N-(Diphenyl­vinyl­idene)-2,6-diisopropyl­aniline

Wolfgang Imhof

doi:10.1107/S1600536808040397

. 2008 Dec 6;65(Pt 1):o25. doi: 10.1107/S1600536808040397

N-(Diphenylvinylidene)-2,6-diisopropylaniline

Wolfgang Imhof ^a,^*

PMCID: PMC2967944 PMID: 21581668

Abstract

The title compound, C₂₆H₂₇N, was prepared by the elimination of water from N-(2,6-diisopropylphenyl)-2,2-diphenylacetamide. The angle at the central C atom of the cumulene measures 172.5 (4)°. Molecules are connected into infinite chains by intermolecular C—H⋯N interactions.

Related literature

For the synthetic procedure, see: Stevens & Singhal (1964 ▶). For related structures, see: Naqvi & Wheatley (1970 ▶); Jochims et al. (1984 ▶); Kuipers et al. (1989 ▶). For general background, see: Imhof (1997a ▶,b ▶). For properties of weak hydrogen bonds, see: Desiraju & Steiner (1999 ▶).

Experimental

Crystal data

C₂₆H₂₇N
M _r = 353.49
Orthorhombic,
a = 8.082 (4) Å
b = 14.308 (4) Å
c = 17.790 (2) Å
V = 2057 (1) Å³
Z = 4
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 173 (2) K
0.3 × 0.2 × 0.2 mm

Data collection

Enraf–Nonius CAD-4 diffractometer
Absorption correction: none
3554 measured reflections
1853 independent reflections
1531 reflections with I > 2σ(I)
R _int = 0.065
θ_max = 24.0°
3 standard reflections frequency: 120 min intensity decay: <0.1%

Refinement

R[F ² > 2σ(F ²)] = 0.040
wR(F ²) = 0.103
S = 0.82
1853 reflections
248 parameters
H-atom parameters constrained
Δρ_max = 0.15 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Data collection: CAD-4 EXPRESS (Enraf–Nonius, 1994 ▶); cell refinement: SET4 (de Boer & Duisenberg, 1984 ▶); data reduction: MolEN (Enraf–Nonius, 1990 ▶); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: XP (Siemens, 1990 ▶); software used to prepare material for publication: SHELXL97.

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536808040397/nc2125sup1.cif

e-65-00o25-sup1.cif^{(21.2KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536808040397/nc2125Isup2.hkl

e-65-00o25-Isup2.hkl^{(91.3KB, hkl)}

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

Table 1. Hydrogen-bond geometry (Å, °).

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5⋯N1ⁱ	0.95	2.72	3.554 (4)	146

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Symmetry code: (i) Inline graphic .

supplementary crystallographic information

Comment

In the course of a study on the organometallic and catalytic chemistry of aromatic imines (Imhof, 1997a,b) we became interested in the reactivity of the vinylogous keteneimines. The latter are prepared by the elimination of water from the corresponding acetamides by P₂O₅ in anhydrous pyridine (Stevens & Singhal, 1964).

As expected the molecular structure of the title compound shows an almost linear cumulene system with an angle of 172.5 (4)° at the central C atom. The bonds C1—C2 and C2—N1 show bond lengths of 1.332 (5) and 1.213 (4) Å, respectively. The dihedral angle between the C1—C8—C14 plane and the aromatic substituent at the imine N atom measures to 52.4 (7)° which means that the substituents at the cumulene system do not show the expected orthogonal arrangement. This is most probably caused by the high steric requirements of the two isopropyl groups in ortho-position. A comparison with related aromatic diphenylvinylidene amines from the literature shows that the corresponding dihedral angle is close to 90° if there is no or just one ortho-substituent present in the aromatic group at nitrogen (p-Br-C₆H₄: 85.6°, Naqvi & Wheatley, 1970; o-Me-C₆H₄: 88.1°, Jochims et al., 1984; p-(N═C═CPh₂)-C₆H₄: 88.4°, Kuipers et al., 1989; p-Me-C₆H₄: 83.9°, Naqvi & Wheatley, 1970). If both ortho-positions are substituted the conformation is no longer orthogonal (o-Me₂-C₆H₃: 51.7°, Jochims et al., 1984) as it is also observed for the title compound. The lone pair at nitrogen is involved in a weak intramolecular hydrogen bond (Desiraju & Steiner, 1999) interaction towards H5 leading to the formation of infinite chains.

Experimental

The title compound was prepared following a literature method (Stevens & Singhal, 1964). A sample of 2 g (5.4 mmol) N-(2,6-Diisopropyl-phenyl)-2,2-diphenyl-acetamide was dissolved in 50 ml of anhydrous pyridine. To this solution 5 g P₂O₅ were added and the mixture was refluxed for 7 h. After cooling the solution was filtered and pyridine was evaporated resulting in a red oily residue. The oil was transferred to a short chromatography column and light petroleum (b.p. 40–60°C) was used to elute a yellow solution of the title compound. Concentration of the solution and cooling to 4°C led to the formation of crystalline material from which the crystal for the structure analysis described herein was collected (yield: 1.56 g, 82%). MS (EI) [m/z, %]: 353 (M⁺, 80), 338 (C₂₅H₂₄N⁺, 22), 186 (C₁₃H₁₆N⁺, 100), 165 (C₁₃H₉⁺, 50), 115 (C₉H₇⁺, 19), 91 (C₇H₇⁺, 37), 77 (C₆H₅⁺, 17), 55 (C₄H₇⁺, 11), 41 (C₃H₅⁺, 35). ¹H NMR (CDCl₃, 298 K) [p.p.m.]: 1.11 (12 H, d, ³J_HH = 6.8 Hz, CH₃), 3.24 (2 H, h, ³J_HH = 6.8 Hz, CH), 7.05–7.34 (15 H, m, CH_ar). ¹³C NMR (CDCl₃, 298 K) [p.p.m.]: 22.4 (CH₃), 28.5 (CH), 72.0 (═C), 123.4 (C_arH), 125.9 (C_arH), 126.3 (C_arH), 127.8 (C_arH), 128.7 (C_arH), 134.8 (C_ar), 136.2 (C_ar), 140.8 (C_ar), 183.4 (═C═).