Synthesis, Structure, and Bonding for Bis(permethylpentalene)diiron

Article pubs.acs.org/IC

Synthesis, Structure, and Bonding for Bis(permethylpentalene)diiron Samantha C. Binding, Jennifer C. Green, William K. Myers, and Dermot O’Hare* Chemistry Research Laboratory, Department of Chemistry, University of Oxford, 12 Mansfield Road, OX1 3TA Oxford, U.K. S Supporting Information *

ABSTRACT: The synthesis of the first homoleptic double metallocene complex of iron, Fe2Pn*2 (Pn* = permethylpentalene, C8Me6) is described. The structural and electronic properties of Fe2Pn*2 have been characterized by NMR and EPR spectroscopy, single crystal X-ray diffraction, magnetic measurements, cyclic voltammetry, and DFT calculations. Fe2Pn*2 adopts a Ci symmetry in the solid state with a Fe−Fe distance of 2.3175(9) Å, slightly lower than the sum of radii in metallic iron. Magnetic measurements in solution, and of the solid phase between 60 and 300 K, indicate that Fe2Pn*2 is a triplet (S = 1) paramagnet, with effective magnetic moments (μeff) of 3.4 and 3.48 μB, respectively. DFT calculations indicate the origin of this high magnetic moment is likely to be unquenched orbital angular momentum contributions from two SOMOs which have metal d character. Cyclic voltammetry studies demonstrate that Fe2Pn*2 can access four charge states (−1, 0, +1, +2).

■

■

INTRODUCTION The discovery of ferrocene revealed to science the pentahapto bonding mode, which is now ubiquitous in metallocene chemistry.1,2 Multimetallic compounds containing linked ferrocenes have since become numerous,3−5 with applications found in anion detection,6,7 boosting antitumor activity of cytotoxic molecules,8,9 and providing redox active labels in biomarkers.10 Pentalene (C8H6, Pn) is an 8π antiaromatic tetraene, which may be considered to consist of two fused cyclopentadienyl (C5H5, Cp) rings. Despite the similarities in structure between the 6π Cp−, 12π [fulvalene]2−, and 10π [pentalene]2− ligands, and the remarkable stabilities of FeCp2 and Fe2Fv2 (Figure 1),11,12 a diiron pentalenyl analogue of bisfulvalenediiron had

RESULTS AND DISCUSSION The reaction of anhydrous Fe(acac)2 with Li2Pn*(TMEDA)x in THF at room temperature yielded a dark solution, from which Fe2Pn*2 was extracted and isolated as a purple-black microcrystalline powder in 23% yield (Scheme 1). The yield is much higher than those reported by Katz et al. for the synthesis of Ni2Pn2 and Co2Pn2.13,15 Yields for other first row M2Pn*2 complexes range from 7 to 55%.14 Scheme 1. Syntheis of Fe2Pn*2

Solid State Structure. Single crystals of Fe2Pn*2 were grown from a THF solution. An inversion center is located between the two iron atoms, and the point symmetry of molecules of Fe2Pn*2 is Ci, resulting from slightly differing coordination of iron to each of the two five-carbon rings (Figure 2). The mean distance between the iron atom and the centroid of the five-membered rings of Pn* (i.e., Fe−Pn*cent) is 1.7365 Å, intermediate between the 1.78 Å M−centroid distance found in 16VE CrCp*216 and the 1.66 Å in 18VE FeCp*2.17 Iron−carbon bond lengths ranging from 2.041(4) to 2.083(5) Å are more similar to the mean Fe−C distances to the C5H5 ring in pentafluoroferrocene than to the electronegatively substituted C5F5 ring (2.05 and 2.00 Å, respectively).18

Figure 1. Ferrocene FeCp2, bisfulvalenediiron Fe2Fv2, and bispentalenediiron Fe2Pn2.

not been reported prior to this work. Initial attempts by Katz et al. to make an iron pentalenide resulted in dimerization of the ligand and formation of a monometallic complex with a single C−C bond between pentalene ligands.13 More recently, previous work in this group found the permethylpentalene (C8Me6, Pn*) is prone to undergo a [2 + 2] dimerization in reactions with FeCl2.14 We demonstrate herein that use of the appropriate iron synthon can allow the isolation and characterization of the elusive, bimetallic double metallocene sandwich compound, Fe2Pn*2. © XXXX American Chemical Society

Received: October 1, 2015

A

DOI: 10.1021/acs.inorgchem.5b02254 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

Figure 3. Plot of 1H solution chemical shifts (δ) vs T−1 for Fe2Pn*2 in toluene-d8.

