1-Butyl-2,3,3-tri­methyl­indol-1-ium iodide

Costa Duarte, R. da; Kommers Reimann, L.; Severo Rodembusch, F.; Gustavo Teixeira Alves Duarte, L.

doi:10.1107/S2414314618011306

organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 3| Part 8| August 2018| x181130

https://doi.org/10.1107/S2414314618011306

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1-Butyl-2,3,3-trimethylindol-1-ium iodide

Rodrigo da Costa Duarte,^a Louise Kommers Reimann,^a Fabiano Severo Rodembusch ^a and Luís Gustavo Teixeira Alves Duarte ^b ^*

^aGrupo de Pesquisa em Fotoquímica Orgânica Aplicada, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil, and ^bChemistry Institute, University of Campinas, Brazil
^*Correspondence e-mail: luis.duarte@iqm.unicamp.br

Edited by W. T. A. Harrison, University of Aberdeen, Scotland (Received 24 July 2018; accepted 7 August 2018; online 14 August 2018)

In the title molecular salt, C₁₅H₂₂N⁺·I⁻, the fused-ring system is slightly puckered [dihedral angle between the five- and six-membered rings = 3.43 (8)°]. In the crystal, very weak C—H⋯I interactions link the cations to the anions. Photophysical data for the title salt in different solvents are presented.

Keywords: crystal structure; indole; cyanine precursor.

CCDC reference: 1860832

Structure description

Recent studies have shown the importance of the indole nucleus with respect to its anticancer activities (Singh et al., 2010 ; Shaveta, 2014 ) and in its biological applications as biosensors (Saikiran et al., 2017 ; Guo et al., 2015 ). As part of our studies of indole derivatives, we report here the crystal structure and optical properties of the title salt, C₁₅H₂₂N⁺·I⁻, bearing a quaternized indolic N atom with a butyl side chain.

The indole ring system (Fig. 1) is slightly puckered [dihedral angle between the rings = 3.43 (8)°]. The key torsion angles of the butyl side chain are N1—C12—C13–C14 = 76.14 (18)° and C12—C13—C14—C15 = 176.26 (16)°. In the crystal, there are possibly some very weak C—H⋯I interactions (Table 1). Given that the van der Waals separation of H and I is 3.18 Å, some of these may barely qualify as directional bonds.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
C5—H5⋯I1	0.95	3.18	3.899 (2)	134
C12—H12A⋯I1ⁱ	0.99	3.29	4.186 (3)	151
C12—H12B⋯I1	0.99	3.28	4.249 (3)	167
C13—H13B⋯I1ⁱⁱ	0.99	3.24	4.172 (3)	158
Symmetry codes: (i) -x+1, -y+1, -z+1; (ii) $[x, -y+{\script{1\over 2}}, z+{\script{1\over 2}}]$ .

Figure 1
The molecular structure of the title compound, with displacement ellipsoids shown at the 50% probability level.

The absorption and emission spectra of the title compound are shown in Fig. 2. The relevant data from UV–Vis absorption spectroscopy in different solvents are presented in Table 2. The compound presents absorption maxima located between 279 and 285 nm related to allowed ¹ππ* electronic transitions. The fluorescence emission spectra were obtained by exciting the compounds at the absorption maxima wavelength. The title compound shows emission in the UV-A region (∼365 nm), with a small solvatochromic effect and a Stokes shift higher than 7500 cm⁻¹.

Table 2
Relevant photophysical data of the UV–Vis absorption and fluorescence emission spectroscopy, where λ_ABS and λ_em are the absorption and emission maxima, respectively (nm), ∊ is the molar absorptivity coefficient (×10⁴ M⁻¹ cm⁻¹) and SS is the Stokes shift (cm⁻¹)

Solvent	λ_ABS	∊	λ_em	SS
Dichloromethane	285	0.79	363	7540
Ethanol	279	2.70	367	8594
Acetonitrile	281	0.89	370	8560

Figure 2
UV–Vis absorption (a) and fluorescence emission (b) spectra in solution (10⁻⁵ M).

