Redox Interconversion of Non-Oxido Vanadium Complexes

Jul 14, 2017 - Complex 3 can be converted to complex 2 through one-electron reduction followed by protonation of thiolate to thiol, or through the rev...
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Redox Interconversion of Non-Oxido Vanadium Complexes Accompanied by Acid−Base Chemistry of Thiol and Thiolate Jyun-An Yan,† Yu-Sen Chen,† Ya-Ho Chang,† Cheng-Yun Tsai,† Chiao-Ling Lyu,† Chun-Gang Luo,† Gene-Hsiang Lee,‡ and Hua-Fen Hsu*,† †

Department of Chemistry, National Cheng Kung University, Tainan 701, Taiwan Department of Chemistry, National Taiwan University, Taipei 106, Taiwan

‡

S Supporting Information *

ABSTRACT: The redox nature of the non-oxido vanadium sulfur center is associated with several biological systems such as vanadium nitrogenase, the reduction of vanadium ion in ascidians, and the function of amavadin, which is a vanadium(IV) natural product contained in Amanita mushrooms. But the related chemistry is less explored and understood compared to oxido vanadium species due to the oxophilic character of high valent vanadium ions. Herein, we present a class of non-oxido vanadium thiolate complexes, [VIII(PS2″SH)2]− (1) (PS2″SH = [P(C6H3-3-Me3Si-2-S)2(C6H3-3Me3Si-2-SH)]2−), [VIV(PS3″)(PS2″SH)]− (2) (PS3″ = [P(C6H3-3Me3Si-2-S)3]3−), [V(PS3″)2]− (3), [V(PS3″)(PS2″SH)] (4), and [VIV(PS3*)2]2− (5a) (PS3* = [P(C6H3-3-Ph-2-S)3]3−), and study their interconversion through the redox and acid−base reactions. Complex 1 consists of a six-coordinate octahedral vanadium center; complexes 2 and 4 are seven-coordinate with distorted capped trigonal prismatic geometry. Vanadium centers of 3 and 5a are both eight-coordinate; the former adopts ideal dodecahedral geometry, but the latter is better viewed as a distorted square antiprism. Complex 1 is oxidized to complex 2 and then to complex 3 with dioxygen. Each one-electron oxidation process is accompanied by the deprotonation of unbound thiol to bound thiolate. Complex 3 is also produced from complex 2 through stepwise addition of Fe(Cp)2+/n-BuLi, or in the reverse order. The formation of 2 from 3 is achieved in the order of adding Co(Cp)2 and acid or, as with the previous complex, inversely. Notably, the reduction of complex 2 to complex 1 accompanying the protonation of bound thiolate to unbound thiol only occurs with the presence of both Co(Cp)2 and acid, indicating a cooperative effect between the metal-centered reduction and bound thiolate protonation. The conversions among these complexes are observed with ESI-MS and UV−vis−NIR spectroscopies. The work demonstrates two-electron redox interconversion in these complexes mediated by transformations between unbound thiol and bound thiolate.

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cluster (M = V and Mo for FeVco and FeMoco, respectively).7 Some studies have suggested that iron sites of the FeMoco “waist” might be a catalytic pocket,8 but the roles of Mo and V sites in FeVco and FeMoco, respectively, are relatively less focused and addressed.9 Thus, knowing the features of vanadium/molybdenum sulfur chemistry can be a conduit for a better understanding of the function of heterometallic sites in nitrogenases. The ancient class of invertebrates Ascidiacea devotes considerable energy to concentrating VIII ions in their blood cells; however, what purpose this serves, or might have served in the distant past, is not known.10 The process whereby these marine animals reduce H2VO4−, acquired from their seawater environment, to VIII, for storage in their blood cells, is also not understood. Glutathione and cysteine may play roles in this redox transformation, either acting as reductants or facilitating redox potential through deprotonation/protonation

INTRODUCTION Metal thiolates interest many researchers because metal− cysteine is involved in various metalloproteins.1 The metal center redox change in accompanying protonation and deprotonation of Cys residue to form metal thiol and thiolate forms, respectively, often plays an important role for the function of enzymes such as heme-thiolate nitric oxide synthase (NOS) and P450 deactivation.2 Vanadium thiolate chemistry has been a focus of study due to its broad application to biology.3 Vanadium sulfur bond or the interaction of vanadium ion with biological S-donors such as glutathione and cysteine is associated with several vanadium related biological systems.4 An example of a vanadium sulfur containing system is vanadium nitrogenase, which catalyzes biological nitrogen fixation.5 It was also found recently to carry out reductive C−C bond coupling with CO and protons.6 Its atomic structure has not been resolved by X-ray crystallography, but the active site, FeV cofactor, likely shares a similar structural motif with FeMo cofactor in Mo-nitrogenase, both consisting of a [MFe7S9C] © 2017 American Chemical Society

Received: April 27, 2017 Published: July 14, 2017 9055

DOI: 10.1021/acs.inorgchem.7b01040 Inorg. Chem. 2017, 56, 9055−9063

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Inorganic Chemistry of thiol/thiolate forms. Amanita mushrooms contain a natural vanadium(IV) complex, called amavadin.11 The structure characterized by X-ray crystallography consists of an eightcoordinate non-oxido VIV center binding to two N-hydroxyiminodicarboxylate ligands.12 Amavadin and its homologues were found to serve as catalysts for oxidation reactions of various substrates,11 as well as for water oxidation reported recently.13 However, the biological function of this natural vanadium compound remains obscure and is conjectured to perhaps be related to the defense system of the organism through the redox chemistry between vanadium ion and sulfur containing bioligands. In addition, the protein tyrosine phosphatase (PTP) is inhibited by vanadate, through the binding of vanadate to cysteinate sulfur at the active site of the enzyme.14 Such inhibition might be associated with how vanadium compounds act to mimic insulin.15 Our laboratory explores the fundamental chemistry of complexes containing vanadium sulfur bonds. However, the current literature offers few examples, notwithstanding our own and others’ efforts, to investigate the fundamental chemistry of vanadium ion using thiolates as supporting ligands.16 Notably, redox chemistry among these complexes has not been addressed extensively. With tris(benzenethiolato)phosphine ligand derivatives,17 several non-oxido mononuclear vanadium complexes in intermediate- to high-valent oxidation states have been obtained in our laboratory (Scheme 1).16k,l High-valent non-

