Synthesis and characterization of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide: X-ray structure of 4-methoxy-3-(sulfanylmethyl)- and 4-chloro-3-(selenenylbenzyl)-N,N- diisopropylpyridine-2-carboxamide

Article abstract of DOI:10.1016/j.jorganchem.2011.03.009

Synthesis of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide (1a and 1b respectively) has been reported. 1a and 1b were lithiated with 2 equiv. of n-BuLi or LDA at -78 °C. Addition of elemental sulfur or selenium to the carbanion led to the formation of corresponding thiolate or selenolate anions respectively. The selenolate anions were aerial oxidized to afford the corresponding diselenides. The thiolate/selenolate anions were quenched with a variety of electrophiles to give unsymmetrical thio/selenoalkanes in moderate to good yields. Reductive cleavage of Se-Se bond has also been studied. The synthesized compounds were characterized by elemental analysis, NMR (¹H, ¹³C and ⁷⁷Se), FT-IR and mass spectral techniques. Crystal structures of two compounds, 6b and 7a, were determined by single crystal X-ray crystallography. Their crystal structure exhibits 1,4-type S?OCH₃ and Se?Cl intramolecular secondary interactions respectively. The relative thermal stability of 3a, 3b and 4a has also been established by thermogravimetric analysis.

Full text of DOI:10.1016/j.jorganchem.2011.03.009

Journal of Organometallic Chemistry 696 (2011) 2406e2413
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis and characterization of chalcogen (S and Se) derivatives
of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide:
X-ray structure of 4-methoxy-3-(sulfanylmethyl)- and
4-chloro-3-(selenenylbenzyl)-N,N-diisopropylpyridine-2-carboxamide
*
Jaspreet S. Dhau , Rupy Dhir, Amritpal Singh
Department of Chemistry, Punjabi University, Patiala 147002, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis of chalcogen (S and Se) derivatives of 4-chloro- and 4-methoxy-N,N-diisopropylpyridine-2-
carboxamide (1a and 1b respectively) has been reported. 1a and 1b were lithiated with 2 equiv. of n-BuLi
or LDA at ꢀ78 ꢁC. Addition of elemental sulfur or selenium to the carbanion led to the formation of
corresponding thiolate or selenolate anions respectively. The selenolate anions were aerial oxidized to
afford the corresponding diselenides. The thiolate/selenolate anions were quenched with a variety of
electrophiles to give unsymmetrical thio/selenoalkanes in moderate to good yields. Reductive cleavage of
SeeSe bond has also been studied. The synthesized compounds were characterized by elemental anal-
ysis, NMR (1H, 13C and 77Se), FT-IR and mass spectral techniques. Crystal structures of two compounds, 6b
and 7a, were determined by single crystal X-ray crystallography. Their crystal structure exhibits 1,4-type
S/OCH3 and Se/Cl intramolecular secondary interactions respectively. The relative thermal stability of
3a, 3b and 4a has also been established by thermogravimetric analysis.
Received 22 January 2011
Received in revised form
24 February 2011
Accepted 3 March 2011
Keywords:
Organochalcogen
Pyridyl carboxamide
Chalcogenides
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
The chemistry of internally chelated organochalcogens with the
chalcogen atom attached to the benzene ring has been extensively
Interest in the field of organochalcogens having EeX (E ¼ S or
Se; X ¼ halogen, O or N) intramolecular secondary interactions
stems from their utility in organic synthesis [1,2], biochemistry
[3e5] and material science [6,7]. These secondary interactions are
known to increase the stability of many organochalcogen
compounds [8,9]. Compared to organoseleniums, their sulfur
congeners are more stable. However, compounds having SeeX
secondary interactions are found to be equally or in some cases
even more stable than the organosulfur compounds devoid of these
interactions [10]. Internally stabilized organoseleniums have
shown much better antioxidant properties, as they form stable
intermediates during the process involving the removal of oxidants
[11]. The metal chalcogenolates containing these moieties also
serve as excellent single source precursors of the semiconducting
materials [12,13]. In addition to these, the organoselenium
compounds containing the pyridyl moieties serves as an efficient
reagents in the selenoxide elimination reactions for the synthesis of
terminal olefins [14].
studied, however, the corresponding pyridine chemistry is relatively
under explored. This is probably due to the lack of efficient meth-
odology for their synthesis. In this paper, we report an efficient and
convenient synthesis of various hitherto unknown internally
chelated organosulfur and -selenium compounds derived from 4-
chloro- and 4-methoxy-N,N-diisopropylpyridine-2-carboxamide (1a
and 1b respectively). Reductive cleavage of SeeSe bond with lithium
aluminum hydride and sodium borohydride has also been studied.
Single crystal X-ray studies of 4-methoxy-3-(sulfanylmethyl)- and 4-
chloro-3-(selenenylbenzyl)-N,N-diisopropylpyridine-2-carboxamide
(6a and 7b respectively) along with thermogravimetric analysis of
3a, 3b and 4a have also been described.
2. Results and discussion
2.1. Preparation of diselenide derivatives of 1a and 1b
Reaction of 1a or 1b with 2 equiv. of n-BuLi in dry THF at ꢀ78 ꢁC
affected lithiation at the b-position of the pyridine ring, resulting in
the formation of reddish brown solution of the carbanion. Insertion
of elemental selenium to the carbanion led to the formation of
* Corresponding author. Tel.: þ91 175 3046409.
E-mail address: jassiv02@yahoo.co.in (J.S. Dhau).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.03.009

J.S. Dhau et al. / Journal of Organometallic Chemistry 696 (2011) 2406e2413
2407
Table 1
corresponding selenolate anion. The selenolate anion, upon hydro-
Preparation of unsymmetrical thio- and selenoalkyl derivatives of 1a and 1b.
lysis and subsequent aerial oxidation offered the corresponding
diselenide 3a and 3b respectively in good yields (Scheme 1). Both
these compounds are high melting solids and are highly stable at
elevated temperatures (upto 260 ꢁC).
