Preparation and characterization of symmetrical bis[4-chloro-2-pyrimidyl] dichalcogenide (S, Se, Te) and unsymmetrical 4-chloro-2-(arylchalcogenyl) pyrimidine: X-ray crystal structure of 4-chloro-2-(phenylselanyl) pyrimidine and 2-(p-tolylselanyl)-4-chlor

Article abstract of DOI:10.1016/j.jorganchem.2010.09.010

Synthesis of a novel class of multinucleate pyrimidine chalcogen (S/Se/Te) derivatives has been successfully attempted for the first time by the selective substitution of chlorine at the C-2 position of 2,4-dichloropyrimidine with nucleophilic dichalcogen

Full text of DOI:10.1016/j.jorganchem.2010.09.010

Journal of Organometallic Chemistry 696 (2011) 835e840
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Preparation and characterization of symmetrical bis[4-chloro-2-pyrimidyl]
dichalcogenide (S, Se, Te) and unsymmetrical 4-chloro-2-(arylchalcogenyl)
pyrimidine: X-ray crystal structure of 4-chloro-2-(phenylselanyl) pyrimidine
and 2-(p-tolylselanyl)-4-chloropyrimidine
,
a
a
b
K.K. Bhasin a , Ekta Arora , S.K. Mehta , T.M. Klapoetke
*
a Department of Chemistry and Centre of Advanced Studies in Chemistry, Panjab University, Chandigarh-160014, India
b Department of Chemistry and Biochemistry, Ludwig Maximilian University, Munich, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis of a novel class of multinucleate pyrimidine chalcogen (S/Se/Te) derivatives has been
successfully attempted for the first time by the selective substitution of chlorine at the C-2 position of
2,4-dichloropyrimidine with nucleophilic dichalcogenide anion E22ꢀ (E ¼ S, Se, Te) to afford bis[4-chloro-
2-pyrimidyl] dichalcogenide. The highly electrophilic nature of 2,4-dichloropyrimidine compared to aryl
chlorides has been further exploited to prepare a variety of 4-chloro-2-(arylchalcogenyl) pyrimidine
compounds by substituting the chlorine exclusively at the C-2 position of 2,4-dichloropyrimidine with
a variety of chalcogen bearing aryl anions ArEꢀ (Ar ¼ phenyl, 1-naphthyl, p-tolyl, 4,6-dimethyl-2-pyr-
imidyl, 2-pyridyl, 4-methyl-2-pyridyl). All the newly prepared symmetrical and unsymmetrical pyr-
imidyl chalcogen compounds have been thoroughly characterized with the help of various spectroscopic
techniques viz., NMR (1H, 13C, 77Se), FT-IR and mass spectrometry (in representative cases). The crystal
structures of 4-chloro-2-(phenylselanyl) pyrimidine and 2-(p-tolylselanyl)-4-chloropyrimidine have
been determined by X-ray crystallography.
Received 25 December 2009
Received in revised form
17 August 2010
Accepted 2 September 2010
Available online 21 September 2010
Keywords:
Selenium
Tellurium
Pyrimidine
Nucleophilic substitution
Ó 2010 Published by Elsevier B.V.
1. Introduction
Avariety of methods for the preparation of symmetrical diorganyl
chalcogenides, R2E and diorganyl dichalcogenides R2E2 (E ¼ S, Se, Te)
Over the last thirty years, many important organic trans-
formations were efficiently achieved using organochalcogen inter-
mediates [1e5] that find extensive application in many diversified
areas, such as metallurgy, chemicals, electronic conductors, and so
on. A majority of these compounds are no longer considered toxic
and some of them are used as antioxidants, enzyme inhibitors,
cytotoxic agents for tumor cells and immunomodulators [6e9].
Organochalcogen compounds containing EeE (E ¼ S, Se, Te) bond
display an extremely rich chemistry and are of particular interest
since these can (a) act as electrophilic [10] and nucleophilic [11]
reagents in organic reactions (b) they exert protective effects
against reactive oxygenspecies in the body [12] (c) haveapplications
in ligand chemistry [13,14] and in various metal organic chemical
vapor deposition (MOCVD) processes as precursors for the forma-
tion of thin films [15,16].
are known. Invariably, these methods are based on the reaction of
alkali metal chalcogenides/dichalcogenides with appropriate hal-
oalkanes in an aqueous or non-aqueous medium. The only difference
in the preparative procedure adopted by various chemists lies in the
generation of the alkali metal chalcogenides/dichalcogenides. Alkali
metal chalcogenides/dichalcogenides can be prepared in situ by
reducing elemental chalcogens by a variety of reducing agents viz.
