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Crystal structure of N,N,N′,N′-tetra­methyl­ethane­di­amine

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aTechnische Universität Dortmund, Fakultät Chemie und Chemische Biologie, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
*Correspondence e-mail: carsten.strohmann@tu-dortmund.de

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 17 November 2021; accepted 23 November 2021; online 1 January 2022)

The title compound N,N,N′,N′-tetra­methyl­ethanedi­amine, C6H16N2, is a bidentate amine ligand commonly used in organolithium chemistry for deaggregation. Crystals were grown at 243 K from n-pentane solution. The complete mol­ecule is generated by a crystallographic center of symmetry and the conformation of the di­amine is anti­periplanar. To investigate the inter­molecular inter­actions, a Hirshfeld surface analysis was performed. It showed that H⋯H (van der Waals) inter­actions dominate with a contact percentage of 92.3%.

1. Chemical context

N,N,N′,N′-tetra­methyl­ethanedi­amine (TMEDA, C6H16N2, 1) consists of two tertiary amine groups linked by an ethyl­ene bridge. It can be used in cross-coupling or in olefin polymerization reactions where, e.g., a complex between di­methyl­nickel and TMEDA is used as a catalyst (Göttker-Schnetmann & Mecking, 2020[Göttker-Schnetmann, I. & Mecking, S. (2020). Organometallics, 39, 3433-3440.]). However, TMEDA is most commonly used in the chemistry of organolithium compounds. The lithium–carbon bond is characterized by its high polarity, as it contains a cationic lithium and carbanionic residues. These organolithium compounds form unreactive aggregates in non-polar solvents, which can be deaggregated by adding Lewis-basic ligands (Gessner et al., 2009[Gessner, V. H., Däschlein, C. & Strohmann, C. (2009). Chem. Eur. J. 15, 3320-3334.]). Compound 1 can be used as such a ligand, which can either chelate the metal center to form commonly dimeric structures or bridge two or more metal centers to form coordination polymers. The dimeric structural motif can be obtained in the butyl lithium TMEDA complex (Nichols & Williard, 1993[Nichols, M. A. & Williard, P. G. (1993). J. Am. Chem. Soc. 115, 1568-1572.]), the enolate structure (Nichols et al., 2007[Nichols, M. A., Leposa, C. M., Hunter, A. D. & Zeller, M. (2007). J. Chem. Crystallogr. 37, 825-829.]) and in the phen­yl(ethyn­yl) lithium (Schubert & Weiss, 1983[Schubert, B. & Weiss, E. (1983). Chem. Ber. 116, 3212-3215.]), whereas the lithium diiso­propyl­amide forms a polymeric structure with 1 bridging the lithium amide groups (Bernstein et al., 1992[Bernstein, M. P., Romesberg, F. E., Fuller, D. J., Harrison, A. T., Collum, D. B., Liu, Q. Y. & Williard, P. G. (1992). J. Am. Chem. Soc. 114, 5100-5110.]) (see scheme). The main benefit of deaggregation is the increased reactivity of organolithium compounds. Accompanying with smaller aggregates, the carbanionic center is more accessible for substrates due to an available coordination site at the metal center (Gessner et al., 2009[Gessner, V. H., Däschlein, C. & Strohmann, C. (2009). Chem. Eur. J. 15, 3320-3334.]). In the case of sterically more demanding ligands, however, the reactivity can even be reduced, since the coordination site at the lithium center can be sterically shielded (Knauer et al., 2019[Knauer, L., Wattenberg, J., Kroesen, U. & Strohmann, C. (2019). Dalton Trans. 48, 11285-11291.]). Quantum chemical considerations of aggregation and deaggregation require knowledge of the energetically most favorable conformer. With knowledge about this conformer, quantum chemical equilibria can be used to calculate reasonable energies, for example to predict the reactivity or the formation of certain aggregates.