Entry Compound
Y
Reagent
R
X
E
S
Yield %
64
1
2
4a
4b
5a
5a
5b
5b
6a
6b
7a
8a
Cl
n-BuLi
eCH2eCH2eCH3 Br
eCH2eCH2eCH3 Br Se 60
eCH3
eCH3
eCH3
eCH3
eC4H9
eCH3
OCH3 n-BuLi
Cl
Cl
OCH3 n-BuLi
OCH3 LDA
3
4
5
6
n-BuLi
LDA
I
I
I
I
I
I
Se 61
Se 82
Se 64
Se 78
Se 57
2.2. Preparation of unsymmetrical 3-sulfanyl- and 3-selenenylalkyl
derivatives of 1a and 1b
7
8
Cl
n-BuLi
OCH3 LDA
Cl
Cl
S
74
The thiolate/selenolate anions, formed by insertion of elemental
sulfur/selenium to the carbanion, were reacted with a variety of
electrophiles (Table 1) at ꢀ78 ꢁC, and then hydrolyzed at room
temperature to give 3-sulfanyl- and 3-selenenylalkyl derivatives of
1a and 1b in moderate to good yields (Scheme 1, Table 1). Further,
in an effort to synthesize bis(selenenyl) ethane, we reacted the
selenolate anion of 1a with 1,2-dibromoethane. However to our
surprise, 4-chloro-(3-selenenylethylbromide)-N,N-diisopropylpyr-
idine-2-carboxamide (8a) was the only product formed. This
suggests toward the substitution of one of the two bromo group
with the selenolate (ReSeꢀ) anion.
In another variation for the synthesis of unsymmetrical deriv-
atives, the carbanion was directly reacted with dibenzyl diselenide
to give the compound 8a in 41% yield. The performance of n-BuLi
vis-a-vis LDA was also tested in the above reactions. It was found
that the yields obtained with LDA were 15e20% more than that
obtained with n-BuLi. Increasing the amount of LDA form 2 to
3 equiv. neither led to the formation of any dilithiated product nor
showed any substantial increase in the yield of the reaction.
9
10
n-BuLi
n-BuLi
eCH2C6H5
eCH2eCH2Br
Cl Se 59
Br Se 40
3a as a representative example. Addition of LiAlH4 powder to
a solution of 3a in dry THF immediately led to the change in the
color of the solution from dark orange to pale yellow with evolution
of hydrogen gas. Addition of iodomethane to this solution afforded
5a in moderate yield. No product due to the action of LiAlH4 on the
carboxamide function was noticed in this reaction. Thus it can be
concluded that LiAlH4 chemoselectively cleaves SeeSe bond
without disturbing the carboxamide group in these compounds.
The use of NaBH4 in ethanol instead of LiAlH4 also led to an efficient
cleavage of SeeSe bond. The selenolate anion thus formed gave 5a
in near quantitative yield on quenching with iodomethane at 40 ꢁC
(Scheme 2).
2.4. Spectroscopic studies
2.3. Reductive cleavage of SeeSe bond in 3a
The synthesized compounds were characterized by elemental
analysis, NMR (1H 13C and 77Se), FT-IR and mass spectral techniques.
Compared to the parent compound (1a and 1b), IR spectra of the
compounds, 3ae8a and 3be6b, did not show any significant change
Reducing agents like lithium aluminum hydride is known to
cleave SeeSe bond in various diorgano diselenides. However, it has
the potential to reduce the carboxamide functional group to the
corresponding amines, aldehydes or alcohols. In light of these
findings, we decided to study the reductive cleavage SeeSe bond in
in the carbonyl stretching frequencies (
y
CO, 1624e1636 cmꢀ1).
CO for 5b and 6b
Interestingly, The peak corresponding to the
y
appears almost at the same frequency. This indicates that the change
Y
O
N
1a, Y = Cl; 1b, Y= OCH3
(i) n-BuLi/LDA (2.0 equiv.)
N(i Pr)2
-78°C, THF
(ii) E
(iii) RX, -78°C
(iv) H2O
(ii) Se
(ii) Se
(ii) (PhCH2Se)2, -78°C
(iii) H2O
(iii) BrCH2CH2Br
(iv) H2O
(iii) H2O, Air
Y
N
Cl
N
Cl
N
Y
Se
SeCH2CH2Br
O
SeCH2Ph
ER
O
O
O
N
8a
4a-7a
4b-6b
N(i Pr)2
N(i Pr)2
7a
(41%)
N(i Pr)2
N(i Pr)2
(40%)
2
3a (65%), Y = Cl;
3b (61%), Y= OCH3
E = S, Se; R = methyl, propyl, butyl, benzyl
Scheme 1. Preparation of symmetrical diselenides and unsymmetrical 3-sulfanyl- and 3-selenenylalkyl derivatives of 1a and 1b.

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J.S. Dhau et al. / Journal of Organometallic Chemistry 696 (2011) 2406e2413
Cl
Cl
(i) LiAlH4, Dry THF
or
Se
SeCH3
NaBH4, C2H5OH
2
(ii) CH3I
O
O
N
N
(55% for LiAlH4)
(80% for NaBH4)
N(i Pr)2
N(i Pr)2
Scheme 2. Reductive cleavage of SeeSe bond with LiAlH4 or NaBH4.
in the chalcogen atom has no effect on the carbonyl stretching
frequencies of these compounds. The 1H NMR spectra of these
compounds shows two singlets in the aromatic region indicating
deprotonation of the parent compound. The spectra contains two
multiplets due to two non-equivalent eCH(CH3)2 groups and two
doublets corresponding to two non-equivalent isopropyl methyl
groups. Also, in the 13C NMR spectra there are two signals for the
methyne carbons and two signals for the methyl carbons. This
suggests restricted rotation about the CeN bond due to resonance
leading to the double bond character between carbon and nitrogen
in the molecule. There is no substantial change in the 13C chemical
shift of the carbonyl carbons in these compounds. In conclusion,
both the IR and the NMR data suggests toward the absence of E/O
(carbonyl) interactions. 77Se NMR of the compound 5a, 5b and 7a
were recorded with diphenyl diselenide as the external standard.
