2-{[(Biphenyl-2-yl)diazen­yl]methyl­idene}-1,3,3-trimethyl­indoline

Graeme J Gainsford; Mohamed Ashraf; Andrew J Kay

doi:10.1107/S1600536811008890

. 2011 Mar 15;67(Pt 4):o893. doi: 10.1107/S1600536811008890

2-{[(Biphenyl-2-yl)diazenyl]methylidene}-1,3,3-trimethylindoline

Graeme J Gainsford ^a,^*, Mohamed Ashraf ^a, Andrew J Kay ^a

PMCID: PMC3099795 PMID: 21754168

Abstract

The title molecule, C₂₄H₂₃N₃, shows some delocalization of charge based on the small [8.0 (2)°] angle between the indolin-2-ylidene ring system and the link methyldiazene C₂N₂ atom plane. A further twist of 17.2 (3)° is subtended between the C₂N₂ plane and its attached benzene ring. The dihedral angle between the biphenyl rings is 47.96(14)°. In the crystal, the molecules pack via C—H⋯π attractive interactions.

Related literature

For applications of azo compounds, see: Möhlmann & van der Vorst (1989 ▶); Zollinger (1987 ▶). For related compounds, see Jones (2004 ▶); Jones & Chrapkowski (2004 ▶); Gainsford et al. (2008 ▶). For a description of the Cambridge Structural Database, see: Allen (2002 ▶).

Experimental

Crystal data

C₂₄H₂₃N₃
M _r = 353.45
Orthorhombic,
a = 14.2968 (17) Å
b = 8.2407 (10) Å
c = 16.2671 (17) Å
V = 1916.5 (4) Å³
Z = 4
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 116 K
0.70 × 0.20 × 0.10 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan [Blessing (1995 ▶) and SADABS (Bruker, 2005 ▶)] T _min = 0.640, T _max = 0.746
34258 measured reflections
1783 independent reflections
1764 reflections with I > 2σ(I)
R _int = 0.041

Refinement

R[F ² > 2σ(F ²)] = 0.037
wR(F ²) = 0.086
S = 1.23
1783 reflections
247 parameters
1 restraint
H-atom parameters constrained
Δρ_max = 0.19 e Å⁻³
Δρ_min = −0.16 e Å⁻³

Data collection: APEX2 (Bruker, 2005 ▶); cell refinement: SAINT (Bruker, 2005 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: ORTEP-3 (Farrugia, 1997 ▶) and Mercury (Macrae et al., 2008 ▶); software used to prepare material for publication: SHELXL97 and PLATON (Spek, 2009 ▶).

Supplementary Material

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536811008890/ez2238sup1.cif

e-67-0o893-sup1.cif^{(21.2KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811008890/ez2238Isup2.hkl

e-67-0o893-Isup2.hkl^{(87.8KB, hkl)}

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

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

Cg1, Cg2 and Cg3 are the centroids of the C19–C24, C4–C9 and C13–C18 rings, respectively.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C1—H1C⋯Cg1ⁱ	0.98	2.86	3.582 (3)	131
C11—H11B⋯Cg3ⁱⁱ	0.98	2.74	3.721 (3)	179
C22—H22⋯Cg2ⁱⁱⁱ	0.95	2.76	3.645 (3)	155

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Symmetry codes: (i) Inline graphic ; (ii) ; (iii) .

Acknowledgments

We thank Dr J. Wikaira of the University of Canterbury, New Zealand, for her assistance with the data collection.

supplementary crystallographic information

Comment

Azo compounds are integral to a number of fields of organic chemistry. While they played a key part in the development of the dye industry (Zollinger, 1987) they are also finding application as the enabling materials for a range of fields including nonlinear optics, photochromism and holographic recording. Dyes based on azobenzene typically exhibit high extinction coefficients and their absorption maxima can usually be tailored to lie anywhere in the visible region via appropriate substitution onto the phenyl rings. Furthermore due to their geometrically rigid structures and large aspect ratios, azobenzene compounds are ideal as mesogens (Möhlmann & van der Vorst, 1989).

