2,5-Bis­(tri­methyl­silyl­ethynyl)­thieno­[3,2-b]­thio­phene

Khan, M.S.; Al-Naamani, R.S.; Ahrens, B.; Raithby, P.R.

doi:10.1107/S160053680401414X

organic compounds

CRYSTALLOGRAPHIC
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ISSN: 2056-9890

Volume 60| Part 7| July 2004| Pages o1202-o1203

https://doi.org/10.1107/S160053680401414X

2,5-Bis(trimethylsilylethynyl)thieno[3,2-b]thiophene

Muhammad S. Khan,^a Ruqaya S. Al-Naamani,^a Birte Ahrens ^b and Paul R. Raithby ^c ^*

^aDepartment of Chemistry, College of Science, Sultan Qaboos University, PO Box 36, Al Khod 123, Sultanate of Oman, ^bDepartment of Chemistry, University of Bath, Bath BA2 7AY, England, and ^cDepartment of Chemistry, University of Bath, Bath BA2 7AY, England, and CCLRC Daresbury Laboratory, Daresbury, Warrington WA4 4AD, England
^*Correspondence e-mail: p.r.raithby@bath.ac.uk

(Received 7 June 2004; accepted 10 June 2004; online 19 June 2004)

2,5-Bis(trimethylsilylethynyl)thieno[3,2-b]thiophene, C₁₆H₂₀S₂Si₂, is a trimethylsilyl-protected diyne. It is a precursor in the formation of platinum and gold diyne complexes and and polyyne polymers. These materials are of interest because of the π-conjugation that extends through the fused oligothienyl linker unit along the rigid backbone of the polymer. In the structure of the title compound, the oligothienyl group is planar, by crystallographic symmetry, and the trimethylsilyl-alkyne groups are essentially linear.

Comment

We report here the structural characterization of the title compound, 2,5-bis(trimethylsilylethynyl)thieno[3,2-b]thiophene, (I), which is a trimethylsilyl-protected diyne. It is a precursor in the formation of the following series of compounds: the terminal diyne, H—C≡C—R—C≡C—H, the dinuclear platinum(II) diyne, [(Ph)(PEt₃)₂Pt—C≡C—R—C≡C—Pt(PEt₃)₂(Ph)], and the platinum(II) polyyne, trans-[(ⁿBu₃P)₂Pt—C≡C—R—C≡C—]_∞ (R = thieno[3,2-b]thiophene-2,5-diyl). Rigid-rod platinum(II) polyynes with the general formula trans-[(ⁿBu₃P)₂Pt—C≡C—R—C≡C—]_∞ (R = conjugated aromatic/hetero-aromatic linker group) are considered to be good model systems to study the triplet excited state in polymers and provide important information on the photophysical processes that occur within them (Khan, Al-Mandhary, Al-Suti, Hisham et al., 2002 ; Khan, Al-Mandhary, Al-Suti, Feeder et al., 2002 ; Khan et al., 2003 ). The incorporation of heavy transition metals, such as platinum, at regular intervals along the rigid polymer backbone introduces a large component of spin-orbit coupling that allows emission from the triplet excited state of the system via spin cross-over processes (Wittmann et al., 1994 ; Beljonne et al., 1996 ; Younus et al., 1998 ; Chawdhury et al., 1999 ). The novel photophysics of the platinum(II) polyynes leads to materials that are useful for applications in modern opto-electronic devices such as light emitting diodes (LEDs), lasers, photocells and field-effect transistors (FETs) (Wilson et al., 2000 ; Wilson, Chawdhury et al., 2001 ; Wilson, Dhoot et al., 2001 ).

The title compound, (I), crystallizes in the monoclinic space group P2₁/c, with two molecules in the unit cell, such that each molecule sits on a crystallographic centre of symmetry at the centre of the bithiophene unit, at the mid-point of the C8—C8a bond (Fig. 1), and the asymmetric unit contains half of one molecule. The bithiophene unit is planar. Within the bithiophene unit, the S—C bond lengths average 1.730 Å, and the C6—C7 and C8—C8a bond lengths (average 1.395 Å) are significantly shorter than the C7—C8 bond, 1.444 (3) Å, consistent with the normal bonding picture for bithiophene, and similar to those found in a binuclear platinum(II) complex bridged by a thieno[3,2-b]thiophene group (Sato et al., 2002 ). The bond parameters associated with the acetylenic units and the trimethylsilyl groups are similar to those in a number of other bis(trimethylsilyl) substituted diyne compounds (Khan, Ahrens et al., 2002 , 2004 ).

There are no short intermolecular contacts within the crystal structure.

