A sulfur-templated Ni-Ni' coordination polymer that relies on a polarizable nickel nitrosyl hub.

The templating properties of a diaza-nickel--dithiolate towards triphenylphosphine gold(I), yielding a [Ni(NS)·2Au(PPh)] complex (T. A. Pinder, S.

From [2Mn2S] Diamond Cores to Butterfly Rhombs: Transformations That Highlight Alternating Peptide Binding Sites.

Thiocarboxamide chelates are known to assemble [2Mn2S] diamond core complexes via μ-S bridges that connect two Mn(CO) fragments. These can exist as and -isomers and interconvert via 16-electron, monomeric intermediates. Herein, we demonstrate that reduction of such Mn derivatives leads to a loss of one thiocarboxamide ligand and a switch of ligand binding mode from an O- to N-donor of the amide group, yielding a dianionic butterfly rhomb with a short Mn-Mn distance, 2.

Site specific redox properties in ligand differentiated di-nickel complexes inspired by the acetyl CoA synthase active site.

Bimetallic transition metal complexes with site-specific redox properties offer a versatile platform for understanding electron polarization, intramolecular electron transfer processes, and customizing electronic and magnetic properties that might impact reactivity and catalyst design. Inspired by the dissymmetric nickel sites in the Acetyl CoA Synthase (ACS) Active Site, three new bimetallic Ni(NS)-Ni(SCR) complexes based on Ni(NS) metalloligand donor synthons, Ni, in mimicry of the nickel site distal to the redox-active iron sulfur cluster of ACS, and nickel dithiolene receiver units, designated as Ni, the nickel proximal to the 4Fe4S cluster, were combined to explore the influence of ligand environment on electronic structure and redox properties of each unit. The combination of synthons gave a matrix of three S-bridged dinickel complexes, characterized by X-ray crystallography, and appropriate spectroscopies.

Development of (NO)Fe(NS) as a Metallodithiolate Spin Probe Ligand: A Case Study Approach.

ConspectusThe ubiquity of sulfur-metal connections in nature inspires the design of bi- and multimetallic systems in synthetic inorganic chemistry. Common motifs for biocatalysts developed in evolutionary biology include the placement of metals in close proximity with flexible sulfur bridges as well as the presence of π-acidic/delocalizing ligands. This Account will delve into the development of a (NO)Fe(NS) metallodithiolate ligand that harnesses these principles.

A single carbon atom controls the geometry and reactivity of Co(NS) complexes.

Three- . two-carbon N-to-N connectors give rise to monomeric, tetrahedral NSCo(II) ( = 4.24 BM) or dimeric [(NS)Co(II)] (diamagnetic) complexes, respectively.

Sulfur Lone Pairs Control Topology in Heterotrimetallic Complexes: An Experimental and Theoretical Study.

Heterotrimetallic complexes with (NS)M metallodithiolates, M = Ni, [Fe(NO)], and [Co(NO)], as bidentate chelating ligands to a central trans-Cr(NO)(MeCN) unit were characterized as the first members of a new class, , , . The complexes exhibit a cisoid structural topology, ascribed to the stereoactivity of the available lone pair(s) on the sulfur donors, resulting in a dispersed, electropositive pocket from the N/N and N/S hydrocarbon linkers wherein the Cr-NO site is housed. Computational studies explored alternative isomers (transoid and inverted cisoid) that suggest a combination of electronic and steric effects govern the geometrical selectivity.

Bond Trading: Intramolecular Metal and Ligand Exchange within a NO/Ni/Co Complex.

With the goal of generating hetero-redox levels on metals as well as on nitric oxide (NO), metallodithiolate (N S )Co (NO ), N S = N,N- dibenzyl-3,7-diazanonane-1,9-dithiolate, is introduced as ligand to a well-characterized labile [Ni (NO) ] synthon. The reaction between [Ni (NO )] and [Co (NO )] has led to a remarkable electronic and ligand redistribution to form a heterobimetallic dinitrosyl cobalt [(N S )Ni ∙Co(NO) ] complex with formal two electron oxidation state switches concomitant with the nickel extraction or transfer as Ni into the N S ligand binding site. To date, this is the first reported heterobimetallic cobalt dinitrosyl complex.

