Bis(μ-2-tert-butyl­phenyl­imido-1:2κ2 N:N)chlorido-2κCl-(diethyl ether-1κO)(2η5-penta­methyl­cyclo­penta­dien­yl)lithiumtantalum(V)

Jacqueline M Cole; Michael C W Chan; Vernon C Gibson; Judith A K Howard

doi:10.1107/S1600536811015650

. 2011 May 7;67(Pt 6):m688–m689. doi: 10.1107/S1600536811015650

Bis(μ-2-tert-butylphenylimido-1:2κ² N:N)chlorido-2κCl-(diethyl ether-1κO)(2η⁵-pentamethylcyclopentadienyl)lithiumtantalum(V)

Jacqueline M Cole ^a,^*,^‡, Michael C W Chan ^b, Vernon C Gibson ^c, Judith A K Howard ^d

PMCID: PMC3120624 PMID: 21754594

Abstract

In the title compound, [LiTa(C₁₀H₁₅)(C₁₀H₁₃N)₂Cl(C₄H₁₀O)], the Ta^V atom is coordinated by a η⁵-pentamethylcyclopentadienyl (Cp*) ligand, a chloride ion and two N-bonded 2-tert-butylphenylimide dianions. With respect to the two N atoms, the chloride ion and the centroid of the Cp* ring, the tantalum coordination geometry is approximately tetrahedral. The lithium cation is bonded to both the 2-tert-butylphenylimide dianions and also a diethyl ether molecule, in an approximate trigonal planar arrangement. The Ta⋯Li separation is 2.681 (15) Å. In the crystal, a weak C—H⋯Cl interaction links the molecules. When compared to the 2,6-diisopropylphenylimide analogue (‘the Wigley derivative’) of the title compound, the two structures are conformationally matched with an overall r.m.s. difference of 0.461Å.

Related literature

For related work demonstrating the stabilization of unusual imido metal species via 2,6-diisopropylphenyl substitution, see: Cockcroft et al. (1992 ▶); Glueck et al. (1991 ▶); Anhaus et al. (1990 ▶); Gibson & Poole (1995 ▶); Baldwin et al. (1993 ▶). For conformational analysis of structures, see: Weng et al. (2008 ▶). For van der Waals contact distances, see: Bondi (1964 ▶). For crystal mounting techniques, see: Kottke & Stalke (1993 ▶).

Experimental

Crystal data

[LiTa(C₁₀H₁₅)(C₁₀H₁₃N)₂Cl(C₄H₁₀O)]
M _r = 727.11
Orthorhombic,
a = 19.5365 (12) Å
b = 16.3544 (10) Å
c = 21.3272 (13) Å
V = 6814.2 (7) Å³
Z = 8
Mo Kα radiation
μ = 3.33 mm⁻¹
T = 150 K
0.60 × 0.34 × 0.16 mm

Data collection

Siemens SMART CCD diffractometer
Absorption correction: multi-scan (SADABS; Siemens, 1995 ▶) T _min = 0.346, T _max = 0.666
24495 measured reflections
4848 independent reflections
4792 reflections with I > 2σ(I)
R _int = 0.060
θ_max = 23.3°

Refinement

R[F ² > 2σ(F ²)] = 0.053
wR(F ²) = 0.105
S = 1.23
4848 reflections
337 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 1.29 e Å⁻³
Δρ_min = −0.95 e Å⁻³

Data collection: SMART (Siemens, 1995 ▶); cell refinement: SAINT (Siemens, 1995 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS86 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL93 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶) and Mercury (Macrae et al., 2008 ▶); software used to prepare material for publication: SHELXL93.

Supplementary Material

Crystal structure: contains datablocks I, global. DOI: 10.1107/S1600536811015650/hb5832sup1.cif

e-67-0m688-sup1.cif^{(27.6KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811015650/hb5832Isup2.hkl

e-67-0m688-Isup2.hkl^{(237.6KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected bond lengths (Å).

Ta1—N1	1.842 (6)
Ta1—N2	1.854 (6)
Ta1—Cl1	2.3985 (19)
Li1—N1	2.048 (16)
Li1—N2	2.062 (16)
Li1—O1	1.910 (19)

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Table 2. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C12—H12A⋯Cl1ⁱ	0.95	2.89	3.593 (8)	132

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Symmetry code: (i) Inline graphic .

Acknowledgments

All authors would like to thank the University of Durham for provision of all experimentation carried out in this study. JMC expresses her thanks to the Institut Laue Langevin, Grenoble, France, and the EPSRC, for financial support; the Royal Society for a University Research Fellowship and the University of New Brunswick for the UNB Vice-Chancellor’s Research Chair. MCWC wishes to thank the Research Grants Council of the Hong Kong SAR, China (CityU 100307) for financial support.

supplementary crystallographic information

Comment

The bulky 2,6-diisopropylphenyl substituent has been investigated widely in transition metal imido chemistry, and has been shown to stabilize a variety of unusual imido metal species (Cockcroft et al., 1992; Glueck et al., 1991; Anhaus et al., 1990; Gibson & Poole, 1995). The presence of two bulky ortho isopropyl substituents undoubtedly plays an important role in this stabilization. Imido aryl substituents containing one bulky substituent in the ortho position also offer the possibility for substantial steric protection, not only due to the presence of the large substituent but also as a result of bending at the imido nitrogen. We have thus studied the bis (2 - t-butylphenylimido) chloro (η⁵-pentamethylcyclopentadienyl) tantalum(V) anion (I) with a view to comparing its structure with its previously reported 2,6-diisopropylphenylimido analogue (II) (Baldwin et al., 1993).