Figure 1
View of (I

) (50% probability displacement ellipsoids). Atoms with the suffix A are the symmetry equivalents, related by 1 − x, −y, 1 − z

Experimental

To a solution of 2,5-dibromothieno[3,2-b]thiophene (2.0 g, 6.71 mmol) in ⁱPr₂NH–THF (70 ml, 1:1 v/v) under nitrogen was added a catalytic mixture of CuI (20 mg), Pd(OAc)₂ (20 mg) and PPh₃ (60 mg). The solution was stirred for 20 min at 323 K and then trimethylsilylethyne (1.64 g, 16.7 mmol) was added. The reaction mixture was left, with stirring, for 20 h at 348 K. The solution was allowed to cool down to room temperature, filtered and the solvent mixture removed under reduced pressure. The residue was subjected to silica column chromatography using hexane to afford the title compound as a colourless solid in 85% yield (1.78 g).

Crystal data

C₁₆H₂₀S₂Si₂
M_r = 332.62
Monoclinic, P2₁/c
a = 15.173 (3) Å
b = 5.7317 (12) Å
c = 10.9836 (18) Å
β = 108.220 (9)°
V = 907.3 (3) Å³
Z = 2
D_x = 1.217 Mg m⁻³
Mo Kα radiation
Cell parameters from 3713 reflections
θ = 2.9–25.0°
μ = 0.42 mm⁻¹
T = 170 (2) K
Needle, colourless
0.23 × 0.07 × 0.04 mm

Data collection

Nonius KappaCCD diffractometer
φ and ω scans
Absorption correction: none
2820 measured reflections
1596 independent reflections
1336 reflections with I > 2σ(I)
R_int = 0.022
θ_max = 25.1°
h = −17 → 18
k = −6 → 6
l = −13 → 12

Refinement

Refinement on F²
R[F² > 2σ(F²)] = 0.037
wR(F²) = 0.100
S = 1.05
1596 reflections
94 parameters
H-atom parameters constrained
w = 1/[σ²(F_o²) + (0.0404P)² + 0.7998P] where P = (F_o² + 2F_c²)/3
(Δ/σ)_max < 0.001
Δρ_max = 0.39 e Å⁻³
Δρ_min = −0.26 e Å⁻³

All the aromatic and methyl H atoms were constrained as riding atoms, fixed to the parent atoms with distances of 0.95 and 0.98 Å, respectively, with U_iso(H) set at 1.2 (aromatic H atoms) or 1.5 (methyl H atoms) times U_eq(parent atom).

Data collection: COLLECT (Nonius, 1998 ); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997 ); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997 ); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S160053680401414X/su6114sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S160053680401414X/su6114Isup2.hkl

Computing details top

Data collection: COLLECT (Nonius, 1998); cell refinement: HKL SCALEPACK (Otwinowski & Minor, 1997); data reduction: HKL DENZO and SCALEPACK (Otwinowski & Minor, 1997); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999).

(I) top

Crystal data top

C₁₆H₂₀S₂Si₂	F(000) = 352
M_r = 332.62	D_x = 1.217 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 15.173 (3) Å	Cell parameters from 3713 reflections
b = 5.7317 (12) Å	θ = 2.9–25.0°
c = 10.9836 (18) Å	µ = 0.42 mm⁻¹
β = 108.220 (9)°	T = 170 K
V = 907.3 (3) Å³	Plate, colourless
Z = 2	0.23 × 0.07 × 0.04 mm

Data collection top

Nonius KappaCCD diffractometer	R_int = 0.022
88 2° φ and 32 2° ω scans	θ_max = 25.1°, θ_min = 3.8°
2820 measured reflections	h = −17→18
1596 independent reflections	k = −6→6
1336 reflections with I > 2σ(I)	l = −13→12

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.037	w = 1/[σ²(F_o²) + (0.0404P)² + 0.7998P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.100	(Δ/σ)_max < 0.001
S = 1.05	Δρ_max = 0.39 e Å⁻³
1596 reflections	Δρ_min = −0.26 e Å⁻³
94 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.

