Metallocenes of the Late Transition Metals Cobalt ... - ACS Publications

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Tin-Bridged ansa-Metallocenes of the Late Transition Metals Cobalt and Nickel: Preparation, Molecular and Electronic Structures, and Redox Chemistry Thomas Arnold, Holger Braunschweig,* Alexander Damme, Christian Hörl, Thomas Kramer, Ivo Krummenacher, and Julian Mager Institut für Anorganische Chemie, Julius-Maximilians-Universität Würzburg, Am Hubland, D-97074 Würzburg, Germany S Supporting Information *

ABSTRACT: Using the flytrap approach, paramagnetic ansa-metallocenes of the late transition metals cobalt and nickel containing a tetra-tertbutyldistannane bridge have been prepared. The complexes were identified using a combination of analytical methods (NMR, EPR, cyclic voltammetry, and X-ray crystallography) and further converted to their corresponding cations by one-electron oxidation with ferrocenium hexafluorophosphate. Spectral and structural analyses of the ionic products are consistent with metal-based oxidations.

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INTRODUCTION Metallocenophanes, or ansa-metallocenes, are a popular class of organometallic compounds, which have found use in catalytic processes and materials science. While the success of earlytransition-metal metallocenes as Ziegler−Natta catalysts is documented in the industrial production of polyolefins,1 strained derivatives of the late transition metals are gaining increasing importance, due to their ability to undergo ringopening polymerization (ROP) and to produce metallopolymers with functional properties.2 As the central metal atom, the nature and size of the ansa bridge, and the η5-coordinating ligands are all factors influencing their properties and chemical reactivity, many variations within this group of compounds have been reported.3 In comparison to the many different bridging units known for [n]ferrocenophanes (n = number of bridging atoms), the structural variety of ansa-metallocenes involving late transition metals of the higher groups (i.e., above group 8) is rather limited (see Chart 1 for an overview).3 This phenomenon can be explained in part by the failure to 1,1′-dimetalate these metallocenes, which constitutes a key step in the usual synthesis of metallocenophanes. Hence, several other strategies have been explored. The first examples of ansa-cobaltocenes (I) were based on the reductive coupling of fulvene ligand precursors using metal atoms.4 While it is versatile and offers access to chiral ansa-metallocenes (II),5 the method is restricted to the use of rather large substituents in the 6-position of the fulvene, which results in sterically demanding bridging units. Intramolecular ring-closing olefin metathesis was used to construct the first structurally characterized ansa-nickelocenes (IV),6 in which an unsaturated carbon bridge connects the two cyclopentadienyl fragments.7 Interestingly, the bridge is readily converted into its saturated analogue by hydrogenation, © 2014 American Chemical Society

Chart 1. Structural Motifs (I−VI) for Singly Bridged, Neutral Metallocenophanes of Group 9 and 10 Metalsa

a

Only bridges containing group 14 elements are shown.15

without affecting the π system of the Cp ligands.8 In another approach, the so-called flytrap method,3 which involves the reaction of dianionic bis(cyclopentadienyl) ligand sets with appropriate metal halides, the Manners group synthesized two hydrocarbon-bridged [n]cobaltocenophanes (III; n = 2, 3) with varying lengths of the bridge.9 It is important to note that the more strained system was shown to produce a high-molecularweight polymetallocenium by thermal ring opening and subsequent oxidation.10 In a similar fashion, our group introduced the tetramethyldisilane bridge into both cobalt11 Received: December 18, 2013 Published: March 28, 2014 1659

dx.doi.org/10.1021/om401212n | Organometallics 2014, 33, 1659−1664

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and nickel12 sandwich complexes (V), the latter of which represents the first strained [2]nickelocenophane. Further examples of ansa-bridged metallocenes of the late transition metals (VI) were reported by Prosenc and Heck, obtained by salt metathesis of disodium 1,8-bis(cyclopentadienyl)naphthalene with divalent cobalt13 and nickel14 salts. Herein, we report the preparation of the first tin-bridged [2]cobalto- and [2]nickelocenophanes via the flytrap approach and describe their electronic structure as probed by cyclic voltammetry and EPR spectroscopy.

