Ferrocene and Tetrathiafulvalene Redox Interplay across a Bis

Sep 17, 2013 - Interplay between either two TTF or two Fc moieties across an organometallic bridge has been the focus of recent studies particularly w...
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Ferrocene and Tetrathiafulvalene Redox Interplay across a Bisacetylide−Ruthenium Bridge Antoine Vacher, Frédéric Barrière,* and Dominique Lorcy* UMR CNRS 6226 Institut des Sciences Chimiques de Rennes, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France S Supporting Information *

ABSTRACT: The interplay between two different peripheral electrophores, ferrocene (Fc) and tetrathiafulvalene (TTF), across a bis-acetylide ruthenium organometallic bridge has been studied within the novel complex trans-[Ru(C CMe3TTF)(CCFc)(dppe)2] (3) (HCCMe3TTF = 4-ethynyl-4′,5,5′-trimethyltetrathiafulvalene). A series of experimental data (electrochemistry, UV−visible spectroelectrochemistry, IR and EPR spectroscopy) and comparison with related complexes from the literature and with the properties of the Fc-CCMe3TTF species (4) have allowed the confident assignment of the electron transfer series in 3 and 4. Cyclic voltammetry experiments in dichloromethane in two supporting electrolytes ([NBu4][PF6] and [Na][B(C6H4(CF3)2)4]) have evidenced the extent of the electrostatic effects on the redox potentials in 3. The results of theoretical calculations (DFT) are consistent with these redox potential assignments but suggest some electronic coupling among the three coupled electrophores, the TTF, the Fc, and the Ru(II) center in 3•+ and 32+ and within Fc and TTF in 4•+. Taken together, these data show that the organometallic bis-acetylide ruthenium bridges mediate some appreciable electronic coupling between the two different ferrocene and tetrathiafulvalene electrophores.

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INTRODUCTION

© XXXX American Chemical Society

RESULTS AND DISCUSSION

Synthesis. The synthetic strategy toward the target molecule 3 is outlined in Scheme 1. The synthesis of trans[Ru(CCMe3TTF)(CCFc)(dppe)2], 3, is based on the reaction of ethynylferrocene with the vinylidene derivative [5][OTf]8 in the presence of NaPF6 and triethylamine in dichloromethane, at room temperature and under an inert atmosphere. This reaction was monitored by 31P NMR spectroscopy. The starting material [5][OTf] exhibits two signals at δP = 43.5 ppm and 41.9 ppm due to a nonequivalent environment around the phosphorus atoms. During the course of the reaction, the loss of this set of signals is concomitant with the growth of a novel peak at δP = 52.5 ppm. This single peak indicates the equivalence of the four phosphorus atoms due to the trans arrangement of the two alkynyl ligands and is assigned to complex 3 (Scheme 1). 3 was successfully isolated in 65% yield as an orange powder by slow diffusion of pentane in a concentrated solution of the complex in dichloromethane under an inert atmosphere. We also prepared the reference complex 4, where Fc is directly linked to the TTF derivative via a single alkyne bridge. This was carried out through Sonogashira coupling of iodoMe3 -TTF and ethynylferrocene catalyzed by CuI and PdCl2(PPh3)2 in the presence of diisopropylamine. Complex 4 was obtained in 45% yield as an orange powder (Scheme 1).

Ferrocene (Fc) and tetrathiafulvalene (TTF) are among the most studied electrophores either as electroactive probes or as precursors of molecular materials.1,2 Indeed, both of them exhibit chemically and electrochemically reversible oxidation processes, either one monoelectronic oxidation to ferrocenium for Fc or two successive monoelectronic oxidations to the cation radical and dicationic species for TTF. Interplay between either two TTF or two Fc moieties across an organometallic bridge has been the focus of recent studies particularly with respect to the generation and characterization of mixed valence species.3−5 Among the organometallic bridges considered, the bis-acetylide−ruthenium linker has been shown to promote the generation of mixed valence species in both the Fc and TTF series, respectively in trans-[Ru(CCFc)2(dppm or dppe)2], 1,6 and in trans-[Ru(CCMe3TTF)2(dppe)2], 24 (Chart 1). In this context, and given the similar range for the first oxidation potential of Fc and TTF derivatives,7 we sought to investigate the electronic properties of a novel organometallic complex with a redox-active bis-acetylide−ruthenium central core flanked by these two different Fc and TTF electrophores, namely, trans-[Ru(CCMe3TTF)(CCFc)(dppe)2], 3. In order to assess the effect of the organometallic bridge on the interplay between the Fc and TTF moieties, we also prepared and studied the derivative 4, where Fc and TTF are directly linked via an alkyne bridge. Herein, we present the synthesis, spectroscopic and electrochemical investigations carried out on both complexes. The results and assignments of the electron transfer series are also critically discussed on the basis of DFT calculations.

