4-tert-Butyl-2-[2-(1,3,3-trimethyl­indolin-2-yl­idene)ethyl­idene]cyclo­hexa­none

Graeme J Gainsford; Mohamed Ashraf; Andrew J Kay

doi:10.1107/S1600536811014590

. 2011 Apr 29;67(Pt 5):o1210. doi: 10.1107/S1600536811014590

4-tert-Butyl-2-[2-(1,3,3-trimethylindolin-2-ylidene)ethylidene]cyclohexanone

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

PMCID: PMC3089154 PMID: 21754509

Abstract

The title molecule, C₂₃H₃₁NO, has two alternative cyclohexanone configurations at the 4-position in a ratio of 0.663 (3):0.337 (3). The plane of the five-membered planar ring in the indolin-2-ylidene subtends an angle of 2.19 (7)° with its fused aromatic ring, an angle of 16.24 (8)° with the plane of the major cyclohexanone configuration and an angle of 8.54 (15)° with the bridging planar ethylidene C atoms. These last atoms subtend an angle of 8.37 (16)° with the mean plane through the major cyclohexanone configuration. The molecules pack approximately parallel to the ( Inline graphic 01) plane via C—H⋯π and C—H⋯O interactions.

Related literature

For background information on potential applications of NLO (organic nonlinear optical material) compounds, see: Denk et al. (1990 ▶); Ma et al. (2002 ▶); Parthenopoulos & Rentzepis (1989 ▶). For synthesis details, see: Ainsworth (1963 ▶). For related compounds, see: Kawamata et al. (1998 ▶); Higham et al. (2010 ▶); Bhuiyan et al. (2011 ▶); Teshome et al. (2011 ▶). For the Cambridge Structural Database, see: Allen (2002 ▶). For graph-set notation of hydrogen bonds, see: Bernstein et al. (1995 ▶).

Experimental

Crystal data

C₂₃H₃₁NO
M _r = 337.49
Monoclinic,
a = 9.7327 (4) Å
b = 17.2187 (6) Å
c = 12.1303 (4) Å
β = 100.045 (2)°
V = 2001.69 (13) Å³
Z = 4
Mo Kα radiation
μ = 0.07 mm⁻¹
T = 116 K
0.62 × 0.49 × 0.25 mm

Data collection

Bruker APEXII CCD diffractometer
Absorption correction: multi-scan (Blessing, 1995 ▶) T _min = 0.668, T _max = 0.746
44399 measured reflections
4500 independent reflections
3690 reflections with I > 2σ(I)
R _int = 0.043

Refinement

R[F ² > 2σ(F ²)] = 0.050
wR(F ²) = 0.134
S = 1.05
4500 reflections
308 parameters
5 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 0.26 e Å⁻³
Δρ_min = −0.21 e Å⁻³

Data collection: APEX2 (Bruker, 2005 ▶); cell refinement: SAINT (Bruker, 2005 ▶); data reduction: SAINT and SADABS (Sheldrick, 1995 ▶); 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/S1600536811014590/jj2085sup1.cif

e-67-o1210-sup1.cif^{(35.7KB, cif)}

Structure factors: contains datablocks I. DOI: 10.1107/S1600536811014590/jj2085Isup2.hkl

e-67-o1210-Isup2.hkl^{(220.5KB, hkl)}

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

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

Cg1 is the centroid of the C1–C6 ring.

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5⋯O1ⁱ	0.95	2.45	3.3293 (19)	154
C9—H9A⋯Cg1ⁱⁱ	0.98	2.65	3.5705 (17)	156

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

Acknowledgments

The authors thank Dr J. Wikaira of the University of Canterbury for her assistance in the data collection.

