Synthesis of [Mo3S4] Clusters from Half-Sandwich Molybdenum(V

Article Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

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Synthesis of [Mo3S4] Clusters from Half-Sandwich Molybdenum(V) Chlorides and Their Application as Platforms for [Mo3S4Fe] Cubes Yasuhiro Ohki,*,† Ryota Hara,† Kenichiro Munakata,† Mizuki Tada,†,‡ Tsutomu Takayama,§ Yoichi Sakai,§ and Roger E. Cramer∥ †

Department of Chemistry, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan Research Center for Materials Science and Integrated Research Consortium on Chemical Sciences, Nagoya University, Nagoya 464-8602, Japan § Department of Chemistry, Daido University, Takiharu-cho, Minami-ku, Nagoya 457-8530, Japan ∥ Department of Chemistry, University of Hawaii, Manoa, 2545 McCarthy Mall, Honolulu, Hawaii 96822-2275, United States

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S Supporting Information *

ABSTRACT: Triangular [Mo3S4] clusters are known to serve as platforms to accommodate a metal atom M, furnishing cubic [Mo3S4M] clusters. In this study, three [Mo3S4] clusters supported by η5-cyclopentadienyl (CpR) ligands, [CpR3Mo3S4]+ (CpR = C5Me4SiMe3, C5Me4SiEt3, and C5Me4H), were synthesized via half-sandwich molybdenum chlorides CpRMoCl4. In the cyclic voltammogram of the [Mo3S4] cluster having C5Me4H ligands, a weak feature appeared in addition to the [CpR3Mo3S4]0/− redox process, indicating the interaction between [CpR3Mo3S4]− and the [NnBu4] cation of the electrolyte, while such a feature was less significant for the C5Me4SiR3 variants. The [Mo3S4] clusters with bulky C5Me4SiR3 ligands were successfully applied as platforms to accommodate an Fe atom to furnish cubic [Mo3S4Fe] clusters. On the other hand, the corresponding reactions of the less bulky C5Me4H analogue gave complex mixtures.

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ligands before or after incorporation of the fourth metal.4 A previously reported procedure to replace aqua ligands in [Mo3S4(H2O)9]4+ by CpR ligands generates [Mo3S4(THF)n]4+ via dehydration and subsequent treatment with toxic thallium salts such as Tl(C5H5) or Tl(C5H4CH3).13d,e An analogous reaction using Na(C5H5) instead of Tl(C5H5) was reported to give a complex mixture, which was attributed to the reduction of [Mo3S4(THF)n]4+ by Na(C5H5).13d In agreement with this result, our preliminary attempt to incorporate η5-C5Me5 ligands through the reaction of [Mo3S4(THF)n]4+ with K(C5Me5) was unsuccessful and gave a complex mixture. CpR-supported [Mo3S4] clusters can also be made by the reactions of (C5H5)Mo{P(OPh)3}(CO)2H with sulfide sources,13a and C−S bond cleavage of (C5Me5)Mo(StBu)313c,f has been used for large-scale synthesis.17 In this study, we synthesized some half-sandwich molybdenum chlorides CpRMoCl4 (CpR = C5Me4SiMe3 (1a), C5Me4SiEt3 (1b), and C5Me4H (1c)), which can serve as synthons for various organo-molybdenum complexes. These half-sandwich complexes were converted into the [Mo3S4] clusters via reaction with LiStBu to generate CpRMo(StBu)3, followed by treatment with [(C5H5)2Fe][PF6]. A one-pot reaction of (C5Me4H)MoCl4/Li2S2/KC8 was found to give a slightly better yield of the C5Me4H-supported [Mo3S4] cluster 3c. The steric effect of

INTRODUCTION Transition metal−sulfur clusters are known to exhibit redox processes of varying potentials due to factors such as the core structures, the supporting ligands on the metals, and the media, as well as the component transition elements.1,2 Moreover, some triangular metal−sulfur clusters are able to accommodate an additional metal atom (i.e., the fourth metal) to furnish cubic structures. For example, the active site of the aconitase enzyme, which catalyzes the interconversion between citrate and isocitrate, features an inactive triangular [Fe3S4] cluster, which can accommodate an iron atom, thus becoming an active cubic [Fe4S4] cluster.2 An analogous metal-incorporating function has been demonstrated with triangular [Mo3S4] clusters,3 for which various supporting ligands have been employed, e.g., H2O,4 cyanide,5 dithiophosphates,6 iminodiacetate, 7 phosphines,8 diamines,9,10 oxalate,11 hydrotris(pyrazolyl)borate (Tp),12 thiourea,10 and η5-cyclopentadienyls (CpR).13 Some of the resultant cubic clusters, particularly those with CpR supporting ligands, have been applied as precursors in homogeneous catalysis9,14−16 as well as in the activation of N2.17 Furthermore, the [Mo3S4] clusters containing Mo−H moieties have been found to catalyze the reduction of nitroarenes and hydrodefluorination of fluorinated pyridines.18 We became interested in the effect of auxiliary CpR ligands on the metal-incorporating function of the [Mo3S4] clusters. As a platform, aqua-supported [Mo3S4(H2O)9]4+ is rather versatile, as its aqua ligands can be replaced by various other © XXXX American Chemical Society

Received: February 1, 2019

A

DOI: 10.1021/acs.inorgchem.9b00309 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry the CpR supporting ligands of the [Mo3S4] clusters was examined by employing these clusters as platforms for the synthesis of cubic [Mo3S4Fe] clusters.

1a−1c in CH2Cl2 at ambient temperature showed S = 1/2 signals at g = 1.992 (1a), 1.982 (1b), and 1.993 (1c) (Table 1 and Figure S7), and these g-values are comparable to those reported for analogues.19,22 The molecular structure of 1b was determined by means of a single-crystal X-ray diffraction study (Figure 1). It is interesting and surprising to note that 1b is the

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RESULTS AND DISCUSSION Synthesis of Half-Sandwich Molybdenum Chlorides. CpRMoCl4 (CpR = C5Me4SiMe3 (1a), C5Me4SiEt3 (1b), and C5Me4H (1c)) were synthesized in a manner similar to the synthesis of (C5Me5)MoCl4,19 on a multigram scale, from sequential reactions of Mo(CO)6 with LiCpR in THF under reflux and then with MeI at ambient temperature to furnish a dark yellow solid, followed by treatment with PCl5 in CH2Cl2 (Scheme 1). The new ligand precursor for 1b, triethylScheme 1

Figure 1. Molecular structure of (C5Me4SiEt3)MoCl4 (1b) with thermal ellipsoids set at 50% probability. Note that two independent molecules appeared in an asymmetric unit, and one of these is shown in this figure. Selected bond distances (Å): Mo−Cl 2.341(3)− 2.382(3), Mo−C 2.333(8)−2.421(8), and C1−Si 1.936(9).

first CpRMoCl4 complex reported with an X-ray structure, based on our survey through the Cambridge Structural Database. Unfortunately, 1b crystallizes as very thin needles leading to a weak data set, which results in uncertainty in the metrical parameters. Within experimental errors, there is nothing remarkable about the structure of 1b, and therefore, we will not discuss it further. Synthesis and Characterization of [CpR3Mo3S4]+. The half-sandwich complexes 1a-c were converted into the corresponding [Mo3S4] clusters according to Scheme 2,

(tetramethylcyclopentadienyl)silane (C5Me4HSiEt3), was prepared from K(C5Me4H)20 and Et3SiCl in toluene and used without further purification. The previously reported synthesis of (C5Me5)MoCl4 includes isolation of the carbonyl-methyl complex (C5Me5)Mo(CO)3Me before treatment with PCl5.19 In this study, however, the corresponding complexes with a CpR ligand were formed as crude dark yellow materials, which were directly subjected to reactions with PCl5 to reduce the number of manipulations. Complexes 1a−1c were isolated as reddish purple solids in 61−77% yields based on Mo(CO)6. Consistent with the paramagnetism of the products, the 1H NMR spectra of 1a and 1b in CDCl3 exhibited broad signals of C5Me4SiR3 (Table 1 and Figures S1 and S2), while the