Special Issue: Ferrocene - Beauty and Function Received: August 4, 2013

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Chart 1

Scheme 1

Table 1. Oxidation Potentials, E1/2 (V vs SCE), and IR νCC Stretching Frequencies (cm−1) compound

E1 TTF

Me3TTF-CC-H Fc-CC-H Me3TTF-CC-Fc 4 TTF-Fca9 5 TTF-CHCH-Fcb10 6 Cp*(dppe)Fe-CC-Me3TTFc11 7 transClRu(dppe)2(CC-Fc) transClRu(dppe)2(CC-Me3TTF)8 transRu(dppe)2(CC-Fc)(CC-Me3TTF) 3

0.38

E2 FeII/III

E3 TTF

E4 Ru

0.89 0.59 0.67 0.71 0.44 −0.11d 0.12

0.34 0.35 0.26 0.38 0.07 0.07

0.28

2090 2105 2188

0.90 0.85 0.77 0.84 0.52 0.62

IR νCC

0.84 1.15 1.18

2022 2061 2029 2050 2030

a

E in V vs SCE, 0.1 M Bu4NClO4 in PhCN. bE in V vs Ag/AgCl 0.1 M Bu4NPF6 in CH3CN. cE in V vs SCE in CH2Cl2 0.1 M Bu4NPF6. dIn Cp*(dppe)Fe moiety.

Ru complex (2029 cm−1) reported previously4,8 and, hence, indicates a higher degree of conjugation in 3. Electrochemical Studies. The redox behavior of the complexes 3 and 4 was first investigated by cyclic voltammetry (CV) in CH2Cl2 using [NBu4][PF6] as supporting electrolyte. In order to assign the redox processes to the different electrophores, i.e., Fc, TTF, and Ru, we also considered the redox potentials of Fc-ethyne and Me3TTF-ethyne (Table 1). The CV of complex 3 displays four reversible systems indicating the stepwise formation of five oxidation states from the neutral to the fully oxidized species 34+ (E1 = 0.07 V; E2 = 0.28 V; E3 = 0.62 V; E4 = 1.18 V, vs SCE) in accordance with the presence of the three electrophores (Figure 1, red curve). The CV of complex 4 exhibits three reversible oxidation processes indicating the stepwise formation of four oxidation

IR Spectroscopy. The stretching frequency of the acetylenic bond measured with IR spectroscopy gives preliminary insights on the degree of conjugation between the redox-active moieties. Complexes 3 and 4 exhibit IR vibration bands localized at νCC = 2050−2030 and 2188 cm−1, respectively. In complex 4, the νCC stretching frequency is higher than that observed for Me3TTF-ethyne and Fc-ethyne, where it is found at 2090 and 2105 cm−1, respectively. This suggests that despite the alkyne bridge, there is little conjugation between the two electrophores in 4. In complex 3 however the νCC (2050−2030 cm−1) lies at lower energy than in TTF-ethyne or Fc-ethyne. The νCC stretching frequency in 3 is also close to that observed for the bis(TTFacetylide)-Ru 2 complex (2028 cm−1) or for the TTF-acetylideB

