Filling a Gap: Electrochemical Property Comparison of the Completed

Article pubs.acs.org/IC

Filling a Gap: Electrochemical Property Comparison of the Completed Compound Series [Mo2(DArF)n(O2C‑Fc)4−n] (DArF = N,N′‑Diarylformamidinate; O2C‑Fc = Ferrocenecarboxylate) Xu-Min Cai,† Teresa K. Meister,† Alexander Pöthig,‡ and Fritz E. Kühn*,†,‡ †

Molecular Catalysis, Department of Chemistry and Catalysis Research Center (CRC), Technische Universität München (TUM), Lichtenbergstraße 4, 85747 Garching bei München, Germany ‡ CRC, Ernst-Otto-Fischer-Straße 1, 85747 Garching bei München, Germany S Supporting Information *

ABSTRACT: The reaction of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis1) with two electronically different N,N′-diarylformamidinate (DArF) ligands (DArF = N,N′-bis(p-trifluoromethylphenyl)formamidinate (DTfmpF), N,N′-bis(p-anisyl)formamidinate (DAniF)) results in the isolation of the tris- and monosubstituted complexes [Mo2(DTfmpF)3(O2C-Fc)] (2a) and [Mo2(DAniF)(O2C-Fc)3] (2b). These complexes complete the series of [Mo2(DArF)n(O2C-Fc)4−n] (n = 4−0) type compounds, thus allowing for a comprehensive study. On the basis of the oxidation potential E1/2([Mo2]4+/[Mo2]5+) of all Mo2 complexes, ligand basicity is found to decrease in the order DAniF− > DTfmpF− > Fc−CO2− ≫ CH3CN. In addition, no direct electronic interaction between the trans-positioned Fc units in complex 2b is detected, which is attributed to the full overlap of all Fc oxidation processes. Furthermore, the low-energy absorption bands of compounds 2a,b are located at different positions in their respective UV−vis spectra.

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INTRODUCTION Multiply bonded metal−metal (MM) complexes coordinated by mixed ligands have attracted broad interest in the past, as they offer access to supramolecular structures and exhibit informative electrochemical properties.1−14 Current research efforts are directed towards the corresponding building blocks, i.e. isolated molecules. Previous reports can be divided into two main categories: (1) synthetic work aiming for the development of molecular wires via axial linkage based on single molecules15−22 and (2) studies of the electronic and photophysical properties23−30 of the single molecules in order to explore possible applications in catalysis31,32 and biochemistry.33 So far, several examples for dinuclear complexes coordinated by two mixed ligands, [Ru2(DArF)n(O2CCH3)4−nCl] (n = 4− 0),34−37 [Mo2(DArF)n(NCCH3)8−2n][BF4]4−n (n = 4−0),38−41 and [Mo2(DAniF)n(O2CCH3)4−n] (n = 4−0),40−43 have been reported.12,14,42,44−47 These might be applicable as building blocks for supramolecular structures. In theory, six configurations of Mo2 complexes coordinated by two different bridging ligands are feasible (Figure 1). There are numerous examples of the Tetra,41 Bis,15,16,19,40 and Non43,48 species, while the synthesis of the Tris and Mono species is generally found to be synthetically challenging. A limited number of trissubstituted Mo2 complexes [Mo2(DArF)3(O2C-R)]42,49−53 have been synthesized, while only one monosubstituted © XXXX American Chemical Society

Figure 1. Full series of Mo2 complexes with mixed ligands (carboxylate and formamidinate). The terminologies Tetra, Tris, Bis, Mono, and Non are based on the number of formamidinate ligands.

example of the composition [Mo2(o-DMophF)(O2C-Me)3] (o-DMophF = N,N′-bis(2-methoxyphenyl)formamidinate)54 has been reported to date. It has been established that ligand basicity is largely proportional to the electronic donating ability of a given ligand, thus decreasing in the order DArF− ≈ Fc−CO2− > CH3CN.15 In order to shed more light on the ambiguous ligand basicity when DArF− and Fc−CO2− are compared, both the mono- and the tris-substituted complexes [Mo2(DArF)n(O2CFc)4−n] (n = 1, 3) were targeted in order to quantitatively Received: October 8, 2015

A

DOI: 10.1021/acs.inorgchem.5b02329 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. Synthesis of Compounds 2a,b

Figure 2. Perspective drawing of the molecular structure of 2a (left; thermal ellipsoids are shown at a probability level of 50%) and side view (right). Aryl groups are shown as wireframes, and hydrogen atoms (except for those on the DTfmpF− bridges) are omitted for clarity.

of a similar experiment with a ratio of DTfmpF− to cis-1 of 3), it is evident that the tris-substitution of Fc−CO2− by DTfmpF− already occurs when the DTfmpF− to cis-1 ratio is 2:1, indicating that Fc−CO2− is readily exchanged by DTfmpF−. In addition to the bis- and tris-substituted complexes, the monosubstituted species [Mo2(DTfmpF)(O2C-Fc)3] is obtained as a side product (Figures S5 and S6 in the Supporting Information). On the other hand, the major species obtained from the reaction of cis-1 and 3 equiv of DAniF− is the previously published trans-[Mo2(DAniF)2(O2C-Fc)2].15 Interestingly, the mono-substituted complex [Mo2(DAniF)(O2CFc)3] (2b) can be isolated as a side product. It has been structurally characterized via NMR spectroscopy (Figure S11 in the Supporting Information) and X-ray crystallography (Figure 3). On the basis of the results described above, it is assumed that, in general, a mixture of the composition [Mo2(DArF)n(O2C-Fc)4−n] (n = 3−1) is formed in which the prevalent product is determined by the chosen reaction conditions and the nature of the chosen basic formamidinate ligand, which in turn determines the stability of the (intermediately formed) mono, bis, etc. substitution product. Therefore, the synthesis and characterization of the full series [Mo2(DArF)n(O2C-Fc)4−n] (n = 0−4) can now be presented, completing the previously published work on the complexes [Mo2(DArF)4],41 [Mo2(DArF)2(O2C-Fc)2],15 and [Mo2(O2CFc)4].48 Crystal Structures. Single crystals suitable for X-ray diffraction experiments were obtained for 2a,b from a solution