[PPh4][2] in a yield of 55% (based on VO(acac)2). Adding 1 equiv of [Fe(Cp)2][PF6] to complex 2 in CH3CN gave a deep blue solution. The reaction mixture was displaced at −30 °C for 2 days to produce a crystalline solid of [V(PS3″)(PS2″SH)] (4) with a yield of 79%. The electronic spectrum of complex 4 exhibits intense absorption bands at 591 nm (ε = 9.16 × 103 M−1 cm−1) and 878 nm (ε = 6.71 × 103 M−1 cm−1) that are characteristic for thiyl radical-bound metal species (Figure S1).16k,19 Thus, the electronic structure of complex 4 is speculated to have a resonance form between VV−thiolate and VIV−thiyl radical species. A detailed investigation is underway in our laboratory. The 51V NMR spectrum of 4 exhibits a single peak at 1034 ppm (relative to VOCl3), appearing more downfield compared to the eight-coordinate complex 3 (483 ppm). Thus, the difference of coordination number, i.e., from eight (complex 3) to seven (complex 4), might vary the 51V chemical shift dramatically. In general, the 51V nucleus is more deshielded in complexes with S donors than those with N/O ones due to the increasing polarizability.20 For instance, complexes 3, 4, and [VV2(PS3″)2(μ-E2)(μ-E)] (1027 and 765 ppm for E = Se and S, respectively)21 have more downfield 51 V shifts than N/O ligated oxidized amavadin analogues (approximately −200 to −300 ppm).20a,22 In addition, the noninnocent nature of ligands such as catecholates also tunes 51 V nucleus in a deshielded manner.23 The PS3″ ligand in complexes 3 and 4 has a noninnocent character that might also give rise to low shielding. [V(PS3*)2]2− (5a) (PS3* = [P(C6H3-3-Ph-2-S)3]3−) was generated from the reaction of VO(acac)2 and Li3[PS3*] (PS3* = [P(C6H3-3-Ph-2-S)3]3−) in a 1:2 ratio in ethanol. An orange solution was produced and layered with tetrapropylammonium bromide to give a crystalline solid of [NPr4]2[5a]·C2H5OH in a yield of 77% (based on VO(acac)2). X-ray Structures. The molecular structures of complexes 1−4 and 5a have been well characterized by X-ray crystallography. Those of 1 and 3 were reported previously.16k,l The crystallographic data are summarized in Table S1. The selected bond distances and angles are listed in Tables S2−S4. The structure of [PPh4][V(PS3″)(PS2″SH)] ([PPh4][2]), was solved, but a higher resolution of data for complex 2 is provided when the countercation AsPh4+ is used. The ORTEP diagrams of 2, 4, and 5a are shown in Figures 1−3, respectively. Complexes 2 and 4 both embrace seven-coordinate vanadium centers with distorted capped trigonal prismatic geometry by binding to a tetradentate PS3″ ligand and a tridentate PS2SH″ ligand where the thiol group remains unbound. The average V−S distances of 2 and 4 are 2.430 and 2.403 Å, respectively. The hydrogen bonding interaction is found between bound thiolate and unbound thiol (S6···S1 = 3.591 Å for 2 and S6···S3 = 3.580 Å for 4). The structure of complex 5a consists of an eight-coordinate vanadium center with two PS3* ligands bound through two phosphine donors and six thiolate groups. The geometry is closer to a square antiprism with P2, S1, S5, S6 atoms forming a plane and P1, S2, S3, S4 forming the other. The average of the V−S bond distance is 2.554 Å. Examples of eight-coordinate vanadium complexes are rare. Other than complex 3, the reported ones include amavadin and its analogues with N-hydroxyiminodicarboxylate ligand derivatives.12,20a,24 A series of Schiff base ligands containing a tetradentate ONNO donor set also provide very stable eight-coordinate VIV complexes.25 In addition, tetrakis(phenyldithioacetato)vanadium(IV) and tetrakis(dithiobenzoato)vanadium(IV) complexes have a coordination

Scheme 1. Overall Reactions

oxido vanadium complexes are relatively rare compared to oxido ones, and their properties are very different from each other.18 In this work, we demonstrate a two-electron redox interconversion accompanying deprotonation/protonation of thiol/thiolate groups among a class of non-oxido vanadium thiolate complexes.

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RESULTS AND DISCUSSION Synthesis and Characterization. Syntheses and characterization of [VIII(PS2″SH)2]− (1) and [V(PS3″)2]− (3) (PS2″SH = [P(C6H3-3-Me3Si-2-S)2(C6H3-3-Me3Si-2-SH)]2− and PS3″ = [P(C6H3-3-Me3Si-2-S)3]3−) have been reported previously by our laboratory.16k,l According to spectroscopic data, the electronic structure of the vanadium center in 3 is better described as resonance forms between VV−thiolate and VIV− thiyl radical species.16k [VIV(PS3″)(PS2″SH)]− (2) was obtained from the reaction of Li3[PS3″] and VO(acac)2 in methanol with a 2:1 ratio. The generated reddish-brown solution was layered with [PPh4]Br to give a crystalline solid of 9056

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eight-coordinated complexes are all D2d triangular dodecahedron. Complex 5a is an exceptional case that has geometry closer to square antiprism. Electrochmical Studies. Cyclic voltammograms (CVs) of complexes were measured under N2 atmosphere with ferrocene (Fc) as an external standard. The potentials are referenced versus the Fc+/Fc couple as summarized in Table 1. CVs of complexes 1 and 5a display no reversible waves in both oxidation and reduction processes. The CV of complex 2 shows a reversible wave at −1.356 V as one-electron reduction process and an irreversible wave at −0.442 V as an oxidation process (Figure S2). The former is likely associated with a VIII/VIV couple and the latter is related to a VIV/VV one, but the possibility of S-based oxidations should not be excluded. Complexes 3 displays two waves in the reduction process: the first one at −1.017 V is reversible, and the second one at −1.750 V is irreversible (Figure S3). Complex 4 shows two reversible waves in the reduction processes at −0.675 V and −1.710 V (Figure S4). In 3 and 4, the first reduction process might be associated with both metal-center and ligand-center reduction, considering the noninnocent feature of PS3″ ligands in both complexes. The second reduction process in both is clearly relevant to the VIII/VIV couple. In general, the redox potential (E1/2) varies dramatically with the difference of the coordination number (CN); E1/2 is lower while CN is increasing, as shown in Table 1.16i In contrast, the change of the donor atoms tunes the potential in a less pronounced manner. For instance, the potentials of the corresponding couples in six-coordinate VIV complexes with P2S4 and P2O4 donor sets are quite similar.27 Metal-Centered Oxidation Accompanying Deprotonation of Unbound Thiol to Bound Thiolate. Complex 1 in solid state was stable in air for hours. However, it can be oxidized to 2 rapidly in solution state by reacting with dioxygen (Scheme 1). The reaction was monitored by UV−vis−NIR spectra. As shown in Figure 4, with the addition of dioxygen, the spectrum of 1 in CH3CN was gradually changed to that of 2 in 8 min. The transformation was marked by the appearance of three isosbestic points, 390, 445, and 521 nm. The formation of complex 2 was nearly quantitative. After 8 min, the absorption bands were gradually disappearing, indicating that complex 2 deteriorated in an aerobic condition. No intermediate was observed during this process. However, adding dioxygen to a CH3CN solution of isolated complex 2 caused the spectrum to gradually change to one similar to the isolated 3 in 18 min, but the formation of 3 only reached a maximum of 50%. The conversion was marked by the appearance of two isosbestic points, 400 and 800 nm (Figure 5). After 18 min, the spectrum gradually diminished. The formation of complex 3 by the exposure of complex 2 to the air was also observed in 51V NMR and 31P NMR spectra (Figures S5 and S6). The 51V NMR spectrum of complex 2 in CD3CN gave no signal, but a peak at 467 ppm attributed to the 51 V nucleus of 3 appeared after adding air into the sample solution, but dissipated a few hours later. The same observation was seen in 31P NMR. The characteristic 31P peak at 104 ppm (relative to PPh3) of complex 3 appeared and then disappeared while air was injected to the sample solution of 2. In addition, a sharp new peak at 30.7 ppm was detected, likely generated by the corresponding phosphine oxide of PS3″ after ligand oxygenation and dissociated from the metal center. ESI-MS spectrometry was also used to monitor the process of complex 2 reacting with air. The reaction was measured by