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respectively). In these cases, the first oxidation process was assigned to the oxidation of the TTF core into the cation radical species, and the comparatively lower potential rationalized by the increase of the electron density on the TTF core(s) due to the metal acetylide substitution. On these grounds, the first oxidation of 3 is also tentatively assigned to the oxidation of the TTF core, strongly affected by the electron-rich Ru(II) acetylide subtituent. The second oxidation process occurs at E2 = 0.28 V and is assigned to the oxidation of the Fc moiety. Indeed, considering the redox potentials of the oxidation of Fc in [Fc-CC-Ru(dppe)2Cl] (E = 0.12 V), the anodic shift (160 mV) found in 3 can be easily explained by the presence of the mocationic charge on the TTF moiety, whose effect is efficiently transmitted to Fc across the bis-acetylide Ru linker. The third oxidation process is attributed to the oxidation of the TTF cation radical to the TTF dication. This assignment is supported by the large potential shift of this redox process in the weakly coordinating supporting electrolyte (see Figure 1 and discussion below). This potential shift is indeed too large to be solely accounted for by electronic coupling and/or by the vicinal positive charge(s) already borne out by neighboring redox-active groups. This is better rationalized by oxidation of a redox-active group, itself already bearing a positive charge (i.e., TTF•+). In addition, the third oxidation occurs at a potential close to those observed in related complexes such as in trans[Ru(CCMe3TTF)2(dppe)2],4 2 (0.58 V vs SCE), or in trans[RuCl(CCMe3TTF)(dppe)2]8 (0.52 V vs SCE) and assigned to the second oxidation of the TTF. The fourth and last oxidation step is then logically attributed to the Ru II/III couple, which is shifted anodically compared to transClRu(dppe)2(CC-Fc) due to the presence of a dicationic charge on the TTF moiety and a monocationic charge on the Fc center acting as strong electron acceptors. The SOMO(−1) of 32+, likely involved in this fourth oxidation, lends further support to this assignment with the following nuance: it is found to be delocalized on the ruthenium center and the TTF moiety across the alkynyl bridge (cf. Figure S6 in the SI). To investigate the electrostatic contribution to the potential difference between the various oxidation processes, the redox behavior of 3 was recorded in the weakly coordinating electrolyte CH2Cl2-[Na][BarF].12 In these conditions, the CV displays three reversible systems (E1 = 0.03 V; E2 = 0.32 V; E3 = 0.89 V, vs SCE). As observed in Figure 1, the potential difference between the two first oxidation systems is slightly affected by the nature of the electrolyte. Indeed the ΔE (E2 − E1) is 210 mV in CH2Cl2-[NBu4][PF6], while it amounts to 290 mV in CH2Cl2-[Na][BarF]. Conversely, the third redox system is anodically shifted by 270 mV in the weakly coordinating electrolyte. This leads to a potential difference between the second and third process (ΔE = E3 − E2) of 570 mV in CH2Cl2-[Na][BarF] compared with 340 mV found in CH2Cl2-[NBu4][PF6]. This is consistent with the assignments of the redox potentials proposed above as the smaller ΔE (E2 − E1) corresponds to different and further apart electroactive

Figure 1. CVs of 3 in CH2Cl2-[NBu4][PF6] (red) and in CH2Cl2[Na][BarF] (black, BarF− is −B(C6H4(CF3)2)4, unassigned impurity at ca. 0.7 V). E in V vs SCE, ν = 100 mV s−1.

states from the neutral to the trication species 33+ (E1 = 0.34 V; E2 = 0.67 V; E3 = 0.90 V vs SCE). Interestingly, the redox potentials in 3 and 4 are clearly different even if the two peripheral redox-active moieties (Fc and TTF) are common. Actually, the redox potentials observed for 4 are close to those observed for Me3TTF-ethyne (E1 = 0.38 V; E2 = 0.89 V vs SCE) and Fc-ethyne (E1 = 0.59 V vs SCE) measured in the same conditions. Consequently, the first oxidation process of 4 is assigned to the oxidation of the TTF core into the cation radical species. Compared with Me3TTF-ethyne the redox potential for the first oxidation of 4 is shifted by 40 mV to lower values, signifying the slightly different electronic effect of the different substitution at the TTF core. The second oxidation step corresponds to the oxidation of the ferrocene, which is positively shifted by 80 mV compared with Fc-ethyne. This is partly ascribed to the presence of the positive charge of the oxidized TTF in the vicinity of the ferrocene moiety in 4•+. The third and last oxidation step is then logically assigned to the oxidation of the TTF cation radical into the dication. Actually, the redox behavior of 4 is close to that observed for compound 5,9 where Fc is directly linked to the TTF moiety, or to the ethylenic analogue 610 (Chart 2 and Table 1). This tends to indicate that the nature of the bridge here does not modify significantly the nature of the interactions between the two electrophores, as both behave independently. This result is also reminiscent of the behavior of a closely related derivative with a Cp*(dppe)Fe center (7, Chart 2), for which the redox potentials of the TTF were not modified by the presence of the metallic fragment.11 Conversely, the first redox system of 3 is observed at a significantly less anodic potential (E1 = 0.07 V). This is reminiscent of what was previously observed for the complexes trans-[RuCl(CCMe3TTF)(dppe)2]8 and trans-[Ru(C CMe3TTF)2(dppe)2]4 (E1 = 0.07 and 0.05 V vs SCE, Chart 2

