Disulfide Ligands Research Articles

Rhenium(V) Tris(pyrazolyl)borate Thiolate Complex with the Disulfide Bridging Ligand: Synthesis and Structure

The reaction of TpReOCl(StBu) (Tp = tris(pyrazolyl)borate anion) with sodium disulfide in dimethoxyethane affords the new binuclear rhenium complex [TpReO(μ-StBu)]2(μ-S2) (I). Complex I can also be synthesized by the reaction of TpReO(StBu)2 with a suspension of manganese(II) bromide in toluene accompanied by the dealkylation of one of the ligands to form one more new complex [TpReO]2(μ-S2)(μ-S) (II) containing the bridging sulfide and disulfide ligands. The structures of two crystalline solvates of complex I with dichloromethane containing the molecules with different conformations of the Re2S2 fragment (Ia and Ib) and complex II are studied by X-ray diffraction (XRD) (CIF files ССDC nos. 2262677, 2262678, and 2267423 for Ia, Ib, and II, respectively).

Bis[tris-(diiso-butyl-dithio-carbamato)-μ3-sulfido-tri-μ2-di-sulfido-trimolybdenum(IV)] sulfide tetra-hydro-furan monosolvate.

The title compound, [Mo3(C9H18NS2)3(S2)3S]2S, crystallizes on a general position in the monoclinic space group P21/n (No. 14). The cationic [Mo3S7(S2CNiBu2)3]+ fragments are joined by a mono-sulfide dianion that forms close S⋯S contacts to each of the di-sulfide ligands on the side of the Mo3 plane opposite the μ3 2- ligand. The two Mo3 planes are inclined at an angle of 40.637 (15)°, which gives the assembly an open clamshell-like appearance. One μ6-S2-⋯S2 2- contact, at 2.4849 (14) Å, is appreciably shorter than the remaining five, which are in the range 2.7252 (13)-2.8077 (14) Å.

Diamidocarbene-derived palladium and nickel-sulfur clusters.

Novel palladium and nickel-sulfur clusters were synthesized using a diamidocarbene-derived carbon disulfide ligand. Structural characterization revealed a tetranuclear metal-sulfur cluster geometry with each metal center exhibiting square-planar coordination. The ligand was redox-active, accommodating oxidation states ranging from 0 to -2.

Engaging a Non-catalytic Cysteine Residue Drives Potent and Selective Inhibition of Caspase-6.

Caspases are a family of cysteine-dependent proteases with important cellular functions in inflammation and apoptosis, while also implicated in human diseases. Classical chemical tools to study caspase functions lack selectivity for specific caspase family members due to highly conserved active sites and catalytic machinery. To overcome this limitation, we targeted a non-catalytic cysteine residue (C264) unique to caspase-6 (C6), an enigmatic and understudied caspase isoform. Starting from disulfide ligands identified in a cysteine trapping screen, we used a structure-informed covalent ligand design to produce potent, irreversible inhibitors (3a) and chemoproteomic probes (13-t) of C6 that exhibit unprecedented selectivity over other caspase family members and high proteome selectivity. This approach and the new tools described will enable rigorous interrogation of the role of caspase-6 in developmental biology and in inflammatory and neurodegenerative diseases.

NMP makes the difference - facilitated synthesis of [FeFe] hydrogenase mimics.

To overcome the limitations of high reaction temperatures and long reaction times of conventional synthesis routes towards [FeFe] hydrogenase (H2ase) mimicking complexes, we introduced a more efficient synthesis route in the presence of aprotic polar co-solvents such as N-methyl-2-pyrrolidone (NMP). Versatile (di)thiol or disulfide ligands as well as selenium and tellurium analogues were converted to their corresponding complexes. While both reaction times and temperatures were reduced significantly, yields could be increased. Intensive kinetic monitoring of the formation of two [FeFe] H2ase mimics via UV-vis spectroscopy was performed, revealing an increase of the rate constant by one order of magnitude compared to that obtained in the same reaction without NMP. IR spectroscopic examination of the formation of the 1,3-propandithiole analogue (2a) revealed the appearance of a side product, analyzed by IR and UV-vis spectroscopy and mass spectrometry, which was proposed to be a NMP monosubstituted triirondodecacarbonyl (Fe3(CO)11NMP) cluster. Reacting triirondodecacarbonyl (Fe3(CO)12) with NMP in the absence of any additional ligand yielded this species as well. Quantum chemical simulations of Fe3(CO)11NMP indicated structural rearrangements including the omission of bridging carbonyls (μ-CO). Similar observations were made on utilizing other aprotic polar co-solvents.