supplementary crystallographic information

Comment

Organic nonlinear optical (NLO) materials show much promise due to their potential application in areas such as optical power limiting, optical data storage and two-photon fluorescence imaging (Ma et al., 2002; Parthenopoulos & Rentzepis, 1989; Denk et al., 1990). Such compounds are typically push–pull conjugated systems that can be modified by altering either the donor, acceptor or conjugated interconnect moieties. However these modifications can involve trade-offs insofar as improvements to the nonlinear optical properties typically result in compounds that are more complex to prepare, have lower stabilities and higher optical losses. Conjugated ketones are useful intermediates for increasing the chain length and/or substituting different donors and acceptors onto a basic chromophore backbone. This is because conjugated ketones are quite reactive species and are able to undergo a range of carbon–carbon double bond forming reactions including the Wittig reaction, Knoevenagel condensation and Peterson olefination. With this in mind, and in line with our ongoing work on the development of novel organic NLO compounds, we sought to prepare the title compound 3 using the method outlined in Fig. 1. This compound is a useful synthon for the preparation of a range of chromophore systems as it contains an electron-rich indoline donor unit and a conjugated ketone onto which a range of acceptors can be coupled. The title molecule 3 is conveniently prepared in excellent yield by the condensation of 4-tert-butyl-2-hydroxymethylenecyclohexanone 1 with Fisher's base 2. Compound 1 was prepared from 4-tert-butylcyclohexanone using the general procedure reported by Ainsworth (1963).

Compound REFCODES below are from the CSD (Version 5.32, with Feb. 2011 updates; Allen, 2002). In the title compound 3 (Fig. 2), the cyclohexanone ring exists in two configurations, S (C18a) and R (C18b), in the ratio a:b of 0.663 (3):0.337 (3). This model made chemical sense, was stable in refinement, with insignificant difference Fourier residual density. The data supported refinement in the centrosymmetric space group P2₁/n even though there were 57 weak reflections (with intensities between values between 0.08 (2) and 0.87 (7)) that violated the n glide absence condition. Refinement in P2₁ did not improve the fit significantly as would be expected with such weak contributing data, and gave some very large correlations between thermal and positional parameters of the n glide related molecules.

The closest comparable structures for the cyclochexanone section of the molecule is QADZUQ, 4-tert-butyl-2,6-bis(4-methylbenzylidene)cyclohexanone (Kawamata et al., 1998) which has a mirror plane passing through the carbonyl, tert-butyl and their bound ring C atoms. A comparision of the cyclohexanone dimensions indicates that some electronic delocalization along the ethylidene chain is observed with the C14—C15 bond length shortened (1.472 (2), 1.490 Å), the C13—C14 bond length lengthened (1.3619 (18), 1.332 Å) and the C12—C13 bond shortened (1.4204 (19), 1.466 Å) for 3 and QADZUQ respectively. The dienone-ether macrocyclic compound WUYMIN (Higham et al., 2010) also contains copies of the 4-tert-butyl-cyclohexanone at a lower resolution (R 9.0%), with similar configurational disorder in the ratio of 0.70:0.30 as observed here.

As noted before in related indoline-based compounds there is minor buckling between the planar 5- and 6-membered rings in the indolin-2-ylidene ring of 2.19 (7)° compared with 1.81 (13)° in compound 17 (Teshome et al., 2011) and 1.38 (9)° in compound TMIPI (Bhuiyan et al., 2011). The interplanar angles confirm the consistent twist along the electronic delocalization plane: 8.54 (15)° between the 5-membered indoline ring (N1,C1,C6–C8) and the ethylidene atoms plane (C8,C12–C14) with a further 8.37 (16)° angle subtended between the latter and the average plane through the major configuration cyclohexanone atoms (C14–C16, C17a, C18a and C19). The indoline dimensions are identical to those found in the above-listed compounds.

The molecules are held in the lattice by weak C—H···π interactions (Table 1) over cell inversion centres and C—H···O hydrogen bonds, the latter forming C(10) motifs (Bernstein et al., 1995), Fig. 3.

Experimental

To a stirred solution of Fisher's base 2 (0.865 g, 5 mmole) in methanol was added compound 1 (0.91 g, 5 mmole). The mixture was refluxed for 2 h by which time its colour had changed from deep red to brown. The solvent was removed at reduced pressure and the residue purified by crystallization in ethanol, giving the title compound 3 as a yellow solid (1.5 g, 88% yield). X-ray quality crystals were grown by slow evaporation from methanol. m.p.: 450 K.