Triphenylamine Derivatives with Para-Disposed Pendant Electron

Article pubs.acs.org/Organometallics

Triphenylamine Derivatives with Para-Disposed Pendant ElectronRich Organoiron Alkynyl Substituents: Defining the Magnetic Interactions in a Trinuclear Iron(III) Trication Guillaume Grelaud,†,‡ Olivier Cador,† Thierry Roisnel,† Gilles Argouarch,† Marie P. Cifuentes,‡ Mark G. Humphrey,*,‡ and Frédéric Paul*,† †

UMR CNRS 6226 Sciences Chimiques de Rennes, Université de Rennes 1, Campus de Beaulieu, 35042 Rennes Cedex, France Research School of Chemistry, Australian National University, Canberra, Australian Capital Territory 0200, Australia

‡

S Supporting Information *

ABSTRACT: The syntheses of two triarylamine derivatives featuring one and three electron-rich Fe(II) “(η2-dppe)(η5C5Me5)FeCC−” pendant substituents in para position(s) on the aryl rings (1, 2) is reported, along with those of their corresponding radical tri- and monocations (13+, 2+). The former species (13+) constitutes a new organometallic triradical. The magnetic interactions between the Fe(III) units in this novel trication were investigated by NMR and SQUID. Its ground spin state was shown to be a doublet, with a “mean” antiferromagnetic coupling constant of J ≈ −14 cm−1 between the unpaired spins, from consideration of the classic Hamiltonian for a symmetric C3v triradical: H = −2J(Sa·Sb + Sb·Sc + Sc·Sa).

J

compound 1, along with that of a mononuclear complex (2) modeling a “branch” of the compound, (ii) the synthesis and characterization of the corresponding Fe(III) derivatives 1[PF6]3 and 2[PF6], along with a study of their magnetic susceptibility, and (iii) a discussion based on the available NMR data of the possible causes of the doublet spin found for 1[PF6]3, illustrating how 1H NMR can be usefully exploited to study the electronic structure of such Fe(III) organometallic radicals.

udicious spatial or topologic arrangements of spin carriers can lead to molecular architectures possessing sizable total spins and eventually behaving as molecular magnets.1 This occurs when dominant ferromagnetic coupling can be obtained between the various unpaired spins of the molecule.2 Although such approaches have been extremely fruitful with purely inorganic spin carriers,3 and also with purely organic examples,4 very few examples have been reported utilizing organometallic spin carriers thus far.5,6 In order to enhance our understanding of the structural/topological features that might afford highspin derivatives, some of us are systematically studying the magnetic properties of carbon-rich polynuclear derivatives containing several conjugated “[(η2-dppe)(η5-C5Me5)FeC C−]+” fragments.6,7 In this contribution, we investigate the magnetic properties of the triarylamine-bridged trication 1[PF6]3 (Chart 1). Because of its sp2-hybridized central nitrogen atom8,9 and the spin alternation usually observed (by NMR) between neighboring carbons of the aryl acetylide ligand with related Fe(III) radicals,10,11 a quartet magnetic ground state (GS) was anticipated for 1[PF6]3.12 Indeed, according to Hund’s rule, a symmetric polyradical with nondisjoint magnetic orbitals should result in a ground state (GS) exhibiting maximum spin.13,14 However, in contrast with these purely topologic considerations, an example of a triphenylamine-bridged organic triradical (3) exhibiting a doublet ground state (GS) has been previously reported by Iwamura and co-workers.9,15 It was therefore of considerable interest to examine the related organometallic triradical 13+. Accordingly, we report herein the following; (i) the synthesis of the trinuclear Fe(II) precursor of © 2012 American Chemical Society

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RESULTS Synthesis and Characterization of the Fe(II) Complexes. The organometallic complexes 1 and 2 were synthesized from the corresponding tris- and mono-p-ethynyl triphenylamine precursors and from the Fe(II) chloride complex (η2-dppe)(η5-C5Me5)FeCl (3). The desired compounds were obtained following a classic activation−deprotonation reaction (Scheme 1),16,17 and were fully characterized (see the Experimental Section). The solid-state structure of 2 was also confirmed by X-ray diffraction (Figure 1). This compound crystallizes in the monoclinic space group P21/a with four molecules in the asymmetric unit and two dichloromethane solvates (see the Experimental Section).16,18 The important information here is the sp2 hybridization of the central nitrogen atom, indicated by the coplanarity of the nitrogen atom N45 and the three surrounding carbon atoms Received: July 14, 2011 Published: February 10, 2012 1635

dx.doi.org/10.1021/om2006358 | Organometallics 2012, 31, 1635−1642

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Chart 1. View of the Targeted (Poly)Radical Cations 13+ and 2+ and of the Known Related Triradical 3