The 50% probability thermal ellipsoid plot of the molecular structure of (I) is given in Figure 1. Selected bond distances and angles are given in Table 1. Fractional coordinates and anisotropic displacement parameters are provided in supplementary material.

The overall bond geometry of the title compound is generally similar to its 2,6-diisopropylphenylimido analogue. In particular, the Ta(1)—N(1) and Ta(1)—N(2) distances and Ta(1)—N(1)—C(11) and Ta(1)—N(2)—C(21) angles are comparable [1.844 (6) Å, 1.848 (6) Å, 165.9 (5)° and 161.7 (5)° repectively].

However, several geometrical differences exist between the two compounds as a result of the presence of a more bulky aryl imido substituent in this case.

In the 2,6-diisopropylphenylimido structure, the planes of the arylimido and Cp* rings are approximately parallel to each other to minimize steric repulsion between the respective isopropyl and methyl groups. The situation for the 2 - t-butylphenylimido congener is comparable, except that the single bulky tert-butyl substituent on each imido ligand is now positioned in a less congested orientation away from the [µ-Li(OEt₂)]+ moiety, such that they point in a similar direction to the Ta—Cl vector.

This steric alleviation is shown in Figure 2, which also illustrates the overall conformational difference between the two structures. This structure overlay was generated by matching the following respective atom pairs in each molecule: Ta, N, Li, O, Cp* and phenyl C atoms (Weng et al., 2008). These atoms are conformationally matched with an overall root-mean-square difference of 0.461 Å. The geometric differences between the tert-butyl and disopropyl phenyl substituents are emphasized by the visual offset to this conformationally matched molecular fragment. A full list of individual atomic pairwise deviations from a perfect match is given in supplementary information.

The Ta(1)—Li(1) distance of 2.68 (1)Å is slightly longer than in the Wigley derivative, being the only other reported. We presume that this is also consequent upon the greater steric repulsion from the tertiary butyl groups compared to the isopropyl groups of the phenylimido ligands.

The atoms in the OEt₂ fragment of the subject compound display large isotropic displacement parameters. Given the terminal nature of this fragment, significant thermal motion is likely the cause, although positional disorder cannot be excluded. In contrast, the analogous displacement parameters in the Wigley derivative appear regular, being comparable in size to other terminal carbon atoms in the main part of the structure.

The structure of (I) contains a weak C12—H12A···Cl1 interaction [H···Cl = 2.89 (2) Å, symmetry code: 3/2 - x, 1/2 + y, z; c.f. sum of van der Waals radii of H and Cl = 2.95 Å (Bondi, 1964)]. This links adjacent molecules forming chains which are almost parallel to the y-axis (see Figure 3). Adjacent chains are arranged anti-parallel to each other thus completing the three-dimensional structure. In contrast, no hydrogen-bonds or short non-bonded contacts are present in the diisopropylphenyl structure, as deduced from a search in Materials Mercury (Macrae et al., 2008).

Experimental

A solution of LiNH(2-^tBuC₆H₄) (1.717 g, 11.07 mmol) in Et₂O (80 ml) was added dropwise to a stirred solution of Cp*TaCl₄ (1.267 g, 2.77 mmol) in Et₂O (80 ml) at 0 °C. This mixture was allowed to warm up to room temperature and stirred for 24 h. The resultant yellow/brown solution was filtered from the white residue of LiCl, concentrated and cooled to -30 °C to yield long yellow crystals of (I) (yield: 1.47 g, 73%).

Elemental analysis for C₃₄H₅₁N₂OClLiTa (727.14) found (required): %C = 56.17 (56.16), %H = 7.10 (7.07), %N = 3.82 (3.85).

Mass Spectrometry data (EI, m/z, ³⁵Cl): 646 [M - LiOEt₂]⁺.

¹H NMR data (400 MHz, C₆D₆, 298 K): 0.57 (broad t, OCH₂CH₃), 1.62 (s, 18H, CMe₃), 2.08 (s, 15H, C₅Me₅), 2.69 (broad q, OCH₂CH₃), 6.64 (d, ²H, J = 7.6 Hz, H³), 6.70, 7.05 (two t, 4H, J = 7.4 Hz, H⁴ and H⁵), 7.32 (d, 2H, J = 7.8 Hz, H⁶).

¹³C NMR data (100 MHz, C₆D₆, 298 K): 11.2 (q, J = 127 Hz, C₅Me₅), 14.4 (q, J = 127 Hz, OCH₂CH₃), 29.6 (q, J = 125 Hz, CMe₃), 35.7 (s, CMe₃), 64.6 (t, J = 143 Hz, OCH₂CH₃), 116.7 (s, C₅Me₅), 118.9, 125.3, 126.3, 126.9 (doublets, J = 154–159 Hz, C^3–6), 140.5 (s, C²), 158.9 (s, C¹).