define the ligand basicity using E1/2([Mo2]4+/[Mo2]5+) in comparison to their respective bis-substituted analogues [Mo2(DArF)2(O2C-Fc)2]. To this end, the synthesis and investigation of electrochemical properties of the species [Mo2(DTfmpF)3(O2C-Fc)] (2a/Tris) and [Mo2(DAniF)(O2C-Fc)3] (2b/Mono), which are part of the [Mo2(DArF)n(O2C-Fc)4−n] (n = 4−0)15,41,48 series, are reported in this work. This series of complexes are promising candidates for the synthesis of molecular wires due to the differing redox activities of the otherwise closely related compounds.

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RESULTS AND DISCUSSION Syntheses. As shown in Scheme 1, the reaction conditions are similar to those published recently by our group,15 with DArF− ligands prepared independently via reacting the corresponding formamidine (HDArF) with sodium methoxide in CH3CN. The obtained base is then injected into the solution, containing precursor cis-1. The reaction of dark red cis-1 with the first 2 equiv of DTfmpF− results in a brown suspension after 30 min, while a large amount of brown precipitate is produced immediately after the injection of the last fraction of the base solution. Upon comparison of the 1H NMR spectra of the crude brown precipitate (Figure S4 in the Supporting Information) obtained from an experiment using a DTfmpF− to cis-1 ratio of 2:1 and the pure product 2a (Figure S7 in the Supporting Information) (which is the major species B


Article

Inorganic Chemistry

Figure 3. Perspective drawing of the molecular structure of 2b (left; thermal ellipsoids are shown at a probability level of 50%) and side view (right). Aryl groups are shown as wireframes, and hydrogen atoms (except for that on the DAniF− bridge) are omitted for clarity.

of the respective complex in CH2Cl2 layered with n-pentane. The resulting structures revealed the tris- and monosubstitution of DArF− in 2a,b, respectively (Figures 2 and 3). The crystallographic data are summarized in Table 1, and selected bond lengths and angles are given in Table 2.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for Compounds 2a,b Mo1−Mo2 C1−C5 C2−C15 C3−C25 Fe1···Fe2 Fe1···Fe3 Fe2···Fe3 C5···C25 C5···C15 C15···C25 Fe1−C5−C25−Fe2 N1−Mo1−Mo2−N6 N2−Mo2−Mo1−N5 N3−Mo1−Mo2−O2 N4−Mo2−Mo1−O1 N1−Mo1−Mo2−O4 N2−Mo2−Mo1−O3 O1−Mo1−Mo2−O6 O2−Mo2−Mo1−O5

Table 1. Crystallographic Data for Compounds 2a,b formula Mr cryst habit cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρc (g cm−3) F(000) T (K) μ (mm−1) no. of data/restraints/ params GOF (F2) R1,a wR2b (I > 2σ(I)) R1, wR2 (all data) Rint

2a

2b

C56H36N6F18FeMo2O2 1414.64 clear, intense orange fragment triclinic P1̅ 13.0579(6) 14.6896(7) 15.3071(7) 91.966(2) 98.829(2) 111.382(2) 2688.6(2) 2 1.747 1404 123 0.838 10223/81/822

C48H42N2Fe3Mo2O8 1134.26 clear, intense redorange fragment triclinic P1̅ 11.5238(9) 13.0164(9) 15.4293(13) 106.699(2) 107.655(2) 92.419(3) 2090.9(3) 2 1.802 1140 123 1.659 7668/70/616

1.039 0.0255, 0.0635 0.0288, 0.0660 0.0397

1.100 0.0253, 0.0620 0.0281, 0.0635 0.0324

R1 = ∑(||Fo| − |Fc||)/∑|Fo|. ∑[w(Fo2)2]}1/2. a

b

2a

2b

2.0834(2) 1.464(3)

2.0871(3) 1.462(4) 1.466(4) 1.469(3) 10.6812 9.9954 7.1711 8.3553 6.1400 5.4485 20.80

176.22 173.26 178.04 178.58 −178.94 174.83 175.32 −176.88

and O−Mo1−Mo2−O of 176.89 and 176.10° for 2b, respectively. For the tris-substituted complex 2a, the aryl groups on the trans-positioned DTfmpF− ligands face in opposite directions, while those two on the DTfmpF− ligand opposite to the Fc moiety are twisted almost perpendicularly. As for the monosubstituted complex 2b, the trans-positioned Fc units have an identical orientation, with a torsion angle Fe1−C5−C25−Fe2 of 20.80° in comparison to −171.22 and 180.0° in trans-[Mo 2 (DAniF) 2 (O 2 C-Fc) 2 ] 15 and trans[Mo2(O2C-Fc)2(DPPX)2][BF4]2 (DPPX = diphosphine),16 illustrating the nonlinearity of the two trans-arranged Fc− CO2− moieties that might affect the electronic interaction between the distal Fc units (vide infra). The Mo−Mo bond lengths of 2.0834(2) and 2.0871(3) Å in 2a,b, respectively, lie in the typical range for tetra-chelating Mo2 complexes coordinated by DArF−,1,41 similar to those in the bis-substituted complex [Mo2(DArF)2(O2C-Fc)2]15 and about 0.05 Å shorter than that of 2.1315(7) Å in the bis-chelating precursor cis-1.2 The remaining bond lengths of 2a,b are very similar to those of their Non, Bis, and Tetra analogues,15,41,48 although with different ligation numbers. With regard to 2b, the

