Diseleno[2,3-b:3′,2′-d]selenophene and Diseleno[2,3-b:3′,2′-d] thiophene: Building Blocks for the Construction of [7]Helicenes

Article abstract of DOI:10.1021/acs.joc.7b01362

New building blocks, 2,5-di(trimethylsilanyl)diseleno[2,3-b:3′,2′-d]selenophene ((TMS)₂-DSS) and 2,5-di(trimethylsilanyl)diseleno[2,3-b:3′,2′-d]thiophene ((TMS)₂-DST), for helicenes were obtained from selenophene with total yields of 54 and 61%. From (TMS)₂-DSS and (TMS)₂-DST, selenophene-based hetero[7]helicenes, 5,5′-di(trimethylsilanyl)benzo[1,2-b:3,4-b′]bis(diseleno[2,3-b:3′,2′-d]thiophene) (rac-1), and 5,5′-di(trimethylsilanyl)benzo[1,2-b:3,4-b′]bis(diseleno[2,3-b:3′,2′-d]selenophene) (rac-2) were prepared. The overall yields from selenophene were approximately 6.5 and 6.1%, respectively. Intermolecular interactions such as C-Se, C-S, and Se-Se were observed in the crystal packings of rac-1 and rac-2. In addition, the absorption behaviors of rac-1 and rac-2 were investigated.

Full text of DOI:10.1021/acs.joc.7b01362

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Note
Diseleno[2,3-b:3#,2#-d]selenophene(DSS) and Diseleno[2,3-b:3#,2#-
d]thiophene(DST): Building Blocks for the Construction of [7]Helicenes
Wan Xu, Longlong Wu, Maohong Fang, Zhiying Ma, Zhen Shan, Chunli Li, and Hua Wang
J. Org. Chem., Just Accepted Manuscript • DOI: 10.1021/acs.joc.7b01362 • Publication Date (Web): 27 Sep 2017
Downloaded from http://pubs.acs.org on September 27, 2017
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Diseleno[2,3-b:3′,2′-d]selenophene(DSS) and Diseleno[2,3-b:3′,2′-d]
thiophene(DST): Building Blocks for the Construction of
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[
7]Helicenes
†
†
*
*
Wan Xu , Longlong Wu , Maohong Fang, Zhiying Ma, Zhen Shan, Chunli Li and Hua Wang
Engineering Research Center for Nanomaterials, Henan University, Kaifeng, 475004, P. R. China
E-mail: chunli79@126.com; hwang@henu.edu.cn
†
These authors contributed equally to this work.
rac-1
rac-2
Abstract
New building blocks, 2,5-di(trimethylsilanyl)-diseleno[2,3-b:3′,2′-d]selenophene
(TMS) -DSS) and 2,5-di(trimethylsilanyl)-diseleno[2,3-b:3′,2′-d]thiophene((TMS) -
(
2
2
DST) for helicenes were obtained from selenophene with total yields of 54% and 61%.
From (TMS) -DSS and (TMS) -DST, selenophene-based hetero[7]helicenes, 5,5′-
2
2
di(trimethylsilanyl)benzo[1,2-b:3,4-b′]bis(diseleno[2,3-b:3′,2′-d]thiophene)(rac-1)
and 5,5′-di(trimethylsilanyl)benzo[1,2-b:3,4-b′]bis(diseleno[2,3-b:3′,2′-d]selenophene)
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(
rac-2) were prepared. The overall yields from selenophene were approximately 6.5%
and 6.1%, respectively. Intermolecular interactions such as C–Se, C–S and Se–Se
were observed in the crystal packings of rac-1 and rac-2. In addition, the absorption
behaviors of rac-1 and rac-2 were investigated.
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Helicenes are defined as ortho-fused aromatic compounds, which have interesting
π-conjugated helical structures and are widely applied in asymmetric catalysis,
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molecular recognition, and circularly polarized luminescence materials. Helicenes are
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generally divided into carbohelicenes and heterohelicenes. Thiahelicene is a kind of
carbon-sulfur helicene that contains all sulfur atoms down the lateral edge of
molecular scaffolds, and all thiophene units cross-conjugated and fused to form
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helical structure. Rajca et al. have synthesized series of thiahelicenes such as [5]-,
3
b,4
[
7]-, [9]-, [11]thiahelicenes.
Wang et al. have reported series of studies about the
1
,3b,5
synthesis of carbon-sulfur helicenes, double helicenes, and triple helicenes.
They
have also successfully modulated the position of the absorption peaks of carbon-sulfur
1
double helicenes by changing their spacer group.
Selenophene is a close analog of thiophene. In general, substitution of sulfur with
selenium leads to many differences. The atom size of selenium is larger than that of
sulfur (covalent radii are 1.20 and 1.05 Å, respectively) and selenium is more
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polarizable because of the larger number of electrons. In solid state, selenium-
containing compounds often undergo increased Se–Se interactions, which confer
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ordering on molecular scale and result in well-aligned solid-state packing, and show
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,7
excellent charge-transport properties.