Magnetic coupling between Fe(NO) spin probe ligands through diamagnetic Ni, Pd and Pt tetrathiolate bridges.

Reaction of the nitrosylated-iron metallodithiolate ligand, paramagnetic (NO)Fe(NS), with [M(CHCN)][BF] salts (M = Ni, Pd, and Pt; = 4 or 6) affords di-radical tri-metallic complexes in a stairstep type arrangement ([FeMFe], M = Ni, Pd, and Pt), with the central group 10 metal held in a MS square plane. These isostructural compounds have nearly identical (NO) stretching values, isomer shifts, and electrochemical properties, but vary in their magnetic properties. Despite the intramolecular Fe⋯Fe distances of 6 Å, antiferromagnetic coupling is observed between {Fe(NO)} units as established by magnetic susceptibility, EPR, and DFT studies.

Chirality-Guided Isomerization of MnS Diamond Core Complexes: A Mechanistic Study.

Occasioned by the discovery of a ligand transfer from M(NS) to Mn in Mn(CO)Br, the resulting HNS ligand-tethered dimanganese complex, (μ-,'-ethylenebis(mercaptoacetamide))[Mn(CO)], was found to have myriad analogues of the type (μ-S-E)[Mn(CO)], making up an under-studied class containing MnS rhombs. The attempt to synthesize a nontethered version resulted in a solid-state structure in an -conformation. However, a direct comparison of the Fourier-transform infrared spectra of the tethered versus nontethered complexes in combination with theoretical frequency calculation suggested the coexistence of - and -isomers and their interconversion in solution.

Cooperative redox and spin activity from three redox congeners of sulfur-bridged iron nitrosyl and nickel dithiolene complexes.

The synthesis of sulfur-bridged Fe-Ni heterobimetallics was inspired by Nature's strategies to "trick" abundant first row transition metals into enabling 2-electron processes: redox-active ligands (including pendant iron-sulfur clusters) and proximal metals. Our design to have redox-active ligands on each metal, NO on iron and dithiolene on nickel, resulted in the observation of unexpectedly intricate physical properties. The metallodithiolate, (NO)Fe(NS), reacts with a labile ligand derivative of [Ni(SCPh)], Ni, yielding the expected S-bridged neutral adduct, , containing a doublet {Fe(NO)}.

Zinc thiotropolone combinations as inhibitors of the SARS-CoV-2 main protease.

Numerous organic molecules are known to inhibit the main protease of SARS-CoV-2, (SC2M), a key component in viral replication of the 2019 novel coronavirus. We explore the hypothesis that zinc ions, , bind to the SC2M enzyme in combination with lipophilic tropolone and thiotropolone ligands, , block substrate docking, and inhibit function. This study combines synthetic inorganic chemistry, protease activity assays, and computational modeling.

Dinitrosyl iron complexes (DNICs) as inhibitors of the SARS-CoV-2 main protease.

By repurposing DNICs designed for other medicinal purposes, the possibility of protease inhibition was investigated in silico using AutoDock 4.2.6 (AD4) and in vitro via a FRET protease assay.

Linear and Bent Nitric Oxide Ligand Binding in an Asymmetric Butterfly Complex: .

Two synthetic approaches to install metallodithiolate ligands on molybdenum centers using the synthons [Mo(CHCN)] and (NS)Co(NO) [NS = ,-bis(2-mercaptoethyl)-1,4-diazacycloheptane and NO = nitric oxide], or [Mo(NO)(CHCN)] (CHCN = acetonitrile) and [(NS)Co] lead to a bis-nitrosylated, trimetallic dication, . This unique asymmetric butterfly complex, with = 1, has a bent NO within the small {Co(NO)} wing (denoted as ), reflecting Co(NO), and is S-bridged to a linear {Mo(NO)} diamagnetic unit. The latter is further S-bridged to a pentacoordinate (NS)Co(CHCN) donor in the larger wing and is the origin of the two unpaired electrons, denoted as .