Figure 1. ORTEP diagram of [AsPh4][V(PS3″)(PS2″SH)]·2CH3OH ([AsPh4][2]·2CH3OH) with 35% thermal ellipsoids (left). The countercation, AsPh4+, solvated molecules and hydrogen atoms except the one (H6) in the thiol group are omitted for clarity. H6 atom is found in the electron density map. The drawing shows a capped trigonal prism with P2 in the capped position; (S2, S4, S5) and (P1, S1, S3) form two triangle faces (right).

Figure 2. ORTEP diagram of [V(PS3″)(PS2″SH)] (4) with 35% thermal ellipsoids (left). The hydrogen atoms except the one (H6) in the thiol group are omitted for clarity. H6 atom is found in the electron density map. The drawing shows a capped trigonal prism with P2 in the capped position; (S2, S4, S5) and (P1, S1, S3) form two triangle faces (right).

Figure 3. ORTEP diagram of [NPr4]2[5a]·C2H5OH with 35% thermal ellipsoids (left). The counter cations, solvated molecules, and hydrogen atoms are omitted for clarity. The drawing shows a square antiprism with (S2, P1, S3, S5) and (S1, S4, P2, S6) forming two square planes (right).

number of eight.26 Interestingly, the geometries of the vanadium centers adopted in amavadin and these synthetic 9057

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Table 1. Redox Potentials E1/2 (V) of Several Non-Oxido Vanadium Complexes (in V vs Fc+/Fc) Obtained from Cyclic Voltammograms CN [VIVLP2]a [VIV(P2S4′)]b [NEt4][VIV(PS3′)(PS2′SCH3)]c [PPh4][VIV(PS3″)(PS2″SH)] ([PPh4][2])

6 6 7 7 CN

H

[V(PS3″)(PS2″S )] (4) [NEt4][V(PS3″)2] ([NEt4][3])

7 8

donor atoms P2O2 P2S2 P2S3 P2S3 donor atoms P2S3 P2S4

E1/2ox1

E1/2red1

solvent

−0.175 −0.107 −0.605 −0.442d

−1.060 −0.872 −1.561 −1.365

CH2Cl2 CH2Cl2 CH2Cl2 CH3CN solvent

ref 27 ref 16i ref 16i this work ref

THF CH3CN

this work this work

E1/2red1

E1/2red2

−0.675 −1.017

−1.710 −1.750d

ref

a P L = [P(C6H5)(C6H2-3,5-(t-butyl)2-2-O)2]2−. bP2S4′ was formed by the oxidative coupling of two PS3′ ligands via a disulfide bond, PS3′ = [P(C6H3-5-CH3-2-S)3]3−. cPS2′SCH3 = [P(C6H3-5-CH3-2-S)2(C6H3-5-CH3-2-SCH3)]2−. dIrreversible.

Figure 6. Bar chart plot of relative abundance for specific species after adding dioxygen to 2 in CH3CN. The sample was taken for the ESIMS measurement every 5 min. The ratio of each species is deconvoluted from the ESI-MS spectra (see Figure S7).

Figure 4. Variation of UV−vis−NIR spectra of [VIII(PS2″SH)2]1− (1) in CH3CN (1.1 × 10−4 M) (red line) exposed to dioxygen (blue line). The spectrum was taken every 2 min in the course of 8 min. Inset: the spectrum of isolated complex 2 in CH3CN.

different times is shown in Figure 6. Although the charge of the complex as well as readiness of desolvation might vary intensities of ESI-MS signals, the data in Figure 6 offers a general profile for the reaction of 2 with dioxygen for the formation of 3. It is consistent with NMR data that complex 3 forms temporarily and then decays through oxygenation. Considering that the vanadium center of complex 3 has a very high coordination number (eight), [3 + O] and [3 + 2O] are likely ligand-based rather than metal-center oxygenation species of 3. Hydrogen Atom Abstraction of Unbound Thiol in Complex 2. The hydrogen atom of unbound thiol in complex 2 can be abstracted by TEMPO ((2,2,6,6-tetramethylpiperidin1-yl)oxyl) to form complex 3 and TEMPO-H. As shown in Figure 7, the final spectrum of complex 2 with the addition of TEMPO took on the appearance of complex 3. The formation yield was approximately 80%. The Formation of Complex 3 from Complex 2 by Stepwise Oxidation and Deprotonation. The formation of [V(PS3″)2]− (3) can be achieved from [VIV(PS3″)(PS2″SH)]− (2) via one-electron oxidation, and followed by the deprotonation of unbound thiol. The process was monitored by UV−vis−NIR spectroscopy, as shown in Figure 8. The addition of Fe(Cp)2+ to the solution of complex 2 led to a spectrum similar to that of [V(PS3″)(PS2″SH)] (4). Continually adding n-BuLi to the above solution caused the absorption pattern to resemble that of 3. Alternatively, complex 3 can be formed from complex 2 by stepwise reaction with the base first and the oxidant later. The addition of n-BuLi to complex 2 in CH3CN produced a green intermediate and is

Figure 5. Variation of UV−vis−NIR spectra of [VIV(PS3″)(PS2″SH)]− (2) in CH3CN (1.88 × 10−4 M) exposed to the dioxygen. The spectrum was taken every 6 min in the course of 18 min. Inset: the spectrum of isolated complex 3 in CH3CN.

taking the sample every 5 min after dioxygen was added to a CH3CN solution of complex 2, as shown in Figure S7. The relative abundance of peaks was deconvoluted to ion peaks at 1194.15 m/z, 1193.15 m/z, 1210.15 m/z, 1209.21 m/z, and 1225.14 m/z associated with [2], [3], [2 + O], [3 + O], and [3 + 2O] species, respectively. The composition of each species at 9058

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Figure 7. UV−vis−NIR spectra of [VIV(PS3″)(PS2″SH)]− (2) in CH3CN (1.88 × 10−4 M) (red line) and after the addition of TEMPO (blue line).