Figure 2. Solid state structure of Fe2Pn*2. Wing-tip (WT) methyls C10, C13; nonwing-tip (NWT) methyls C9, C11, C12, C14; WT carbons C2, C5; NWT carbons C1, C3, C4, C6; bridgehead carbons C7, C8. Ellipsoids shown at 50% probability. Hydrogen atoms have been excluded for clarity.

temperature dependence can be described by the equation: δ(T) = δ0 + δP/T, where δ(T) is the chemical shift at temperature T, δ0 gives the chemical shift of each proton in the high temperature limit, and δp is a constant that quantifies the temperature dependence of the chemical shift of a specific resonance. The parameter, δp has values of 5760 ppm K−1 for the NWT methyl protons of Fe2Pn*2 and −31300 ppm K−1 for the WT protons. The difference in magnitude and sign of δp is thought to arise from differing spin polarization on the carbon atoms around the Pn* ring (see DFT). Magnetic Susceptibility. The bulk magnetic susceptibility of a 12 mM solution of Fe2Pn*2 in toluene-d8, measured on a 500 MHz spectrometer at 353 K using the Evans method,23 yielded an effective magnetic moment (μeff) of 3.4 μB per molecule. This is higher than the 2.83 μB expected for a triplet with spin-only contributions to the moment, and the 2.44 μB for two noninteracting doublets [i.e., (2 × 1.732)1/2]. The temperature dependence of the solid state magnetic susceptibility of Fe2Pn*2 was measured between 5 and 300 K. The molar magnetic susceptibility data for Fe2Pn*2 for a zerofield cooled and field cooled sample coincide above 5 K (Figure 4), indicating the absence of long-range interactions between spins. Above 60 K the plot of χmol−1 versus T can be fitted to

The planes of the two C8 ligands lie parallel to each other with a small fold angle of 0.8(3)°, as has been found for all i other M2Pn2 complexes except Ti2Pn(1,4‑Si Pr3)2.14,19 Within each C5 ring, however, deviation from planarity is seen in the hinge angles [i.e., the mean angle between the least-squares mean plane (LSMP) of the bridgehead and nonwing-tip (NWT) carbons and the LSMP of the NWT and wingtip (WT) carbons] and in Fe2Pn*2 has values of 6.96° and 5.87°. These are larger than the 1.54° hinge angle predicted by DFT geometry optimizations (vide infra), but consistent with a trend observed on crossing the symmetrically substituted M2Pn*2 series.14 The 8.07% shift toward η3 coordination in Fe2Pn*2 is very close to the 9% predicted for Fe2Pn2.20 In Fe2Pn*2, the metal−metal distance of 2.3175(9) Å is lower than the sum of radii in metallic iron (2.52 Å in a 12coordinate environment)21 and thus is within the range for metal−metal bonding. A diiron bond has been proposed at much longer separation of 2.686(1) Å for the syn-coordinated diiron complex [Fe2(μ-X)(CO)4(μ−η5,η5-C8H8)], [where X = C(OR)Ar or CAr “carbyne”];22 however, the rigid structure of the Pn* ligands forces syn-sandwiched metal atoms to be held in close proximity, and hence, the metal−metal distance alone is not a good indicator of bond formation. NMR Spectroscopy. A solution of Fe2Pn*2 in toluene-d8 exhibits two broad resonances in the 1H NMR indicating D2h symmetry in solution; the resonances at −89.10 and 12.04 ppm were assigned to the wing-tip (12H) methyl and nonwing-tip (24H) methyl protons, respectively, based on their relative intensities. Despite employing wide 13C NMR sweep widths and 2D experiments, only one 13C resonances could be located at −199.7 ppm. A variable temperature 1H NMR study between −70 and 50 °C revealed a temperature dependence of the chemical shifts for the methyl 1H resonances (Figure 3). The resonance for the wing-tip methyl protons underwent a very large change in shift of over 50 ppm in magnitude and opposite in sign to the nonwing-tip methyl group, which varied by only 19 ppm over the same range. The linear relationship between chemical shift (δ) and T−1 (Figure 3), signifies simple Curie−Weiss paramagnetism over this temperature range. The inverse