wR2 = {∑[w(Fo2 − Fc2)2]/

2a,b both crystallize in a triclinic space group, illustrating their lack of symmetry in comparison to the corresponding bissubstituted complexes.15 The packing pattern (Figures S1 and S2 in the Supporting Information) reveals that both products have a Z value of 2, with the aryl rings inclined to pack together (π-stacking). A slightly distorted eclipsed coordination geometry for the Mo2 core is observed in both side views, with average torsion angles N−Mo1−Mo2−N and N−Mo1− Mo2−O of 174.74 and 178.31° for 2a and N−Mo1−Mo2−O C


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Inorganic Chemistry

[Mo2(DTfmpF)2(O2C-Fc)2],15 while the broad peak observed in 2b at around 480 nm corresponds to the shoulder absorption at 450 nm in trans-[Mo2(DAniF)2(O2C-Fc)2].15 The red shift of around 30 nm in 2b (similar to the broad peak at 490 nm in cis-1) in comparison to that in 2a results in the different colors of these complexes (red for 2b and orange for 2a). For Mo2 complexes, the characteristic absorbance in the region of 400−500 nm can be assigned to a δ → δ* transition, resulting in the color yellow, as seen for [Mo2(O2CCH3)4]55 and [Mo2(DAniF)4].41 However, in addition to this typical δ → δ* transition, there should be significant involvement of metal to ligand charge transfer (MLCT) processes, especially for 2b, illustrated by the broad absorption beyond 500 nm. Most likely, the metal (δ) to ligand (π* of the C5H5 anions) charge transfer is responsible for the orange and red colors for 2a,b, respectively.42 The different high-energy absorptions in the UV region may be ascribed to ligand-based charge transfer (bands between 240 and 280 nm) and ligand to metal charge transfer (the remaining absorption bands and shoulders at around 300 nm).41,56 Electrochemical Investigations. Our previously published complexes cis-1 and [Mo2(DArF)2(O2C-Fc)2]15 exhibit oxidation potentials E1/2(Fc/Fc+) of roughly 0.30−0.40 V, although the oxidation sequence between [Mo2]4+/[Mo2]5+ and Fc/Fc+ has been inversed thorugh ligand exchange of CH3CN by DArF−. Similar E1/2(Fc/Fc+) values are found in diphosphine-coordinated complexes trans-[Mo 2 (O 2 CFc)2(DPPX)2][BF4]2.16 The data presented above indicate that the Mo2 moiety is influenced directly by the ligands DArF−, DPPX, and CH3CN, while the oxidation potential of Fc−CO2− remains largely unchanged regardless of the other ligands in the complex. On the basis of the observed E1/2([Mo2]4+/[Mo2]5+) values of these known complexes, a stronger electronic donating ability of DAniF− in comparison to DTfmpF− can be derived due to the facile oxidation of [Mo2]4+ in trans-[Mo2(DAniF)2(O2C-Fc)2] (−0.24 V) in comparison to cis-[Mo2(DTfmpF)2(O2C-Fc)2] (0.15 V). However, the relation of DArF− and Fc−CO2− with respect to electrondonating ability still remains elusive. In order to distinguish the electronic donating ability of DArF− and Fc−CO2−, both cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were performed in a 0.10 M CH2Cl2 solution of [n-Bu4N][PF6] electrolyte for both tris- and mono-substituted complexes 2a,b. The results of this investigation are shown in Figure 5 and Figure S18 in the Supporting Information. Relevant data obtained from all figures and previous results are collected in Table 3. The potential is referenced to Fc/Fc+.

three Fc units feature three different orientations: the head-totail direction as in cis-1, the opposite-directed configuration between the other two cis-positioned Fc units, and the same direction of the trans-positioned Fc moieties. The edge to edge distances between two trans-positioned Fc moieties of 8.36 Å (C5···C25) and 10.68 Å (Fe1···Fe2) in 2b are similar to those of 8.37 and 10.78 Å in the analogous trans[Mo2(DAniF)2(O2C-Fc)2],15 while the distances of 5.45 and 7.17 Å for C15···C25 and Fe2···Fe3 are close to 5.67 and 7.42 Å and to 5.67 and 7.27 Å found in the analogous head-to-tail arrayed complexes cis-[Mo2(DPhF)2(O2C-Fc)2] and cis[Mo2(DTfmpF)2(O2C-Fc)2], respectively.15 NMR Spectroscopy. Complexes 2a,b are diamagnetic and therefore suitable for NMR spectroscopy in CD2Cl2 (Figures S7−S12 in the Supporting Information). The 13C NMR spectrum of 2a is relatively complex due to the coupling of the phenyl carbons to the fluorine atoms in the −CF3 group of the two cis-positioned DTfmpF− groups, resulting in six quadruplet resonances in the aryl region. Respective 3JCF and 1 JCF coupling constants of 3.70 and 270 Hz can be found in comparison to cis-[Mo2(DTfmpF)2(O2C-Fc)2],15 while the 2JCF coupling constant is difficult to determine due to the occurrence of two similar quadruple signals in a relatively narrow region. Detailed 2D NMR analyses of complex 2a can be found in Figures S3 and S13−S15 in the Supporting Information. For complex 2b, two distinct sets of signals can be observed for Fc in 1H NMR, indicating the asymmetry of the three Fc units, where the Fc group opposite to DAniF− displays upfield-shifted signals (4.95, 4.39, and 4.08 ppm, respectively) in comparison to those on the trans-positioned Fc moieties (5.03, 4.43, and 4.12 ppm, respectively). This is in accordance with the stronger electronic donating ability of DAniF− in comparison to Fc−CO2−, which will be further discussed as part of the electrochemical investigations (vide infra). UV−Vis Spectroscopy. The UV−vis absorption spectra of products 2a,b in CH2Cl2 are shown in Figure 4. A comparison