However, limited research has been accorded to selenophene derivatives than
thiophene derivatives, especially in its synthesis and organic functional materials,
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,8
because the preparation of these derivatives is difficult. As such, replacing sulfur
with selenium remains a big challenging, yet at the same time rewarding, endeavor.
By comparison, bearing larger atom size, less electronegativity, and more polarization,
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selenium leads to obvious differences in numbers of properties. Inspired by the
specificity of selenium, we investigate the synthesis of selenophene-based helicenes,
and develop their key synthetic routes and processing conditions. In addition, we hope
to modulate the inner helix climb and turn in-plane of benzohetero[7]helicene by
changing the number of selenophenes.
In this study, we use diseleno[2,3-b:3′,2′-d]selenophene(DSS) and diseleno[2,3-
b:3′,2′-d]thiophene(DST) as building blocks for helicenes. We likewise report the
synthesis and crystal structures of two new kinds of selenophene-based helicenes,
namely, rac-1 and rac-2. The UV-vis absorption spectral behaviors of rac-1 and rac-2
are also described.
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Synthesis of (TMS) -DSS, (TMS) -DST, rac-1, and rac-2
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The synthetic route of (TMS) -DSS and (TMS) -DST is shown in Scheme 1.
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Through bromination, trimehtylsilanyl(TMS-) protection, bromine dance, CuCl2
oxidative coupling, and cyclization with selenium and bis(phenylsulfonyl)sulfide
(
(PhSO ) S), (TMS) -DSS, and (TMS) -DST were obtained from selenophene with
2 2 2 2
total yields of 54% and 61%.
2,5-Dibromoselenophene(3) was prepared from selenophene according to
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literature method. Following Br/Li exchange of 3 with n-BuLi, chlorotrimethylsilane
was added to produce 5-bromo-2-trimethylsilanylselenophene(4) with yield of 94%.
Highly efficient bromine dance reaction was observed in 4 using lithium
diisopropylamide(LDA) to generate 4-bromo-2-trimethylsilanylselenophene(5) with
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5% yield. Following Li/Br exchange in 5 with n-BuLi, resultant aryllithium was
oxidized with CuCl to afford 5,5′-di(trimethylsilanyl)-3,3′-diselenophene(6) with
2
8
8% yield. n-BuLi was introduced to deproton in 6 to give dilithiated 6. One side, the
reaction of dilithiated 6 with selenium gave the mixture of (TMS) -DSS and 2,5-
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di(trimethylsilanyl)-diseleno[2,3-c:3′,2′-e][1,2]diseleninecyclohexadienes(7).
Separating (TMS) -DSS and 7 mixture is problematic owing to their similar solubility
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and polarity. However, 7 can be successfully converted into (TMS) -DSS by heating
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o
mixture of 7 and Cu nanopowder at 140-150 C for several minutes without solvent.
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The preparation yield of (TMS) -DSS from 6 is about 75%. For another, (TMS) -DST
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can be prepared through reaction of dilithiated 6 and (PhSO ) S with 85% yield.
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In the synthesis of rac-1 and rac-2, oxidative photocyclization of 1,2-
diarylethylenes is the crucial step(Scheme 2). 2-Bromo-5-(trimethylsilanyl)diseleno-
[
2,3-b:3′,2′-d]thiophene(8a) and 2-bromo-5-(trimethylsilanyl)diseleno[2,3-b:3′,2′-d]
selenophene(8b) could be obtained with yields of 90% and 83%, by treating (TMS)2-
5
a
DST and (TMS) -DSS with NBS in mixture solvent(HOAc-CHCl ), respectively.
2
3
Following Li/Br exchange on 8a and 8b with n-BuLi, N,N-dimethylformamide(DMF)
was added to produce 5-trimethylsilanyl-diseleno[2,3-b:3′,2′-d]thiophene-2-
carbaldehyde(9a)
and
5-trimethylsilanyl-diseleno[2,3-b:3′,2′-d]selenophene-2-
carbaldehyde(9b). After intermolecular McMurry reaction of 9a and 9b using
TiCl /Zn/pyridine,
bis(2-trimethylsilanyl-diseleno[2,3-b:3′,2′-d]thiophene-5-
bis(2-trimethylsilanyl-diseleno[2,3-b:3′,2′-d]selenophene-5-
4
yl)ethane(10a)
and
yl)ethane(10b) were obtained with yields of 41% and 56%, respectively. Following
oxidative photocyclization of 10a and 10b in the presence of iodine in dry benzene
via irradiation of 450 W Hg medium pressure lamp, rac-1 and rac-2 were prepared
with yields of 40% and 35%, respectively. From selenophene, the steps in creating
rac-1 and rac-2 with yields of 6.5% and 6.1%, respectively, are shown as follows.
