A modified synthesis of tellurophene using NaBH4 to generate sodium telluride

Article abstract of DOI:10.1016/j.jorganchem.2008.04.022

A modified synthesis of tellurophene by reaction of diacetylene with sodium telluride is described. The primary modification involves the convenient in situ generation of sodium telluride by reduction of tellurium metal with NaBH₄ in water.

Full text of DOI:10.1016/j.jorganchem.2008.04.022

Journal of Organometallic Chemistry 693 (2008) 2463–2464
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Journal of Organometallic Chemistry
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Note
A modified synthesis of tellurophene using NaBH to generate sodium telluride
4
Daniel P. Sweat, Chad E. Stephens *
Department of Chemistry and Physics, Augusta State University, 2500 Walton Way, Augusta, GA 30904, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
A modified synthesis of tellurophene by reaction of diacetylene with sodium telluride is described. The
primary modification involves the convenient in situ generation of sodium telluride by reduction of
tellurium metal with NaBH in water.
4
Received 19 March 2008
Received in revised form 14 April 2008
Accepted 14 April 2008
Ó 2008 Elsevier B.V. All rights reserved.
Available online 22 April 2008
Keywords:
Tellurophene
Sodium telluride
Diacetylene
1
,4-Dichloro-2-butyne
1
. Introduction
Tellurophene derivatives have received increased attention in
sodium in liquid ammonia [9]. A procedure involving the in situ
generation of the telluride by reduction of tellurium with sodium
formaldehyde sulfoxylate (Rongalite) has also been described
[10], but it utilizes the expensive bis(trimethylsilyl)-1,3-butadiyne
as a substitute for diacetylene [11]. This particular procedure has
also been difficult for us to reproduce, with reduction of the tellu-
rium not proceeding in suitable fashion in our hands. We thus set
out to develop a modified synthesis, with the most desirable being
one that not only utilizes in situ generated sodium telluride, but
also the less expensive 1,4-dichloro-2-butyne as a source of diacet-
ylene. In this note, we describe our favorable results.
recent years, most notably as potential components of advanced
materials [1] and as substrates for the laser-induced chemical
vapor deposition (CVD) of tellurium metal films [2]. There is also
interest in tellurophenes as potential medicinal agents, particularly
as selenium heterocycles have been shown to possess unique bio-
logical activities [3]. The development of synthetic methodology
for tellurophenes has likewise received increased attention. For
example, Zeni and coworkers have recently described the transi-
tion metal-catalyzed coupling of 2-bromotellurophenes with
either acetylenes [4] or thiols [5]. Others have also developed
new chemistry in this area, such as that involving bi- and ter-tel-
lurophenes [1] and 3-iodotellurophenes [6]. Despite this recent
work, however, tellurophene chemistry remains a relatively under-
developed field, with a major hurdle being the lack of availability
of the parent heterocycle, as noted recently by several authors
2
. Results and discussion
Having had difficulty in generating sodium telluride in situ by
reduction of tellurium with sodium formaldehyde sulfoxylate, we
looked for other possible reducing agents. Upon review of the liter-
ature, the most appealing to us was NaBH , particularly as it can be
4
used in an aqueous solvent system [12]. We thus explored this
approach.
[
1b,4,5,7].
For our own work, we were in need of multi-gram quantities of
tellurophene. The original synthesis [8] of this compound involves
the reaction of sodium telluride (Na Te) with diacetylene, an
4
In contrast to the sulfoxylate, the reaction of NaBH with tellu-
2
rium metal in water gave, in our hands, clear evidence of telluride
formation (exothermic reaction, formation of characteristic violet
color) (Scheme 1). After just 20 min, telluride formation was
deemed complete and the diacetylene was then introduced into
the reaction mixture by heating 1,4-dichloro-2-butyne (1.5 equiv.)
with KOH in a separate flask connected by a gas line. Methanol was
also added at this point to the telluride suspension to help solubi-
lize the diacetylene. Importantly, the entire system was kept under
nitrogen throughout the process, as sodium telluride is very oxy-
gen sensitive.
unstable gas [9]. Neither of these two starting materials are com-
mercially available. A modification involving the in situ generation
of diacetylene from commercially available 1,4-dichloro-2-butyne
has subsequently been described [9]. Unfortunately, this procedure
is still limited by the need to prepare and isolate the unstable tel-
luride before hand, such as by reduction of tellurium metal with
*
Corresponding author. Tel.: +1 706 667 4995; fax: +1 706 434 5597.
E-mail address: cstephe7@aug.edu (C.E. Stephens).
0
022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.04.022