Change in the substituent around selenium atom results in large
change in the magnitude of chemical shift in its spectra. The sele-
nium signal in the spectrum of 5a appears downfield at 162.04
Fig. 2. TGA, DTA and Dr. TGA curves of 3b.
(
d
ppm) when compared to 5b (93.79,
d
ppm), whereas, the signal in
(ppm). The ES mass spectra
2.5. Thermogravimetric studies
7a appears further downfield at 302.38
d
of organoselenium compounds gave distinct molecular ion peaks
with characteristic isotopic patterns. In addition to the molecular ion
peak, the mass spectrum of 3b exhibits a peak corresponding to
ReSee(Se)6eSeeR species at m/z 943. However, no product corre-
sponding to this polyselenide species was isolated from the reaction
mixture. The mass spectrum of all the unsymmetrical chalcogenides
(4ae8a, 4be6b) not only showed a signal corresponding to the
molecular ion peak but also exhibited a peak at double the m/z value
of the molecular ion peak. In this case also no such species was
found in any of the reaction products. Therefore, it appears that
formation of the polyselenide species occurs only under the mass
spectroscopic conditions.
Thermal stability of 3a is clearly depicted from the TG/DTA
curves shown in Fig. 1. The compound 3a is thermally stable upto
256 ꢁC and then decomposes in three stages. A large reaction
interval of 341 ꢁC suggests that this compound decomposes very
slowly. DTG shows two peak maxima at 293 ꢁC and 382 ꢁC as the
maximum rate of decomposition. The compound 3b is thermally
stable upto 266 ꢁC (Fig. 2). After this temperature it undergoes
decomposition in two stages. No residue was left in the pan after
the full scan. This suggests that volatile selenium containing
intermediates are formed during the decomposition process.
Reaction interval of 353 ꢁC is slightly higher that of 3a.
In order to compare the thermal stability of unsymmetrical
selenides, we investigated the thermal behavior of 4b. The
mg/
g
0.00
Fig. 1. TGA, DTA and Dr. TGA curves of 3a.
Fig. 3. TGA, DTA and Dr. TGA curves of 4a.

J.S. Dhau et al. / Journal of Organometallic Chemistry 696 (2011) 2406e2413
2409
Table 3
a
The shorter intramolecular distances (Å) in 6b and 7a ()
.
Atoms in 6b
Distance
Atoms in 7a
Distance
S(1)eO(1)
O(1)eH(5B)
O(2)eH(8C)
O(2)eH(10B)
e
2.992 (3.32)
2.328 (2.72)
2.483 (2.72)
2.524 (2.72)
e
Se (1)eCl(1)
O(1)eC(19)
O(1)eC(19)
O(1)eC(17)
O(1)eH(19C)
3.345 (3.65)
3.045 (3.22)
3.028 (3.22)
2.814 (3.22)
2.481 (2.72)
a
Values in the parenthesis is the sum of the van der Waals radii.
2,20-dipryidyl disulfide (1.782 Å) [15] and the C(Sp3)eS bond length
[1.787 (4) Å] is significantly shorter than that found in other
organosulfur compounds having C(Sp3)eS bond [16,17].
Fig. 4. Molecular structure of 6b with atom numbering scheme.
Selected bond length and angles of 7a are given in Table 2 and
its molecular structures with atom numbering scheme is shown in
Fig. 5a. The molecule crystallizes in tetragonal P-42(1)c space
group with cell parameters (a ¼ 21.517(2) Å, b ¼ 21.517(2) Å,
compound 4b is thermally stable upto 212 ꢁC after which it
decomposes in two steps (Fig. 3) leaving behind 9.52% residue,
which is less than the expected percentage of selenium (22.3%)
present in the sample. DTG curve confirmed the two step decom-
position, showing maximum rates of decomposition at 310 ꢁC and
359 ꢁC. Reaction interval of 165 ꢁC suggests that the decomposition
is faster than 3a and 3b. From above discussion it is clear that the
thermal stability of these compounds is in the following order:
3b > 3a > 4b
c ¼ 8.2988(13) Å,
a
¼ 90ꢁ,
b
¼ 90ꢁ,
g
¼ 90ꢁ,). The coordination
geometry around Se is V-shaped with bond angle C(8)eSe(1)eC(7)
of 98.01(18)ꢁ. Intramolecular secondary 1,4-type Se(1)eCl(1)
interaction was noticed in this compound (Fig. 5b, Table 3). The
1,4-type chalcogeneheteroatom secondary interactions are very
rare and greatly influence the structural features of the
compounds [18,19]. Similar to 6b, no SeeO(carbonyl) secondary
interaction was noticed. The dihedral angle between the planes
containing the amide group and pyridine ring are orthogonal to
each other with CeO(carbonyl) bond pointing away from the
selenium center. This is the reason behind the absence of any
1,5-SeeO(carbonyl) intramolecular interactions. This observation
is reflected in very small change in its carbonyl stretching
frequency with respect to the parent compound (1a). It has been
found that the compounds showing 1,5-SeeO(carbonyl) interac-
tions have selenium and oxygen atoms in the same plane [20]. The
compounds which don’t have SeeO secondary interactions have
both these atoms in different planes [21]. The crystal packing
diagram of 7a (Fig. 6) shows short intermolecular distances
between atoms listed in Table 4. Weak intermolecular C(3)eH(3)e
Se (CeHeSe angle of 126ꢁ) and C(3)eH(3)eH(16A) interactions
results in a V-shaped geometry around the H(3) with an angle H
(16A)eH(3)eSe(1) of 72.69ꢁ. The rare CeHeSe intermolecular
secondary interactions have been reported in compounds with
CeHeSe angle of 129ꢁ [22]. The C(Sp3)eSe bond length is longer
and the C(Sp2)eSe bond length is comparable to that found in tris
(2-pyridylseleno) methane [23]. The selenium atom is planar with
the pyridine ring whereas, it is orthogonal to the benzyl ring. The
bond angles and bond length of the pyridine ring is comparable to
that in dipyridyl diselenide [24].