Figure 4. UV−vis spectra of compounds 2a,b in CH2Cl2. No absorption bands are observed beyond 700 nm.

of UV−vis data of 2a,b to their respective analogues, i.e. 2a and cis-[Mo 2 (DTfmpF) 2 (O 2 C-Fc) 2 ] 15 and 2b and trans[Mo2(DAniF)2(O2C-Fc)2],15 is depicted in Figures S16 and S17 in the Supporting Information. Complexes 2a,b show absorption bands similar to those of their corresponding analogues15 in the high-energy absorption area (200−400 nm), while slight differences can be observed in the low-energy region (400−700 nm, Figures S16 and S17 in the Supporting Information). The low-energy absorption of 2a at 450 nm as a shoulder is similar to that of 460 nm in cis-

Figure 5. DPVs of Mo2 complexes 2a,b recorded in a 0.10 M CH2Cl2 solution of [n-Bu4N][PF6]. electrolyte All potential values are referenced to Fc/Fc+. D


Article

Inorganic Chemistry Table 3. Electrochemical Dataa for All Compounds (vs Fc/Fc+) E1/2 (V) compd cis-1 2a cis-[Mo2(DTfmpF)2 (O2C-Fc)2]15 2b trans-[Mo2(DAniF)2 (O2C-Fc)2]15

Mo24+/Mo25+ 0.82 0.02

Fc/Fc+

Fc/Fc2+

Fc/Fc3+

Fc+/Fc2+

ΔE1/2b (mV)

0.38

100

0.40

100

0.36 0.32

0.15 −0.18

0.28

−0.24

0.30

0.32

a

Cyclic and differential pulse voltammograms were recorded in a 0.10 M [n-Bu4N][PF6] solution (CH2Cl2 as solvent) on a Gamry Reference 600 voltammetric analyzer with a platinum working electrode (diameter 1 mm), a Pt/Ti wire auxiliary electrode, and a Ag/AgCl reference electrode. The concentration of all the samples was 3.0 mM, and all potential values were referenced to Fc/Fc+. bCalculated from the difference between E1/2(Fc+/ Fc2+) and E1/2(Fc/Fc+) obtained from DPV.

seen in 2b. This implies that the third Fc unit plays a role in mediating the electronic interaction between the two transarranged Fc units. Because of the stronger electronic donating effect of DAniF− over Fc−CO2−, the Fc opposite to DAniF− is assumed to be oxidized first, followed by the two transpositioned Fc units. As a consequence, the respective d orbitals of Mo2 that play a role in the trans electronic interaction might be deformed, giving rise to a weakening of trans electronic interaction. This may be ascribed as well to the nonlinearity of the two trans-arranged Fc−CO2− moieties that might affect the electronic communication between the distal Fc units (vide supra).

It can be concluded from the reported complexes [Mo2(DArF)2(O2C-Fc)2] that E1/2([Mo2]4+/[Mo2]5+) occurs at lower potentials than E1/2(Fc/Fc+) due to the peak integral ratio observed in DPVs.15 However, it is not facile to define the oxidation sequence in complex 2a directly, since two oneelectron redox processes are found in DPV (Figure 5). On the basis of the data presented above, i.e. that oxidation of Fc is observed in the range of 0.30−0.40 V independent of other equatorial ligands, it is reasonable to assign E1/2([Mo2]4+/ [Mo2]5+) and E1/2(Fc/Fc+) to 0.02 and 0.32 V in 2a, respectively. The negatively shifted oxidation potential of E1/2([Mo2]4+/[Mo2]5+) at 0.02 V in the tris-substituted complex 2a is lower than 0.15 V in the bis-substituted complex cis-[Mo2(DTfmpF)2(O2C-Fc)2]; therefore, it can be concluded that the electronic donating ability of DTfmpF− is stronger than that of Fc−CO2−. Furthermore, both redox processes in 2a are reversible (Figure S18 in the Supporting Information). As for complex 2b, E1/2([Mo2]4+/[Mo2]5+) can be unequivocally assigned at −0.18 V, as is explicitly shown via the peak integral ratio of 1/3 in DPV (Figure 5). Likewise, it can be concluded that the electronic donating ability of DAniF− is stronger than that of Fc−CO 2 − on comparison of E1/2([Mo2]4+/[Mo2]5+) values in the mono- and bis-substituted complexes 2b (−0.18 V) and trans-[Mo2(DAniF)2(O2C-Fc)2] (−0.24 V), which is in accordance with the results of NMR spectroscopy (vide supra). In addition, an E1/2([Mo2]4+/ [Mo2]5+) value of −0.18 V in 2b indicates the ready oxidation of the Mo2 center, in accordance with the rapid decomposition of 2b in air. For these mono-, bis-, and tris-substituted complexes, the oxidation potential of Fc/Fc+ remains in the range of 0.30−0.40 V regardless of the substitution pattern. In summary, the ΔE 1/2 ([Mo 2 ]4+/[Mo 2 ]5+) values of comparable partners, i.e. 2a and cis-[Mo2(DTfmpF)2(O2CFc)2], 2b and trans-[Mo2(DAniF)2(O2C-Fc)2], and cis[Mo2(DTfmpF)2(O2C-Fc)2] and trans-[Mo2(DAniF)2(O2CFc)2], amount to −0.13, 0.06, and 0.39 V, respectively. The largest difference of E1/2([Mo2]4+/[Mo2]5+) = 0.64 V can be found between cis-1 (0.82 V) and [Mo2(NCCH3)10][BF4]4 (1.46 V).16 This illustrates that the electronic donating ability is proportional to ligand basicity in this complex series and decreases in the order DAniF− > DTfmpF− > Fc−CO2− ≫ CH3CN. In addition, it is worthwhile to discuss the electronic interactions in compound 2b, since three redox-active Fc units are coordinated. Unlike trans-[Mo2(DAniF)2(O2C-Fc)2], where an electronic coupling with a clear ΔE1/2 value of ca. 100 mV can be observed in DPV, a broad peak at around 0.32 V is

