Synthesis of unsymmetrical pyridyl aryl selenides by the reductive cleavage of SeSe bond

Article abstract of DOI:10.1080/10426500801900980

An efficient protocol for the synthesis of novel hitherto unknown substituted and unsubstituted phenyl pyridyl selenides from dipyridyl/diphenyl diselenides and phenyl/pyridyl halides in the presence of copper catalysed system, Cu2O/Mg/bpy is being presen

Full text of DOI:10.1080/10426500801900980

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Synthesis of Unsymmetrical
Pyridyl Aryl Selenides by the
Reductive Cleavage of Se─Se
Bond
K. K. Bhasin a , Shivani Doomra b , Gurjeet Kaur c
, Ekta Arora a , Neelam Singh a , Yogesh Nagpal a ,
Rajeev Kumar a , Rishu a , T. M. Klapoetke d & S. K.
Mehta a
a Department of Chemistry and Centre of Advanced
Studies in Chemistry , Panjab University ,
Chandigarh, India
b Department of Chemistry , D.A.V.College-10 ,
Chandigarh, India
c Department of Chemistry , G.C.G.-11 ,
Chandigarh, India
d Department of Chemistry and Biochemistry ,
Ludwig Maximilians University , Munich, Germany
Published online: 29 Oct 2008.
To cite this article: K. K. Bhasin , Shivani Doomra , Gurjeet Kaur , Ekta Arora ,
Neelam Singh , Yogesh Nagpal , Rajeev Kumar , Rishu , T. M. Klapoetke & S. K. Mehta
(2008) Synthesis of Unsymmetrical Pyridyl Aryl Selenides by the Reductive Cleavage
of Se─Se Bond, Phosphorus, Sulfur, and Silicon and the Related Elements, 183:4,
992-997, DOI: 10.1080/10426500801900980
To link to this article: http://dx.doi.org/10.1080/10426500801900980
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Phosphorus, Sulfur, and Silicon, 183:992–997, 2008
Copyright © Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426500801900980
Synthesis of Unsymmetrical Pyridyl Aryl Selenides by the
Reductive Cleavage of Se Se Bond
K. K. Bhasin,1 Shivani Doomra,2 Gurjeet Kaur,3
Ekta Arora,1 Neelam Singh,1 Yogesh Nagpal,1
Rajeev Kumar,1 Rishu,1 T. M. Klapoetke,4 and S. K. Mehta1
1Department of Chemistry and Centre of Advanced Studies in
Chemistry, Panjab University, Chandigarh, India
2Department of Chemistry, D.A.V.College-10, Chandigarh, India
3Department of Chemistry, G.C.G.-11, Chandigarh, India
4Department of Chemistry and Biochemistry, Ludwig Maximilians
University, Munich, Germany
An efficient protocol for the synthesis of novel hitherto unknown substituted and
unsubstituted phenyl pyridyl selenides from dipyridyl/diphenyl diselenides and
phenyl/pyridyl halides in the presence of copper catalysed system, Cu O/Mg/bpy
2
is being presented. All the synthesized selenides are either light yellow coloured
liquids or low melting solids. All the newly synthesized compounds have been thor-
oughly characterized by elemental analysis employing various spectroscopic tech-
1
13
77
niques viz., infrared, multinuclear NMR ( H, C, Se) and mass spectrometry
(in representative cases).
Keywords Copper; phenyl; pyridyl; reductive cleavage; selenide
INTRODUCTION
Chemistry of alkyl, aryl, and mixed alkyl aryl selenides has devel-
oped rapidly for the last two decades and find extensive applica-
tions in organic synthesis,1 organic superconductors,2 MOCVD,3 and
biochemistry.4 It is curious to note that the analogous chemistry of
pyridyl derivatives has remained neglected over the years probably due
to non-availability of a convenient and efficient synthesis.
Recently, the chemistry of pyridyl derivatives has attracted the at-
tention of the scientific community due to their unique properties, which
Shivani Doomra is thankful to UGC for teacher-fellowship and leave of absence from
DAV College Abohar during the course of these investigations. KKB is thankful to DST
for financial assistance vide Sanction No.SR/SI/IC-02/2003.
The authors gratefully acknowledge the Department of Science and Technology,
New Delhi, for financial support.
Address correspondence to Shivani Doomra, Department of Chemistry, D.A.V.College-
10, Chandigarh 160 011, India. E-mail: sdoomra@yahoo.co.in
992