Figure 9. UV−vis−NIR spectra of [VIV(PS3″)(PS2″SH)]− (2) in CH3CN (1.88 × 10−4 M) (red line) after the addition of 1 equiv of nBuLi (gray line), followed by the addition of 1 equiv of [Fe(Cp)2]PF6 (blue line).

Figure 8. UV−vis−NIR spectra of [VIV(PS3″)(PS2″SH)]− (2) in CH3CN (1.88 × 10−4 M) (red line) after the addition of 1 equiv of [Fe(Cp)2]PF6 (gray line), followed by the addition of 1 equiv of nBuLi (blue line).

Figure 10. UV−vis−NIR spectra of [V(PS3″)2][NEt4] (3) in CH3CN (2.1 × 10−4 M, red line) after the addition of 1 equiv of CoCp2 (dark gray line) followed by the addition of 1 equiv of [LutH]BAr′ (blue).

likely to have a composition of [VIV(PS3″)2]2− through the deprotonation of unbound thiol to thiolate. Our attempt to isolate this green intermediate is still unsuccessful. Continually adding Fe(Cp)2+ as an oxidant to the resulting green solution caused the UV−vis−NIR spectrum change to one similar to that of isolated complex 3 (Figure 9). The yield of forming complex 3 from complex 2 by stepwise oxidation and deprotonation, or through the reversed order, is nearly quantitative. The Formation of Complex 2 from Complex 3 by Stepwise Reduction and Protonation. Complex 3 can be converted to complex 2 through one-electron reduction followed by protonation of thiolate to thiol, or through the reverse order. As shown in Figure 10, adding Co(Cp)2 to a solution of 3 caused the spectrum to change and have features similar to those of [V(PS3*)2]2− (5a) (Figure S3). Thus, the one-electron reduced species of complex 3, [V(PS3″)2]2− (5), even though not yet isolated, likely has the same structural motif as [V(PS3*)2]2− (5a). Interestingly, the spectrum yielded from adding the base to complex 2, mentioned previously as a green intermediate, clearly differed from that of 5, which was produced from one-electron reduction of complex 3. It is likely that they have the same chemical composition, [VIV(PS3″)2]2−,

but are structural isomers; however, evidence of this is needed. Continually adding the acid, [LutH]BAr′, to the resultant, the spectrum changed to one identical to that of complex 2. Complex 2 was also formed via an alternative pathway, adding the acid first followed by the reductant to a solution of complex 3, as demonstrated in the spectra shown in Figure 11. With the addition of triflic acid, TfOH, to a THF solution of 3, the spectrum changed to one resembling that of [V(PS3″)(PS2″SH)] (4). Continually adding Co(Cp)2 resulted in a spectrum similar to that of 2. The formation yields of complex 2 from complex 3 via both pathways (reduction/protonation or protonation/reduction) are nearly quantitative. The Formation of Complex 1 from Complex 2 by a Cooperative Effect between Protonation and Reduction. Adding Co(Cp)2 to a solution of [VIV(PS3″)(PS2″SH)]− (2) in the presence of [LutH]BAr′ leads to the formation of [VIII(PS2″SH)2]− (1), as shown in Figure 12. The yield is nearly quantitative. The VIV center was reduced to VIII in conjunction with the protonation of bound thiolate to form unbound thiol. Interestingly, either adding Co(Cp)2 or H+ individually does not change the spectrum of complex 2. It 9059

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converted to the eight-coordinate [V(PS3″)2]− (3). The reaction also occurs in the reverse direction; stepwise reduction/protonation or protonation/reduction brings complex 3 to complex 2. Importantly, a cooperative effect between metal-centered reduction and bound thiolate protonation is observed for the conversion of [VIV(PS3″)(PS2″SH)]− (2) to [VIII(PS2″SH)2]− (1); a VIV is reduced to VIII in conjunction with the protonation of bound thiolate to thiol followed by the dissociation of the thiol donor. The work shows the versatile nature of non-oxido vanadium complexes in terms of oxidation state and coordination number with the structural motif remaining robust. The thiol/thiolate donor acts as a mediator through acid−base chemistry to facilitate the change of the ligation environment of the vanadium center. The flexibility of oxidation state accompanying the change of coordination number for non-oxido vanadium centers might indicate that the vanadium site in FeVco has the capability of acting as an electron buffer without losing the structural integrity of the cofactor. In the blood cells of ascidians, even the reduction of vanadate to oxidovanadium(IV) has been indicated to associate with glutathione via a change of thiol to disulfide; however, the process for further reduction to vanadium(III) species still remains unsolved.28 Our work demonstrates that protonation of a biological S-donor followed by dissociation might facilitate the redox transformation of vanadium ions from high to intermediate oxidation states.

Figure 11. UV−vis−NIR spectra of [V(PS3″)2][NEt4] (3) in THF (1.6 × 10−4 M, red line) after the addition of 1 equiv of TfOH (dark gray line) followed by the addition of 1 equiv of CoCp2 (blue line).

