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The (3R*,3'R*) configuration of the title compound, C18H16N2S2, (I), has been unambiguously elucidated by X-­ray analysis. Mol­ecules of (I) have C2 symmetry to a good approximation and a strongly folded shape. The interplanar angle between the two halves of a mol­ecule is 67.11 (6)°.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270100004194/jz1394sup1.cif
Contains datablocks I, global

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270100004194/jz1394Isup2.hkl
Contains datablock I

CCDC reference: 147643

Comment top

1,1'-Dimethyl-3,3'-biindoline-2,2'-dithione, (I), a central intermediate in our synthetic work (Schroth et al., 2000), was obtained by oxidative dimerization of indolinethione, (II), using iodine in methanolic solution (Hino et al., 1969). The product is, in principle, able to exist in two diastereomeric forms differing in the chirality at the 3- and 3'-positions. Apart from the (3R*,3'R*) configuration, as formulated for (I), the (3R*,3'S*) counterpart must also be considered {the prefix (3R*,3'R*) corresponds to dl, and (3R*,3'S*) [(3R,3'S) = (3S,3'R)] to meso in the older IUPAC recommendations}. According to NMR spectroscopic characterization and thin layer chromatography findings, the product is homogeneous. Furthermore, its regeneration from the dithiolate, (III), by acidification provides evidence that the (3R*,3'R*) configuration is thermodynamically favoured with respect to the steric alternative (3R*,3'S*) (Schroth et al., 2000). An exact assignment, however, was lacking until now. \sch

A comparison with 1,1'-dimethyl-3,3'-bipyrrolidine-2,2'-dithione, (IV), is useful. This compound arose from the corresponding thiopyrrolidone, (V), via deprotonation and treatment with iodine (Tamaru et al., 1978). Here, the assignment of the (3R*,3'R*) configuration was based on chemical transformations and the assumption that a Cope-type rearrangement of the disulfide formed as the major product, (VI), should proceed through a chair-like arrangement.

In order to classify unequivocally the configuration of compound (I), an X-ray analysis has been performed. Its result confirms the presence of the (racemic) (3R*,3'R*) diastereomer.

The molecular structure of (I) and the atomic numbering used are shown in Fig. 1. The molecule has a strongly folded shape and exhibits C2 symmetry to a good approximation; the (non-crystallographic) twofold axis is a perpendicular bisector of the C2—C11 bond. With respect to the bond lengths, the only significant deviation from the C2 symmetry is shown by C4—C5 and C13—C14, which differ by 0.023 (4) Å. The two indoline ring systems are planar to a good approximation, the r.m.s. deviations of the fitted endocyclic atoms being 0.013 (N1,C1—C8) and 0.021 Å (N2,C10—C17), respectively. The maximum deviations of the S and methyl-C atoms from the corresponding least squares planes are not greater than 0.1 Å. The dihedral angle subtended by the two planes is 67.11 (6)° and the antiperiplanar conformation is illustrated by the torsion angle C1—C2—C11—C10 = 174.8 (2)°.

Most of the bond lengths and angles in (I) agree well with expectation but some details are worthy of discussion. The N atoms in (I) are sp2-hybridized (the bond angles sum to 360.0° at N1 and 359.9° at N2). Due to their different environment, the non-equivalent endocyclic N—C bonds have significantly unequal lengths. The standard values for an Nsp2—Csp2 single or double bond are given as 1.40 and 1.29 Å, respectively, in the literature (Rademacher, 1987). Compared with these values, N1—C4 [1.424 (3) Å] and N2—C13 [1.413 (3) Å] are slightly longer than a normal single bond and N1—C1 [1.335 (3) Å] and N2—C10 [1.339 (4) Å] are near the average between a single and a double bond. On checking the 1998 version of the Cambridge Structural Database (Allen & Kennard, 1993), it appeared that no crystal structure containing a bis(thioxindole) moiety is known. Of the corresponding bis(oxindoles), the racemic (Suyama et al., 1994) and meso (Kato et al., 1985) forms of 1,1',3,3'-tetramethylleucoisoindigo are the most suitable for structural comparison. In their crystal structures the above discussed N—C bond lengths also differ, but less remarkably, by about 0.04 Å. The C2—C11 bond linking the molecular halves has a normal length of 1.537 (2) Å in (I), whereas in the bis(oxindoles) it is markedly lengthened (1.581 and 1.575 Å, respectively).

