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metal-organic compounds
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access(η4-Cyclooctatetraene)(η8-cyclooctatetraene)iodidotantalum(V)
aDepartment of Chemistry, 207 Pleasant Street SE, University of Minnesota, Minneapolis, MN 55455, USA
*Correspondence e-mail: brennessel@chem.rochester.edu
The title complex, [Ta(η4-C8H8)(η8-C8H8)I], lies across a crystallographic mirror plane that includes the TaV atom and the iodide ligand. One cyclooctatetraene (cot) ring is η4-coordinating and is bisected by the mirror plane. The fold angle between the plane of the coordinating butadiene portion and the middle plane of the ring is 27.4 (4)°. An additional minor fold angle of 9.3 (7)° exists between the final plane in the ring and the middle plane. The other cot ring is η8-coordinating and is also cut by the mirror plane. In this case, the ring is disordered over the mirror plane, and one position is modeled with appropriate restraints and constraints with respect to distances, angles and displacement parameters (the second position is generated by symmetry). This ring is nearly planar, with an r.m.s. deviation of only 0.05 Å when all eight C atoms are included in the calculation. Pairs of intermolecular η8-cot rings are parallel stacked and slightly off center, with a centroid–centroid distance of 3.652 Å. No other significant intermolecular interactions are observed. The compound is of interest as the first structurally characterized mixed halogen–cot complex of the group 5 metals and contains the longest terminal Ta—I distance [3.0107 (5) Å] reported to date.
CCDC reference: 1005544
Related literature
For synthesis of the precursor tris(naphthalene)tantalate, see: Brennessel et al. (2002![[Brennessel, W. W., Ellis, J. E., Pomije, M. K., Sussman, V. J., Urnezius, E. & Young, V. G. Jr (2002). J. Am. Chem. Soc. 124, 10258-10259.]](../../../../../../logos/arrows/e_arr.gif "Brennessel, W. W., Ellis, J. E., Pomije, M. K., Sussman, V. J., Urnezius, E. & Young, V. G. Jr (2002). J. Am. Chem. Soc. 124, 10258-10259.")
). For related MX(cot)2, M = Nb, Ta, X = Cl, Me, Ph, see: Schrock et al. (1976). For the only other structurally characterized η8-coordinated cyclooctatetraenetantalum species to date, (η-1,4-bis(trimethylsilyl)cot)Me3Ta, see: Clegg & McCamley (2005). For the compound containing the previous longest terminal Ta—I distance, see: Berneri et al. (1998). For Zr(cot)2, which also contains both η4-cot and η8-cot units, see: Cloke et al. (1994). For a description of the Cambridge Structural Database, see: Allen (2002).
![[Scheme 1]](lh5707scheme1.gif)
Experimental
Crystal data
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Data collection: SMART (Bruker, 2003); cell SAINT (Bruker, 2003); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL.
Supporting information
CCDC reference: 1005544
contains datablocks I, global. DOI: https://doi.org/10.1107/S1600536814012379/lh5707sup1.cif
Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S1600536814012379/lh5707Isup2.hkl
Under argon, a yellow-orange solution of [Na(THF)6][Ta(η4-C10H8)3] (Brennessel et al., 2002) in tetrahydrofuran (THF) was combined with three equiv. of 1,3,5,7-cyclooctatetraene (cot) at room temperature and stirred for 24 h to provide a deep purple solution of [Na(THF)x][Ta(cot)3]. of the latter (Brennessel et al., 2002) with bis(triphenylphosphine)iminium chloride, PPN+Cl-, in ethanol under argon, provided a purple-brown precipitate of [PPN][Ta(cot)3] in 67% yield. The latter was reacted with one equiv. of elemental iodine in THF at 205 K, followed by warming to room temperature over a four hour period. Following filtration to remove poorly soluble PPN+I-, a deep red-purple solid of composition TaI(cot)2 was isolated in 49% yield. 1H NMR (300 MHz, 298 K, THF-d8, δ, p.p.m.) 5.53 (s, 8H, cot), 6.27 (s, 8H, cot). Suitable single crystals of the product were grown from a pentane-layered THF solution over a period of several days at 273 K.