LiAlH4 [17], R4NþBH4ꢀ [18], LiEt3BH [19], HOCH2SO2Na [20], and Na/
NH3 [21]. In literature use of some metals like indium [22],
lanthanum [23], samarium [24] and their salts [25] have also been
reported to cleave chalcogenechalcogen bond. A number of alkyl/
aryl selenides have been prepared by the direct nickel (__) [26] and
copper (__)-catalyzed [27,28] coupling of selenide anions with aryl
iodides. Different synthetic procedures for the preparation of the
pyridyl selenium and tellurium compounds are also documented in
the literature. Jerchel et al. [29] were the first to synthesize bis(4-
pyridyl) diselenide and bis(4-pyridyl) selenide by reacting N-pyridyl
(4-pyridinium) chloride with hydrogen selenide. Tanji et al. [30]
reported the formation of alkyl pyridyl telluride by reacting bromo-
pyridine with lithium alkyltellurolate. Recently, Bhasin and Singh
* Corresponding author. Tel.: þ91 172 2534407; fax: þ91 172 2545074.
E-mail address: kkbhasin@pu.ac.in (K.K. Bhasin).
0022-328X/$ e see front matter Ó 2010 Published by Elsevier B.V.
doi:10.1016/j.jorganchem.2010.09.010

836
K.K. Bhasin et al. / Journal of Organometallic Chemistry 696 (2011) 835e840
[31] prepared various methyl-substituted bis(2-pyridyl) dichalcoge-
nides (Se, Te) by using hydrazine hydrate as a reducing agent in basic
medium using DMF as a solvent. Compared to the chemistry of
pyridylchalcogen compounds, synthesis of pyrimidyl chalcogen
moieties has not received much attention although the importance of
compounds having a pyrimidine nucleus has been well documented
in literature as anti-inflamatory [32], antitumor [33] agents etc. 5-
Alkyl- or 5-alkylaryl-substituted pyrimidine derivatives are useful
intermediates in the synthesis of antiviral nucleosides. Schinazi et al.
[34] reported the synthesis and the biological activity of several 5-
(phenylselenenyl)-pyrimidine nucleosides as potential antimicrobial
agents. A variety of newly synthesized 6-phenylselenenyl acyclic
pyrimidines [35,36] have recently been found to have potent anti-
human immunodeficiency- virus-type-1 (HIV-1) activity. Bardos
et al. [37] have synthesized successfully 5-selenium-substituted
derivatives of uracil, 20-deoxyuridine, and 20-deoxyuridylic acid.
Curiously, no attempt has been made to synthesize and characterize
bis[4-chloro-2-pyrimidyl] dichalcogenide and 4-chloro-2-(arylchal-
cogenyl) pyrimidine compounds so, we wish to report herein
a convenient method for preparation of hitherto unknown titled
pyrimidyl chalcogen compounds.
7.64e7.62 (d, J ¼ 6.0 Hz, 1H) ppm. 13C NMR:
d
¼ 164.7, 160.0, 149.0,
118.0. C8H4N4S2Cl2: calcd. C 32.98, H 1.37, N 19.24; found C 33.10, H
1.78, N 19.68.
2.1.2. Bis[4-chloro-2-pyrimidyl] diselenide 1b
Yield: 65%, red crystalline solid. M.p.88e92ꢁ C. Rf (10% Et2O/
hexane) .39. IR (KBr):
n .
2924, 1538, 1401, 1323, 582 cmꢀ1 1H NMR
(300 MHz, CCl4/CDCl3, 25 ꢁC):
d
¼ 8.30e8.28 (d, J ¼ 6.0 Hz, 1H),
7.58e7.56(d,J¼ 6.0 Hz,1H) ppm.13C NMR:
¼ 167.9, 161.1, 158.8, 118.7.
d
MS-EI: m/e (%): 387 ([C8H4N4Cl2Se2]þ, 18), 384 ([C8H2N4Cl2Se2]þ, 10),
227 ([C8H2N4Cl2]þ, 50). C8H4N4Se2Cl2; calcd. C 24.80, H 1.03, N 14.47;
found: C 25.10, H 1.36, N 14.07.
2.1.3. Bis[4-chloro-2-pyrimidyl] ditelluride 1c
Yield: 55%, black solid. M.p.104e106ꢁ C. Rf (10% Et2O/hexane)
.34. IR (KBr): n
2923, 1535, 1397, 1319, 571 cmꢀ1. 1H NMR (300 MHz,
CCl4/CDCl3, 25ꢁ C):
d
¼ 8.11e8.07 (d, J ¼ 12.0 Hz, 1H), 7.84e7.80 (d,
J ¼ 12.0 Hz, 1H) ppm. 13C NMR:
d
¼ 165.2, 160.9, 158.2, 126.7.