Figure 4. Plots of the temperature dependence of the inverse molar magnetic susceptibility (χ−1) and effective magnetic moment (μeff) for Fe2Pn*2. B

DOI: 10.1021/acs.inorgchem.5b02254 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

are in good agreement with the experimental results. The C−C distances of the rings are all very similar, reflecting the fact that bonding to the iron atoms does not disrupt the aromaticity of the ligand. Therefore, the closer coordination of the metal atoms to the WT carbons than to the bridgehead carbons is not well-described by a resonance structure with allylic or η3coordination. The first excited singlet state is calculated to lie 0.48 eV above the triplet state, consistent with the 0.51 eV gap predicted for Fe2Pn2.20 Population of thermally accessibly excited states would be expected when energy differences are on the order of magnitude of the thermal energy, kT, (210 cm−1 at 298 K). The 3870 cm−1 energy gap here corresponds to a 3.2 ppb population of the excited state at 298 K, therefore population of this level is not significant. It was found that the lowest-lying quintet configuration is 0.73 eV higher in energy than the triplet. The molecular orbital diagram for Fe2Pn*2, first published in 2008,14 is reproduced in Figure 5 along with the Kohn−Sham

the Curie−Weiss law with a Curie constant (C) of 1.51 emu K mol−1 and a Weiss constant (θ) of −12.3 K. A Curie constant of 1.51 corresponds to a μeff of 3.48 μB, which is in good agreement with μeff measured in solution (vide supra). The magnetic susceptibility data suggest that Fe2Pn*2 has a well-defined triplet (S = 1) configuration between 60 and 300 K. The small negative value for the Weiss constant indicates some short-range antiferromagnetic spin−spin interactions at low temperature. Bimetallic diiron complexes with a triplet ground state are relatively rare. The bridged diiron compounds [(CpFe)2(μCO)2(μ-ER2)] (E = Ge and Si; R = 2,4,6-C6H2Me3 and 2,4,6C6H2iPr3) have comparable Fe−Fe distances of 2.303−2.310 Å and triplet ground states,24,25 while the neutral syn-diiron complexes of cyclooctatetraene, [Fe 2 (μ-C(OR)R) (CO)4(C8H8)], contain longer Fe−Fe separations, yet are diamagnetic.22 The Curie paramagnetism exhibited by 32 total number of electron (TNE)20 species Fe2Pn*2 contrasts with the isoelectronic linked metallocene, bisfulvalene dichromium, which is diamagnetic.26 EPR Spectroscopy. X-band CW-EPR spectra for a glassy toluene solution of Fe2Pn*2 over a range of temperatures between 5 and 160 K at varying microwave powers reveal a broad feature that is centered about g ∼ 3 together with other minority features around g ∼ 2 (Figure S3). Double integration of the broad feature shows an increase in signal intensity with increasing temperature that is consistent with magnetic susceptibility data. The broad signal is from a fast relaxing spin system, as exemplified in its power saturation behavior: even at 5 K it is not saturated up to 10 mW, while features near g = 2 are extensively saturated (Figure S4). The EPR behavior for Fe2Pn*2 is reminiscent of studies on nickelocene, which fails to give an EPR signal due to the large zero-field splitting (D0 = 33.6 cm−1) of the ground triplet state.27 A D0 value for Fe2Pn*2 cannot be reliably calculated using the data presently available. DFT Calculations. Quantum chemical calculations were performed using the Amsterdam Density Functional package28,29 using density functional methods with a BP functional30,31 and triple-ζ32 Slater type basis orbitals. The geometry of Fe2Pn*2 was optimized with singlet, triplet, and quintet spin states, the lowest energy confirming a triplet ground state. No symmetry was used in the optimization, but the result was a structure of D2h symmetry, confirmed as a minimum by a frequency calculation. The Fe−Fe distance calculated using this method is 2.357 Å [i.e., longer than the 2.3175(9) Å found experimentally]. Calculated structural parameters for the D2h structure are given in Table 1, alongside the corresponding crystallographically determined values. Overall, the calculated values Table 1. Selected Bond Lengths and Distances for Fe2Pn*2