The η8-cot ligand is modeled as disordered over a crystallographic mirror plane (50:50). Bond lengths and angles in the η8-cot ligand were restrained to be similar to those of their neighbors. Anisotropic displacement parameters for pairs of atoms opposite to each other were constrained to be equivalent, and those of symmetry-related atom pair C11 and C12 were heavily restrained to be similar. H atoms were placed geometrically and treated as riding atoms: C—H = 0.95 Å with Uiso(H) = 1.2Ueq(C).
Bis(cyclooctatetraene)iodotantalum, TaI(cot)2, is the first structurally authenticated mixed halogen-cot complex of a group 5 metal (Fig. 1). In prior work, reaction of MCl5, M = Nb, Ta, with two equivalents of K2[cot] was suggested to afford the chloro analogs, MCl(cot)2 (Schrock et al., 1976). Although these compounds were not isolated or fully characterized in solution, the 1H NMR spectrum of the niobium complex in CD2Cl2 at 273 K showed two singlets in a 1:1 ratio at δ 5.49 and 6.24 p.p.m., in excellent agreement with those observed for TaI(cot)2 in THF-d8, see below. Thus, our study provides additional support for the existence of NbCl(cot)2 and TaCl(cot)2 and suggests that the latter contain η4– and η8-cot groups, as observed in TaI(cot)2. Structural features of the η4-cot group in TaI(cot)2 are nearly identical to the one present in [Ta(cot)3]1- (Brennessel et al., 2002). For example, the η4-cot-(centroid)-Ta distances in these two species are 2.023 and 2.025 Å, respectively. The only other structurally characterized η8-cot-Nb or –Ta complex for comparison is TaMe3(cot") (Clegg & McCamley, 2005), where cot" = 1,4-bis(trimethylsilyl)cyclooctatetraene, in which the η8-cot"-(centroid)-Ta distance, 1.627 Å, is slightly longer than the corresponding distance in TaI(cot)2, 1.606 Å, likely owing to the more bulky nature of cot" versus cot. The only surprising feature in the structure of TaI(cot)2 is the unusually long Ta–I distance of 3.0108 (5) Å, which exceeds the prior "record" value of 2.9621 (7) Å, observed in the 7-coordinate complex, TaI(CO)4(tmen), tmen = 1,2-bis(dimethylamino)ethane (Berneri et al., 1998). Because the η4 and η8 units in the formally Zr(IV) complex, Zr(cot)2 (Cloke et al., 1994) and TaI(cot)2 are quite analogous in structure and binding to the respective metals, the tantalum complex is best formulated to contain Ta(V).
For synthesis of the precursor tris(naphthalene)tantalate, see: Brennessel et al. (2002). For related MX(cot)2, M = Nb, Ta, X = Cl, Me, Ph, see: Schrock et al. (1976). For the only other structurally characterized octahapto-coordinated cyclooctatetraenetantalum species to date, (η-1,4-bis(trimethylsilyl)cot)Me3Ta, see: Clegg & McCamley (2005). For the compound containing the previous longest terminal Ta—I distance, see: Berneri et al. (1998). For Zr(cot)2, which also contains both η4-cot and η8-cot units, see: Cloke et al. (1994). For a description of the Cambridge Structural Database, see: Allen (2002).
Data collection: SMART (Bruker, 2003); cell SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).