Scheme 1. Synthesis of the Fe(II) Complexes 1 and 2

C42, C46, and C52, a typical environment for sp2-hybridized nitrogen atoms in triarylamines.8,9 Both compounds are redox-active, with chemically reversible Fe(III)/Fe(II) metal-centered oxidation processes near −0.2 V vs SCE and triarylamine-based oxidations near 0.8 V (Table 1 and Figure 2). For 1, two stepwise metal-centered oxidations are apparent, suggesting that some electronic communication takes place through the central nitrogen atom. The second and third oxidations are, however, not resolved and appear as a single wave. For the model complex 2,18 the redox potential is consistent with a sizable electron-releasing power for the diphenylamine substituent.19 The oxidation of the amine center in 1 or 2 is shifted toward more negative potentials relative to that of tris(4-bromophenyl)amine (1.16 V vs SCE),20 suggesting a net electron-releasing effect for the “[(η2dppe)(η5-C5Me5)FeCC−]+” fragment in para position(s).21 Synthesis and Characterization of the Fe(III) Complexes. The corresponding Fe(III) radical cations were

isolated after oxidation of 1 and 2 with ferrocenium hexafluorophosphate and were extensively characterized by spectroscopic methods to ensure the identity and purity of the isolated samples;16,22,23 in particular, the NMR spectra of 1[PF6]3 and 2[PF6] show characteristic proton signals for each compound (Figure 3), the assignment of which could be confirmed by polarization transfer studies (see the Supporting Information). The phenylamine protons of both compounds are clearly detected, indicating a symmetric structure for 1[PF6]3 in solution from room temperature to −120 °C. Particularly noteworthy is that the signals of protons Ha and Hb in the trication (Chart 2) are overall more narrow and less shifted than are the signals of the corresponding protons in 2[PF6], their paramagnetic shift in 13+ being roughly two-thirds of that in 2+ when the corresponding Fe(II) complexes are used as diamagnetic references. The temperature dependences of the magnetization of 1[PF6]3 and 2[PF6] have been recorded in the 2−300 K 1636


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Figure 3. 1H NMR spectra for 1[PF6]3 (a) and 2[PF6] (b) in dichloromethane-d2 at 300 K. The numbering of selected protons is according to Chart 2. Signals corresponding to diamagnetic impurities (solvent) are designated by asterisks.

Figure 1. ORTEP representation of complex 2 with displacement ellipsoids at the 50% probability level.

Table 1. Electrochemical Data for Complexes 1 and 2a compd

E° (ΔEpb)

attribution

1

−0.23(0.06)c −0.15(0.13)c 0.76(0.09) −0.20(0.09) 0.76(0.07)

Fe1(III)/Fe1(II) Fe2−3(III)/Fe2−3(II) NAr3+/NAr3 Fe(III)/Fe(II) NAr3+/NAr3

2

ΔE° 0.08c

the liquid nitrogen ESR spectrum (g = 2.13). The small decrease of χMT below 20 K can be attributed to small antiferromagnetic intermolecular and/or saturation effects due to the external dc magnetic field applied (5 kOe).9 The room-temperature value of χMT of a powdered sample of 1[PF6]3 is, as expected assuming a weakly coupled system, 3 times higher than that for 2[PF6] (3 × 0.45 = 1.35 cm3 K mol−1). However, χMT decreases continuously on lowering the temperature, with χMT = 0.48 cm3 K mol−1 at 2 K (Figure 3). The decrease of χMT clearly attests to the dominance of intramolecular antiferromagnetic interactions between the three spins. Indeed, even in the absence of solid-state structural data for 1[PF6]3, it is difficult to imagine how intermolecular interactions through the bulky dppe ligand or through η5C5Me5 could be responsible for the loss of effective magnetic moment. Furthermore, should this be the case, the ground state (GS) should be nonmagnetic, whereas the field dependence of the magnetization at 2 K follows a Brillouin function for a spin 1 /2 with g = 2.21 (see the Supporting Information, Figure S2). From a consideration of the Heisenberg−Dirac−Van Vleck Hamiltonian (eq 1), which represents the superexchange interactions between three local spins 1/2 of an ideal triradical of C3v symmetry, the analytical expression of the temperature dependence of χMT can be deduced (eq 2) with an equal average Zeeman factor for the three magnetic sites.2 The best agreement is obtained with J = −14.1(6) cm−1 and g = 2.27(2) (Figure 3). While the agreement with such a simple model is relatively poor,24 possibly because of the breakdown of the ideal C3v symmetry of 1[PF6]3 in the solid state, the overall match is nevertheless consistent with the interaction between the local spins being antiferromagnetic.