Fe1···Fe1′ Fe1···Pn*cent Fe1−C1 Fe1−C2 Fe1−C7 Fe1−C8 C1−C2 C7−C8 C1−C7

bond lengths and distances (Å)

calculated parameters

2.3175(9) 1.737(2), 1.736(2) 2.070(4) 2.057(4) 2.210(4), 2.217(4) 2.215(4), 2.222(5) 1.451(8) 1.438(7) 1.446(5)

2.36 1.76 2.09 2.07

Figure 5. MO diagram calculated for D2h symmetry for Fe2Pn*2, indicating the two SOMOs and selected Kohn−Sham orbitals.

principal levels, calculated in this work. The two highest occupied orbitals are the half-populated, metal-based 12b2g and 10b3g levels, displaying dyz and dxz character, respectively (when the xz plane reflects one Pn* ligand onto the other and contains both iron atoms, the line between which defines the z direction). These two orbitals are effectively degenerate. The two SOMOs and the highest fully occupied orbital (14b1u) all have Fe−Fe antibonding character (Figure 5). Fragment analysis afforded a decomposition of the bonding in

1.45 1.45 1.46 C

DOI: 10.1021/acs.inorgchem.5b02254 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

square root of the scan rate, and the difference in peak potentials (Epa − Epc) for features I and II were found to be ca. 240 and 520 mV, respectively (cf., 57 mV for a fully reversible single-electron transfer event at 298 K). Both of these results indicate processes II and III occur quasi-reversibly. Wave I can then be ascribed to the reduction Fe2Pn*2 → [Fe2Pn*2]−. Similar quasi-reversible features are observed in all voltammograms of permethylpentalene complexes, at potentials below −2.5 V versus Fc0/+14,39 and have been consistently attributed to a −1 ⇌ 0 couple. The isostructural complexes Mn2Pn*2 and Co2Pn*2 each exhibit only one reduction and one oxidation couple within the solvent window.14 A second quasi-reversible oxidation potential has only been observed for Ni2Pn*2. The 32 TNE complex [(C10H8)2V2(CO)2]2+, by comparison, exhibits only a single, irreversible oxidation, corresponding to formation of the monoanion.26 In homobimetallic complexes containing a symmetrically substituted bridging ligand, the comproportionation constant,

terms of the MOs of the Fe2 dimer and the Pn* ligand and enabled an estimation of the Fe−Fe bond order. The result was an order of 0.26, implying a weak but net favorable interaction between the two Fe2+ atoms, but no Fe−Fe bond, consistent with the iron atoms each receiving six electrons from each pentalene ligand. The magnetic data indicates an orbital contribution to the triplet magnetic moment with a calculated giso = 2.461 (μeff = 2g2iso). We can speculate that the near degeneracy of the top two occupied orbitals and their Fe−Fe π character, with unequal contribution from the two πg orbitals, may be responsible for the significant increase of μeff compared with the spin-only value. The spin densities calculated for the atoms are shown in Table 2. The positive spin density found for the nonwing tip Table 2. Calculated Spin Densities for Fe2Pn*2 by Mulliken Population Analysis metal Fe NWT WT bridgehead

