Neutral and Cationic Zirconium Hydrides Supported by a Dianionic

Article pubs.acs.org/Organometallics

Neutral and Cationic Zirconium Hydrides Supported by a Dianionic (NNNN)-Type Macrocycle Ligand Heiko Kulinna, Thomas P. Spaniol, and Jun Okuda* Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1, D-52056 Aachen, Germany S Supporting Information *

ABSTRACT: Hydrogenation of bis(trimethylsilylmethyl) zirconium complex [Zr(Me2TACD)(CH2SiMe3)2] (1), prepared by reacting [Zr(CH2SiMe3)4] with 1,7-dimethyl-1,4,7,10tetraazacyclododecane (Me2TACD)H2, gave dinuclear alkyl hydride complex [Zr(Me2 TACD)(CH 2 SiMe 3 ) 2 (μ-H) 2 Zr(Me2TACD)] (2). According to NMR spectroscopic and single-crystal X-ray diffraction studies, 2 exhibits a Cs-symmetrical structure with two distinct zirconium centers, one eight- and the other seven-coordinate, bridged by an amido donor and two hydrides. Abstraction of the trimethylsilylmethyl groups by the weak Brønsted acid [NEt3H][B(3,5-C6H3Cl2)4] gave the monocationic mono(alkyl) dihydride [Zr(Me2TACD)(CH2SiMe3)(μ-H)2Zr(Me2TACD)][B(3,5-C6H3Cl2)4] (3) and the dicationic hydride complex [Zr(Me2TACD)(THF)2(μ-H)2Zr(Me2TACD)][B(3,5-C6H3Cl2)4]2 (4). X-ray crystallography of the cationic complexes 3 and 4 revealed a Cs-symmetrical dinuclear structure derived from that of 2.

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singlet at δ 2.29 ppm, and the CH2CH2 protons as multiplets of an ABCD spin pattern centered at δ 3.47, 2.41, and 2.23 ppm. The resonance for ZrCH2 was recorded at δ 0.16 and 41.6 ppm in the 1H and 13C NMR spectrum, respectively. According to the crystal structure, the coordination around the six-coordinate zirconium atom can be described as distorted trigonal prismatic (Figure 1). The Zr−N distances (Zr− N(amido) Zr1−N1: 2.1027(12), Zr1−N3: 2.0981(12) Å, Zr− N(amine) Zr1−N2: 2.4238(12), Zr1−N4: 2.4324(13) Å) are in the expected range of corresponding Zr−N distances (2.038(4)−2.242(4) Å for Zr−N(amido)9 and 2.377(4)− 2.977(1) Å for Zr−N(amine)9) for polydentate ligands with amine and amido donors. The angle at α-carbon atoms C11 and C15 of 113.96(7)° and 114.53(7)° do not indicate any distortion, as expected for the 16-electron zirconium center. The structure of 1 compares well with that of the cationic Me3TACD complex [Zr(Me3TACD)(CH2SiMe3)2][B(3,5C6H3Cl2)4]6 and the isoelectronic neutral rare-earth metal dialkyl complex [M(Me3TACD)(CH2SiMe3)2] (M = Sc,8d Y8e). When the dialkyl complex 1 was treated with 1 bar of dihydrogen in pentane, formation of mixed alkyl hydride complex 2 was observed with concomitant formation of only 1 equiv of SiMe4 per zirconium. The 1H NMR spectrum of 2 shows Cs-symmetry in solution, but two sets of Me2TACD ligands are recognized. Broad resonances for the CH2CH2 groups at room temperature indicate flexible behavior of the