![[Figure 1]](./lh5707fig1thm.gif) | Fig. 1. The structure of the molecule without hydrogen atoms, showing the atom numbering. Only one of the two positions of the disordered ligand is shown. Displacement ellipsoids are drawn at the 50% probability level. |
| [Ta(C8H8)2I] | F(000) = 952 |
| Mr = 516.14 | Dx = 2.527 Mg m−3 |
| Monoclinic, C2/m | Mo Kα radiation, λ = 0.71073 Å |
| a = 14.3626 (14) Å | Cell parameters from 937 reflections |
| b = 11.0200 (11) Å | θ = 2.4–27.5° |
| c = 9.3467 (9) Å | µ = 10.36 mm−1 |
| β = 113.522 (2)° | T = 173 K |
| V = 1356.4 (2) Å3 | Block, red-purple |
| Z = 4 | 0.10 × 0.10 × 0.10 mm |
| Siemens SMART CCD platform diffractometer | 1520 reflections with I > 2σ(I) |
| Radiation source: normal-focus sealed tube | Rint = 0.020 |
| ω scans | θmax = 27.5°, θmin = 2.4° |
| Absorption correction: multi-scan (SADABS; Sheldrick, 2012) | h = −18→18 |
| Tmin = 0.318, Tmax = 0.431 | k = −14→14 |
| 8110 measured reflections | l = −12→12 |
| 1636 independent reflections |
| Refinement on F2 | Primary atom site location: structure-invariant direct methods |
| Least-squares matrix: full | Secondary atom site location: difference Fourier map |
| R[F2 > 2σ(F2)] = 0.017 | Hydrogen site location: inferred from neighbouring sites |
| wR(F2) = 0.040 | H-atom parameters constrained |
| S = 1.08 | w = 1/[σ2(Fo2) + (0.018P)2 + 5.3173P] where P = (Fo2 + 2Fc2)/3 |
| 1636 reflections | (Δ/σ)max = 0.003 |
| 97 parameters | Δρmax = 1.04 e Å−3 |
| 96 restraints | Δρmin = −0.72 e Å−3 |
| [Ta(C8H8)2I] | V = 1356.4 (2) Å3 |
| Mr = 516.14 | Z = 4 |
| Monoclinic, C2/m | Mo Kα radiation |
| a = 14.3626 (14) Å | µ = 10.36 mm−1 |
| b = 11.0200 (11) Å | T = 173 K |
| c = 9.3467 (9) Å | 0.10 × 0.10 × 0.10 mm |
| β = 113.522 (2)° |
| Siemens SMART CCD platform diffractometer | 1636 independent reflections |
| Absorption correction: multi-scan (SADABS; Sheldrick, 2012) | 1520 reflections with I > 2σ(I) |
| Tmin = 0.318, Tmax = 0.431 | Rint = 0.020 |
| 8110 measured reflections |
| R[F2 > 2σ(F2)] = 0.017 | 96 restraints |
| wR(F2) = 0.040 | H-atom parameters constrained |
| S = 1.08 | Δρmax = 1.04 e Å−3 |
| 1636 reflections | Δρmin = −0.72 e Å−3 |
| 97 parameters |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