[Scheme 1]

2. Structural commentary

Compound 1 crystallizes from n-pentane solution at 243 K in the monoclinic crystal system in space group P21/c. The asymmetric unit consists of half of the mol­ecule, with the other half generated by crystallographic inversion symmetry. The mol­ecular structure of 1 is presented in Fig. 1[link] and selected bond angles are given in Table 1[link]. The bond lengths for 1 are typical for C—C and C—N bonds and show no irregularities. The ethyl­ene fragment is arranged in a staggered conformation where the nitro­gen atoms are arranged in an anti­periplanar arrangement with N1—C3—C3i—N1i [symmetry code: (i) −x, 1 − y, 1 − z] = 180.0° by symmetry. The conformations of the C1—N1—C3—C3i and C2—N1—C3—C3i groupings are anti [torsion angle = 167.33 (6)°] and gauche [–71.17 (8)°], respectively.

Table 1
Comparison of the bond angles (°) between the crystal structure and the quantum computed structure.

Atoms Crystal structure Calculated
C2—N1—C1 109.26 (5) 110.29
C2—N1—C3 111.96 (5) 110.26
N1—C3—C3′ 112.37 (6) 112.32
[Figure 1]
Figure 1
Crystal structure of 1 showing 50% displacement ellipsoids. Symmetry code: (i) −x, 1 − y, 1 − z.

A quantum chemical geometry optimization was performed at the M062X/6-31+G(d,p) (Walker et al., 2013[Walker, M., Harvey, A. J. A., Sen, A. & Dessent, C. E. H. (2013). J. Phys. Chem. A, 117, 12590-12600.]) theory level using Gaussian 16 (Frisch et al., 2016[Frisch, M. J., Trucks, G. W., Schlegel, H. B., Scuseria, G. E., Robb, M. A., Cheeseman, J. R., Scalmani, G., Barone, V., Petersson, G. A., Nakatsuji, H., Li, X., Caricato, M., Marenich, A. V., Bloino, J., Janesko, B. G., Gomperts, R., Mennucci, B., Hratchian, H. P., Ortiz, J. V., Izmaylov, A. F., Sonnenberg, J. L., Williams-Young, D., Ding, F., Lipparini, F., Egidi, F., Goings, J., Peng, B., Petrone, A., Henderson, T., Ranasinghe, D., Zakrzewski, V. G., Gao, J., Rega, N., Zheng, G., Liang, W., Hada, M., Ehara, M., Toyota, K., Fukuda, R., Hasegawa, J., Ishida, M., Nakajima, T., Honda, Y., Kitao, O., Nakai, H., Vreven, T., Throssell, K., Montgomery, J. A. Jr, Peralta, J. E., Ogliaro, F., Bearpark, M. J., Heyd, J. J., Brothers, E. N., Kudin, K. N., Staroverov, V. N., Keith, T. A., Kobayashi, R., Normand, J., Raghavachari, K., Rendell, A. P., Burant, J. C., Iyengar, S. S., Tomasi, J., Cossi, M., Millam, J. M., Klene, M., Adamo, C., Cammi, R., Ochterski, J. W., Martin, R. L., Morokuma, K., Farkas, O., Foresman, J. B. & Fox, D. J. (2016). Gaussian 16. Revision C01. Gaussian Inc., Wallingford, CT, USA. https://www.gaussian.com.]). The calculated geometry is shown in Fig. 2[link] and the bond angles are shown in Table 1[link]. The angles of C2—N1—C1 and C2—N1—C3 differ by about 1° between the crystal structure and the quantum chemical calculated structure. Since these are gas phase calculations, this difference can be neglected. However, the N1—C3—C3 bond angles are in the same range. Therefore, we may assume that the presented conformation is at a local energy minimum.

[Figure 2]
Figure 2
Structure of 1 obtained by geometry optimization at the M062X/6–31+g(d,p) theory level.