Experimental top

Compound (I) was synthesized according to the literature method of Hino et al. (1969), recrystallized from benzene and vacuum dried to give colourless prisms [thin layer chromatography with benzene/n-hexane (2:1): Rf = 0.15; m.p. 455 K].

Refinement top

The quadrants ±h+k+l and ±h-k-l were measured. H atoms were located by a difference Fourier synthesis and refined with isotropic displacement parameters, with the exception of the methyl-H atom positions, which were idealized by geometrical considerations and allowed to rotate but not tip.

Computing details top

Data collection: DIF4 (Stoe & Cie 1991); cell refinement: DIF4; data reduction: REDU4 (Stoe & Cie 1991); program(s) used to solve structure: SHELXS86 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP/PC (Siemens 1990); software used to prepare material for publication: SHELXL97.

Figures top
[Figure 1] Fig. 1. The molecular structure and atomic numbering of (I). Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as spheres of arbitrary radii.
(3R*,3'R*)-1,1'-Dimethyl-3,3'-biindoline-2,2'-dithione top
Crystal data top
C18H16N2S2F(000) = 1360
Mr = 324.45Dx = 1.307 Mg m3
Monoclinic, C2/cMo Kα radiation, λ = 0.71073 Å
a = 17.635 (5) ÅCell parameters from 80 reflections
b = 8.418 (2) Åθ = 7.6–13.9°
c = 22.591 (5) ŵ = 0.32 mm1
β = 100.50 (3)°T = 293 K
V = 3297.5 (14) Å3Prism, yellow
Z = 80.49 × 0.21 × 0.15 mm
Data collection top
Stoe STADI4 four-circle
diffractometer
Rint = 0.036
Radiation source: fine-focus sealed tubeθmax = 25.0°, θmin = 1.8°
Planar graphite monochromatorh = 2020
scan width (ω) = 1.05–1.20, scan ratio 2θ:ω = 1.00k = 1010
5790 measured reflectionsl = 2626
2895 independent reflections3 standard reflections every 60 min
1664 reflections with I > 2σ(I) intensity decay: 3.4%
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.042Hydrogen site location: difmap except H9A to H9C and H18A to H18C geom
wR(F2) = 0.106H atoms treated by a mixture of independent and constrained refinement
S = 0.99Calculated w = 1/[σ2(Fo2) + (0.057P)2]
where P = (Fo2 + 2Fc2)/3
2895 reflections(Δ/σ)max = 0.023
241 parametersΔρmax = 0.19 e Å3
0 restraintsΔρmin = 0.27 e Å3
Crystal data top
C18H16N2S2V = 3297.5 (14) Å3
Mr = 324.45Z = 8
Monoclinic, C2/cMo Kα radiation
a = 17.635 (5) ŵ = 0.32 mm1
b = 8.418 (2) ÅT = 293 K
c = 22.591 (5) Å0.49 × 0.21 × 0.15 mm
β = 100.50 (3)°
Data collection top
Stoe STADI4 four-circle
diffractometer
Rint = 0.036
5790 measured reflections3 standard reflections every 60 min
2895 independent reflections intensity decay: 3.4%
1664 reflections with I > 2σ(I)
Refinement top
R[F2 > 2σ(F2)] = 0.0420 restraints
wR(F2) = 0.106H atoms treated by a mixture of independent and constrained refinement
S = 0.99Δρmax = 0.19 e Å3
2895 reflectionsΔρmin = 0.27 e Å3
241 parameters
Special details top

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.

Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

8.0116 (0.0103) x − 7.3936 (0.0047) y + 1.4381 (0.0217) z = 2.7772 (0.0124)

* 0.0249 (0.0020) C1 * −0.0211 (0.0021) C2 * −0.0039 (0.0023) C3 * −0.0097 (0.0025) C4 * −0.0100 (0.0026) C5 * 0.0024 (0.0029) C6 * 0.0117 (0.0026) C7 * 0.0042 (0.0024) C8 * 0.0015 (0.0020) N1 0.0011 (0.0044) C9 0.1001 (0.0026) S1

Rms deviation of fitted atoms = 0.0126

14.9230 (0.0102) x + 0.7081 (0.0057) y + 8.2036 (0.0164) z = 11.7156 (0.0106)

Angle to previous plane (with approximate e.s.d.) = 67.11 (0.06)