Preparation of one-dimensional coordination polymers of a flexible tripyridyl disulfide with diverse topologies

The combination of a novel flexible tripyridyl disulfide (L) and coinage metal (CuII and AgI) salts yields diverse types of one-dimensional coordination polymers exhibiting loop chain, ribbon, and ladder topologies.

Structural investigations and reactivity of cobalt(II)–disulfide compounds

Controlling the bio-inspired redox conversion of Co(II)–disulfide compounds to their related Co(III)–thiolate complexes is a perplexing task as the factors triggering this reaction are not fully understood. Three disulfide ligands 2,2′–disulfanediylbis(N,N-bis((3,5–dimethyl-1H–pyrazol–1–yl)methyl)ethan-1-amine) (LmpzSSLmpz), 3,3′-disulfanedylbis(N,N-bis(pyridin-2-ylmethyl)propan-1-amine) (LpSSLp), and 2,2′-disulfanediylbis(N,N-bis(6-methylpyridin-2–ylmethyl)ethan-1–amine) (L3SSL3) with different chain lengths and pyrazole or pyridine groups were reacted with cobalt(II) salts and the resulting complexes were studied for their potential to form Co(III)–thiolate complexes. Crystal structures of [Co2(LmpzSSLmpz)(Br)4] [1Br], [Co2(LmpzSSLmpz)(NCS)4] [1NCS], [Co2(LpSSLp)(NCS)4] [2NCS], and [Co2(L3SSL3)(Cl)4] [3Cl] show that generally the disulfide sulfur donors do not coordinate to the cobalt(II) centers, resulting in dinuclear structures containing two 5-coordinate cobalt centers. However, a unique asymmetric structure is found in [1Br] in which one of the sulfur atoms coordinates to one of the cobalt ions. Thiocyanate–induced Co(III)–thiolate formation in the presence of either ligand LmpzSSLmpz or LpSSLp is evidently unsuccessful, as Co(II)–disulfide complexes were obtained. The reaction of the Co(II)–disulfide complexes with 8-quinolinol suggest that redox conversion to Co(III)–thiolate complexes may take place, but the reactions are not clean.

Antifungal activity, antibiofilm and synergic effect of diallyl disulfide and diallyl trisulfide against Candida albicans

The objective of the present study was to determine the antifungal activity, antibiofilm and synergic effect of the compounds diallyl disulfide and diallyl trisulfide in combination with antifungal agents against clinical isolates of Candida albicans, including also a computational study. Antimicrobial sensitivity tests were performed using the broth microdilution method to determine the minimum inhibitory concentration against C. albicans strains and modulatory activity using the checkerboard technique. The biofilm formation was evaluated by biomass quantification using the violet crystal staining method. For the study of molecular docking computer simulations. The constituents showed relevant antifungal activity against strains of C. albicans. In the modulatory activity assay, demonstrated a synergistic interaction with fluconazole and amphotericin B, with an increase in its antifungal action. The diallyl disulfide, diallyl trisulfide and fluconazole ligands formed complexes with ALS3 enzyme. Then, both compounds were considered promising products for the development of new drugs to prevent candidiasis.

Reactivity between late first-row transition metal halides and the ligand bis(2-pyridylmethyl)disulfide: Vibrantly-colored compounds with variable molecular geometries influenced by metal-sulfur interactions