3. Supra­molecular features

The crystal packing of compound 1 is shown in Fig. 3[link]. For the investigation of close contacts and inter­molecular inter­actions, a Hirshfeld surface analysis (Spackman & Jayatilaka, 2009[Spackman, M. A. & Jayatilaka, D. (2009). CrystEngComm, 11, 19-32.]) was carried out: Fig. 4[link] illustrates the Hirshfeld surface mapped over dnorm in the range from −0.072 to 1.201 arbitrary units and the related fingerprint plots generated by CrystalExplorer (Spackman et al., 2021[Spackman, P. R., Turner, M. J., McKinnon, J. J., Wolff, S. K., Grimwood, D. J., Jayatilaka, D. & Spackman, M. A. (2021). J. Appl. Cryst. 54, 1006-1011.]; McKinnon et al., 2007[McKinnon, J. J., Jayatilaka, D. & Spackman, M. A. (2007). Chem. Commun. pp. 3814-3816.]). Weak van der Waals H⋯H contacts are the largest region (92.3%). The remaining 6.7% are generated by N⋯H contacts, whereby C⋯H contacts do not contribute to crystal packing. In addition, no red spots are visible, which leads to the conclusion that the packing of the crystal is caused only by van der Waals inter­actions. The absence of packing effects such as hydrogen bonds also suggests that the most energetically favorable conformer is present.

[Figure 3]
Figure 3
A view along the b-axis direction of the crystal packing of 1.
[Figure 4]
Figure 4
Two-dimensional fingerprint plots of 1, (a) showing all contributions, (b) showing the H/H contributions and (c) showing the contributions of nitro­gen and hydrogen (blue areas). The corresponding surfaces obtained by Hirshfeld surface analysis are also displayed.

4. Database survey

There are a large number of compounds where 1 is used as a ligand. Selected examples found in the Cambridge Structural Database (CSD, version 5.41, update of May 2020; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) include dilithium bis­(tri­methyl­sil­yl)-o-xylene bis(tetra­methyl­ethanedi­amine) (CSD refcode BECWEL; Lappert et al., 1982[Lappert, M. F., Raston, C. L., Skelton, B. W. & White, A. H. (1982). J. Chem. Soc. Chem. Commun. pp. 14-15.]), allyl lithium N,N,N′,N′-tetra­methyl­ethanedi­amine (BITNEX; Köster & Weiss, 1982[Köster, H. & Weiss, E. (1982). Chem. Ber. 115, 3422-3426.]), tetra­sodium tetra­kis­(tetra­methyl­ethylenedi­amine) octa­chloro­ditungsten (BORZUD; Cotton et al., 1982[Cotton, F. A., Mott, G. N., Schrock, R. R. & Sturgeoff, L. G. (1982). J. Am. Chem. Soc. 104, 6781-6782.]), sodium (2,2,6,6-tetra­methyl­piperidin-1-ide)ferrocenyl-t-butyl-zinc N,N,N′,N′-tetra­methyl­ethane-1,2-di­amine solvate (BUQJII; Clegg et al., 2015[Clegg, W., Crosbie, E., Dale-Black, S. H., Hevia, E., Honeyman, G. W., Kennedy, A. R., Mulvey, R. E., Ramsay, D. L. & Robertson, S. D. (2015). Organometallics, 34, 2580-2589.]), hexa­kis­(μ2-meth­yl)-tris­(tetra­methyl­ethylenedi­amine­lithium)methyl­thorium(IV) tetra­methyl­ethylenedi­amine (COSZOZ; Lauke et al., 1984[Lauke, H., Swepston, P. J. & Marks, T. J. (1984). J. Am. Chem. Soc. 106, 6841-6843.]), dilithium tri­benzyl­idene­methane bis­(tetra­methyl­ethylenedi­amine) (COZJUW; Wilhelm et al., 1984[Wilhelm, D., Dietrich, H., Clark, T., Mahdi, W., Kos, A. J., Schleyer, P. v. R. (1984). J. Am. Chem. Soc. 106, 7279-7280.]), cyclo­penta­dienyl sodium tetra­methyl­ethylenedi­amine (CPNATM10; Aoyagi et al., 1979[Aoyagi, T., Shearer, H. M., Wade, K. & Whitehead, G. (1979). J. Organomet. Chem. 175, 21-31.]).

