Facile deoxygenation of telluroxides, tellurones and selenones with nickel boride at ambient temperature

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Facile Deoxygenation of Telluroxides,
Tellurones and Selenones with Nickel
Boride at Ambient Temperature
Jitender M. Khurana a & Anshika Lumb a
a Department of Chemistry, University of Delhi, Delhi, -110007, India
Version of record first published: 19 Jan 2012.
To cite this article: Jitender M. Khurana & Anshika Lumb (2012): Facile Deoxygenation of
Telluroxides, Tellurones and Selenones with Nickel Boride at Ambient Temperature, Organic
Preparations and Procedures International: The New Journal for Organic Synthesis, 44:1, 96-101
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Organic Preparations and Procedures International, 44:96–101, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 0030-4948 print / 1945-5452 online
DOI: 10.1080/00304948.2012.643702
Facile Deoxygenation of Telluroxides, Tellurones
and Selenones with Nickel Boride
at Ambient Temperature
Jitender M. Khurana and Anshika Lumb
Department of Chemistry, University of Delhi, Delhi-110007, India
Nickel boride has been reported as a convenient and efficient reagent in numerous
transformations.1–5 It is superior to many other metal catalysts due to its low cost, ease
of preparation and handling, non-pyrophoric nature and easy removal. Unlike its initial ap-
plications as a heterogeneous catalyst, nickel boride is used as a reducing agent without aid
of hydrogen as it contains adsorbed hydrogen.1 Nickel boride, prepared in situ, has been re-
ported for a variety of applications such as, reductions,6 deoxygenations,7 desulfurizations,8
etc. In continuation of our studies on the deoxygenation of sulfoxides and selenoxides,9 and
in view of the paucity of the reagents for the deoxygenation of chalcogenide monoxides10–12
and especially chalcogenide dioxides,13 we attempted to develop new methodologies using
nickel boride and now report the deoxygenation of aryl, alkyl and aralkyl telluroxides,
tellurones and selenones with nickel boride generated in situ from nickel(II) chloride and
sodium borohydride in different solvents at ambient temperature to give the corresponding
tellurides and selenides respectively.
Di(4-tolyl)telluroxide (1a) was chosen as a model substrate to investigate and opti-
mize the conditions for the deoxygenation. The reactions were carried with nickel boride
generated in situ in different solvents such as MeOH, THF, DMF and dioxane, and in
different molar ratios of substrate to nickel boride. It was observed that deoxygenation of
di(4-tolyl)telluroxide could be achieved with anhydrous NiCl2 and sodium borohydride
in dry THF using 1:1:3 molar ratio of substrate:NiCl2:NaBH4 at ambient temperature to
give 86% of di(4-tolyl)telluride (2a). The protocol was then extended to a variety of aryl,
alkyl and aralkyl telluroxides. All the telluroxides underwent deoxygenation to give corre-
sponding tellurides in high yields (Table 1). Halo substituents were unaffected under these
Submitted May 20, 2011.
Address correspondence to Jitender M. Khurana, Department of Chemistry, University of Delhi,
Delhi-110007, India. E-mail: jmkhurana1@yahoo.co.in
96

Deoxygenation of Telluroxides, Tellurones, and Selenones
97
Table 1
Deoxygenation of Telluroxides (1a–g) with Nickel Boridea
Substrate (s)
Product
Yield (%)
mp (◦C)
lit. mp (◦C)
Time (min)
1a
1b
1c
1d
1e
1f
2a
2b
2c
2d
2e
2f
86
87
84
82
78
80
85
66–68
54–56
116–120
90–92
Liquid
Liquid
68–70
64–6514
54–5514
118–12015
89–9016
Liquid23
Liquid13
-
10
15
75
180
120
60
1g
2g
15
a) Ratio of substrate:NiCl2:NaBH4 is 1:1:3 except for 1d which is 1:2:6.
conditions (Eq. 1).
O
NiCl2/NaBH4
R
Te R′
R
Te R′
(1)
r.t., dry THF
2
1
a) R = R′ = 4-MeC6H4
d) R = R′ = 4-ClC6H4
g) R = R′ = MeO2CC6H4
b) R = R′ = 4-OMeC6H4 c) R = R′ = 4-BrC H
6
4
e) R = R′ = C4H9
f) R = C6H5, R′ = Me
While the reactions of di(4-tolyl)telluroxide (1a) in dioxane and DMF were sluggish,
reaction in dry MeOH using molar ratios 1:1:3 of substrate:NiCl2:NaBH4 was complete in
3 min but yielded only 44% of di(4-tolyl)telluride (2a); this could be due to the formation
of detellurized product as well. The reaction of di(4-carbomethoxyphenyl)telluroxide (1g)
under above conditions (i.e molar ratio 1:1:3 of substrate:NiCl2:NaBH4 in dry MeOH)
yielded di(4-carbomethoxyphenyl)telluride (2g) (42%) and methyl benzoate (45%) (Eq. 2).
However, methyl benzoate was not formed when the reaction was carried out in dry THF.
This result suggests that detellurization is competing with deoxygenation when the reaction
is carried out in methanol. This is possibly due to the enhanced reactivity of nickel boride
in protic solvent (MeOH) as compared to aprotic solvent (THF).
NiCl2/NaBH4
4-(MeO2CC6H4)2Te
PhCO2Me
+
4-(MeO2CC6H4)2Te
O
(2)
r.t., MeOH
1g
2g
The scope of the reagent was also investigated for the deoxygenation of tellurones, se-
lenones and sulfones. The reactions of di(4-tolyl)tellurone (3a) and diphenyl selenone
(3g) were carried out under the optimized conditions used for telluroxides but deoxygena-
tion was incomplete even with higher molar ratios of catalyst to substrate:NiCl2:NaBH4
(1:5:15). The reactions were then attempted in different solvents at different tempera-
tures using varying molar ratios of substrate to nickel boride to achieve the complete

