Crystal structure of 1,2-bis­­[(2-tert-butyl­phen­yl)imino]­ethane

The whole molecule of the title compound, C₂₂H₂₈N₂, (I), is generated by inversion symmetry. The mol­ecule is rather similar to that of 2,3-bis­[(2-tert-butyl­phen­yl)imino]­butane, (II), a di­imine ligand comprising similar structural features [Ferreira et al. (2006). Acta Cryst. E62, o4282–o4284]. Both ligands crystallize with the –N=C(R)—C(R)=N– group around an inversion centre, in a trans configuration. Comparing the two structures, it may be noted that the independent planar groups in both mol­ecules [the central link, –N=C(R)—C(R)=N–, and the terminal aromatic ring] subtend an angle of 69.6 (1)° in (II) and 49.4 (2)° in (I). Ferreira and co-workers proposed that such angle deviation may be ascribed to the presence of two non-classical intra­molecular hydrogen bonds and steric factors. In fact, in (I), similar non-classical hydrogen bonds are observed, and the larger angular deviation in (II) may be assigned to the presence of methyl groups in the di­imino fragment, which can cause steric hindrance due to the presence of bulky tert-butyl substituents in the aromatic rings. The C=N bond lengths are similar in both compounds and agree with comonly accepted values.

1. Related literature

For general properties of di­imines, see: Rix & Brookhart (1995); Hissler et al. (2000); Ramakrishnan et al. (2011a). For the inter­action of di­imine–metal complexes with DNA, see: Wang et al. (2004); Tan et al. (2008); Ramakrishnan et al. (2011b). For a related structure, see: Ferreira et al. (2006).

2. Experimental

2.1. Crystal data

• C₂₂H₂₈N₂

• M_r = 320.46

• Monoclinic, P 2₁ /n

• a = 12.333 (3) Å

• b = 6.4740 (13) Å

• c = 12.519 (3) Å

• β = 95.22 (3)°

• V = 995.5 (3) ų

• Z = 2

• Mo Kα radiation

• μ = 0.06 mm⁻¹

• T = 293 K

• 0.3 × 0.17 × 0.07 mm

2.2. Data collection

• Nonius KappaCCD diffractometer

• 21498 measured reflections

• 1811 independent reflections

• 1284 reflections with I > 2σ(I)

• R_int = 0.072

2.3. Refinement

• R[F² > 2σ(F²)] = 0.049

• wR(F²) = 0.119

• S = 1.06

• 1811 reflections

• 109 parameters

• H-atom parameters constrained

• Δρ_max = 0.13 e Å⁻³

• Δρ_min = −0.15 e Å⁻³

Table 1
Hydrogen-bond geometry (Å, °)

-

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C10—H10B⋯N1	0.960	2.405 (2)	3.055 (3)	124.8 (3)
C11—H11C⋯N1	0.960	2.414 (2)	3.064 (3)	124.6 (2)

Data collection: COLLECT (Nonius, 2004); cell refinement: DIRAX/LSQ (Duisenberg, 1992); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

Supporting information

S1. Chemical context

The design and development of effective anti­cancer metallodrugs has become one of the more important areas in pharmaceutical industry and academia. Nonetheless, side effects associated with these complexes and the development of tumor resistance has led to the search for new generations of metal based anti­cancer agents. Di­imine compounds have been employed in many applications, including olefin polymerization, luminescence studies and metallodrug synthesis. (Rix & Brookhart, 1995; Hissler et al., 2000; Ramakrishnan et al., 2011a) The inter­action of di­imine Cobalt, Ruthenium and Iron complexes with DNA has attracted much attention during the last decade. (Wang et al., 2004; Tan et al. 2008; Ramakrishnan et al., 2011b). The anti­tumoral screening activity of potential metallodrugs with distinct nitro­gen based ligands has helped researchers to understand how factors as size, geometry and electronic structure can contribute to DNA binding thus allowing to categorize which factors are important to enhance metallodrug performance. We report herein on the crystal structure of C₂₂H₂₈N₂ (I)