INTRODUCTION Zirconium hydride complexes are important reagents in organic synthesis,1 reduce small molecules such as carbon monoxide,2 and activate dinitrogen.3 They exhibit a polarized metal hydride bond at a relatively strong Lewis acidic and oxophilic metal center that can be modulated by the ancillary ligand set. Whereas zirconocene hydrides4 and their derivatives have been extensively used,2a,i,3a,5 zirconium hydrides supported by hard donor ligand sets still remain relatively unexplored. They could be expected to exhibit reactivity patterns distinct from those reported for zirconocene hydrides.6 Recently, Fryzuk, Martins, et al. have introduced dianionic macrocyclic ligands based on cyclam7 as supporting ligands for neutral hydride complexes.3a We have reported (di)cationic zirconium hydride complexes that contain formally monoanionic (NNNN)-type macrocyclic ligands based on cyclen.6 Here we report the synthesis and characterization of a neutral dinuclear zirconium hydride complex stabilized by the dianionic macrocycle (Me2TACD)2− derived from 1,7-dimethyl-1,4,7,10-tetraazacyclododecane, (Me2TACD)H2. This L4X2-type or 12-electron-donor ligand has previously been shown to effectively support Lewis base free rare-earth metal alkyl and hydride compounds.8a−c

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RESULTS AND DISCUSSION Solvent-free bis(trimethylsilylmethyl) complex 1 was prepared in good yield by reacting light- and temperature-sensitive [Zr(CH2SiMe3)4] with (Me2TACD)H2 at room temperature in benzene and crystallized from pentane as relatively robust yellow crystals (Scheme 1). 1 was characterized by NMR spectroscopy and by single-crystal X-ray diffraction. The NMR spectra in benzene-d6 are consistent with C2v-symmetry. Both methyl groups of the Me2TACD ligand appear as a sharp © XXXX American Chemical Society

Special Issue: Mike Lappert Memorial Issue Received: August 11, 2014

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Scheme 1. Synthesis of 1, 2, 3, and 4 Starting from [Zr(CH2SiMe3)4] and (Me2TACD)H2a

a

A = B(3,5-C6H3Cl2)4−.

Figure 1. Molecular structure of 1 with displacement parameters at the 50% probability level. All hydrogen atoms are omitted for clarity.

Figure 2. Molecular structure of 2 with displacement parameters at the 50% probability level. All H atoms except for the bridging hydrides are omitted for clarity. Carbon atoms C12, C13, and C19 are shown with only one split position.

macrocyclic ligands. Further hydrogenation did not give any tractable compounds. Below 0 °C, the broad resonances become sharp and three singlet resonances at δ 3.02, 2.62, and 1.85 ppm (T = −20 °C) in a ratio of 3:6:3 for the methyl groups of Me2TACD are detected (Figure S1). This suggests that in one Me2TACD ligand, the two methyl groups are equivalent, whereas in the other the methyl groups are distinct, in agreement with the structure in the solid state (Figure 3). Above 0 °C, broad resonances for the second Me2TACD are observed, which become sharp again above 40 °C. We explain this by a rotation of one macrocycle, while the other remains tightly bonded to both metals via the amido bridge. The resonance for the hydride is detected at δ 5.52 ppm and appears to decoalesce below −60 °C, although clear low-temperature spectra could not be obtained even below −80 °C. We assume that more complicated dynamic processes occur at ambient temperature. They may include the presence of the monomer [Zr(Me2TACD)(CH2SiMe3)(H)], dissociation into ion pairs

[Zr(Me2TACD)(CH2SiMe3)]+[Zr(Me2TACD)(CH2SiMe3)(H)2]−,8c and other processes on the NMR time scale. A single-crystal X-ray structure of 2 confirms the presence of two distinct zirconium centers (Figure 2). The first zirconium center, Zr1, is coordinated to four nitrogen, two hydride, and two carbon atoms in a distorted square prismatic geometry. The second zirconium atom, Zr2, is bonded to five nitrogen and two hydride atoms, forming a distorted capped prism. The distance between both zirconium centers (Zr1···Zr2 3.2443(3) Å) is shorter than in other dimeric zirconium hydride complexes with two bridging hydride atoms and is comparable to [{(Me2N)3Zr(μ-NMe2)2(μ-H)}2Zr] (Zr···Zr: 3.2296(8), 3.2347(7) Å).10 The distances between zirconium and the amine groups (Zr1−N2 2.6004(14), Zr1−N4 2.5952(14), Zr2−N6 2.4161(13), Zr2−N8 2.4458(14) Å) are in the range of reported distances (Zr−N(amine) 2.377(4)−2.977(1) Å).9 The bond lengths between zirconium and the amido atom N1 B