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a
Scheme 1. Synthetic route to (TMS) -DSS and (TMS) -DST
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a
Reagents and conditions: (a) NBS(2.2 equiv), CHCl , r.t.; (b) (i) n-BuLi(1.0 equiv),
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Et O, -78 C/2 h; (ii) TMSCl(1.5 equiv), -78 C/0.5 h; (c) (i) LDA(1.3 equiv), THF, -
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78 C/6 h; (d) (i) n-BuLi(1.0 equiv), Et O, -78 C/2 h; (ii) CuCl (2.0 equiv), -55 C/2
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h to r.t.; (e) (i) n-BuLi(2.1 equiv), Et O, 0 C/2 h; (ii) Se(5.0 equiv), -55 C/2 h to r.t.;
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(f) Cu(5.0 equiv), 145 C/0.5 h; (g) (i) n-BuLi(2.1 equiv), Et O, 0 C/2 h; (ii)
2
o
(
PhSO ) S(1.02 equiv), -78 C/2 h.
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Scheme 2. Synthetic route to rac-1 and rac-2
a
o
Reagents and conditions: (a) NBS(1.05 equiv), CHCl /HOAc(8/1), 0 C/2 h; (b) (i) n-
3
o
o
BuLi(1.05 equiv), Et O, -78 C/2 h; (ii) DMF(2.0 equiv), -78 C/1 h; (c) TiCl (5.0
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equiv), Zn(10.0 equiv), pyridine(5.0 equiv), THF; (d) hv, iodine(0.5 equiv), toluene.
Crystallographic analysis for (TMS) -DSS, rac-1, and rac-2
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A
B
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Figure 1. Molecular structures for (TMS) -DSS, rac-1, and rac-2 and space fill mode
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for rac-1 and rac-2. (A) Molecular structure for (TMS) -DSS, (B) side view for
2
(TMS) -DSS, (C) molecular structure for rac-1, (D) side view for rac-1, (E) space fill
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mode for rac-1, (F) molecular structure for rac-2, (G) side view for rac-2, and (H)
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space fill mode for rac-2. Carbon, selenium, sulfur, and silicon atoms are depicted
with thermal ellipsoids set at 30% probability level, and all hydrogen atoms are
omitted for clarity.
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The molecular structures of (TMS) -DSS, rac-1, and rac-2 are all confirmed
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through single-crystal analysis(Figure 1). In (TMS) -DSS, two (TMS) -DSS
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molecules pair together. All selenophene rings are approximately coplanar(Figures 1A,
o
o
1
B). The C25-C27-C13-C14 and C20-C22-C23-C16 torsion angles are 5.4 and 4.3 ,
o
respectively. The interplanar angle of two (TMS) -DSS molecules is 84.8 . With the
2
formation of benzene ring from 10a, rac-1 is compressed with helical
structure(Figures 1C, 1D, 1E). The distance between H5A–H20A is 2.96 Å, which is
larger than that of H2–H17 in bis(trimethylsilanyl)benzohexathia[7]helicene (2.72
5b
Å). Repulsion of the facing terminal selenophene rings results in an interplanar
angle of 51.8° between the terminal selenophene rings, which is larger than that of the
5
b
terminal thiophene units in bis(trimethylsilanyl)benzohexathia[7]helicene. Angles
o
o
between the least-squares planes of neighboring rings are between 3.4 and 12.3 .
With benzene ring as reference, the inner(C5, C6, C8, C11, C12, C16, C19, C20)
o
helix climbs 2.94 Å and turns in-plane by 318.9 , which are larger than those in
5
b
bis(trimethylsilanyl)benzohexathia[7]helicene. This difference may be explained by
the average bond length of C-Se (1.88 Å) in rac-1 being longer than that of C-S (1.73
o
Å), and the average bond angle of C-Se-C (86.1 ) being smaller than that of C-S-C
o
5b
(
90.1 ) in bis(trimethylsilanyl)benzohexathia[7]helicene. Crystal packing of rac-
1(Figure S41) reveals that each rac-1 molecule interacts with six adjacent molecules
through intermolecular C–Se(3.58, 3.57 and 3.52 Å), C–S(3.44 Å), and Se–Se(3.75 Å)
interactions.
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With the formation of benzene ring from 10b, rac-2 is compressed into the
helix(Figures 1F, 1G, 1H). The distance between H5A–H20A is 3.15 Å, which is
larger than that of in rac-1. The interplanar angle between terminal selenophene rings
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o
is 49.0 , which is smaller than that of in rac-1. The angles between the least-squares
o
o
planes of neighboring rings are between 7.5 and 10.8 . With benzene ring as
reference, the inner (C5, C6, C8, C10, C15, C16, C19, C20) helix climbs 2.98 Å and
o
turns in-plane by 324.9 , which are larger than that of in rac-1. The average bond
o
length of C-Se is 1.88 Å, and the average bond angle of C-Se-C is 86.0 . Crystal
packing of rac-2(Figure S41) reveals that each rac-2 molecule interacts with five
adjacent molecules through intermolecular C–Se(3.55, 3.60 Å) and Se–Se(3.73, 3.76
5
b
Å) interactions. From bis(trimethylsilanyl)benzohexathia[7]helicene to rac-1 and
rac-2, the inner helix climb and turn in-plane gradually become larger. The result
shows that modification of the inner helix climb and turn in-plane of
benzohetero[7]helicene, including thiophene and selenophene, can be achieved by
changing the number of thiophenes and selenophenes.
Figure 2. UV-vis absorption spectra of (TMS) -DST, (TMS) -DSS, rac-1, and rac-2 in
2
2
-5
dichloromethane at room temperature([C] = 1 × 10 M).