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RESULTS AND DISCUSSION Synthesis. The neutral tin-bridged [2]metallocenophanes of cobalt (1) and nickel (2) were prepared by treatment of the previously reported doubly lithiated flytrap ligand (LiC5H4)2(Sn2tBu4)16 with the corresponding anhydrous metal dichloride [MCl2(dme)] (M = Co, Ni; dme = 1,2dimethoxyethane) in THF (Scheme 1). While compound 1 was obtained in 62% yield as a dark brown solid, compound 2 was isolated in 50% yield as a dark green solid after recrystallization from pentane at −30 °C.

Figure 1. Molecular structures of 1 (left) and 2 (right) with thermal ellipsoids set at the 50% probability level (hydrogen atoms are not shown). Selected bond lengths (Å) and angles (deg): 1, Ct1−Ct2 3.441, Co1−Ct1 1.748, Co1−Ct2 1.721, Sn1−Sn2 2.8369(3), Sn1− C1 2.153(2), Sn2−C6 2.159(2), C1−Sn1−Sn2−C6 12.87, Ct1−Co− Ct2 177.15; 2, Ct1−Ct2 3.628, Ni1−Ct1 1.814, Ni1−Ct2 1.817, Sn1− Sn2 2.848(2), Sn1−C1 2.156(2), Sn2−C6 2.157(1); C1−Sn1−Sn2− C6 13.28, Ct1−Ni1−Ct2 175.92 (Ct is defined as the Cp ring centroid).

compare well with those of the flytrap ligand precursor (C5H5)(tBu)2Sn−Sn(tBu)2(C5H5) (2.8489(5) Å) and related Sn2tBu4-bridged metallocenophanes.16,17 In addition, it is interesting to note that the bond distances in the Cp rings of compound 1 are highly irregular (cf. Cp ring C1−C2 1.427(3), C2−C3 1.434(3), C3−C4 1.394(4), C4−C5 1.433(3), C5−C1 1.429(3) Å; see Figure 1), produced by population of a metalring antibonding orbital. The alternation of the C−C bonds in the Cp ligand is reminiscent of an “ene-allyl”-like structure, which reflects the π-bonding interactions within the ring in the singly occupied molecular orbital (SOMO). Electrochemical Measurements. We assessed the redox properties of both metallocenophanes [M(C5H4)2(Sn2tBu4)] (M = Co (1) and Ni (2)) by using cyclic voltammetry. The measurements of both compounds show chemically reversible redox events, which can be ascribed to metal-centered redox processes (Figures 2 and 3). In the case of 1, two chemically reversible redox pairs centered at half-wave potentials of E1/2 = −1.32 and −2.43 V vs Fc/Fc+ (Fc = ferrocene) are observed, corresponding to the [Co(C5H4)2(Sn2tBu4)]0/+ and [Co(C5H4)2(Sn2tBu4)]0/− couples, respectively (Figure 2). The redox potentials for the one-