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CONCLUSION The two novel Mo2 paddlewheel complexes [Mo2(DTfmpF)3(O2C-Fc)] (2a) and [Mo2(DAniF)(O2CFc)3] (2b) bearing ferrocenecarboxylate and substituted formamidinate ligands have been isolated from the reaction of the cis precursor (cis-1) and the corresponding DArF− ligands. A mixture of different species is observed in the crude product for both reactions, while the configuration of the preferentially crystallized product could be identified via singlecrystal X-ray crystallography and NMR spectroscopy. On the basis of the presented synthetic results, a comprehensive study of a complete series of multiple redox-active Mo2 complexes [Mo2(DArF)n(O2C-Fc)4−n] (n = 4−0) is presented. Using the obtained E1/2([Mo2]4+/[Mo2]5+) values, a ligand basicity order (which correlates to the ligand electronic donating ability) can be established according to DAniF− > DTfmpF− > Fc−CO2− ≫ CH3CN. Further synthetic design of structural motifs can be carried out utillizing this ligand basicity order, especially for multiple redox-active complexes that are intended for the synthesis of molecular wires.

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EXPERIMENTAL SECTION

General Procedure and Materials. All preparations and reactions were carried out under argon using standard Schlenk techniques. All solvents were dried using standard procedures.57 N,N′Bis(p-trifluoromethylphenyl)formamidine (HDTfmpF) and N,N′-bis(p-anisyl)formamidine (HDAniF) were synthesized by following published procedures.58 The precursor cis-1 was prepared according to a literature procedure2 and is in this paper referred to the formula [Mo2(O2C-Fc)2(NCCH3)4][BF4]2 after overnight drying. NMR measurements were performed on Bruker AVANCE-DPX 400 MHz and Avance-DRX 400 MHz spectrometers (1H, 400.13 MHz; 13C, 100.62 MHz; 19F, 376.5 MHz). Chemical shifts are reported in ppm and are referenced to the solvent as internal standard. Elemental analyses were carried out at the microanalytical laboratory of the E


Article

Inorganic Chemistry

were performed on a single crystal coated with perfluorinated ether. The crystal was fixed on the top of a glass fiber and transferred to the diffractometer. The crystal was frozen under a stream of cold nitrogen. A matrix scan was used to determine the initial lattice parameters. Reflections were merged and corrected for Lorentz and polarization effects, scan speed, and background using SAINT.60 Absorption corrections, including odd- and even-ordered spherical harmonics, were performed using SADABS.60 Space-group assignments were based on systematic absences, E statistics, and successful refinement of the structures. Structures were solved by direct methods as implemented in the APEX2 software package59 based on SHELXS9761 and were refined against all data using SHELXLE62 in conjunction with SHELXL-2014.63 Hydrogen atoms were assigned to ideal positions and refined using a riding model with an isotropic thermal parameter 1.2 times that of the attached carbon atom (1.5 times for methyl hydrogen atoms). If not mentioned otherwise, nonhydrogen atoms were refined with anisotropic displacement parameters. Full-matrix least-squares refinements were carried out by minimizing ∑w(Fo2 − Fc2)2 with the SHELXL-9764 weighting scheme. Neutral atom scattering factors for all atoms and anomalous dispersion corrections for the non-hydrogen atoms were taken from ref 65. Images of the crystal structures were generated by MERCURY.66

