2-(2,2-Dibromo­ethen­yl)thio­phene

The title compound, C₆H₄Br₂S, represents a versatile building block for the preparation of π-conjugated redox-active thienyl oligomers and metal-mediated cross-coupling reactions. This is due to the presence of an electrochemically active thienyl heterocycle and a reactive dibromo­vinyl substituent, which easily undergoes dehydro­bromination in the presence of n-butyl­lithium to afford 2-ethynyl­thio­phene. In the molecule, the alkenyl unit and the thio­phene ring are almost coplanar with an angle of 3.5 (2)° between the normals of the best planes of the thio­phene ring and the vinyl moiety.

Key indicators

• Single-crystal X-ray study
• T = 173 K
• Mean [sigma](C-C) = 0.007 Å
• R factor = 0.058
• wR factor = 0.139
• Data-to-parameter ratio = 20.3

checkCIF/PLATON results

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Alert level C
PLAT341_ALERT_3_C Low Bond Precision on  C-C Bonds (x 1000) Ang ..          7
PLAT918_ALERT_3_C Reflection(s) # with I(obs) much smaller I(calc)          1

Alert level G
PLAT072_ALERT_2_G SHELXL First  Parameter in WGHT Unusually Large.       0.11

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   2 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   1 ALERT type 2 Indicator that the structure model may be wrong or deficient
   2 ALERT type 3 Indicator that the structure quality may be low
   0 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

The title compound (Scheme 1, Fig. 1), which is easily accessible from thiophene-2-carbaldehyde via the Corey-Fuchs reaction, has over the last 30 years become a versatile starting material for a variety of organic transformations and a precursor in material science. This interest is due to the conjugation between the electrochemically active thienyl heterocycle with the reactive halogenated olefin moiety. Originally it was used for the preparation of terthiophenes (Beny et al., 1982). Recent applications include Pd-catalyzed cross-coupling reactions (Herz et al., 1999; Rao et al., 2010) as well as the synthesis of imidazo[1,5-α]pyridines (Zhang et al., 2010).

In the course of our interest in developing new π-conjugated dihalovinyl compounds R—C(H)═CX₂ with functional groups (R = imine, ferrocenyl, [2,2]paracyclophane) as substrates for oxidative addition reactions across low-valent noble metals, we have recently reported the synthesis and crystal structures of 4-2',2'-dibromovinyl[2,2]paracyclophane (Clément et al. 2007a) and (2,2-dibromovinyl)ferrocene (Clément et al. 2007b). With this aim in mind, we also prepared the title compound 2-(2,2-dibromoethenyl)thiophene. A survey of the CSD data base revealed that neither 2-vinylthiophene nor a halogenated derivative of the types [C₄H₃S—C(H)═C(H)X] or [C₄H₃S—C(H)═CX₂] (X = halogen) had been structurally characterized yet. The most related molecule found is 2-thienylmethylenemalononitrile [C₄H₃S—C(H)═C(CN)₂] (Mukherjee et al., 1984). In the latter compound, the angle between the normals of the two planar parts of the molecule, the thiophene cycle and the dicyanovinyl moiety, amounts to 3.6 (5)°. In the title compound, the corresponding angle lies in the same range [3.5 (2)°]. A somewhat larger angle of 10.4° has been determined for (2,2-dibromovinyl)ferrocene [Fc—C(H)═CBr₂] (Clément et al., 2007b), whereas in 4-(2',2'-dibromovinyl)[2,2]paracyclophane [PCP—C(H)═CBr₂] an angle of 51.1° has been observed significantly deviating from coplanarity (Clément et al., 2007a). The length of the vinylic C1—C2 double bond [1.335 (7) Å] matches well with those of [PCP—C(H)═CBr₂] [1.320 (3)°] and [Fc—C(H)═ CBr₂] [1.318 (4) Å] (Clément et al., 2007a; Clément et al., 2007b). A similar bond length of 1.353 (5) Å has also been reported for [C₄H₃S—C(H)═C(CN)₂] (Mukherjee et al., 1984).