2.6. Solid state structural features of 6b and 7a
Fig. 4 shows the molecular geometry and the crystallographic
numbering scheme of 6b. Selected bond lengths and angles are
listed in Table 2. The molecule crystallizes in orthorhombic Pbca
space group with cell parameters (a ¼ 14.730(5) Å, b ¼ 13.396(5) Å,
c ¼ 15.065(5) Å,
a
¼ 90ꢁ,
b
¼ 90ꢁ,
g
¼ 90ꢁ).
An interesting aspect in the structure of 6b is the presence of
intramolecular secondary 1,4-type S/OCH3 interaction. The S(1)e
O(1) atomic distance is 2.992 Å, which is significantly shorter than
the sum of their van der Waals radii of 3.32 Å. Short intramolecular
contacts are also observed between O(2)eH(8C) and O(2)eH(10B)
(Table 3). No interaction is observed between sulfur and the
carbonyl oxygen as oxygen atom points away from the sulfur
center. Short intermolecular distances between O(2)eH(5A), O(2)e
C(5), H(5C)eH(13C) and C(5)eH(13C) (Table 4) are also observed in
the crystal structure. The SeMe unit is oriented out of the plane of
the pyridine ring [torsion angle C(1)eC(14)eS(1)eC(5) of ꢀ53.2ꢁ]
mainly due to the steric effects of the ortho groups. The geometry
around the sulfur is ‘V’ shaped with a C(14)eS(1)eC(5) angle of
104.03 (19)ꢁ and the geometry around C(9) and C(12) is distorted
tetrahedral due steric overcrowding. The C(Sp2)eS bond length
[1.777 (4) Å] is slightly shorter than that found in 5,50-dibromo-
Table 2
Bond lengths [Å] and angles [ꢁ] for 6b and 7a.
Compound 6b
N(2)eC(7)
O(1)eC(1)
C(9)eC(8)
C(7)eN(2)eC(12)
N(2)eC(9)eC(8)
O(2)eC(7)eN(2)
C(11)eC(12)eH(001)
Compound 7a
C(1)eC(7)
C(9)eCl(1)
C(13)eN(2)
C(1)eC(7)eSe(1)
C(8)eC(12)eC(13)
N(2)eC(14)eC(16)
C(14)eN(2)eC(17)
1.348(5)
1.337(5)
1.512(6)
122.3(4)
112.5(3)
124.7(4)
110(4)
N(2)eC(12)
O(1)eC(6)
C(4)eC(7)
C(12)eN(2)eC(9)
C(8)eC(9)eC(10)
C(11)eC(12)eC(13)
C(9)eC(8)eH(8A)
1.468(6)
1.446(5)
1.519(6)
116.8(3)
112.3(4)
112.5(5)
109.5
O(2)eC(7)
C(14)eS(1)
S(1)eC(5)
C(4)eC(14)eS(1)
C(14)eC(4)eC(7)
N(2)eC(12)eH(001)
C(14)eS(1)eC(5)
1.229(5)
1.777(4)
1.787(5)
118.9(3)
120.1(4)
102(3)
104.03(19)
1.501(6)
1.723(4)
1.338(5)
111.2(3)
120.0(4)
112.7(4)
116.8(4)
C(7)eSe(1)
C(12)eC(13)
C(14)eN(2)
C(9)eC(8)eSe(1)
O(1)eC(13)eN(2)
C(16)eC(14)eC(15)
C(8)eSe(1)eC(7)
1.974(4)
1.517(5)
1.465(5)
122.8(3)
124.5(4)
112.4(4)
98.01(18)
C(8)eSe(1)
C(13)eO(1)
C(14)eC(16)
N(1)eC(12)eC(13)
O(1)eC(13)eC(12)
C(13)eN(2)eC(17)
1.924(4)
1.232(5)
1.527(7)
114.7(3)
116.7(4)
120.7(4)

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J.S. Dhau et al. / Journal of Organometallic Chemistry 696 (2011) 2406e2413
Table 4
The shorter intermolecular distances (Å) in 6b and 7a ()a.
Atoms in 6b
Distance
Atoms in 7a
Distance
O(2)eH(5A)
O(2)eC(5)
H(5C)eH(13C)
C(5)eH(13C)
e
e
e
2.365 (2.72)
3.203 (3.22)
2.365 (2.4)
2.886 (2.9)
e
e
e
Se (1)eH(3)
H(16A)eH(3)
H(14)eC(15)
O(1)eH(10)
N(1)eH(11)
H(7B)eC(2)
H(7B)eC(3)
3.031 (3.1)
2.358 (2.4)
2.830 (2.9)
2.561 (2.72)
2.730 (1.75)
2.782 (2.9)
2.825 (2.9)
a
Values in the parenthesis is the sum of the van der Waals radii.
3. Conclusion
Synthesis of organochalcogen (S, Se) compounds derived from
1a and 1b has been achieved by a method involving lithiation of 1a
and 1b with LDA/n-BuLi. The yield of the reaction involving the use
of LDA is better than that obtained in case of n-BuLi. The IR and 13C
NMR spectra of the prepared compounds indicates toward the
absence of EeO (carbonyl) interactions. The single crystal X-ray
structures of 6b and 7a substantiate the above facts, and establishes
the presence of 1,4-type S/OeCH3 and Se/Cl intramolecular
secondary interactions.
Fig. 6. Crystal packing of 7a.
recorded in CDCl3 using TMS as internal standard on Bruker AC,
400 MHz spectrometer. 77Se NMR spectra were recorded in CDCl3
using diphenyl diselenide as external standard on Bruker AMX500
spectrometer. The ESI mass spectra were taken on Water Q-TOF
Micro spectrometer. The elemental analysis was carried out by
using Elementar VarioMICRO analyzer. The thermogravimetric
analysis was done on Shimadzu DTG 60H (simultaneous TG/DTA
module). The samples were loaded on an Alumina crucible and
heated under nitrogen at the rate of 20 ꢁC/min. Compound 1a and
1b was prepared by literature method [25].