C

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Figure 2. UV−vis−NIR monitoring from 0 to 0.2 V (top left), from 0.2 to 0.32 V (top right), from 0.36 to 0.8 V (bottom left), and of the overall process (bottom right), electrochemical oxidation of 3 in 0.2 M CH2Cl2-[NBu4][PF6].

shifted to 1365 nm, and upon oxidation to the third oxidation process, the intensity of this broad band increased and shifted toward higher energy at λmax = 1222 nm (Figure 2 bottom left). If we summarize the overall process (Figure 2 bottom right), upon gradual oxidation of 3, the intensity of the lowest energy band gradually increases and is shifted toward higher energy with a bandwidth narrowing. This behavior is similar to that of trans-[Ru(CCMe3TTF)2(dppe)2]4 and consistent with a primary TTF oxidation in 3. Back-electrolysis to the neutral state permits the quasi-quantitative recovery of the initial spectrum unless polycharged species are generated for too long (on the order of hours). Theoretical Calculations. Geometry optimizations were carried out on complexes 3 and 4 [DFT, Gaussian03, B3LYP/ LanL2DZ]. As shown in Figure 3, the HOMO of 3 is found delocalized over the TTF and the bis(acetylide)−Ru linker with poor contribution found on the Fc fragment and on the carbon atoms of the distal dithiole ring. The nature of the calculated HOMO of 3 is akin of that of the HOMO found for trans[Ru(CCMe 3 TTF)Cl(dppe) 2 ] 8 and trans-[Ru(C CMe3TTF)2(dppe)2]4 (2) for the Ru-acetylide-TTF moiety. The HOMO of 4, however, is found symmetric and mainly localized on the TTF core with very little contribution from the alkyne and Fc centers. We also note that the calculated energy of the HOMO of 3 (−4.20 eV) is close to the energy level of the HOMO in 2 (−4.21 eV),4 while a strong stabilization of the HOMO of 4 is obtained (−4.75 eV). This is fully consistent with the redox properties of 3 and 4 and with the assignments of the first redox potential to the TTF core in both complexes (vide supra). The more electron rich TTF core in 3, influenced by the electron-donating Ru fragment, is accordingly significantly easier to oxidize with a calculated highest occupied

moieties being still slightly electrostatically coupled. The larger effect observed on the ΔE (E3 − E2) is easily rationalized by the electrostatic repulsion on the same electrophore (TTF) due to the low ion pairing effect of the CH2Cl2-[Na][BarF]. In these conditions, and due to the large anodic shift of the oxidation processes, the last and fourth oxidation involving the ruthenium center is shifted outside of the available potential window. This result is reminiscent of what we previously observed for the ruthenium complex bearing two TTF-acetylide moieties, namely, trans-[Ru(CCMe3TTF)2(dppe)2],4 and confirms that the Ru-bisacetylide linker allows some electronic coupling between two peripheral electrophores, in the present case of different nature, namely, Fc and TTF. EPR Measurements. The mono-oxidized species were obtained by adding one equivalent of an oxidizing agent, NOPF6, to a solution of complexes 3 and 4 in CH2Cl2. At room temperature, the solution EPR spectra display a single line at g = 2.014 and g = 2.009, respectively. This is characteristic of an organic-based radical and is consistent with the assignment of a TTF-based first oxidation process in complexes 3 and 4. UV−Vis−NIR Spectroelectrochemical Investigations. UV−vis−NIR spectroelectrochemical investigations were carried out on a dichloromethane solution of 3 (c = 2.9 × 10−4 M). The neutral complex exhibits absorption bands in the visible range at λmax = 323 nm (ε = 21000 L mol−1 cm−1), close to that observed for [RuCl(CCMe3TTF)(dppe)2] and trans[Ru(CCMe3TTF)2(dppe)2]. Gradual oxidation to the mono-oxidized species 3•+ (Figure 2 top left) leads to the growth of two new absorption bands centered at λmax = 450 and 1446 nm, the latter being a broad absorption band (ε = 5000 L mol−1 cm−1). Interestingly, upon oxidation to the bis-oxidized species, the broad absorption band centered at 1446 nm was D