Scheme 1. Preparation of the Distanna[2]metallocenophane Complexes 1 and 2

The paramagnetic character of the neutral metallocenophanes 1 and 2 is evident in the 1H NMR spectra, where the ligand resonances appear over a wide chemical shift range of about −60 (1) to −260 ppm (2), thus indicating the successful coordination of the metal ions by the ansa-bis(cyclopentadienyl) ligand (cf. also EPR Spectroscopy). Notably, the two sets of nonequivalent cyclopentadienyl protons in compound 1 appear at very different chemical shifts, δ −1.22 and −58.0 ppm (both broad). For the d8 20electron ansa-nickelocene 2 these protons appear at δ −239 and −253 ppm, respectively. This can be explained by a significant amount of unpaired spin density delocalized on the cyclopentadienyl ligands, as expected for metallocenes with more than 18 valence electrons, in which the unpaired electrons occupy orbitals that have considerable ligand character. Crystalline material suitable for X-ray diffraction was obtained for both species by recrystallization from a saturated pentane solution at −30 °C. The molecular structures are shown in Figure 1, together with selected structural parameters. The η5-coordinating Cp (Cp = cyclopentadienyl) ligands in complexes 1 and 2 only slightly deviate from a parallel orientation with tilt angles α of 2.64 (1) and 4.60° (2). Thus, the tetra-tert-butyldistannane bridge introduces only a small amount of molecular strain. This is also reflected in the Ct1− M−Ct2 angle (Ct = ring centroids), which is close to 180° in both species (177.2° (1) and 175.9° (2), respectively). The Sn−Sn bond lengths in 1 (2.8369(3) Å) and 2 (2.848(2) Å) are in the range of typical Sn(sp3)−Sn(sp3) single bonds and

Figure 2. Cyclic voltammogram for 1 in 0.1 M [nBu4N][PF6]/THF solution at a scan rate of 0.2 V s−1. Three cyclic potential sweeps are shown. 1660


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The oxidation product of complex 1 is diamagnetic and shows the expected AA′BB′ pattern for the Cp protons and a singlet resonance for the equivalent tBu protons in its proton NMR spectrum, consistent with C2v symmetry in solution. The 119 Sn NMR resonance appears at δ −3.2 ppm with a tin−tin coupling constant of 1J(119Sn,117Sn) = 680 Hz, confirming the retention of the sandwich structure upon one-electron oxidation.20 In addition, the PF6 anion was identified by its characteristic septet splitting in its 31P NMR spectrum (1JPF = 711 Hz). The 18-valence-electron cobaltoceniumphane salt ([1][PF6]) was further characterized by X-ray analysis. Singlecrystal material was obtained by recrystallization from toluene at room temperature. Complex [1][PF6] crystallizes in the orthorhombic space group Pna21, with two independent molecules per unit cell (Figure 4a). As the two molecules are Figure 3. Combined cyclic voltammograms of 2 in THF and CH2Cl2 solution, each with a 0.1 M concentration of [nBu4N][PF6] and a scan rate of 250 mV s−1.

electron oxidation and reduction are comparable to the values previously measured for the Si2Me4-bridged derivative (−1.27 and −2.40 V vs Fc/Fc+)11 and the unbridged system ([CoCp2]: E1/2 = −1.25 and −2.19 V vs Fc/Fc+ in CH3CN).18 A closer examination of the redox potentials of the parent metallocene and its two-atom-bridged counterparts suggests an increased HOMO−LUMO energy gap for the ansa derivatives, mainly caused by a higher lying LUMO level (more negative electrochemical reduction potential). The cyclic voltammetric data for complex 2 shows two chemically reversible oxidations (THF, E1/2 = −0.46 and +0.39 V vs Fc/Fc+; CH2Cl2, E1/2 = −0.52 and +0.49 V vs Fc/Fc+; Figure 3) and one partially chemically reversible reduction (THF, E1/2 = −2.30 V vs Fc/Fc+). Thus, the redox profile of ansa-nickelocene 2 with four accessible redox states (−1, 0, +1, and +2) closely resembles the electrochemical behavior of related bis(η5-cyclopentadienyl)nickel(II) derivatives, including the parent nickelocene ([NiCp2], E1/2 = −2.12, −0.23, and +0.57 V vs Fc/Fc+ in THF).19 In comparison to [NiCp2], the formal reduction and oxidation potentials of complex 2 are consistently more negative, indicating that the metal center in 2 is more electron rich. This can be attributed to the electronic influence of the Sn2tBu4 bridge, which falls in the range of a bridging naphthalene substituent (E1/2 = −2.29, −0.52, and +0.49 V vs Fc/Fc+ in CH3CN).14 Synthesis and Characterization of Cationic [2]Metalloceniumphanes (M = Co, Ni). Given the high redox flexibility of both ansa-metallocenes, we set out to investigate their oxidation chemistry in more detail. One-electron oxidation of the neutral precursors to the [MCp2]+ (M = Co, Ni) cations was achieved by oxidation with ferrocenium hexafluorophosphate ([FeCp2][PF6], E1/2 = 0.0 V; Scheme 2).

