Facile synthesis of benzimidazolin-2-chalcogenones: Nature of the carbon-chalcogen bond

Article abstract of DOI:10.1016/j.jorganchem.2012.07.025

A new method using chalcogen nucleophiles E^2-/E₂ ^2- (E = S, Se, Te) for the convenient and high yield synthesis of benzimidazolin-2-chalcogenones has been developed. The reaction of strong nucleophiles E^2-/E₂^2- with various benzimidazolium salts under mild conditions afforded benzimidazolin-2- chalcogenones (10a-10g) in better yield compared to the other methods involving E⁰ powder. Benzimidazolin-2-tellurones were found to be unstable when pyridyl/phenyl groups were bonded to one of the nitrogens of the benzimidazolium salts and the reaction led to the isolation of the corresponding diamines (12a and 12b). The selenones/tellurones could be easily oxidized to the corresponding dihaloderivatives (16a-16e) by the reaction of the chalcogenones with bromine/iodine. The nature of the carbon-chalcogen double bond has been investigated with the help of single crystal X-ray, NMR spectroscopy and Density Functional Theory (DFT) calculations.

Full text of DOI:10.1016/j.jorganchem.2012.07.025

Journal of Organometallic Chemistry 717 (2012) 61e74
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Facile synthesis of benzimidazolin-2-chalcogenones: Nature
of the carbonechalcogen bond
,
b
Sudesh T. Manjare a, Sagar Sharma a, Harkesh B. Singh a , Ray J. Butcher
*
a Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
b Department of Chemistry, Howard University, 525 College Street NW, Washington, DC 20059, USA
a r t i c l e i n f o
a b s t r a c t
A new methodusing chalcogennucleophiles E2ꢀ/E22ꢀ (E¼ S, Se, Te) for the convenientand highyield synthesis
of benzimidazolin-2-chalcogenones has been developed. The reaction of strong nucleophiles E2ꢀ/E22ꢀ with
various benzimidazolium salts under mild conditions afforded benzimidazolin-2-chalcogenones (10ae10g)
in better yield compared to the other methods involving E0 powder. Benzimidazolin-2-tellurones were
found to be unstable when pyridyl/phenyl groups were bonded to one of the nitrogens of the benzimida-
zolium salts and the reaction led to the isolation of the corresponding diamines (12a and 12b). The selenones/
tellurones could be easily oxidized to the corresponding dihaloderivatives (16ae16e) by the reaction of the
chalcogenones with bromine/iodine. The nature of the carbonechalcogen double bond has been investigated
with the help of single crystal X-ray, NMR spectroscopy and Density Functional Theory (DFT) calculations.
Ó 2012 Elsevier B.V. All rights reserved.
Article history:
Received 22 May 2012
Received in revised form
7 July 2012
Accepted 15 July 2012
Keywords:
Chalcogenone
Thione
Selenone
Tellurone
Dihalochalcogenone
DFT
1. Introduction
chalcogen sources such as CSe2, thiophosgene, etc. instead of
elemental chalcogens [16,17].
The chemistry of N-heterocyclic carbenes (NHCs) and their
metal complexes [1,2] is of considerable current interest due to
their applications in homogeneous catalysis [3] and medicinal
chemistry [4]. The successful applications of N-heterocyclic carbene
(NHC) based catalysts include; carbonecarbon cross-coupling
reactions [5], olefin metathesis [6], hydrosilylation [7], and CO/
ethylene copolymerization [8]. The N-heterocyclic carbenes play an
important role both as reactive intermediates and as ligands in
complexes of metal and metalloid centers because of highly
nucleophilic character [9].
The chalcogen derivatives of NHC have been studied by several
groups. The first chalcogenone, 1,3-dialkylimidazole-2-thione was
synthesized by reacting the corresponding iodide salt with sulfur
powder in methanol in the presence of potassium carbonate [10].
Arduengo et al. reported synthesis of the thione and tellurium
analogs (1) [11,12]. The chalcogen(IV) compounds (2) have been
synthesized by treating chalcogenones with halogens/halogenating
agents [13,14]. Devillanova and co-workers have synthesized
stable bis(selenones) and their halogen derivatives [15]. The ben-
zimidazolin-2-chalcogenones have been synthesized using other
Recently, our group and others have extensively studied the
synthesis, structure and reactivity of diaryl diselenide (3e5) (Fig. 1)
[18], stabilized by intramolecular secondary bonding interaction.
Some derivatives exhibit excellent glutathione peroxides-like (GPx-
like) activities. In view of the interesting reactivity and GPx-like
activities shown by intramolecularly coordinated organo-
chalcogen systems, we envisaged to synthesize a new series of
organochalcogen compounds stabilized by intramolecular coordi-
nation with carbene carbon as the donor atom instead of hetero-
atoms (N, O). In this paper we report the attempted synthesis of
organochalcogen derivatives stabilized by carbene carbon as the
donor atom. Various commonly used strategies explored for the
synthesis of the desired dichalcogenides stabilized by carbene
donors always led to the facile formation of the chalcogenone
derivatives in very good yields. In view of the interesting observa-
tions, we systematically explored the reaction for developing
a
facile high yield synthetic route for benzimidazolin-2-
chalcogenones and their halogen derivatives.
We have further synthesized a series of benzimidazolin-2-
chalcogenones (chalcogen ¼ S, Se, Te) with different substituent
groups at the benzimidazolium nitrogen and their halogen deriv-
atives to enable study of the effect of the substituent groups at
benzimidazole nitrogen on the stability of N-heterocyclic chalco-
genones, nature of C]E bond (E ¼ S, Se, Te) and the relative charges
* Corresponding author.
E-mail address: chhbsia@chem.iitb.ac.in (H.B. Singh).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.07.025