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EXPERIMENTAL SECTION

General Procedures. Manipulations, reactions, and transfers were conducted under nitrogen according to Schlenk techniques or in a glovebox (nitrogen gas). Solvents as diethyl ether, THF, and n-hexane are refluxed over sodium/benzophenone desiccant until the indicator benzophenone shows the deep violet color to give pure oxygen- and water-free solvent. Acetonitrile and dichloromethane were dried by distillation from CaH2 and P2O5. Methanol was dried by distillation from CaO. Ligands H3[PS3″] and H3[PS3*] (PS3 = [P(C6H3-3Me3Si-2-S)3]3−, PS3* = [P(C6H3-3-Ph-2-S)3]3−) were synthesized according to the literature procedures.17 [LutH][BAr′4] (LutH = 2,6lutidinium and Ar′ = 3,5-(CF3)2C6H3)29 was also prepared by following the literature procedures. [PPh4][VIII(PS2″SH)2] ([PPh4][1]) and [N(Et)4][V(PS3″)2] ([NEt4][3]) were synthesized by following the procedures reported in our laboratory.16k,l Others reagents were used from commercial purchases. Physical Methods. Infrared spectra were measured in aerobic atmosphere with a PerkinElmer RX I at room temperature. The IR samples were prepared in glovebox by mixing with KBr prior to measurement. UV−vis−NIR spectra were recorded in the range of 190 to 1100 nm with a Hewlett-Packard 8453 spectrophotometer at room temperature. For the reaction with dioxygen monitored by UV−vis− NIR spectroscopy, dioxygen, obtained from a gas cylinder, was filled into a flask from which a gas-tight syringe was then filled. A small amount of this was injected into the cuvette through the septum followed, by the spectral measurement. 1H and 31P NMR spectra were taken by the use of a BRUKER AMX500 spectrometer. 51V NMR spectra were taken by the use of a BRUKER AVIIIHD700X spectrometer. The samples were prepared in a sealed NMR tube under nitrogen atmosphere in a glovebox. 1H NMR was referenced to the residual proton peaks of solvents. 31P NMR and 51V NMR were referenced to −6 ppm of PPh3 and 0 ppm of VOCl3 as external standards, respectively. Cyclic voltamograms (CVs) were obtained by using a three-component system consisting of a platinum disk working electrode, a platinum wire auxiliary electrode, and a Ag/Ag(NO3) (0.01 M in CH3CN) as the reference electrode. The experiments were performed in CH3CN or THF by using tetrabutylammonium tetrafluoroborate as the supporting electrolyte. The ferrocenium/ ferrocene (Fc+/Fc) couple was measured as an external standard. The data of elemental analysis data were measured by Chia-Chen Tsai at

Figure 12. UV−vis−NIR spectra of [VIV(PS3″)(PS2″SH)]− (2) in CH3CN (1.6 × 10−4 M, red line) after the addition of 1 equiv of [LutH]BAr′ (gray line) followed by the addition of 1 equiv of CoCp2 (blue line).

indicates a cooperative effect between vanadium-center reduction and thiolate protonation followed by the dissociation of forming thiol.

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CONCLUSIONS Chemistry of non-oxido vanadium complexes are relatively less explored compared to oxido ones in part because of the oxophilic nature of vanadium ion. In this work, a class of nonoxido vanadium thiolate complexes has been obtained by using PS3 ligand derivatives. The system is robust and can undergo two-electron and two-proton reversible transformations. With the addition of dioxygen, a metal center is oxidized from VIII to VIV and then to a formal charge of VV species. Each oneelectron oxidation process accompanies the deprotonation of unbound thiol to bound thiolate. The coordination number of the vanadium center is therefore increasing from six to seven and then to eight. However, further oxidation with dioxygen leads to the ligand−base oxygenation that dissociate from the metal center eventually. By stepwise oxidation/deprotonation or deprotonation/oxidation with a one-electron oxidant and a base, the seven-coordinate [VIV(PS3″)(PS2″SH)]− (2) can be 9060

DOI: 10.1021/acs.inorgchem.7b01040 Inorg. Chem. 2017, 56, 9055−9063

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Instrument Center of National Cheng Kung University with Elemetar vario EL III. The electrospray ionization mass spectra were obtained by Ming-Feng Chen at Instrument Development Center of National Cheng Kung University with the LTQ Orbitrap XL, Thermo-Fisher spectrometer. For the time-course experiments, the CH3CN solution of 2 was prepared in a glovebox. After dioxygen was injected into the sample solution through the septum with a gas-tight syringe, the sample was taken every 5 min for various measurements. X-ray Structure Determination. Crystallographic data and structure refinement parameters of [AsPh4][2]·2CH3OH, 4, and [(NPr4)2][5a]·C2H5OH are summarized in Table S1. Selected bond lengths and angles are listed in Tables S2−S4. Each crystal was mounted on a glass fiber and quickly coated in epoxy resin. Diffraction measurement of [AsPh4][2]·2CH3OH and [(NPr4)2][5a]·C2H5OH were performed with a Nonius Kappa diffractometer equipped with a CCD detector. Diffraction measurements of 4 were taken on a Bruker SMART CCD diffractometer. Least-squares refinement of the positional and anisotropic thermal parameters for the contribution of all non-hydrogen atoms and fixed hydrogen atoms was based on F2. A SADABS absorption correction was made.30 The SHELXTL structural refinement program was employed.31 All non-hydrogen atoms were refined with anisotropic displacement factors. The electron density of H6 atom in complex 2 and H6 atom in complex 4 are located in diffraction map. Other hydrogen atoms were calculated using the riding model. CCDC 1539202, CCDC 1539206, and CCDC 1542149 contain the supplementary crystallographic data of 2, 4, and 5a, respectively, for this paper.32 Synthesis of [PPh4][V(PS3″)(PS2″SH)]([PPh4][2]). A methanol solution of H3[PS3″] (0.100 g, 0.174 mmol), Li (0.004 g, 0.571 mmol), and VO(acac)2 (0.023 g, 0.087 mmol) was stirred for 40 min to generate a deep red-brown solution. The solution was layered with [PPh4]Br (0.037 g, 0.088 mmol) in methanol to give a crystalline solid of [PPh4][2] (0.081 g, 0.053 mmol, ca. 54.3% based on VO(acac)2). Anal. Calcd for C75H84P3S6Si6V: C, 61.02; H, 6.11; S, 12.53. Found: C, 60.28; H, 6.15; S, 12.29. Electronic absorption in CH3CN (λ, nm; ε, M−1 cm−1): 513 (4.90 × 103), 560 (5.20 × 103), 693 (5.13 × 103). 31P NMR (CD3CN, 500 MHz): 22.4 ppm (PPh4+). ESI-MS: calcd for [C54H73P2S6Si6V]− 1194.15, found 1194.15. IR (KBr,νS−H, cm−1): 2354. Synthesis of [V(PS3″)(PS2″SH)] (4). An acetonitrile solution of [PPh4][2] (0.100 g, 0.065 mmol) was added to a solution of [Fe(Cp)2][PF6] (0.022 g, 0.065 mmol) to generate a deep blue solution. The reaction mixture was replaced at −30 °C for 2 days to give a crystalline solid of 4 (0.0613 g, 0.051 mmol, ca. 78.7%). Anal. Calcd for C54H73P2S6Si6V: C, 54.23; H, 6.15; S, 16.09. Found: C, 53.97; H, 6.23; S, 15.60. Electronic absorption in THF (λ, nm; ε, M−1 cm−1): 591 (9.16 × 103), 878 (6.71 × 103). 51V NMR (d8-THF, 700 MHz): 1034 ppm (downfield relative to VOCl3). ESI-MS: calcd for [C54H73P2S6Si6V]− 1194.15, found 1194.15. IR (KBr,νS−H, cm−1): 2466 Synthesis of [(NPr4)2][V(PS3*)2] ([(NPr4)2][5a]). A mixture of H3[PS3*] (0.1 g, 0.1704 mmol), lithium (0.0071 g, 1.01 mmol), and VO(acac)2 (0.0226 g, 0.0852 mmol) in ethanol generated an orange-brown solution. After layering the solution of tetrapropylammonium bromide, NPr4Br (0.0455 g, 0.1704 mmol), in ethanol, dark brown crystals were precipitated out to give the product (0.10437 g, 0.0656 mmol, ca. 77%). Electronic absorption in CH2Cl2 (λ, nm; ε, M−1 cm−1): 655 (1.69 × 103). Anal. Calcd for C100H92N2O2P2S6V: N, 1.66; C, 71.35; H, 6.95; S, 11.43. Found: N, 1.48; C, 70.67; H, 6.84; S, 11.86.