4. Experimental
4.1. General
All experiments were carried out in dry oxygen free nitrogen
atmosphere. Infrared spectra were recorded between KBr pellets on
a PerkineElmer Model 1430. 1H NMR and 13C NMR spectra were
4.2. General method for the preparation of chalcogenolate anion of
1a and 1b
To a vigorously stirred solution of 1a (0.962 g, 4 mmol) or 1b
(0.90 g, 4 mmol) in dry THF at ꢀ78 ꢁC, n-BuLi (1.39 N in hexane,
6.0 ml, 8 mmol) was added drop-wise. The reaction mixture was
stirred for 2 h at the same temperature. To the dark red solution of
the carbanion, elemental selenium (0.632 g, 8 mmol) or sulfur
(0.257 g, 8 mmol) was added and the reaction mixture was slowly
brought to the room temperature. After the complete dissolution of
elemental chalcogen the reaction was subjected to conditions
described below.
4.2.1. Bis[3-(4-chloro-N,N-diisopropylpyridine-2-carboxamide)]
diselenide (3a)
The selenolate anion of 1a formed as above was hydrolyzed at
room temperature by adding 20 ml of water. The reaction mixture
was subjected to aerial oxidation for 30 min. The organic layer was
extracted with diethyl ether (3 ꢂ 50 ml) and dried over anhydrous
sodium sulfate. The solvent was removed on a rota-evaporator and
the crude residue was purified by column chromatography using
silica gel (60e120 mesh) and using hexaneeethyl acetate as eluent
(5:4). Yield 0.83 g (65%), m.p. 232e233 ꢁC, 1H NMR: CDCl3, 400 MHz
d
(ppm): 8.34e8.35 (d, J ¼ 5.2 Hz, 2H), 7.34e7.35 (d, J ¼ 5.2 Hz, 2H),
3.55e3.61 (m, J ¼ 6.6 Hz, 2H), 3.43e3.49 (m, J ¼ 6.8 Hz, 2H),
1.48e1.49 (d, J ¼ 6.8 Hz, 12H,), 1.03e1.04 (d, J ¼ 6.6 Hz, 12H). 13C
NMR: CDCl3, 400 MHz
d (ppm): 165.4, 160.2, 150.7, 148.4, 123.9,
123.6, 50.0, m 45.0, 19.6, 19.0. IR (KBr, cmꢀ1): 2970, 1628, 1537, 1477,
1427,1367,1325,1296,1208,1132,1060, 850, 728, 616. MS (ESI): 639
[Mþ$ 80Se]. Anal. Calcd (%) for C24H32Cl2N4O2Se2: C, 45.21, H, 5.02, N,
8.79. Found: C, 45.35, H, 5.30, N, 8.55.
Fig. 5. a: Molecular structure of 7a with atom numbering scheme. b: Molecular
structure of 7a exhibiting intramolecular non-bonded interactions.

J.S. Dhau et al. / Journal of Organometallic Chemistry 696 (2011) 2406e2413
2411
4.2.2. Bis[3-(4-methoxy-N,N-diisopropylpyridine-2-carboxamide)]
495. MS (ESI): 335 [Mþ$
,
80Se, 36Cl], Anal. Calcd (%) for
diselenide (3b)
C13H19ClN2OSe: C, 46.80, H, 5.74, N, 8.39. Found: C, 46.83, H, 5.88,
N, 8.23.
The selenolate anion of 1b was hydrolyzed and subjected to
aerial oxidation for 30 min. The reaction mixture was worked-up as
described above. Yield: 0.76 g (61%), 1H NMR: CDCl3, 400 MHz
4.3.4. 4-Methoxy-3-(selenenylmethyl)-N,N-diisopropylpyridine-2-
carboxamide (5b)
d
(ppm): 8.35e8.37 (d, J ¼ 5.7 Hz, 2H), 6.75e6.77 (d, J ¼ 5.7 Hz, 2H),
3.7 (s, 6H), 3.48e3.55 (m, J ¼ 6.6 Hz, 2H), 3.40e3.47 (m, J ¼ 6.8 Hz,
2H), 1.46e1.48 (d, J ¼ 6.8 Hz, 12H,), 1.01e1.03 (d, J ¼ 6.6 Hz, 12H). IR
(KBr, cmꢀ1): 2924, 1710, 1624, 1364, 1218, 1089, 927, 770, 668, 530.
MS (ESI): 631 [M þ H]þ 630 [Mþ$ 80Se], 629 [M ꢀ H]þ. Anal. Calcd
(%) for C26H38N4O4Se2: C, 49.69, H, 6.09, N, 8.91. Found: C, 49.76, H,
6.03, N, 8.49.
Electrophile: Iodomethane (1.14 g, 0.5 ml, 8 mmol). Yield: 0.84 g
(64%, n-BuLi), 1.02 g (78%, LDA), m.p. 140e142 ꢁC, 1H NMR: CDCl3,
400 MHz
d
(ppm): 8.47e8.48 (d, J ¼ 4.8 Hz, 1H), 6.91e6.92 (d,
J ¼ 4.8 Hz,1H), 4.0 (s, 3H), 3.55e3.58 (m,1H), 3.43e3.46 (m,1H), 2.3
(s, 3H),1.60e1.62 (d, J ¼ 6.8 Hz, 6H),1.22e1.24 (d, J ¼ 6.6 Hz, 6H). 13C
NMR: CDCl3, 400 MHz d (ppm): 167.0,166.7,160.5,150.6,117.1,106.1,
56.2, 50.8, 45.8, 20.6, 20.2, 18.1. 77Se NMR:
d (ppm): 93.79. IR (KBr,
4.3. General method for the preparation of unsymmetrical
3-sulfanyl- and 3-selenenylalkyl derivatives of 1a and 1b
cmꢀ1): 3018, 2922, 2848, 1628, 1565, 1432, 1364, 1218, 1163, 1034,
770, 668, 530. MS (ESI): 329 [(M ꢀ H)þ, 80Se], 330, [Mþ$
,
80Se], 331
[(M þ H)þ, 80Se]. Anal. Calcd (%) for C14H22N2O2Se: C, 51.07, H, 6.73,
The chalcogenolate anion of 1a/1b was cooled to ꢀ78 ꢁC and the
desired electrophile (8 mmol) was added drop-wise. The reaction
mixture was slowly brought to room temperature and stirred for
30 min. The nitrogen supply to the reaction mixture was stopped.