ring C

methyl C

mean methyl H

0.143 −0.046 −0.0328

−0.0005 0.0047

0.0001 −0.0017

0/2

Kc = e ΔE1/2 F / RT , for the reaction [A]n+1 + [A]n−1 → 2 [A]n offers an indication of electron delocalization between the metal centers in the complex.40 The Kc value of [Fe2Pn*2]+ is greater than 106 (Table 3), so according to the Robin-Day classification of mixed-valence compounds,41 [Fe2Pn*2]+ is stabilized by charge delocalization and can be described as a fractionally valent species.41 Kc is similar in magnitude to bisfulvalene dichromium26 but much smaller than the 1.2 × 1017 reported for Ni2Pn*2.14 Nuclear reorganization is likely to be similar for these isostructural complexes.42 In Fe2Pn*2, one SOMO has π and one δ symmetry with respect to ligand overlap, while in Ni2Pn*2, the HOMO has π bonding character and a greater ligand component so can facilitate stronger delocalization in the mixed-valence species.43 At scan rates of 1 V s−1, event IV was consistently observed with a midpeak potential of −0.095 V. Peak-to-peak separations ranging from 150 mV (at 0.1 V s−1) to 270 mV (at 1 V s−1) indicate quasi-reversibility. [FeCp2]+ and [FeCp*2]+ have been reported to undergo one-electron oxidations at 0.94 and 0.52 V versus Fc0/+, respectively, in liquid sulfur dioxide at low temperatures.44 The first and second oxidation waves of Fe2Pn*2 occur at significantly lower potential than Fc0/+; feature IV is therefore tentatively assigned to the unusual formation of a stable trication, [Fe2Pn*2]3+, which forms irreversibly at slow scan rates. Feature V in the scan at 0.01 V s−1 (which is only observed when feature IV is irreversible, see SI) would thus show electrochemical oxidation of the chemical breakdown product of oxidation IV. However, this assignment is tentative as oxidation potentials for monometallic metallocenes should correlate reasonably well with the ionization potentials,45 but for Fe2Pn*2, this is not the case. This could be due to the close proximity of the second metal atom.

1.1

ring carbons is a reflection of their contribution to 10b3g and 12b2g. However, spin polarization around the ring results in greater absolute spin density on the wing-tip carbons of opposite sign. The net spin density transmitted to the attached methyl hydrogens is of the same direction as the ring carbons. Thus, if a contact interaction dominates the observed isotropic NMR shifts,33−35 the observation that the wing-tip protons experience an upfield shift that is greater than the downfield shift of the nonwing-tip hydrogens is in agreement with the calculation. Electrochemistry. Cyclic voltammetry experiments were conducted on solutions of Fe 2 Pn* 2 in THF with a tetrabutylammonium hexafluorophosphate electrolyte. Full scans of the accessible solvent window at 0.01 and 0.1 V s−1 reveal four quasi-reversible redox events (I, II, III, and IV, Figure S2 and Table 3). Table 3. Electrochemical Data for Processes I to IV from Cyclic Voltammograms of Fe2Pn*2 vs Fc0/+a

a

I

II

III

IV

[M2]−/0

[M2]0/+

[M2]+/2+

[M2]2+/3+

ΔE1/20/2

−2.84

−1.15

−0.51

0.09

−0.60

a

Potentials in volts, using E1/2 = (Epa + Epc)/2. aEpc.

Waves II and III are assigned to the [Fe2Pn*2]0/+ and [Fe2Pn*2]+/2+ couples, respectively, based on comparison with the isoelectronic 32 TNE complex bisfulvalene dichromium, which undergoes two one-electron oxidations in acetonitrile, at −1.29 V (0 ⇌ + 1) and −0.63 V (+1 → + 2) vs Fc0/+.26,36 Complex Fe2Pn*2 requires slightly more anodic potentials to effect these transfers, which may result from the higher effective nuclear charge of Fe compared to Cr.37 Wave II is centered at a midpeak potential more negative than the corresponding FeCp*20/1+ couple (E1/2 of −0.44 V),38 indicating it is easier to oxidize the bimetallic complex Fe2Pn*2. The anodic and cathodic peak currents in voltammograms collected over the central region do not vary linearly with the

■

CONCLUSIONS

We have successfully isolated and characterized a syncoordinated diiron sandwich compound of a pentalene ligand. Fe2Pn*2 adopts a centrosymmetric parallel ring geometry in the solid state with a Fe−Fe distance of 2.3175(9) Å. Magnetic measurements in both solution and solid phase indicates that Fe2Pn*2 is paramagnetic with an unusual orbitally contributed triplet ground state. Fe2Pn*2 is highly redox active in solution; the cyclic voltammetry experiments reveal at least four accessible charge states. D

DOI: 10.1021/acs.inorgchem.5b02254 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

■

CH3]+, 398 [M+−Fe−2CH3]+, 185 [Pn*−H]+. 1H NMR (500 MHz, C7D8, 298 K): δ 12.04 (24H, br s, H4), −89.10 (12H, br s, H5).