Figure 4. Molecular structures of (a) [1][PF6] and (b) [2][PF6], with thermal ellipsoids at the 50% probability level. Only one of the two crystallographically distinct molecules of [1][PF6] in the asymmetric unit is shown. Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (deg): [1][PF6], Ct1− Ct2 3.263, Co1−Ct1 1.629, Co1−Ct2 1.634, Sn1−C1 2.191(4), Sn2− C6 2.194(4), Sn1−Sn2 2.8295(4), C1−Sn1−Sn2−C6 16.40, Ct1− Co−Ct2 178.31; [2][PF6], Ct1−Ct2 3.433, Co1−Ct1 1.716, Co1− Ct2 1.719, Sn1−C1 2.175(3), Sn2−C6 2.179(3), Sn1−Sn2 2.8311(3), C1−Sn1−Sn2−C6 26.62, Ct1−Ni−Ct2 176.28 (Ct is defined as the Cp ring centroid).

structurally nearly identical, only one will be discussed here. As a consequence of the oxidation of the cobalt center, the metal− ring centroid distances are shortened by about 0.1 Å. In contrast, the Sn−Sn bond is almost unchanged, which results in a twist of this bond with respect to the Ct1−Co−Ct2 axis (Ct = centroids of the Cp ligands). Thus, the Cp ligands of [1][PF6] deviate more from an eclipsed conformation (with a twist angle of 16.40°) in comparison to the neutral system (1) but stay virtually parallel to each other (tilt angle α = 1.3°). Similarly, chemical oxidation of complex 2 with [Fc][PF6] afforded the nickeloceniumphane [2][PF6] in 71% yield as a brown solid after recrystallization from toluene. The 1H NMR spectrum of the paramagnetic complex with a d7 electronic configuration shows two broad signals at low frequency (δ −49 and −115 ppm) for the inequivalent cyclopentadienyl protons and a sharper resonance for the tert-butyl protons (δ 1.72 ppm), akin to those for the isoelectronic cobalt complex 1 (vide supra). This suggests that the cationic complex [2][PF6] has a spin density distribution similar to that of 1. X-ray structural and elemental analysis support the assigned ionic structure (Figure 4b). The molecular structure of [2][PF6] shows the same trends in comparison to its neutral precursor 2 as the cobalt derivative: i.e., shortened metal to ligand bond lengths, a

Scheme 2. Synthesis of the [2]Cobaltoceniumphane and [2]Nickeloceniumphane Salts

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(CW) X-band EPR spectra of 2 in frozen toluene solution remain silent down to temperatures of 4 K. The CW EPR spectrum of the cationic, 19-valence-electron [2]nickeloceniumphane [2][PF6] displays a rhombic g tensor (g1 = 2.050, g2 = 2.000, and g3 = 1.831) with no evidence for electron−nuclear spin interactions (Figure 5).22 This is in accord with the unpaired spin density being primarily localized on the nickel atom and the π system of the Cp rings. The two most abundant nickel isotopes, 58Ni and 60Ni, have a nuclear spin of I = 0 and therefore do not lead to hyperfine splittings. The observed magnetic parameters are in good agreement with the only other known nickeloceniumphane, which contains a three-atom naphthalene bridge (g1 = 2.050, g2 = 2.008, and g3 = 1.868).25