The roles of chalcogenides in O protection of Hase active sites.

At some point, all HER (Hydrogen Evolution Reaction) catalysts, important in sustainable HO splitting technology, will encounter O and O-damage. The [NiFeSe]-Hases and some of the [NiFeS]-Hases, biocatalysts for reversible H production from protons and electrons, are exemplars of oxygen tolerant HER catalysts in nature. In the hydrogenase active sites oxygen damage may be extensive (irreversible) as it is for the [FeFe]-Hase or moderate (reversible) for the [NiFe]-Hases.

Self-Assembled Nickel-4 Supramolecular Squares and Assays for HER Electrocatalysts Derived Therefrom.

Solid-state structures find a self-assembled tetrameric nickel cage with carboxylate linkages, [Ni(NS'O)I(CHCN)] ([]), resulting from sulfur acetylation by sodium iodoacetate of an [NiNS] dimer in acetonitrile. Various synthetic routes to the tetramer, best described from XRD as a molecular square, were discovered to generate the hexacoordinate nickel units ligated by NS, iodide, and two carboxylate oxygens, one of which is the bridge from the adjacent nickel unit in []. Removal of the four iodides by silver ion precipitation yields an analogous species but with an additional vacant coordination site, [], a cation but with coordinated solvent molecules.

Effects of Glutathione and Histidine on NO Release from a Dimeric Dinitrosyl Iron Complex (DNIC).

Rates of NO release from synthetic dinitrosyl iron complexes (DNICs) are shown to be responsive to coordination environments about iron. The effect of biologically relevant cellular components, glutathione and histidine, on the rate of NO release from a dimeric, "Roussin's Red Ester", DNIC with bridging μ-S thioglucose ligands, SGlucRRE or [(μ-SGluc)Fe(NO)] (SGluc = 1-thio-β-d-glucose tetraacetate), was investigated. From the Griess assay and X-band EPR data, decomposition of the product from the histidine-cleaved dimer, [(SGluc)(N)Fe(NO)], generated Fe(III) and increased the NO release rate in aqueous media when compared to the intact SGlucRRE precursor.

Synthetic Metallodithiolato Ligands as Pendant Bases in [FeFe], [Fe[Fe(NO)]], and [(μ-H)FeFe] Complexes.

The development of ligands with specific stereo- and electrochemical requirements that are necessary for catalyst design challenges synthetic chemists in academia and industry. The crucial aza-dithiolate linker in the active site of [FeFe]-Hase has inspired the development of synthetic analogues that utilize ligands which serve as conventional σ donors with pendant base features for H binding and delivery. Several MNS complexes (M = Ni, [Fe(NO)], [Co(NO)], etc.

Metal-Templated, Tight Loop Conformation of a Cys-X-Cys Biomimetic Assembles a Dimanganese Complex.

With the goal of generating anionic analogues to MN S ⋅Mn(CO) Br we introduced metallodithiolate ligands, MN S prepared from the Cys-X-Cys biomimetic, ema ligand (ema=N,N'-ethylenebis(mercaptoacetamide); M=Ni , [V ≡O] and Fe ) to Mn(CO) Br. An unexpected, remarkably stable dimanganese product, (H N (CH C=O(μ-S)) )[Mn(CO) ] resulted from loss of M originally residing in the N S pocket, replaced by protonation at the amido nitrogens, generating H ema . Accordingly, the ema ligand has switched its coordination mode from an N S cavity holding a single metal, to a binucleating H ema with bridging sulfurs and carboxamide oxygens within Mn-μ-S-CH -C-O, 5-membered rings.

Controlling O Reactivity in Synthetic Analogues of [NiFeS]- and [NiFeSe]-Hydrogenase Active Sites.