Synthesis and crystallization

A mixture of phenylhydrazine hydrochloride (5.56 mmol), 3-methylbutan-2-one (6.67 mmol), H₂SO₄ (9.36 mmol) and 20 ml of a solution of acetone–ethanol (1:1 v/v) was refluxed under stirring for 4 h (Fig. 3). The progress of the reaction was monitored by thin-layer chromatography (TLC). The solvent was partially evaporated and the pH adjusted to 4. The organic layer was separated from the aqueous phase by liquid–liquid extraction with dichloromethane (3 × 30 ml). The organic layer was dried with Na₂SO₄, filtered and concentrated. It is worth mentioning that it was necessary to perform a salting-out step for the separation of the layers. No additional treatments were performed for the indole quaternization step. The indole quaternization was afforded by addition of indole (1.9 mmol) to an excess of iodobutane (9.9 mmol) in acetonitrile, previously saturated with N₂. The reaction was conducted under reflux temperature and stirring under a nitrogen atmosphere for 18 h. The reaction was monitored by TLC. The reaction crude was poured into ethyl acetate (50 ml) and allowed to stir under heating for 30 min. Thereafter, the supernatant was removed and the process was repeated three times. The resulting solid was filtered off and dried (yield 70%). The crystallization was performed with addition of methanol to dissolve the solid followed by the addition of ethyl acetate (m.p. 490 K).

Figure 3
Synthesis scheme for the title compound.

¹H NMR (CDCl₃, 400 MHz): δ (ppm) 7.65 (m, 1H), 7.56 (m, 3H), 4.65 (t, 2H, J = 8.0 Hz), 3.10 (s, 3H), 1.91 (m, 2H), 1.63 (s, 6H), 1.49 (m, 2H), 0.98 (t, 3H, J = 8.0 Hz). ¹H NMR (DMSO-d₆, 300 MHz): δ (ppm) 7.74 (m, 1H), 7.61 (m, 1H), 4.67 (t, 2H, J = 7.5 Hz), 3.13 (s, 3H), 1.96 (m, 2H), 1.67 (s, 6H), 1.53 (m, 2H), 1.01 (t, 3H, J = 6.0 Hz) ¹³C NMR (DMSO-d₆, 75 MHz): δ (ppm) 195.5, 141.5, 140.7, 130.0, 129.4, 123.4, 115.3, 54.6, 49.7, 29.8, 23.1, 20.0, 17.0, 13.6.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3. The H atoms were refined as riding on their attached C atoms; the methyl groups were allowed to rotate, but not to tip, to best fit the electron density. The constraint U_iso(H) = kU_eq(C), with k = 1.2 for CH and CH₂ groups and k = 1.5 for methyl groups was applied.

Table 3
Experimental details

Crystal data
Chemical formula	C₁₅H₂₂N⁺·I⁻
M_r	343.23
Crystal system, space group	Orthorhombic, Pbca
Temperature (K)	150
a, b, c (Å)	15.631 (12), 11.614 (8), 16.976 (11)
V (Å³)	3082 (4)
Z	8
Radiation type	Mo Kα
μ (mm⁻¹)	2.06
Crystal size (mm)	0.37 × 0.10 × 0.09

Data collection
Diffractometer	Bruker APEX CCD detector
Absorption correction	Multi-scan (SADABS; Bruker, 2015 )
T_min, T_max	0.637, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections	41973, 3784, 3166
R_int	0.037
(sin θ/λ)_max (Å⁻¹)	0.668

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.019, 0.047, 1.03
No. of reflections	3784
No. of parameters	158
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.49, −0.38
Computer programs: APEX and SAINT (Bruker, 2013 ), SHELXT (Sheldrick, 2015a ), SHELXL2017 (Sheldrick, 2015b ) and OLEX2 (Dolomanov et al., 2009 ).