62
S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
R
H
Mes
R
N
X
E
X
CHO
Se
NMe2
X
X
N
N
Se
Te
)
)
2
Se
Fe
)
N
N
R
2
2
CHO
Mes
1
4
5
2
3a R = H
3b
R = Me
X = Cl, H
Mes = mesityl X = Cl, I
E = S, Se, Te
R = Me, Et, i-Pr
Fig. 1. Chalcogen derivatives.
on the chalcogen atoms. We have also probed in depth the nature of
the bond between carbene carbon and chalcogens using DFT
calculations.
In view of these initial results, we next set out to systematically
explore the utility of this method for the synthesis of benzimida-
zolin-2-chalcogenones using method B.
The n-butyl substituted thione 10a was synthesized by reacting
benzimidazolium salt (8c) with disodium disulfide [22]. Similarly
selenones (10be10e) were prepared from the corresponding salts
(8ae8d). The plausible mechanism for the high yield formation of
chalcogenones by method B is shown in Scheme 3.
2. Results and discussion
2.1. Synthesis
The high yields of the chalcogenones derived from the less
reactive benzimidazolium salts compared to the more reactive
imidazolium salts, we believe, is due to the more facile attack of the
strong nucleophiles, E22ꢀ (E ¼ S, Se and Te) compared to weaker
nucleophiles, E0 (E ¼ S, Se and Te). When one chalcogen nucleo-
phile E2ꢀ (i.e. Na2Se) rather than two chalcogen nucleophile,
(Na2E2) was used, the reaction afforded 10d in excellent yield (more
than 98%).
The synthesis of the tellurones derived from benzimidazolium
salts having electron-withdrawing groups on the nitrogen turned
out to be much more difficult as compared with their sulfur and
selenium analogs. The n-butyl- and iso-propyl substituted tellur-
ones (10f and 10g) could be easily synthesized by treating the
corresponding salts (8c and 8d) with an in situ generated disodium
ditelluride. The tellurones are stable at room temperature in the
solid state; however, they slowly decomposed in solution to give
a tellurium mirror. Attempted synthesis of compounds 11 from salt
8 using all three methods was unsuccessful. The reaction afforded
compounds 12a [23] and 12b in moderate yield (Scheme 4). The
cleavage of the carbene carbon from benzimidazole ring in 12a and
12b may be due to the destabilization of C]Te bond by the electron
withdrawing groups present on the benzimidazolium nitrogen and
the steric crowding near the carbene carbon.
The precursor benzimidazolium salts were prepared by two
different routes; 1) nucleophilic substitution at the nitrogen atoms
of the imidazole, or 2) multi-component reactions for the genera-
tion of the N,N0-substituted heterocycles [19]. Compounds 7ae7d
were prepared by alkylation [5] or arylation [20] of benzimid-
azole (6). The N,N0-substituted benzimidazolium salts 8ae8d were
synthesized from the respective N-substituted benzimidazoles
7ae7d and 2-bromobenzylbromide (Scheme 1) [21].
The synthesis of carbene stabilized dichalcogenides 9a and 9b
was attempted by two different methods (Scheme 2). The synthesis
of 9a and 9b was attempted by the lithiation (method A) of salt 8c
with n-BuLi at different concentrations (1 eqv, 2 eqv or 3 eqv)
followed by the addition of selenium/tellurium powder in dry THF
and oxidative work up. However, the reactions always afforded
benzimidazolin-2-chalcogenones 10d and 10f (30e40%), instead of
the desired compounds. Method B involved the addition of 8c to an
in situ generated solution of disodium diselenides/disodium ditel-
lurides (1 eqv) in the presence of potassium tert-butoxide in THF.
The reaction, again, led to the isolation of same products (10d and
10f) in much better yield (60e80%) when compared to method A.
When derivatives 10d and 10f were prepared by the conventional
method C i.e., by treatment of salt 8c with potassium tert-butoxide
in THF followed by selenium/tellurium, the yield of the desired
product (10d and 10f) were poor (20e30%).
To establish the effect of the electron withdrawing group, the
synthesis of 1,3-bis(2-bromobenzyl)-1H-benzo[d]imidazole-2(3H)-
Br
N
N
N
Method A
Method B
C
Br
N
R
N
R
N
H
6
R
Yield
82%
37%
71%
68%
Method
R
2-Py
Ph
(
8a
8b
8c
)
A
A
B
B
2-Py
Ph
(
7a
7b
7c
)
(
)
)
(
)
)
n-Bu
(
(
n-Bu
(
(
i-Pr
8d
)
i
-Pr
7d
)
Reagents and conditions: A) Benzotriazole, DMSO.
B) 30% aq. NaOH, 1.5% equiv Bu4NBr, 1.2 equiv bromoalkane, 3 h, 55 C;
C) 2-bromobenzylbromide, 1,4-dioxane, reflux
t
-BuOK, arylbromide, CuI;
o
Scheme 1. Synthesis of benzimidazolium salts.