98
Khurana and Lumb
Table 2
Deoxygenation of Tellurones (3a–o) and Selenones with Nickel Boridea
Substrate (s)
Product
Yield (%)
mp (◦C)
lit. mp (◦C)
Time (min)
3a
3b
3c
3d
3e
3f
3g
3h
3i
3j
3k
3l
3m
3n
3o
2a
2b
2c
2d
2e
2f
4g
4h
4i
4j
4k
4l
4m
4n
4o
83
84
79
76
79
78
88
86
82
84
84
85
75
83
84
66–68
54–56
116–118
90–92
Liquid
Liquid
Liquid
40–42
66–68
52–54
94–96
112–114
Liquid
Liquid
Liquid
64–6514
54–5514
118–12015
89–9016
Liquid23
Liquid13
Liquid16
4413
10
25
15
20
10
20
20
120
60
60
120
60
120
180
180
6913
55–5613
95–9613
114–11513
Liquid18
Liquid18
Liquid13
a) Ratio of substrate:NiCl2:NaBH4 is 1:1:3 except for 3h and 3o which is 1:2:6.
deoxygenation. MeOH:H2O (1:1, v/v) was found to be the solvent of choice. Deoxygena-
tions of di(4-tolyl)tellurone (3a) and diphenyl selenone (3g) were complete with a 1:1:3
molar ratio of substrate:NiCl2:NaBH4 in MeOH:H2O (1:1) at ambient temperature leading,
to high yields of di(4-tolyl) telluride (2a) and diphenyl selenide (4g), respectively. Subse-
quently, various aryl, alkyl and aralkyl tellurones and selenones underwent deoxygenation
in high yields to the corresponding tellurides and selenides in methanol:water (1:1, v/v) at
ambient temperature (Table 2).
O
NiCl2/NaBH4
R
X
R′
R
X
R′
r.t., MeOH:H2O
(1:1)
O
3
(3)
2,4
c)
f)
i) R = R
a) R = R
′
= 4-MeC6H4, X = Te
= 4-ClC6H4, X = Te
= C6H 5,X = Se
= 4-OMeC6H4, X = Se k) R = R
= C4H9, X = Se
b) R = R
e) R = R
h)
′
= 4-OMeC6H4, X = Te
= C4H9, X = Te
= CH2C6H5, X = Se
= 4-ClC6H4, X = Se
= C12H25, X = Se
R = R
′ = 4-BrC6H4, X = Te
d) R = R
′
′
′
R = C6H5, R' = Me, X = Te
g) R = R
j) R = R
m) R = R
′
′
′
R = R
′
′
= 4-MeC6H4, X = Se
= 4-BrC6H4, X = Se
′
l) R = R
n)
R = R
′
o) R = C3H7, R′ = 4-MeC6H4, X =Se
No deselenized or detellurized products were obtained under these conditions. The
amount of water plays a crucial role in the reaction. The use of higher amounts of water
resulted in sluggish or incomplete reactions while lowering the amount of water resulted in
the formation of a mixture of products. Sulfones were unaffected under these and all other
conditions attempted by us.