Since 1 plays a major role in organolithium chemistry, it also finds application in the group of Strohmann et al. Thus, some publications are included here: t-butyl lithium N,N,N′,N′-tetra­methyl­ethanedi­amine (Gessner & Strohmann, 2008[Gessner, V. H. & Strohmann, C. (2008). J. Am. Chem. Soc. 130, 14412-14413.]), isopropyl lithium N,N,N′,N′-tetra­methyl­ethanedi­amine (Stroh­mann et al., 2008[Strohmann, C., Gessner, V. H. & Damme, A. (2008). Chem. Commun. pp. 3381-3383.]), (di­ethyl­amino)­diphenyl­sil­yl) N,N,N′,N′-tetra­methyl­ethanedi­amine (Strohmann et al., 2006[Strohmann, C., Däschlein, C. & Auer, D. (2006). J. Am. Chem. Soc. 128, 704-705.]), [(R)-({[(S)-2-(meth­oxy­meth­yl)pyrrolidin-1-yl]meth­yl}di­meth­yl­sil­yl)(phen­yl)meth­yl]lithium N,N,N′,N′-tetra­methyl­ethane­di­amine (Strohmann et al., 2003[Strohmann, C., Buchold, D. H. M., Seibel, T., Wild, K. & Schildbach, D. (2003). Chem. Ber. pp. 3453-3463.]), methyl lithium N,N,N′,N′-tetra­methyl­ethanedi­amine (Gessner et al., 2011[Gessner, V. H., Koller, S. G., Strohmann, C., Hogan, A.-M. & O'Shea, D. F. (2011). Chemistry, 17, 2996-3004.]) and zinc bromide N,N,N′,N′-tetra­methyl­ethanedi­amine (Eckert et al., 2013[Eckert, P. K., Vieira, I., Gessner, V. H., Börner, J., Strohmann, C. & Herres-Pawlis, S. (2013). Polyhedron, 49, 151-157.]).

5. Synthesis and crystallization

N,N,N′,N′-Tetra­methyl­ethanedi­amine (C6H16N2, 1) was purchased by Sigma-Aldrich and was used without further purification. A solution of TMEDA (0.5 mmol) in n-pentane (1 ml) was prepared at 243 K and 1 crystallized in the form of colorless blocks.

6. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. For both compounds, the H atoms were positioned geometrically (C—H = 0.95–1.00 Å) and refined using a riding model, with Uiso(H) = 1.2Ueq(C) for CH2 and CH hydrogen atoms and Uiso(H) = 1.5Ueq(C) for CH3 hydrogen atoms.

Table 2
Experimental details

Crystal data
Chemical formula C6H16N2
Mr 116.21
Crystal system, space group Monoclinic, P21/c
Temperature (K) 100
a, b, c (Å) 5.6987 (13), 8.311 (2), 8.453 (2)
β (°) 106.954 (9)
V3) 382.92 (18)
Z 2
Radiation type Mo Kα
μ (mm−1) 0.06
Crystal size (mm) 0.56 × 0.35 × 0.30
 
Data collection
Diffractometer Bruker Venture D8
Absorption correction Multi-scan (SADABS; Krause et al., 2015[Krause, L., Herbst-Irmer, R., Sheldrick, G. M. & Stalke, D. (2015). J. Appl. Cryst. 48, 3-10.])
Tmin, Tmax 0.371, 0.567
No. of measured, independent and observed [I > 2σ(I)] reflections 16732, 1720, 1434
Rint 0.037
(sin θ/λ)max−1) 0.813
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.038, 0.110, 1.05
No. of reflections 1720
No. of parameters 39
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.41, −0.15
Computer programs: APEX2 and SAINT (Bruker, 2018[Bruker (2018). APEX2 and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]), SHELXT (Sheldrick, 2015a[Sheldrick, G. M. (2015a). Acta Cryst. A71, 3-8.]), SHELXL2014/7 (Sheldrick, 2015b[Sheldrick, G. M. (2015b). Acta Cryst. C71, 3-8.]) and OLEX2 (Dolomanov et al., 2009[Dolomanov, O. V., Bourhis, L. J., Gildea, R. J., Howard, J. A. K. & Puschmann, H. (2009). J. Appl. Cryst. 42, 339-341.]).