The reactivity between late first-row transition metal halides and the disulfide-containing ligand bis(2-pyridylmethyl)disulfide was examined. From this survey, a series of mononuclear, four- and five-coordinate metal compounds were prepared and characterized. Single-crystal X-ray diffraction was employed to analyze the molecular structures in the solid state. The four-coordinate, tetrahedral compounds adopt either the form MLX2 (M = Zn; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) where the disulfide ligand is coordinated in a bidentate fashion by two nitrogen donors, or MLX (M = Cu; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) where the ligand is tridentate, coordinating via one sulfur and two nitrogen donors. The five-coordinate metal compounds, though varying significantly with regard to molecular geometry due to metal-sulfur interaction strength, adopt the form MLX2 (M = Zn, Cu, Co; L = bis(2-pyridylmethyl)disulfide; X = Cl, Br) with the ligand serving as a tridentate scaffold employing one sulfur and two nitrogen donors. The crystal structures ZnLCl2•CHCl3 and ZnLBr2•CHCl3 are isomorphous as are the structures ZnLCl2•CH2Cl2, ZnLBr2•CH2Cl2, and CoLBr2•CH2Cl2. The crystal structure of CoLCl2 is a kryptoracemate, having an enantiomeric pair within the asymmetric unit. Although chemically-identical, both hands of CoLCl2 have strikingly different Co–S distances: 2.599(2) versus 2.755(2) Å. Based on the X-ray crystal structures, the choice of halide does not appear to significantly influence the molecular geometry. For the solvated crystal structures, the identity of the solvent molecule has a drastic effect on the metal-sulfur distances. Compounds that contain metal-sulfur coordination do not appreciably affect the disulfide bond, as determined by X-ray crystallography and Raman spectroscopy. In addition to the standard analytical methods, variable-temperature NMR and UV–vis–NIR spectroscopy was utilized to gain insight into the solution behavior of the vibrantly-colored compounds.

Cobalt(II)-disulfide compounds with the unusual PF2O2– anion. ligand-dependent redox conversion to a cobalt(III)-thiolate complex

Herein we describe the synthesis of the cobalt(II) disulfide compounds [CoII2(LxSSLx)(μ–PO2F2)2](PF6)2 and [CoII2(LxSSLx)(NO3)4] (x = 1: di-2-(bis(2-pyridylmethyl)amino)-ethyl disulfide; x = 2: di-2-((6-methyl-2-pyridylmethyl)(2-pyridylmethyl)amino)-ethyl disulfide). The crystal structures show the cobalt(II) centers in [CoII2(LxSSLx)(μ-PO2F2)2](PF6)2 to be in distorted octahedral geometries, whereas in [CoII2(L1SSL1)(NO3)4] the geometries are distorted trigonal bipyramidal. The cobalt(II) centers in [CoII2(LxSSLx)(PO2F2)2](PF6)2 are coordinated by three nitrogen and one sulfur donor atom of the disulfide ligand, and two oxygen atoms of two bridging difluoridophosphate anions. The cobalt(II) centers in [CoII2(L1SSL1)(NO3)4] are coordinated by three nitrogen donors of the ligand and three oxygen atoms of one monodentate and one bidentate nitrate anion, the latter two oxygen atoms together occupying one of the equatorial sites of the trigonal bipyramid. It was found that the dinuclear compound [CoII2(L1SSL1)(PO2F2)2](PF6)2 is stable as such in methanol and dichloromethane solution, but in acetonitrile redox conversion occurs forming the cobalt(III) thiolate compound [CoIII(L1S)(MeCN)2]2+. The compound [CoII2(L1SSL1)(NO3)4] and the disulfide compounds of the ligand L2SSL2 do not show this redox conversion and remain in the disulfide form in all investigated solvents.

Probing the redox-conversion of Co(II)-disulfide to Co(III)-thiolate complexes: the effect of ligand-field strength.

The redox-conversion reaction of cobalt(II)-disulfide to cobalt(III)-thiolate complexes triggered by addition of the bidentate ligand 2,2'-bipyridine has been investigated. Reaction of the cobalt(II)-disulfide complex [Co2(L1SSL1)(X)4] (L1SSL1 = di-2-(bis(2-pyridylmethyl)amino)-ethyldisulfide; X = Cl or Br) [1X] with 2,2'-bipyridine (bpy) resulted in the formation of two different products, namely the cobalt(III)-thiolate complex [Co(L1S)(bpy)]X2 and the unexpected side product [Co2(L1SSL1)(bpy)2(X)2]X2. Crystals of [Co2(L1SSL1)(bpy)2(Cl)2](BPh4)2 [2Cl](BPh4)2 obtained after anion exchange showed the cobalt(II) ions to be in octahedral geometries with the nitrogen donors of the disulfide ligand arranged in a facial conformation and the chloride ion trans to the tertiary amine nitrogen. Remarkably, this side product cannot be converted to the cobalt(III)-thiolate compound [Co(L1S)(bpy)](SbF6)2 [3](SbF6)2 by removal of the chloride ion with use of a silver salt, as this causes scrambling of the ligands, resulting in the formation of [Co(bpy)3]n+. [Co(L1S)(bpy)](SbF6)2 was obtained in a pure form by addition of bpy to a solution in acetonitrile of the compound [Co(L1S)(MeCN)2]2+ [4]2+. Addition of NEt4Cl to [3](SbF6)2 regenerates the cobalt(II)-disulfide complex [1Cl] as confirmed spectroscopically. DFT studies revealed that the conversion from [1Cl] to [3]2+ most likely occurs via the hypothetical intermediate species [2Cl]2+mer, in which the nitrogen atoms of the disulfide ligand are arranged in a meridional conformation. Interestingly, the estimated d-orbital splitting energy of [3]2+ is lower than that of [4]2+, indicating that the ligand-field strength of bpy is lower than anticipated, which hampers clean conversion in the redox-conversion reaction. This study shows that the redox-conversion reaction between cobalt(II)-disulfide and cobalt(III)-thiolate complexes is intricate rather than straightforward.

