Molybdenum-dependent nitrogenases catalyze the transformation of dinitrogen into ammonia under ambient conditions. The active site (FeMo cofactor) is the structurally and electronically complex weak-field metal cluster [MoFeSC] built of FeS and MoFeSC portions connected by three sulfur bridges and containing an interstitial carbon atom centered in an Fe trigonal prism. Chemical synthesis of this cluster is a major challenge in biomimetic inorganic chemistry. One synthetic approach of core ligand metathesis has been developed based on the design and synthesis of unprecedented incomplete ([(Tp*)WFeSQ]) and complete ([(Tp*)WFeSQ]) cubane-type clusters containing bridging halide (Q = halide). These clusters are achieved by template-assisted assembly in the presence of sodium benzophenone ketyl reductant; products are controlled by reaction stoichiometry. Incomplete cubane clusters are subject to a variety of metathesis reactions resulting in substitution of a -bridging ligand with other bridges such as N, MeO, and EtS Reactions of complete cubanes with MeSiN and S undergo a redox metathesis process and lead to core ligand displacement and formation of [(Tp*)WFeS(-Q)Cl] (Q = MeSiN, S). This work affords entry to a wide variety of heteroleptic clusters derivable from incomplete and complete cubanes; examples are provided. Among these is the cluster [(Tp*)WFeS(-NSiMe)Cl], one of the very few instances of a synthetic Fe-S cluster containing a light atom (C, N, O) in the core, which constitutes a close mimic of the [MoFeSC] fragment in FeMo cofactor. Superposition of them and comparison of metric information disclose a clear structural relationship [Tp* = tris(3,5-dimethyl-1-pyrazolyl)hydroborate(1-)].
The rational synthesis of iron–sulfur clusters with excellent control of the core ligands has been a significant challenge in biomimetic chemistry. In this work, the rational construction of versatile Mo–Fe–S cubane clusters was realized using a LEGO strategy. (LEGO is a line of plastic construction toys consisting of various interlocking plastic bricks which can be assembled and connected in different ways to construct versatile objects. Herein we use "LEGO strategy" as an analogy for the stepwise synthetic methodology, and we use "brick" to represent a corner atom of the cubane structure.) Through careful synthetic control, the ⟨Fe⟩, ⟨S⟩, and ⟨Cl⟩ bricks were mounted piece-by-piece onto the basic ⟨MoS3⟩ frame to stepwise construct the incomplete cubane core ⟨MoFe2S3Cl⟩ and the complete cubane core ⟨MoFe3S3Cl⟩. The significantly elongated Fe–Cl bonds for the bridging chlorides in the ⟨MoFe2S3Cl⟩ and ⟨MoFe3S3Cl⟩ cores permit ligand metatheses to introduce 2p donors at the bridging sites, which used to be a challenge in traditional iron–sulfur chemistry. Therefore, in subsequent controlled reactions, the bridging ⟨Cl⟩ bricks of the ⟨MoFe2S3Cl⟩ and ⟨MoFe3S3Cl⟩ frames could be easily replaced by ⟨N⟩ , ⟨O⟩, or ⟨S⟩ bricks to generate the ⟨MoFe2S3N⟩, ⟨MoFe2S3O⟩, ⟨MoFe3S3N⟩, and ⟨MoFe3S4⟩ cluster cores, demonstrating more choices for the LEGO synthetic strategy. The series of Mo–Fe–S clusters and their derivatives, together with related synthetic strategies, offers a good platform and methodology for biomimetic chemistry in relation to nitrogenase, especially the FeMo cofactor.
Incorporation of monatomic 2p ligands into the core of iron-sulfur clusters has been researched since the discovery of interstitial carbide in the FeMo cofactor of Mo-dependent nitrogenase,but has proven to be asynthetic challenge.Herein, two distinct synthetic pathwaysa re rationalized to install nitride ligands into targeted positions of W-Fe-S clusters, generating unprecedented nitride-ligated iron-sulfur clusters, namely [(Tp*) 2 W 2 Fe 6 (m 4 -N) 2 S 6 L 4 ] 2À (Tp* = tris(3,5-dimethyl-1-pyrazolyl)hydroborate(1À), L = Cl À or Br À ). 57 Fe Mçssbauer study discloses metal oxidation states of W IV 2 Fe II 4 Fe III 2 with localized electron distribution, which is analogous to the midvalent iron centres of FeMo cofactor at resting state.G ood agreement of Mçssbauer data with the empirical linear relationship for Fe-S clusters indicates similar ligand behaviour of nitride and sulfide in such clusters,p roviding useful reference for reduced nitrogen in an itrogenase-like environment.Scheme 1. Distinct synthetic pathwayso fcluster 3.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.
Carbon black (CB) is commonly used to support Pt as an electrocatalyst in fuel cells. However, it is easily corroded in electrochemical reactions, such as in the oxygen reduction reaction (ORR), leading to catalyst degradation. In this paper, we report results of protecting the CB using an ultrathin 5 nm film of niobium oxide conformally coated on the CB using a new coating technique. Electrochemical test in ORR shows only a 1.7 % activity loss after 5000 cycles, demonstrating an excellent durability of the electrocatalyst. Compared to the electrocatalyst without niobium oxide coating, it shows a 25 mV improvement in half-wave potentials, indicative of a better kinetics. A positive shift in binding energy was found in Pt 4 f, implying electron delocalization has occurred when Pt is interfaced with the niobium oxide support. The activity enhancement is attributed to the electronic structure change in the electrocatalyst as a result of metal-support interactions.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.