Synthesis of Unsymmetrical Pyridyl Aryl Selenides
993
endear them to new and exciting applications in organic synthesis and
biochemistry.5 In recognition of its importance, renewed efforts have
evolved for the convenient methodologies of their synthesis.
Literature is swamped with several synthetic procedures for the
preparation of alkyl, aryl and mixed alkyl aryl selenides. All these meth-
ods employ a reducing agent to reduce elemental selenium-to-selenium
dianion (Se2− and Se22−) viz. NaBH4,6 LiAlH4,7 R4N+BH−,8 LiEt3BH,
4
9
HOCH2SO2Na,10 Na/NH3,11 and so on, followed by quenching with
alkyl/aryl halides. Another versatile approach towards the synthesis of
unsymmetrical organoselenium compounds involve the formation of in-
termediate selenolates RSe− generated insitu by reductive cleavage of
Se-Se bond in diorganyl diselenides. Reductive cleavage of Se-Se bond
can be realized with a galaxy of reducing agents such as N2H4.H2O,12
R4N+BH4−,8 NaBH4,13 LiEt3BH, 9 and so on. In recent times, some met-
als like indium,14 lanthanum,15samarium,16and their salts17 have also
been reported to cleave Se Se bond.
Catalytic procedures are considered more applicable, however,
as many functional groups cannot withstand harsh reaction con-
ditions. Various complexes such as Pd(PPh3)4,18 (bpy)2NiBr2,19 and
RhCl(PPh3)230 have been successfully exploited to prepare unsymmetri-
cal selenides. A number of selenides have been prepared by the direct
nickel (II)21 and copper (II)22-catalyzed coupling of a diselenide with
aryl iodides.. In this paper, we wish to report a mild, convenient, and
economical method for the synthesis of pyridyl phenyl selenides using
eco-friendly reagents.
RESULTS AND DISCUSSION
Mautner et al.23 synthesized 2,2ꢀ-dipyridyl diselenide by reacting 2-
bromo pyridine with toxic hydrogen selenide. Later, many research
groupsmodified this procedure by developing safe and convenient meth-
ods for their preparation by reducing elemental selenium with sodium
borohydride in different solvents.24 Researchers used different method-
ologies, in the subsequent years, explored variations of the published
procedures to improve the yield of 2,2ꢀ-dipyridyl diselenide. Bhasin
et al.25have developed and optimized the conditions for the preparation
of stable substituted dipyridyl diselenides by the bromine exchange of
2-bromo methyl substituted pyridine using n-butyl lithium in THF at
−78◦C that avoids the use of toxic gases coupled with better yields.
In pursuance of our work on the synthesis of dipyridyl diselenides, we
report herein a convenient, operationally simple, and facile synthetic
route for the synthesis of hitherto unknown substituted and unsub-
stituted pyridyl phenyl selenides. The method involves the reductive

994
K. K. Bhasin et al.
cleavage of dipyridyl/diphenyl diselenides in DMF at 110◦–120◦C using
the catalyzed system Cu2O/Mg/bpy. The intermediate selenolate anion
generated in situ by the slow addition of dipyridyl/diphenyl diselenides
to the heterogenous system was followed by quenching with different
electrophiles as depicted in Scheme 1.
SCHEME 1 Synthesis of unsymmetric phenyl pyridyl selenides.
All the reactions were carried out in the presence of oxygen free ni-
trogen. The mixed pyridyl selenides thus prepared are all stable com-
pounds and can be purified by column chromatography. All the synthe-
sized phenyl pyridyl selenides are light yellow coloured liquids or low
melting solids. The compounds dissolve readily in organic solvents and
have a shelf life of several months without any sign of decomposition
even at room temperature under nitrogen atmosphere.
EXPERIMENTAL
All the manipulations were carried under a dry and deoxygenated
nitrogen atmosphere to prevent the oxidation of oxygen sensitive
selenium intermediates. Elemental selenium (Himedia) was stored
in a desiccator prior to use. Diphenyl26 and dipyridyl27 diselenides
were prepared by literature methods. DMF was distilled using K2CO3
and stored on molecular sieves. Bromobenzene (Aldrich) and other
chemicals were of analytical grade and used without further purifi-
cation. 2-Bromopyridine and 2,5-dibromopyridine were preparedfrom
the corresponding 2-aminopyridines 28(Aldrich). 1H, 13C, and 77Se
NMR spectra were recorded on a Jeol AL 300 MHz spectrometer in
CDCl3, using Me4Si as an internal standard for 1H and 13C NMR.
Me2Se was used as an external reference for 77Se NMR; Infrared
spectra were obtained between KBr plates on a Perkin-Elmer model
1430 spectrophotometer. C, H, and N analysis was performed on a

