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  1. The reactivity of the novel Re( i ) catalyst [Re( C12 Anth-py 2 )(CO) 3 Br] is modulated by its interactions with the covalent organic framework (COF) TFB-BD. The complex catalyzes either reductive etherification, oxidative esterification, or transfer hydrogenation depending on its local environment (embedded in TFB-BD, in homogeneous solution or co-incubated with TFB-BD, respectively). The results highlight that COFs can drastically modulate the reactivity of homogeneous catalysts.
    Free, publicly-accessible full text available October 27, 2023
  2. We report the synthesis and reactivity of a model of [Fe]-hydrogenase derived from an anthracene-based scaffold that includes the endogenous, organometallic acyl(methylene) donor. In comparison to other non-scaffolded acyl-containing complexes, the complex described herein retains molecularly well-defined chemistry upon addition of multiple equivalents of exogenous base. Clean deprotonation of the acyl(methylene) C–H bond with a phenolate base results in the formation of a dimeric motif that contains a new Fe–C(methine) bond resulting from coordination of the deprotonated methylene unit to an adjacent iron center. This effective second carbanion in the ligand framework was demonstrated to drive heterolytic H 2 activation across the Fe( ii ) center. However, this process results in reductive elimination and liberation of the ligand to extrude a lower-valent Fe–carbonyl complex. Through a series of isotopic labelling experiments, structural characterization (XRD, XAS), and spectroscopic characterization (IR, NMR, EXAFS), a mechanistic pathway is presented for H 2 /hydride-induced loss of the organometallic acyl unit ( i.e. pyCH 2 –CO → pyCH 3 +CO). The known reduced hydride species [HFe(CO) 4 ] − and [HFe 3 (CO) 11 ] − have been observed as products by 1 H/ 2 H NMR and IR spectroscopies, as well as independent synthesesmore »of PNP[HFe(CO) 4 ]. The former species ( i.e. [HFe(CO) 4 ] − ) is deduced to be the actual hydride transfer agent in the hydride transfer reaction (nominally catalyzed by the title compound) to a biomimetic substrate ([ Tol Im](BAr F ) = fluorinated imidazolium as hydride acceptor). This work provides mechanistic insight into the reasons for lack of functional biomimetic behavior (hydride transfer) in acyl(methylene)pyridine based mimics of [Fe]-hydrogenase.« less
  3. 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.
  4. 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.