S2. Structural commentary

The crystal structure of 2,3-Bis(2-tert-butyl­phenyl­imino)­butane, C₂₄H₃₂N₂ (II), a di­imine ligand comprising similar structural features was already reported. (Ferreira et al., 2006). Both ligands crystallize with the –N=C(R)—C(R)=N– group around an inversion centre, in a trans configuration. Comparing the two structures, it may be noted that the independent planar groups in both molecules (the central link, –N=C(R)—C(R)=N–, and the terminal aromatic ring) subtend an angle of 69.6 (1)° in (II) and 49.4 (2)° in (I). Ferreira and co-workers proposed that such angle deviation may be ascribed to the presence of two non classical hydrogen bonds and steric factors. In fact, in the title compound, similar non-classical hydrogen bonds were observed: C10—H10B···N1 and C11—H11C···N1. (Fig 1 and Table 1) The greater angle deviation in (II) may be assigned to the presence of methyl groups in the di­imino fragment, which can cause steric hindrance due to the presence of bulky tert-butyl substituents in the aromatic rings. The C=N bond lengths are similar to the corresponding ones in (II) and agree well with what is expected for this bonding mode.

S3. Synthesis and crystallization

To a solution of 2-tert-butyl­aniline (3.6 g; 26 mmol) in 15 mL de methanol, 1.5 mL of glyoxal solution (40 % in water; 13 mmol) was added. The resulting mixture was stirred overnight at room temperature. The yellow precipitate was filtered off, dried under vacuum for 2 days. Slow evaporation of the filtrate gave crystals suitable for single-crystal XRD studies. (Yield: 90 %)

S4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. The H atoms were placed into the calculated idealized positions. All H atoms were refined with fixed individual displacement parameters [U_iso(H) = 1.2U_eq (Csp²) or 1.5U_eq (methyl group)] using a riding model.

Related literature

For general properties of diimines, see: Rix & Brookhart (1995); Hissler et al. (2000); Ramakrishnan et al. (2011a). For the interaction of diimine–metal complexes with DNA, see: Wang et al. ( 2004); Tan et al. (2008); Ramakrishnan et al. (2011b). For related structures, see: Ferreira et al. (2006).

Computing details

Data collection: COLLECT (Nonius, 2004); cell refinement: DIRAX/LSQ (Duisenberg, 1992); data reduction: EVALCCD (Duisenberg et al., 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 for Windows (Farrugia, 2012); software used to prepare material for publication: WinGX (Farrugia, 2012).

Figures

	Fig. 1. View of (I) (50% probability displacement ellipsoids). The dashed lines indicate the proposed non-classical intramolecular hydrogen bonds. [Symmetry code: (') 1 - x, 1 - y, -z.]
	Fig. 2. Comparison of the structures of (a) (I) and (b) (II).

2-tert-Butyl-N-{2-[(2-tert-butylphenyl)imino]ethylidene}aniline

Crystal data

C22H28N2	F(000) = 348
Mr = 320.46	Dx = 1.069 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 21498 reflections
a = 12.333 (3) Å	θ = 3.6–25.4°
b = 6.4740 (13) Å	µ = 0.06 mm^−1
c = 12.519 (3) Å	T = 293 K
β = 95.22 (3)°	Plate, yellow
V = 995.5 (3) Å^3	0.3 × 0.17 × 0.07 mm
Z = 2

Data collection

Nonius KappaCCD diffractometer	1284 reflections with I > 2σ(I)
Horizonally mounted graphite crystal monochromator	Rint = 0.072
Detector resolution: 9 pixels mm^-1	θmax = 25.4°, θmin = 3.6°
CCD scans	h = −14→14
21498 measured reflections	k = −7→7
1811 independent reflections	l = −15→15