Synthesis of Unsymmetrical Pyridyl Aryl Selenides
995
Perkin-Elmer 2400 CHN analyzer. Mass spectra were obtained on a VG
7070H mass spectrometer. Separation and purification of compounds
were done by column chromatography performed on activated silica
gel using hexane as eluant.
General Procedure for the Synthesis of Unsymmetrical
Selenides
In a 50 ml flame dried three necked round bottom flask (200 mg) acti-
vated magnesium, (28 mg) cuprous oxide, (62 mg) 2,2ꢀ-bipyridyl were
taken in 15 ml dried DMF. Diphenyl diselenide (0.62 g, 2 mmol) was
added to the above mixture followed by quenching with substituted 2-
bromopyridines (4 mmol). The mixture was stirred at 110oC for 15–20
h. The colour of the reaction mixture changed from red to dark brown
within 20–25 min. Stirring and refluxing was continued until the com-
pletion of the reaction, which is monitored by TLC. After evaporation
of the solvent, the residue obtained was dissolved in dichloromethane.
Ionic impurities were removed by washing the organic extract repeat-
edly with distilled water. The combined organic fractions were dried
over anhydrous sodium sulphate and the solvent was evaporated on
rota-evaporator. The product thus obtained was purified over silica
column using hexane as eluant. Using this methodology, a number of
compounds were prepared which were characterized through elemental
analysis and various spectroscopic techniques.
Unsymmetrical Pyridyl Phenyl Selenides
2-Pyridyl phenyl selenide, (C5H4NSeC6H5), [1].. Yellow viscous liq-
1
uid; Yield: 60 %; H NMR (CDCl3/TMS): δ 8.29–8.31 (d, 1H, 3.6Hz),
7.56–7.63 (m, 2H), 7.26–7.33 (m, 4H), 6.85–6.9 (m, 2H); 13C NMR
(CDCl3/TMS): δ 158.7, 149.53, 136.12, 129.12, 128.79, 127.66, 123.8,
119.99; 77Se NMR: δ 469.859; I.R. (KBr, cm−1): 3408.3,2984.1, 2924.9,
1951.3, 1734.8, 1569.7, 1476.3, 1302.4, 1275.5, 1147.6, 1042.7, 985.3,
840.2, 477.7, 461.3; MS (EI, %): 234 (85), 232 (70), 154 (30), 78(80);
Anal. Calcd. : C, 56.17; H, 3.82; N, 5.95%; Found; C, 56.50; H, 3.53; N,
5.72%.
3-Methyl-2-pyridyl phenyl selenide, (CH3C5H3NSeC6H5), [2].. Yel-
1
low viscous liquid; Yield: 70%; H NMR (CDCl3/TMS): δ 8.09(s, 1H),
7.50–7.55(m, 2H), 7.17–7.34(m, 4H), 6.84–6.88(q, 1H), 2.26(s, 3H); 13
C
NMR (CDCl3/TMS): δ 156.3, 147.2, 136.4, 136.3, 135.5, 133.2, 128.9,
128.7, 128.0, 127.8, 120.6, 20.0; I.R. (KBr, cm−1): 3049.6, 2924.2, 2361.3,
1569.5, 1440.2, 1389.3, 1193.4, 1124.8, 1066.1, 1022.1, 987.6, 786.9,
736.8, 689.1, 661.5, 469.7; Anal. Calcd. : C, 57.83; H, 4.41; N, 5.62 %;
Found; C, 57.69; H, 4.34; N, 5.54 %.