EXPERIMENTAL SECTION

■

General Considerations. Air and moisture sensitive reactions were performed on a dual-manifold vacuum/N2 line using standard Schlenk techniques or in a N2 filled MBraun Unilab glovebox. Glassware was heated in an oven at 170 °C for at least 1 h prior to use. Reagents were purchased from Sigma-Aldrich or Alfa Aesar and were used without further purification unless otherwise stated. Iron(II) acetylacetonate was dried at 10−2 mbar overnight, stored in the glovebox, and freshly sublimed prior to use. Li2Pn*TMEDAx was prepared according to literature methods.46 Crystallography. A single crystal was mounted on a MiTeGen Micromounts using perfluoropolyether oil and cooled rapidly to 150 K in a stream of nitrogen gas using an Oxford Cryosystems Cryostream unit.47 Data were collected on an Agilent SuperNova A diffractometer (Cu Kα radiation, λ = 1.54180 Å). Raw frame data were reduced using CrysAlisPro.48,49 The structure was solved using a charge-flipping algorithm with Superflip50 and refined using full-matrix least-squares refinement on all F2 data using the CRYSTALS program suite.51−53 In general, distances and angles were calculated using the full variance− covariance matrix. Centroids, planes, and dihedral angles were calculated using PLATON,54 and Ortep-3 was used to render molecular structures.55 Computational Methods. Density functional calculations were performed with the ADF program package.28,29 Geometry optimization calculations were carried out at the BP30,31 level of DFT. For geometry optimizations the triple-ζ32 Slater type basis sets were used. CW-EPR Spectra. CW-EPR spectra were collected in the Centre for Advanced Electron Spin Resonance (CAESR). X-band measurements were performed with a Bruker-Biospin EMXplus spectrometer equipped with a PremiumX microwave bridge, a cylindrical TE011mode resonator (SHQE-W), an ESR-900 liquid helium cryostat, and an ITC-503s temperature controller (Oxford Instruments). Cyclic Voltammetry Measurements. CV measurements were carried out in a three-electrode configuration, with a silver pseudoreference electrode, a glassy-carbon working electrode, and a platinum auxiliary electrode, all sourced from Bioanalytical Systems, within a Saffron Omega Scientific glovebox under anhydrous nitrogen on a PARAMETEK VersaSTAT 3 potentiostat. The supporting electrolyte (0.1 M [NnBu4][PF6] in THF) was freshly prepared, thoroughly degassed, and scanned prior to use. The electrodes were immersed in 10 mL of a 1 mM solution of the analyte. All potentials were referenced to an internal ferrocene/ferrocenium (Fc0/+) couple by addition of ferrocene to each sample and recording its potential under identical conditions. Magnetic Susceptibilities. Magnetic susceptibilities were measured on powdered samples with a Quantum Design MPMS-5 SQUID magnetometer. The accurately weighed samples were placed in a gelatin capsule and loaded into a nonmagnetic plastic straw before being lowered into the cryostat. Experimental susceptibility data were collected over a temperature range of 5−300 K under an applied field of 3000 G and corrected for underlying diamagnetism using Pascal’s constants.56 The mass magnetic susceptibility, χg, of bimetallic molecules is expressed per mole of molecules. Synthesis of Fe2Pn*2. A red solution of Fe(acac)2 (321.7 mg, 1.27 mmol) in 5 mL THF was added to a slurry of Li2Pn*TMEDA0.102 (272.8 mg, 1.29 mmol) in 10 mL of THF at room temperature with vigorous stirring. The mixture instantly darkened and was stirred at room temperature for 18 h. THF was removed in vacuo and the black residue dried at 10−2 mbar for 2 h. The product was extracted with benzene (200 mL) via filter cannula, the solution turning from brown to purple as it became more dilute. The extraction was reduced past minimum volume to 10 mL, transferred to a mini-Schlenk flask, and stored at 9 °C for 2 days. After decanting the solution and drying at 30 °C for 1 h, a 57 mg crop of microcrystalline Fe2Pn*2 was isolated as a purple-black powder. Recrystallization from the concentrated supernatant yielded a second crop of crystals. Total yield 70.4 mg, 0.145 mmol, 23%. Elemental analysis found (calculated) for C28H36Fe2 (MW = 484.28) (%): C, 69.31 (69.44); H, 7.34 (7.49). HRMS m/z = 484.1552 (predicted 484.1517) [M]+, 428 [M−Fe]+, 413 [M−Fe−

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.5b02254. General experimental details, and additional characterizing data (EA, HRMS, NMR, IR, UV−vis, CV, EPR) (PDF) Additional characterizing data (CIF)

■

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS We thank SCG Chemicals Co. Ltd for funding, Dr. T.A.Q. Arnold for assistance with collection of the crystal structure data, and Dr. A.L. Thompson for refinement advice.