ic/ia 1 1 1 1 1

a

All E° values are in V vs SCE. Conditions: CH2Cl2 solvent, 0.1 M [NnBu4][PF6] supporting electrolyte, 20 °C, Pt electrode, sweep rate 0.1 V s−1. The ferrocene/ferrocenium (FcH/FcH+) complex was used as an internal reference for potential measurements. bDifference between cathodic and anodic peak potentials. cApparent values deduced from shoulders.

Figure 2. Cyclic voltammograms showing the metal- and nitrogencentered oxidations of 1 (a) and 2 (b) in dichloromethane at 20 °C (0.1 M [NnBu4][PF6], 0.1 V/s).

H = −2J(Sa ·S b + S b ·Sc + Sc ·Sa)

( 3J ) ( kT )

1 + 5 exp Ng 2β2 kT χMT = 3J 4k 1 + exp

temperature range. At room temperature, the χMT product of a powdered sample of 2[PF6] is equal to 0.45 cm3 K mol−1 and remains almost constant on lowering the temperature (Figure 4). Thus, the mononuclear complex 2[PF6] behaves as a lowspin (S = 1/2) complex. The Zeeman factor extracted from the room-temperature value, assuming an isolated S = 1/2 (g = 2.19) spin, is consistent with the average g value deduced from

(1)

(2)

The inverse temperature dependence of the paramagnetic shifts in solution in the 300−100 K temperature range (see the Supporting Information) is also in agreement with this model. Thus, the paramagnetic shifts of the mononuclear complex 1637


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Chart 2. 1H Nuclei Numbering Corresponding to the Proposed Assignment for 1[PF6]3 and 2[PF6]

Å), and their shifts will be essentially influenced by the contact contribution. In particular, crucial information can be gained on the sign of the spin density carried by the nearby carbon atom, which determines the direction of the paramagnetic shifts of these protons.11 Two main conclusions stem from these NMR measurements. First, while the aryl group linked to the Fe(III) center in 2[PF6] experiences a much larger spin density than do the other two, the presence of spin density of alternating sign on neighboring carbon atoms of the two other rings is clearly apparent. Such a polarization is indicative of the presence of unpaired spin density in the π manifold. Given that the spin density spreads across the complete arylamine fragment in 2[PF6], it must be transmitted through the nitrogen center. Thus, the downfield shifts of Hc and He (Chart 2) are clearly indicative of positive spin density present on the attendant carbons, while the upfield shift of Hd reveals a negative spin density on the neighboring carbon atom, in line with a spin polarization symmetric to that observed for the phenylene ring directly bonded to the Fe(III) center (Chart 3). This reveals

Figure 4. Thermal variation of χMT for powdered samples of 1[PF6]3 (open circles) and 2[PF6] (filled circles) with the curve of best fit (full line) for 1[PF6]3 from the model described in the text.

2[PF6] exhibit a linear dependence on 1/T, in accord with its magnetic susceptibility obeying a Curie law, while the corresponding plots obtained for the protons of 1[PF6]3 deviate slightly from linearity and exhibit a slight inward curvature more apparent for the aromatic protons of the triarylamine spacer (see the Supporting Information), in line with the existence of an antiferromagnetic interaction between the three electronic spins in solution and consistent with that detected in the solid state.7,25 Unfortunately, for a triradical such as 1[PF6]3, it is difficult to extract the coupling constant from such plots when no data are available regarding the hyperfine coupling operative in the various spin states in thermal equilibrium.26 Nevertheless, the present data suggest that the antiferromagnetic interaction between spins in 1[PF6]3 is not just an intermolecular interaction governed by the packing in the solid state, but that it has a real intramolecular origin.