Bond lenths and angles of the thienyl moiety may be considered as normal and deserve no further comment. The unit cell consists of 4 molecules which are held together by weak interactions only (Fig. 2). These consist of the short Br1—Br2 distance [3.6501 (9) Å, Br1_5-Br2_2] as well as the short distances between Br2 and the carbon atoms of the thiophene ring [3.604 (5) Å, Br2_2-C4; 3.479 (6) Å, Br2_2-C5; 3.624 (5) Å, Br2_2-C6].

Related literature

The title compound was first prepared in 1980, see: Bestmann et al. (1980). For an alternative synthesis using a Corey–Fuchs reaction, see: Beny et al. (1982). For a structural comparison with 2,2-dibromovinyl[2,2]paracyclophane [PCP—C(H)═CBr₂], (2,2-dibromovinyl)ferrocene [Fc—C(H)═CBr₂], and 2-thienylmethylenemalononitrile [C₄H₃S—C(H)═C(CN)₂], see: Clément et al. (2007a,b) and Mukherjee et al. (1984), respectively. For recent applications, see: Herz et al. (1999); Rao et al. (2010); Zhang et al. (2010).

S2. Experimental

Triphenylphosphine (4.20 g, 16.0 mmol), CBr₄ (5.31 g, 16.0 mmol) and zinc dust (1.05 g, 16.0 mmol) were placed in a Schlenk tube and 40 ml of CH₂Cl₂ were slowly added. The mixture was stirred at room temperature for 28 h. Then, 2-thiophenecarboxaldehyde (0.89 g, 8.00 mmol) in CH₂Cl₂ (10 ml) was added and stirring was continued for further 2 h. The reaction mixture was extracted with three 50 ml portions of pentane. CH₂Cl₂ was added when the reaction mixture became too viscous for further extractions. The extracts were filtered and evaporated under reduced pressure. The crude product was purified by column chromatography on silica gel with CH₂Cl₂/petroleum ether (1:4). Slow evaporation afforded white crystals of 2-(2,2-dibromoethenyl)thiophene (yield: 90%). Characterization data have been previously described in the literature. (Beny et al., 1982)

S3. Refinement

H atoms were refined using a riding model in their ideal geometric positions using the riding model approximation with U_iso(H) = 1.2U_eq(C) for all H atoms.

Computing details

Data collection: EXPOSE in IPDS (Stoe & Cie, 1999); cell refinement: CELL in IPDS (Stoe & Cie, 1999); data reduction: INTEGRATE in IPDS (Stoe & Cie, 1999); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures

	Fig. 1. Molecular structure of the title compound with thermal ellipsoids drawn at the 50% probability level.
	Fig. 2. Crystal packing of 2-(2,2-dibromoethenyl)thiophene. Symmetry operations: (1) x, y, z; (2) -x, y - 1/2, -z - 1/2; (3) -x, -y - 1, -z; (4) x, -y + 1/2, z - 1/2; (5) x - 1, y, z; (6) x, y -1, z; (7) x - 1, -y + 1/2, z - 1/2; (8) -x, -y - 1, -z - 1.

2-(2,2-Dibromoethenyl)thiophene

Crystal data

C6H4Br2S	F(000) = 504
Mr = 267.97	Dx = 2.341 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 980 reflections
a = 9.6843 (19) Å	θ = 2.2–27.0°
b = 7.2379 (14) Å	µ = 10.84 mm^−1
c = 11.484 (2) Å	T = 173 K
β = 109.16 (3)°	Plates, colourless
V = 760.4 (3) Å^3	0.4 × 0.4 × 0.2 mm
Z = 4

Data collection

Stoe IPDS diffractometer	1444 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.064
ϕ scans	θmax = 27.0°, θmin = 2.2°
Absorption correction: numerical (FACEIT in IPDS; Stoe & Cie, 1999)	h = −11→12
Tmin = 0.188, Tmax = 0.658	k = −9→9
6492 measured reflections	l = −14→14
1667 independent reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.058	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.139	H-atom parameters not refined
S = 1.04	w = 1/[σ^2(Fo^2) + (0.1099P)^2] where P = (Fo^2 + 2Fc^2)/3
1667 reflections	(Δ/σ)max < 0.001
82 parameters	Δρmax = 1.36 e Å^−3
0 restraints	Δρmin = −1.73 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.