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it can be noticed that the alkyne bond lengths close to the TTF, CC-TTF, in 3, 3•+, and 32+ are longer than in 4, 4•+, and 42+ by about 0.03 Å. This indicates that within the different redox states of 3 a higher degree of conjugation is observed than in 4 and is consistent with the IR results, as the νCC stretching frequency in 3 was found at a lower energy than in complex 4. The calculated central CC bond length for the neutral TTF, 1.349 and 1.348 Å for 3 and 4, respectively, is lengthened in the oxidized species, 1.355 and 1.369 Å for 3•+ and 4•+, respectively, in accordance with the oxidation of the TTF core. Table 2. Selected Calculated Bond Distances (Å) for 3, 4, 3•+, 4•+, 32+, and 42+ 3 4 3+ 4+ 32+ 42+

Figure 3. Frontier molecular orbitals (HOMO and LUMO) and calculated energy levels for 3 (left) and 4 (right) shown with a cutoff of 0.04 [e/bohr3]1/2.

molecular orbital lying at a relatively high energy. The LUMO is centered on the Ru moiety in 3 and on the Fc-acetylide while in 4. In the monooxidized state (Figure 4), it can be noticed

CC-TTF

Ru-CC-Fc

CC (TTF)

1.251 1.229 1.257 1.233 1.259 1.229

1.247

1.349 1.348 1.355 1.369 1.377 1.389

1.254 1.257

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CONCLUSION In summary, we have synthesized two new complexes where a ferrocene and a tetrathiafulvalene electrophore are connected either by an organic linkage, 4, or by an organometallic one as in 3. The comparative experimental and theoretical studies carried out on these two complexes have allowed the assignment of the oxidation processes sequence and have highlighted the role of the bis-acetylide−Ru linker to mediate electronic coupling between the two inequivalent peripheral redox centers. The noninnocence of this redox ménage à trois is ascribed first to the relatively close redox potential of the peripheral electrophores taken individually, to the bis-acetylide linker, which permits some electronic delocalization, and most of all to the ruthenium(II) center, which despite its higher redox potential remains in the range that makes this coupling possible and effective. Related studies from our group13 and based on a more thermodynamically stable platinum(II) redox state are instructive in this respect, as they show that such a center is much less efficient for allowing coupling between different or similar electrophores.

Figure 4. Highest singly occupied molecular orbitals (SOMO) and calculated energy levels for 3•+ and 32+ (left) and for 4•+ and 42+ (right) shown with a cutoff of 0.04 [e/bohr3]1/2.

that the SOMO of 3•+ is found to have a pronounced delocalized character not only over the Fc-acetylide-Ru fragments but also with a significant TTF contribution. This delocalized nature is at variance with the pure ferrocenyl-based assignment made above for the second oxidation of 3 and highlights the properties of the ruthenium−organometallic bridge for partial delocalization of the unpaired electron in 3•+. The calculated nature of the SOMO in 4•+ is found to have a strong Fc contribution with nevertheless a significant TTF contribution as well. Again this is not inconsistent with the assignment of the second oxidation process of 4 to the ferrocenyl center, but the calculations suggest some electronic delocalization at the cationic state. The SOMO of 42+ however (Figure 4) with its evident TTF character is in line with the assignment based on the experimental data, while that of 32+ retains a delocalized character. The geometries of the dicationic states for 32+ and 42+ were calculated in the singlet and in the triplet states. In both cases the triplet state is clearly the most stable configuration by 0.51 eV for 32+ and by 1.08 eV for 42+. In the optimized geometries