Technische Universität München. UV−vis spectra were recorded with a Jasco V-550 spectrophotometer. Solution spectra were measured in a quartz cell with a 1 cm path length (background: solvent vs solvent), with a sample concentration of 30 μM. Cyclic and differential pulse voltammograms were recorded in a 0.10 M [n-Bu4N][PF6] solution (CH2Cl2 as solvent) on a Gamry Reference 600 voltammetric analyzer with a platinum working electrode (diameter 1 mm), a Pt/Ti wire auxiliary electrode, and a Ag/AgCl reference electrode. The concentrations of all the samples were 3.0 mM, and all potential values were referenced to Fc/Fc+. Synthesis of [Mo2(DTfmpF)3(O2C-Fc)] (2a/Tris). A solution of 3 equiv of N,N′-bis(p-trifluoromethylphenyl)formamidine (199 mg, 600 μmol) and NaOCH3 (32.4 mg, 600 μmol) in CH3CN (20 mL) was stirred for 15 min and then slowly added to a CH3CN (14 mL) solution of 1 equiv of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis-1; 198 mg, 200 μmol). This mixture was a brown suspension when 2 equiv of the base solution was injected, and a large amount of brown precipitate appeared immediately as the last equivalent was added. The reaction mixture was stirred overnight at room temperature to yield a brown solid and a light brown solution. The solid was separated and dried under reduced pressure. The obtained brown solid was redissolved in 6 mL of CH2Cl2 and layered with n-pentane (10 mL). Large, bright orange, air-stable crystals formed over two nights. The orange crystals were collected, washed with n-pentane, and dried under vacuum. Compound 2a was obtained in a crystalline yield of 60%. 1H NMR (CD2Cl2): δ 8.73 (s, 2H, NCHN_cis to Fc-CO2), 8.62 (s, 1H, NCHN_trans to Fc-CO2), 7.44 (d, 8H, Hph), 7.06 (d, 4H, Hph), 6.83 (d, 8H, Hph), 6.17 (d, 4H, Hph), 5.14 (t, 2H, Hcp), 4.49 (t, 2H, Hcp), 4.07 (s, 5H, Hcp). 13C NMR (CD2Cl2): δ 181.7 (COO−), 157.2 (NCHN), 156.5 (NCHN), 152.4 (Cph−N), 151.9 (Cph−N), 127.3 (q, Cph, 3JCF = 3.70 Hz), 126.8 (q, Cph, 3JCF = 3.70 Hz), 124.8 (q, Cph, 1 JCF = 270 Hz), 124.6 (q, Cph, 1JCF = 270 Hz), 122.4 (Cph), 122.2 (Cph), 74.02 (Cquat‑cp), 72.03 (Ccp), 71.73 (Ccp), 70.73 (Ccp). 19F NMR (CD2Cl2): δ −62.46 (s, CF3), −62.70 (s, CF3). Anal. Calcd for (C56H36F18FeMo2N6O2) = [Mo2(DTfmpF)3(O2C-Fc)]: C, 47.55; H, 2.57; N, 5.94; F, 24.2. Found: C, 47.66; H, 2.51; N, 5.94; F, 24.7. Synthesis of [Mo2(DAniF)(O2C-Fc)3] (2b/Mono). A solution of 3 equiv of N,N′-bis(p-anisyl)formamidine (HDAniF) (154 mg, 600 μmol) and NaOCH3 (32.4 mg, 600 μmol) in CH3CN (20 mL) was stirred for 5 min and then immediately added to a CH3CN (14 mL) solution of 1 equiv of cis-[Mo2(O2C-Fc)2(NCCH3)4][BF4]2 (cis-1; 198 mg, 200 μmol). No obvious precipitate could be observed in the first 3 h, and the reaction mixture was stirred overnight at room temperature to yield a very small amount of an orange solid and a red brownish solution. The solid was separated and dried under reduced pressure. The obtained orange solid was redissolved in 5 mL of CH2Cl2 and layered with n-pentane (8 mL). A small amount of large crystals and precipitate both appeared, verified as a mixture of 2b and both cis- and trans-[Mo2(DAniF)2(O2C-Fc)2] by 1H NMR spectroscopy. Therefore, a secondary crystallization was necessary to obtain the pure product, with the crystals of the first crystallization dried and redissolved in 4 mL of CH2Cl2 and layered with n-pentane (6 mL) and diethyl ether (1 mL). Large, bright red, air- and moisture-sensitive crystals formed over two nights. The red crystals were collected, washed with n-pentane, and dried under vacuum. Compound 2b was obtained as a minor product in a crystalline yield of 8%. 1H NMR (CD2Cl2): δ 8.74 (s, 1H, NCHN), 7.07 (d, 4H, Hph), 6.88 (d, 4H, Hph), 5.03 (t, 4H, Hcp), 4.95 (t, 2H, Hcp), 4.43 (t, 4H, Hcp), 4.39 (t, 2H, Hcp), 4.12 (s, 10H, Hcp), 4.08 (s, 5H, Hcp), 3.78 (s, 6H, OCH3). 13 C NMR (CD2Cl2): δ 181.7 (COO−), 181.2 (COO−), 157.5 (Cph‑OCH3), 157.2 (NCHN), 142.6 (Cph−N), 123.7 (Cph), 115.2 (Cph), 74.38 (Cquat‑cp), 73.88 (Cquat‑cp), 71.91 (Ccp), 71.78 (Ccp), 70.94 (Ccp‑overlapped), 70.86 (Ccp), 70.67 (Ccp). Anal. Calcd for (C48H42Fe3Mo2N2O8) = [Mo2(DAniF)(O2C-Fc)3]: C, 50.83; H, 3.73; N, 2.47. Found: C, 50.98; H, 3.80; N, 2.56. X-ray Structure Determination. Data were collected on a singlecrystal X-ray diffractometer equipped with a CCD detector (Bruker APEX II, κ-CCD), a rotating anode (Bruker AXS, FR591) with Mo Kα radiation (λ = 0.71073 Å), and a Montel mirror monochromator (2a,b) by using the APEX2 software package.59 The measurements

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02329. CCDC 1428786 (2a) and CCDC 1428787 (2b) also contain supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac. uk/data_request/cif. Spectroscopic and crystallographic details (PDF) X-ray crystallographic data (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail for F.E.K. (Chair of Inorganic Chemistry): fritz. [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Support from the China Scholarship Council (stipend to X.M.C.) and the Stiftung Stipendienfonds des Fonds der Chemischen Industrie (stipend to T.K.M.), the Institut für Siliciumchemie, and the TUM Graduate School are gratefully acknowledged. Additionally, we thank Dominik Höhne for experimental assistance.