C8H4N4Te2Cl2: calcd. C 19.87, H 0.828, N 11.59; found C 19.42, H
0.980, N 12.00.
2.2. General procedure for synthesis of unsymmetrical pyrimidyl
chalcogenides
2. Materials and methods
All experiments were carried out in dry oxygenefree nitrogen
atmosphere. Sodium borohydride (Loba, purity > 99.5%), elemental
selenium (Hi-media, purity > 99%), elemental sulfur (Hi-media,
purity > 99%), elemental tellurium (Hi-media, purity > 99.5%) and
uracil (Hi-media, purity > 95%) were newly purchased and stored
in dessicator prior to use. 2,4-Dichloropyrimidine [38], diphenyl
diselenide [39], diphenyl ditelluride [40], dinaphthyl diselenide
[41], dipyridyl diselenide [31] and dipicolyl diselenide [31] were
prepared by reported methods. IR spectra were recorded between
KBr plates on a PerkineElmer Model 1430 ratio recording spec-
trometer. 1H NMR and 13C NMR spectra were recorded in CCl4/
CDCl3 using tetramethylsilane as an internal standard and 77Se with
dimethylselenide as an external reference on a Jeol 300 MHz
spectrometer. The mass spectra were obtained on Q-TOF micro
mass spectrometer. Carbon, Hydrogen and Nitrogen were esti-
mated micro analytically on a PerkineElmer 2400 CHN Elemental
analyzer.
To a solution of Ar2E2 (E ¼ Se, Ar ¼ phenyl, 1-naphthyl, p-tolyl,
4,6-dimethyl-2-pyrimidyl, 2-pyridyl, 4-methyl-2-pyridyl, E ¼ S,
Te, Ar ¼ phenyl, 5 mmol) in 50 ml of C2H5OH-DMF (3:2) was
added NaBH4 (0.44 g, 12 mmol) in parts with continuous stirring
at 0e5 C and the mixture was stirred for nearly 1 h at room
temperature till the reduction was complete as indicated by the
formation of colorless solution. The arylchalcogenide anion thus
prepared was then alkylated with 2,4-dichloropyrimidine (1.49 g,
10 mmol) dissolved in 15 ml of DMF. After completion of the
reaction ethanol was evaporated off in vacuo and the residue was
extracted with dichloromethane (20 ꢂ 3 ml). The combined
extract was then washed with water, dried (Na2SO4) and evapo-
rated to leave the crude product; which was purified by column
chromatography over silica gel (hexaneeethyl acetate) to furnish
pure product.
2.2.1. 4-Chloro-2-(phenylthio) pyrimidine 2a
Yield: 85%, white crystalline solid. M.p.39e42ꢁ C. Rf (10% Et2O/
2.1. Synthesis of bis[4-chloro-2-pyrimidyl] dichalcogenide
hexane) .40. IR (KBr):
691 cmꢀ1. 1H NMR (300 MHz, CCl4/CDCl3, 25ꢁ C):
J ¼ 6.0 Hz,1H), 7.50e7.38 (m, 5H), 6.52e6.50 (d, J ¼ 6.0 Hz,1H) ppm.
13C NMR:
n
2923, 2361, 1548, 1400, 1330, 1192,
d
¼ 8.06e8.04 (d,
To a vigorously stirred mixture of elemental chalcogen (S/Se/Te
75 mmol) and ethanol (30 ml), sodium borohydride (1.85 g,
50 mmol) was added slowly at 0 ꢁC. The mixture was stirred for
nearly 6 h at room temperature during which time the reduction
was complete as indicated by the complete consumption of the
chalcogen. The reduction of chalcogen is indicated by the color
change of the reaction mixture i.e. deep red color in the case of
selenium, brown color in the case of sulfur and purple color in the
case of tellurium. A solution of 2,4-dichloropyrimidine (14.9 g,
100 mmol) dissolved in 15 ml ethanol was added dropwise. And the
reaction was monitored by TLC till completion. After the comple-
tion of reaction, it was diluted with about 250 ml of distilled water
and extracted in dichloromethane (3 ꢂ 50 ml). The organic layer
was collected and solvent evaporated to get the crude product in
solid form. The product was further subjected to purification on
a silica column using hexaneeethyl acetate as eluant (5:1).
d
¼ 172.7, 171.6, 160.4, 157.4, 157.0, 126.9. C10H7N2SCl:
calcd. C 53.93, H 3.14, N 12.58; found C 53.47, H 3.38, N 12.08.