The reaction mixture was hydrolyzed and extracted with diethyl
ether (3 ꢂ 50 ml). The organic layer was dried over anhydrous
sodium sulfate. The solvent was removed on a rota-evaporator and
the crude residue was purified by column chromatography using
silica gel and hexane-ethyl acetate as eluent (10:3).
N, 8.51. Found: C, 50.96, H, 6.89, N, 8.47.
4.3.5. 4-Chloro-3-(selenenylbutyl)-N,N-diisopropylpyridine-2-
carboxamide (6a)
Electrophile: 1-Iodobutane (1.472 g, 0.91 ml, 8 mmol). Yield:
0.85 g (57%), m.p. low melting point solid. 1H NMR: CDCl3, 400 MHz
d
(ppm): 8.31e8.32 (d, J ¼ 5.3 Hz, 1H), 7.28.7.27 (d, J ¼ 5.3 Hz, 1H),
3.44e3.50 (m, J ¼ 6.8 Hz, 1H), 3.32e3.38 (m, J ¼ 6.7 Hz, 1H), 2.9 (s,
broad peak, 2H), 1.54e1.61 (m, J ¼ 7.2e7.6 Hz, 2H,), 1.51e1.53 (d,
J ¼ 6.8 Hz, 6H), 1.31e1.36 (m, 7.3e7.6 Hz, 2H), 1.10 (s, broad peak,
6H), 0.80e0.84 (t, J ¼ 7.4 Hz, 3H). 13C NMR: CDCl3, 400 MHz
4.3.1. 4-Chloro-3-(sulfanylpropyl)-N,N-diisopropylpyridine-2-
carboxamide (4a)
d
(ppm): 167.1, 162.8, 151.2, 149.6, 124.1, 122.6, 50.9, 45.9, 32.1, 30.1,
Electrophile: 1-Bromopropane (0.984 g, 0.73 ml, 8 mmol). Yield:
22.8, 20.5, 13.5. IR (KBr, cmꢀ1): 2970, 1643, 1537, 1469, 1368, 1258,
0.8 g (64%), m.p. 68e70 ꢁC, 1H NMR: CDCl3, 400 MHz
d
(ppm):
1211, 1136, 1040, 830, 728, 634, 604, 531. MS (ESI): 377, [Mþ$ 80Se,
,
8.32e8.33 (d, J ¼ 5.2 Hz, 1H), 7.28e7.29 (d, J ¼ 5.2 Hz, 1H),
3.44e3.51 (m, J ¼ 6.8 Hz, 1H), 3.28e3.34 (m, J ¼ 6.6 Hz, 1H),
2.86e2.90 (m, 2H), 1.52e1.53 (d, J ¼ 6.7 Hz, 6H,), 1.32e1.37 (m, 2H),
1.05e1.12 (broad doublet, 6H), 0.81e0.85 (t, J ¼ 7.3 Hz, 3H). 13C
36Cl]. Anal. Calcd (%) for C16H25ClN2OSe: C, 51.15, H, 6.71, N, 7.45.
Found: C, 51.47, H, 6.71, N, 7.29.
4.3.6. 4-Methoxy-3-(sulfanylmethyl)-N,N-diisopropylpyridine-2-
carboxamide (6b)
NMR: CDCl3, 400 MHz
d (ppm): 166.3, 162.0, 151.2, 149.3, 127.6,
124.4, 51.0, 45.9, 38.3, 36.1, 31.4, 22.9, 21.8, 20.5,13.6. IR (KBr, cmꢀ1):
2929, 2435, 2132, 1716, 1636, 1439, 1364, 1218, 1090, 771, 670, 530.
MS (ESI): 314 [Mþ$]. Anal. Calcd (%) for C15H23ClN2OS: C, 57.22, H,
7.36, N, 8.90, S, 10.18. Found: C, 57.52, H, 7.33, N, 8.11, S, 9.31.
Electrophile: Iodomethane (1.14 g, 0.5 ml, 8 mmol). Yield: 0.83 g,
(74%), m.p. 142e143 ꢁC, 1H NMR: CDCl3, 400 MHz
d (ppm):
8.32e8.33 (d, J ¼ 5.8 Hz, 1H), 6.71e6.73 (d, 5.8 Hz, 1H), 3.90 (s, 3H),
3.44e3.48 (m, 1H), 3.37e3.40 (m, 1H), 2.29 (s, 3H), 1.51e1.53 (d,
J ¼ 6.8 Hz, 6H), 1.08e1.09 (d, 6H). 13C NMR: CDCl3, 400 MHz
4.3.2. 4-Methoxy-3-(selenenylpropyl)-N,N-diisopropylpyridine-2-
carboxamide (4b)
d (ppm): 167.5, 166.5, 160.7, 150.6, 111.7, 105.9, 56.2, 50.9, 45.9, 29.7,
20.6, 20.2, 8.3. IR (KBr, cmꢀ1): 2922, 2435, 1629, 1560, 1458, 1364,
1338,1217, 1035, 756, 667, 530, 458. MS (ESI): 282 [M]þ$. Anal. Calcd
(%) for C14H22N2O2S: C, 59.54, H, 7.85, N, 9.91, S, 11.35. Found: C,
59.71, H, 7.81, N, 9.64, S, 11.01.
Electrophile: 1-Bromopropane (0.984 g, 0.73 ml, 8 mmol). Yield:
0.86 g (60%), m.p. 46e48 ꢁC, 1H NMR: CDCl3, 400 MHz
d (ppm):
8.39e8.40 (d, J ¼ 5.6 Hz, 1H), 6.73e6.75 (d, J ¼ 5.7 Hz, 1H), 3.95 (s,
3H), 3.44e3.56 (m, J ¼ 6.8, 6.2, 6.7 Hz, 2H), 2.86e2.91 (t, J ¼ 7.3,
7.4 Hz, 2H), 1.66.1.69 (m, 2H), 1.56e1.65 (d, J ¼ 8.0 Hz, 6H), 1.15e1.17
(d, J ¼ 6.6 Hz, 6H), 0.95e0.98 (t, J ¼ 7.3, 7.4 Hz, 3H). 13C NMR: CDCl3,
4.3.7. 4-Chloro-3-(selenenylbenzyl)-N,N-diisopropylpyridine-2-
carboxamide (7a)
Method A: Electrophile: Benzyl chloride (1.01 g, 0.92 ml,
8 mmol). Yield: 1.0 g, (59%).