Recently, we have become interested in developing photoswitchable molecules in order to alter the refractive index of a given material via photo-induced rather than electrically induced means (as occurs in nonlinear optical materials). As part of this we have been exploring how the placement of different substituents (e.g. donors, acceptors or neutral) on the backbone of various azo dyes affects the speed and reversibility of the photo- and thermal isomerization processes. Included in these studies have been a suite of compounds containing an indoline donor, an azo linker and a variety of substituents attached to the terminal nitrogen atom of the azo moiety. The molecules are easily prepared via diazotization of the corresponding aryl amine of the terminal substituent and coupling of the resultant diazonium salt with Fisher's base. The reaction is exemplified in Fig. 1 using 2-aminobiphenyl, 1, as the aromatic amine and which yielded the title compound, 3, in 80% yield.

Compound REFCODES below are from the Cambridge Structural Database (Version 5.31, with Aug 2010 updates; Allen, 2002). The asymmetric unit contents and labels of 3 are shown in Fig. 2. The bond lengths and angles, with the exception of those involving atom C12, are essentially identical with those reported by Jones in 2004 [EZUCUX, EZUDAE (Jones, 2004)) and YADTIH (Jones & Chrapkowski (2004)]. In these latter three compounds, where only a phenyl (or para-substituted phenyl) ring was bound to N3, an additional indol-2-ylidene ring was bonded to C12 rather than the hydrogen here (H12). The mean C12—C2 and C12—N2 distances for the three structures were 1.386 (5) and 1.395 (2) Å compared with 1.361 (4) and 1.362 (4) Å here. There are smaller consistent, but barely significant, differences with the N1—C9 and N1—C2 average bond lengths being longer (0.11 (5) Å) and shorter (0.08 (5) °) than found here. These differences can be attributed to extended charge delocalization through the N1—C2—C12—N2 chain that is not observed in the three reference cationic structures.

There is minor buckling beteween the 5- & 6-membered rings in the indol-2-ylidene ring of 1.09 (14) ° compared with 0.46 (14) ° in EZUDAE. The interplanar angles confirm the consistent twist along the delocalization plane: 8.0 (2) ° between the indol-2-ylidene (N1, C2–C9) and the C2,C12,N2,N3 planes, and a further 17.2 (3) ° angle subtended between the latter and the phenyl ring (C14–C18). The biphenyl rings are at 47.96 (14) ° to each other. This is another point of difference with the related compounds, where the "out of plane" indol-2-ylidene ring bound to C12 is at ~80 ° to the mean plane through the phenyl ring bound to N3.

The molecules are held in the lattice by a concerted set of C–H···π interactions shown in Table 1 and Fig. 3. Entry 2 in Table 1 is included because the second methyl hydrogen on C1 (H1A) interacts with atoms C14 & C15 in an adjacent (Cg3) ring. We note that the acidic proton H12 is not positioned to interact with adjacent N2 or N3 acceptors as observed in related compounds with cyano N atoms (e.g. structure (II) in Gainsford et al., 2008). This packing highlights the main difference between this structure and the reference compounds which have extensive hydrogen bonding (C–H···O) to the perchlorate anion and no significant C–H···π interactions.

Experimental

To conc. sulfuric acid (4 ml) was added 2-aminobiphenyl 1 (5 mmol) and the reaction was stirred and cooled to 273–278 K. A solution of sodium nitrite (380 mg, 5.5 mol) in 10 ml of water was added slowly and the reaction stirred at 273–278 K for 30 min. To this mixture, was added a solution of Fisher's base, 2, (865 mg, 5 mmol) in 20 ml of glacial acetic acid and the reaction was then stirred for a further 2 h at 273–278 K. The reaction mixture was then poured into water and neutralized with aqueous sodium carbonate. The resulting precipitate was collected by filtration, washed with water and dried over sodium sulfate. Recrystallization (ethanol) gave the title compound 3 as a deep red solid; Yield: 80%. Crystals were prepared by slow evaporation in methanol. m.p. 417.8–419.3 K. ¹H NMR (DMSO-d₆, 500 MHz): 7.58 (d, 1H, J = 10 Hz), 7.46–7.40 (m, 5H), 7.35–7.31 (m, 2H), 7.29–7.25 (m, 2H), 7.22 (s, 1H), 7.09 (d, 1H, J = 10 Hz), 7.02 (t, 2H), 3.31(s, 3H), 1.71(s, 6H). ¹³C NMR (DMSO-d₆, 125 MHz): 28.66, 29.58, 108.23, 115.62, 121.61, 121.87, 126.58, 126.99, 127.54, 127.81, 128.05, 130.30, 131.53, 137.72, 139.35, 139.70, 144.08, 150.79, 165.97. Mass spec: found: M⁺ 354.1972; 354.1970 (calc); Δ = 0.6 p.p.m..