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  1. Abstract

    The one‐step syntheses, X‐ray structures, and spectroscopic characterization of synthetic iron clusters, bearing either inorganic sulfides or thiolate with interstitial carbide motifs, are reported. Treatment of iron carbide carbonyl clusters [Fenn‐C)(CO)m]x(n=5,6;m=15,16;x=0,−2) with electrophilic sulfur sources (S2Cl2, S8) results in the formation of several μ4‐S dimers of clusters, and moreover, iron‐sulfide‐(sulfocarbide) clusters. The core sulfocarbide unit {C−S}4−serves as a structural model for a proposed intermediate in the radicalS‐adenosyl‐L‐methionine biogenesis of the M‐cluster. Furthermore, the electrophilic sulfur strategy has been extended to provide the first ever thiolato‐iron‐carbide complex: an analogous reaction with toluylsulfenyl chloride affords the cluster [Fe55‐C)(SC7H7)(CO)13]. The strategy described herein provides a breakthrough towards developing syntheses of biomimetic iron‐sulfur‐carbide clusters like FeMoco.

     
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  2. null (Ed.)
    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. 
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  3. The interest in methyl group C–H bond activation near or bound to iron-containing clusters is of key biological importance, due to the broad relevance of radical SAM reactions. Specifically, such processes are implicated in the biogenesis of the interstitial carbide found in the nitrogenase FeMoco active site. In this work, we find that the diamagnetic, methyl-thiolate capped iron–carbonyl cluster anion [(CH 3 S)Fe 3 (CO) 9 ] − (1) undergoes facile C–H hydrogen atom abstraction upon treatment with TEMPO. The process leads to (i) eradication of the CH 3 moiety, (ii) formation of a sulfide bridge, and (iii) cluster dimerization—thereby generating the ‘dimer of trimers’ cluster [K(benzo-15-crown-5) 2 ] 2 [(SFe 2 (CO) 12 ) 2 Fe(CO) 2 ] (2). In contrast, the corresponding isopropyl variant [Fe 3 (S i Pr)(CO) 9 ] − (3) does not react with TEMPO . Mass spectrometry confirmed the presence of TEMPOH, as well as CO oxidation vis a vis CO 2 and 2,2,6,6-tetramethylpiperidine. GC-MS measurements of the headspace reveal that the ultimate fate of the methyl carbon is likely incorporation into multiple products—one of which may be a volatile low mass hydrocarbon—rather than carbon/carbide incorporation. 
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