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.049	H-atom parameters constrained
wR(F^2) = 0.119	w = 1/[σ^2(Fo^2) + (0.0452P)^2 + 0.2479P] where P = (Fo^2 + 2Fc^2)/3
S = 1.06	(Δ/σ)max < 0.001
1811 reflections	Δρmax = 0.13 e Å^−3
109 parameters	Δρmin = −0.15 e Å^−3

Special details

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

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
N1	0.46712 (12)	0.1526 (2)	0.10801 (11)	0.0485 (4)
C1	0.47499 (15)	0.0981 (3)	0.01174 (14)	0.0520 (5)
H1	0.4486	0.1842	−0.0442	0.062*
C2	0.41192 (14)	0.3400 (3)	0.12810 (12)	0.0440 (4)
C3	0.31398 (16)	0.3836 (3)	0.06876 (15)	0.0622 (6)
H3	0.2873	0.292	0.0155	0.075*
C4	0.25541 (18)	0.5595 (4)	0.08691 (17)	0.0736 (7)
H4	0.19	0.587	0.0465	0.088*
C5	0.29551 (17)	0.6930 (3)	0.16573 (18)	0.0694 (6)
H5	0.2576	0.8134	0.1783	0.083*
C6	0.39173 (16)	0.6496 (3)	0.22646 (15)	0.0559 (5)
H6	0.4171	0.7428	0.2795	0.067*
C7	0.45274 (13)	0.4721 (2)	0.21188 (13)	0.0413 (4)
C8	0.55778 (14)	0.4249 (3)	0.28333 (14)	0.0476 (4)
C9	0.58580 (19)	0.5962 (4)	0.36621 (18)	0.0777 (7)
H9A	0.5955	0.7244	0.3298	0.117*
H9B	0.6518	0.5612	0.409	0.117*
H9C	0.5276	0.6101	0.4117	0.117*
C10	0.65538 (15)	0.4063 (4)	0.21568 (17)	0.0701 (6)
H10A	0.6639	0.533	0.1775	0.105*
H10B	0.6429	0.295	0.1654	0.105*
H10C	0.7203	0.3791	0.2619	0.105*
C11	0.54410 (18)	0.2230 (3)	0.34482 (16)	0.0684 (6)
H11A	0.4834	0.2354	0.3872	0.103*
H11B	0.6091	0.1959	0.3909	0.103*
H11C	0.5313	0.1113	0.2948	0.103*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
N1	0.0604 (9)	0.0429 (9)	0.0420 (8)	0.0096 (7)	0.0034 (7)	−0.0089 (7)
C1	0.0685 (12)	0.0456 (10)	0.0416 (10)	0.0134 (9)	0.0028 (8)	−0.0051 (8)
C2	0.0546 (10)	0.0405 (10)	0.0380 (9)	0.0103 (8)	0.0092 (7)	−0.0021 (7)
C3	0.0662 (13)	0.0709 (14)	0.0482 (11)	0.0188 (11)	−0.0016 (9)	−0.0108 (10)
C4	0.0681 (14)	0.0872 (17)	0.0650 (13)	0.0346 (13)	0.0029 (11)	0.0000 (12)
C5	0.0734 (14)	0.0550 (13)	0.0827 (15)	0.0288 (11)	0.0235 (12)	0.0000 (11)
C6	0.0639 (12)	0.0415 (11)	0.0650 (12)	0.0040 (9)	0.0201 (10)	−0.0096 (9)
C7	0.0496 (10)	0.0348 (9)	0.0417 (9)	−0.0007 (8)	0.0171 (7)	−0.0024 (7)
C8	0.0514 (10)	0.0432 (10)	0.0489 (10)	−0.0055 (8)	0.0089 (8)	−0.0081 (8)
C9	0.0799 (15)	0.0730 (15)	0.0787 (15)	−0.0088 (12)	−0.0013 (12)	−0.0280 (12)
C10	0.0513 (11)	0.0795 (16)	0.0811 (15)	0.0017 (11)	0.0144 (10)	−0.0068 (12)
C11	0.0809 (14)	0.0659 (14)	0.0554 (12)	−0.0091 (12)	−0.0105 (10)	0.0094 (10)