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CCDC 1539202, 1539206, and 1542149 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/ data_request/cif, or by emailing [email protected]. uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Hua-Fen Hsu: 0000-0001-8021-193X Author Contributions

The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by Ministry of Science and Technology in Taiwan (MOST 105-2113-M-006-001) and National Cheng Kung University in Taiwan. We thank MingFeng Chen in Establishment of the Instrument Development Center at National Cheng Kung University for assisting with the measurements of ESI-MS data.

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REFERENCES

(1) (a) Rao, P. V.; Holm, R. H. Synthetic Analogues of the Active Sites of Iron Sulfur Proteins. Chem. Rev. 2004, 104, 527−560. (b) Solomon, E. I.; Gorelsky, S. I.; Dey, A. Metal−Thiolate Bonds in Bioinorganic Chemistry. J. Comput. Chem. 2006, 27, 1415−1428. (2) (a) Perera, R.; Sono, M.; Sigman, J. A.; Pfister, T. D.; Lu, Y.; Dawson, J. H. Neutral thiol as a proximal ligand to ferrous heme iron: Implications for heme proteins that lose cysteine thiolate ligation on reduction. Proc. Natl. Acad. Sci. U. S. A. 2003, 100 (7), 3641−3646. (b) Zhong, F.; Lisi, G. P.; Collins, D. P.; Dawson, J. H.; Pletneva, E. V. Redox-dependent stability, protonation, and reactivity of cysteinebound heme proteins. Proc. Natl. Acad. Sci. U. S. A. 2014, 111 (3), E306−E315. (c) Smith, A. T.; Pazicni, S.; Marvin, K. A.; Stevens, D. J.; Paulsen, K. M.; Burstyn, J. N. Functional Divergence of HemeThiolate Proteins: A Classification Based on Spectroscopic Attributes. Chem. Rev. 2015, 115, 2532−2558. (3) Rehder, D. Bioinorganic Vanadium Chemistry; John Wiley & Sons: 2008. (4) (a) Crans, D. C.; Smee, J. J.; Gaidamauskas, E.; Yang, L. The chemistry and Biochemistry of vanadium and the biological activities exerted by vanadium compounds. Chem. Rev. 2004, 104, 849−902. (b) Crans, D. C.; Zhang, B.; Gaidamauskas, E.; Keramidas, A. D.; Willsky, G. R.; Roberts, C. R. Is Vanadate Reduced by Thiols under Biological Conditions? Changing the redox Potential of V(V)/V(IV) by Complexation in Aqueous Solution. Inorg. Chem. 2010, 49, 4245− 4256. (5) Robson, R. L.; Eady, R. R.; Richardson, T. H.; Miller, R. W.; Hawkins, M.; Postgate, J. R. The alternative nitrogenase of Azotobacter chroococcum is a vanadium enzyme. Nature 1986, 322, 388−390. (6) Lee, C. C.; Hu, Y.; Ribbe, M. W. Vanadium Nitrogenase Reduces CO. Science 2010, 329, 642. (7) (a) Hu, Y.; Lee, C. C.; Ribbe, M. W. Vanadium nitrogenase: A two-hit wonder? Dalton Trans. 2012, 41, 1118−1127. (b) Rees, J. A.; Bjornsson, R.; Schlesier, J.; Sippel, D.; Einsle, O.; DeBeer, S. The Fe−

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DOI: 10.1021/acs.inorgchem.7b01040 Inorg. Chem. 2017, 56, 9055−9063