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Chart 3. Spin Polarization Deduced from 1H NMR Measurements on 2[PF6]

that an inversion of the polarization of the π manifold takes place when proceeding through the nitrogen atom, as expected for an antiferromagnetic coupler. Second, on the basis of the magnitude of the isotropic 1H NMR shifts and broadness of the signals, a much lower spin density is experimentally observed on the three equivalent 1,4phenylene units of 1[PF6]3, compared to that present in the bridging phenylene unit of 2[PF6]. Actually, the averaged spin density present on the organic spacer of 1[PF6]3 significantly exceeds one-third of that of 2[PF6], the value expected for a pure doublet state where the unpaired spin is delocalized over three metallic end groups (Scheme 2) but is clearly below that expected for a pure quartet species.7 This observation is probably attributable to the presence of a thermal equilibrum

DISCUSSION

The magnetic susceptibility measurements clearly reveal that a sizable antiferromagnetic interaction takes place between the spins of the unpaired electrons in the corresponding radical trication 1[PF6]3, in contrast to our initial expectations. In this context, the 1H NMR shifts of 1[PF6]3 relative to those of the mononuclear model complex 2[PF6] prove quite informative. As previously discussed on several occasions, the NMR shifts recorded for the arylamino protons of both compounds can be considered as good probes of the spin densities on the adjacent carbon atoms averaged between the various spin isomers in thermal equilibrium in solution.7,11 Indeed, all these nuclei are remote from the metal center (>5 1638


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Scheme 2. VB Formulation of the Excited Quartet (Q) and GS Doublet (D1−n & D′1−n) States of 13+a

a

For each VB mesomer, antiferromagnetically coupled electrons are represented in red.

formational effects are certainly averaged in solution, due to rapid rotation of the aryl groups on the amine, in line with only one averaged effective J value. However, in solid samples, packing effects might stabilize such conformations for which the 3-fold symmetry of 1[PF6]3 is broken. This, in turn, would lead to slightly different antiferromagnetic intramolecular (and intermolecular) coupling between unpaired spins.24,29 As a result, only an approximate fit of the magnetic susceptibility data measured in the solid state can be obtained using the Hamiltonian corresponding to the idealized symmetric molecule (eqs 1 and 2).9,15 Conclusions. Two new organometallic triarylamino derivatives featuring three (1) or one (2) “(η2-dppe)(η5C5Me5)FeCC−” substituents in para position(s) on the aryl rings have been synthesized and characterized. The corresponding Fe(III) complexes 1[PF6]3 and 2[PF6] were also isolated and characterized. The trinuclear oxidation product constitutes a novel organometallic triradical with a doublet GS (and a mean antiferromagnetic coupling of JFeFe = −14.1 cm−1 between the unpaired spins), as established by magnetic susceptibility (SQUID) measurements on solid samples of 1[PF6]3 and by 1H VT-NMR experiments in d2dichloromethane. Further, the use of 1H NMR evidenced (i) a diminution of the global π-spin density on the triarylamino spacer in 1[PF6]3 compared to 2[PF6] and (ii) the inversion of the polarization of the π manifold when proceeding through nitrogen. In line with previous work by Iwamura and coworkers on related purely organic triarylamino-bridged triradicals,9,15 this confirms that the triarylamine spacer behaves as an antiferromagnetic coupler, possibly via a superexchange mechanism. On the basis of these studies, we therefore conclude that not only the topology, but also the number of π electrons influences the magnetic coupling through such spacers, and that this is regardless of the nature (organic vs organometallic) of the S = 1/2 spin carriers.9

between polyradicals in the doublet and quartet states, dominated by the doublet state.27 Thus, the NMR data obtained for these Fe(III) compounds strongly support the idea that, in the organometallic triradical 1[PF6]3, the nitrogen bridging atom acts as an antiferromagnetic coupler between two of the branches. Given the observation of a strong absorption at low energy (above 850 nm) attributable to a ligand to metal charge transfer (LMCT) band for both (poly)radicals 1[PF6]3 and 2[PF6],7,22 this magnetic interaction most likely proceeds via a superexchange mechanism, as previously proposed for the related organic radical 3.15 Fully consistent with the 1H NMR results, 1[PF6]3 exhibits a doublet rather than a quartet ground state, as established by SQUID measurements. While the overlap between the topologically nondisjointed (but spatially separated) magnetic orbitals (or NMBOs)13 with coextensive filled π-MOs of the central triphenylamine fragment is certainly reduced by the cationic charges of the Fe(III) organometallic end groups in the trication, relative to that in the mononuclear cation 2[PF6] taken as model,27 this decrease is apparently not sufficient to sever the quite large coupling between unpaired spins that is operative in 1[PF6]3. As revealed by the X-ray structure of 2[PF6] (Figure 1), the three aryl groups cannot all be coplanar for steric reasons due to the interaction between the ortho (to amino) hydrogens. As a consequence, the various π manifolds on each aryl group are tilted and certainly rotate freely in solution.28 On the basis of the polarization of the π manifold established by 1H NMR measurements on 2[PF6], a conformation where two rings are coplanar would maximize the antiferromagnetic interaction between them, leaving the remaining branch in a perpendicular conformation with one unpaired spin on it. Thus, any such conformation where the ideal C3v symmetry of the molecule is broken would certainly further stabilize the doublet state over the quartet state and lead to different J values for intramolecular interactions between unpaired electronic spins. These con1639