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EXPERIMENTAL SECTION

General Procedures. All the reactions were performed under an argon atmosphere using standard Schlenk techniques. The solvents were purified and dried by standard methods. The vinylidene derivative [5][OTf]8 and Me3TTFI14 were synthesized according to literature procedures. Sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (Na[BarF]) was purchased from Aldrich. NMR spectra were recorded on a Bruker AV300III spectrometer. Chemical shifts are reported in ppm referenced to TMS for 1H NMR and 13C NMR and to H3PO4 for 31P NMR. Mass spectra were recorded with a Varian MAT 311 instrument by the Centre Régional de Mesures Physiques de l’Ouest, Rennes. Cyclic voltammetry experiments were carried out on a 10−3 M solution of 3 in CH2Cl2, containing 0.2 M [NBu4][PF6] or 10−2 M [Na][B(C6H4(CF3)2)4] as supporting electrolyte. Voltammograms were recorded at 0.1 V s−1 on a platinum disk electrode (A = 1 mm2). The potentials were measured versus the KClsaturated calomel electrode (SCE). The spectroelectrochemical setup was referenced versus SCE in 0.2 M CH2Cl2-[NBu4][PF6]. A Cary 5 spectrophotometer was employed to record the UV−vis−NIR spectra. The EPR measurements were performed on a Bruker ESP-300E XE

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band spectrometer. The EPR study was carried out on a CH2Cl2 solution of 3 with one equivalent of the oxidizing agent NOPF6. Synthesis of trans-[Ru(CCMe3TTF)(CCFc)] (3). To a solution of ethynylferrocene (0.203 mmol; 49 mg), complex 5 (0.40 mmol; 144 mg), and NaPF6 (0.351 mmol, 59 mg) in CH2Cl2 (25 mL) was added freshly distilled Et3N (1 mL), and the solution was stirred at room temperature for 40−48 h. This reaction was monitored by 31P NMR until all starting reactant was used. The solution was filtered, and the solvent was evaporated under vacuum. The residue was dissolved in CH2Cl2 (30 mL), washed with distilled water several times, dried over Na2SO4, filtered, and evaporated in vacuo. A brown-orange powder was obtained after washing with pentane (30 mL). The product was purified by precipitation in CH2Cl2 (30 mL) and pentane (100 mL). A brown-orange powder was obtained in good yield (65%). 1 H NMR (CDCl3): δ 1.99 (broad, 9H, CH3), 2.57−2.75 (m, 8H, CH2), 3.93 (m, 2H, Cp), 4.01 (m, 2H, Cp), 4.10 (s, 5H, Cp), 6.96− 7.64 (m, 40H, Ar). 31P NMR (CDCl3): δ 52.5 (s, 4P). 13C NMR (CDCl3): δ 136.3 (Cipso Ar dppe), 135.7 (Cipso Ar dppe), 133.6 (CH Ar dppe), 132.9 (CH Ar dppe), 128.1 (CH Ar dppe), 127.3 (CH Ar dppe), 126.2 (TTF), 125.9 (TTF), 67.8 (Cp), 67.2 (Cp), 64.8 (Cp), 64.7 (Cp), 30.6 (CH2 dppe, |1JPC + 3JPC| = 24.1 Hz), 21.3 (TTF), 14.2 (CH3), 13.0 (CH3). IR (KBr): 2050, 2030 cm−1 (s, νCC). HRMS (EI): m/z calculated for C75FeH66P4RuS4 1376.13853; found 1376.1388. Synthesis of Me3TTF-CC-Fc (4). To a solution of iodoMe3TTF (0.83 mmol; 309 mg) in 20 mL of THF were added CuI (32 mg; 10% M), PdCl2(PPh3)2 (100 mg; 10% M), and ethynylferrocene (200 mg; 0.83 mmol). Diisopropylamine (0.56 mL) was added to the reaction mixture, and the solution was stirred at room temperature for 48 h. The solvent was removed under vacuum, and the crude product was eluted on a silica gel column using dichloromethane/petroleum ether (1/1) as eluent. Complex 4 was obtained as an orange powder in 45% yield. 1H NMR (CDCl3): δ 1.96 (s, 6H, CH3), 2.16 (s, 3H, CH3), 4.22 (s, 5H, Cp), 4.26 (m, 2H, Cp), 4.46 (m, 2H, Cp). 13C NMR (CDCl3): δ 135.1 (TTF), 131.1 (TTF), 127.5 (TTF), 121.9 (TTF), 121.5, 109.6, 94.0 (CC), 70.5 (Cp), 69.1 (Cp), 68.1 (Cp), 62.9 (Cp), 14.8, (CH3), 12.7 (CH3). IR (KBr): 2200 cm−1 (νCC). HRMS: calculated for C21FeH18S4 453.96353; found 453.9635.