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 (Ų)

	x	y	z	Uiso*/Ueq
Br1	0.90429 (5)	0.69525 (7)	0.15399 (5)	0.0306 (2)
Br2	0.75506 (5)	0.94572 (7)	0.30330 (4)	0.0290 (2)
C1	0.7287 (5)	0.7946 (6)	0.1647 (4)	0.0214 (9)
C2	0.5999 (5)	0.7559 (7)	0.0803 (4)	0.0225 (9)
H2	0.6061	0.6818	0.0139	0.027*
C3	0.4530 (5)	0.8068 (6)	0.0720 (4)	0.0188 (8)
C4	0.3277 (5)	0.7471 (7)	−0.0213 (4)	0.0225 (9)
H4	0.3305	0.6695	−0.0873	0.027*
C5	0.1970 (6)	0.8134 (7)	−0.0080 (5)	0.0307 (11)
H5	0.1026	0.7857	−0.0637	0.037*
C6	0.2213 (5)	0.9216 (7)	0.0939 (5)	0.0289 (10)
H6	0.1455	0.9771	0.1174	0.035*
S	0.40366 (13)	0.94655 (17)	0.17497 (12)	0.0265 (3)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Br1	0.0220 (3)	0.0379 (4)	0.0324 (3)	0.00528 (18)	0.0097 (2)	−0.0004 (2)
Br2	0.0268 (3)	0.0342 (3)	0.0250 (3)	−0.00466 (18)	0.0072 (2)	−0.00800 (17)
C1	0.024 (2)	0.021 (2)	0.0202 (19)	0.0009 (16)	0.0089 (17)	0.0037 (16)
C2	0.024 (2)	0.020 (2)	0.024 (2)	0.0027 (18)	0.0104 (18)	0.0016 (17)
C3	0.024 (2)	0.0157 (19)	0.0183 (19)	0.0008 (15)	0.0095 (17)	0.0015 (15)
C4	0.024 (2)	0.020 (2)	0.024 (2)	0.0029 (17)	0.0083 (18)	0.0041 (17)
C5	0.020 (2)	0.034 (3)	0.036 (3)	−0.0005 (18)	0.005 (2)	0.006 (2)
C6	0.022 (2)	0.028 (2)	0.037 (3)	−0.0003 (18)	0.011 (2)	0.003 (2)
S	0.0256 (6)	0.0287 (6)	0.0277 (6)	0.0006 (4)	0.0121 (5)	−0.0054 (4)

Geometric parameters (Å, º)

Br1—C1	1.887 (5)	C4—C5	1.408 (7)
Br2—C1	1.878 (5)	C4—H4	0.95
C1—C2	1.335 (7)	C5—C6	1.362 (8)
C2—C3	1.442 (6)	C5—H5	0.95
C2—H2	0.95	C6—S	1.714 (5)
C3—C4	1.397 (7)	C6—H6	0.95
C3—S	1.738 (4)
C2—C1—Br2	124.9 (4)	C3—C4—H4	123.3
C2—C1—Br1	121.3 (4)	C5—C4—H4	123.3
Br2—C1—Br1	113.7 (3)	C6—C5—C4	112.4 (5)
C1—C2—C3	131.4 (4)	C6—C5—H5	123.8
C1—C2—H2	114.3	C4—C5—H5	123.8
C3—C2—H2	114.3	C5—C6—S	112.6 (4)
C4—C3—C2	124.1 (4)	C5—C6—H6	123.7
C4—C3—S	109.8 (3)	S—C6—H6	123.7
C2—C3—S	126.1 (3)	C6—S—C3	91.9 (2)
C3—C4—C5	113.3 (4)