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Inorganic Chemistry V Cofactor of Vanadium Nitrogenase Contains an Interstitial Carbon Atom. Angew. Chem., Int. Ed. 2015, 54, 13249−13252. (8) Hoffman, B. M.; Lukoyanov, D.; Yang, Z.-Y.; Dean, D. R.; Seefeldt, L. C. Seefeldt Mechanism of Nitrogen Fixation by Nitrogenase: The Next Stage. Chem. Rev. 2014, 114, 4041−4062. (9) Rees, J. A.; Bjornsson, R.; Kowalska, J. K.; Lima, F. A.; Schlesier, J.; Sippel, D.; Weyhermüller, T.; Einsle, O.; Kovacs, J. A.; DeBeer, S. Comparative electronic structures of nitrogenase FeMoco and FeVco. Dalton Trans. 2017, 46, 2445−2455. (10) (a) Ueki, T.; Yamaguchi, N.; Romaidi; Isago, Y.; Tanahashi, H. Vanadium accumulation in ascidians: A system overview. Coord. Chem. Rev. 2015, 301−302, 300−308. (b) Ueki, T.; Michibata, H. Molecular mechanism of the transport and reduction pathway of vanadium in ascidians. Coord. Chem. Rev. 2011, 255, 2249. (c) Michibata, H.; Yamaguchi, N.; Uyama, T.; Ueki, T. Molecular biological approaches to the accumulation and reduction of vanadium by ascidians. Coord. Chem. Rev. 2003, 237, 41−51. (11) da Silva, J. A. L.; da Silva, J. J. R. F.; Pombeiro, A. J. L. Amavadin, a vanadium natural complex: Its role and applications. Coord. Chem. Rev. 2013, 257, 2388−2400. (12) Berry, R. E.; Armstrong, E. M.; Beddoes, R. L.; Collison, D.; Ertok, S. N.; Helliwell, M.; Garner, C. D. The structure characterization of Amavadin. Angew. Chem., Int. Ed. 1999, 38, 795−797. (13) Domarus, M.; Kuznetsov, M. L.; Marçalo, J.; Pombeiro, A. J. L.; da Silva, J. A. L. d. Amavadin and Homologues as Mediators of Water Oxidation. Angew. Chem., Int. Ed. 2016, 55, 1489−1492. (14) Huyer, G.; Liu, S.; Kelly, J.; Moffat, J.; Payette, P.; Kennedy, B.; Tsaprailis, G.; Gresser, M. J.; Ramachandran, C. Mechanism of inhibition of protein-tyrosine phosphatases by Vanadate and Pervanadate. J. Biol. Chem. 1997, 272 (2), 843−851. (15) Rehder, D. Biological and medicinal aspects of vanadium. Inorg. Chem. Commun. 2003, 6, 604−617. (16) (a) Tsagkalidis, W.; Rehder, D. Characterization of bio-related vanadium and zinc complexes containing tetradentate dithiolatedisulfide, -diamine and -amine-amide ligands. JBIC, J. Biol. Inorg. Chem. 1996, 1, 507−514. (b) Nanda, K. K.; Sinn, E.; Addison, A. W. The first oxovanadium(V)-thiolate complex, [VO(SCH2CH2)3N]. Inorg. Chem. 1996, 35 (11), 1−2. (c) Cornman, C. R.; Stauffer, T. C.; Boyle, P. D. Oxidation of a Vanadium(V)-Dithiolate Complex to a Vanadium(V)-Disulfenate Complex. J. Am. Chem. Soc. 1997, 119, 5986−5987. (d) Nekola, H.; Wang, D.; Grüning, C.; Gätjens, J.; Behrens, A.; Rehder, D. Thiofunctional vanadium complexes. Inorg. Chem. 2002, 41, 2379−2384. (e) Davies, S. C.; Hughes, D. L.; Janas, Z.; Jerzykiewicz, L. B.; Richards, R. L.; Sanders, J. R.; Silverston, J. E.; Sobota, P. Vanadium Complexes of the N(CH2CH2S)33‑ and O(CH2CH2S)22‑ Ligands with Coligands Relevant to Nitrogen Fixation Processes. Inorg. Chem. 2000, 39 (16), 3485−3498. (f) Janas, Z.; Sobota, P. Aryloxo and thiolato vanadium complexes as chemical models of the active site of vanadium nitrogenase. Coord. Chem. Rev. 2005, 249, 2144−2155. (g) Hsu, H.-F.; Chu, W.-C.; Hung, C.-H.; Liao, J.-H. The First Example of a Seven-coordinate Vanadium(III) Thiolate Complex Containing the Hydrazine Molecule, an Intermediate of Nitrogen Fixation. Inorg. Chem. 2003, 42, 7369− 7371. (h) Chu, W.-C.; Wu, C.-C.; Hsu, H.-F. Catalytic Reduction of Hydrazine to Ammonia by a Vanadium Thiolate Complex. Inorg. Chem. 2006, 45, 3164−3166. (i) Hsu, H.-F.; Su, C.-L.; Gopal, N. O.; Wu, C.-C.; Chu, W.-C.; Tsai, Y.-F.; Chang, Y.-H.; Liu, Y.-H.; Kuo, T.S.; Ke, S.-C. Redox Chemistry in the reaction of oxovanadium(V) with thiolate containing ligands: The isolation and characterization of nonoxovanadium(IV) complexes containing the forming disulfide and thioether. Eur. J. Inorg. Chem. 2006, 2006, 1161−1167. (j) Ye, S.; Neese, F.; Ozarowski, A.; Smirnov, D.; Krzystek, J.; Telser, J.; Liao, J.H.; Hung, C.-H.; Chu, W.-C.; Tsai, Y.-F.; Wang, R.-C.; Chen, K.-Y.; Hsu, H.-F. Family of V(III)-Tristhiolato Complexes Relevant to Functional Models of Vanadium Nitrogenase: Synthesis and Electronic Structure Investigations by Means of High-Frequency and -Field Electron Paramagnetic Resonance Coupled to Quantum Chemical Computations. Inorg. Chem. 2010, 49 (3), 977−988. (k) Chang, Y.-H.; Su, C.-L.; Wu, R.-R.; Liao, J.-H.; Liu, Y.-H.; Hsu, H.-F. An Eight-

