)-1′-phenylethyl)imidazol-2-ylidene), were prepared in good yields from the reactions of Fe{N(SiMe 3 ) 2 } 2 with imidazolium salts. While the iron atom of 1a has a tetrahedral geometry, replacement of the chlorides by methyl groups via treatment of 1a with MeLi led to the formation of the square-planar complex trans-(IMes) 2 FeMe 2 (2). The molecular structures of complexes 1a,b and 2 were identified by means of single-crystal X-ray diffraction analysis. Complexes 1a,b and 2 are good catalyst precursors in the transfer hydrogenation of 2′-acetonaphthone, and complex 2 also efficiently catalyzes the hydrosilylation of 2′-acetonaphthone.

An oxygen-encapsulated iron sulfido cluster, [(DmpS)Fe(4)S(3)O][(DmpS)Fe(4)S(3)](μ-SDmp)(2)(μ-OCPh(3)) (2; Dmp = 2,6-(mesityl)(2)C(6)H(3)), has been synthesized by the reaction of the preformed dinuclear iron thiolate/alkoxide [(Ph(3)CO)Fe](2)(μ-SDmp)(2) (1) with (1/8)S(8) and (1/4)H(2)O in toluene. In the [Fe(8)S(6)O] core, the oxygen atom bridges unsymmetrically two incomplete Fe(4)S(3) cubes, and two coordinatively unsaturated iron atoms are weakly bound to mesityl rings. Relevance of the cluster structure of 2 to the nitrogenase FeMo cofactor and its substrate binding mode is discussed.

A diamine-bridged bis-N-heterocyclic carbene ligand was synthesized as imidazolium salts with chloride or triflate counteranions. Deprotonation of the chloride salt by an iron bis-amide complex or addition of the free diamine-biscarbene ligand to FeCl 2 led to the formation of an Fe(II) dichloride complex having a diamine-bis-carbene ligand, in which the iron atom is in a highly distorted octahedral geometry with weak Fe-N interactions. This iron complex was found to catalyze the hydrosilylation of acetophenone.

The synthesis, structures, and reactivity of dinuclear Fe 0 complexes of N-heterocyclic carbenes (NHCs, denoted as L) are reported. The NHC adducts of ferric chloride (L)FeCl 3 were prepared from the reactions of FeCl 3 with L in toluene. The reduction of (L)FeCl 3 with KC 8 resulted in the formation of the dinuclear Fe 0 complexes Fe 2 {μ-η 1 (C):η 6 (arene)-L} 2 (2a, L = 1,3-bis(2,4,6trimethylphenyl)imidazol-2-ylidene (IMes); 2b, L = 1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr)), in which NHC ligands bridge two iron atoms using one of the arene rings as an η 6 ligand. Their magnetic properties are different: 2a is paramagnetic and 2b is diamagnetic. The dinuclear complexes 2a,b serve as precursors for monomeric (NHC)Fe 0 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) 2 Fe(AdNNNNAd) (4).