2.2.2. 4-Chloro-2-(phenylselanyl) pyrimidine 2b
Yield: 75%, white crystalline solid. M.p.49e51ꢁ C. Rf (10% Et2O/
hexane) .37. IR (KBr):
n
2924, 1542, 1518, 1478, 1439, 790, 668,
¼ 8.08e8.06 (d,
592 cmꢀ1. 1H NMR (300 MHz, CCl4/CDCl3, 25ꢁ C):
d
J ¼ 6.0 Hz, 1H), 7.70e7.66 (d, J ¼ 12.0 Hz, 2H) 7.52e7.41 (m, 3H),
6.71e6.69 (d, J ¼ 6.0 Hz, 1H) ppm. 13C NMR:
¼ 162.6, 161.3, 160.8,
d
159.8, 157.2, 120.0. 77Se NMR :
d
¼ 500 ppm. MS-EI: m/e (%): 271.4
([C10H7N2SeClþ1]þ,100), 269.4 ([C10H7N2SeCl-1]þ, 8). C10H7N2SeCl:
calcd. C 44.36, H 2.58, N 10.35; found C 44.40, H 2.16, N 9.98.
2.2.3. 4-Chloro-2-(phenyltelluryl) pyrimidine 2c
Yield: 64%, yellow crystalline solid. M.p.48e50ꢁ C. Rf (10% Et2O/
hexane) .34. IR (KBr):
NMR(300 MHz, CCl4/CDCl3, 25ꢁ C):
(d, J ¼ 15.0 Hz, 1H), 7.43e7.33 (d, 2H), 6.85e6.80 (d, J ¼ 15.0 Hz,
1H) ppm. 13C NMR:
¼ 165.4, 160.9, 156.3, 141.3, 130.4, 130.0,
124.8,124.4,112.3. MS-EI: m/e (%): 318.6 ([C10H7N2TeCl]þ, 34.5), 231.8
n
2922,1536,1509,1396,1321, 661, 574 cmꢀ1.1H
2.1.1. Bis[4-chloro-2-pyrimidyl] disulfide 1a
d
¼ 7.96e7.86 (m, 3H), 7.50e7.45
Yield: 68%, white solid. M.p. 82e85 ꢁC. Rf (10% Et2O/hexane) .43.
IR (KBr):
n
2924, 1539, 1400, 1327, 787, 681, 623 cmꢀ1 1H NMR
d
(300 MHz, CCl4/CDCl3, 25ꢁ C):
d
¼ 8.39e8.37 (d, J ¼ 6.0 Hz, 1H),

K.K. Bhasin et al. / Journal of Organometallic Chemistry 696 (2011) 835e840
837
([C4H2N2Te]þ, 74), 190.9 ([C10H7N2Cl]þ, 17). C10H7N2TeCl: calcd. C
37.85, H 2.20, N 8.83; found C 37.76, H 2.39, N 8.79.
2.2.8. 2-(4-Methylpyridin-2-ylselanyl)-4-chloropyrimidine 2h
Yield: 47%, yellow crystalline solid. M.p.55e57ꢁ C. Rf (10% Et2O/
hexane) 0.27. 1H NMR(300 MHz, CCl4/CDCl3, 25ꢁ C):
(d, J ¼ 6.0 Hz, 1H), 7.64e7.61 (d, J ¼ 9.0 Hz, 1H), 7.57e7.54 (d,
J ¼ 9.0 Hz, 1H), 7.37e7.35 (d, J ¼ 6.0 Hz, 1H), 6.75e6.71 (t, 1H), 2.52
(s, 3H) ppm. C10H8N3SeCl: calcd. C 42.10, H 2.80, N 14.73; found C
42.35, H 2.72, N 14.62.
d
¼ 8.40e8.38
2.2.4. 2-(p-tolylselanyl)-4-chloropyrimidine 2d
Yield: 76%, light yellow crystalline solid. M.p.75e78ꢁ C. Rf (10%
Et2O/hexane) .36. IR (KBr):
n 2924, 1542, 1399, 1324, 1665, 834,
669 cmꢀ1. 1H NMR(300 MHz, CCl4/CDCl3, 25ꢁ C):
d
¼ 8.27e8.20 (d,
J ¼ 21.0 Hz, 1H), 7.73e7.68 (d, J ¼ 15.0 Hz, 2H), 7.30e7.25 (d,
J ¼ 15.0 Hz, 2H), 6.81e6.74 (d, J ¼ 21.0 Hz, 1H), 2.45 (s, 3H) ppm. 13C
2.3. X-ray crystallographic studies
NMR:
d
¼ 176.0, 160.6, 157.1, 140.5, 136.8, 131.9, 121.3, 119.2, 118.3,
117.5, 21.5. MS-EI: m/e (%): 284 ([C11H9N2SeCl]þ, 100), 227
([C8H4N4Cl2]þ, 8), 204 ([C11H9N2Cl]þ, 41). C11H9N2SeCl: calcd. C
46.39, H 3.16, N 9.84; found C 46.89, H 3.50, N 9.44.