996
K. K. Bhasin et al.
4-Methyl-2-pyridyl phenyl selenide, (CH3C5H3NSeC6H5), [3].. Yel-
1
low viscous liquid; Yield: 70%; H NMR (CDCl3/TMS): δ 7.99–8.08(d,
1H, 26.1Hz), 7.44–7.54(m, 2H), 7.07–7.23(m, 3H), 6.61–6.65(m, 2H),
2.0(s, 3H); 13C NMR (CDCl3/TMS): δ 157.8, 149.0, 146.9, 135.6, 128.8,
128.1, 127.6, 124.2, 121.1, 20.4; 77Se NMR: δ 467.05; I.R. (KBr, cm−1):
3435.3, 3054.6, 2920.7, 2358.7, 1584.2, 1454.4, 1375.8, 1277.4, 1267.9,
1116.2, 1077.8, 1022.6, 819.6, 741.7, 692.3, 520.3, 471.5; Anal. Calcd. :
C, 57.83; H, 4.41; N, 5.62 %; Found; C, 57.53; H, 4.91; N, 5.82 %.
5-Methyl-2-pyridyl phenyl selenide, CH3C5H3NSeC6H5. Yellow vis-
cous liquid ; Yield: 70%; 1H NMR (CDCl3/TMS): δ 8.15(s,1H), 7.52–
7.61(m,2 H), 7.17–7.27(m,3H), 7.05–7.09(m, 1H), 6.80–6.84(m,1H),
2.13(s,3 H); 13C NMR (CDCl3/TMS): δ 154.24, 149.80, 136.96, 135.39,
130.41, 129.54, 128.17, 127.9, 18.89; 77Se NMR: δ 464.11; I.R.(KBr ,
cm−1): 2921.2, 1724.4, 1584.2, 1555.9, 1364.6, 1274.6, 1223.2, 1072.7,
1022.8, 999.9, 816.4, 640, 474.6; Anal. Calcd. : C, 57.83; H, 4.41; N,
5.62%; Found; C, 57.62; H, 4.57; N, 5.75%.
6-Methyl-2-pyridyl phenyl selenide, CH3C5H3NSeC6H5.:. Yellow vis-
cous liquid ; Yield: 70%; 1H NMR (CDCl3/TMS): δ 7.56 (s,2H),7.23–
7.25(d,3H,6Hz),7.10–7.15(t,1H),6.61–6.73(dd,2H),2.39(s,3H); 13C NMR
(CDCl3/TMS) : δ 158.5, 158.1, 136.4, 136.0, 129.40, 128.5, 127.9, 120.8,
120.7, 119.8, 119.5, 24.07; I.R.( KBr , cm−1): 3053.8, 2923.1, 2852.3,
1577.2, 1476.0, 1388.6, 1327.1, 1302.5, 1248.9, 1161.2, 1086.7, 1065.7,
1021.8, 999.1, 842.6, 774.1, 740.4, 61.6, 663.8, 546.9, 474.5;Anal. Calcd.:
C, 57.83; H, 4.41; N, 5.62 %; Found; C, 57.91; H, 4.34; N, 5.56 %.
5-Bromo-2-pyridyl phenyl selenide, BrC5H3NSeC6H5:. Yellow
low melting solid; Yield: 70%; 1H NMR (CDCl3/TMS): δ 8.45–
8.47(d,1H,2.1 Hz), 7.59–7.68(d,1H,1.5 Hz),7.38–7.56 (m,5H) , 6.83–
6.86(d,1H,4.8 Hz); 13C NMR (CDCl3/TMS) : δ 157.3, 150.6, 139.8, 136.2,
129.8 ,129.0,127.4,124.4,117.4; 77Se NMR : δ 473.09; I.R.(KBr , cm−1):
3055.3, 2923.2, 1550.3, 1476.2, 1347.6, 1310.3, 1270.5,1211.7, 1179.3,
1071.7, 1020, 958.3, 918.2, 767.8, 670.0, 622.9, 591.3, 499.0, 476.0; MS
(EI, %) 311(100), 234( 30 ), 157(45), 77( 80 ); Anal. Calcd. : C, 42.03; H,
2.54; N, 4.45%; Found; C, 41.89; H, 2.96; N, 4.78%
In summary, most of these synthetic protocols in the literature suf-
fer from one or the other disadvantages viz., lengthy synthetic steps,
harsh reaction conditions, expensive reducing agents, contamination
of desired products with impurities, non-reproducible results and sen-
sitive to aerial oxidation. The present paper takes into account these
constraints in developing a mild, more convenient, commercially vi-
able, and efficient reaction for the synthesis of desired phenyl pyridyl
selenides under neutral conditions.

Synthesis of Unsymmetrical Pyridyl Aryl Selenides
997
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