Refinement. The η8-cot ligand is modeled as disordered over a crystallographic mirror plane (50:50). Bond lengths and angles in the η8-cot ligand were restrained to be similar to those of their neighbors. Anisotropic displacement parameters for pairs of atoms opposite to each other were constrained to be equivalent, and those of symmetry-related atom pair C11 and C12 were heavily restrained to be similar. H atoms were placed geometrically and treated as riding atoms: C—H = 0.95 Å with Uiso(H) = 1.2Ueq(C). |
| x | y | z | Uiso*/Ueq | Occ. (<1) | |
| Ta1 | 0.28337 (2) | 0.5000 | 0.16766 (2) | 0.01915 (6) | |
| I1 | 0.26793 (2) | 0.5000 | −0.16320 (4) | 0.02953 (8) | |
| C1 | 0.1203 (2) | 0.4365 (4) | 0.0278 (4) | 0.0312 (8) | |
| H1 | 0.1043 | 0.4003 | −0.0715 | 0.037* | |
| C2 | 0.1398 (3) | 0.3549 (3) | 0.1493 (5) | 0.0356 (9) | |
| H2 | 0.1770 | 0.2859 | 0.1413 | 0.043* | |
| C3 | 0.1160 (3) | 0.3522 (4) | 0.2844 (5) | 0.0455 (11) | |
| H3 | 0.1214 | 0.2729 | 0.3271 | 0.055* | |
| C4 | 0.0875 (3) | 0.4358 (5) | 0.3660 (5) | 0.0531 (13) | |
| H4 | 0.0626 | 0.4012 | 0.4371 | 0.064* | |
| C5 | 0.4245 (10) | 0.3628 (8) | 0.2362 (15) | 0.039 (3) | 0.5 |
| H5 | 0.4396 | 0.2896 | 0.1962 | 0.047* | 0.5 |
| C6 | 0.3753 (8) | 0.3428 (9) | 0.3361 (12) | 0.038 (4) | 0.5 |
| H6 | 0.3574 | 0.2602 | 0.3398 | 0.046* | 0.5 |
| C7 | 0.3473 (7) | 0.4163 (9) | 0.4297 (10) | 0.042 (2) | 0.5 |
| H7 | 0.3298 | 0.3703 | 0.5013 | 0.050* | 0.5 |
| C8 | 0.3375 (6) | 0.5382 (8) | 0.4486 (9) | 0.042 (3) | 0.5 |
| H8 | 0.3127 | 0.5560 | 0.5266 | 0.051* | 0.5 |
| C9 | 0.3558 (12) | 0.6407 (8) | 0.3790 (17) | 0.039 (3) | 0.5 |
| H9 | 0.3318 | 0.7123 | 0.4097 | 0.047* | 0.5 |
| C10 | 0.4007 (7) | 0.6649 (8) | 0.2747 (12) | 0.038 (4) | 0.5 |
| H10 | 0.4011 | 0.7488 | 0.2518 | 0.046* | 0.5 |
| C11 | 0.4453 (7) | 0.5925 (8) | 0.1965 (11) | 0.042 (2) | 0.5 |
| H11 | 0.4749 | 0.6393 | 0.1400 | 0.050* | 0.5 |
| C12 | 0.4570 (5) | 0.4667 (6) | 0.1811 (8) | 0.042 (3) | 0.5 |
| H12 | 0.4949 | 0.4481 | 0.1208 | 0.051* | 0.5 |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| Ta1 | 0.01532 (9) | 0.02046 (10) | 0.01810 (10) | 0.000 | 0.00291 (7) | 0.000 |
| I1 | 0.03124 (17) | 0.03438 (18) | 0.02409 (16) | 0.000 | 0.01224 (13) | 0.000 |
| C1 | 0.0182 (15) | 0.045 (2) | 0.0268 (17) | −0.0062 (15) | 0.0053 (13) | −0.0106 (16) |
| C2 | 0.0215 (17) | 0.0272 (18) | 0.049 (2) | −0.0006 (14) | 0.0037 (16) | −0.0047 (16) |