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REFERENCES

(1) Cotton, F. A.; Murillo, C. A.; Walton, R. A. Multiple Bonds Between Metal Atoms, 3rd ed.; Springer: New York, 2005. (2) Cai, X.-M.; Höhne, D.; Köberl, M.; Cokoja, M.; Pöthig, A.; Herdtweck, E.; Haslinger, S.; Herrmann, W. A.; Kühn, F. E. Organometallics 2013, 32, 6004−6011. (3) Höhne, D.; Herdtweck, E.; Pöthig, A.; Kühn, F. E. Dalton Trans. 2014, 43, 15367−15374. (4) Cao, Z.; Xi, B.; Jodoin, D. S.; Zhang, L.; Cummings, S. P.; Gao, Y.; Tyler, S. F.; Fanwick, P. E.; Crutchley, R. J.; Ren, T. J. Am. Chem. Soc. 2014, 136, 12174−12183. (5) Wilkinson, L. A.; McNeill, L.; Patmore, N. J. J. Am. Chem. Soc. 2013, 135, 1723−1726. (6) Forrest, W. P.; Cao, Z.; Hassel, K. M.; Ren, T. Inorg. Chem. 2012, 51, 3261−3269. F


Article

Inorganic Chemistry

(41) Lin, C.; Protasiewicz, J. D.; Smith, E. T.; Ren, T. Inorg. Chem. 1996, 35, 6422−6428. (42) Cotton, F. A.; Liu, C. Y.; Murillo, C. A.; Villagrán, D.; Wang, X. J. Am. Chem. Soc. 2003, 125, 13564−13575. (43) Stephenson, T. A.; Bannister, E.; Wilkinson, G. J. Chem. Soc. 1964, 2538−2541. (44) Han, M. J.; Liu, C. Y.; Tian, P. F. Inorg. Chem. 2009, 48, 6347− 6349. (45) Cotton, F. A.; Li, Z.; Liu, C. Y.; Murillo, C. A.; Villagrán, D. Inorg. Chem. 2006, 45, 767−778. (46) Cotton, F. A.; Li, Z.; Liu, C. Y.; Murillo, C. A. Inorg. Chem. 2006, 45, 9765−9770. (47) Cotton, F. A.; Liu, C. Y.; Murillo, C. A.; Villagrán, D.; Wang, X. J. Am. Chem. Soc. 2004, 126, 14822−14831. (48) Cotton, F. A.; Falvello, L. R.; Reid, A. H.; Tocher, J. J. H. J. Organomet. Chem. 1987, 319, 87−97. (49) Han, L.-J. Acta Crystallogr., Sect. E: Struct. Rep. Online 2011, 67, m256. (50) Albert Cotton, F.; Jin, J.-Y.; Li, Z.; Liu, C. Y.; Murillo, C. A. Dalton Trans. 2007, 2328−2335. (51) Yamaguchi, Y.; Ozaki, S.; Hinago, H.; Kobayashi, K.; Ito, T. Inorg. Chim. Acta 2005, 358, 2363−2370. (52) Cotton, F. A.; Donahue, J. P.; Murillo, C. A. J. Am. Chem. Soc. 2003, 125, 5436−5450. (53) Cotton, F. A.; Ilsley, W. H.; Kaim, W. Inorg. Chem. 1981, 20, 930−934. (54) Wu, Y.-Y.; Chen, J.-D.; Liou, L.-S.; Wang, J.-C. Inorg. Chim. Acta 2002, 336, 71−79. (55) Brignole, A. B.; Cotton, F. A. Inorg. Synth. 2007, 13, 81−89. (56) Cotton, F. A.; Feng, X.; Matusz, M. Inorg. Chem. 1989, 28, 594− 601. (57) Armarego, W. L. F.; Chai, C. Purification of Laboratory Chemicals; Elsevier Science: Amsterdam, 2009; pp 25−30. (58) Binobaid, A.; Iglesias, M.; Beetstra, D. J.; Kariuki, B.; Dervisi, A.; Fallis, I. A.; Cavell, K. J. Dalton Trans. 2009, 7099−7112. (59) APEX Suite of Crystallographic Software, APEX 2, Version 2008.4; Bruker AXS Inc., Madison, WI, USA, 2008. (60) SAINT, version 7.56a, SADABS, version 2008.1; Bruker AXS Inc., Madison, WI, USA, 2008. (61) Sheldrick, G. M. SHELXS-97; University of Gö ttingen, Göttingen, Germany, 1998. (62) Huebschle, C. B.; Sheldrick, G. M.; Dittrich, B. J. Appl. Crystallogr. 2011, 44, 1281−1284. (63) Sheldrick, G. M. SHELXL-2014; University of Göttingen, Göttingen, Germany, 1998. (64) Sheldrick, G. M. SHELXL-97; University of Gö ttingen, Göttingen, Germany, 1998. (65) Wilson, A. J. C. International Tables for Crystallography; Kluwer Academic: Dordrecht, The Netherlands, 1992. (66) Macrae, C. F.; Bruno, I. J.; Chisholm, J. A.; Edgington, P. R.; McCabe, P.; Pidcock, E.; Rodriguez-Monge, L.; Taylor, R.; Streek, J. v. d.; Wood, P. A. J. Appl. Crystallogr. 2008, 41, 466−470.