2
464
D.P. Sweat, C.E. Stephens / Journal of Organometallic Chemistry 693 (2008) 2463–2464
Cl
from flask B. After the 2 h, flask B was removed from the heat and
Te
flask A was exposed to air. The resulting black suspension in flask A
was filtered over Celite and extracted with pentane after addition
of brine. The extracts were combined and concentrated on a rotary
evaporator at atmospheric pressure. The remaining dark liquid was
distilled at reduced pressure (house vacuum) using a short Vigreux
column (8 cm) to give 4.28–6.42 g (32–48% yield, n = 4) of tellur-
ophene as a light red liquid boiling at 120 °C (lit. bp [9] 91–92 °C
Cl
NaBH4, H2O
KOH/H O, 1,4-dioxane, Δ
2
MeOH
Na2Te
+
Te
1
at 100 mmHg). The product was pure by GC. H NMR (400 MHz,
Scheme 1. Synthesis of tellurophene by in situ generation of Na
diacetylene.
2
Te and
CDCl
dd, J = 5.6, 2.8 Hz). C NMR (100.6 MHz, CDCl
at 77.5 ppm): d 126.7 (s), 138.3 (s). MS (EI, m/z, %): 182 (C
3
, TMS reference at 0.0 ppm): d 7.83 (dd, J = 5.6, 2.4 Hz), 8.95
1
3
(
3
, solvent reference
4 4
H
1
30
+
130
+
After stirring for 2 h, the reaction mixture was immediately ex-
tracted and the residue distilled under vacuum to give telluroph-
ene as a pale red liquid in 32–48% yield. As a comparison, the
comparable literature procedure which uses pre-formed sodium
telluride, as well as ꢀ5 molar equivalents of 1,4-dichloro-2-butyne
Te , 100), 130 ( Te , 74), 51 (45), 40 (23). These data are con-
sistent with those previously published [9,10].
As an alternative to direct distillation, the extract could be trea-
ted with a 30% solution of bromine in methanol to give 1,1-dib-
romotellurophene as a highly insoluble red solid (11.4 g, 45%) (in
this case, diethyl ether was used as an extraction solvent in place
of pentane). This adduct (m.p. 125 °C dec; lit mp [9] 125 °C dec)
was immediately reduced back to tellurophene by stirring for
20 min in a solution of 26 g NaHSO3 and 16 g K CO dissolved in
(
4
compared to our 1.5 equiv.), reportedly gives an average yield of
8% [9]. As an alternative to distillation, we could isolate the insol-
uble 1,1-dibromotellurophene adduct [9] as a red solid in 45% yield
by addition of methanolic Br to the extract. Reduction of this ad-
2
2
3
duct back to tellurophene using bisulfite, followed by extraction
and distillation, gave tellurophene in 37% overall yield as a yellow
liquid, which was identical otherwise with the pale red samples
prepared by direct distillation.
water (200 mL). This mixture was then extracted with ether, dried
(Na SO ) and distilled under reduced pressure as above to give
2
4
5.0 g (37% overall yield) of a yellow liquid boiling at 120 °C.
The tellurophene was stored in a freezer (0 °C) and showed no
visual degradation over the course of several months. The 1,1-dib-
romotellurophene was stored in a closed amber vial at room tem-
perature and decomposed to a black metallic solid over the course
of several months.
3
. Conclusion
In conclusion, a modified synthesis of tellurophene involving
the in situ generation of sodium telluride by reduction of tellurium
with NaBH in water is presented. With this procedure, telluroph-
ene can be conveniently prepared in 32–48% yield using just
.5 molar equivalents of 1,4-dichloro-2-butyne as a commercial
source of diacetylene, and without the need to first prepare, and
isolate, the unstable sodium telluride.
Acknowledgements
4
1
This work was supported by the Bill and Melinda Gates Founda-
tion. Financial support from our Department is also acknowledged.
Appendix A. Supplementary material
4
. Experimental
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2008.04.022.
Complete details for the synthesis of tellurophene by this meth-
od are given below:
To a 500 mL 3-neck round bottom flask (flask A) equipped with
gas inlet, condenser and addition funnel was added Te powder
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2
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