Iron-catalyzed arene C-H hydroxylation.

The sustainable, undirected, and selective catalytic hydroxylation of arenes remains an ongoing research challenge because of the relative inertness of aryl carbon-hydrogen bonds, the higher reactivity of the phenolic products leading to over-oxidized by-products, and the frequently insufficient regioselectivity. We report that iron coordinated by a bioinspired -cystine–derived ligand can catalyze undirected arene carbon-hydrogen hydroxylation with hydrogen peroxide as the terminal oxidant. The reaction is distinguished by its broad substrate scope, excellent selectivity, and good yields, and it showcases compatibility with oxidation-sensitive functional groups, such as alcohols, polyphenols, aldehydes, and even a boronic acid. This method is well suited for the synthesis of polyphenols through multiple carbon-hydrogen hydroxylations, as well as the late-stage functionalization of natural products and drug molecules.

Recyclable chalcopyrite sorbent for mercury removal from coal combustion flue gas

The development of cost-effective and high-efficient technologies for degrading Hg0 pollution from coal combustion flue gas remains a tremendous challenge. In this work, an earth-abundant mineral, i.e., chalcopyrite (CuFeS2), was adopted as an efficient trap for Hg0 sequestration. The CuFeS2 exhibited approximately excellent Hg0 removal performances in a wide temperature ranging from 40 to 100 °C. Typical flue gas components including oxygen (O2), sulfur dioxide (SO2), nitrogen monoxide (NO), and water vapor (H2O) negligibly interfered the Hg0 adsorption ability, which further solidify the application potential of CuFeS2 in coal-fired power plant. The Hg0 adsorption capacity and uptake rate was 37.24 mg·g−1 and 63.40 μg·g−1·min−1, respectively, significantly suppressing those of commercial activated carbons. The superior performance of CuFeS2 were primarily attributed that the disulfide ligands (S22−) could oxidize Hg0 into Hg2+ and subsequently immobilize Hg2+ into mercury sulfide (HgS). The spent CuFeS2 sorbent could be replenished and regenerated by a thermal decomposition method, which pronouncedly save the operation cost. Therefore, the CuFeS2 is a potential trap for cost-effective and efficient Hg0 remediation from coal combustion flue gas.

Exploration of Theoretical and Antioxidant Mimetic Activities of Binuclear Copper(II) and Nickel(II) Coordination Complexes

Three dinuclear copper(II) and nickel(II) complexes viz. [Cu2(La)(py)2]·(ClO4)2 (1), [Ni2(Lb)(ImH)2]·(ClO4)2 (2) and [Ni2(Lc)(H2O)2]·(ClO4)2 (3) were designed and synthesized using disulfide and auxiliary ligands as functional models for antioxidant superoxide dismutase enzyme (where, H2La-H2Lc = disulfide ligands bearing S-S bond, py = pyridine, ImH = imidazole). The disulfide ligands were synthesized by condensation reaction of 2-(2-(2-aminophenyl)disulfanyl)benzeneamine with 3-bromo-2-hydroxy-5-nitrobenzaldehyde; 5-bromo-2-hydroxybenzaldehyde and 3,5-dichloro- 2-hydroxybenzaldehyde, respectively. All the compounds were characterized by various spectrometry methods. The molecular docking study was performed against penicillin binding protein 4 (PBP4) active site pocket and E. coli DNA Gyrase B ATPase domain to evaluate the possible mechanism of antibacterial property of disulfide ligands. The results revealed that H2La-H2Lc possess higher binding affinity for active site of PBP4 and Gyrase B ATPase domain. The present study also demonstrated that disulfide compounds have potential to inhibit the PBP4 and Gyrase B ATPase domain and can be developed as lead compounds. In addition, antioxidant superoxide dismutase (SOD) activity is also discussed of these complexes. The antioxidant superoxide measurements show that complexes behave as superoxide mimic in alkaline nitro blue tetrazolium chloride (NBT) assay.