* 0.0383 (0.0019) C10 * −0.0187 (0.0019) C11 * −0.0218 (0.0020) C12 * −0.0209 (0.0023) C13 * −0.0218 (0.0024) C14 * 0.0141 (0.0025) C15 * 0.0258 (0.0025) C16 * −0.0017 (0.0021) C17 * 0.0067 (0.0018) N2 − 0.0229 (0.0040) C18 0.0994 (0.0024) S2

Rms deviation of fitted atoms = 0.0214

Refinement. Refinement of F2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F2, conventional R-factors R are based on F, with F set to zero for negative F2. The threshold expression of F2 > σ(F2) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F2 are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
S10.47085 (4)0.22738 (10)0.54668 (3)0.0618 (3)
S20.36455 (5)0.21374 (12)0.75862 (3)0.0778 (3)
N10.33494 (11)0.0865 (3)0.51114 (9)0.0465 (5)
N20.38333 (12)0.0958 (3)0.73988 (9)0.0537 (6)
C10.38766 (13)0.1490 (3)0.55488 (11)0.0426 (6)
C20.35741 (13)0.1339 (3)0.61356 (11)0.0408 (6)
C30.28249 (13)0.0468 (3)0.59512 (10)0.0416 (6)
C40.27082 (13)0.0229 (3)0.53347 (11)0.0447 (6)
C50.20720 (16)0.0520 (4)0.50240 (14)0.0632 (9)
C60.15350 (17)0.1055 (5)0.53550 (15)0.0734 (10)
C70.16355 (16)0.0840 (4)0.59643 (14)0.0663 (9)
C80.22813 (14)0.0070 (4)0.62719 (12)0.0534 (7)
C90.34157 (16)0.0814 (4)0.44748 (11)0.0649 (9)
H9A0.35500.18490.43490.097*
H9B0.29320.04920.42380.097*
H9C0.38090.00670.44210.097*
C100.38775 (14)0.0556 (4)0.72262 (11)0.0500 (7)
C110.41652 (14)0.0553 (3)0.66338 (11)0.0418 (6)
C120.43032 (13)0.1171 (3)0.65277 (11)0.0424 (6)
C130.40882 (14)0.2024 (4)0.69935 (11)0.0503 (7)
C140.41488 (19)0.3667 (4)0.70240 (17)0.0699 (9)
C150.4454 (2)0.4420 (5)0.65781 (17)0.0757 (10)
C160.46747 (18)0.3597 (4)0.61193 (16)0.0657 (9)
C170.45990 (16)0.1957 (4)0.60819 (13)0.0527 (7)
C180.35434 (19)0.1465 (5)0.79337 (13)0.0831 (11)
H18A0.35750.05960.82120.125*
H18B0.38490.23350.81200.125*
H18C0.30160.17960.78210.125*
H20.3504 (12)0.244 (3)0.6289 (10)0.042 (7)*
H50.2030 (15)0.075 (3)0.4617 (13)0.070 (9)*
H60.1078 (16)0.151 (4)0.5161 (12)0.074 (9)*
H70.1247 (15)0.118 (3)0.6195 (12)0.071 (8)*
H80.2383 (14)0.016 (3)0.6715 (12)0.061 (8)*
H110.4623 (13)0.116 (3)0.6684 (10)0.042 (7)*
H140.4002 (15)0.410 (3)0.7368 (13)0.066 (9)*
H150.4516 (19)0.565 (5)0.6604 (15)0.109 (12)*
H160.4909 (16)0.409 (4)0.5790 (14)0.082 (10)*
H170.4765 (16)0.131 (4)0.5803 (13)0.070 (10)*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
S10.0543 (4)0.0662 (6)0.0715 (5)0.0201 (4)0.0286 (4)0.0055 (4)
S20.0879 (6)0.0898 (7)0.0590 (5)0.0057 (5)0.0217 (4)0.0261 (5)
N10.0435 (12)0.0581 (15)0.0393 (12)0.0040 (11)0.0115 (9)0.0028 (11)
N20.0493 (13)0.0694 (18)0.0417 (12)0.0046 (12)0.0060 (10)0.0072 (12)
C10.0438 (15)0.0372 (15)0.0495 (15)0.0004 (11)0.0157 (12)0.0024 (12)
C20.0401 (14)0.0405 (17)0.0437 (14)0.0017 (12)0.0123 (11)0.0037 (12)
C30.0340 (13)0.0485 (16)0.0428 (14)0.0024 (11)0.0084 (10)0.0056 (12)
C40.0357 (13)0.0561 (18)0.0428 (15)0.0036 (12)0.0083 (11)0.0071 (13)
C50.0493 (17)0.093 (3)0.0449 (17)0.0145 (16)0.0020 (14)0.0024 (17)
C60.0418 (16)0.110 (3)0.063 (2)0.0250 (19)0.0031 (14)0.0098 (19)
C70.0389 (16)0.097 (3)0.064 (2)0.0143 (16)0.0094 (14)0.0180 (19)