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The UV-vis absorption spectra for (TMS) -DST, (TMS) -DSS, rac-1, and rac-2
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are shown in Figure 2. (TMS) -DST and (TMS) -DSS have similar absorption
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behavior with maximum absorption peak at 288 nm. Rac-1 and rac-2 have similar
absorption behavior compared with bis(trimethylsilanyl)benzohexathia-[7]helicene
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b
(
absorption peaks at 264, 332, and 347 nm). Rac-1 and rac-2 are significantly red-
shifted than bis(trimethylsilanyl)benzohexathia[7]helicene and show two major
absorption bands at the ranges of 280-325 nm (Band-I) and 325-385 nm (Band-II). In
Band-I, rac-1 shows a maximum absorption peak at 289 nm. Rac-1 has π-electron
delocalization, including helical distortion and possible conjugation through the
selenium and sulfur atoms with two major absorption peaks at 349 and 363 nm in
Band-II.
To obtain the effects of molecular structure and electron distribution on
spectroscopic properties of rac-1 and rac-2, electronic structure and excited-state
14
calculations of these compounds were determined using the Gaussian 09 . Visualized
HOMO and LUMO distributions and calculated frontier orbital energies for rac-1 and
rac-2 are presented in Supporting Information(Figure S34). The predicted UV-vis
spectra are consistent with experimental curves(Figure S35), and transition
contributions are listed(Table S1). The absorption peak of 289 nm in Band-I is
characterized
mainly
by
the
contributions
of
HOMO→LUMO+10,
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HOMO−1→LUMO+5, and HOMO→LUMO+3. The absorption peaks of 349 and
3
63 nm in Band-II are characterized mainly by the contributions of
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HOMO−1→LUMO and HOMO→LUMO, respectively. Rac-2 has π-electron
delocalization including helical distortion and possible conjugation through selenium
atoms with two major absorption peaks at 353 and 366 nm in Band-II, and shows
maximum absorption peak at 288 nm and shoulder peak at 310 nm in Band-I. The
absorption and shoulder peaks in Band-I are characterized mainly by the contributions
of HOMO−3→LUMO+2 and HOMO→LUMO+3, respectively. Absorption peaks in
Band-II are characterized mainly by the contributions of HOMO→LUMO and
HOMO−1→LUMO, respectively. In Band-II, slight bathochromic shifts can be
observed from rac-1 to rac-2; however, rac-1 and rac-2 are significantly red-shifted
5b
than bis(trimethylsilanyl)benzohexathia[7]helicene.
In addition, we have evaluated the transitions states between two chiral states
using DFT calculations. We directly consider simplified models of the molecules,
named as rac-1-H and rac-2-H. In which, the TMS groups in rac-1 and rac-2 are
replaced by hydrogen atoms. As presented in Figure S36, S37, the isomerization
barriers of rac-1-H and rac-2-H are estimated to be 35.4 and 37.7 kcal/mol,
respectively.
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In conclusion, from selenophene, (TMS) -DSS and (TMS) -DST, were used as
2
2
building blocks for helicenes. Using these molecules, two new kinds of selenophene-
based helicenes, namely, rac-1 and rac-2, were successfully prepared. Single-crystal
analysis shows the predicted twofold symmetry for rac-1 and rac-2 and the existence
of multiple short contacts, including C–Se, C–S, and Se–Se interactions. From
0
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5
b
bis(trimethylsilanyl)benzohexathia[7]helicene to rac-1 and rac-2, the inner helix
climb and turn in-plane gradually become larger, and the UV-vis absorption spectra
red shifts with increasing of selenophene number. (TMS) -DSS and (TMS) -DST can
2
2
be used not only as building blocks for selenophene-based helicenes but also for
1
0
preparation of new types of organic functional materials based on selenophene. The
current work provides a foundation for the development of selenophene chemistry.
Experimental Section
General Procedures and Materials. Ether and tetrahydrofuran (THF) for use on
vacuum line were freshly distilled from sodium/benzophenone prior to use. t-BuLi
(
pentane) and n-BuLi (hexane) were obtained from Energy Chemical, prior to use,
11
their concentrations were determined by titration with N-pivaloyl-o-toluidine.
Column chromatography was carried out on silica gel (300-400 mesh). Analytical
thin-layer chromatography was performed on glass plates of Silica Gel GF-254 with
detection by UV. Standard techniques for synthesis under inert atmosphere, using
gasbag and Schlenk glassware equipped with an 8-mm PTFE vacuum stop-cock were
employed. All starting materials and reagents were commercially available.