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washed with additional Et2O (10 mL). The process was repeated using n-pentane instead of Et2O, and the resulting brown solid was dried in vacuo (0.715 g, 95%). IR (KBr, cm−1): ν 1614 (s, FeCC), 837 (vs, PF6−). 31P{1H} NMR (80 MHz, CDCl3): δ 88.4 (s, Pdppe), −143.1 (sept, PF6−). 1H NMR (200 MHz, CDCl3): δ 7.62−7.19 (m, 60H, HAr), 6.62 (d, 6H, 3JH,H = 8 Hz, HNAr3), 6.27 (d, 6H, 3JH,H = 8 Hz, HNAr3), 5.07 (t, 3H, 4JP,H = 4 Hz, Hvinylidene), 3.12 (m, 6H, CH2/dppe), 2.56 (m, 6H, CH2/dppe), 1.61 (s, 45H, C5(CH3)5). The vinylidene complex [{(η2-dppe)(η5-C5Me5)FeCCH-1,4C6H4}3N][PF6]3 (1-v[PF6]3; 0.715 g, 0.283 mmol) was suspended in THF (20 mL), and tBuOK (0.312 g, 2.83 mmol) was added to the stirred solution. Stirring was maintained for an additional 10 min, and the solvents and volatiles were removed in vacuo. The orange solid was taken up in toluene (20 mL) and filtered through a short pad of Celite (2 × 2 cm). The Celite plug was washed with toluene (3 × 10 mL), and the toluene extracts were evaporated to dryness. The residue was dissolved in the minimum amount of CH2Cl2, and the title acetylide complex 1 was precipitated as an orange-red solid by addition of MeOH to the CH2Cl2 extract. The precipitate was collected by cannula filtration and washed with additional MeOH (10 mL). The process was repeated using n-pentane instead of MeOH, and 1 was collected as an orange solid which was dried under high vacuum (0.545 g, 92%). Anal. Calcd for C132H129Fe3NP6: C, 76.12; H, 6.24; N, 0.67. Found: C, 76.27; H, 6.31; N, 0.76. HRMS (ESI): m/z calcd for C132H129Fe3NP6 [M]+ 2081.6599, found 2081.6623. IR (KBr, cm−1): ν 2048 (vs, νCC). 31P{1H} NMR (80 MHz, C6D6, ppm): δ 101.8 (s, Pdppe). 1H NMR (200 MHz, C6D6, ppm): δ 8.07 (m, 12H, HAr), 7.35− 7.08 (m, 60H, HAr), 2.67 (m, 6H, CH2/dppe), 1.87 (m, 6H, CH2/dppe), 1.56 (s, 45H, C5(CH3)5). 13C{1H} NMR (50 MHz, C6D6, ppm): δ 144.3 (s, Cquat/Ar3N), 140.4−124.4 (m, Cquat and CHdppe&Ar3N), 133.1 (t, 3 JP,C = 45 Hz, Fe CC), 120.2 (s, Fe CC), 87.7 (s, C5(CH3)5), 31.8 (m, CH2/dppe), 10.5 (s, C5(CH3)5). UV−vis (CH2Cl2, nm): λmax (ε × 10−3 M−1 cm−1) 403 (46.4). Synthesis of [{(η2-dppe)(η5-C5Me5)FeCC(1,4-C6H4)}3N][PF6]3 (1[PF6]3). The complex {(η2-dppe)(η5-C5Me5)FeCC(1,4-C6H4)}3N (1; 0.208 g, 0.10 mmol) and [Fe(η5-C5H5)2][PF6] (0.0993 g, 0.30 mmol) were dissolved in THF (10 mL) and stirred for 1 h at ambient temperature. Solvents were removed under vacuum, and the remaining black residue was dissolved in the minimum amount of CH2Cl2. Subsequently, n-pentane was added to the CH2Cl2 solution to precipitate a solid, which was collected by filtration. The solid was reprecipitated twice from CH2Cl2/n-pentane, washed with n-pentane (10 mL), and dried in vacuo to give the title compound as a black solid (0.235 g, 93%). Anal. Calcd for C132H129F18Fe3NP9·2CH2Cl2: C, 59.88; H, 4.99; N, 0.52. Found: C, 59.41; H, 5.05; N, 0.47. IR (KBr, cm−1): ν 1965 (vs, νCC), 837 (vs, PF6). 1H NMR (200 MHz, CD2Cl2, ppm): δ 19.5 (s, HAr/NAr3), 7.9 (s, HAr/dppe), 7.4 (s, HAr/dppe), 6.8 (s, HAr/dppe), 6.5 (s, HAr/dppe), 4.2 (s, HAr/dppe), 2.7 (s, HAr/dppe), −2.4 (s, CH2/dppe), −8.9 (broad s, C5(CH3)5), −39.6 (broad s, HAr/NAr3). EPR (CH2Cl2/1,2-C2H4Cl2, 77 K): g = 2.061 (broad signal). UV−vis−near-IR (CH2Cl2, nm): λmax (ε × 10−3 M−1 cm−1) 258 (86.8), 356 (44.8), 438 (21.0), 906 (26.6), 1777 (1.2). Synthesis of (η2-dppe)(η5-C5Me5)Fe[CC(4-C6H4NPh2)] (2). The complex (η2-dppe)(η5-C5Me5)FeCl (3; 0.625 g, 1.0 mmol), KPF6 (0.22 g, 1.20 mmol), and 4-ethynyl-N,N-diphenylaniline (0.323 g, 1.20 mmol) were dissolved in a mixture of MeOH (10 mL) and THF (10 mL) and stirred for 18 h at room temperature. Solvents were removed in vacuo, the dark solid extracted with CH2Cl2 (3 × 10 mL), and the volume of the combined extracts reduced to 5 mL. The vinylidene salt was precipitated by addition of Et2O to the CH2Cl2 extract and collected by filtration. The resulting solid was precipitated from CH2Cl2/n-pentane, washed with n-pentane (10 mL), and dried under vacuum, yielding 2-v[PF6] as a brown solid (0.89 g, 89%). IR (KBr, cm−1): ν 1618 (s, FeCC), 831 (s, PF6−). 31P{1H} NMR (80 MHz, CDCl3, ppm): δ 88.5 (s, Pdppe), −143.1 (sept, PF6−). 1H NMR (200 MHz, CDCl3, ppm): δ 7.65−7.03 (m, 30H, HAr), 6.69 (d, 2H, 3 JH,H = 8 Hz, C6H4), 6.21 (d, 2H, 3JH,H = 8 Hz, C6H4), 5.07 (t, 1H, 4 JP,H = 4 Hz, Hvinylidene), 3.10 (m, 2H, CH2/dppe), 2.56 (m, 2H, CH2/dppe), 1.61 (s, 15H, C5(CH3)5).