Scheme 2

Table 1. 1H NMR and ESR Spectra of Complexes 1a−1ca 1a

1b

1cb

1

C5Me4R SiMe3, SiEt3

g-value

H NMR (CDCl3, ppm) −5.25 −6.95 −13.0 −12.8 0.98 1.48 (CH3) 2.58 (−CH2−) ESR (CH2Cl2, room temp) 1.992 1.982

b b

1.993

a

The samples were dissolved in CDCl3 and CH2Cl2 for NMR and ESR, respectively. bSolubility of 1c was not sufficiently high in CDCl3 or CD2Cl2 to observe broad paramagnetic signals in the 1H NMR spectrum.

while the intermediary thiolate complexes CpRMo(StBu)3 (CpR = C5Me4SiMe3 (2a), C5Me4SiEt3 (2b), and C5Me4H (2c)) were not isolated. Thus, in the initial step, CpRMoCl4 (1a−1c) was treated with 4 equiv of LiStBu to generate a mixture containing CpRMo(StBu)3 as the major product (Scheme 2 top). In the 1H NMR of hexane extracts containing 2a−2c, some signals of uncharacterized minor byproducts appeared (Figures S9−S11). Single crystals of 2a and 2c were

solubility of 1c in CDCl3 or CD2Cl2 was not sufficiently high to observe paramagnetic 1H NMR signals. Even though complex 1c dissolved well in dimethyl sulfoxide or dimethylformamide, this process accompanies a color change from reddish purple to yellow, possibly due to the coordination of these solvents to give (C5Me4H)MoCl4(solv). Analogous phosphine adducts (C5Me4R)MoCl4(phosphine) (R = Me, Et) have been crystallographically identified.21 The ESR spectra of B


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Inorganic Chemistry manually picked out under a microscope from the residual crystalline solids. X-ray diffraction (Figure 2 and Figure S12)

Scheme 3

Figure 2. Molecular structure of 2a with atomic displacement parameters set at 50% probability. Note that crystals of 2a for crystallographic analysis were manually separated from other unidentified crystalline materials under a microscope, before they decompose in air. Selected bond distances (Å): Mo−S1 2.2792(5), Mo−S2 2.2962(6), Mo−S3 2.3290(6), and Si−C1 1.8867(12).

sponding reaction resulted in the formation of a mixture of crystals containing a cubic cluster [(C5Me4H)4Mo4S4][PF6] (B) as the major product. Cluster B was characterized only by X-ray crystallographic analysis (Figure S14), because of the presence of crystalline solids of 3c and some other unidentified byproducts. Even though the one-pot reaction depicted in Scheme 3 provided the better yield of 3c, this reaction should not be applied to a large-scale synthesis because of the safety reasons. The reactants Li2S2 and KC8 are prepared from metallic lithium and potassium, respectively,24,25 and KC8 easily ignites upon air exposure. Due to the limitation in the reaction scale and the limited improvement in the product yield, analogous reactions were not examined with complexes 1a and 1b. The cationic [Mo3S4] clusters 3a−3c are diamagnetic, and they were characterized based on the 1H and 13C{1H} NMR spectra (Figures S15−S17), while their electrospray-ionization mass spectra (ESI-MS) supported their chemical formulas (Figures S18−S20). Furthermore, cyclic voltammograms of 3a−3c were measured to investigate the influence of the CpR ligands (Figures 3 and S21). As summarized in Table 2, the limited electronic influence of CpR ligands was indicated by the comparable potentials of two reversible reduction processes at E1/2 = −1.05 (3a), − 1.00 (3b), and −1.11 (3c) V and at E1/2 = −2.19 (3a), − 2.18 (3b), and −2.09 (3c) V vs Ag/Ag(NO3), which are ascribed to the [CpR3Mo3S4]+/0 and [CpR3Mo3S4]0/− couples, respectively. A notable feature in the voltammogram of 3c is the appearance of an additional but relatively weak reduction wave at E1/2 = −2.25 V, which can be attributed to the reduction of [NnBu4][(C5Me4H)3Mo3S4] featuring an interaction between the electrochemically generated anion [(C5Me4H)3Mo3S4]− and the [NnBu4]+ cation of the electrolyte. An analogous weak feature has been observed for the C 5 Me 5 analogue at E 1 / 2 = −2.33 V besides the [(C5Me5)3Mo3S4]0/− redox couple at E1/2 = −2.13 V.26 The potential of the weak feature overlaps that of [K(18-crown6)][(C5Me5)3Mo3S4], for which it has been shown that there is an interaction between the [K(18-crown-6)]+ cation and the μS atoms of the [(C5Me5)3Mo3S4]− anion in solution.26 Such weak features are less significant in the voltammograms of clusters 3a and 3b supported by bulky C5Me4SiR3 ligands, possibly because the −SiR3 groups hinder the interaction between the μ-S atoms of the [CpR3Mo3S4]− anion and the [NnBu4]+ cation. In fact, the −SiR3 groups of 3a and 3b stick out of the open triangular face of the [Mo3S4] core, serving as fences around the μ-S atoms (vide infra, e.g. Figure 5). All of the new [Mo3S4] clusters 3a−3c were structurally identified by means of X-ray crystallographic analysis (Figure 4 and Figures S22−23). As listed in Table 3, the Mo−Mo, Mo-

revealed that the Mo−S distances in 2a and 2c are comparable to those of (C5Me5)Mo(StBu)3.13c From the reaction mixture containing 2c, crystals of a byproduct (C5Me4H)2Mo2(μS)2(μ-StBu)2 (A) were also manually separated, and the molecular structure of A was determined (Figure S13). Complexes 2a−2c are air-sensitive, rendering their isolation from byproducts difficult. Therefore, the mixtures containing 2a−2c were used in the following steps without further purification. For the synthesis of [Mo3S4] clusters, mixtures containing 2a−2c were treated with [Cp2Fe][PF6] in CH2Cl2 (Scheme 2 bottom), in an analogous manner to the synthesis of the C5Me5 analogue.13f From the greenish brown reaction mixture of 2a and [Cp2Fe][PF6], air-stable [(C5Me4SiMe3)3Mo3S4][PF6] (3a) was isolated as a green solid in 33% yield (based on 1a) after column chromatography on neutral alumina. Similarly, [(C 5 Me 4 SiEt 3 ) 3 Mo 3 S 4 ][PF 6 ] (3b) and [(C5Me4H)3Mo3S4][PF6] (3c) were isolated in 32% (based on 1b) and 15% (based on 1c) yields, respectively. Even though Mo(IV)-thiolate complexes 2a−2c were treated with an oxidant [Cp2Fe][PF6] in these reactions, the resultant [Mo3S4] clusters 3a−3c adopt the same Mo(IV) state, indicating the involvement of some reduction processes. A possibility is the reductive formation of tBuS-StBu, that is compatible with the reduction of the number of sulfur atoms in this reaction and the previously reported reaction of a Mo(V) complex (C5Me5)MoCl4 with LiStBu furnishing a Mo(IV) complex (C5Me5)Mo(StBu)3 and tBuS-StBu.23 Detailed pathways for the cleavage of multiple C−S bonds in the synthesis of 3a−3c remain unclear, while the following three possibilities have been proposed for the conversion of a Mo(IV) complex (C5Me5)Mo(StBu)3 into a Mo(VI) complex (C5Me5)Mo(S)2(StBu) in the presence of hydrazines;23 (a) an internal redox reaction, (b) deprotonation of a Mo-SC(CH3)3 moiety, and (c) hemolytic C−S bond cleavage. As the yield of 3c was relatively low, we sought an alternative synthetic pathway and found that 3c can be obtained in 34% yield from the reaction of 1c with Li2S2 (0.8 equiv) and KC8 (1.0 equiv) followed by treatment with an aqueous solution of [NH4][PF6] (Scheme 3). Although the 3:2:7 ratio of 1c, Li2S2, and KC8 seems suitable by assuming the ideal composition of [(C5Me4H)3Mo3S4][Cl] as the primary product, the correC


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Inorganic Chemistry

Figure 4. Molecular structure of 3a with thermal ellipsoids set at 50% probability. Selected bond distances (Å): Mo1−Mo2 2.8098(4), Mo1−Mo3 2.8065(3), Mo2−Mo3 2.8188(4), Mo1−S1 2.2943(8), Mo1−S3 2.2954(7), Mo1−S4 2.3248(5), Mo2−S1 2.2824(7), Mo2− S2 2.2893(7), Mo2−S4 2.3249(7), Mo3−S2 2.2835(9), Mo3−S3 2.2827(8), Mo3−S4 2.3287(5), Si1−C1 1.902(2), Si2−C13 1.882(3), and Si3−C25 1.897(3).