Supporting information


Computing details top

Data collection: APEX2 (Bruker, 2018); cell refinement: SAINT (Bruker, 2018); data reduction: SAINT (Bruker, 2018); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2014/7 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

N,N,N',N'-Tetramethylethane-1,2-diamine top
Crystal data top
C6H16N2F(000) = 132
Mr = 116.21Dx = 1.008 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
a = 5.6987 (13) ÅCell parameters from 352 reflections
b = 8.311 (2) Åθ = 3.5–22.8°
c = 8.453 (2) ŵ = 0.06 mm1
β = 106.954 (9)°T = 100 K
V = 382.92 (18) Å3Block, colourless
Z = 20.56 × 0.35 × 0.30 mm
Data collection top
Bruker Venture D8
diffractometer
1720 independent reflections
Radiation source: microfocus sealed X-ray tube, Incoatec Iµs1434 reflections with I > 2σ(I)
HELIOS mirror optics monochromatorRint = 0.037
Detector resolution: 10.4167 pixels mm-1θmax = 35.3°, θmin = 3.5°
φ and ω scansh = 99
Absorption correction: multi-scan
(SADABS; Krause et al., 2015)
k = 1313
Tmin = 0.371, Tmax = 0.567l = 1213
16732 measured reflections
Refinement top
Refinement on F2Primary atom site location: dual
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.038H-atom parameters constrained
wR(F2) = 0.110 w = 1/[σ2(Fo2) + (0.0452P)2 + 0.073P]
where P = (Fo2 + 2Fc2)/3
S = 1.05(Δ/σ)max < 0.001
1720 reflectionsΔρmax = 0.41 e Å3
39 parametersΔρmin = 0.15 e Å3
0 restraints
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
N10.25269 (10)0.34528 (6)0.53636 (6)0.01749 (12)
C10.49338 (12)0.33807 (9)0.65977 (9)0.02394 (15)
H1A0.57940.44040.66080.036*
H1B0.58960.25050.63200.036*
H1C0.47250.31850.76920.036*
C20.12526 (13)0.19303 (8)0.53563 (9)0.02363 (14)
H2A0.09760.17640.64360.035*
H2B0.22530.10480.51340.035*
H2C0.03280.19550.44940.035*
C30.11367 (10)0.48144 (7)0.57161 (7)0.01782 (13)
H3A0.22070.57760.59520.021*
H3B0.06310.45730.67160.021*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
N10.0167 (2)0.0154 (2)0.0197 (2)0.00035 (16)0.00420 (16)0.00150 (16)
C10.0170 (3)0.0261 (3)0.0265 (3)0.0025 (2)0.0028 (2)0.0043 (2)
C20.0244 (3)0.0157 (3)0.0297 (3)0.0014 (2)0.0063 (2)0.0015 (2)
C30.0176 (2)0.0163 (2)0.0174 (2)0.00014 (19)0.00177 (17)0.00102 (18)
Geometric parameters (Å, º) top
N1—C11.4624 (9)C2—H2A0.9800
N1—C21.4580 (9)C2—H2B0.9800
N1—C31.4610 (8)C2—H2C0.9800
C1—H1A0.9800C3—C3i1.5246 (12)
C1—H1B0.9800C3—H3A0.9900
C1—H1C0.9800C3—H3B0.9900
C2—N1—C1109.26 (5)N1—C2—H2C109.5
C2—N1—C3111.96 (5)H2A—C2—H2B109.5
C3—N1—C1109.75 (5)H2A—C2—H2C109.5
N1—C1—H1A109.5H2B—C2—H2C109.5
N1—C1—H1B109.5N1—C3—C3i112.37 (6)
N1—C1—H1C109.5N1—C3—H3A109.1
H1A—C1—H1B109.5N1—C3—H3B109.1
H1A—C1—H1C109.5C3i—C3—H3A109.1
H1B—C1—H1C109.5C3i—C3—H3B109.1
N1—C2—H2A109.5H3A—C3—H3B107.9
N1—C2—H2B109.5
C1—N1—C3—C3i167.33 (6)N1—C3—C3i—N1i180.0
C2—N1—C3—C3i71.17 (8)
Symmetry code: (i) x, y+1, z+1.
Comparison of the bond angles (°) between the crystal structure and the quantum computed structure. top
AtomsCrystal structureCalculated
C2—N1—C1109.26 (5)110.29
C2—N1—C3111.96 (5)110.26
N1—C3—C3'112.37 (6)112.32
 

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