1,3-Bis[(−)-(S)-(1-phenyl­eth­yl)imino­meth­yl]benzene

Tania García; Sylvain Bernès; Marcos Flores-Alamo; Guadalupe Hernández; René Gutiérrez

doi:10.1107/S1600536811021556

. 2011 Jun 11;67(Pt 7):o1648–o1649. doi: 10.1107/S1600536811021556

1,3-Bis[(−)-(S)-(1-phenylethyl)iminomethyl]benzene

Tania García ^a, Sylvain Bernès ^a,^*, Marcos Flores-Alamo ^b, Guadalupe Hernández ^c, René Gutiérrez ^c

PMCID: PMC3151960 PMID: 21837052

Abstract

The title compound, C₂₄H₂₄N₂, is an enantiomerically pure bis-aldimine, which displays twofold crystallographic symmetry, with two C atoms of the central benzene ring lying on the symmetry axis. The imine group is slightly twisted from the benzene core, with a dihedral angle of 12.72 (16)° between the benzene ring and the C=N—C^* plane. The terminal phenyl rings make an angle of 66.44 (4)° and are oriented in opposite directions with respect to the benzene ring. In the crystal, molecules interact weakly through a C—H⋯π interaction involving the phenyl rings, and form chains along the 2₁ screw-axis in the [100] direction.

Related literature

For the structure of the analogous molecule with naphthyl in place of phenyl, see: Espinosa Leija et al. (2009 ▶). For the structure of the isoformular molecule with a 1,4-disubstituted benzene ring, see: García et al. (2010 ▶). For the Pd(II) and Pt(II) coordination complexes formed using the title ligand, see: Fossey et al. (2007 ▶). For background to the synthesis carried out in solvent-free conditions, see: Tanaka & Toda (2000 ▶); Jeon et al. (2005 ▶).

Experimental

Crystal data

C₂₄H₂₄N₂
M _r = 340.45
Orthorhombic,
a = 21.1309 (7) Å
b = 5.6572 (2) Å
c = 8.2290 (3) Å
V = 983.71 (6) Å³
Z = 2
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 130 K
0.33 × 0.26 × 0.14 mm

Data collection

Oxford Diffraction Xcalibur Atlas Gemini diffractometer
Absorption correction: analytical [CrysAlis PRO (Oxford Diffraction, 2009 ▶) based on expressions derived by Clark & Reid (1995 ▶)] T _min = 0.980, T _max = 0.991
6971 measured reflections
1161 independent reflections
1027 reflections with I > 2σ(I)
R _int = 0.025

Refinement

R[F ² > 2σ(F ²)] = 0.029
wR(F ²) = 0.073
S = 1.06
1161 reflections
154 parameters
Only H-atom coordinates refined
Δρ_max = 0.09 e Å⁻³
Δρ_min = −0.17 e Å⁻³

Data collection: CrysAlis CCD (Oxford Diffraction, 2009 ▶); cell refinement: CrysAlis RED (Oxford Diffraction, 2009 ▶); data reduction: CrysAlis RED; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: SHELXTL (Sheldrick, 2008 ▶) and Mercury (Macrae et al., 2006 ▶); software used to prepare material for publication: SHELXTL.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536811021556/lr2012sup1.cif

e-67-o1648-sup1.cif^{(19.1KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536811021556/lr2012Isup2.hkl

e-67-o1648-Isup2.hkl^{(57.5KB, hkl)}

Supplementary material file. DOI: 10.1107/S1600536811021556/lr2012Isup3.mol

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

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

Cg is the centroid of the C1–C6 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C3—H3⋯Cgⁱ	0.92 (2)	2.97 (2)	3.7265 (18)	140.7 (18)

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Symmetry code: (i) Inline graphic .

Acknowledgments

Support from VIEP-UAP: GUPJ-NAT10-G (2011) is acknowledged.

supplementary crystallographic information

Comment

The title compound was synthesized in an almost quantitative yield, using a one-step solvent-free route. Such procedures are becoming primordial in organic synthetic methods, in order to minimize the quantity of toxic waste and byproducts and to decrease the amount of solvents in the reaction media and/or during the following workups. Indeed, solvent-free reactions or solid-state reactions have been particularly developed these last years. (Jeon et al., 2005; Tanaka & Toda, 2000).