Diffraction quality single crystals of 4-chloro-2-(phenylselanyl)
pyrimidine (2b) and 2-(p-tolylselanyl)-4-chloropyrimidine (2d)
wereobtained by the slowevaporation of dichloromethaneehexane
solution of the corresponding compounds. Colorless crystals of (2b)
and light yellow crystals of (2d) were obtained. Suitable crystals
were chosen from a crop of crystals and mounted on glass fibers and
data sets were collected on Nonius MACH3 diffractometer for the
cell determination and intensity data collection. The diffraction data
2.2.5. 4-Chloro-2-(naphthalen-2-ylselanyl) pyrimidine 2e
Yield: 57%, yellow crystalline solid. M.p.104e108ꢁ C. Rf (10%
Et2O/hexane) .30. IR (KBr):
1H NMR(300 MHz, CCl4/CDCl3, 25ꢁ C):
8.03e7.99 (m, 2H), 7.91e7.87 (t, 2H), 7.62e7.44 (m, 3H), 6.34e6.33
(d, 1H) ppm. 13C NMR:
¼ 175.0, 160.6, 157.2, 137.4, 134.5, 134.4,
n .
2925, 1541, 1399, 1324, 791, 669 cmꢀ1
d
¼ 8.27e8.22 (t, 1H),
were collected using monochromatic Mo Ka radiation at 293(2) K
d
and 150 (2) K for (2b) and (2d) respectively. The details of crystal
structure determination and refinement parameters for (2b) and
(2d) are given in Table 3 and Table 4 respectively.
Crystal structure was solved by direct methods (SHELXS-97)
[42] and refined by full matrix least squares method.
131.9, 128.9, 128.1, 127.7, 126.2, 124.3, 118.73. 77Se NMR:
d
¼ 428 ppm. MS-EI: m/e (%): 320 ([C14H9N2SeCl]þ, 15), 318.0
([C14H7N2SeCl]þ, 34), 316.0 ([C14H5N2SeCl]þ,13). C14H9N2SeCl calcd.
C 52.41, H 2.80, N 8.73; found C 52.71, H 2.89, N 8.45.
2.2.6. 2-(4,6-Dimethylpyrimidin-2-ylselanyl)-4-chloropyrimidine 2f
Yield: 54%, white crystalline solid. M.p.148e149ꢁ C. Rf (10% Et2O/
3. Results and discussion
hexane) .28. IR (KBr, cmꢀ1):
n 2925,1581, 1543, 1398, 1328, 844, 640.
The research on the synthesis of the pyrimidine and its analogues
has been going on continuously in search of new biologically active
molecules. It is anticipated that pyrimidyl chalcogen compounds
mayalso display the redox activity like other selenium derivatives of
aniline, pyridine and quinoline. As a resultof ourongoing project, we
have reported an efficient synthetic route to bis(4-dimethylamino-
2-pyrimidyl)dichalcogenides [43] (1aec) by exploring the reaction
of dichalcogenide anion E22ꢀ in dimethylformaamide as the solvent.
In this case, chlorine atom at C-2 position of 2,4-dichlropyrimidine is
substituted by the in situ generated E22ꢀ (E ¼ S, Se, Te) anion. In
addition, substitutionat C-4 positionbydimethylaminogroupis also
facilitated bythe dimethylformaamide used as a solvent. Thus, it was
considered of interest to use another solvent i.e. absolute ethanol
instead of DMF that would lead to retention of the chlorine at the C-4
position of 2,4-dichloropyrimidine. The reaction scheme for the
1H NMR(300 MHz, CCl4/CDCl3, 25ꢁ C):
d
¼ 8.36e8.34 (d, J ¼ 6.0 Hz,
2H), 8.31e8.29 (d, J ¼ 6.0 Hz, 2H), 6.79 (s, 1H), 2.39 (s, 6H) ppm. 13C
NMR:
d
¼ 167.69, 157.33,122.15, 118.23, 23.86. C10H9N4SeCl: calcd. C
39.93, H 2.99, N 18.63; found: C 40.20, H 3.13, N 18.37.
2.2.7. 4-Chloro-2-(pyridin-2-ylselanyl) pyrimidine 2g
Yield: 65%, yellow powder. M.p.44e48 ꢁC. Rf (10% Et2O/hexane)
.24. IR (KBr):
(300 MHz, CCl4/CDCl3, 25ꢁ C):
8.17e8.15 (d, J ¼ 6.0 Hz, 1H), 7.69e7.61 (m, 2H), 7.33e7.29 (d, 1H),
n .