C5Me4SiMe3 (4a), C5Me4SiEt3 (4b), and C5Me4H (4c)), which were not isolated but separated from the side products (KPF6 and graphite). The formation of intermediary clusters 4a−4c was suggested by the 1H NMR spectra in C6D6, where broad paramagnetic signals of CpR ligands appeared (Figures S25−S27). Cluster 4c was additionally identified by means of an X-ray diffraction analysis (Figure S24). Without further purification, the neutral clusters 4a−4c were treated with 1 equiv Na(C10H8) in THF converting them into the anionic form [CpR3Mo3S4]−, and then FeCl2 (1 equiv) was added. KC8 can be used in the second reduction process also, as was demonstrated by the isolation of [K(18-crown-6)][(C5Me5)3Mo3S4],26 while an interaction between the [K(18crown-6)]+ cation and the μ-S atoms of the [(C5Me5)3Mo3S4]− anion resulted in the slower reaction with metal halides. 26 Two cubic [Mo 3 S 4 Fe] clusters CpR3Mo3S4FeCl (CpR = C5Me4SiMe3 (5a), C5Me4SiEt3 (5b)) were successfully synthesized (Scheme 4), while an uncharacterizable complex mixture was obtained when the C5Me4H variant was employed. Clusters 5a and 5b exhibited broad 1H NMR signals of the CpR ligands (Figures S29 and S30) and their ESI-MS spectra revealed weak features for the parent cations [5a]+ or [5b]+ as well as intense signals for the Fe-dissociated species [(C5Me4SiR3)3Mo3S4]+ (Figures S32 and S33), in analogy with (C5Me5)3Mo3S4FeCl.26 The molecular structures of 5a and 5b were unequivocally confirmed by single crystal X-ray analysis (Figures 6 and S28). The orientation of CpR ligand, which was found in the [Mo3S4] platforms (Figure 5), is retained in the cubic clusters 5a and 5b; thus, the −SiR3 groups offer steric protection around the Fe atom. The limited

Figure 3. Cyclic voltammograms of 3a−3c in THF at room temperature. Measurement conditions: scan rate = 0.1 V/s; concentration = 4.0 mM; concentration ([nBu4N][PF6]) = 0.2 M; working electrode = glassy carbon; reference electrode = Ag/AgNO3; counter electrode = Pt.

(μ-S), and Mo-(μ3-S) distances are comparable among 3a−3c, further indicating the limited electronic influence of the CpR ligands on the metrical parameters. A notable feature common to 3a and 3b is the position of the −SiR3 groups, which are oriented toward the outer sphere of the [Mo3S4] cores minimizing the steric congestion. Thus, only one −SiR3 group incorporated into each CpR ligand efficiently modifies the steric properties of the [Mo3S4] platform (Figure 5). Application of [Mo3S4] Clusters as Platforms to Accommodate an Fe Atom. In our recent studies, the anionic cluster [(C5Me5)3Mo3S4]− was found to serve as a versatile acceptor of first-row transition metal (M) halides to form cubic [Mo3S4M] clusters.17,26 In order to examine the utility of the new [Mo3S4] clusters as platforms, analogous cluster anions [CpR3Mo3S4]− were generated from the cationic clusters [CpR3Mo3S4]+ (3a−3c) in a stepwise manner and reacted with FeCl2, while analogous [3 + 1] approaches have been applied for the synthesis of [Mo3S4Fe] clusters supported by Tp or dmpe (1,2-bis(dimethylphosphino)ethane).12,27 The one-electron reduction of 3a−3c by KC8 (1 equiv) in THF resulted in the formation of neutral clusters CpR3Mo3S4 (CpR =

Table 2. Electrochemical Properties (V vs Ag/Ag+) of [CpR3Mo3S4][PF6] (3a−3c) and [Cp*3Mo3S4][PF6]a in THF at Room Temperature CpR R

+/0

E1/2[Cp 3Mo3S4] E1/2[CpR3Mo3S4]0/−

C5Me4SiMe3 (3a)

C5Me4SiEt3 (3b)

C5Me4H (3c)

C5Me5 ([Cp*3Mo3S4]+)

−1.05 −2.19

−1.00 −2.18

−1.11 −2.09

−1.09 −2.13

a

See ref 26; Cp* = C5Me5 D


Article

Inorganic Chemistry Table 3. Selected Bond Distances (Å) of [CpR3Mo3S4][PF6] (3a−3c) CpR

C5Me4SiMe3 (3a)

C5Me4SiEt3 (3b)

C5Me4H (3c)

Mo−Mo distances (Å) Mo−(μ-S) distances (Å) Mo−(μ3-S) distances (Å)

2.8065(3)−2.8188(4) 2.2824(7)−2.2954(7) 2.3248(5)−2.3287(5)

2.8076(5)−2.8103(5) 2.2566(12)−2.2970(10) 2.3195(9)−2.3243(9)

2.7945(4)−2.8098(4) 2.2831(8)−2.3089(7) 2.3159(6)−2.3181(6)

Figure 5. Side views of the cationic parts of clusters 3a−3c. The Mo (dark blue) and S (yellow) atoms are drawn in a ball-and-stick model. Only two of the CpR ligands are included in a space-filling model, while the other CpR ligand is omitted to show the [Mo3S4] cores.

Scheme 4

Figure 6. Molecular structure of (C5Me4SiMe3)3Mo3S4FeCl (5a) with thermal ellipsoids set at 50% probability. Selected bond distances (Å): Mo1−Mo1* 2.8888(14), Mo1−Mo2 2.8675(12), Mo1−Fe 2.7666(14), Mo1−S1 2.343(2), Mo1−S2 2.3286(18), Mo1−S3 2.3453(19), Mo2−Fe 2.7912(18), Mo2−S1 2.3364(16), Mo2−S1* 2.3364(16), Mo2−S2 2.331(3), Fe−Cl 2.214(3), Fe−S1 2.2405(18), Fe−S1* 2.2405(18), Fe−S3 2.250(3), Si1−C1 1.895(7), and Si2− C13 1.884(9).

electronic effect of the CpR ligands is evident not only from the metrical parameters of the cubic [Mo3S4Fe] cores but also from the 57Fe Mössbauer spectra (Figures 7 and S34) and the electrochemical properties (Figure S31), which are nearly identical among 5a, 5b, and (C5Me5)3Mo3S4FeCl (Table 4). As the Fe(II) state and the triplet state of (C5Me5)3Mo3S4FeCl have been identified based on the structural parameters, solution magnetic moment, and the Mössbauer parameters, in combination with the DFT simulations,26 the same electronic state should be applicable to 5a and 5b.

Figure 7. 57Fe Mössbauer spectrum of crystalline 5a at zero field and 78 K. The Doppler velocity scale was calibrated by using the roomtemperature Mössbauer spectrum of α-iron foil.