C80.0394 (15)0.076 (2)0.0458 (17)0.0009 (14)0.0110 (12)0.0095 (15)
C90.0658 (19)0.090 (2)0.0427 (16)0.0089 (17)0.0192 (14)0.0044 (16)
C100.0424 (14)0.067 (2)0.0394 (14)0.0039 (14)0.0037 (11)0.0057 (15)
C110.0372 (14)0.0464 (17)0.0414 (14)0.0062 (13)0.0060 (11)0.0063 (12)
C120.0351 (13)0.0427 (17)0.0459 (15)0.0032 (12)0.0017 (11)0.0016 (13)
C130.0432 (15)0.055 (2)0.0480 (16)0.0042 (14)0.0027 (12)0.0027 (15)
C140.073 (2)0.060 (3)0.070 (2)0.0113 (18)0.0059 (18)0.019 (2)
C150.081 (2)0.049 (2)0.086 (3)0.0014 (18)0.0129 (19)0.010 (2)
C160.064 (2)0.057 (2)0.071 (2)0.0088 (17)0.0029 (16)0.0142 (19)
C170.0477 (16)0.055 (2)0.0524 (18)0.0017 (14)0.0005 (13)0.0113 (16)
C180.083 (2)0.118 (3)0.0520 (18)0.008 (2)0.0221 (16)0.020 (2)
Geometric parameters (Å, º) top
S1—C11.649 (2)C4—C51.365 (4)
S2—C101.650 (3)C5—C61.384 (4)
N1—C11.335 (3)C6—C71.367 (4)
N1—C41.424 (3)C7—C81.382 (4)
N1—C91.465 (3)C10—C111.515 (3)
N2—C101.339 (4)C11—C121.498 (4)
N2—C131.413 (3)C12—C131.383 (3)
N2—C181.459 (3)C12—C171.384 (4)
C1—C21.522 (3)C13—C141.388 (4)
C2—C31.502 (3)C14—C151.379 (5)
C2—C111.537 (3)C15—C161.361 (5)
C3—C81.379 (3)C16—C171.388 (4)
C3—C41.385 (3)
C1—N1—C4112.14 (19)C7—C6—C5121.6 (3)
C1—N1—C9124.7 (2)C6—C7—C8120.8 (3)
C4—N1—C9123.2 (2)C3—C8—C7118.5 (3)
C10—N2—C13111.9 (2)N2—C10—C11107.6 (2)
C10—N2—C18124.5 (3)N2—C10—S2126.3 (2)
C13—N2—C18123.5 (3)C11—C10—S2126.2 (2)
N1—C1—C2107.7 (2)C12—C11—C10103.5 (2)
N1—C1—S1126.02 (18)C12—C11—C2114.1 (2)
C2—C1—S1126.27 (19)C10—C11—C2110.7 (2)
C3—C2—C1103.3 (2)C13—C12—C17119.8 (3)
C3—C2—C11116.0 (2)C13—C12—C11107.8 (2)
C1—C2—C11112.03 (19)C17—C12—C11132.3 (3)
C8—C3—C4119.4 (2)C12—C13—C14121.7 (3)
C8—C3—C2132.5 (2)C12—C13—N2109.1 (3)
C4—C3—C2108.2 (2)C14—C13—N2129.2 (3)
C5—C4—C3122.8 (2)C15—C14—C13117.3 (3)
C5—C4—N1128.6 (2)C16—C15—C14121.8 (4)
C3—C4—N1108.6 (2)C15—C16—C17121.0 (3)
C4—C5—C6116.9 (3)C12—C17—C16118.4 (3)
C4—N1—C1—C22.1 (3)C13—N2—C10—S2179.02 (18)
C9—N1—C1—C2178.5 (2)C18—N2—C10—S22.1 (4)
C4—N1—C1—S1177.6 (2)N2—C10—C11—C122.5 (3)
C9—N1—C1—S11.8 (4)S2—C10—C11—C12178.55 (18)
N1—C1—C2—C32.7 (3)N2—C10—C11—C2120.2 (2)
S1—C1—C2—C3176.9 (2)S2—C10—C11—C258.8 (3)
N1—C1—C2—C11128.2 (2)C3—C2—C11—C1249.3 (3)
S1—C1—C2—C1151.4 (3)C1—C2—C11—C1268.9 (3)
C1—C2—C3—C8178.2 (3)C3—C2—C11—C1067.0 (3)
C11—C2—C3—C855.3 (4)C1—C2—C11—C10174.8 (2)
C1—C2—C3—C42.4 (3)C10—C11—C12—C132.1 (3)
C11—C2—C3—C4125.3 (2)C2—C11—C12—C13118.3 (2)
C8—C3—C4—C50.1 (4)C10—C11—C12—C17176.6 (3)
C2—C3—C4—C5179.4 (3)C2—C11—C12—C1763.0 (3)
C8—C3—C4—N1179.2 (2)C17—C12—C13—C141.0 (4)
C2—C3—C4—N11.3 (3)C11—C12—C13—C14179.9 (2)
C1—N1—C4—C5178.8 (3)C17—C12—C13—N2177.8 (2)
C9—N1—C4—C50.6 (5)C11—C12—C13—N21.0 (3)
C1—N1—C4—C30.5 (3)C10—N2—C13—C120.7 (3)
C9—N1—C4—C3179.9 (2)C18—N2—C13—C12178.2 (2)
C3—C4—C5—C60.3 (5)C10—N2—C13—C14178.1 (3)
N1—C4—C5—C6178.9 (3)C18—N2—C13—C143.0 (4)
C4—C5—C6—C70.1 (5)C12—C13—C14—C151.8 (4)
C5—C6—C7—C80.2 (6)N2—C13—C14—C15176.9 (3)
C4—C3—C8—C70.3 (4)C13—C14—C15—C161.2 (5)
C2—C3—C8—C7179.6 (3)C14—C15—C16—C170.2 (5)
C6—C7—C8—C30.4 (5)C13—C12—C17—C160.3 (4)
C13—N2—C10—C112.0 (3)C11—C12—C17—C16178.2 (3)
C18—N2—C10—C11176.8 (2)C15—C16—C17—C120.9 (5)