Method B: To a vigorously stirred solution of 1a (0.962 g,
4 mmol) in dry THF at ꢀ78 ꢁC, n-BuLi (1.39 N in hexane, 6.0 ml,
8 mmol) was added drop-wise. The reaction mixture was stirred for
2 h at the same temperature. To the dark red solution of the carb-
anion, dibenzyl diselenide (2.74 g, 8 mmol) was added and the
reaction mixture was slowly brought to the room temperature and
worked-up as described above. Yield: 0.71 g, (41%) m.p.104e106 ꢁC,
400 MHz
d
(ppm): 167.1, 167.0, 161.0, 150.3, 111.2, 105.8, 99.9, 56.2,
50.9, 45.9, 32.2, 23.6, 20.6, 14.4, 1.02. IR (KBr, cmꢀ1): 2966, 1625,
1566, 1468, 1427, 1371, 1335, 1296, 1212, 1132, 1039, 817, 751, 616.
MS (ESI): 359 [M þ H]þ. Anal. Calcd (%) for C16H26N2O2Se: C, 53.78,
H, 7.33, N, 7.84. Found: C, 53.69, H, 7.22, N, 7.58.
4.3.3. 4-Chloro-3-(selenenylmethyl)-N,N-diisopropylpyridine-2-
carboxamide (5a)
Electrophile: Iodomethane (1.14 g, 0.5 ml, 8 mmol). Yield: 0.81 g
(61%, n-BuLi), 1.1 g (82%, LDA) m.p. 82e84 ꢁC, 1H NMR: CDCl3,
1H NMR: CDCl3, 400 MHz
d
(ppm): 8.32e8.33 (d, J ¼ 5.2 Hz, 1H),
400 MHz
d
(ppm): 8.39e8.41 (d, J ¼ 5.3 Hz, 1H), 7.36e7.37 (d,
7.23e7.24 (d, J ¼ 5.2 Hz, 1H), 7.17e7.22 (m, 2H), 7.09e7.16 (m, 3H),
4.19 (s, 2H), 3.45e3.52 (m, J ¼ 6.8 Hz, 1H), 3.33e3.39 (m, J ¼ 6.6 Hz,
1H), 1.53e1.55 (d, J ¼ 6.9 Hz, 6H), 1.08e1.09 (d, J ¼ 6.6 Hz, 6H). 13C
J ¼ 5.2 Hz, 1H), 3.52e3.59 (m, J ¼ 6.9 Hz, 1H), 3.3e3.42 (m,
J ¼ 6.7 Hz, 1H), 2.3 (s, 3H), 1.59e1.69 (d, J ¼ 6.9 Hz, 6H,), 1.18e1.20
(d, 6.6 Hz, 6H), 0.9 (t, 3H). 13C NMR: CDCl3, 400 MHz
d
(ppm):
NMR: CDCl3, 400 MHz d (ppm): 167.2, 163.1, 151.6, 149.9, 137.5,
166.9, 161.9, 151.1, 149.3, 124.3, 123.4, 51.0, 46.0, 20.5, 20.1, 9.6. 77Se
NMR:
(ppm): 162.04. IR (KBr, cmꢀ1): 2968, 2361, 1629, 1547, 1466,
1422, 1370, 1331, 1209, 1162, 1098, 916, 824, 733, 634, 605, 532,
129.2, 128.4, 127.1, 124.0, 122.6. 77Se NMR:
cmꢀ1): 2968, 2363, 1631, 1542, 1475, 1424, 1368, 1324, 1212, 1039,
866, 763, 724, 594. MS (ESI): 441 [Mþ$ 80Se, 36Cl]. Anal. Calcd (%) for
d (ppm): 302.38. IR (KBr,
d
,

2412
J.S. Dhau et al. / Journal of Organometallic Chemistry 696 (2011) 2406e2413
Table 5
brought to room temperature and stirred for 2 h. The pale yellow
solution was again cooled to 0 ꢁC and iodomethane (0.05 ml,
0.88 mmol) was added drop-wise. The resulting solution was stir-
red overnight and hydrolyzed with 20 ml of water the next day. The
usual workup procedure afforded 5a in 55% (0.14 g) yield.
Method B: To a vigorously stirred solution of 3a (0.1 g,
0.16 mmol) in absolute ethanol at 0 ꢁC, NaBH4 (0.015 g, 0.39 mmol)
was added in small installments. The reaction mixture was slowly
brought to room temperature and stirred for 3 h at 40 ꢁC. The pale
yellow solution was again cooled to 0 ꢁC and iodomethane
(0.025 ml, 0.44 mmol) was added drop-wise. The resulting solution
was stirred overnight 40 ꢁC and hydrolyzed with 20 ml of water the
next day. The usual workup procedure afforded 5a in 80% (0.085 g)
yield.
Crystal data collection and structure refinement parameters of compound 6b and 7a.
Empirical formula
Formula weight
Temperature
Wavelength
Crystal system
Space group
Unit cell
dimensions
a
C14 H22 N2 O2S
282.40
293(2) K
0.71069 Å
Orthorhombic
Pbca
C19 H23Cl N2OSe
409.80
293(2) K
0.71073 Å
Tetragonal
P-42(1)c
14.730(5) Å
13.396(5) Å
15.065(5) Å
90.0(5)ꢁ.
21.517(2) Å
21.517(2) Å
8.2988(13) Å
90.0ꢁ
b
c
a
b
90.0(5)ꢁ.
90.0ꢁ
90.0ꢁ
g
90.0(5)ꢁ.