| C3 | 0.0277 (19) | 0.047 (2) | 0.047 (2) | −0.0136 (18) | −0.0006 (18) | 0.020 (2) |
| C4 | 0.0250 (18) | 0.105 (4) | 0.027 (2) | −0.011 (2) | 0.0080 (16) | 0.017 (2) |
| C5 | 0.024 (6) | 0.055 (6) | 0.029 (6) | 0.012 (5) | 0.001 (3) | −0.019 (5) |
| C6 | 0.027 (9) | 0.027 (3) | 0.045 (13) | −0.007 (3) | −0.002 (5) | 0.008 (3) |
| C7 | 0.0205 (16) | 0.079 (8) | 0.0247 (18) | −0.008 (2) | 0.0078 (14) | 0.001 (2) |
| C8 | 0.0210 (15) | 0.079 (8) | 0.0248 (17) | −0.008 (2) | 0.0071 (13) | 0.000 (2) |
| C9 | 0.024 (6) | 0.055 (6) | 0.029 (6) | 0.012 (5) | 0.001 (3) | −0.019 (5) |
| C10 | 0.027 (9) | 0.027 (3) | 0.045 (13) | −0.007 (3) | −0.002 (5) | 0.008 (3) |
| C11 | 0.0205 (16) | 0.079 (8) | 0.0247 (18) | −0.008 (2) | 0.0078 (14) | 0.001 (2) |
| C12 | 0.0210 (15) | 0.079 (8) | 0.0248 (17) | −0.008 (2) | 0.0071 (13) | 0.000 (2) |
| Ta1—C1 | 2.290 (3) | C3—H3 | 0.9500 |
| Ta1—C1i | 2.290 (3) | C4—C4i | 1.416 (11) |
| Ta1—C6 | 2.359 (10) | C4—H4 | 0.9500 |
| Ta1—C9 | 2.397 (13) | C5—C6 | 1.396 (9) |
| Ta1—C5 | 2.402 (12) | C5—C12 | 1.410 (9) |
| Ta1—C10 | 2.408 (9) | C5—H5 | 0.9500 |
| Ta1—C7 | 2.429 (9) | C6—C7 | 1.365 (9) |
| Ta1—C11 | 2.454 (9) | C6—H6 | 0.9500 |
| Ta1—C8 | 2.459 (8) | C7—C8 | 1.369 (9) |
| Ta1—C12 | 2.474 (7) | C7—H7 | 0.9500 |
| Ta1—C2 | 2.560 (4) | C8—C9 | 1.381 (9) |
| Ta1—C2i | 2.560 (4) | C8—H8 | 0.9500 |
| Ta1—I1 | 3.0107 (5) | C9—C10 | 1.392 (9) |
| C1—C2 | 1.386 (5) | C9—H9 | 0.9500 |
| C1—C1i | 1.400 (8) | C10—C11 | 1.399 (9) |
| C1—H1 | 0.9500 | C10—H10 | 0.9500 |
| C2—C3 | 1.435 (6) | C11—C12 | 1.410 (9) |
| C2—H2 | 0.9500 | C11—H11 | 0.9500 |
| C3—C4 | 1.359 (7) | C12—H12 | 0.9500 |
| C1—Ta1—C1i | 35.6 (2) | C7—Ta1—I1 | 151.54 (19) |
| C1—Ta1—C6 | 109.2 (3) | C11—Ta1—I1 | 77.9 (2) |
| C1i—Ta1—C6 | 141.1 (2) | C8—Ta1—I1 | 163.56 (16) |
| C1—Ta1—C9 | 132.6 (3) | C12—Ta1—I1 | 73.25 (16) |
| C1i—Ta1—C9 | 106.3 (3) | C2—Ta1—I1 | 101.77 (9) |
| C6—Ta1—C9 | 89.0 (3) | C2i—Ta1—I1 | 101.77 (9) |
| C1—Ta1—C5 | 121.5 (3) | C2—C1—C1i | 130.4 (2) |
| C1i—Ta1—C5 | 155.1 (3) | C2—C1—Ta1 | 84.5 (2) |
| C6—Ta1—C5 | 34.1 (2) | C1i—C1—Ta1 | 72.20 (10) |
| C9—Ta1—C5 | 98.3 (3) | C2—C1—H1 | 114.8 |
| C1—Ta1—C10 | 148.7 (2) | C1i—C1—H1 | 114.8 |
| C1i—Ta1—C10 | 113.2 (2) | Ta1—C1—H1 | 118.6 |
| C6—Ta1—C10 | 99.5 (3) | C1—C2—C3 | 133.9 (4) |
| C9—Ta1—C10 | 33.7 (2) | C1—C2—Ta1 | 62.89 (19) |