more twisted conformation (C1−Sn1−Sn2−C6 = 26.62°), a nearly unchanged tin−tin distance, and a small tilt angle (α = 3.7°). The observed chemical and electrochemical reversibility of the Ni(III)/Ni(IV) redox couple in the cyclic voltammogram prompted us to synthesize a dicationic species, which would be isoelectronic with [1][PF6] and the neutral distanna[2]ferrocenophane, previously reported by our group.17 However, our attempts to isolate the 18-valence-electron species with AgPF6 as oxidizing agent have been unsuccessful so far.21 EPR Spectroscopy. The paramagnetic complexes 1, 2, and [2][PF6] were all investigated by EPR spectroscopy. The EPR spectrum of compound 1 in frozen toluene shows a wellresolved cobalt hyperfine structure at 70 K, which is reproduced well by the spin Hamiltonian parameters of g1,2,3 = 2.114, 2.074, 1.888 and A1,2,3 = 428, 153, 104 MHz (see Figure 5).22 The

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SUMMARY Using the flytrap method, we have synthesized the first tinbridged metallocenophanes of cobalt (1) and nickel (2), which represent rare examples of covalently linked ansa-metallocenes of the late transition metals. Crystallographic data indicate that the tetra-tert-butyldistannane bridge introduces only a small amount of molecular strain. The [2]metallocenophanes show a remarkable redox flexibility, as judged by cyclic voltammetry, and are readily oxidized by ferrocenium hexafluorophosphate to their corresponding cations. While the 18-electron cobaltoceniumphane [1][PF6] is diamagnetic, the 19-electron nickeloceniumphane [2][PF6] is paramagnetic, with an S = 1/2 spin system that is observed at low temperatures in the EPR spectrum.

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EXPERIMENTAL SECTION

General Considerations. All experiments were carried out under an inert atmosphere of dry argon using either standard Schlenk line techniques or a glovebox. Solvents were dried according to standard procedures, freshly distilled prior to use, degassed, and stored under argon over activated molecular sieves (4 Å). Deuterated benzene (C6D6) was degassed by three freeze−pump−thaw cycles and stored over molecular sieves (4 Å). Li2[(C5H4)tBu2SnSntBu2(C5H4)],16 [CoCl2(dme)],27 and [NiCl2(dme)]28 were prepared according to published methods. [FeCp2][PF6] was obtained commercially and used without further purification. NMR spectra were recorded on a Bruker AMX 400 or a Bruker Avance 500 NMR spectrometer. 1H and 13 C{1H} NMR spectra were referenced to external TMS via the residual protio solvent (1H) or the solvent itself (13C). 119Sn, 31P, and 19 F NMR spectra were referenced to Me4Sn, 85% H3PO4, and CFCl3, respectively. Coupling constants are reported in Hz, and all chemical shifts are reported in ppm. Abbreviations for NMR data are as follows: s = singlet, bs = broad singlet, d = doublet, and sept = septet. Elemental analyses were performed on a Vario Micro Cube (Elementar Analysensysteme GmbH) or a CHNS-932 (Leco) elemental analyzer. CW EPR measurements at X-band (9.38 GHz) were carried out at low temperature (70−80 K) using a Bruker ELEXSYS E580 CW/FT EPR spectrometer equipped with an Oxford Instruments helium cryostat (ESR900) and a MercuryiTC temperature controller. The spectral simulations were performed using MATLAB 8.0 and the EasySpin 4.5.1 toolbox.29 Synthesis of [Co(η5-C5H4)2(Sn2tBu4)] (1). To a cooled THF solution (−78 °C) of (LiC5H4)2(Sn2tBu4) (100 mg, 0.164 mmol) was added [CoCl2(dme)] (35 mg, 0.159 mmol). The resulting mixture was warmed to room temperature and stirred for 16 h. After removal of the solvent the residue was taken up in pentane and filtered to remove the lithium salt. The filtrate was concentrated and stored at −30 °C for crystallization. Compound 1 was isolated in 62% yield as a brown crystalline solid (64 mg, 98 μmol). Single crystals suitable for X-ray analysis were obtained after recrystallization from pentane at −30 °C. 1 H NMR (400 MHz, C6D6, room temperature): δ 1.91 (s, 36 H,