Water-Soluble α-Amino Acid Complexes of Molybdenum as Potential Antidotes for Cyanide Poisoning: Synthesis and Catalytic Studies of Threonine, Methionine, Serine, and Leucine Complexes.

Water-soluble complexes are desirable for the aqueous detoxification of cyanide. Molybdenum complexes with α-amino acid and disulfide ligands with the formula K[(L)Mo2O2(μ-S)2(S2)] (L = leu (1), met (2), thr (3), and ser (4)) were synthesized in a reaction of [(DMF)3MoO(μ-S)2(S2)] with deprotonated α-amino acids; leu, met, thr, and ser are the carboxylate anions of l-leucine, l-methionine, l-threonine, and l-serine, respectively. Potassium salts of α-amino acids (leu (1a), met (2a), thr (3a), and ser (4a)) were prepared as precursors for complexes 1-4, respectively, by employing a nonaqueous synthesis route. The ligand exchange reaction of [Mo2O2(μ-S)2(DMF)6](I)2 with deprotonated α-amino acids afforded bis-α-amino acid complexes, [(L)2Mo2O2(μ-S)2] (6-8). A tris-α-amino acid complex, [(leu)2Mo2O2(μ-S)2(μ-leu + H)] (5; leu + H is the carboxylate anion of l-leucine with the amine protonated), formed in the reaction with leucine. 5 crystallized from methanol with a third weakly bonded leucine as a bridging bidentate carboxylate. An adduct of 8 with SCN- coordinated, 9, crystallized and was structurally characterized. Complexes 1-4 are air stable and highly water-soluble chiral molecules. Cytotoxicity studies in the A549 cell line gave IC50 values that range from 80 to 400 μM. Cyclic voltammetry traces of 1-8 show solvent-dependent irreversible electrochemical behavior. Complexes 1-4 demonstrated the ability to catalyze the reaction of thiosulfate and cyanide in vitro to exhaustively transform cyanide to thiocyanate in less than 1 h.

SYNTHESIS AND CHARACTERIZATION OF N-(4-ACETYLPHENYL)-N-(DIPHENYLPHOSPHINO)- P,P-DIPHENYLPHOSPHINOUS AMIDE DERIVATIVES: APPLICATION OF A Pd(ΙΙ) DERIVATIVE AS A PRE-CATALYST IN THE SUZUKI CROSS-COUPLING REACTION

The reaction of p-aminoacetophenone with two equivalents of chlorodiphenylphosphine yields the (p-CH3CO)C6H4N(PPh2)2 ligand (1) in a good yield. The oxidation of 1 with elemental sulfur or grey selenium gives the corresponding disulfide and diselenide bis(phosphanyl)amine ligands (p-CH3CO)C6H4N(P(E)Ph2)2 (E = S(2), Se(3)), respectively. Reactions of 1 with group-10B metals afford $$cis\text{-}M\text{C}{{\text{l}}_{\text{2}}}[\mathbf{1}-{}_{k}^{2}P,P]\ (M=\text{Pd}\,(\mathbf{4}),\ \text{Pt}\,(\mathbf{5})),$$ respectively. Compounds 1-5 are identified and characterized by multinuclear NMR spectroscopy (1H, 13C, 31P, 77Se NMR), IR spectroscopy, and the elemental analysis. Crystal structure determinations are carried out for 2 and 3. The application of the Pd(II) complex as a pre-catalyst in the Suzuki cross-coupling reaction is also investigated.