Strategies for limiting, or reversing, the degradation of air-sensitive, base metal catalysts for the hydrogen evolution/oxidation reaction on contact with adventitious O are guided by nature's design of hydrogenase active sites. The affinity of oxygen for sulfur and selenium, in [NiFeS]- and [NiFeSe]-Hase, yields oxygenated chalcogens under aerobic conditions, and delays irreversible oxygen damage at the metals by maintaining the NiFe core structures. To identify the controlling features of S-site oxygen uptake, related (μ-E)(μ-S') (E = S or Se, = (η-CH)Fe(CO)) complexes were electronically tuned by the para-substituent on μ-EPhX (X = CF, Cl, H, OMe, NMe) and compared in aspects of communication between Ni and Fe.

Toward the Optimization of Dinitrosyl Iron Complexes as Therapeutics for Smooth Muscle Cells.

In this study, dinitrosyl iron complexes (DNICs) are shown to deliver nitric oxide (NO) into the cytosol of vascular smooth muscle cells (SMCs), which play a major role in vascular relaxation and contraction. Malfunction of SMCs can lead to hypertension, asthma, and erectile dysfunction, among other disorders. For comparison of the five DNIC derivatives, the following protocols were examined: (a) the Griess assay to detect nitrite (derived from NO conversion) in the absence and presence of SMCs; (b) the 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2 H-tetrazolium (MTS) assay for cell viability; (c) an immunotoxicity assay to establish if DNICs stimulate immune response; and (d) a fluorometric assay to detect intracellular NO from treatment with DNICs.

Proton affinity studies of nickel NS complexes and control of aggregation.

The thiolate ligands of [NiFe]-Hase enzymes have been implicated as proton-binding sites for the reduction/oxidation of H/H. This study examines the ligand effect on reactivity of NiNS complexes with an array of acids in methanol solution. UV-Vis absorption spectroscopy is utilized to observe the transformation from the monomeric species to a trimetallic complex that is formed after proton-induced ligand dissociation.

Oxygen uptake in complexes related to [NiFeS]- and [NiFeSe]-hydrogenase active sites.

A biomimetic study for S/Se oxygenation in Ni(μ-EPh)(μ-SN)Fe, (E = S or Se; SN = Me-diazacycloheptane-CHCHS); Fe = (η-CH)Fe(CO) complexes related to the oxygen-damaged active sites of [NiFeS]/[NiFeSe]-Hases is described. Mono- and di-oxygenates (major and minor species, respectively) of the chalcogens result from exposure of the heterobimetallics to O; one was isolated and structurally characterized to have Ni-O-Se-Fe-S connectivity within a 5-membered ring. A compositionally analogous mono-oxy species was implicated by (CO) IR spectroscopy to be the corresponding Ni-O-S-Fe-S complex; treatment with O-abstraction agents such as P(-tolyl) or PMe remediated the O damage.

Structural and Electronic Responses to the Three Redox Levels of Fe(NO)N S -Fe(NO).

The nitrosylated diiron complexes, Fe (NO) , of this study are interpreted as a mono-nitrosyl Fe(NO) unit, MNIU, within an N S ligand field that serves as a metallodithiolate ligand to a dinitrosyl iron unit, DNIU. The cationic Fe(NO)N S ⋅Fe(NO) complex, 1 , of Enemark-Feltham electronic notation {Fe(NO)} -{Fe(NO) } , is readily obtained via myriad synthetic routes, and shown to be spin coupled and diamagnetic. Its singly and doubly reduced forms, {Fe(NO)} -{Fe(NO) } , 1 , and {Fe(NO)} -{Fe(NO) } , 1 , were isolated and characterized.

Oxygen-Tolerant H Production by [FeFe]-Hase Active Site Mimics Aided by Second Sphere Proton Shuttle.

The instability of [FeFe]-Hases and their biomimetics toward O renders them inefficient to implement in practical H generation (HER). Previous investigations on synthetic models as well as natural enzymes proved that reactive oxygen species (ROS) generated on O exposure oxidatively degrades the 2Fe subcluster within the H-cluster active site. Recent electrochemical studies, coupled with theoretical investigations on [FeFe]-Hase suggested that selective O reduction to HO could eliminate the ROS, and hence, tolerance against oxidative degradation could be achieved ( Nat.