Figure 5. Continuous-wave X-band (9.38 GHz) EPR spectra of (a) complex [2][PF6] (T = 60 K) and (b) complex 1 (T = 70 K).

observed g values and the highly anisotropic 59Co hyperfine couplings compare well with the spectroscopic data for the Si2Me4- and naphthalene-bridged derivatives.11,13 However, in comparison to the unbridged cobaltocene, the magnetic properties are significantly different, mainly due to effects arising from dynamic Jahn−Teller distortions of the orbitally degenerate 2E1g ground state in D5-symmetric [CoCp2].23 For the ansa-nickelocene 2, with an effective electron spin of S = 1, the dipole−dipole coupling between the two unpaired electrons (zero-field splitting, ZFS) has to be included in the spin Hamiltonian. The magnitude of this interaction often precludes an EPR response, as is the case for instance for the parent nickelocene.24 It can be speculated that a relatively large zero-field splitting can also be held responsible for the lack of an EPR signal for the ansa-nickelocene 2. Continuous-wave 1662


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2.051 mm−1, F(000) = 1756, T = 100(2) K, R1 = 0.0454, wR2 = 0.0624, 7139 independent reflections (2θ ≤ 52.74°), 391 parameters. Crystallographic data have been deposited with the Cambridge Crystallographic Data Center as supplementary publication nos. CCDC-967780 (1), CCDC-967781 ([1][PF6]), CCDC-967782 (2), and CCDC-992838 ([2][PF6]). These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www. ccdc.cam.ac.uk/data_request/cif.