The limited electronic influence of the CpR ligand on the properties of the [Mo3S4] clusters is supported by a variety of spectroscopic and structural data. On the other hand, the steric properties of the [Mo3S4] platforms were found to be modulated by only one −SiR3 group incorporated in the CpR ligand, by directing the −SiR3 groups toward the open triangular face of the [Mo3S4] core. Steric protection imposed by the CpR ligands appeared to influence the metalincorporating function of the [Mo3S4] clusters, and the

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CONCLUSION This work has provided a versatile synthetic route to a series of [Mo 3 S 4 ] clusters supported by Cp R ligands (CpR = C5Me4SiMe3, C5Me4SiEt3, C5Me4H). Their precursors, halfsandwich Mo(V) chlorides CpRMoCl4, are available on a multigram scale, and therefore, one can use these as starting materials for various CpR-supported molybdenum complexes. E


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Inorganic Chemistry

Table 4. Selected Interatomic Distances (Å), the Mössbauer Parameters (mm/s), and the Electrochemical Properties (V vs Ag/Ag+) of the Cubane-Type Clusters CpR3Mo3S4FeCl (CpR = C5Me4SiMe3 (5a), C5Me4SiEt3 (5b), and C5Me5) CpR Fe−S distances (Å) Fe−Cl distance (Å) Fe−Mo distances (Å) Mo−Mo distances (Å) isomer shiftc(mm/s) quadrupole splitting (mm/s) line width at half-hight (mm/s) E1/2 (V) [CpR3Mo3S4FeCI]+/0 E1/2 (V) [CpR3Mo3S4FeCI]0/− rest potential (V)

C5Me4SiMe3 (5a)

C5Me4SiEt3 (5b)

selected interatomic distances (Å) 2.2405(18)−2.250(3) 2.2433(11)−2.2460(11) 2.214(3) 2.2086(11) 2.7666(14)−2.7912(18) 2.7759(8)−2.7874(8) 2.8675(12)−2.8888(14) 2.8714(6)−2.8799(7) Mössbauer parameters (mm/s)b 0.562(2) 0.555(2) 0.254(4) 0.310(3) 0.322(8) 0.315(5) redox potentials (V, vs Ag/Ag+) −0.19 −0.09 −2.06 −2.13 −0.53 −0.57

C5Me5 (Cp*3Mo3S4FeCla) 2.2456(8)−2.2457(12) 2.2095(13) 2.7777(6)−2.7914(8) 2.8577(6)−2.8697(5) 0.563(3) 0.266(5) 0.326(8) −0.17 −2.02 −0.49

a See ref 26; Cp* = C5Me5 bMeasured at zero-field and 78 K with polycrystalline samples. cCalibrated by using the room-temperature Mössbauer spectrum of α-iron foil.

of Mo(CO)6 (23.7 g, 89.7 mmol) was added to the solution, and the mixture was refluxed for 2 days. The resulting brown mixture was cooled to room temperature and treated with MeI (17.0 mL, 273 mmol), followed by stirring for 3 h. The volatile materials were removed under reduced pressure. The residue was extracted multiple times with hexane (ca. 1 L in total) and filtered through Celite. Evaporation of hexane afforded a dark yellow solid. We speculate that this solid contains (C5Me4SiMe3)Mo(CO)3Me as the major component, based on analogy to the C5Me5 variant. This dark yellow solid was used in the next step without any characterization or further purification to minimize the number of manipulations. The dark yellow solid was dissolved in CH2Cl2 (85 mL), and the solution was carefully added to PCl5 (37.5 g, 180 mmol) in a flask equipped with a reflux condenser and a bubbler. Ice-cooling of the flask is recommended during the addition of a CH2Cl2 solution of molybdenum complex, to avoid abrupt CO evolution. After heating to reflux for 16 h, the mixture was cooled to room temperature, giving a dark purple suspension. Hexane (150 mL) was added to the mixture to further precipitate the product. The product was isolated by filtration of the suspension to collect the reddish purple solid followed by washing with hexane (300 mL) and Et2O (50 mL), and drying under vacuum (29.1 g, 67.5 mmol, 75%). 1H NMR (CDCl3): δ 0.98 (SiMe3), −5.25 (C5Me4SiMe3), −13.0 (C5Me4SiMe3). ESR (CH2Cl2, rt): g = 1.992. Anal. Calcd for C12H21Cl4MoSi: C, 33.43; H, 4.91. Found: C, 33.89; H, 5.01. C5Me4HSiEt3. K(C5Me4H) was prepared according to the literature procedure.20 A toluene (170 mL) suspension of K(C5Me4H) (18.2 g, 114 mmol) was treated with a toluene (200 mL) solution of Et3SiCl (17.5 g, 116 mmol). After being stirred for 2 days at room temperature, the mixture was evaporated under reduced pressure. The product was extracted multiple times with hexane (ca. 1 L in total) from the resultant oily residue, and the extract was filtered through Celite. The filtrate was evaporated under reduced pressure to afford an orange oil of C5Me4HSiEt3 (25.6 g, 108 mmol, 95%), which was used without further purification. 1H NMR (C6D6): δ 0.55 (q, J = 7.3 Hz, SiCH2CH3), 0.95 (t, J = 7.3 Hz, SiCH2CH3), 1.82 (C5Me4HSiEt3), 1.95 (C5Me4HSiEt3), 2.89 (C5Me4HSiEt3). 13C{1H} NMR (C 6 D 6 ): δ 3.0 (SiCH 2 CH 3 ), 7.6 (SiCH 2 CH 3 ), 11.0 (C5Me4HSiEt3), 14.3 (C5Me4HSiEt3), 51.6 (C5Me4HSiEt3), 133.0 (C5Me4HSiEt3), 135.3 (C5Me4HSiEt3). 29Si{1H} NMR (C6D6): δ 7.3. (C5Me4SiEt3)MoCl4 (1b). In a similar manner to the synthesis of 1a, a solution of Li(C5Me4SiEt3) was prepared from C5Me4HSiEt3 (18.7 g, 79.3 mmol) in THF (250 mL) and a hexane solution of n BuLi (2.76 M, 29.0 mL, 80.0 mmol) at 0 °C. Mo(CO)6 (20.9 g, 79.2 mmol) was then added and the mixture was refluxed for overnight. The resulting brown mixture was cooled to room temperature, treated with MeI (15.0 mL, 241 mmol), stirred for 3 h, and evaporated under reduced pressure. The dark orange residue was extracted multiple

successful synthesis of cubic [Mo3S4Fe] clusters was realized with the C5Me5SiR3 ligands as well as the previously reported C5Me5 variant, while the analogue with less bulky C5Me4H ligands did not furnish the corresponding [Mo3S4Fe] cluster. In light of the successful applications of cubic [Mo3S4M] clusters in homogeneous catalysis9,14−16 and in the activation of N2,17 the new [Mo3S4] clusters should provide access to various cubic [Mo3S4M] clusters for applications in catalysis and small molecule activation.

■

EXPERIMENTAL SECTION

General Considerations. All reactions were carried out under an atmosphere of N2 or Ar using either Schlenk-line or glovebox techniques. Hexane, toluene, THF, Et2O and CH2Cl2 were purified by passing over columns of activated alumina and a supported copper catalyst supplied by Hansen & Co. Ltd. Deuterated solvents were dried and vacuum-transferred prior to use. 1H NMR spectra were recorded on JEOL JNM ECS600 or ECS500 spectrometers. UV−vis spectra were measured on a JASCO V770 spectrometer. ESR spectra of 1a−1c were recorded on a Bruker EMX-plus spectrometer or a JEOL JES-FA200 spectrometer at X-band frequencies. Elemental analyses were carried out on powdered crystalline samples sealed in tin capsules under N2, using an Elementar Analytical vario MICRO cube elemental analyzer. Cyclic voltammograms were measured in a single-compartment cell under a N2 atmosphere at room temperature using a BAS ALS-660A electrochemical analyzer. The supporting electrolyte, 0.2 M tetrabutylammonium hexafluorophosphate ([nBu4N][PF6]), was recrystallized from THF prior to use. All potentials are referenced to Ag/AgNO3. Mössbauer measurements were performed in a conventional transmission mode on a Mössbauer spectrometer (Topologic Systems Co. Model-222) using a 57Co(Rh) source (925 MBq). The spectral curve fitting was conducted out by using MossWinn 4.0Pre on the assumption of the sum of the Lorentzian curves. The Doppler velocity scale was calibrated with respect to α-iron at room temperature, and the isomer shifts are given relative to α-iron. Low-temperature experiments were carried out in a glovebox using a Techno Sigma UCR-150-GB. Li2S2,24 KC8,25 and K(C5Me4H)20 were synthesized according to the reported procedures. All other chemicals were purchased from common commercial sources and used without further purification. (C5Me4SiMe3)MoCl4 (1a). A solution of Li(C5Me4SiMe3) was prepared from a THF (150 mL) solution of C5Me4HSiMe3 (20 mL, 87.7 mmol) and a hexane solution of nBuLi (2.76 M, 35.0 mL, 93.1 mmol) at 0 °C. Caution! The following steps need to be conducted in a fume hood, as CO gas evolves on the progress of the reaction. The evolved CO needs to be released through a bubbler to a f ume hood. A white solid F