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

	x	y	z	U_iso*/U_eq
S1	0.55976 (4)	−0.07228 (11)	0.35782 (6)	0.0324 (2)
Si1	0.82072 (4)	0.56440 (11)	0.30149 (6)	0.0245 (2)
C1	0.88762 (18)	0.3625 (5)	0.2313 (3)	0.0378 (6)
H1A	0.9153	0.2391	0.2932	0.057*
H1B	0.9368	0.4493	0.2108	0.057*
H1C	0.846	0.2927	0.1529	0.057*
C2	0.75124 (18)	0.7738 (5)	0.1809 (2)	0.0370 (6)
H2A	0.7053	0.6884	0.1127	0.055*
H2B	0.7923	0.8614	0.1441	0.055*
H2C	0.7194	0.8822	0.222	0.055*
C3	0.89848 (18)	0.7245 (5)	0.4417 (2)	0.0403 (7)
H3A	0.863	0.8458	0.4686	0.06*
H3B	0.9492	0.7967	0.4177	0.06*
H3C	0.9241	0.6152	0.5126	0.06*
C4	0.73868 (16)	0.3931 (4)	0.3582 (2)	0.0290 (6)
C5	0.68058 (15)	0.2953 (4)	0.3936 (2)	0.0269 (5)
C6	0.61124 (15)	0.1820 (4)	0.4346 (2)	0.0259 (5)
C7	0.57692 (14)	0.2577 (4)	0.5332 (2)	0.0235 (5)
H7	0.5956	0.394	0.584	0.028*
C8	0.50819 (15)	0.0909 (4)	0.5434 (2)	0.0250 (5)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
S1	0.0330 (4)	0.0353 (4)	0.0331 (4)	−0.0076 (3)	0.0165 (3)	−0.0039 (3)
Si1	0.0244 (4)	0.0256 (4)	0.0260 (4)	−0.0033 (3)	0.0113 (3)	0.0012 (3)
C1	0.0400 (15)	0.0373 (15)	0.0427 (15)	0.0019 (12)	0.0226 (13)	0.0000 (12)
C2	0.0428 (15)	0.0325 (14)	0.0362 (14)	0.0019 (12)	0.0132 (12)	0.0056 (12)
C3	0.0372 (15)	0.0473 (17)	0.0367 (14)	−0.0116 (13)	0.0119 (12)	−0.0053 (13)
C4	0.0293 (13)	0.0317 (14)	0.0273 (12)	−0.0017 (11)	0.0105 (10)	0.0005 (10)
C5	0.0255 (12)	0.0291 (13)	0.0262 (12)	−0.0006 (11)	0.0083 (10)	0.0012 (10)
C6	0.0215 (12)	0.0268 (13)	0.0277 (12)	−0.0033 (10)	0.0055 (10)	0.0041 (10)
C7	0.0188 (11)	0.0307 (13)	0.0218 (11)	−0.0074 (10)	0.0076 (9)	0.0041 (10)
C8	0.0230 (12)	0.0271 (12)	0.0244 (11)	−0.0010 (10)	0.0069 (10)	0.0014 (9)

Geometric parameters (Å, º) top

S1—C8ⁱ	1.718 (2)	C8—S1ⁱ	1.718 (2)
S1—C6	1.742 (2)	C1—H1A	0.98
Si1—C4	1.840 (2)	C1—H1B	0.98
Si1—C2	1.853 (3)	C1—H1C	0.98
Si1—C1	1.858 (3)	C2—H2A	0.98
Si1—C3	1.863 (3)	C2—H2B	0.98
C4—C5	1.207 (3)	C2—H2C	0.98
C5—C6	1.424 (3)	C3—H3A	0.98
C6—C7	1.409 (3)	C3—H3B	0.98
C7—C8	1.444 (3)	C3—H3C	0.98
C8—C8ⁱ	1.381 (4)	C7—H7	0.95

C8ⁱ—S1—C6	90.76 (11)	Si1—C1—H1C	109.47
C4—Si1—C2	107.07 (11)	H1A—C1—H1B	109.51
C4—Si1—C1	108.86 (12)	H1A—C1—H1C	109.49
C2—Si1—C1	111.67 (12)	H1B—C1—H1C	109.46
C4—Si1—C3	107.67 (11)	Si1—C2—H2A	109.43
C2—Si1—C3	110.11 (13)	Si1—C2—H2B	109.49
C1—Si1—C3	111.28 (13)	Si1—C2—H2C	109.50
C5—C4—Si1	175.1 (2)	H2A—C2—H2B	109.42
C4—C5—C6	179.3 (3)	H2A—C2—H2C	109.49
C7—C6—C5	126.2 (2)	H2B—C2—H2C	109.49
C7—C6—S1	114.33 (16)	Si1—C3—H3A	109.46
C5—C6—S1	119.50 (17)	Si1—C3—H3B	109.48
C6—C7—C8	107.8 (2)	Si1—C3—H3C	109.47
C8ⁱ—C8—C7	115.1 (2)	H3A—C3—H3B	109.47
C8ⁱ—C8—S1ⁱ	112.0 (2)	H3A—C3—H3C	109.44
C7—C8—S1ⁱ	132.87 (18)	H3B—C3—H3C	109.51
Si1—C1—H1A	109.44	C6—C7—H7	126.19
Si1—C1—H1B	109.46	C8—C7—H7	126.05

Symmetry code: (i) −x+1, −y, −z+1.

Acknowledgements

We thank the Sultan Qaboos University, Oman, the Royal Society of Chemistry for a Journals Grant for International Authors (to MSK), and the DAAD for funding (to BA).

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