Structural data

CCDC reference: 1860832

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314618011306/hb4247sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314618011306/hb4247Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S2414314618011306/hb4247Isup3.cml

checkCIF report

Computing details top

Data collection: APEX (Bruker, 2013); cell refinement: SAINT (Bruker, 2013); data reduction: SAINT (Bruker, 2013); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL2017 (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

1-Butyl-2,3,3-trimethylindol-1-ium iodide top

Crystal data top

C₁₅H₂₂N⁺·I⁻	D_x = 1.480 Mg m⁻³
M_r = 343.23	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 9006 reflections
a = 15.631 (12) Å	θ = 2.6–28.2°
b = 11.614 (8) Å	µ = 2.06 mm⁻¹
c = 16.976 (11) Å	T = 150 K
V = 3082 (4) Å³	Needle, light brown
Z = 8	0.37 × 0.10 × 0.09 mm
F(000) = 1376

Data collection top

Bruker APEX CCD detector diffractometer	3166 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.037
Absorption correction: multi-scan (SADABS; Bruker, 2015)	θ_max = 28.3°, θ_min = 2.4°
T_min = 0.637, T_max = 0.746	h = −8→20
41973 measured reflections	k = −15→15
3784 independent reflections	l = −22→22

Refinement top

Refinement on F²	Primary atom site location: dual
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.019	H-atom parameters constrained
wR(F²) = 0.047	w = 1/[σ²(F_o²) + (0.0198P)² + 1.6747P] where P = (F_o² + 2F_c²)/3
S = 1.03	(Δ/σ)_max = 0.001
3784 reflections	Δρ_max = 0.49 e Å⁻³
158 parameters	Δρ_min = −0.37 e Å⁻³
0 restraints

Special details top

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

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
C1	0.30279 (12)	0.35676 (13)	0.65813 (9)	0.0198 (3)
C2	0.21170 (11)	0.31229 (14)	0.65947 (9)	0.0199 (3)
C3	0.21293 (11)	0.23111 (13)	0.59009 (9)	0.0179 (3)
C4	0.29095 (10)	0.24303 (13)	0.55103 (9)	0.0165 (3)
C5	0.31022 (11)	0.18740 (14)	0.48120 (9)	0.0201 (3)
H5	0.362745	0.199361	0.454265	0.024*
C6	0.24721 (12)	0.11220 (14)	0.45275 (9)	0.0222 (4)
H6	0.257625	0.070940	0.405389	0.027*
C7	0.16967 (12)	0.09619 (14)	0.49194 (10)	0.0229 (4)
H7	0.129118	0.043056	0.471549	0.028*
C8	0.15075 (11)	0.15720 (15)	0.56079 (10)	0.0218 (3)
H8	0.097231	0.148388	0.586626	0.026*
C9	0.18792 (12)	0.25620 (17)	0.73851 (10)	0.0286 (4)
H9A	0.230985	0.198271	0.752297	0.043*
H9B	0.131775	0.219254	0.733967	0.043*
H9C	0.185859	0.315308	0.779666	0.043*
C10	0.15024 (14)	0.41470 (17)	0.64136 (12)	0.0337 (4)
H10A	0.154360	0.472001	0.683564	0.050*
H10B	0.091326	0.386260	0.637986	0.050*
H10C	0.166415	0.450183	0.591146	0.050*
C11	0.34125 (13)	0.42907 (15)	0.72083 (10)	0.0280 (4)
H11A	0.365790	0.379431	0.761679	0.042*
H11B	0.297002	0.478211	0.744126	0.042*
H11C	0.386361	0.477354	0.698117	0.042*
C12	0.43452 (11)	0.34915 (14)	0.57497 (10)	0.0204 (3)
H12A	0.447583	0.428413	0.592736	0.024*
H12B	0.440974	0.346896	0.516979	0.024*
C13	0.49862 (11)	0.26586 (14)	0.61218 (10)	0.0213 (3)
H13A	0.556043	0.301760	0.610894	0.026*
H13B	0.482947	0.254517	0.668152	0.026*
C14	0.50385 (13)	0.14869 (16)	0.57259 (11)	0.0285 (4)
H14A	0.516312	0.159241	0.515870	0.034*
H14B	0.447852	0.109433	0.577200	0.034*
C15	0.57325 (15)	0.0730 (2)	0.60951 (15)	0.0459 (6)
H15A	0.574132	−0.002022	0.583103	0.069*
H15B	0.561002	0.062175	0.665637	0.069*
H15C	0.629065	0.110399	0.603421	0.069*
N1	0.34412 (9)	0.32083 (11)	0.59593 (8)	0.0172 (3)
I1	0.42439 (2)	0.38097 (2)	0.32579 (2)	0.02455 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.0245 (9)	0.0142 (7)	0.0206 (7)	0.0005 (7)	0.0002 (7)	0.0011 (6)
C2	0.0207 (8)	0.0199 (7)	0.0190 (7)	0.0025 (7)	0.0021 (7)	−0.0027 (6)
C3	0.0187 (8)	0.0179 (7)	0.0171 (7)	0.0019 (6)	−0.0002 (6)	0.0010 (6)
C4	0.0167 (8)	0.0145 (7)	0.0183 (7)	0.0003 (6)	−0.0029 (6)	0.0008 (5)
C5	0.0209 (8)	0.0220 (8)	0.0175 (7)	0.0011 (7)	0.0021 (7)	0.0009 (6)
C6	0.0275 (9)	0.0223 (8)	0.0168 (7)	0.0034 (7)	−0.0052 (7)	−0.0024 (6)
C7	0.0234 (9)	0.0214 (8)	0.0240 (8)	−0.0029 (7)	−0.0080 (7)	−0.0002 (6)
C8	0.0166 (8)	0.0256 (8)	0.0231 (8)	−0.0009 (7)	−0.0012 (7)	0.0017 (6)
C9	0.0289 (10)	0.0345 (9)	0.0223 (8)	−0.0065 (8)	0.0055 (8)	−0.0006 (7)
C10	0.0342 (11)	0.0331 (9)	0.0337 (10)	0.0159 (9)	−0.0002 (9)	−0.0058 (8)
C11	0.0369 (11)	0.0229 (8)	0.0242 (8)	−0.0073 (8)	0.0005 (8)	−0.0061 (7)
C12	0.0190 (8)	0.0192 (7)	0.0229 (8)	−0.0051 (7)	0.0015 (7)	0.0021 (6)
C13	0.0180 (8)	0.0243 (8)	0.0216 (8)	−0.0032 (7)	0.0010 (7)	0.0017 (6)
C14	0.0268 (10)	0.0278 (8)	0.0309 (9)	0.0041 (8)	−0.0046 (8)	−0.0028 (7)
C15	0.0403 (13)	0.0395 (12)	0.0580 (14)	0.0189 (11)	−0.0151 (11)	−0.0138 (10)
N1	0.0183 (7)	0.0146 (6)	0.0186 (6)	−0.0018 (5)	−0.0004 (6)	−0.0001 (5)
I1	0.02565 (7)	0.02731 (7)	0.02070 (6)	−0.00322 (5)	0.00032 (5)	−0.00084 (4)