Article

Inorganic Chemistry times with hexane (500 mL in total), filtered through Celite, and evaporated. The dark orange residue was dissolved in CH2Cl2 (30 mL), and the solution was added to PCl5 (32.9 g, 158 mmol). After heating to reflux for overnight, the mixture was cooled to room temperature. The product was isolated by filtration of a CH2Cl2 suspension to collect the reddish purple solid, followed by repeated washing with Et2O (20 mL × 5) until the filtrate becomes light purple (23.0 g, 48.6 mmol, 61%). 1H NMR (CDCl3): δ 2.58 (SiCH2CH3), 1.48 (SiCH2CH3), − 6.95 (C5Me4SiEt3), − 12.8 (C5Me4SiEt3). ESR (CH 2 Cl 2 , room temperature): g = 1.982. Anal. Calcd for C15H27Cl4MoSi: C, 38.07; H, 5.75. Found: C, 37.39; H, 5.60. We have been unable to obtain satisfactory elemental analysis values for this compound. Even though several attempts have been made with crystals in diffraction quality or a ground powder, the samples afforded low carbon and hydrogen values, which may be due to incomplete combustion or thermal degradation. The addition of a combustion accelerator (WO3 powder) did not improve the results. Regardless, some measurements and the successful reactions with this compound indicated its sufficient purity as a precursor. (C5Me4H)MoCl4 (1c). In a similar manner to the synthesis of 1a, a suspension of Li(C5Me4H) was prepared from C5Me4H2 (35.0 mL, 0.229 mol) in THF (450 mL) and a hexane solution of nBuLi (2.76 M, 85.0 mL, 0.235 mol) at 0 °C. Mo(CO)6 (59.1 g, 0.224 mol) was then added and the mixture was refluxed for 2 days. The resulting brown mixture was cooled to room temperature and treated with MeI (42.0 mL, 0.67 mol), followed by stirring for 3 h. The volatile materials were removed under reduced pressure. The residue was extracted multiple times with hexane (ca. 1.7 L in total) and filtered through Celite. Evaporation of hexane afforded a reddish orange solid. The solid was dissolved in CH2Cl2 (50 mL), and the solution was added to ice-cooled PCl5 (93.3 g, 0.448 mol). After heating to reflux for 16 h, the mixture was cooled to room temperature. The product was isolated as a reddish purple solid, by filtration of a CH2Cl2 suspension followed by washing with Et2O (150 mL) until the filtrate becomes nearly colorless (54.3 g, 0.151 mol, 68%). ESR (CH2Cl2, room temprature): g = 1.993. Anal. Calcd for C9H13Cl4Mo: C, 30.12; H, 3.65. Found: C, 30.48; H, 3.77. [(C5Me4SiMe3)3Mo3S4][PF6] (3a). A solution of LiStBu was prepared from a THF (40 mL) solution of tBuSH (11.3 mL, 0.10 mol) and a hexane solution of nBuLi (2.76 M, 36.2 mL, 0.10 mol) at 0 °C. The solution of LiStBu was added to a THF (90 mL) suspension of 1a (10.0 g, 0.023 mol) at 0 °C to furnish a dark green (almost black) solution. After being stirred for 30 min, the mixture was gradually warmed to room temperature and evaporated under reduced pressure. The residue was extracted multiple times with hexane (ca. 400 mL in total). The extract was filtered through a glass frit to remove LiCl, and the filtrate was evaporated to dryness. The formation of (C5Me4SiMe3)Mo(StBu)3 (2a) at this stage was supported by the 1H NMR (C6D6) signals δ 1.97 (C5Me4SiMe3), 1.65 (C5Me4SiMe3), 1.77 (StBu), and 0.31 (SiMe3), while some other minor signals also appeared (Figure S9). [(C5H5)2Fe][PF6] (2.76 g, 8.3 mmol) and CH2Cl2 (200 mL) were added to the residue at room temperature. The resultant mixture was stirred for 20 h to afford a greenish brown solution, which was evaporated to dryness. The following steps were carried out under air in a fume hood, as the product is air-stable but the unpurified material smells unpleasant. After washing the residue with hexane (200 mL), the residue was extracted with a mixture of acetone and hexane (1/3 v/v). The product was purified by a column chromatography on neutral alumina (4 × 20 cm). The acetone-hexane solution was mounted on alumina, and the compounds were eluted gradually with acetone-hexane (1/3 v/v) and then with acetone-hexane (1/2 v/v). The green band was collected, and the solvents were removed under reduced pressure. The chromatography was repeated once again under the same condition with fresh alumina, to further purify the green product by removing brownish materials. The green residue was dissolved in a minimal amount of THF (40 mL), and hexane (ca. 110 mL) was layered on top of the THF solution. Slow diffusion of two layers at room temperature led to the formation of green plates of 3a·THF (3.06 g, 2.51 mmol, 33%). 1H NMR (CDCl3): δ 1.84 (C5Me4SiMe3),