EXPERIMENTAL SECTION

General Considerations. All reactions and workup procedures were carried out under dry, high-purity argon using standard Schlenk

Table 2. Crystal Data and Data Collection and Refinement Parameters for 2 formula fw cryst syst space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm−3) cryst size (mm) F(000) abs coeff (mm−1) no. of total and unique rflns no. of variables/rflns >2σ(I) final R Rw goodness of fit/F2 (Sw)

C56H53FeNP2 857.78 monoclinic P21/a 10.7646(4) 32.2519(8) 13.6095(5) 90.0 104.140(3) 90.0 4581.8(3) 4 1.244 0.54 × 0.30 × 0.04 1808 0.437 39 491/10 384 (R(int) = 0.0606) 95 551 0.0513 0.1244 1.036

techniques.30 All solvents were freshly distilled and purged with argon before use. Infrared spectra were obtained on a Bruker IFS28 FT-IR spectrometer (400−4000 cm−1). NMR spectra were acquired at 298 K on a Bruker DPX200 instrument. Chemical shifts are given in ppm and referenced to the residual nondeuterated solvent signal31 for 1H and 13 C and external H3PO4 (0.0 ppm) for 31P NMR spectra. Cyclic voltammograms were recorded in dry CH2Cl2 solutions (containing 0.10 M [NnBu4][PF6], purged with argon, and maintained under an argon atmosphere) using an EG&G-PAR Model 263 potentiostat/ galvanostat. The working electrode was a Pt disk, the counter electrode a Pt wire, and the reference electrode a saturated calomel electrode (SCE). The FeCp20/+ couple (E1/2 = 0.46 V, ΔEp = 0.09 V; ipa/ipc = 1) was used as an internal calibrant for the potential measurements.20 Near-IR and UV−visible spectra were recorded as CH2Cl2 solutions, using a 1 cm long quartz cell in a Cary 5000 spectrometer. EPR spectra were recorded on a Bruker EMX-8/2.7 (X-band) spectrometer at 77 K (liquid nitrogen). The dc magnetic susceptibility measurements were performed on solid polycrystalline samples with a Quantum Design MPMS-XL SQUID magnetometer between 2 and 300 K. These measurements were all corrected for the diamagnetic contribution as calculated with Pascal’s constants. Elemental analysis and highresolution mass spectra were performed at the “Centre Regional de Mesures Physiques de l’Ouest” (CRMPO), Université de Rennes 1. (η2-dppe)(η5-C5Me5)FeCl (3),32 4-ethynyl-N,N-diphenylaniline,33 tris(4-ethynylphenyl)amine,33 and [(η5-C5H5)2Fe][PF6]20 were prepared as described in the literature; t-BuOK was recrystallized from THF34 and stored/opened under argon. Other chemicals were purchased from commercial suppliers and used as received. Synthesis of {(η2-dppe)(η5-C5Me5)FeCC(1,4-C6H4)}3N (1). The complex (η2-dppe)(η5-C5Me5)FeCl (3; 0.656 g, 1.05 mmol), KPF6 (0.193 g, 1.05 mmol), and tris(4-ethynylphenyl)amine (0.095 g, 0.30 mmol) were dissolved in a mixture of THF (10 mL) and MeOH (10 mL). The reaction medium was stirred and heated at 40 °C for 2 days, cooled to room temperature, and solvents were removed under vacuum. The vinylidene complex 1-v[PF6]3 was extracted with CH2Cl2 (3 × 10 mL), and the volume of the combined extracts was reduced to 5 mL. Et2O was added to the CH2Cl2 extract to precipitate the desired 1-v[PF6]3 as a dark solid, which was collected by cannula filtration and 1640


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scattering factors were taken from the literature.39 Crystal data and data collection and refinement parameters for 2 are given in Table 2.