Experimental details

Crystal data
Chemical formulaC18H16N2S2
Mr324.45
Crystal system, space groupMonoclinic, C2/c
Temperature (K)293
a, b, c (Å)17.635 (5), 8.418 (2), 22.591 (5)
β (°) 100.50 (3)
V3)3297.5 (14)
Z8
Radiation typeMo Kα
µ (mm1)0.32
Crystal size (mm)0.49 × 0.21 × 0.15
Data collection
DiffractometerStoe STADI4 four-circle
diffractometer
Absorption correction
No. of measured, independent and
observed [I > 2σ(I)] reflections
5790, 2895, 1664
Rint0.036
(sin θ/λ)max1)0.594
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.042, 0.106, 0.99
No. of reflections2895
No. of parameters241
H-atom treatmentH atoms treated by a mixture of independent and constrained refinement
Δρmax, Δρmin (e Å3)0.19, 0.27

Computer programs: DIF4 (Stoe & Cie 1991), DIF4, REDU4 (Stoe & Cie 1991), SHELXS86 (Sheldrick, 1990), SHELXL97 (Sheldrick, 1997), XP/PC (Siemens 1990), SHELXL97.

Selected geometric parameters (Å, º) top
S1—C11.649 (2)N2—C131.413 (3)
S2—C101.650 (3)C1—C21.522 (3)
N1—C11.335 (3)C2—C111.537 (3)
N1—C41.424 (3)C10—C111.515 (3)
N2—C101.339 (4)
N1—C1—C2107.7 (2)N2—C10—C11107.6 (2)
N1—C1—S1126.02 (18)N2—C10—S2126.3 (2)
C1—C2—C11112.03 (19)C10—C11—C2110.7 (2)
C3—C2—C11—C1249.3 (3)C3—C2—C11—C1067.0 (3)
C1—C2—C11—C1268.9 (3)C1—C2—C11—C10174.8 (2)
 

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