1542, 1449, 1401, 1323, 827, 670 cmꢀ1 1H NMR
d
¼ 8.58e8.56 (d, J ¼ 6.0 Hz, 1H),
7.27e7.24 (m, 1H) ppm. 13C NMR:
d
¼ 157.3, 150.9, 137.5, 130.3,
120.4, 120.3. MS-EI: m/e (%): 271 ([C9H6N3SeCl]þ, 100), 236
([C9H6N3Se]þ, 10). C9H6N3SeCl: calcd. C 39.85, H 2.21, N 15.49;
found C 39.97, H 2.13, N 15.38.
Cl
Cl
N
Cl
N
N
N
N
NaBH4/C2H5OH
0-50C
2-
N
Cl
E2
2E
E
E
1 a-c
Cl
Na BH4 /C2H5 OH -D M F,r.t
C l
N
Ar-E-E-Ar
N
E
Ar
0 -50C
N
,
2 a-h
N
Cl
(1 a-c) E =S, Se, Te
(2a) E = S, Ar = C6H5, (2 b, 2d-h) E = Se, Ar = C6H5, p-CH3C6H5, C10H7, C6N2H7, C5NH4, C6NH6.
(2c) E = Te, Ar = C6H5
Scheme 1. Reaction scheme for the synthesis of some symmetrical and unsymmetrical pyrimidyl chalcogen (E ¼ S, Se, Te) compounds.

838
Step 1
K.K. Bhasin et al. / Journal of Organometallic Chemistry 696 (2011) 835e840
2 NaBH4 + 3E + 6 C2H5OH
Step 2
Na2E2 + H2E + 2 B(OEt)3 + 6H2
Cl
Cl
N
Cl
Cl
N
N
N
_E-E_
N
N
N
E
E
1 a-c
Cl
N
Cl
Scheme 2. Mechanism for the synthesis of symmetrical chalcogen compounds (E ¼ S,
Se, Te) compounds.
Fig. 1. ORTEP diagram showing the conformation and atom numbering scheme for 4-
chloro-2-(phenylselanyl) pyrimidine (2b).
synthesis of the titled compounds uses sodium borohydride to carry
out not only the reduction of elemental chalcogens but also for the
reductive cleavage of chalcogenechalcogen bond in diaryl dichalc-
ogen compounds.
signals appear up field with respect to the protons of 2,4-dichloro-
pyrimidine. 13C NMR spectra of bis[4-chloro-2-pyrimidyl] dichalc-
ogen compounds (1aec) display 13C signal of the pyrimidyl group
In order to solubilize completely the starting dichalcogen
compounds as well as its nucleophilic borane complex, [(ArE)B
(OC2H5)3]ꢀ, two volumes of DMF were added to three volumes of
ethanol. Addition of DMF as a co-solvent improved the yield by
solubilizing the diaryl chalcogenolate ion [44]. DMF being a highly
polar solvent can be easily removed by simply washing with water.
The entire scheme involving sodium borohydride as reducing
agent was found effective for the synthesis of symmetrical and
unsymmetrical pyrimidyl chalcogen compounds (1aec, 2aeh)
(Scheme 1). The mechanism involved in the reaction is represented
by Scheme 2 and Scheme 3. The advantage of this methodology to
synthesize unsymmetrical chalcogen compounds is the selective
nucleophilic substitution of chlorine atom at C-2 position of 2,
4-dichloropyrimidine by arylchalcogenide anion (ArEꢀ) resulting in
the formation of C(Pym)-E bond.
with values in the range of 118.0e167.0 (d, ppm). The carbon signal of
4-chloro-2-(arylchalcogenyl) pyrimidine(2aeh) includes signals
from both the pyrimidine ring as well as the aryl group. The mass
spectra for 2-(p-tolylselanyl)-4-chloropyrimidine (2d) and 4-chloro-
2-(pyridin-2-ylselanyl) pyrimidine (2g) show that the molecular ion
peak is observed as base peak at m/z value 284 and 271 respectively.
[M þ 1] and [M e 1] peaks are observed for 4-chloro-2-(phenyl-
selanyl) pyrimidine (2b). The fragment ions containing selenium
show a highly characteristic and definite pattern of signal intensities
depending on the natural abundance of various isotopes of selenium.