The vinylidene complex [(η2-dppe)(η5-C5Me5)FeCCH(4C6H4NPh2)][PF6] (2-v; 0.89 g, 0.89 mmol) was suspended in THF (20 mL), and tBuOK (0.30 g, 2.67 mmol) was added to the stirred suspension. After 10 min of stirring, all solvent and volatiles were removed in vacuo. The red residue was taken up in toluene (20 mL) and filtered throught a Celite pad (2 × 2 cm). The pad was washed with toluene (3 × 10 mL), and the extracts were taken to dryness. The red solid was dissolved in the minimum amount of CH2Cl2, and the acetylide complex precipitated as an orange powder by addition of MeOH at 0 °C. The precipitate was collected by cannula filtration, washed with MeOH (10 mL), and reprecipitated from dichloromethane/n-pentane at −90 °C. After removal of the supernatant and washing of the solid with additional n-pentane (10 mL), the title compound (0.715 g, 93%) was dried in vacuo. The sample subjected to elemental analysis was additionally reprecipitated from dichloromethane/MeOH mixtures. X-ray-quality crystals of 2 were grown by slow diffusion of methanol into a dichloromethane solution of the complex. Anal. Calcd for C56H53FeNP2·CH4O: C, 76.93; H, 6.46; N, 1.57. Found: C, 76.92; H, 6.11; N, 1.67. HRMS (ESI): m/z calcd for C56H53FeNP2 [M]+ 857.30027, found, 857.3002. IR (KBr, cm−1): ν 2062 (s, νCC). 31P{1H} NMR (80 MHz, C6D6, ppm): δ 101.6 (s, Pdppe). 1H NMR (200 MHz, C6D6, ppm): δ 8.08−8.00 (m, 4H, HAr/dppe), 7.33−6.99 (m, 28H, HAr), 6.85−6.78 (m, 2H, HAr), 2.65 (m, 2H, CH2/dppe), 1.83 (m, 2H, CH2/dppe), 1.55 (s, 15H, C5(CH3)5). 13 C{1H} NMR (50 MHz, C6D6, ppm): δ 148.8 (s, Cquat/ArNPh2), 143.4 (s, Cquat/ArNPh2), 140.8−122.2 (m, Cquat and CHdppe&ArNPh2), 136.5 (t, 3 JP,C = 40 Hz, Fe CC), 119.9 (s, Fe CC), 87.8 (s, C5(CH3)5), 31.0 (m, CH2, dppe), 10.5 (s, C5(CH3)5). UV−vis (CH2Cl2, nm): λmax (ε × 10−3 M−1cm−1) 367 (19.5). Synthesis of [(η2-dppe)(η5-C5Me5)Fe[CC-1,4-(C6H4)NPh2]][PF6] (2[PF6]). The complex (η2-dppe)(η5-C5Me5)Fe[CC(4C6H4NPh2)] (2; 0.429 g, 0.50 mmol) and [(η5-C5H5)2Fe][PF6] (0.157 g, 0.475 mmol) were dissolved in THF (20 mL) and stirred for 1 h at ambient temperature. THF was removed in vacuo, and the black solid was dissolved in the minimum amount of CH2Cl2. Subsequently, n-pentane was added to precipitate a solid. The supernatant was removed and the solid reprecipitated twice from CH2Cl2/n-pentane. The precipitate was collected by filtration, washed with n-pentane (10 mL), and dried under high vacuum, yielding the title compound as a d a r k y e l l o w s o l i d ( 0. 4 4 5 g , 9 3% ) . A n a l . C a l c d f o r C56H53F6Fe1NP3·1/2CH2Cl2: C, 64.92; H, 5.21; N, 1.34. Found: C, 65.12; H, 5.37; N, 1.16. IR (KBr, cm−1): ν 1965 (vs, νCC), 832 (s, PF6−). 