1.72 (C5Me4SiMe3), 0.57 (SiMe3). 13C{1H} NMR (CDCl3): δ 124.7 (C5Me4SiMe3), 111.3 (C5Me4SiMe3), 100.8 (C5Me4SiMe3), 15.4 (C5Me4SiMe3), 12.2 (C5Me4SiMe3), 2.9 (SiMe3). Cyclic voltammetry (THF): E1/2 = −1.05 V, −2.09 V (vs Ag/AgNO3). UV−vis (CH2Cl2): λmax = 246 (ε 5.4 × 104 cm−1 M−1), 338 (ε 7.0 × 103 cm−1 M−1), 411 (ε 4.9 × 103 cm−1 M−1) nm. ESI-MS (THF): m/z = 996.95 ([3a]+). Anal. Calcd for C40H71F6Mo3OPS4Si3: C, 39.60; H, 5.90; S, 10.57. Found: C, 39.17; H, 5.81; S, 10.72. [(C5Me4SiEt3)3Mo3S4][PF6] (3b). This compound was synthesized in a similar manner to the synthesis of 3a. A solution of LiStBu, which was prepared from tBuSH (9.51 mL, 0.084 mol) in THF (40 mL) and a hexane solution of nBuLi (2.76 M, 30.4 mL, 0.084 mol), was added to 1b (10.0 g, 0.021 mol) at 0 °C. After being stirred for 30 min, the volatile materials were removed at room temperature. The black compound was extracted with hexane (ca. 400 mL in total), filtered, and evaporated. The formation of (C5Me4SiEt3)Mo(StBu)3 (2b) at this stage was supported by the 1H NMR (C6D6) signals at δ 1.99 (C5Me4SiEt3), 1.64 (C5Me4SiEt3), 1.76 (StBu), 1.06 (SiEt3), and 0.91 (SiEt3), while some other unidentified signals also appeared in the spectrum (Figure S10). [(C5H5)2Fe][PF6] (2.32 g, 7.0 mmol) and CH2Cl2 (200 mL) were added to the residue, and the mixture was stirred overnight at room temperature. After evaporation and washing with hexane (200 mL), the product was purified by column chromatography as noted in the synthesis of 3a, while hexane, acetone-hexane (1/4 v/v), and acetone-hexane (1/2 v/v) were sequentially used as the eluting solvents. The green band was collected and evaporated to dryness. The chromatography was repeated under the same condition with fresh alumina. The green residue was dissolved in a minimal amount of THF (ca. 12 mL), and hexane (150 mL) was carefully layered. Slow diffusion of two layers at room temperature led to the formation of green plates of 3b·THF (3.04 g, 2.26 mmol, 32%). 1H NMR (CDCl3): δ 1.71 (C5Me4SiEt3, two signals overlapped), 1.03 (q, J = 7.6 Hz, SiEt3), 0.96 (t, J = 7.6 Hz, C5Me4SiEt3). 13C{1H} NMR (CDCl3): δ 125.1 (C5Me4SiEt3), 111.4 (C5Me4SiEt3), 99.6 (C5Me4SiEt3), 15.8 (C5Me4SiEt3), 12.5 (C5Me4SiEt3), 8.2 (SiEt3), 6.6 (SiEt3). Cyclic voltammetry (THF): E1/2 = −1.00 V, − 2.18 V (vs Ag/AgNO3). UV−vis (CH2Cl2): λmax = 413 (ε 1.8 × 103 cm−1 M−1), 608 (ε 8.7 × 102 cm−1 M−1) nm. ESIMS (THF): m/z = 1123.2 ([3b] + ). Anal. Calcd for C49H89F6Mo3OPS4Si3: C, 43.93; H, 6.70; S, 9.57. Found: C, 43.55; H, 6.28; S, 9.22. [(C5Me4H)3Mo3S4][PF6] (3c). Method A, from 1c, LiStBu, and [(C5H5)2Fe][PF6]. In a similar manner to the synthesis of 3a, a mixture of tBuSH (12.6 mL, 112 mmol) in THF (40 mL) and a hexane solution of nBuLi (2.76 M, 40.4 mL, 112 mmol) was added to 1c (10.0 g, 27.9 mmol) at 0 °C and stirred for 30 min. After removal of the volatile materials at room temperature, the residue was extracted with hexane (400 mL). The extract was filtered and evaporated to dryness. The formation of (C5Me4H)Mo(StBu)3 (2c) at this stage was supported by the 1H NMR (C6D6) signals δ 1.73 (C5Me4H), 1.57 (C5Me4H), and 1.75 (StBu), while some other unidentified signals also appeared in the spectrum (Figure S11). [(C5H5)2Fe][PF6] (3.08 g, 9.3 mmol) and CH2Cl2 (200 mL) were added, and the mixture was stirred overnight at room temperature. After evaporation and washing with hexane (100 mL), the product was purified by column chromatography as noted in the synthesis of 3a, while acetone− hexane (1/1 v/v) was used as the eluting solvent. The deep green band was collected and evaporated to dryness. The chromatography was repeated under the same condition with fresh alumina. The green residue was dissolved in a minimal amount of CH2Cl2 (ca. 20 mL), and hexane (150 mL) was carefully layered. Slow diffusion of two layers at room temperature led to the formation of dark green crystals of 3c (1.30 g, 1.40 mmol, 15%). Method B, from 1c, Li2S2, and KC8. 1c (501 mg, 1.39 mmol), Li2S2 (87.1 mg, 1.12 mmol), and KC8 (188 mg, 1.39 mmol) were mixed in a flask, and THF (25 mL) was vacuum transferred onto the solid mixture. After filling the flask with N2, the frozen mixture was gradually warmed. As soon as a part of THF melted, the mixture was vigorously stirred. The reddish brown mixture finally became greenish brown after stirring overnight at room temperature. The mixture was G


Article

Inorganic Chemistry

Table 5. Crystal Data and Refinement Summary for(C5Me4SiEt3)MoCl4 (1b), (C5Me4SiMe3)Mo(StBu)3 (2a), (C5Me4H)Mo(StBu)3 (2c), (C5Me4H)2Mo2(μ-S)2(μ-StBu)2(A), [(C5Me4H)4Mo4S4][PF6] (B), [(C5Me4SiMe3)3Mo3S4][PF6] (3a), [(C5Me4SiEt3)3Mo3S4][PF6] (3b), [(C5Me4H)3Mo3S4][PF6] (3c), (C5Me4H)3Mo3S4 (4c), (C5Me4SiMe3)3Mo3S4FeCl (5a), and (C5Me4SiEt3)3Mo3S4FeCl (5b) formula formula wt (g mol−1) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g/cm3) max. 2θ (deg) no. of reflections no. of variables R1a wR2b GOFc formula formula wt (g mol−1) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g/cm3) max. 2θ (deg) no. of reflections no. of variables R1a wR2b GOFc formula formula wt (g mol−1) crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g/cm3) max. 2θ (deg) no. of reflections no. of variables R1a

1b

2a

2c

A

C15H27Cl4MoSi 473.22 triclinic P1̅ (no. 2) 11.221(4) 12.783(5) 14.368(5) 91.999(15) 101.810(13) 90.019(16) 2016.0(13) 4 1.560 55.0 9034 393 0.0881 0.2500 0.974 B

C24H48MoS3Si 556.85 monoclinic P21/n (no. 14) 18.111(4) 9.6701(19) 18.702(4)

C21H38.5MoS3 483.16 triclinic P1̅ (no. 2) 9.6371(7) 15.8729(12) 33.545(2) 77.681(3) 84.964(4) 89.916(3) 4993.1(6) 8 1.285 55.1 22866 899 0.0258 0.0621 1.037 3b

C26H44Mo2S4 676.75 triclinic P1̅ (no. 2) 10.344(4) 11.309(5) 14.830(6) 101.712(4) 101.369(5) 115.810(5) 1446.8(10) 2 1.553 55.1 6630 289 0.0683 0.1752 1.026 3c

C36H52F6Mo4PS4 1141.77 monoclinic Cc (no. 9) 17.435(3) 14.253(2) 16.407(3) 91.537(3) 4075.7(12) 4 1.861 55.0 8352 460 0.0240 0.0596 1.020

116.926(5) 2920.3(11) 4 1.266 55.1 6697 262 0.0190 0.0540 1.049 3a·(toluene) C36H63F6Mo3PS4Si3 1141.17 triclinic P1̅ (no. 2) 12.3612(10) 13.3090(11) 16.6444(15) 76.617(7) 75.550(8) 71.414(7) 2478.7(4) 2 1.529 55.1 11356 523 0.0296 0.0820 1.020

C45H81F6Mo3PS4Si3 1267.39 monoclinic P21/c (no. 14) 18.137(2) 13.4671(15) 23.894(3)

C27H45F6Mo3PS4 930.68 monoclinic P21/c (no. 14) 8.5177(10) 17.746(2) 21.743(3)

111.214(3)

93.011(2)

5440.6(12) 4 1.547 55.3 12607 571 0.0449 0.1375 1.085

4c

5a

3282.0(7) 4 1.883 55.0 7514 370 0.0256 0.0713 0.990 5b·(hexane)0.36

C27H39Mo3S4 779.67 Cubic Pa3̅ (no. 205) 17.904(3)

C36H63ClFeMo3S4Si3 1087.51 orthorhombic Cmc21 (no. 36) 16.999(7) 18.396(7) 14.547(6)

C47.15H86.02ClFeMo3S4Si3 1244.61 monoclinic P21/n (no. 14) 24.238(6) 11.603(3) 41.136(10) 106.592(3)

5739.2(17) 8 1.805 55.0 2208 103 0.0227

4548(3) 8 1.588 55.1 5391 229 0.0403 H

11088(5) 8 1.493 55.1 25459 1072 0.0357 DOI: 10.1021/acs.inorgchem.9b00309 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Table 5. continued 4c wR2b GOFc

5a

0.0461 0.930

0.0844 0.922

5b·(hexane)0.36 0.0940 1.009

I > 2σ(I), R1= Σ||F0| − |Fc||/Σ|F0|. bRefined with all data, wR2 = [{Σw(F02 − Fc2)2}/Σw(F02)2]1/2. cGOF = [{Σw(F02 − Fc2)2}/(N0 − Np)]1/2, where N0 and Np denote the numbers of reflection data and parameters.