(7) Cai, X.-M.; Zhang, X.-Y.; Savchenko, J.; Cao, Z.; Ren, T.; Zuo, J.L. Organometallics 2012, 31, 8591−8597. (8) Köberl, M.; Cokoja, M.; Bechlars, B.; Herdtweck, E.; Kühn, F. E. Dalton Trans. 2011, 40, 11490−11496. (9) Xi, B.; Xu, G.-L.; Fanwick, P. E.; Ren, T. Organometallics 2009, 28, 2338−2341. (10) Cotton, F. A.; Murillo, C. A.; Villagrán, D.; Yu, R. J. Am. Chem. Soc. 2006, 128, 3281−3290. (11) Xu, G.-L.; Crutchley, R. J.; DeRosa, M. C.; Pan, Q.-J.; Ren, T. J. Am. Chem. Soc. 2005, 127, 13354−13363. (12) Cotton, F. A.; Lin, C.; Murillo, C. A. Inorg. Chem. 2001, 40, 478−484. (13) Cotton, F. A.; Lin, C.; Murillo, C. A. J. Am. Chem. Soc. 2001, 123, 2670−2671. (14) Cotton, F. A.; Donahue, J. P.; Lin, C.; Murillo, C. A. Inorg. Chem. 2001, 40, 1234−1244. (15) Cai, X.-M.; Zimmermann, T. K.; Pöthig, A.; Kühn, F. E. Inorg. Chem. 2015, 54, 6631−6640. (16) Cai, X.-M.; Riener, K.; Herdtweck, E.; Pöthig, A.; Kühn, F. E. Inorg. Chem. 2015, 54, 3272−3280. (17) Fritsch, N.; Wick, C. R.; Waidmann, T.; Dral, P. O.; Tucher, J.; Heinemann, F. W.; Shubina, T. E.; Clark, T.; Burzlaff, N. Inorg. Chem. 2014, 53, 12305−12314. (18) Fischer, N. V.; Alam, M. S.; Jum’h, I.; Stocker, M.; Fritsch, N.; Dremov, V.; Heinemann, F. W.; Burzlaff, N.; Müller, P. Chem. - Eur. J. 2011, 17, 9293−9297. (19) Brown, D. J.; Chisholm, M. H.; Gallucci, J. C. Dalton Trans. 2008, 1615−1624. (20) Mahapatro, A. K.; Ying, J.; Ren, T.; Janes, D. B. Nano Lett. 2008, 8, 2131−2136. (21) Lin, C.; Kagan, C. R. J. Am. Chem. Soc. 2003, 125, 336−337. (22) Cotton, F. A.; Lin, C.; Murillo, C. A. Chem. Commun. 2001, 11− 12. (23) Chisholm, M. H.; Durr, C. B.; Gustafson, T. L.; Kender, W. T.; Spilker, T. F.; Young, P. J. J. Am. Chem. Soc. 2015, 137, 5155−5162. (24) Chisholm, M. H.; Brown-Xu, S. E.; Spilker, T. F. Acc. Chem. Res. 2015, 48, 877−885. (25) Chisholm, M. H. Coord. Chem. Rev. 2015, 282−283, 60−65. (26) Brown-Xu, S. E.; Chisholm, M. H.; Durr, C. B.; Spilker, T. F.; Young, P. J. Chem. Sci. 2015, 6, 1780−1791. (27) Brown-Xu, S. E.; Chisholm, M. H.; Durr, C. B.; Lewis, S. A.; Spilker, T. F.; Young, P. J. Chem. Sci. 2014, 5, 2657−2666. (28) Brown-Xu, S. E.; Chisholm, M. H.; Durr, C. B.; Lewis, S. A.; Naseri, V.; Spilker, T. F. Chem. Sci. 2013, 4, 2105−2116. (29) Brown-Xu, S. E.; Chisholm, M. H.; Durr, C. B.; Gustafson, T. L.; Naseri, V.; Spilker, T. F. J. Am. Chem. Soc. 2012, 134, 20820−20826. (30) Bunting, P.; Chisholm, M. H.; Gallucci, J. C.; Lear, B. J. J. Am. Chem. Soc. 2011, 133, 5873−5881. (31) Tsurugi, H.; Hayakawa, A.; Kando, S.; Sugino, Y.; Mashima, K. Chem. Sci. 2015, 6, 3434−3439. (32) Tsurugi, H.; Yamada, K.; Majumdar, M.; Sugino, Y.; Hayakawa, A.; Mashima, K. Dalton Trans. 2011, 40, 9358−9361. (33) Li, Z.; David, A.; Albani, B. A.; Pellois, J.-P.; Turro, C.; Dunbar, K. R. J. Am. Chem. Soc. 2014, 136, 17058−17070. (34) Angaridis, P.; Cotton, F. A.; Murillo, C. A.; Villagrán, D.; Wang, X.-P. Inorg. Chem. 2004, 43, 8290−8300. (35) Stephenson, T. A.; Wilkinson, G. J. Inorg. Nucl. Chem. 1966, 28, 2285−2291. (36) Angaridis, P.; Berry, J. F.; Cotton, F. A.; Lei, P.; Lin, C.; Murillo, C. A.; Villagrán, D. Inorg. Chem. Commun. 2004, 7, 9−13. (37) Ren, T.; DeSilva, V.; Zou, G.; Lin, C.; Daniels, L. M.; Campana, C. F.; Alvarez, J. Inorg. Chem. Commun. 1999, 2, 301−304. (38) Chisholm, M. H.; Cotton, F. A.; Daniels, L. M.; Folting, K.; Huffman, J. C.; Iyer, S. S.; Lin, C.; Macintosh, A. M.; Murillo, C. A. J. Chem. Soc., Dalton Trans. 1999, 1387−1392. (39) Cotton, F. A.; Wiesinger, K. J. Inorg. Chem. 1991, 30, 871−873. (40) Cotton, F. A.; Liu, C. Y.; Murillo, C. A. Inorg. Chem. 2004, 43, 2267−2276. G


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