| C5—Ta1—C10 | 89.3 (3) | C3—C2—Ta1 | 115.0 (2) |
| C1—Ta1—C7 | 110.4 (3) | C1—C2—H2 | 113.0 |
| C1i—Ta1—C7 | 125.5 (2) | C3—C2—H2 | 113.0 |
| C6—Ta1—C7 | 33.1 (2) | Ta1—C2—H2 | 92.4 |
| C9—Ta1—C7 | 63.2 (3) | C4—C3—C2 | 135.3 (4) |
| C5—Ta1—C7 | 63.4 (3) | C4—C3—H3 | 112.4 |
| C10—Ta1—C7 | 87.0 (3) | C2—C3—H3 | 112.4 |
| C1—Ta1—C11 | 154.0 (2) | C3—C4—C4i | 132.7 (3) |
| C1i—Ta1—C11 | 130.1 (2) | C3—C4—H4 | 113.7 |
| C6—Ta1—C11 | 88.8 (3) | C4i—C4—H4 | 113.7 |
| C9—Ta1—C11 | 63.9 (3) | C6—C5—C12 | 134.7 (8) |
| C5—Ta1—C11 | 64.5 (3) | C6—C5—Ta1 | 71.3 (5) |
| C10—Ta1—C11 | 33.4 (2) | C12—C5—Ta1 | 76.0 (6) |
| C7—Ta1—C11 | 95.0 (3) | C6—C5—H5 | 112.7 |
| C1—Ta1—C8 | 118.50 (19) | C12—C5—H5 | 112.7 |
| C1i—Ta1—C8 | 111.9 (2) | Ta1—C5—H5 | 136.9 |
| C6—Ta1—C8 | 63.8 (3) | C7—C6—C5 | 133.8 (8) |
| C9—Ta1—C8 | 33.0 (2) | C7—C6—Ta1 | 76.2 (6) |
| C5—Ta1—C8 | 87.1 (3) | C5—C6—Ta1 | 74.6 (6) |
| C10—Ta1—C8 | 63.7 (3) | C7—C6—H6 | 113.1 |
| C7—Ta1—C8 | 32.5 (2) | C5—C6—H6 | 113.1 |
| C11—Ta1—C8 | 86.0 (3) | Ta1—C6—H6 | 129.8 |
| C1—Ta1—C12 | 139.89 (19) | C6—C7—C8 | 137.5 (9) |
| C1i—Ta1—C12 | 148.81 (18) | C6—C7—Ta1 | 70.7 (6) |
| C6—Ta1—C12 | 64.7 (2) | C8—C7—Ta1 | 75.0 (6) |
| C9—Ta1—C12 | 87.5 (4) | C6—C7—H7 | 111.3 |
| C5—Ta1—C12 | 33.6 (2) | C8—C7—H7 | 111.3 |
| C10—Ta1—C12 | 64.3 (3) | Ta1—C7—H7 | 144.5 |
| C7—Ta1—C12 | 85.7 (3) | C7—C8—C9 | 133.9 (9) |
| C11—Ta1—C12 | 33.2 (2) | C7—C8—Ta1 | 72.5 (6) |
| C8—Ta1—C12 | 95.1 (2) | C9—C8—Ta1 | 71.0 (6) |
| C1—Ta1—C2 | 32.60 (13) | C7—C8—H8 | 113.1 |
| C1i—Ta1—C2 | 62.58 (13) | C9—C8—H8 | 113.1 |
| C6—Ta1—C2 | 78.9 (2) | Ta1—C8—H8 | 143.0 |
| C9—Ta1—C2 | 122.1 (2) | C8—C9—C10 | 135.7 (8) |
| C5—Ta1—C2 | 101.3 (2) | C8—C9—Ta1 | 76.0 (6) |
| C10—Ta1—C2 | 155.6 (2) | C10—C9—Ta1 | 73.6 (6) |
| C7—Ta1—C2 | 78.5 (3) | C8—C9—H9 | 112.2 |
| C11—Ta1—C2 | 165.8 (2) | C10—C9—H9 | 112.2 |
| C8—Ta1—C2 | 94.66 (19) | Ta1—C9—H9 | 134.1 |
| C12—Ta1—C2 | 132.81 (18) | C9—C10—C11 | 133.9 (9) |
| C1—Ta1—C2i | 62.58 (13) | C9—C10—Ta1 | 72.7 (6) |
| C1i—Ta1—C2i | 32.60 (13) | C11—C10—Ta1 | 75.1 (6) |
| C6—Ta1—C2i | 136.4 (2) | C9—C10—H10 | 113.0 |
| C9—Ta1—C2i | 74.0 (3) | C11—C10—H10 | 113.0 |
| C5—Ta1—C2i | 169.2 (3) | Ta1—C10—H10 | 135.0 |
| C10—Ta1—C2i | 88.2 (2) | C10—C11—C12 | 135.4 (8) |
| C7—Ta1—C2i | 106.0 (2) | C10—C11—Ta1 | 71.5 (5) |