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H NMR and C NMR spectra were recorded on 300 or 400 MHz NMR
instrument using CDCl as solvent. IR spectra were obtained using an FT-IR
3
instrument. HRMS analysis was carried out on a mass spectrometer equipped with
DART-Positive. Melting point determination was taken on a Melt-Temp apparatus
and was uncorrected. The X-ray crystallographic analyses were performed using
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crystals of compounds (TMS) -DSS, rac-1 and rac-2 with the size 0.43 × 0.16 × 0.14,
2
0
.41 × 0.12 × 0.09, 0.34 × 0.25 × 0.06 mm, respectively. The intensity data were
collected with the ω scan mode (296 K) on diffractometer with CCD detector using
Mo K radiation (λ = 0.71073Å). The data were corrected for Lorentz and polarisation
α
1
2
effects and absorption corrections were performed using SADABS program. The
crystal structures were solved using the SHELXTL program and refined using full
13
matrix least squares. Further details are in the deposited CIFs. Slow evaporation of
solutions of (TMS) -DSS, rac-1 and rac-2 in CHCl -CH OH (1:3, 2:3, 1:1, v/v) was
2
3
3
employed, respectively for growing single crystals. The predicted absorption spectra
were computed within the TD-DFT/PCM approaches based on b3lyp/6-31g* level.
HOMO and LUMO distributions and isomerization barriers of rac-1-H and rac-2-
H(i.e. the TMS replaced by hydrogen atom) at the b3lyp/6-31g* level.
Synthesis of 2,5-dibromoselenophene (3)
Selenophene (1.76 g, 13.4 mmol) was dissolved in CHCl (45 mL), NBS (5.26 g,
3
29.6 mmol, 2.2 equiv) was added in one portion, and afterward the orange solution
was stirred at room temperature for about 10 h. The reaction mixture was quenched
with H O at room temperature, extracted with CH Cl (3 × 15 mL) and then washed
2
2
2
with saturated Na S O (20 mL) and water (2× 20 mL). After drying over MgSO , the
2
2
3
4
solvent was removed under vacuum. The residue was purified by column
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o
chromatography on silica gel with petrol ether (60-90 C) as eluent to yield 3 (3.54 g,
9
1%) as a light yellow liquid. From another reaction on the 5.21 g scale of
1
selenophene, 10.33 g (90%) of 3 was obtained. H NMR (400 MHz, CDCl ) δ = 7.00
3
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(
s, 2H) (this data is agreement with the analyses reported in the literature).
Synthesis of 2-bromo-5-(trimethylsilanyl)selenophene (4)
To a solution of 3 (1.95 g, 6.8 mmol) in dry ethyl ether (30 mL), n-BuLi (2.9 mL,
o
2
.3 M in hexane, 6.7 mmol, 1.0 equiv) was added dropwise at -78 C. After keeping at
o
o
-
78 C for 2 h, TMSCl (1.3 mL, 10.2 mmol, 1.5 equiv) was added at -78 C, then the
reaction mixture was kept at -78 °C for 0.5 h, then warmed up slowly to ambient
o
temperature overnight. The reaction mixture was quenched with H O at -78 C,
2
extracted with CH Cl (3 × 20 mL) and then washed with H O (3× 25 mL). After
2
2
2
drying over MgSO , the solvent was removed under vacuum. The residue was
4
o
purified by column chromatography on silica gel with petrol ether (60-90 C) as
eluent to yield 4 (1.78 g, 94%) as a light yellow liquid. From another reaction on the
1
1
1.71 g scale of 3, 10.43 g (91%) of 4 was obtained. H NMR (CDCl , 400 MHz) δ
3
(
ppm) 7.28 (d, J = 3.6 Hz, 1H), 7.21 (d, J = 3.6 Hz, 1H), 0.29(s, 9H) (this data is
1
5
agreement with the analyses reported in the literature).
Synthesis of 4-bromo-2-(trimethylsilanyl)selenophene (5)
n-BuLi (1.7 mL, 2.5 M in hexane, 4.3 mmol, 1.3 equiv) was added dropwise to
o
diisopropylamine (0.7 mL, 5.0 mmol, 1.5 equiv) in THF (5 mL) at 0 C. After 0.5 h at
o
0 C, the prepared LDA solution was transferred by syringe into a solution of 4
o
o
(0.9361 g, 3.3 mmol) in THF (40 mL) at -78 C. After 6 h at -78 C, methanol was
added to quench the reaction. The reaction mixture was extracted with CH Cl (3 × 15
2
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mL) and washed with saturated NaCl (20 mL) and H O (2 × 20 mL), and then dried
2
over MgSO . After the removal of the solvent under vacuum, the residue was purified
4
10
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60
o
by column chromatography on silica gel with petrol ether (60-90 C) as eluent to yield
5
(0.8882 g, 95%) as a light yellow liquid. From another reaction on the 4.1059 g
1
scale of 4, 3.7149 g (90%) of 5 was obtained. H NMR (CDCl , 400 MHz): δ 8.10 (s,
3
1
H), 7.41 (s, 1H), 0.31 (s, 9 H) (this data is agreement with the analyses reported in
1
5
the literature).