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(6) (a) Colbert, M. C. B.; Lewis, J.; Long, N. J.; Raithby, P. R.; White, A. J. P.; Williams, D. J. J. Chem. Soc., Dalton Trans. 1997, 99−104. (b) Jones, N. D.; Wolf, M. O.; Giaquinta, D. M. Organometallics 1997, 16, 1352−1354. (c) Lebreton, C.; Touchard, D.; Le Pichon, L.; Daridor, A.; Toupet, L.; Dixneuf, P. H. Inorg. Chim. Acta 1998, 272, 188−196. (7) Saad, A.; Barrière, F.; Levillain, E.; Vanthuyne, N.; Jeannin, O.; Fourmigué, M. Chem.Eur. J. 2010, 16, 8020−8028. (8) Vacher, A.; Barrière, F.; Roisnel, T.; Lorcy, D. Chem. Commun. 2009, 7200−7202. (9) Iyoda, M.; Takano, T.; Otani, N.; Ugawa, K.; Yoshida, M.; Matsuyama, H.; Kuwatani, Y. Chem. Lett. 2001, 12, 1310−1311. (10) Moore, A. J.; Skabara, P. J.; Bryce, M. R.; Batsanov, A. S.; Howard, J. A. K.; Daley, S. T. A. K. J. Chem. Soc., Chem. Commun. 1993, 417−419. (11) Miyazaki, A.; Ogyu, Y.; Justaud, F.; Ouahab, L.; Cauchy, T.; Halet, J.-F.; Lapinte, C. Organometallics 2010, 29, 4628−4638. (12) (a) Barrière, F.; Geiger, W. E. J. Am. Chem. Soc. 2006, 128, 3980−3989. (b) Geiger, W. E.; Barrière, F. Acc. Chem. Res. 2010, 43, 1030−1039. (c) Barrière, F.; LeSuer, R. J.; Geiger, W. E. Electrochemical advances using fluoroarylborate anion supporting electrolytes. In Trends in Molecular Electrochemistry; PombeiroA. J. L., Amatore, C., Eds.; Fontis Media, Marcel Dekker, 2004; Chapter 13, pp 413−444. (13) (a) Shin, K.-S.; Jung, Y. J.; Lee, S.-K.; Fourmigué, M.; Barrière, F.; Bergamini, J.-F.; Noh, D.-Y. Dalton Trans. 2008, 5869−5871. (b) Lee, S.-K.; Shin, K.-S.; Noh, D.-Y.; Jeannin, O.; Barrière, F.; Bergamini, J.-F.; Fourmigué, M. Chem. Asian J. 2010, 5, 169−176. (c) Vacher, A.; Barrière, F.; Camerel, F.; Bergamini, J.-F.; Roisnel, T.; Lorcy, D. Dalton Trans. 2013, 42, 383−394. (14) John, D. E.; Moore, A. J.; Bryce, M. R.; Batsanov, A. S.; Howard, J. A. K. Synthesis 1998, 826−828.

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S Supporting Information *

Computational details and NMR spectra. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected]. *E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the CINES (Montpellier, France) for allocation of computing time. REFERENCES

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dx.doi.org/10.1021/om400777v | Organometallics XXXX, XXX, XXX−XXX