research communications
N,N,N′,N′-tetramethylethanediamine
ofaTechnische Universität Dortmund, Fakultät Chemie und Chemische Biologie, Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
*Correspondence e-mail: carsten.strohmann@tu-dortmund.de
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%.
Keywords: crystal structure; Hirshfeld surface analysis; bidentate ligand.
CCDC reference: 2123810
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). 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). 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), the enolate structure (Nichols et al., 2007) and in the phenyl(ethynyl) lithium (Schubert & Weiss, 1983), whereas the lithium diisopropylamide forms a polymeric structure with 1 bridging the lithium amide groups (Bernstein et al., 1992) (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). 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). 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.
2. Structural commentary
Compound 1 crystallizes from n-pentane solution at 243 K in the monoclinic in P21/c. The 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 and selected bond angles are given in Table 1. 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 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.
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A quantum chemical geometry optimization was performed at the M062X/6-31+G(d,p) (Walker et al., 2013) theory level using Gaussian 16 (Frisch et al., 2016). The calculated geometry is shown in Fig. 2 and the bond angles are shown in Table 1. The angles of C2—N1—C1 and C2—N1—C3 differ by about 1° between the 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.
3. Supramolecular features
The crystal packing of compound 1 is shown in Fig. 3. For the investigation of close contacts and intermolecular interactions, a Hirshfeld surface analysis (Spackman & Jayatilaka, 2009) was carried out: Fig. 4 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; McKinnon et al., 2007). 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.
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) include dilithium bis(trimethylsilyl)-o-xylene bis(tetramethylethanediamine) (CSD refcode BECWEL; Lappert et al., 1982), allyl lithium N,N,N′,N′-tetramethylethanediamine (BITNEX; Köster & Weiss, 1982), tetrasodium tetrakis(tetramethylethylenediamine) octachloroditungsten (BORZUD; Cotton et al., 1982), 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), hexakis(μ2-methyl)-tris(tetramethylethylenediaminelithium)methylthorium(IV) tetramethylethylenediamine (COSZOZ; Lauke et al., 1984), dilithium tribenzylidenemethane bis(tetramethylethylenediamine) (COZJUW; Wilhelm et al., 1984), cyclopentadienyl sodium tetramethylethylenediamine (CPNATM10; Aoyagi et al., 1979).
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), isopropyl lithium N,N,N′,N′-tetramethylethanediamine (Strohmann et al., 2008), (diethylamino)diphenylsilyl) N,N,N′,N′-tetramethylethanediamine (Strohmann et al., 2006), [(R)-({[(S)-2-(methoxymethyl)pyrrolidin-1-yl]methyl}dimethylsilyl)(phenyl)methyl]lithium N,N,N′,N′-tetramethylethanediamine (Strohmann et al., 2003), methyl lithium N,N,N′,N′-tetramethylethanediamine (Gessner et al., 2011) and zinc bromide N,N,N′,N′-tetramethylethanediamine (Eckert et al., 2013).
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 . 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.