■

REFERENCES

(1) Wilkinson, G.; Rosenblum, M.; Whiting, M. C.; Woodward, R. B. J. Am. Chem. Soc. 1952, 74, 2125−2126. (2) Pfab, W.; Fischer, E. O. Z. Anorg. Allg. Chem. 1953, 274, 316− 322. (3) Manners, I. Adv. Organomet. Chem. 1995, 37, 131−168. (4) Barlow, S.; O'Hare, D. Chem. Rev. 1997, 97, 637−670. (5) Chandrasekhar, V. In Inorganic and Organometallic Polymers; Springer-Verlag: Berlin, 2005; pp 303−324. (6) Romero, T.; Orenes, R. A.; Tárraga, A.; Molina, P. Organometallics 2013, 32, 5740−5753. (7) Kelly, M. J.; Tirfoin, R.; Gilbert, J.; Aldridge, S. J. Organomet. Chem. 2014, 769, 11−16. (8) Braga, S. S.; Silva, A. M. S. Organometallics 2013, 32, 5626−5639. (9) Goitia, H.; Nieto, Y.; Villacampa, M. D.; Kasper, C.; Laguna, A.; Gimeno, M. C. Organometallics 2013, 32, 6069−6078. (10) Wang, B.; Takahashi, S.; Du, X.; Anzai, J. Biosensors 2014, 4, 243−256. (11) Hedberg, F. L.; Rosenberg, H. J. Am. Chem. Soc. 1969, 91, 1258−1259. (12) Rausch, M. D.; Kovar, R. F.; Kraihanzel, C. S. J. Am. Chem. Soc. 1969, 91, 1259−1261. (13) Katz, T. J.; Acton, N.; McGinnis, J. J. Am. Chem. Soc. 1972, 94, 6205−6206. (14) Ashley, A. E.; Cooper, R. T.; Wildgoose, G. G.; Green, J. C.; O’Hare, D. J. Am. Chem. Soc. 2008, 130, 15662−15677. (15) Katz, T. J.; Acton, N. J. Am. Chem. Soc. 1972, 94, 3281−3283. (16) Blümel, J.; Herker, M.; Hiller, W.; Köhler, F. H. Organometallics 1996, 15, 3474−3476. (17) Freyberg, D. P.; Robbins, J. L.; Raymond, K. N.; Smart, J. C. J. Am. Chem. Soc. 1979, 101, 892−897. (18) Suenkel, K. J. Am. Chem. Soc. 2015, 137, 126−129. (19) Kilpatrick, A. F. R.; Green, J. C.; Cloke, F. G. N.; Tsoureas, N. Chem. Commun. 2013, 49, 9434−9436. (20) Bendjaballah, S.; Kahlal, S.; Costuas, K.; Bévillon, E.; Saillard, J.Y. Chem. - Eur. J. 2006, 12, 2048−2065. (21) Wells, A. F. Structural Inorganic Chemistry, 5th ed.; Clarendon Press: Oxford, 1984. (22) Chen, J.; Li, D.; Yu, Y.; Jin, Z.; Zhou, Q.; Wei, G. Organometallics 1993, 12, 3885−3889. (23) Schubert, E. M. J. Chem. Educ. 1992, 69, 62. E