The molecular structure of the title compound is as expected. The imine groups N1═C8 are found in the E configuration, which is known to be more stable than Z. The molecule is placed on a crystallographic twofold axis, passing through benzene atoms C10 and C11 (Fig. 1). Imine groups are not fully conjugated with the benzene core: the dihedral angle between C7—N1═ C8 and benzene mean-planes is 12.72 (16)°. The benzene ring makes an angle of 69.35 (5)° with the phenyl group, and terminal phenyl rings make an angle of 66.44 (4)°. Although the analogous bis-imine bearing a naphthyl group in place of phenyl crystallizes in the same space group, P2₁2₁2, and with identical molecular symmetry, it is stabilized in a different conformation compared to the title molecule. For instance, imine groups are almost perfectly conjugated with the benzene ring (dihedral angle between benzene and C^*—N═C planes less than 0.6°; Espinosa Leija et al., 2009). The title molecule and the naphthyl analogue are also differentiated by the fact that the latter crystallized with lattice solvent, CH₂Cl₂. The title molecule also shows a different conformation to that of the isoformular compound with a central 1,4-disubsituted benzene ring (García et al., 2010): in that case, the molecule crystallizes in P2₁2₁2₁ and is placed in general position (C₁ point group).

The crystal structure (Fig. 2) features chains of molecules placed along the 2₁ screw-axis in the [100] direction, which interact trough rather weak C3—H3···π contacts involving phenyl groups C1···C6. The H3···π separation is 2.97 (2) Å, and the C3—H3···π angle 140.7 (18)°.

Interestingly, (Fossey et al. 2007) reported on the synthesis of chiral bis-aldimine NCN–pincer complexes, where the NCN ligand is derived from the title compound by deprotonation at C10. These authors probed the catalytic activity of Pd(II) and Pt(II) complexes, where the ancillary ligand is an halide ion, Br^- or Cl^-, for Pd and Pt complexes, respectively. The studied reaction, a classical Michael addition between methyl 2-cyanopropanoate and methyl vinyl ketone, showed that addition was not stereocontrolled. This poor selectivity was related to conformational flexibility of the chiral phenylethyl moiety of the ligand. Indeed, that point is confirmed by our structure, since a poor overlay is observed for this part of the molecule, when attempting to fit the title molecule and the main ligand in the complexes. However, differences in point symmetry also deserve to be considered regarding the catalytic activity: the title molecule belongs to C₂ point-group, while complexes prepared by Fossey et al. crystallize in space group P2₁2₁2₁, the whole complexes being placed in general positions. The complexes used for the Michael addition thus actually displayed the non-crystallographic C₂ symmetry.

Experimental

Under solvent-free conditions, (S)-(–)-1-phenylethylamine (0.45 g, 3.72 mmol) and benzene-1,3-dicarboxaldehyde (0.25 g, 1.86 mmol) in a 2:1 molar ratio were mixed at room temperature, obtaining a white solid. The crude was recrystallized twice from CH₂Cl₂, affording colorless crystals of the title compound. Yield: 92%; m.p. 80–82 °C. Analysis: [α]²⁵_D = -71.4 (c=1, CHCl₃). FT—IR (KBr): 1645 cm^-1 (C=N). ¹H-NMR (400 MHz, CDCl₃/TMS) δ = 1.58 (d, 6H, CHCH₃), 4.53 (q, 2H, CH), 7.22–8.11 (m, 14H, Ar—CH), 8.36 (s, 2H, HC=N). ¹³C-NMR (100 MHz, CDCl₃/TMS) δ = 24.7 (CCH₃), 69.6 (CHCH₃), 126.5 (Ar), 126.8 (Ar), 128.2 (Ar), 128.3 (Ar), 128.7 (Ar), 130.0 (Ar), 136.6 (Ar), 144.8 (Ar), 158.9 (HC=N). MS—EI: m/z= 340 (M⁺).