Coordinate Vanadium Thiolate Complex with Charge Delocalization between V(V)Thiolate and V(IV)Thiyl Radical Forms. J. Am. Chem. Soc. 2011, 133, 5708−5711. (l) Chen, T.-T.; Chen, Y.-S.; Chang, Y.H.; Wang, J.-C.; Tsai, Y.-F.; Lee, G.-H.; Kuo, T.-S.; Hsu, H.-F. Activation of dichloromethane by a V(III) thiolate complex: an example of S-based nucleophilic reactivityin an early transition metal thiolate. Chem. Commun. 2013, 49, 1109−1111. (m) Hall, N.; Orio, M.; Jorge-Robin, A.; Gennaro, B. a.; Marchi-Delapierre, C.; Duboc, C. Vanadium Thiolate Complexes for Efficient and SelectiveSulfoxidation Catalysis: A Mechanistic Investigation. Inorg. Chem. 2013, 52, 13424− 13431. (n) Wang, D.; Behrens, A.; Farahbakhsh, M.; Gätjens, J.; Rehder, D. Formation, Preservation, and Cleavage of the Disulfide Bond by Vanadium. Chem. - Eur. J. 2003, 9 (8), 1805−1813. (o) Komuro, T.; Matsuo, T.; Kawaguchi, H.; Tatsumi, K. Synthesis of a Vanadium(III) Tris(arythiolato) Complex and Its Reactions with Azide and Azo Compounds: Formation of a Sulfenamide Complex via Cleavage of an Azo NN Bond. Inorg. Chem. 2005, 44, 175−177. (p) Taniyama, N.; Ohki, Y.; Tatsumi, K. Synthesis of V/Fe/S Clusters Using Vanadium(III) Thiolate Complexes Bearing a Phenoxide-Based Tridentate Ligand. Inorg. Chem. 2014, 53, 5438−5446. (17) Block, E.; Ofori-Okai, G.; Zubieta, J. 2-Phosphino- and 2Phosphinylbenzenethiols: New Ligand Types. J. Am. Chem. Soc. 1989, 111, 2327−2329. (18) Kundu, S.; Mondal, D.; Bhattacharya, K.; Endo, A.; Sanna, D.; Garribba, E.; Chaudhury, M. Nonoxido Vanadium(IV) Compounds Involving Dithiocarbazate-Based Tridentate ONS Ligands: Synthesis, Electronic and Molecular Structure, Spectroscopic and Redox Properties. Inorg. Chem. 2015, 54, 6203−6215 and references therein. (19) Kimura, S.; Bill, E.; Bothe, E.; Weyhermuller, T.; Wieghardt, K. Phenylthiyl Radical Complexes of Gallium(III), Iron(III), and Cobalt(III) and Comparison with Their Phenoxyl Analogues. J. Am. Chem. Soc. 2001, 123 (25), 6025−6039. (20) (a) Smith, P. D.; Berry, R. E.; Harben, S. M.; Beddoes, R. L.; Helliwell, M.; Collison, D.; Garner, C. D. New vanadium(IV) and V(V) analogues of Amavadin. J. Chem. Soc., Dalton Trans. 1997, 4509− 4516. (b) Rehder, D.; Weidemann, C.; Duch, A.; Priebsch, W. Vanadium-51 shielding in vanadium(V) complexes: a reference scale for vanadium binding sites in biomolecules. Inorg. Chem. 1988, 27 (3), 584−587. (c) Sendlinger, S. C.; Nicholson, J. R.; Lobkovsky, E. B.; Huffman, J. C.; Rehder, D.; Christou, G. Reactivity Studies of Mononuclear and Dinuclear Vanadium-Sulfide-Thiolate Compounds. Inorg. Chem. 1993, 32, 204−210. (21) Wu, H.-M.; Chang, Y.-H.; Tsai, Y.-F.; Hsu, K.-F.; Lee, G.-H.; Hsu, H.-F. Non-oxido divanadium(IV) and divanadium(V) thiolate complexes with a new type of chalcogenide bridging motif. Dalton Trans. 2015, 44, 4468−4473. (22) Ooms, K. J.; Bolte, S. E.; Baruah, B.; Choudhary, M. A.; Crans, D. C.; Polenova, T. 51V solid-state NMR and density functional theory studies of eight-coordinate non-oxo vanadium complexes: oxidized amavadin. Dalton Trans. 2009, 3262. (23) (a) Cornman, C. R.; Colpas, G. L.; Hoeschele, J. D.; Kampf, J.; Pecoraro, V. L. Implication for the spectroscopic assignment of vanadium biomoleculs: Structural and spectroscopic characterization of monooxovanadium(V) complexes containing catecholate and hydroximam basd noninnocent ligans. J. Am. Chem. Soc. 1992, 114, 9925−9933. (b) Chatterjee, P. B.; Goncharov-Zapata, O.; Quinn, L. L.; Hou, G.; Hamaed, H.; Schurko, R. W.; Polenova, T.; Crans, D. C. Characterization of Noninnocent Metal Complexes Using Solid-State NMR Spectroscopy: o-Dioxolene Vanadium Complexes. Inorg. Chem. 2011, 50, 9794−9803. (24) (a) Carrondo, M. A. A. F. d. C. T.; Duarte, M. T. L. S.; Pessoa, J. C.; Silva, J. A. L.; Silva, J. J. R. F. d.; Vaz, M. C. T. A.; Vilas-Boas, L. F. Bis-(N-hydroxy-iminodiacetate)vanadate(IV), a synthetic model of amavadin. J. Chem. Soc., Chem. Commun. 1988, 1158−1159. (b) Armstrong, E. M.; Beddoes, R. L.; Calviou, L. J.; Charnock, J. M.; Collison, D.; Ertok, N.; Naismith, J. H.; Garner, C. D. The Chemical Nature of Amavadin. J. Am. Chem. Soc. 1993, 115, 807−808. (c) Hubregtse, T.; Kooijman, H.; Spek, A. L.; Maschmeyer, T.; Sheldon, R. A.; Arends, I. W. C. E.; Hanefeld, U. Study on the 9062

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Article

Inorganic Chemistry isomerism in meso-amavadin and an amavadin analogue. J. Inorg. Biochem. 2007, 101 (101), 900−908. (25) Sutradhar, M.; Mukherjee, G.; Drew, M. G. B.; Ghosh, S. Simple General Method of Generating Non-oxo, Non-amavadine Model Octacoordinated Vanadium(IV) Complexes of Some Tetradentate ONNO Chelating Ligands from Various Oxovanadium(IV/V) Compounds and Structural Characterization of One of Them. Inorg. Chem. 2007, 46, 5069−5075. (26) Bonamico, M.; Dessy, G.; Fares, V.; Scaramuzza, L. Structural studies of eight-co-ordinate metal complexes. Part I. Crystal and molecular structures of tetrakis(phenyldithioacetato)vanadium(IV) and tetrakis(dithiobenzoato)vanadium(IV). J. Chem. Soc., Dalton Trans. 1974, 1258−1263. (27) Paine, T. K.; Weyhermüller, T.; Slep, L. D.; Neese, F.; Bill, E.; Bothe, E.; Wieghardt, K.; Chaudhuri, P. Nonoxovanadium(IV) and Oxovanadium(V) Complexes with mixed O, X, O-donor Ligands (X = S, Se, P, or PO). Inorg. Chem. 2004, 43, 7324−7338. (28) Yamamoto, S.; Matsuo, K.; Michibata, H.; Ueki, T. Role of cysteine residues in the V(V)-reductase activity of Vanabin2. Inorg. Chim. Acta 2014, 420, 47−52. (29) (a) Yandulov, D. V.; Schrock, R. R. Reduction of dinitrogen to ammonia at a well-protected reaction site in molybdenum triamido complex. J. Am. Chem. Soc. 2002, 124, 6252−6253. (b) Reger, D. L.; Wright, T. D.; Little, C. A.; Lamba, J. J. S.; Smith, M. D. Control of the stereochemical impact of the lone pair in lead(II) tris(pyrazolyl)methane complexes. Improved preparation of Na{B[3,5-(CF3) (2)C6H3](4)}. Inorg. Chem. 2001, 40 (15), 3810−3814. (30) Sheldrick, G. M., SADABS, Siemens Area Detector Absorption Correction Program; University of Göttingen: Göttingen, Germany, 1996. (31) Sheldrick, G. M., SHELXTL; Program for Crystal Structure Determination; Siemens Analytical X-ray Instruments Inc.: Madison, WI, 1994. (32) The CIF check reports of Complexes 2 and 5a indicate Alert level B, PLAT910_ALERT_3_B Missing # of FCF Reflection(s) Below Theta(Min). They are caused by the X-ray beam stop, thus the reflection is not integrated for data reduction.

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NOTE ADDED AFTER ASAP PUBLICATION This paper was published on the Web on July 14, 2017, with complexes 2 and 3 incorrectly transposed. The corrected version was reposted on July 24, 2017.

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DOI: 10.1021/acs.inorgchem.7b01040 Inorg. Chem. 2017, 56, 9055−9063