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Figure 4. Molecular structure of the cationic part of 4 with displacement parameters at the 50% probability level. All H atoms except for the bridging hydride are omitted for clarity. Carbon atom C27 is shown with only one split position.

Figure 3. Molecular structure of the cationic part of 3 with displacement parameters at the 50% probability level. All H atoms except for the bridging hydrides are omitted for clarity. Carbon atoms C21, C22, and C23 are shown with only one split position.

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CONCLUSION Hydrogenolysis of the neutral zirconium dialkyl complex 1 supported by the macrocyclic dianionic Me2TACD ligand gave the neutral alkyl hydride complex. This complex unexpectedly is dinuclear with two zirconium centers bridged by two hydrides and an amido group of the Me2TACD ligand. This results in one fixed and one flexible coordination mode of the two macrocyclic ligands. Selective abstraction of the alkyl groups gave the mono- and dicationic dihydride complexes 3 and 4. The absence of coordinated THF in the monocationic monoalkyl dihydride complex results in a shorter Zr···Zr distance. Reactivity studies are currently under way.

indicate an unsymmetrical bridge (Zr1−N1 2.4440(13), Zr2− N1 2.2092(13) Å); both distances are longer than to the remaining amido groups (Zr1−N3 2.1282(14), Zr2−N5 2.1208(14), Zr2−N7 2.1046(14) Å), which are in the expected range (Zr−N(amido): 2.038(4)−2.242(4) Å).9 Abstraction of one alkyl group from 2 with 1 equiv of the Brønsted acid [NEt3H][B(3,5-C6H3Cl2)4] resulted in the formation of cationic complex [Zr(Me2TACD)(CH2SiMe3)(μ-H)2Zr(Me2TACD)][B(3,5-C6H3Cl2)4] (3). The 1H NMR spectrum of 3 indicates dynamic behavior in solution with broad and sharp resonances for the two Me2TACD ligands (see the SI). Three sharp singlets for the methyl groups are observed below 0 °C, indicating a similar structure in solution to that found for 2. The resonance for the hydrides in 3 is shifted toward low field from 5.39 ppm in 2 to 5.74 ppm due to the cationic charge. According to a single-crystal X-ray structure determination of 3, the dinuclear structure is retained with one trimethylsilylmethyl ligand coordinated at one of the zirconium centers (Figure 3). The Zr···Zr distance of 3.2046(7) Å is shorter than in 2 (3.2443(3) Å). The Zr1−N1 bond distance is decreasing from 2.4440(13) Å to 2.308(4) Å, while the Zr2− N1 bond becomes longer. The cationic charge also explains the contraction of the Zr−C(alkyl) bonds (from 2.3818(16)− 2.3961(15) Å in 2 to 2.241(8) Å in 3). The fact that THF is not coordinated to Zr1 could indicate the stabilization by an agostic interaction11 of the alkyl group with Zr1. The Zr1− C21A−Si1 angle in 3 of 126.1(4)° (Zr1−C21B−Si1 135.2(9)°) is in the same range as in 2 (Zr1−C21−Si1 134.33(8)° and Zr1−C25−Si2 125.53(8)°), excluding a γ-agostic interaction.12 Further abstraction of the remaining alkyl group with the Brønsted acid [NEt3H][B(3,5-C6H3Cl2)4] led to the dicationic dimeric zirconium hydride [{Zr(Me2TACD)(μ-H)}2(THF)2][B(3,5-C6H3Cl2)4]2 (4). In the 1H NMR spectrum the hydride resonance is detected at δ 5.18 ppm due to the Lewis-donor effect of two coordinated THF molecules (see the SI). According to a single-crystal X-ray structure determination, the coordination geometry is similar to 2 and 3 (Figure 4). The distance between both zirconium atoms is virtually unchanged at 3.2488(6) Å. The distances between zirconium and the amine groups decrease from 2.4161(13)−2.6004(14) Å in 2 to 2.353(4)−2.437(4) Å in 3 to 2.420(4)−2.477(4) Å in the molecular dication 4.