a

centrifuged to remove an insoluble solid, and the supernatant was treated with an aqueous solution (25 mL) of [NH4][PF6] (382 mg, 3.62 mmol). After removal of all volatile materials under reduced pressure, the residue was extracted with CH2Cl2 (10 mL). The solution was centrifuged to remove a small amount of insoluble material, and layered with hexane (50 mL). Slow diffusion between the two layers led to the formation of dark green crystals of 3c (147 mg, 0.159 mmol, 34%), which were collected after washing with Et2O (5 mL) and drying under vacuum. 1H NMR (CDCl3): δ 2.17 (C5Me4H), 2.00 (C5Me4H), 5.07 (C5Me4H). 13C{1H} NMR (CDCl3): δ 114.4 (C5Me4H), 113.7 (C5Me4H), 93.9 (C5Me4H), 14.5 (C5Me4H), 12.8 (C5Me4H). Cyclic Voltammetry (THF): E1/2 = −1.11 V, − 2.09 V (vs Ag/AgNO3). UV−vis (CH2Cl2): λmax = 226 (ε 4.8 × 104 cm−1 M−1), 335 (ε 6.0 × 103 cm−1 M−1), 409 (ε 3.9 × 103 cm−1 M−1), 595 (ε 9.8 × 102 cm−1 M−1), 688 (ε 7.6 × 102 cm−1 M−1) nm. ESI-MS (THF): m/z = 778.89 ([3c]+). Anal. Calcd for C27H39F6Mo3PS4: C, 35.07; H, 4.25; S, 13.87. Found: C, 34.65; H, 4.50; S, 13.59. (C5Me4SiMe3)3Mo3S4FeCl (5a). A THF (50 mL) solution of 3a (1.02 g, 0.89 mmol) was treated with KC8 (130 mg, 0.96 mmol) and stirred overnight at room temperature. After evaporation to dryness, the residue was extracted with hexane (45 mL) and centrifuged. Hexane was removed under reduced pressure to give a green solid of (C5Me4SiMe3)3Mo3S4 (4a), which exhibits broad 1H NMR signals in C6D6 at δ 14.8 (C5Me4SiMe3), 0.38 (C5Me4SiMe3), and 1.22 (SiMe3) (Figure S25). This green solid was dissolved in THF (30 mL) and cooled to −90 °C. A THF solution of Na(C10H8) (19.5 mM, 46 mL, 0.90 mmol) was added, and the mixture was gradually warmed to room temperature, giving a brownish green solution. The solution was again cooled to −90 °C, and FeCl2 (115 mg, 0.91 mmol) was added. The mixture was gradually warmed to room temperature and stirred for 2 days, furnishing a red-brown suspension. The volatile materials were removed, and the residue was extracted with toluene (40 mL), separating an insoluble solid. The solution was concentrated to ca. 1/4 in volume, and stored at −35 °C to give a mixture of dark orange crystals of 5a·(toluene) (plates) and 5a (needles). The solvent was removed under reduced pressure after grinding, giving a brown powder of 5a (730 mg, 0.672 mmol, 75% based on 3a). 1H NMR (C6D6): δ 3.18 (w1/2 = 85 Hz, SiMe3), 1.35 (w1/2 = 430 Hz, C5Me4SiMe3), − 0.20 (w1/2 = 260 Hz, C5Me4SiMe3). Cyclic voltammetry (THF): E1/2 = −0.19 V, − 2.06 V (vs Ag/AgNO3). ESI-MS (THF): a weak signal was observed at m/z = 1087.76 ([5a]+) and intense signals of degradation products appeared at m/z = 996.84 ([3a]+) and 979.88 ([3a − S + O]+). Mössbauer spectrum (mm/s, 78 K): IS = 0.562(2) and QS = 0.254(4). Anal. Calcd for C36H63ClFeMo3S4Si3: C, 39.76; H, 5.84; S, 11.79. Found: C, 39.48; H, 5.48; S, 11.79. (C5Me4SiEt3)3Mo3S4FeCl (5b). A THF (100 mL) solution of 3b· THF (3.23 g, 2.41 mmol) was treated with KC8 (380 mg, 2.81 mmol) and stirred overnight at room temperature. After evaporation to dryness, the residue was extracted with hexane (70 mL), centrifuged, and evaporated to give a green solid of (C5Me4SiEt3)3Mo3S4 (4b) (1.39 g, 1.24 mmol, 51%), which exhibits broad 1H NMR signals in C6D6 at δ 14.3 (C5Me4SiEt3), 1.40 (SiEt3), and 1.13 (SiEt3), and 0.54 (C5Me4SiEt3) (Figure S26). A part of the green solid (1.05 g, 0.935 mmol) was dissolved in THF (30 mL) and cooled to −90 °C. A THF solution of Na(C10H8) (19.8 mM, 56 mL, 1.10 mmol) was added, and the mixture was gradually warmed to room temperature. The solution was again cooled to −90 °C, and FeCl2 (144 mg, 1.10 mmol) was added. The mixture was gradually warmed to room temperature and stirred overnight, furnishing a red-brown suspension. The volatile

materials were removed, and the residue was extracted with a mixture of hexane (20 mL) and THF (2 mL) and filtered. The solution was stored at −35 °C to give dark brown crystals of 5b·(hexane)0.36 (530 mg, 0.426 mmol, 46% based on 4b). 1H NMR (C6D6): δ 2.95 (w1/2 = 80 Hz, SiEt3), 1.65 (w1/2 = 200 Hz, SiEt3 + C5Me4SiEt3), − 0.46 (w1/2 = 420 Hz, C5Me4SiEt3). Cyclic voltammetry (THF): E1/2 = −0.09 V, − 2.13 V (vs Ag/AgNO3). ESI-MS (THF): a weak signal was observed at m/z = 1214.07 ([5b]+) and intense signals of degradation products appeared at m/z = 1123.17 ([3b]+) and 1107.19 ([3b − S + O]+). Mössbauer spectrum (mm/s, 78 K): IS = 0.555(2) and QS = 0.310(3). Anal. Calcd for C45H81ClFeMo3S4Si3·(C6H14)0.36: C, 45.42; H, 6.97; S, 10.32. Found: C, 45.13; H, 6.56; S, 10.12. Generation of (C5Me4H)3Mo3S4 (4c). 3c (198 mg, 0.214 mmol) was mixed with 1.1 equiv of KC8 (31.9 mg, 0.236 mmol) in THF (15 mL) at room temperature, and the solvent was removed after stirring overnight at room temperature. The residue was extracted with toluene (15 mL), and the extract was filtered and cooled at −35 °C to give dark green crystals of (C5Me4H)3Mo3S4 (4c) (111 mg, 0.142 mmol, 67%), which was characterized only by the 1H NMR (C6D6) signals at δ 25.2 (C5Me4H), 9.9 (C5Me4H), and 6.7 (C5Me4H) (Figure S27) and the X-ray crystallographic analysis (Figure S24). X-ray Crystallographic Structure Determinations. Crystal data and refinement parameters for clusters 1b, 2a, 2c, 3a−3c, A, B, 4c, 5a, and 5b are summarized in Table 5. Single crystals were coated with oil (Immersion Oil, type B: Code 1248, Cargille Laboratories, Inc.) and mounted on loops. Diffraction data were collected at −100 °C under a cold N2 stream on a Rigaku RA-Micro7 spectrometer equipped with a PILATUS 200 K detector, using graphitemonochromated Mo Kα radiation (λ = 0.710690 Å). Eighteen preliminary data frames were measured at 0.5° increments of ω in order to determine the crystal quality and preliminary unit cell parameters. Intensity images were also measured at 0.5° increments of ω. The frame data were integrated using the CrystalClear program package, and the data sets were corrected for absorption using the REQAB program. Calculations were performed with the CrystalStructure program package. All structures were solved by direct methods and refined by full-matrix least-squares. Anisotropic refinement was applied to all non-hydrogen atoms except some disordered carbon atoms. All hydrogen atoms were allocated calculated positions. The structural analysis of 1b revealed residual electron densities for the Mo and Cl atoms from a secondary crystal, which refined to 4.7% occupancy. Crystals of this material grew as starburst clusters of fine needles, so that we needed to break these into small pieces to find single-crystal components. Consequently, the data set was weak and peaks of secondary crystals appeared. The Shelxl program does not allow refinement of this type of twin, and therefore the metrical results of 1b are not discussed in this paper. In the structural analysis of 3b, disorder was found for a single methylene carbon (C25). Addition of methylene hydrogen atoms on C25B at calculated positions inevitably led to the short H···H contacts between H atoms on a nearby ethyl group (H atom on C23), leading to the appearance of Alerts A and B in the automatic cif-check program. In the unit cell of 5b·(hexane)0.36, there are five sites for a solvent (hexane) carbon chain, which spans unit cells forming a crystaltransiting helix. In the infinite chain, a hexane molecule and a blank fill 7 (6 + 1) successive sites. The pattern repeats after 5 cycles, and therefore 30 (6 × 5) carbon atoms are stored in 35 (7 × 5) sites, leading to the 6/7 (30/35) occupancy for carbon and the formula of 5b·(hexane)0.36. I


Article

Inorganic Chemistry The atomic coordinates were deposited with the Cambridge Crystallographic Data Centre, Cambridge CB2 1EK, UK under CSD reference numbers 1894505−1894515.