| C11—Ta1—C2i | 116.8 (2) | C12—C11—Ta1 | 74.2 (5) |
| C8—Ta1—C2i | 82.4 (2) | C10—C11—H11 | 112.3 |
| C12—Ta1—C2i | 149.84 (18) | C12—C11—H11 | 112.3 |
| C2—Ta1—C2i | 77.28 (17) | Ta1—C11—H11 | 141.1 |
| C1—Ta1—I1 | 76.97 (9) | C11—C12—C5 | 133.7 (8) |
| C1i—Ta1—I1 | 76.97 (9) | C11—C12—Ta1 | 72.6 (5) |
| C6—Ta1—I1 | 118.5 (2) | C5—C12—Ta1 | 70.4 (6) |
| C9—Ta1—I1 | 132.5 (2) | C11—C12—H12 | 113.1 |
| C5—Ta1—I1 | 89.0 (3) | C5—C12—H12 | 113.1 |
| C10—Ta1—I1 | 100.3 (2) | Ta1—C12—H12 | 143.8 |
| C1i—C1—C2—C3 | 38.6 (5) | C7—C8—C9—C10 | −8 (3) |
| Ta1—C1—C2—C3 | 99.6 (4) | Ta1—C8—C9—C10 | −47.7 (16) |
| C1i—C1—C2—Ta1 | −60.97 (17) | C7—C8—C9—Ta1 | 39.5 (14) |
| C1—C2—C3—C4 | −18.5 (8) | C8—C9—C10—C11 | 1 (2) |
| Ta1—C2—C3—C4 | 57.1 (5) | Ta1—C9—C10—C11 | −47.7 (12) |
| C2—C3—C4—C4i | −13.5 (6) | C8—C9—C10—Ta1 | 48.4 (16) |
| C12—C5—C6—C7 | −7 (2) | C9—C10—C11—C12 | 6 (2) |
| Ta1—C5—C6—C7 | −52.8 (12) | Ta1—C10—C11—C12 | −41.4 (14) |
| C12—C5—C6—Ta1 | 46.1 (13) | C9—C10—C11—Ta1 | 47.0 (12) |
| C5—C6—C7—C8 | 14 (2) | C10—C11—C12—C5 | 3 (2) |
| Ta1—C6—C7—C8 | −37.9 (15) | Ta1—C11—C12—C5 | −38.2 (13) |
| C5—C6—C7—Ta1 | 52.2 (12) | C10—C11—C12—Ta1 | 40.7 (14) |
| C6—C7—C8—C9 | −2 (3) | C6—C5—C12—C11 | −6 (2) |
| Ta1—C7—C8—C9 | −39.1 (15) | Ta1—C5—C12—C11 | 38.8 (13) |
| C6—C7—C8—Ta1 | 36.9 (15) | C6—C5—C12—Ta1 | −44.7 (13) |
| Symmetry code: (i) x, −y+1, z. |
Experimental details
| Crystal data | |
| Chemical formula | [Ta(C8H8)2I] |
| Mr | 516.14 |
| Crystal system, space group | Monoclinic, C2/m |
| Temperature (K) | 173 |
| a, b, c (Å) | 14.3626 (14), 11.0200 (11), 9.3467 (9) |
| β (°) | 113.522 (2) |
| V (Å3) | 1356.4 (2) |
| Z | 4 |
| Radiation type | Mo Kα |
| µ (mm−1) | 10.36 |
| Crystal size (mm) | 0.10 × 0.10 × 0.10 |
| Data collection | |
| Diffractometer | Siemens SMART CCD platform |
| Absorption correction | Multi-scan (SADABS; Sheldrick, 2012) |
| Tmin, Tmax | 0.318, 0.431 |
| No. of measured, independent and observed [I > 2σ(I)] reflections | 8110, 1636, 1520 |
| Rint | 0.020 |
| (sin θ/λ)max (Å−1) | 0.649 |
| Refinement | |
| R[F2 > 2σ(F2)], wR(F2), S | 0.017, 0.040, 1.08 |
| No. of reflections | 1636 |
| No. of parameters | 97 |
| No. of restraints | 96 |
| H-atom treatment | H-atom parameters constrained |
| Δρmax, Δρmin (e Å−3) | 1.04, −0.72 |