Synthesis of 5,5′-di(trimethylsilanyl)-3,3′-diselenophene (6)
To a solution of 5 (0.8720 g, 3.1 mmol) in dry ethyl ether (20 mL), n-BuLi (1.2
o
mL, 2.5 M in hexane, 3.0 mmol, 1.0 equiv) was added dropwise at -78 C. After
o
keeping at -78 C for 2 h, dry CuCl (0.8310 g, 6.2 mmol, 2.0 equiv) was added. The
2
o
reaction mixture was kept at -55 C for 2 h, then warmed up slowly to ambient
o
temperature overnight. The reaction mixture was quenched with methanol at -78 C,
extracted with CH Cl (3 × 15 mL) and then washed with H O (3× 20 mL). After
2
2
2
drying over MgSO , the solvent was removed under vacuum. The residue was
4
o
purified by column chromatography on silica gel with petrol ether (60-90 C) as
o
eluent to yield 6 (0.5500 g, 88%) as a light yellow solid. Mp: 68-69 C. From another
1
reaction on the 3.3088 g scale of 5, 2.1660 g (91%) of 6 was obtained. H NMR
1
3
(CDCl , 400 MHz) δ (ppm) 8.28 (s, 2H), 7.76 (s, 2H), 0.35(s, 18H), C NMR(CDCl ,
3
3
1
00 MHz): δ 148.63, 142.35, 136.51, 129.87, 0.29. HRMS (DART-Positive) m/z:
+
[
M+H] calcd for C H Se Si 406.9663; found 406.9662. IR(KBr): 3124, 3026,
14 23
2
2
-1
2
947, 2892 cm .
Synthesis of 2,5-di(trimethylsilanyl)-diseleno[2,3-b:3′,2′-d]thiophene
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(
(TMS) -DST)
2
n-BuLi (0.76 mL, 2.4 M in hexane, 1.9 mmol, 2.1 equiv) was added dropwise
o
into a solution of 6 (0.3598 g, 0.9 mmol) in Et O (30 mL) at 0 C, then the reaction
2
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mixture was kept for 2 h. (PhSO ) S (0.2851 g, 0.9 mmol, 1.02 equiv) was added at -
2
2
o
o
7
8 C, the reaction mixture was kept at -78 C for 2 h, then warmed up slowly to
ambient temperature overnight. The reaction mixture was quenched with methanol at
o
-78 C, extracted with CH Cl (3 × 15 mL) and then washed with water (3× 10 mL).
2
2
After drying over MgSO , the solvent was removed under vacuum. The residue was
4
o
purified by column chromatography on silica gel with petrol ether (60-90 C) as
o
eluent to yield (TMS) -DST (0.3284 g, 85%). Mp: 76-78 C. From another reaction
2
1
on the 1.70 g scale of 6, 1.49 g (82%) of (TMS) -DST was obtained. H NMR (CDCl ,
2
3
1
3
3
1
00 MHz) δ (ppm) 7.76 (s, 2H), 0.36(s, 18H), C NMR(CDCl , 75 MHz): δ 150.61,
3
+
43.69, 143.54, 127.76, 0.24. HRMS (DART-Positive) m/z: [M+H] calcd for
-1
C H SSe Si 436.9232; found 436.9229. IR(KBr): 3037, 2956, 2894 cm .
14
21
2
2
Synthesis of 2,5-di(trimethylsilanyl)-diseleno[2,3-b:3′,2′-d]selenophene
((TMS) -DSS)
2
n-BuLi (3.3 mL, 2.4 M in hexane, 7.8 mmol, 2.1 equiv) was added dropwise into
o
a solution of 6 (1.5026 g, 3.7 mmol) in Et O (30 mL) at 0 C, then the reaction
2
mixture was kept for 2 h. Dry Se (metals basis) (1.4675 g, 18.6 mmol, 5.0 equiv) was
o
o
added at -78 C, the reaction mixture was kept at -55 C for 2 h, then warmed up
slowly to ambient temperature overnight. The reaction mixture was quenched with
o
methanol at -78 C, extracted with CH Cl (3 × 25 mL) and then washed with water
2
2
(3× 30 mL). After drying over MgSO , the solvent was removed under vacuum. The
4
residue was purified by column chromatography on silica gel with petrol ether (60-90
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o
C) as eluent to yield the mixture of (TMS) -DSS and 7. The mixture and Cu
2
o
nanopowder were heated to 145 C without use of any solvent for 0.5 h, (TMS) -DSS
2
(1.3413 g) as a light yellow solid was obtained, the preparation yield of (TMS) -DSS
2
10
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60
o
from 6 was 75%. Mp: 125-127 C. From another reaction on the 0.1061 g scale of 6,
1
0.0909 g (72%) of (TMS) -DSS was obtained. H NMR (CDCl , 400 MHz) δ (ppm)
2
3
1
3
7
1
.79 (s, 2H), 0.36(s, 18H), C NMR(CDCl , 100 MHz): δ 152.15, 145.61, 141.29,
3
+
29.24, 0.27. HRMS (DART-Positive) m/z: [M+H] calcd for C H Se Si 484.8672;
1
4
21
3
2
+
found 484.8670, and m/z: [M+NH ] calcd for C H Se Si N 500.8859; found
3
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2
-1
5
00.8621. IR(KBr): 3040, 2950, 2897 cm
Synthesis of 2-bromo-5-(trimethylsilanyl)diseleno[2,3-b:3′,2′-d]thiophene
(selenophene) (8a, 8b)
(TMS) -DST (0.3284 g, 0.76 mmol) was dissolved in CHCl (20 mL), NBS
2
3
(0.1420 g, 0.80 mmol, 1.05 equiv) was dissolved in 16 mL HOAc-CHCl (v/v = 1/3)
3
o
and added dropwise under good stirring at 0 C. After stirring for 2 h, the reaction
mixture was quenched with H O and extracted with CH Cl (3 × 10 mL), then washed
2
2
2
with saturated NaHCO (20 mL) and water (2 × 20 mL). The organic layer was dried
3
over anhydrous MgSO . After the solvent was removed under vacuum, the residue
4
was washed with 3 × 5 mL hexane to yield 8a (0.3001 g, 90%) as a reddish brown oil.