1H NMR (400 MHz, CD2Cl2, ppm): δ 27.2 (broad s, HAr/NAr3), 11.2 (s, HAr/NAr3), 9.0 (broad s, CH2/dppe), 8.1 (s, HAr/dppe), 6.7 (s, HAr/dppe), 4.1 (s, HAr/dppe), 3.9 (s, HAr/dppe), 3.4 (s, HAr/dppe), 1.6 (s, HAr/NAr3), 1.3 (s, HAr/NAr3), −4.0 (broad s, CH2/dppe), −10.2 (broad s, C5(CH3)5), −58.8 (very broad s, HAr/NAr3). EPR (CH2Cl2/1,2C2H4Cl2, 77 K): g1 = 1.989, g2 = 2.037, g3 = 2.336. UV−vis−nearIR (CH2Cl2, nm): λmax (ε × 10−3 M−1.cm−1) 282 (40.0), 304 (sh, 32.6), 327 (sh, 29.0), 432 (10.1), 880 (14.4), 1704 (0.4). Crystallography. Data collection of crystals of 2 was performed on a KappaCCD diffractometer, at 120(2) K, with graphitemonochromated Mo Kα radiation (λ = 0.710 73 Å). The structure was solved by direct methods using the SIR97 program35 and then refined with full-matrix least-squares methods based on F2 (SHELX97)36 with the aid of the WINGX37 program. The contribution of the disordered solvents to the calculated structure factors was estimated following the BYPASS algorithm, implemented as the SQUEEZE option in PLATON.38 A cavity of 110 Å3 was estimated by the SQUEEZE procedure, leading to a 27-electron content, which could correspond to approximatively half a molecule of dichloromethane. A new data set, free of solvent contribution, was then used in the final refinement. The complete structures were refined with SHELXL9736 by the full-matrix least-squares technique. All non-hydrogen atoms were refined with anisotropic atomic displacement parameters. H atoms were finally included in their calculated positions. A final refinement on F2 with 10 384 unique intensities and 546 parameters converged at Rw(F2) = 0.1244 (R(F) = 0.0513) for 6667 observed reflections with I > 2σ(I) (Bruker AXS BV diffractometer). Atomic

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ASSOCIATED CONTENT

* Supporting Information S

Figures giving UV−vis spectra for all compounds and 1H NMR spectra, assignment, and temperature dependence of selected protons of 1[PF6]3 and 2[PF6] and a CIF file giving crystallographic data for 2. This material is available free of charge via the Internet at http://pubs.acs.org. Final atomic positional coordinates, with estimated standard deviations, bond lengths and angles, and anisotropic thermal parameters, have also been deposited at the Cambridge Crystallographic Data Centre and were allocated the deposition number CCDC 832626.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected] (F.P.); mark. [email protected] (M.G.H.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS G.G. thanks Region Bretagne for partial support of a Ph.D. scholarship. S. Sinbandhit (CRMPO-UMR 6226) and A. Bondon (PRISM-UMR CNRS 6026) are kindly acknowledged for their assistance during the NMR studies. The CNRS (PICS program No. 5676) is acknowledged for financial support. M.G.H. holds an ARC Australian Professorial Fellowship, and M.P.C. holds an ARC Australian Research Fellowship.

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REFERENCES

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Triphenylamine Derivatives with Para-Disposed Pendant Electron

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