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N. Synthetic, Spectroscopic, X-ray Structural, and Quantum-Chemical Studies of Cyanothiomolybdates with Mo2S, Mo2S2Mo3S4 and Mo4S4 Cores: A Remarkable Class of Species Existing with Different Electron Populations and Having the Same Central Units as the Ferredoxins. Inorg. Chem. 1985, 24, 2872−2884. (6) (a) Keck, H.; Kuchen, W.; Mathow, J.; Wunderlich, H. Coordinatively Unsaturated Trinuclear Molybdenum-Sulfur Cluster Chelates with Dithiophosphinato Bridge. Angew. Chem., Int. Ed. Engl. 1982, 21, 929−930. (b) Huang, J. Q.; Huang, J. L.; Shang, M. Y.; Lu, S. F.; Lin, X. T.; Lin, Y. H.; Huang, M. D.; Zhuang, H. H.; Lu, J. X. Structure and reactivity of molybdenum clusters with loose coordination site, Mo3S4[S2P(OEt)2]4L. Pure Appl. Chem. 1988, 60, 1185−1192. (7) Shibahara, T.; Kuroya, H. Preparation of Trinuclear Molybenum (IV) ion, Mo 3 S 4 4+ and X-ray Structure of Ca[Mo 3 S 4 {HN(CH2CO2)2}3] ·11.5H2O. Polyhedron 1986, 5, 357−361. (8) (a) Fedorov, V. E.; Mishchenko, A. V.; Fedin, V. P. Cluster Transition Metal Chalcogenide Halides. Russ. Chem. Rev. 1985, 54, 408−423. (b) Saito, T.; Yamamoto, N.; Yamagata, T.; Imoto, H. Synthesis and Crystal Structures of Trinuclear Molybdenum Chloro Sulfido Clusters Coordinated with Triethylphosphine and Methanol. Chem. Lett. 1987, 16, 2025−2028. (c) Cotton, F. A.; Llusar, R.; Eagle, C. T. Triangular Trinuclear Cluster Compounds: Molybdenum and Tungsten Complexes of the Type [M3S4(diphos)3X3]+ with X = Cl and H. J. Am. Chem. Soc. 1989, 111, 4332−4338. (d) Cotton, F. A.; Kibala, P. A.; Matusz, M.; McCaleb, C. S.; Sandor, R. B. W. Synthesis and Structural Characterization of Three New Trinuclear Group VI Clusters. Inorg. Chem. 1989, 28, 2623−2630. (e) Fedin, V. P.; Sokolov, M. N.; Mironov, Y. V.; Kolesov, B. A.; Tkachev, S. V.; Fedorov, V. Y. Triangular Thiocomplexes of Molybdenum: Reactions with Halogens, Hydrohalogen Acids and Phosphines. Inorg. Chim. Acta 1990, 167, 39−45. (9) Pedrajas, E.; Sorribes, I.; Guillamón, E.; Junge, K.; Beller, M.; Llusar, R. Efficient and Selective N-Methylation of Nitroarenes under Mild Reaction Conditions. Chem. - Eur. J. 2017, 23, 13205−13212. (10) Gushchin, A. L.; Laricheva, Y. A.; Abramov, P. A.; Virovets, A. V.; Vicent, C.; Sokolov, M. N.; Llusar, R. Homoleptic Molybdenum Cluster Sulfides Functionalized with Noninnocent Diimine Ligands: Synthesis, Structure, and Redox Behavior. Eur. J. Inorg. Chem. 2014, 2014, 4093−4100. (11) Cotton, F. A.; Dori, Z.; Llusar, R.; Schwotzer, W. The Mo3S44+ Aquo Ion. J. Am. Chem. Soc. 1985, 107, 6734−6735. (12) Yamauchi, T.; Takagi, H.; Shibahara, T.; Akashi, H. Syntheses and Characterization of Oxygen/Sulfur-Bridged Incomplete CubaneType Clusters, [Mo3S4Tp3]+ and [Mo3OS3Tp3]+ and a Mixed-Metal Cubane-Type Cluster, [Mo 3 FeS4 ClTp3 ]. X-ray Structures of [Mo3S4Tp3]Cl, [Mo3OS3Tp3]PF6 and [Mo3FeS4ClTp3]. Inorg. Chem. 2006, 45, 5429−5437. (13) (a) Vergamini, P.; Vahrenkamp, H.; Dahl, L. F. Organometallic Chalcogen Complexes. XXIV. Synthesis, Structure, and Bonding of [Mo 3 (η 5-C 5 H 5 )3 S 4 ]+ [Sn(CH 3 ) 3Cl2 ] − Containing a Triangular Molybdenum(IV) Cluster Cation with Doubly and Triply Bridging Sulfur Atoms. J. Am. Chem. Soc. 1971, 93, 6327−6329. (b) Beck, W.; Danzer, W.; Thiel, G. Polynuclear π-Cyclopentadienyl-SulfurMolybdenum Complexes from Propylene Sulfide and π-Cyclopentadienylcarbonylmolybdenum Hydrides. Angew. Chem., Int. Ed. Engl. 1973, 12, 582−583. (c) Cramer, R. E.; Yamada, K.; Kawaguchi, H.; Tatsumi, K. Synthesis and Structure of a Mo3S4 Cluster Complex with Seven Cluster Electrons. Inorg. Chem. 1996, 35, 1743−1746. (d) Rink, B.; Brorson, M.; Scowen, I. J. New Heterometallic CubaneLike Clusters [{(η5-Cp)Mo}3S4{M’(CO)3}](pts) (M’ = Cr, Mo, W; pts = p-Toluenesulfonate) Obtained by Ligand Substitution Reactions and Insertion of {M’(CO)3} Fragments. Organometallics 1999, 18, 2309−2313. (e) Herbst, K.; Rink, B.; Dahlenburg, L.; Brorson, M. Heterobimetallic Cubane-like Cluster CompoundsPrepared as the Homologous Series[(η5-Cp’)3Mo3S4M’(PPh3)]+ (M’ = Ni, Pd, Pt). Crystal Structures Show that Platinum Is Smaller than Palladium. Organometallics 2001, 20, 3655−3660. (f) Takei, I.; Suzuki, K.; Enta, Y.; Dohki, K.; Suzuki, T.; Mizobe, Y.; Hidai, M. Synthesis of a New

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.9b00309. Supportive spectroscopic data, molecular structures of 2c, A, B, 3b, 3c, 4c, and 5b, and electrochemical properties (PDF) Accession Codes

CCDC 1894505−1894516 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], 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

*(Y.O.) E-mail: [email protected]. ORCID

Yasuhiro Ohki: 0000-0001-5573-2821 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was financially supported by Grant-in-Aids for Scientific Research (16H04116 and 18H04246) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (MEXT) and the Takeda Science Foundation. We are grateful to Prof. K. Awaga and Prof. M. M. Matsushita for providing access to instruments, and to Prof. S. Muratsugu for generous advice on electrochemical measurements.

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REFERENCES

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Synthesis of [Mo3S4] Clusters from Half-Sandwich Molybdenum(V

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