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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).

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-bis-carbene ligand to FeCl2 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.

A novel chiral coordination polymer, [Cu(C(6)H(5)CH(OH)COO)(μ-C(6)H(5)CH(OH)COO)] (1-L and 1-D), was synthesized through a reaction of copper acetate with L-mandelic acid at room temperature. Although previously reported copper mandelate prepared by hydrothermal reaction was a centrosymmetric coordination polymer because of the racemization of mandelic acid, the current coordination polymer shows noncentrosymmetry and a completely different structure from that previously reported. The X-ray crystallography for 1-L revealed that the copper center of the compound showed a highly distorted octahedral structure bridged by a chiral mandelate ligand in the unusual coordination mode to construct a one-dimensional (1D) zigzag chain structure. These 1D chains interdigitated each other to give a layered structure as a result of the formation of multiple aromatic interactions and hydrogen bonds between hydroxyl and carboxylate moieties at mandelate ligands. The coordination polymer 1-L belongs to the noncentrosymmetric space group of C2 to show piezoelectric properties and second harmonic generation (SHG) activity.

The reactions of Fe(2)Mes(4) (1; Mes = mesityl) with bulky thiols, namely, HSDmp (Dmp = 2,6-dimesitylphenyl), HSDxp (Dxp = 2,6-dixylylphenyl), and HSBtip [Btip = 2,6-(2,4,6-(i)Pr(3)C(6)H(2))(2)C(6)H(3)], provided a series of iron(II) mesityl complexes bearing bulky thiolate ligands. These iron complexes are the thiolate-bridged dinuclear complexes Fe(2)Mes(2)(mu-SAr)(mu-Mes) (2a, Ar = Dmp; 2b, Ar = Dxp), the 1,2-dimethoxyethane (DME) adducts (DME)Fe(SAr)(Mes) (3a, Ar = Dmp; 3b, Ar = Dxp), the mixed-valence Fe(I)-Fe(II) dinuclear complexes (Mes)Fe(mu-SAr)(mu-S Ar) Fe (4a, Ar = Dmp; 4b, Ar = Dxp), and a low-coordinate mononuclear complex (B tipS) Fe(Mes) (5). An [Fe(8)S(7)] cluster [Fe(4)S(3)(SDmp)](2)(mu-SDmp)(2)(mu-SMes)(mu(6)-S) (6), the core structure of which is topologically relevant to that of the FeMo-cofactor of nitrogenase, was obtained from the reaction of 3a or 4a with S(8). The mu-SMes ligand in 6 is formed via insertion of a sulfur atom into the Fe-C(Mes) bond. The formation of cluster 6 from 3a or 4a demonstrates that organoiron complexes are applicable as precursors for iron-sulfur clusters.

Reactions of manganese(II) dichlorides bearing a N-heterocyclic carbene ligand (L), [MnCl(μ-Cl)(L)]2 (1a, L = 1,3-diisopropyl-4,5-dimethylimidazole-2-ylidene (IiPr); 1b, L = 1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene (IMes); 1c, L = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene (IPr)) with MeLi afford the dinuclear dimethylmanganese(II) complexes, [MnMe(μ-Me)(L)]2 (2a, L = IiPr; 2b, L = IMes; 2c, L = IPr). Complexes 2a-c achieve nucleophilic substitution of Si(OEt)4 to selectively form MeSi(OEt)3. Related arylmanganese(II) complexes analogously react with Si(OEt)4 to afford ArSi(OEt)3 and Ar2Si(OEt)2 (Ar = Ph, 2,6-Me2(C6H3)). Kinetic studies support an associative mechanism for the observed transformation of Si(OEt)4, in which both the manganese species and Si(OEt)4 are involved in the rate-limiting step.