1
13
H NMR (CDCl , 300 MHz) δ (ppm) 7.68 (s, 1H), 7.63 (s, 1H), 0.37(s, 9H), C
3
NMR(CDCl , 75 MHz): δ 151.33, 143.93, 142.43, 139.76, 138.37, 127.41, 125.20,
3
+
1
14.68, 0.20. HRMS (DART-Positive) m/z: [M+H] calcd for C H BrSSe Si
1
1
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6
-1
4
42.7938; found 442.7933. IR(KBr): 3037, 2952, 2854 cm .
1
8
b: reddish brown oil in yield of 83% (0.0930 g), H NMR (CDCl , 300 MHz) δ
3
13
0
1
2
3
4
5
6
7
8
9
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1
2
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(ppm) 7.71 (s, 1H), 7.65 (s, 1H), 0.36(s, 9H), C NMR (CDCl , 75 MHz): δ 152.84,
3
1
45.88, 142.09, 140.57, 136.02, 128.95, 126.75, 115.48, 0.23. HRMS (DART-
+
Positive) m/z: [M+H] calcd for C H BrSe Si 490.7382; found 490.7378. IR(KBr):
1
1
12
3
-1
2945, 2852 cm .
Synthesis of 5-trimethylsilanyl-diseleno[2,3-b:3′,2′-d]thiophene(selenophene)-2-
carbaldehyde (9a, 9b)
n-BuLi (0.3 mL, 2.4 M in hexane, 0.75 mmol, 1.05 equiv) was added dropwise
o
o
to 8a (0.3167 g, 0.72 mmol) in THF (30 mL) at -78 C. After 2 h at -78 C, DMF (0.1
o
mL, 1.44 mmol, 2.0 equiv) was added at -78 C and kept 0.5 h, then the reaction
mixture warmed up slowly to ambient temperature overnight. The reaction mixture
was quenched with H O, extracted with CH Cl (3 × 15 mL). The organic layer was
2
2
2
washed with saturated NaHCO (20 mL) and water (2 × 20 mL), and then dried over
3
MgSO . The residue was purified by column chromatography on silica gel with petrol
4
o
ether (60-90 C)/CH Cl (v/v = 2/1) as eluent to yield 9a (0.2017 g, 72%) as a brown
2
2
1
solid. Mp: 126-128 °C. H NMR (CDCl , 300 MHz) δ (ppm) 9.84 (s, 1H), 8.28 (s,
3
13
1
1
H), 7.79 (s, 1H), 0.38 (s, 9H). C NMR(CDCl , 75 MHz): δ 184.12, 152.67, 150.62,
3
48.57, 144.37, 144.11, 141.21, 131.01, 127.26, 0.19. HRMS (DART-Positive) m/z:
+
[
M+H] calcd for C H OSSe Si 392.8782; found 392.8779. IR(KBr): 2950, 2843,
1
2
13
2
-1
1
661 cm .
o
1
9b: brown solid in yield of 60% (0.1351 g), Mp: 143-145 C. H NMR (CDCl ,
3
1
3
3
00 MHz) δ (ppm) 9.82 (s, 1H), 8.28 (s, 1H), 7.82 (s, 1H), 0.38 (s, 9H).
C
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NMR(CDCl , 75 MHz): δ 183.74, 153.82, 152.08, 147.88, 145.88, 143.55, 142.03,
3
+
1
4
32.19, 128.67, 0.21. HRMS (DART-Positive) m/z: [M+H] calcd for C H OSe Si
12 13
3
-1
40.8226; found 440.8227. IR(KBr): 2966, 2902, 1646 cm .
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Synthesis of bis(2-trimethylsilanyl-diseleno[2,3-b:3′,2′-d]thiophene(selenophene)-
5-yl)ethane (10a, 10b)
TiCl (0.14 mL, 1.28 mmol, 5.0 equiv) was carefully added into dry THF (10 mL)
4
o
o
at 0 C. After keeping at 0 C for 20 min, zinc dust (0.1675 g, 2.56 mmol, 10.0 equiv)
o
was added, and then the mixture was refluxed at 100 C for 2 h. After that, pyridine
(0.11 mL, 1.28 mmol, 5.0 equiv) was added and the mixture was refluxed for another
1
h. After cooling to ambient temperature, a solution of 9a (0.1000 g, 0.26 mmol) in
o
dry THF (5 mL) was added and the reaction mixture was refluxed at 100 C for 18 h.