DOI: 10.1021/acs.inorgchem.5b02254 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry (24) Tobita, H.; Izumi, H.; Ohnuki, S.; Ellerby, M. C.; Kikuchi, M.; Inomata, S.; Ogino, H. J. Am. Chem. Soc. 1995, 117, 7013−7014. (25) Mohamed, B. A. S.; Kikuchi, M.; Hashimoto, H.; Ueno, K.; Tobita, H.; Ogino, H. Chem. Lett. 2004, 33, 112−113. (26) Smart, J. C.; Pinsky, B. L. J. Am. Chem. Soc. 1980, 102, 1009− 1015. (27) Baltzer, P.; Furrer, A.; Hulliger, J.; Stebler, A. Inorg. Chem. 1988, 27, 1543−1548. (28) ADF, 2010. (29) Te Velde, G.; Bickelhaupt, F. M.; van Gisbergen, S. J. A.; Fonseca Guerra, C.; Baerends, E. J.; Snijders, J. G.; Ziegler, T. J. Comput. Chem. 2001, 22, 931−967. (30) Becke, A. D. Phys. Rev. A: At., Mol., Opt. Phys. 1988, 38, 3098− 3100. (31) Perdew, J. P.; Yue, W. Phys. Rev. B: Condens. Matter Mater. Phys. 1986, 33, 8800−8802. (32) Kendall, R. A.; Dunning, T. H.; Harrison, R. J. J. Chem. Phys. 1992, 96, 6796. (33) Rettig, M. F.; Drago, R. S. Chem. Commun. 1966, 891. (34) Rettig, M. F.; Drago, R. S. J. Am. Chem. Soc. 1969, 91, 1361− 1370. (35) Schachtschneider, J. H.; Prins, R.; Ros, P. Inorg. Chim. Acta 1967, 1, 462−466. (36) Connelly, N. G.; Geiger, W. E. Chem. Rev. 1996, 96, 877−910. (37) Zanello, P. Inorganic Electrochemistry: Theory, Practice and Applications; Royal Society of Chemistry: London, 2003. (38) Aranzaes, J. R.; Daniel, M.-C.; Astruc, D. Can. J. Chem. 2006, 84, 288−299. (39) Kilpatrick, A. F. R. Bimetallic Complexes of d- and f-Block Metals with Pentalene Ligands, Ph.D. Thesis, University of Sussex, 2014. (40) Aguirre-Etcheverry, P.; O’Hare, D. Chem. Rev. 2010, 110, 4839− 4864. (41) Robin, M. B.; Day, P. Adv. Inorg. Chem. Radiochem. 1968, 10, 247−422. (42) Nielson, R. M.; Golovin, M. N.; McManis, G. E.; Weaver, M. J. J. Am. Chem. Soc. 1988, 110, 1745−1749. (43) McManis, G. E.; Nielson, R. M.; Weaver, M. J. Inorg. Chem. 1988, 27, 1827−1829. (44) Sharp, P. R.; Bard, A. J. Inorg. Chem. 1983, 22, 2689−2693. (45) Bard, A. J.; Garcia, E.; Kukharenko, S.; Strelets, V. V. Inorg. Chem. 1993, 32, 3528−3531. (46) Ashley, A. E.; Cowley, A. R.; O'Hare, D. Chem. Commun. 2007, 1512−1514. (47) Cosier, J.; Glazer, A. M. J. Appl. Crystallogr. 1986, 19, 105. (48) Otwinowski, Z.; Minor, W. In Methods in Enzymology; Carter, C. W., Sweet, R. M., Eds.; Academic Press: Waltham, MA, 1997; p 276. (49) CrysAlisPro; Oxford Diffraction Ltd.: Abingdon, Oxfordshire, U.K., 2011. (50) Palatinus, L.; Chapuis, G. J. Appl. Crystallogr. 2007, 40, 786− 790. (51) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin, D. J. J. Appl. Crystallogr. 2003, 36, 1487. (52) Cooper, R. I.; Thompson, A. L.; Watkin, D. J. J. Appl. Crystallogr. 2010, 43, 1100. (53) Carruthers, J. R.; Watkin, D. J. Acta Crystallogr., Sect. A: Cryst. Phys., Diffr., Theor. Gen. Crystallogr. 1979, 35, 698−699. (54) Spek, A. L. J. Appl. Crystallogr. 2003, 36, 7. (55) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565. (56) Bain, G. A.; Berry, J. F. J. Chem. Educ. 2008, 85, 532.

F

DOI: 10.1021/acs.inorgchem.5b02254 Inorg. Chem. XXXX, XXX, XXX−XXX