C(CH3)3), −1.22 (bs, 4 H, η5-C5H4), −58.0 ppm (bs, 4 H, η5-C5H4). Anal. Calcd: C, 47.82; H, 6.79. Found: C, 48.04; H, 6.72. Synthesis of [Ni(η5-C5H4)2(Sn2tBu4)] (2). In a procedure similar to that for compound 1, a THF solution (20 mL) of (LiC5H4)2(Sn2tBu4) (100 mg, 0.164 mmol) at −78 °C was treated with [NiCl2(dme)] (35 mg, 0.159 mmol). The mixture was stirred for 16 h while it was warmed to ambient temperature. The solvent was removed in vacuo and the residue extracted with pentane to remove the lithium salt. Evaporation of the solvent and recrystallization from pentane at −30 °C afforded the product as green crystals in 50% yield (52 mg, 80 μmol). 1H NMR (400 MHz, C6D6, room temperature): δ 2.46 (s, 36 H, C(CH3)3), −239 (bs, 4 H, η5-C5H4), −253 ppm (bs, 4 H, η5-C5H4). Anal. Calcd: C, 47.84; H, 6.79. Found: C, 48.44; H, 6.96. Synthesis of [Co(η5-C5H4)2(Sn2tBu4)][PF6] ([1][PF6]). Compound 1 (20 mg, 31 μmol) and [FeCp2][PF6] (10 mg, 30 μmol) were dissolved in 1 mL of benzene at room temperature, and the mixture was stirred for 2 h. The solvent was evaporated and the solid residue washed with pentane (5 × 1 mL). Recrystallization from benzene (or toluene) gave [1][PF6] as a yellow-green solid in 70% yield (17 mg, 21 μmol). 1H NMR (400 MHz, C6D6, room temperature): δ 5.74 (s, 4 H, η5-C5H4), 5.31 (s, 4 H, η5-C5H4), 1.21 ppm (s, 36 H, C(CH3)3, 3JSnH = 71, 74 Hz). 13C NMR (100 MHz, C6D6, room temperature): δ 99.4, 91.5, 87.4, 34.0, 32.5 ppm. 19F NMR (376 MHz, C6D6, room temperature): δ −70.0 ppm (d, 1JPF = 710 Hz). 31P NMR (162 MHz, C6D6, room temperature): δ −143 ppm (sept, 1JPF = 711 Hz). 119Sn NMR (149 MHz, C6D6, room temperature): δ −3.2 ppm (s, 1JSnSn = 680 Hz). Synthesis of [Ni(η5-C5H4)2(Sn2tBu4)][PF6] ([2][PF6]). [2][PF6] was prepared by using the same procedure as for compound [1][PF6]. Complex 2 (20 mg, 31 μmol) and [FeCp2][PF6] (10 mg, 30 μmol) were dissolved in benzene (1 mL), and the mixture was stirred for 2 h at room temperature. The solvent was removed and the residue washed five times with pentane (1 mL). Recrystallization from toluene afforded the product as a dark brown solid in 71% yield (17 mg, 21 μmol). 1H NMR (400 MHz, C6D6, room temperature): δ 1.72 (s, 36 H, C(CH3)3), −49.0 (bs, 4 H, η5-C5H4), −115 ppm (bs, 4 H, η5C5H4). 19F NMR (376 MHz, C6D6, room temperature): δ −70.0 ppm (d, 1JPF = 711 Hz). 31P NMR (162 MHz, C6D6, room temperature): δ −140 ppm (sept, 1JPF = 711 Hz). Anal. Calcd: C, 39.15; H, 5.56. Found: C, 39.91; H, 5.31. X-ray Crystallographic Studies. The crystal data of 1, [1][PF6], 2, and [2][PF6] were collected on a Bruker X8APEX diffractometer with a CCD area detector and multilayer mirror monochromated Mo Kα radiation. The structure was solved using direct methods, refined with the Shelx software package, and expanded using Fourier techniques.26 All non-hydrogen atoms were refined anisotropically. Hydrogen atoms were included in structure factor calculations. All hydrogen atoms were assigned to idealized geometric positions. Crystal data for 1: C26H44CoSn2, Mr = 652.92, red block, 0.34 × 0.326 × 0.095 mm3, monoclinic space group P21/n, a = 16.7838(15) Å, b = 9.1993(8) Å, c = 18.4042(16) Å, β = 110.145(3)°, V = 2667.8(4) Å3, Z = 4, ρcalcd = 1.626 g cm−3, μ = 2.482 mm−1, F(000) = 1308, T = 100(2) K, R1 = 0.0273, wR2 = 0.0570, 5722 independent reflections (2θ ≤ 53.70°), 274 parameters. Crystal data for [1][PF6]: C26H44CoF6PSn2, Mr = 797.89, yellow block, 0.11 × 0.095 × 0.03 mm3, orthorhombic space group Pna21, a = 37.404(3) Å, b = 17.1777(13) Å, c = 9.5402(7) Å, V = 6129.8(8) Å3, Z = 8, ρcalcd = 1.729 g cm−3, μ = 2.255 mm−1, F(000) = 3168, T = 100(2) K, R1 = 0.0387, wR2 = 0.0551, 12547 independent reflections (2θ ≤ 53.56°), 674 parameters. Crystal data for 2: C26H44NiSn2, Mr = 652.70, green block, 0.24 × 0.21 × 0.10 mm3, monoclinic space group P21/n, a = 16.7500(10) Å, b = 9.2037(6) Å, c = 18.4955(11) Å, β = 110.252(3)°, V = 2675.0(3) Å3, Z = 4, ρcalcd = 1.621 g cm−3, μ = 2.559 mm−1, F(000) = 1312, T = 100(2) K, R1 = 0.0174, wR2 = 0.0368, 5703 independent reflections (2θ ≤ 53.56°), 274 parameters. Crystal data for [2][PF6]: C32H50F6NiPSn2, Mr = 875.78, red plate, 0.17 × 0.17 × 0.03 mm3, monoclinic space group P21/c, a = 16.5462(11) Å, b = 11.9479(8) Å, c = 18.1212(13) Å, β = 102.818(2)°, V = 3493.1(4) Å3, Z = 4, ρcalcd = 1.665 g cm−3, μ =