In IR spectra of these compounds, vibrations due to pyrimidyl and
aryl groups can be easily identified. A strong and sharp band at
2900e2930 cmꢀ1 has been assigned to aromatic CeH stretching and is
consistent with the values found for CeH stretching vibrations
in aromatic compounds. [45,46] An intense band around 1500e
1550 cmꢀ1 can be assigned to aromatic C]C stretching vibrations of
the aryl rings, whereas a medium to sharp intensity band between 750
and 900 cmꢀ1 has been assigned to nCeH deformation mode of aromatic
ring. A comparison of nEeC (where E ¼ S, Se, Te) stretching bands in
pyrimidyl chalcogenides reveals a regular trend in the variation of nEeC
absorption frequencies. In bis[4-chloro-2-pyrimidyl] dichalcogen
compounds (1aec) and 4-chloro-2-(arylchalcogenyl) pyrimidine
The bis[4-chloro-2-pyrimidyl] dichalcogen compounds (1aec)
and 4-chloro-2-(arylchalcogenyl) pyrimidine (2aeh) thus prepared
are stable enough to be purified by column chromatography (silica
gel using hexaneeethyl acetate). The compounds are soluble in
conventional organic solvents and have a long shelf life without any
sign of decomposition even at room temperature.
(2aeh) a CeCl band is observed near 620e700 cmꢀ1
.
3.1. Spectroscopic studies
1H NMR characterization of bis[4-chloro-2-pyrimidyl] dichalc-
ogen compounds (1aec) shows that the proton at C-5 of
bis[4-chloro-2-pyrimidyl] ditelluride (1c) is shifted up field due to
greater shielding of protons by tellurium metal as compared to sele-
nium metal in bis[4-chloro-2-pyrimidyl] diselenide(1b). The reso-
nance signals of pyrimidine ring in all of the unsymmetrical selenides
show an up field shift for H-5 protons relative to those of the corre-
sponding bis[4-chloro-2-pyrimidyl]diselenide(1b). Nevertheless, the
3.2. Solid-state structures: crystal structure determination of
4-chloro-2-(phenylselanyl) pyrimidine (2b) and 2-(p-tolylselanyl)-
4-chloropyrimidine (2d)
To have an understanding of the structural details, single crystal
X-ray diffraction of 4-chloro-2-(phenylselanyl) pyrimidine (2b) and
2-(p-tolylselanyl)-4-chloropyrimidine (2d) was carried out.
perspective view and atom numbering scheme of (2b) and (2d) are
A
Ar-E-E-Ar + 2 NaBH4 + 6 C2H5OH
2 ArE-Na+ + 2 B(OEt)3
Cl
Cl
N
N
_
ArE
Cl
N
N
E Ar
2 a-h
(2a) E = S, Ar = C6H5, (2 b, 2d-h) E = Se, Ar = C6H5, p-CH3C6H5, C10H7, C6N2H7, C5NH4, C6NH6.
(2c) E = Te, Ar = C6H5
Scheme 3. Mechanism for the synthesis of unsymmetrical chalcogen compounds.

K.K. Bhasin et al. / Journal of Organometallic Chemistry 696 (2011) 835e840
839
Fig. 2. (a) Diagram showing the conformation and atom numbering scheme (b) and the C/Cl and N/H interactions for 2-(p- tolylselanyl)-4-chloropyrimidine (2d).
Table 3
Table 1
Crystal data and structure refinement for (2b).
Selected bond parameters of (2b).
Bond angle (ꢁ)
Formula
C10H7ClN2Se
Bond length (Å)
Formula weight
Temperature/K
Crystal system
Space group
269.59
293(2) K
Monoclinic
P21/a
Se(1)eC(2)
N(1)eC(1)
C(9)eC(10)
C(5)eC(10)
1.904(4)
C(2)eSe(1)eC(5)
C(4)eC(1)eN(1)
N(1)eC(1)eCl(1)
C(6)eC(5)eSe(1)
99.88(15)
129.4(4)
114.0(3)
119.4(3)
1.325(5)
1.359(6)
1.382(5)
Torsion angles (ꢁ)
C(2)eN(1)eC(1)eC(4)
C(3)eN(2)eC(2)eN(1)
C(3)eN(2)eC(2)eSe(1)
Se(1)eC(5)eC(10)eC(9)
A/Å
B/Å
13.3997(14)
5.4254(9)
14.620(9)
101.73(2)
1174.5(5)
4
3.823
1.721
528
24.99
ꢀ15 ꢃ h ꢃ 15,ꢀ6 ꢃ k ꢃ 5,
ꢀ17 ꢃ l ꢃ 17
5605 [R(int) ¼ 0.0251]
1827
127
0.991
0.0369/0.0973
0.0529/0.1013
0.516
0.3(6)
ꢀ0.3(6)
c/Å
B/ꢁ
ꢀ179.4(3)
179.7(3)
Volume/Å3
Z
Absorption coefficient/mmꢀ1
Density calc./mg/m3
F(000)
given (Fig. 1 and Fig. 2 respectively). The important bond parame-
ters for (2b) and (2d) are listed in Table 1 and Table 2 respectively.