Crystal structure of the unusual coordination polymer catena-poly[[gold(I)-μ-1,2-bis-(di-phenyl-phosphino-thio-yl)ethane-κ2 S:S'] di-bromido-aurate(I)

In the title compound, {[Au(C26H24P2S2)][AuBr2]} n , the gold(I) centres of the cation are coordinated by the P=S groups of the di-sulfide ligands to form a chain polymer parallel to the c axis. Both independent gold atoms lie on the same twofold axis, and the midpoint of the H2C-CH2 bond lies on an inversion centre. The anions flank the polymeric chain; they are connected to it by short aurophilic inter-actions and C-H⋯Br contacts, and to each other by Br⋯Br contacts.

Less Reactive Thiol Ligands: Key towards Highly Mucoadhesive Drug Delivery Systems.

As less reactive s-protected thiomers can likely interpenetrate the mucus gel layer to a higher extent before getting immobilized via disulfide bond formation with mucins, it was the aim of this study to develop a novel type of s-protected thiomer based on the less reactive substructure cysteine-N-acetyl cysteine (Cys-NAC) in order to obtain improved mucoadhesive properties. For this purpose, two types of s-protected thiomers, polyacrylic acid-cysteine-mercaptonicotinic acid (PAA-Cys-MNA) and polyacrylic acid-cysteine-N-acetyl cysteine (PAA-Cys-NAC), were synthesized and characterized by Fourier-transform infrared spectroscopy (FT-IR) and the quantification of attached disulfide ligands. The viscosity of both products was measured in the presence of NAC and mucus. Both thiomers were also evaluated regarding swelling behavior, tensile studies and retention time on the porcine intestinal mucosa. The FT-IR spectra confirmed the successful attachment of Cys-MNA and Cys-NAC ligands to PAA. The number of attached sulfhydryl groups was in the range of 660–683 µmol/g. The viscosity of both s-protected thiomers increased due to the addition of increasing amounts of NAC. The viscosity of the mucus increased in the presence of 1% PAA-Cys-MNA and PAA-Cys-NAC 5.6- and 10.9-fold, respectively, in comparison to only 1% PAA. Both s-protected thiomers showed higher water uptake than unmodified PAA. The maximum detachment force (MDF) and the total work of adhesion (TWA) increased in the case of PAA-Cys-MNA up to 1.4- and 1.6-fold and up to 2.4- and 2.8-fold in the case of PAA-Cys-NAC. The retention of PAA, PAA-Cys-MNA, and PAA-Cys-NAC on porcine intestinal mucosa was 25%, 49%, and 76% within 3 h, respectively. The results of this study provide evidence that less reactive s-protected thiomers exhibit higher mucoadhesive properties than highly reactive s-protected thiomers.

Stability, Structure and Reconstruction of 1H-Edges in MoS2.

Density functional studies of the edges of single-layer 1H-MoS2 are presented. This phase presents a rich variability of edges that can influence the morphology and properties of MoS2 nano-objects, play an important role in industrial chemical processes, and find future applications in energy storage, electronics and spintronics. The so-called Mo-100 %S edges vertical S-dimers were confirmed to be stable, however the authors also identified a family of metastable edges combining Mo atoms linked by two-electron donor symmetrical disulfide ligands and four-electron donor unsymmetrical disulfide ligands. These may be entropically favored, potentially stabilizing them at high temperatures as a "liquid edge" phase. For Mo-50 %S edges, S-bridge structures with 3× periodicity along the edge are the most stable, compatible with a Peierls' distortion arising from the d-bands of the edge Mo atoms. An additional explanation for this periodicity is proposed through the formation of 3-center bonds.

Nickel(II)‐Mediated Reversible Thiolate/Disulfide Conversion as a Mimic for a Key Step of the Catalytic Cycle of Methyl‐Coenzyme M Reductase

AbstractAccording to the well‐accepted mechanism, methyl‐coenzyme M reductase (MCR) involves Ni‐mediated thiolate‐to‐disulfide conversion that sustains its catalytic cycle of methane formation in the energy saving pathways of methanotrophic microbes. Model complexes that illustrate Ni‐ion mediated reversible thiolate/disulfide transformation are unknown. In this paper we report the synthesis, crystal structure, spectroscopic properties and redox interconversions of a set of NiII complexes comprising a tridentate N2S donor thiol and its analogous N4S2 donor disulfide ligands. These complexes demonstrate reversible NiII‐thiolate/NiII‐disulfide (both bound and unbound disulfide‐S to NiII) transformations via thiyl and disulfide monoradical anions that resemble a primary step of MCR's catalytic cycle.