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ASSOCIATED CONTENT

* Supporting Information S

CIF files and figures giving crystallographic and NMR spectroscopic data for all compounds. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail for H.B.: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG). REFERENCES

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(11) Braunschweig, H.; Breher, F.; Kaupp, M.; Gross, M.; Kupfer, T.; Nied, D.; Radacki, K.; Schinzel, S. Organometallics 2008, 27, 6427. (12) Braunschweig, H.; Gross, M.; Radacki, K. Organometallics 2007, 26, 6688. (13) Pagels, N.; Prosenc, M. H.; Heck, J. Organometallics 2011, 30, 1968. (14) Trtica, S.; Meyer, E.; Prosenc, M. H.; Heck, J.; Böhnert, T.; Görlitz, D. Eur. J. Inorg. Chem. 2012, 4486. (15) Only selected references are given. For an ansa bridge containing nitrogen, see: Plenio, H.; Burth, D. Angew. Chem., Int. Ed. Engl. 1995, 34, 800. For a triatomic B−X−B bridge (X = F, Cl), see: Herberich, G. E.; Englert, U.; Fischer, A.; Wiebelhaus, D. Eur. J. Inorg. Chem. 2004, 4011. For a recent example of an ansa bridge containing a metal atom, see: Liu, N.; Li, X.; Xu, X.; Wang, Z.; Sun, H. Dalton Trans. 2011, 40, 6886. (16) Arnold, T.; Braunschweig, H.; Damme, A.; Krummenacher, I.; Radacki, K. Organometallics 2014, 33, 254. (17) Bera, H.; Braunschweig, H.; Oechsner, A.; Seeler, F.; Sigritz, R. J. Organomet. Chem. 2010, 695, 2609. (18) The values relative to the saturated calomel electrode (SCE) were converted to ferrocene values by subtracting 0.307 V. See: Geiger, W. E. J. Am. Chem. Soc. 1974, 96, 2632. (19) The electrode potentials vs Ag/AgCl were converted to ferrocene values by subtracting 0.352 V. See ref 7. (20) The one-bond tin−tin coupling constant of [1][PF6] is similar to those for related group 4 distanna[2]metallocenophanes (1J(SnSn) = 850−900 Hz)16 but differs from that of distanna[2]ferrocenophane (1J(SnSn) = 1698 Hz).17 (21) To the best of our knowledge, only one bis(cyclopentadienyl) nickel(IV) complex has proven isolable. See: Robbins, J. L.; Edelstein, N.; Spencer, B.; Smart, J. C. J. Am. Chem. Soc. 1982, 104, 1882. (22) Hyperfine couplings to the protons of the Cp rings were not detected, as well as possible splittings owing to the tin atoms of the ansa bridge. (23) Ammeter, J. H.; Swalen, J. D. J. Chem. Phys. 1972, 57, 678. (24) Baltzer, P.; Furrer, A.; Hulliger, J.; Stebler, A. Inorg. Chem. 1988, 27, 1543 and references therein. (25) Trtica, S. Thesis, University of Hamburg, 2011. (26) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, A64, 112. (27) Fowles, G. W. A.; Rice, D. A.; Walton, R. A. J. Inorg. Nucl. Chem. 1969, 31, 3119. (28) Ward, L. G. L.; Pipal, J. R. Inorg. Synth. 1972, 13, 154. (29) Stoll, S.; Schweiger, A. J. Magn. Reson. 2006, 178, 42.

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Metallocenes of the Late Transition Metals Cobalt ... - ACS Publications

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