details are summarized in Table 2Supporting information
CCDC reference: 2123810
https://doi.org/10.1107/S2056989021012457/hb8002sup1.cif
contains datablock I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989021012457/hb8002Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989021012457/hb8002Isup3.cml
Data collection: APEX2 (Bruker, 2018); cell
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).C6H16N2 | F(000) = 132 |
Mr = 116.21 | Dx = 1.008 Mg m−3 |
Monoclinic, P21/c | Mo Kα radiation, λ = 0.71073 Å |
a = 5.6987 (13) Å | Cell parameters from 352 reflections |
b = 8.311 (2) Å | θ = 3.5–22.8° |
c = 8.453 (2) Å | µ = 0.06 mm−1 |
β = 106.954 (9)° | T = 100 K |
V = 382.92 (18) Å3 | Block, colourless |
Z = 2 | 0.56 × 0.35 × 0.30 mm |
Bruker Venture D8 diffractometer | 1720 independent reflections |
Radiation source: microfocus sealed X-ray tube, Incoatec Iµs | 1434 reflections with I > 2σ(I) |
HELIOS mirror optics monochromator | Rint = 0.037 |
Detector resolution: 10.4167 pixels mm-1 | θmax = 35.3°, θmin = 3.5° |
φ and ω scans | h = −9→9 |
Absorption correction: multi-scan (SADABS; Krause et al., 2015) | k = −13→13 |
Tmin = 0.371, Tmax = 0.567 | l = −12→13 |
16732 measured reflections |
Refinement on F2 | Primary atom site location: dual |
Least-squares matrix: full | Hydrogen site location: inferred from neighbouring sites |
R[F2 > 2σ(F2)] = 0.038 | H-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 reflections | Δρmax = 0.41 e Å−3 |
39 parameters | Δρmin = −0.15 e Å−3 |
0 restraints |
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. |
x | y | z | Uiso*/Ueq | ||
N1 | 0.25269 (10) | 0.34528 (6) | 0.53636 (6) | 0.01749 (12) | |
C1 | 0.49338 (12) | 0.33807 (9) | 0.65977 (9) | 0.02394 (15) | |
H1A | 0.5794 | 0.4404 | 0.6608 | 0.036* | |
H1B | 0.5896 | 0.2505 | 0.6320 | 0.036* | |
H1C | 0.4725 | 0.3185 | 0.7692 | 0.036* | |
C2 | 0.12526 (13) | 0.19303 (8) | 0.53563 (9) | 0.02363 (14) | |
H2A | 0.0976 | 0.1764 | 0.6436 | 0.035* | |
H2B | 0.2253 | 0.1048 | 0.5134 | 0.035* | |
H2C | −0.0328 | 0.1955 | 0.4494 | 0.035* | |
C3 | 0.11367 (10) | 0.48144 (7) | 0.57161 (7) | 0.01782 (13) | |
H3A | 0.2207 | 0.5776 | 0.5952 | 0.021* | |
H3B | 0.0631 | 0.4573 | 0.6716 | 0.021* |
U11 | U22 | U33 | U12 | U13 | U23 | |
N1 | 0.0167 (2) | 0.0154 (2) | 0.0197 (2) | 0.00035 (16) | 0.00420 (16) | 0.00150 (16) |
C1 | 0.0170 (3) | 0.0261 (3) | 0.0265 (3) | 0.0025 (2) | 0.0028 (2) | 0.0043 (2) |
C2 | 0.0244 (3) | 0.0157 (3) | 0.0297 (3) | −0.0014 (2) | 0.0063 (2) | 0.0015 (2) |
C3 | 0.0176 (2) | 0.0163 (2) | 0.0174 (2) | 0.00014 (19) | 0.00177 (17) | −0.00102 (18) |
N1—C1 | 1.4624 (9) | C2—H2A | 0.9800 |
N1—C2 | 1.4580 (9) | C2—H2B | 0.9800 |
N1—C3 | 1.4610 (8) | C2—H2C | 0.9800 |
C1—H1A | 0.9800 | C3—C3i | 1.5246 (12) |
C1—H1B | 0.9800 | C3—H3A | 0.9900 |
C1—H1C | 0.9800 | C3—H3B | 0.9900 |
C2—N1—C1 | 109.26 (5) | N1—C2—H2C | 109.5 |
C2—N1—C3 | 111.96 (5) | H2A—C2—H2B | 109.5 |
C3—N1—C1 | 109.75 (5) | H2A—C2—H2C | 109.5 |
N1—C1—H1A | 109.5 | H2B—C2—H2C | 109.5 |
N1—C1—H1B | 109.5 | N1—C3—C3i | 112.37 (6) |
N1—C1—H1C | 109.5 | N1—C3—H3A | 109.1 |
H1A—C1—H1B | 109.5 | N1—C3—H3B | 109.1 |
H1A—C1—H1C | 109.5 | C3i—C3—H3A | 109.1 |
H1B—C1—H1C | 109.5 | C3i—C3—H3B | 109.1 |
N1—C2—H2A | 109.5 | H3A—C3—H3B | 107.9 |
N1—C2—H2B | 109.5 | ||
C1—N1—C3—C3i | 167.33 (6) | N1—C3—C3i—N1i | 180.0 |
C2—N1—C3—C3i | −71.17 (8) |
Symmetry code: (i) −x, −y+1, −z+1. |
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 |
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