Geometric parameters (Å, º) top

C1—C2	1.515 (3)	C10—H10A	0.9800
C1—C11	1.483 (2)	C10—H10B	0.9800
C1—N1	1.306 (2)	C10—H10C	0.9800
C2—C3	1.509 (2)	C11—H11A	0.9800
C2—C9	1.537 (2)	C11—H11B	0.9800
C2—C10	1.560 (3)	C11—H11C	0.9800
C3—C4	1.395 (2)	C12—H12A	0.9900
C3—C8	1.389 (2)	C12—H12B	0.9900
C4—C5	1.383 (2)	C12—C13	1.529 (2)
C4—N1	1.445 (2)	C12—N1	1.494 (2)
C5—H5	0.9500	C13—H13A	0.9900
C5—C6	1.402 (2)	C13—H13B	0.9900
C6—H6	0.9500	C13—C14	1.520 (2)
C6—C7	1.395 (3)	C14—H14A	0.9900
C7—H7	0.9500	C14—H14B	0.9900
C7—C8	1.398 (2)	C14—C15	1.530 (3)
C8—H8	0.9500	C15—H15A	0.9800
C9—H9A	0.9800	C15—H15B	0.9800
C9—H9B	0.9800	C15—H15C	0.9800
C9—H9C	0.9800

