(η⁴-Cyclo­octa­tetra­ene)(η⁸-cyclo­octa­tetra­ene)iodido­tantalum(V)

The title complex, [Ta(η⁴-C₈H₈)(η⁸-C₈H₈)I], lies across a crystallographic mirror plane that includes the Ta^V 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.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](C-C) = 0.007 Å
• Disorder in main residue
• R factor = 0.017
• wR factor = 0.040
• Data-to-parameter ratio = 16.9

checkCIF/PLATON results

No syntax errors found



Alert level A
PLAT015_ALERT_5_A No _shelx_hkl_file record in SHELXL20xy CIF ...      Please Do !

Alert level C
PLAT242_ALERT_2_C Low       Ueq as Compared to Neighbors for .....        Ta1 Check
PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ....        2.6 Note

Alert level G
PLAT005_ALERT_5_G No _iucr_refine_instructions_details  in the CIF     Please Do !
PLAT083_ALERT_2_G SHELXL Second Parameter in WGHT Unusually Large.       5.32 Why ?
PLAT232_ALERT_2_G Hirshfeld Test Diff (M-X)  Ta1    --  I1      ..        9.0 su
PLAT301_ALERT_3_G Main Residue  Disorder ............ Percentage =         44 Note

Author Response: The \h^8^-cot ligand is modeled as disordered over a crystallographic mirror plane (50:50).

PLAT811_ALERT_5_G No ADDSYM Analysis: Too Many Excluded Atoms ....          ! Info
PLAT860_ALERT_3_G Number of Least-Squares Restraints .............         96 Note

Author Response: Bond lengths and angles in the \h^8^-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.

   1 ALERT level A = Most likely a serious problem - resolve or explain
   0 ALERT level B = A potentially serious problem, consider carefully
   2 ALERT level C = Check. Ensure it is not caused by an omission or oversight
   6 ALERT level G = General information/check it is not something unexpected

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   4 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   3 ALERT type 5 Informative message, check

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S1. Comment

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).

Related literature

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).

S2. Experimental

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]. Cation exchange 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.

S3. 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 U_iso(H) = 1.2U_eq(C).

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: 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).

Figures

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.

(η⁴-Cyclooctatetraene)(η⁸-cyclooctatetraene)iodidotantalum(V)

Crystal data

[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) Å^3	Block, red-purple
Z = 4	0.10 × 0.10 × 0.10 mm

Data collection

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

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.017	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.040	H-atom parameters constrained
S = 1.08	w = 1/[σ^2(Fo^2) + (0.018P)^2 + 5.3173P] where P = (Fo^2 + 2Fc^2)/3
1636 reflections	(Δ/σ)max = 0.003
97 parameters	Δρmax = 1.04 e Å^−3
96 restraints	Δρmin = −0.72 e Å^−3

Special details

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 U_iso(H) = 1.2U_eq(C).

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	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

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
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)

Geometric parameters (Å, º)

Ta1—C1	2.290 (3)	C3—H3	0.9500
Ta1—C1^i	2.290 (3)	C4—C4^i	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—C2^i	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—C1^i	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—C1^i	35.6 (2)	C7—Ta1—I1	151.54 (19)
C1—Ta1—C6	109.2 (3)	C11—Ta1—I1	77.9 (2)
C1^i—Ta1—C6	141.1 (2)	C8—Ta1—I1	163.56 (16)
C1—Ta1—C9	132.6 (3)	C12—Ta1—I1	73.25 (16)
C1^i—Ta1—C9	106.3 (3)	C2—Ta1—I1	101.77 (9)
C6—Ta1—C9	89.0 (3)	C2^i—Ta1—I1	101.77 (9)
C1—Ta1—C5	121.5 (3)	C2—C1—C1^i	130.4 (2)
C1^i—Ta1—C5	155.1 (3)	C2—C1—Ta1	84.5 (2)
C6—Ta1—C5	34.1 (2)	C1^i—C1—Ta1	72.20 (10)
C9—Ta1—C5	98.3 (3)	C2—C1—H1	114.8
C1—Ta1—C10	148.7 (2)	C1^i—C1—H1	114.8
C1^i—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
C1^i—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—C4^i	132.7 (3)
C1^i—Ta1—C11	130.1 (2)	C3—C4—H4	113.7
C6—Ta1—C11	88.8 (3)	C4^i—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
C1^i—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)
C1^i—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
C1^i—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—C2^i	62.58 (13)	C9—C10—Ta1	72.7 (6)
C1^i—Ta1—C2^i	32.60 (13)	C11—C10—Ta1	75.1 (6)
C6—Ta1—C2^i	136.4 (2)	C9—C10—H10	113.0
C9—Ta1—C2^i	74.0 (3)	C11—C10—H10	113.0
C5—Ta1—C2^i	169.2 (3)	Ta1—C10—H10	135.0
C10—Ta1—C2^i	88.2 (2)	C10—C11—C12	135.4 (8)
C7—Ta1—C2^i	106.0 (2)	C10—C11—Ta1	71.5 (5)
C11—Ta1—C2^i	116.8 (2)	C12—C11—Ta1	74.2 (5)
C8—Ta1—C2^i	82.4 (2)	C10—C11—H11	112.3
C12—Ta1—C2^i	149.84 (18)	C12—C11—H11	112.3
C2—Ta1—C2^i	77.28 (17)	Ta1—C11—H11	141.1
C1—Ta1—I1	76.97 (9)	C11—C12—C5	133.7 (8)
C1^i—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
C1^i—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)
C1^i—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—C4^i	−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.