The molybdenum(0) and tungsten(0) carbonyl complexes, [M(CO) n (TMTU) 6−n ] (M = Mo and W; TMTU = tetramethylthiourea; n = 4 and 5), have been prepared by addition of TMTU to the appropriate carbonyl precursors. In the solid state, the compounds are monomeric and feature octahedral coordination geometries about the metal. In the case of [M(CO) 4 (TMTU) 2 ], the TMTU ligands are bound in a cis fashion. Dissolution of cis-[M(CO) 4 (TMTU) 2 ] produces an equilibrium mixture of cis-[M(CO) 4 (TMTU) 2 ], free TMTU, and the putative dimeric species, cis,cis-[M 2 (CO) 8 -(μ-TMTU) 2 ]. Attempts to prepare the tricarbonyl complex, [Mo(CO) 3 (TMTU) 3 ], by addition of TMTU to fac-[Mo-(CO) 3 (η 6 -cycloheptatriene)] results in isolation of cis-[Mo-(CO) 4 (TMTU) 2 ], demonstrating that exchange of CO and TMTU ligands is facile in these compounds. Each of the compounds decomposes readily in the solid state above 110 °C, ultimately forming the tetravalent metal disulfide. Thermolysis reactions of [M(CO) n (TMTU) 6−n ] complexes at 300 °C under an argon atmosphere produces amorphous MS 2 , establishing the utility of these compounds as precursors to molybdenum and tungsten disulfide materials under relatively mild conditions.

We report the synthesis, interconversions and X-ray structures of a set of [mFe-nS]-type carbonyl clusters (where S = S, S or RS; m = 2-3; n = 1-2). All of the clusters have been identified and characterized by single crystal X-ray diffraction, IR and C NMR. Reduction of the parent neutral dimer [μ-(SPh)Fe(CO)] (1) with KC affords an easily separable ∼1 : 1 mixture of the anionic, dimeric thiolate dimer K[Fe(SPh)(CO)(μ-CO)] (2) and the dianionic, sulfido trimer [K(benzo-15-crown-5)][Fe(μ-S)(CO)] (3). Oxidation of 2 with diphenyl-disulfide (PhS) cleanly returns the starting material 1. The Ph-S bond in 1 can be cleaved to form sulfide trimer 3. Oxidation of sulfido trimer 3 with [Fc](PF) in the presence of S cleanly affords the all-inorganic persulfide dimer [μ-(S)Fe(CO)] (4), a thermodynamically stable product. The inverse reactions to form 3 (dianion) from 4 (neutral) were not successful, and other products were obtained. For example, reduction of 4 with KC afforded the mixed valence Fe(i)/Fe(ii) species [((FeS)(CO))Fe] (5), in which the two {FeS(CO)} units serve as bidendate ligands to a Fe(ii) center. Another isolated product (THF insoluble portion) was recrystallized in MeCN to afford [K(benzo-15-crown-5)][((FeS)(CO))(μ-S)] (6), in which a persulfide dianion bridges two {2Fe-S} moieties (dimer of dimers). Finally, to close the interconversion loop, we converted the persulfide dimer 4 into the thiolate dimer 1 by reduction with KC followed by reaction with the diphenyl iodonium salt [PhI](PF), in modest yield. These reactions underscore the thermodynamic stability of the dimers 1 and 4, as well as the synthetic and crystallization versatility of using the crown/K counterion system for obtaining structural information on highly reduced iron-sulfur-carbonyl clusters.

The family of nitrogenase enzymes catalyzes the reduction of atmospheric dinitrogen (N2) to ammonia under remarkably benign conditions of temperature, pressure, and pH. Therefore, the development of synthetic complexes or materials that can similarly perform this reaction is of critical interest. The primary obstacle for obtaining realistic synthetic models of the active site iron-sulfur-carbide cluster (e.g., FeMoco) is the incorporation of a truly inorganic carbide. This review summarizes the present state of knowledge regarding biological and chemical (synthetic) incorporation of carbide into iron-sulfur clusters. This includes the Nif cluster of proteins and associated biochemistry involved in the endogenous biogenesis of FeMoco. We focus on the chemical (synthetic) incorporation portion of our own efforts to incorporate and modify C1 units in iron/sulfur clusters. We also highlight recent contributions from other research groups in the area toward C1 and/or inorganic carbide insertion.

SAM mediated methyl transfer and subsequent hydrogen atom abstraction are key steps in the biogenesis of nitrogenase. A model system was utilized to demonstrate facile C–H abstraction from a methyl-thiolate containing iron–sulfur cluster with TEMPO.

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