Computer programs: SMART (Bruker, 2003), SAINT (Bruker, 2003), SHELXS97 (Sheldrick, 2008), SHELXL2014 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008).
Acknowledgements
This research was supported by the US National Science Foundation and the donors of the Petroleum Research Fund, administered by the American Chemical Society. PV thanks the University of Minnesota for an undergraduate research opportunity program (UROP) award.
References
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Bis(cyclooctatetraene)iodotantalum, TaI(cot)2, is the first structurally authenticated mixed halogen-cot complex of a group 5 metal (Fig. 1). In prior work, reaction of MCl5, M = Nb, Ta, with two equivalents of K2[cot] was suggested to afford the chloro analogs, MCl(cot)2 (Schrock et al., 1976). Although these compounds were not isolated or fully characterized in solution, the 1H NMR spectrum of the niobium complex in CD2Cl2 at 273 K showed two singlets in a 1:1 ratio at δ 5.49 and 6.24 p.p.m., in excellent agreement with those observed for TaI(cot)2 in THF-d8, see below. Thus, our study provides additional support for the existence of NbCl(cot)2 and TaCl(cot)2 and suggests that the latter contain η4– and η8-cot groups, as observed in TaI(cot)2. Structural features of the η4-cot group in TaI(cot)2 are nearly identical to the one present in [Ta(cot)3]1- (Brennessel et al., 2002). For example, the η4-cot-(centroid)-Ta distances in these two species are 2.023 and 2.025 Å, respectively. The only other structurally characterized η8-cot-Nb or –Ta complex for comparison is TaMe3(cot") (Clegg & McCamley, 2005), where cot" = 1,4-bis(trimethylsilyl)cyclooctatetraene, in which the η8-cot"-(centroid)-Ta distance, 1.627 Å, is slightly longer than the corresponding distance in TaI(cot)2, 1.606 Å, likely owing to the more bulky nature of cot" versus cot. The only surprising feature in the structure of TaI(cot)2 is the unusually long Ta–I distance of 3.0108 (5) Å, which exceeds the prior "record" value of 2.9621 (7) Å, observed in the 7-coordinate complex, TaI(CO)4(tmen), tmen = 1,2-bis(dimethylamino)ethane (Berneri et al., 1998). Because the η4 and η8 units in the formally Zr(IV) complex, Zr(cot)2 (Cloke et al., 1994) and TaI(cot)2 are quite analogous in structure and binding to the respective metals, the tantalum complex is best formulated to contain Ta(V).