Volume
Z
Density
2972.7(18) Å3
8
3842.0(8) Å3
8
1.262 Mg/m3
1.417 Mg/m3
4.5. Crystal structure determination and refinement
(calculated)
Absorption
coefficient
F(000)
Crystal size
Theta range for
data collection
Index ranges
0.218 mmꢀ1
2.101 mmꢀ1
Single-crystal X-ray data of 6b and 7a were collected using
1216
1680
graphite-monochromated Mo-K
a
radiation (
l
¼ 0.71073 Å) on
24 ꢂ 18 ꢂ 16 mm3
0.34 ꢂ 0.32 ꢂ 0.28 mm3
“Bruker SMART APEX CCD diffractometer” at 100 K. The linear
absorption coefficients, scattering factors for the atoms and the
anomalous dispersion corrections were taken from the Interna-
tional Tables for X-ray Crystallography [26]. The program SMART was
used for collecting frames of data, indexing reflections, and deter-
mining lattice parameters. The data integration and reduction were
processed with SAINT [27] software. An empirical absorption
correction was applied to the collected reflections with SADABS
[28] using XPREP [29]. All the structures were solved by the direct
method using the program SHELXS-97 [30] and were refined on F2
by the full-matrix least-squares technique using the SHELXL-97
program package. All non-hydrogen atoms were refined with
anisotropic displacement parameters in all the structure. All other
relevant information about the data collection and refinement are
presented in Table 5.
2.46e26.50ꢁ.
1.89e25.48ꢁ.
18ꢃhꢃ18,
26ꢃhꢃ25,
12ꢃkꢃ16,
22ꢃkꢃ26,
18ꢃlꢃ18
ꢀ6ꢃlꢃ10
Reflections collected
Independent
reflections
Completeness
to theta ¼ 25.48ꢁ
Absorption
correction
Max. and min.
transmission
15925
20059
3072 [R(int) ¼ 0.0591]
3554 [R(int) ¼ 0.0905]
theta ¼ 26.50ꢁ99.6%
99.8%
None
None
0.5907 and 0.5352
Refinement method
Full-matrix least-
squares on F2
3072/0/180
Full-matrix least-
squares on F2
3554/0/217
Data/restraints/
parameters
Goodness-of-fit
on F2
1.109
1.044
Final R indices
[I > 2s(I)]
R indices (all data)
R1 ¼ 0.0940,
wR2 ¼ 0.2336
R1 ¼ 0.1093,
wR2 ¼ 0.2445
R1 ¼ 0.0403,
wR2 ¼ 0.0826
R1 ¼ 0.0543,
wR2 ¼ 0.0890
ꢀ0.018(11)
Acknowledgments
We are thankful to the CSIR, New Delhi, India, for financial
support. Additional support from SAP by UGC, New Delhi, is also
acknowledged. We are also thankful to Mr. Avtar Singh, CIL, Punjab
University, Chandigarh, for NMR spectra. Thanks are also
acknowledged to Prof. P. Bhardwaj and Dr. Kamlesh Thapliyal, and
Dr. Sarvendra Kumar IIT, Kanpur, for single crystal X-ray studies on
6b and 7a.
Absolute structure
parameter
Largest diff. peak
and hole
2.593 and ꢀ0.357 e Åꢀ3
0.514 and ꢀ0.527 e Åꢀ3
C19H23ClN2OSe: C, 55.69, H, 5.65, N, 6.83. Found: C, 55.78, H, 5.79, N,
6.66.
Appendix. Supplementary material
4.3.8. 4-Chloro-(3-selenenylethylbromide)-N,N-diisopropylpyridine-
2-carboxamide (8a)
CCDC Nos. 791167 (6b); 791168 (7a) contains the supplementary
crystallographic data for this paper. Crystallographic data for the
structure analysis have been deposited with the Cambridge Crys-
tallographic Data Center. CCDC numbers are 791167 for 4-methoxy-
3-(sulfanylmethyl)-N,N-diisopropylpyridine-2-carboxamide (6b)
and 791168 for and 4-chloro-3-(selenenylbenzyl)-N,N-diisopro-
pylpyridine-2-carboxamide (7a). Copies of this information may be
obtained free of charge from the Director, 12 Union Road, Cam-
bridge CB2 1EZ, UK, fax: þ44 1223 336 033; or e-mail: deposite@
ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk.
Electrophile: 1,2-Dibromoethane (0.75 g, 0.35 ml, 4 mmol).
Yield: 0.68 g, (40%) m.p.100e102 ꢁC, 1H NMR: CDCl3, 400 MHz
d
(ppm): 8.44e8.45 (d, J ¼ 5.3 Hz, 1H), 7.39e7.40 (d, J ¼ 5.2 Hz, 1H),
3.63 (s, broad peak, 2H), 3.51e3.58 (m, J ¼ 6.6 Hz, 1H), 3.37e3.44
(m, J ¼ 6.6 Hz, 1H), 3.40 (s, broad peak, 2H), 1.58e1.60 (d, J ¼ 6.6 Hz,
6H), 1.16e1.18 (d, J ¼ 6.6 Hz, 6H). IR (KBr, cmꢀ1): 2971, 1632, 1537,
1476, 1422, 1367, 1324, 1209, 1161, 1040, 827, 728, 634, 569. MS
(ESI): 427 [Mþ$ 80Se, 35Cl]. Anal. Calcd (%) for C19H23ClN2OSe: C,
,
39.42, H, 4.72, N, 6.57. Found: C, 39.55, H, 4.65, N, 6.70.
4.4. Reductive cleavage of SeeSe bond in 3a
Appendix. Supplementary material
Method A: To a vigorously stirred solution of 3a (0.25 g,
0.4 mmol) in dry THF at 0 ꢁC, powdered LiAlH4 (2.24 g, 0.88 mmol)
was added in small installments. The reaction mixture was slowly
Supplementary data related to this article can be found online at
doi:10.1016/j.jorganchem.2011.03.009.

J.S. Dhau et al. / Journal of Organometallic Chemistry 696 (2011) 2406e2413
2413
[15] K.K. Bhasin, R. Kumar, S.K. Mehta, P. Raghavaiah, C. Jacob, T.M. Klapoetke,
Inorg. Chim. Acta 362 (2009) 2386e2390.
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