Geometric parameters (Å, º)

N1—C1	1.268 (2)	C7—C8	1.536 (2)
N1—C2	1.425 (2)	C8—C9	1.537 (2)
C1—H1	0.93	C9—H9A	0.96
C1—C1^i	1.454 (3)	C9—H9B	0.96
C2—C3	1.388 (2)	C9—H9C	0.96
C2—C7	1.410 (2)	C8—C10	1.538 (2)
C3—C4	1.378 (3)	C10—H10A	0.96
C3—H3	0.93	C10—H10B	0.96
C4—C5	1.370 (3)	C10—H10C	0.96
C5—H5	0.93	C8—C11	1.534 (3)
C4—H4	0.93	C11—H11A	0.96
C5—C6	1.379 (3)	C11—H11B	0.96
C6—C7	1.395 (2)	C11—H11C	0.96
C6—H6	0.93
C1—N1—C2	118.93 (15)	C11—C8—C9	107.72 (16)
N1—C1—C1^i	120.4 (2)	C7—C8—C9	112.06 (15)
N1—C1—H1	119.8	C11—C8—C10	109.68 (16)
C1^i—C1—H1	119.8	C7—C8—C10	110.83 (14)
C3—C2—C7	120.59 (16)	C9—C8—C10	106.81 (16)
C3—C2—N1	119.03 (15)	C8—C9—H9A	109.5
C7—C2—N1	120.24 (15)	C8—C9—H9B	109.5
C4—C3—C2	121.56 (19)	H9A—C9—H9B	109.5
C4—C3—H3	119.2	C8—C9—H9C	109.5
C2—C3—H3	119.2	H9A—C9—H9C	109.5
C5—C4—C3	118.67 (19)	H9B—C9—H9C	109.5
C5—C4—H4	120.7	C8—C10—H10A	109.5
C3—C4—H4	120.7	C8—C10—H10B	109.5
C4—C5—C6	120.33 (19)	H10A—C10—H10B	109.5
C4—C5—H5	119.8	C8—C10—H10C	109.5
C6—C5—H5	119.8	H10A—C10—H10C	109.5
C5—C6—C7	122.91 (18)	H10B—C10—H10C	109.5
C5—C6—H6	118.5	C8—C11—H11A	109.5
C7—C6—H6	118.5	C8—C11—H11B	109.5
C6—C7—C2	115.89 (16)	H11A—C11—H11B	109.5
C6—C7—C8	121.60 (15)	C8—C11—H11C	109.5
C2—C7—C8	122.51 (14)	H11A—C11—H11C	109.5
C11—C8—C7	109.64 (14)	H11B—C11—H11C	109.5
C2—N1—C1—C1^i	−176.3 (2)	C3—C2—C7—C6	−3.0 (2)
C1—N1—C2—C3	44.2 (2)	N1—C2—C7—C6	−178.76 (15)
C1—N1—C2—C7	−139.97 (18)	C3—C2—C7—C8	176.94 (17)
C7—C2—C3—C4	2.2 (3)	N1—C2—C7—C8	1.2 (2)
N1—C2—C3—C4	178.05 (18)	C6—C7—C8—C11	117.87 (18)
C2—C3—C4—C5	−0.1 (3)	C2—C7—C8—C11	−62.0 (2)
C3—C4—C5—C6	−1.0 (3)	C6—C7—C8—C9	−1.7 (2)
C4—C5—C6—C7	0.1 (3)	C2—C7—C8—C9	178.39 (16)
C5—C6—C7—C2	1.9 (3)	C6—C7—C8—C10	−120.91 (18)
C5—C6—C7—C8	−178.02 (17)	C2—C7—C8—C10	59.2 (2)

Symmetry code: (i) −x+1, −y, −z.