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EXPERIMENTAL SECTION

General Considerations. All manipulations were performed under an inert atmosphere of argon using standard Schlenk-line or glovebox techniques. n-Pentane, THF, and Et2O were dried using an MBraun SPS-800 solvent purification system. Cyclohexane, toluene-d8, benzene-d6, and THF-d8 were distilled from sodium/benzophenone ketyl. (Me2TACD)H2,13 [Zr(CH2SiMe3)4],14 and [NEt3H][B(3,5C6H3Cl2)4]6,15 were synthesized according to the literature procedures. All reactions have been performed in the dark by covering all glass vessels with aluminum foil. Hydrogenolysis reactions were performed in a Parr steel reactor (series 4700) with up to 50 bar pressure or in J. Young NMR tubes equipped with a Teflon valve or in Schlenk flasks with 1 bar pressure. NMR spectra were recorded on a Bruker Avance II spectrometer at 25 °C (1H: 400.1 MHz, 13C{1H}: 100.1 MHz, 11B{1H}: 128.4 MHz), unless stated otherwise. Chemical shifts for 1H and 13C{1H} NMR spectra were referenced internally using the residual solvent resonances and reported relative to tetramethylsilane. Elemental analyses were performed by the microanalytical laboratory of this department. The analytical data for the neutral complexes 1 and 2 were consistently low in carbon. This is likely due to metal carbide formation during combustion. This phenomenon has been also observed by other groups for related zirconium complexes.9b,16 [Zr(Me2TACD)(CH2SiMe3)2] (1). A solution of (Me2TACD)H2 (500.0 mg, 2.5 mmol) in 5 mL of benzene was added to a solution of [Zr(CH2SiMe3)4] (1.098 g, 2.5 mmol) in 5 mL of benzene. The mixture was stirred for 1 h at room temperature. After the solvent was removed under reduced pressure, pale yellow crystals suitable for X-ray diffraction were obtained from a concentrated pentane solutions at −30 °C; yield 731 mg (1.58 mmol, 63%). 1H NMR (C6D6): δ 3.47 (m, 4H, CH2), 2.40 (m, 8H, CH2), 2.29 (s, 6H, CH3), 2.22 (m, 4H, CH2), 0.41 (s, 18H, CH3), 0.16 (s, 4H, ZrCH2) ppm. 13C{1H} NMR (C6D6): δ 59.7 (CH2), 54.6 (CH2), 45.4 (NCH3), 41.6 (ZrCH2), 3.7 C