C11—C1—C2	124.28 (15)	H10A—C10—H10B	109.5
N1—C1—C2	111.60 (14)	H10A—C10—H10C	109.5
N1—C1—C11	124.09 (17)	H10B—C10—H10C	109.5
C1—C2—C9	112.64 (14)	C1—C11—H11A	109.5
C1—C2—C10	108.42 (15)	C1—C11—H11B	109.5
C3—C2—C1	100.91 (13)	C1—C11—H11C	109.5
C3—C2—C9	114.81 (15)	H11A—C11—H11B	109.5
C3—C2—C10	109.30 (14)	H11A—C11—H11C	109.5
C9—C2—C10	110.27 (15)	H11B—C11—H11C	109.5
C4—C3—C2	108.68 (14)	H12A—C12—H12B	107.8
C8—C3—C2	131.06 (16)	C13—C12—H12A	109.1
C8—C3—C4	120.19 (15)	C13—C12—H12B	109.1
C3—C4—N1	108.31 (14)	N1—C12—H12A	109.1
C5—C4—C3	123.46 (15)	N1—C12—H12B	109.1
C5—C4—N1	128.23 (15)	N1—C12—C13	112.46 (14)
C4—C5—H5	122.2	C12—C13—H13A	108.6
C4—C5—C6	115.67 (16)	C12—C13—H13B	108.6
C6—C5—H5	122.2	H13A—C13—H13B	107.6
C5—C6—H6	119.0	C14—C13—C12	114.77 (14)
C7—C6—C5	121.94 (16)	C14—C13—H13A	108.6
C7—C6—H6	119.0	C14—C13—H13B	108.6
C6—C7—H7	119.5	C13—C14—H14A	109.3
C6—C7—C8	120.99 (16)	C13—C14—H14B	109.3
C8—C7—H7	119.5	C13—C14—C15	111.80 (16)
C3—C8—C7	117.67 (16)	H14A—C14—H14B	107.9
C3—C8—H8	121.2	C15—C14—H14A	109.3
C7—C8—H8	121.2	C15—C14—H14B	109.3
C2—C9—H9A	109.5	C14—C15—H15A	109.5
C2—C9—H9B	109.5	C14—C15—H15B	109.5
C2—C9—H9C	109.5	C14—C15—H15C	109.5
H9A—C9—H9B	109.5	H15A—C15—H15B	109.5
H9A—C9—H9C	109.5	H15A—C15—H15C	109.5
H9B—C9—H9C	109.5	H15B—C15—H15C	109.5
C2—C10—H10A	109.5	C1—N1—C4	109.97 (14)
C2—C10—H10B	109.5	C1—N1—C12	126.15 (14)
C2—C10—H10C	109.5	C4—N1—C12	123.79 (13)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5···I1	0.95	3.18	3.899 (2)	134
C12—H12A···I1ⁱ	0.99	3.29	4.186 (3)	151
C12—H12B···I1	0.99	3.28	4.249 (3)	167
C13—H13B···I1ⁱⁱ	0.99	3.24	4.172 (3)	158

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, −y+1/2, z+1/2.

Relevant photophysical data of the UV–Vis absorption and fluorescence emission spectroscopy, where λ_abs and λ_em are the absorption and emission maxima, respectively (nm), ε is the molar absorptivity coefficient (× 10⁴ M^-1 cm^-1) and SS is the Stokes shift (cm^-1). top

Solvent	λ_abs	ε	λ_em	SS
Dichloromethane	285	0.79	363	7540
Ethanol	279	2.70	367	8594
Acetonitrile	281	0.89	370	8560

Acknowledgements

The authors acknowlege the agencies CAPES, FAPERGS, CNPq and FAPESP for financial support and fellowships. We thank Professor Dr Teresa Dib Zambon Atvars and the Chemistry Institute of the University of Campinas for the infrastructure and Dr Deborah de A. Simoni for all the valuable discussions.

Funding information

Funding for this research was provided by: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior ; Fundação de Amparo à Pesquisa do Estado do Rio Grande do Sul ; Conselho Nacional de Desenvolvimento Científico e Tecnológico (award No. 470529/2012-1); Fundação de Amparo à Pesquisa do Estado de São Paulo (award Nos. 2009/51605-5 and 2013/16245-2).

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