o
The reaction was quenched with water at 0 C, then extracted with CH Cl (3 × 15 mL)
2
2
and washed with saturated NaHCO (15 mL) and H O (2 × 15 mL), and then dried
3
2
over MgSO . After removing the solvent in vacuum, the residue was washed with
4
o
1
Et O (3 × 5 mL) to yield 10a (0.0397 g, 41%) as a orange solid. Mp: 231-234 C. H
2
NMR (CDCl , 300 MHz) for a mixture of cis and trans isomers of 10a. δ (ppm) 7.71
3
(s), 7.62 (s), 7.48 (s), 6.97 (s), 6.76 (s), 0.38 (s), 0.36 (s). The ratio of integral areas of
1
3
the peaks is 1.5:1:0.5:0.5:1:4.5:9. C NMR (CDCl , 75 MHz): δ 151.28, 151.14,
3
148.93, 145.04, 144.37, 144.34, 142.76, 142.73, 141.33, 141.28, 140.13, 136.96,
1
27.67, 127.59, 126.16, 124.85, 123.56, 120.77, 0.23. HRMS (DART-Positive) m/z:
+
[
M+H] calcd for C H S Se Si 752.7592; found 752.7591. IR(KBr): 2955, 1648,
24 25
2
4
2
-1
9
20, 833 cm .
o
1
1
0b: orange solid in yield of 56% (0.0330 g), Mp: 258-260 C. H NMR (300
1
3
MHz, CDCl ): δ (ppm) 7.74 (s, 2H), 7.51 (s, 2H), 6.98 (s, 2H), 0.37 (s, 18H) C
3
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NMR (CDCl , 75 MHz): δ 152.69, 150.33, 146.25, 143.39, 140.73, 135.13, 129.07,
3
+
1
8
24.93, 122.13, 0.26. HRMS (DART-Positive) m/z: [M+H] calcd for C H Se Si
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6
2
-1
48.6481; found 848.6477. IR(KBr): 2949, 2848, 1510, 916, 835 cm .
0
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9
0
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Synthesis of 5,5'-di(trimethylsilanyl)benzo[1,2-b:3,4-b′]bis(diseleno[2,3-b:3′,2′-
d]thiophene(selenophene)) (rac-1, rac-2)
To a solution of 10a (0.0117 g, 0.016 mmol) in dry toluene (25 mL), iodine
(0.0119 mg, 0.047 mmol, 3.0 equiv) and 2-methyloxirane (0.1 mL) was added. The
reaction solution was irradiated with a 450 W unfiltered Hg medium pressure lamp.
The reaction was monitored by TLC every 15 minutes, and irradiation was stopped
when the 10a was consumed up. The reaction was quenched with saturated Na S O
3
2
3
(
10 mL). The reaction mixture was extracted with CH Cl (3 × 10 mL) and washed
2 2
with H O (3 × 10 mL), and then dried over MgSO . After removing the solvent in
2
4
o
vacuum, the crude product was purified by PTLC with petrol ether (60-90 C)
CH Cl (v/v = 3:1) as developer to yield rac-1 (0.0045 g, 39%) as a light yellow solid.
/
2
2
o
1
Mp: 269-271 C. H NMR (CDCl , 300 MHz) δ (ppm) 7.70 (s, 2H), 7.28 (s, 2H) ,
3
13
0.04 (s, 18H). C NMR (CDCl , 75 MHz): δ 147.73, 146.39, 142.55, 142.44, 138.75,
3
+
1
38.41, 131.67, 130.00, 121.34, -0.04. HRMS (DART-Positive) m/z: [M+H] calcd
-1
for C H S Se Si 750.7435; found 750.7435. IR(KBr): 3085, 3061, 2930 cm .
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2
4
2
o
1
rac-2: light yellow solid in yield of 35% (0.0034 g), Mp: > 300 C. H NMR
13
(
CDCl , 300 MHz) δ (ppm) 7.72 (s, 2H), 7.31 (s, 2H), 0.03 (s, 18H). C NMR
3
(
CDCl , 75 MHz): δ 148.91, 148.05, 143.46, 140.52, 140.27, 137.87, 132.72, 131.01,
3
+
1
20.90, 0.04. HRMS (DART-Positive) m/z: [M+H] calcd for C H Se Si 846.6324;
2
4
23
6
2
-1
found 846.6323. IR(KBr): 3080, 3042, 2920, 2859 cm .
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Acknowledgment We gratefully acknowledge Mr. Pengtao Ma and Mr. Yuquan Feng
for their assistance in the crystal measurements and discussion. This work is
financially supported by the NSFC (51503056, U1304207, and 21672054), the
Innovation Scientists and Technicians Troop Construction Projects of Henan Province
(C20150011), and the Foundation for Distinguished Young Scientists of Henan
University (YQPY20140056).
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Supporting Information Available: Characterization data of all compounds;
crystallographic CIF files of (TMS) -DSS, rac-1, and rac-2; predicted UV/vis spectra,
2
HOMO and LUMO distributions; the calculated frontier orbital energies for rac-1 and
rac-2 and isomerization barriers of rac-1-H and rac-2-H are included. This material is
available free of charge at http://pubs.acs.org.
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