dx.doi.org/10.1021/om500820k | Organometallics XXXX, XXX, XXX−XXX

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Diethyl ether was allowed to diffuse into the reaction mixture to give colorless crystals suitable for X-ray diffraction; yield: 183 mg (96 mmol, 73%). 1H NMR (THF-d8): δ 7.05 (m, 16H, Ph-2), 7.01 (t, 4JHH = 1.9 Hz, 8H, Ph-4), 5.19 (s, 2H, ZrH), 3.77 (m, 2H, CH2), 3.62 (m, 2H, CH2), 3.49 (m, 2H, CH2), 3.32 (m, 4H, CH2), 3.18 (m, 2H, CH2), 3.09 (m, 4H, CH2), 2.97 (m, 6H, CH2), 2.83 (s, 6H, CH3), 2.78 (m, 4H, CH2), 2.72 (s, 6H, CH3), 2.64 (m, 4H, CH2), 2.27 (m, 2H, CH2) ppm. 13C{1H} NMR (THF-d8): δ 165.6 (q, 1JBC = 49.4 Hz, Ph1), 134.1 (d, 2JBC = 1.3 Hz, Ph-2), 133.9 (m, Ph-4), 124.0 (s, Ph-3), 62.6 (s, CH2), 61.5 (s, CH2), 61.1 (s, CH2), 60.6 (s, CH2), 57.1 (s, CH2), 55.7 (s, CH2), 55.2 (s, CH2), 54.4 (s, CH2), 51.1 (s, CH3), 49.0 (br s, CH3) ppm. Anal. Calcd for C76H86B2Cl16N8O2Zr2: C, 47.67; H, 4.53; N, 5.85. Found: C, 48.19; H, 5.48 N, 5.58. Single-Crystal X-ray Structure Analysis of [Zr(Me2TACD)(CH 2 SiMe 3 ) 2 ] (1), [(Me 2 TACD)Zr(μ-H) 2 (μ-Me 2 TACD)Zr(CH 2 SiMe 3 ) 2 ] (2), [(Me 2 TACD)Zr(μ-H) 2 (μ-Me 2 TACD)Zr(CH2SiMe3)][B(3,5-C6H3Cl2)4] (3), and [{Zr(Me2TACD)(μ-H)}2(THF)2][B(3,5-C6H3Cl2)4]2 (4). X-ray diffraction data were collected on a Bruker CCD area-detector diffractometer at 100 K with Mo Kα radiation (graphite monochromator, λ = 0.710 73 Å) using ω scans. The SMART program package was used for the data collection and unit cell determination; processing of the raw frame data was performed using SAINT; absorption corrections were applied with SADABS. The structures were solved by direct methods. Refinement was performed against F2 using all reflections with the program SHELXL-97 as implemented in the program system WinGX. Several carbon atoms showed disorder that could be modeled well with split positions (C12, C13, and C19 in 2, C21, C22, and C23 in 3, as well as C27 in 4). Hydrogen atoms were included in calculated positions except for the hydrides in 2, 3, and 4 (H1 and H2), which were located in a difference Fourier map and refined in their positions. Compound 2 cocrystallizes with cyclohexane; compound 3 cocrystallizes with cyclohexane and thf. Distance restraints were used in the refinement of the disordered solvent molecules in 3. Details are given in the Supporting Information and are available free of charge via the Internet at http://pubs.acs.org (CCDC nos. 1018699−1018702).