Deoxygenation of Telluroxides, Tellurones, and Selenones
99
Thus, we have developed a very efficient and a convenient method for the deoxy-
genation of telluroxides in dry THF, selenones and tellurones in MeOH-H2O (1:1) to the
corresponding chalcogenides at ambient temperature using nickel boride generated in situ.
Experimental Section
All melting points were recorded on Tropical Labequip apparatus and are uncorrected.
IR spectra were recorded on Perkin-Elmer FT-IR SPECTRUM-2000 and NMR spectra
were obtained on Hitachi FT-NMR (60 MHz) and JEOL at 400 MHz using TMS as
internal standard. Mass spectra were acquired on KC-455-TOF Mass Spectrometer (Mi-
cromass, Manchester, UK). THF (S. D. Fine), methanol (S. D. Fine), nickel chloride
hexahydrate (S. D. Fine) and sodium borohydride (E. Merck) were used in all the reactions.
Anhydrous Nickel(II) chloride was prepared by heating Nickel(II) chloride hexahydrate
in a crucible till golden yellow. It was then allowed to cool at room temperature and
stored over calcium chloride in a desiccator. Di(4-carbomethoxyphenyl)telluride and di(4-
carbomethoxyphenyl) telluroxide were prepared by reported methods.30–34 All the products,
except di(4-carbomethoxyphenyl)telluride, are known and were identified by co-TLC with
authentic samples and by mp, IR and NMR spectra which are in good agreement with
reported literature.14–29
General Procedure of Deoxygenation of Telluroxides. In a typical experiment, di(4-
tolyl)telluroxide (1 mmol, 0.325 g), anhydrous nickel chloride (1 mmol, 0.129 g) and dry
THF (10 mL) with a stir bar and were placed in a 50 mL RB flask, fitted with a condenser
and calcium chloride guard tube. Sodium borohydride (3 mmol, 0.114 g) was added to the
mixture and the contents were stirred at room temperature. The progress of the reaction was
monitored by TLC using petroleum ether:ethyl acetate (80:20, v/v) as eluent. After complete
disappearance of the telluroxide, the reaction mixture was cooled to room temperature and
filtered through a Celite pad (∼2.5 cm). The nickel boride precipitate was washed with
ethyl acetate (2 × 5 mL). Water (20 mL) was added to the filtrate, which was extracted with
ethyl acetate (3 × 10 mL). The combined ethyl acetate extract was dried over anhydrous
Na2SO4 and concentrated on a rotary evaporator to give a solid which after drying under
vacuum, was characterized by its mp, IR and 1H NMR spectra as di(4-tolyl)telluride (86%).
Di(4-Carbomethoxyphenyl)telluroxide (1g), mp. 168–170◦C; IR(KBr): 2922, 1725,
1273, 1106, 730 cm−1; 1H-NMR (CDCl3, 60 MHz, ppm): δ 3.9 (s, 6H, -OCH3), 7.8–8.0 (m,
8H, Ar-H); 13C NMR (CDCl3, 400 MHz, ppm): δ 52.22, 129.53, 129.78, 130.36, 137.47,
166.72; MS (ESI) m/z 415.9859.
Anal. Calcd for C16H14O5Te: C, 46.43; H, 3.41. Found: C, 46.62; H, 3.21.
Di(4-Carbomethoxyphenyl)telluride (2g), mp. 66–68◦C; IR(KBr): 2925, 1723, 1584,
1284, 1104, 754, 471 cm−1; 1H-NMR(CDCl3, 60 MHz, ppm): δ 3.9 (s, 6H, -OCH3), 7.8–7.8
(m, 8H, Ar-H); 13C NMR (CDCl3, 400 MHz, ppm): δ 52.22, 129.53, 129.78, 130.36, 137.47,
166.72; MS (ESI) m/z 400.0120.
Anal. Calcd for C16H14O4Te: C, 48.30; H, 3.55; Found: C, 48.53; H, 3.41.
General Procedure of Deoxygenation of Tellurones/Selenones: In a typical reaction,
to a solution of tellurone/selenone (1 mmol) in 10 mL of methanol:H2O (1:1, v/v) in a 50
mL RB flask fitted with a condenser and magnetic stir bar, was added NiCl2.6H2O, followed
by the cautious addition of NaBH4. The reaction mixture was stirred vigorously at room

100
Khurana and Lumb
temperature. After the completion of reaction as monitored by TLC, using CHCl3:MeOH
(60:40, v/v) as eluent, the reaction mixture was worked up as described above. The product
was analyzed by comparison of their mp, IR and 1H NMR spectra with those reported in
literature.
Acknowledgements
Financial assistance by UGC, New Delhi [Project no. F-32-203/2006(SR)], and AL thanks
University of Delhi for the award of UTA.
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