The average CeC bond length in the pyrimidine ring in (2b) and
(2d) is 1.304 Å and 1.329 Å respectively. The SeeC bond lengths in
(2b) are [Se (1)eC (2), 1.904(4) Å], [Se (1)eC (5), 1.914(4) Å] and in
(2d) are [Se (1)eC (1),1.9157(19) Å] and [Se (1)eC (8),1.9023(18) Å].
The average CeC bond length in phenyl ring in (2b) is 1.372 Å and in
tolyl ring in (2d) is 1.390 Å. The observed bond angle C (2)eSe (1)eC
(5) and C (2)eSe (1)eC (5) in (2b) and (2d) is 99.88(15) and 98.39(8)
respectively. These bond angles indicate the distortion of sp3
carbon from its regular tetrahedral geometry and established the
‘V’ shaped geometry about CeSeeC bond. Interestingly, the
compound 2-(p-tolylselanyl)-4-chloropyrimidine (2d) has shown
hydrogen-bonding interactions between the nitrogen atom of
pyrimidyl ring of one crystal unit and hydrogen atom of the
other pyrimidyl ring of other crystal unit. However, the compound
4-chloro-2-(phenylselanyl) pyrimidine (2b) displayed NeH inter-
molecular interactions between nitrogen of pyrimidyl ring
and hydrogen of the phenyl ring within the crystal lattice. Also in
4-chloro-2-(phenylselanyl) pyrimidine (2b), short contacts are
observed between C-3 of the pyrimidine ring and H-4 of the
pyrimidine ring of the other molecule and another C/H interaction
between C-4 of the pyrimidine ring and H-3 of the pyrimidine ring
of the other molecule which is marked from the measured C/H
distances which are less than the vander Waals distance (2.90 Å).
Short contact is apparent between the carbon atom of tolyl ring C
(6) and the chlorine attached to C (9) of the pyrimidyl group of the
other molecule as indicated by distance (3.40 Å), which is shorter
than the sum of their vander Waals radii (3.59 Å) in 2-(p-tolylse-
lanyl)-4-chloropyrimidine (2d).
2 theta/ꢁ
Index ranges
Reflections collected
Reflections unique
Parameters
GOOF
R1/wR2 [I > 2
s
(I)]
R1/wR2 (all data)
largest res.Peak/e Åꢀ3
Table 4
Crystal data and structure refinement for (2d).
Formula
C11H9ClN2Se
Formula weight
Temperature/K
Space group
a/Å
283.61
150 (2) K
P21/c
8.9473(4)
11.9976(6)
10.7913(6)
98.916(3)
1144.41(10)
4
3.481
1.646
560
33.29
b/Å
c/Å
ꢁ
b
/
Volume/Å3
Z
Absorption coefficient/mmꢀ1
Density calc./mg/m3
F(000)
2 theta/ꢁ
Table 2
Index ranges
ꢀ13 ꢃ h ꢃ 13,ꢀ17 ꢃ k
ꢃ 17,ꢀ16 ꢃ l ꢃ 16
51,507 [R(int) 0.0312]
4332
137
1.062
Selected bond parameters of (2d).
Bond length (Å)
Bond angle (ꢁ)
Reflections collected
Reflections unique
Parameters
GOOF
R1/wR2 [I > 2
Se(1)eC(8)
Se(1)eC(1)
N(1)eC(9)
C(4)eC(7)
Cl(1)eC(10)
1.9023(18)
1.9157(19)
1.325(2)
1.505 (3)
1.7390(19)
C(8)eSe(1)eC(1)
N(1)eC(8)eN(2)
C(10)eC(9)eN(1)
N(1)eC(9)eCl(11)
C(6)eC(1)eSe(1)
98.39(8)
121.79(16)
129.14(18)
115.42(14)
120.04(15)
s
(I)]
0.0334/0.1011
0.0453/0.1078
R1/wR2 (all data)

840
K.K. Bhasin et al. / Journal of Organometallic Chemistry 696 (2011) 835e840
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The present report constitutes the first successful attempt to
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Te)and 4-chloro-2-(arylchalcogenyl) pyrimidine compounds by
simple synthetic methodology. These compounds are anticipated to
have potential applications in medicinal field.
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Acknowledgment
KKB is thankful to DST, New Delhi for research grant (SR/S1/IC-
37/2009) and UGC, New Delhi for financial support (37-320/2009,
SR). We are thankful to Prof. P. Mathur, Indian Institute of Tech-
nology, Mumbai for carrying out X-ray crystallographic studies.
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Appendix A. Supplementary material
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CCDC 736021 and 736022 contain the supplementary crystal-
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obtained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
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