(SiCH3) ppm. Anal. Calcd for C18H44N4Si2Zr: C, 46.60; H, 9.56; N, 12.08. Found: C, 34.70; H, 7.39; N, 11.95. [(Me2TACD)Zr(μ-H)2(μ-Me2TACD)Zr(CH2SiMe3)2] (2). A solution of 1 (500 mg, 1.08 mmol) in 10 mL of pentane was treated with dihydrogen (1 bar) for 24 h to give colorless crystals; yield: 320.0 mg (424 μmol, 78%). Single crystals suitable for X-ray diffraction experiments were obtained by hydrogenation in cyclohexane. 1H NMR (80 °C, toluene-d8): δ 5.52 (s, 2H, ZrH), 3.66 (td, 2JHH = 11.4 Hz, 3JHH = 7.1 Hz, 2H, CH2), 3.58 (dt, 2JHH = 11.1 Hz, 3JHH = 5.3 Hz, 4H, CH2), 3.38 (dd, 2JHH = 12.4 Hz, 3JHH = 6.8 Hz, 2H, CH2), 3.13 (ddd,, 2JHH = 13.2 Hz, 3JHH = 10.5 Hz, 3JHH = 3.0 Hz, 2H, CH2), 2.84 (m, 2H, CH2), 2.64 (m, 2H, CH2), 2.60 (s, 6H, CH3), 2.55 (m, 10H, CH3/CH2), 2.41 (t, 3JHH = 5.4 Hz, 8H, CH2), 2.19 (dt, 2JHH = 13.2 Hz, 3JHH = 3.9 Hz, 2H, CH2), 2.11 (m, 2H, CH2), 1.87 (ddd, 2JHH = 12.1 Hz, 3JHH = 4.1 Hz, 3JHH = 3.0 Hz, 2H, CH2), 0.40 (s, 18H, SiCH3), 0.38 (d, 2JHH = 11.2 Hz, 2H, ZrCH2), 0.03 (d, 2JHH = 11.3 Hz, 2H, ZrCH2) ppm. 1 H NMR (toluene-d8): δ 5.43 (s, 2H, ZrH), 3.69 (td, 2JHH = 11.5 Hz, 3JHH = 7.1 Hz, 3H, CH2), 3.50 (br s, 2H, CH2), 3.39 (dd, 2JHH = 12.3 Hz, 3JHH = 7.0 Hz, 3H, CH2), 3.02 (ddd, 2JHH = 13.1 Hz, 3JHH = 10.3 Hz, 3JHH = 2.9 Hz, 3H, CH2), 2.86 (td, 2JHH = 11.9 Hz, 3JHH = 5.9 Hz, 3H, CH2), 2.61 (s, 6H, CH3), 2.51 (br s, 7H, CH3/CH2), 2.32 (m, 5H, CH2), 2.12 (m, 2H, CH2), 1.98 (br s, 2H, CH2), 1.85 (dt, 2JHH = 11.8 Hz, 3JHH = 3.3 Hz, 2H, CH2), 0.51 (s, 18H, SiCH3), 0.43 (d, 2JHH = 11.2 Hz, 2H, ZrCH2), 0.06 (d, 2JHH = 11.2 Hz, 2H, ZrCH2) ppm. 13 C{1H} NMR (25 °C, C6D6): δ 61.5 (br s, CH2), 60.0 (br s, CH2), 59.3 (s, CH2), 58.9 (s, CH2), 57.1 (s, CH2), 55.6 (br s, CH3), 52.4 (s, CH2), 48.4 (s, CH3), 35.0 (s, ZrCH2), 5.9 (s, SiCH3) ppm. 1 H NMR (−20 °C, toluene-d8): δ 5.36 (s, 2H, ZrH), 3.73 (m, 4H, CH2), 3.40 (m, 4H, CH2), 3.02 (s, 3H, CH3), 2.90 (m, 4H, CH2), 2.62 (s, 6H, CH3), 2.54 (m, 6H, CH2), 2.40 (m, 2H, CH2), 2.24 (m, 4H, CH2), 2.04 (m, 6H, CH2), 1.85 (s, 3H, CH3), 1.84 (br s, 2H, CH2), 0.62 (s, 18H, SiCH3), 0.51 (d, 2JHH = 11.3 Hz, 2H, ZrCH2), 0.11 (d, 2 JHH = 11.3 Hz, 2H, ZrCH2) ppm. Anal. Calcd for C14H34N4SiZr: C, 44.51; H, 9.07; N, 14.85. Found: C, 36.42; H, 8.13; N, 15.51. [(Me2TACD)Zr(μ-H)2(μ-Me2TACD)Zr(CH2SiMe3)(THF)][B(3,5C6H3Cl2)4] (3). A solution of [NEt3H][B(3,5-C6H3Cl2)4] (91 mg, 130 μmol) in 2 mL of THF was added to a solution of 2 (100.0 mg, 132 μmol) in 2 mL of THF. A pentane layer was carefully added and allowed to diffuse into the reaction mixture at −30 °C to give colorless crystals; yield: 131 mg (98 μmol, 74%). Single crystals suitable for Xray diffraction were obtained by diffusion of cyclohexane into a THF solution. 1 H NMR (55 °C, THF-d8): δ 7.05 (m, 8H, Ph-2), 6.97 (t, 4JHH = 2.0 Hz, 4H, Ph-4), 5.78 (s, 2H, ZrH), 3.79 (m, 4H, CH2), 3.45 (m, 6H, CH2), 3.27 (m, 3H, CH2), 3.19 (3H, CH2), 3.07 (m, 6H, CH2), 2.97 (m, 4H, CH2), 2.90 (s, 6H, CH3), 2.89 (m, 2H, CH2), 2.81 (m, 3H, CH2) 2.79 (br s, 3H, CH3), 2.72 (m, 4H, CH2), 0.26 (s, 2H, ZrCH2), 0.00 (s, 9H, SiCH3) ppm. 1 H NMR (25 °C, THF-d8): δ 7.04 (m, 8H, Ph-2), 6.99 (t, 4JHH = 2.0 Hz, 4H, Ph-4), 5.74 (s, 2H, ZrH), 3.76 (br s, 6H, CH2), 3.43 (m, 6H, CH2), 3.23 (m, 6H, CH2), 3.06 (br s, 6H, CH3/CH2), 2.96 (m, 2H, CH2), 2.90 (s, 6H, CH3), 2.89 (br m, 4H, CH2), 2.71 (m, 4H, CH2), 2.50 (br s, 3H, CH3), 2.49 (br s, 1H, CH2), 0.23 (s, 2H, ZrCH2), 0.00 (s, 9H, SiCH3) ppm. 13C{1H} NMR (25 °C, THF-d8): δ 165.7 (q, 1JBC = 49.4 Hz, Ph-1),), 134.1 (d, 2JBC = 1.3 Hz, Ph-2), 133.9 (m, Ph-4), 123.9 (s, Ph-3), 63.0 (br s, CH2), 62.5 (s, CH2), 60.7 (br s, CH2), 59.2 (s, CH2), 56.2 (br s, CH2), 55.6 (s, CH2), 51.7 (s, CH3), 50.5 (s, CH2), 49.8 (s, ZrCH2), 46.0 (br s, CH3), 3.7 (s, SiCH3) ppm. 1 H NMR (−20 °C, THF-d8): δ 7.02 (m, 12H, Ph-2/4), 5.69 (s, 2H, ZrH), 3.75 (m, 4H, CH2), 3.43 (m, 5H, CH2), 3.24 (m, 4H, CH2), 3.10 (s, 3H, CH3), 3.06 (m, 6H, CH2), 2.97 (m, 4H, CH2), 2.89 (s, 6H, CH3), 2.87 (m, 4H, CH2), 2.71 (m, 5H, CH2), 2.51 (s, 3H, CH3), 0.19 (s, 2H, ZrCH2), −0.01 (s, 9H, SiCH3) ppm. Anal. Calcd for C52H76BCl8N8OSiZr2: C, 46.81; H, 5.74; N, 8.40. Found: C, 46.58; H, 6.06; N, 8.04. [{Zr(Me2TACD)(μ-H)}2(THF)2][B(3,5-C6H3Cl2)4]2 (4). A solution of [NEt3H][B(3,5-C6H3Cl2)4] (184 mg, 264 μmol) in 2 mL of THF was added to a solution of 2 (100 mg, 132 μmol) in 2 mL of THF.

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ASSOCIATED CONTENT

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AUTHOR INFORMATION

S Supporting Information *

CIF file giving crystallographic data for compounds 1, 2, 3, and 4. This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Author

*Fax: +49 241 92644. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We thank the Fonds der Chemischen Industrie and the Cluster of Excellence “Tailor Made Fuel from Biomass” for financial support. We thank Jacob B. Bilger for his experimental contribution.

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DEDICATION This work is dedicated to Mike Lappert, a great pioneer of organometallic chemistry. REFERENCES

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Organometallics

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dx.doi.org/10.1021/om500820k | Organometallics XXXX, XXX, XXX−XXX