S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
63
Br
N
R
N
8a
A/B
N
N
8b
8c
8d
E
E
E
E
N
N
R
R
Method
R
E
B
B
B
n-Bu
S
(10a)
2-Py Se (10b)
R
Ph,
Se (10c)
n-Bu Se (9a)
n-Bu Te (9b)
A/B/C/D n-Bu, Se (10d)
B
i-Pr,
n-Bu, Te (10f)
i-Pr, Te (10g)
Se (10e)
A/B/C
B
Reagents and conditions: (A) n-BuLi, E powder, THF, -78 oC; (B) Na2E2, THF, t-BuOK;
(C) t-BuOK, E powder, THF; (D) Na2Se, THF, t-BuOK.
Scheme 2. Synthesis of benzimidazolin-2-chalcogenones.
selenone was attempted (Scheme 5). The desired benzimidazole 13
was prepared according to the literature method [24]. The addition
of o-bromobenzyl bromide to (1H-benzo[d]imidazol-1-yl)(phenyl)
methanone (13) in 1,4-dioxane unexpectedly, afforded compound
14. The formation of 14 from 13, presumably, takes place via the
hydrolysis of the benzoyl group in 13 with the traces of water [24].
Salt 14 could also be directly synthesized from the reaction of
benzimidazole with two equivalents of 2-bromobenzylbromide.
The reaction of compound 14 with disodium diselenide gave
a white crystalline product, which was characterized as benzimi-
dazolone 15, instead of the expected 1,3-bis(2-bromobenzyl)-1H-
benzo[d]imidazole-2(3H)-selenone. This, probably, results from the
hydrolysis of 14. Similar hydrolysis reactions of carbenes to imi-
dazolones are reported [24]. The substituted benzimidazolones are
crucial precursors to many pharmacologically active compounds
[25].
in good yield. Similarly, the oxidative addition products 16be16d
were isolated in excellent yields by the reaction of selenones
10be10f with iodine. The reaction of iodine with tellurone 10d
afforded a dark red colored compound 16e in excellent yield
(Scheme 6).
Compounds 16ae16e were characterized by 1H, 13C, 77Se and
125Te NMR spectroscopy. As expected, the bromine derivative
shows more downfield shifts in 77Se NMR (
d
393 ppm) spectrum
compared to the iodine derivatives (wd 218 ppm). For the iodo-
derivatives of selenones, variation of the substituents (2-Py, n-Bu,
i-Pr) at the N of the benzimidazole has no effect on the chemical
shift of the 77Se NMR signal. The iodo derivative of the butyl
substituted tellurone shows a large downfield shift in the 125Te
NMR signal (
d
ꢀ130 ppm in 10f to
d 330 ppm in 16e see in Table 1).
2.2. Single crystal X-ray crystallographic studies
Compounds 10ae10g were characterized by 1H NMR spectros-
copy. The 1H NMR signal for the acidic NCHN proton (around
2.2.1. Molecular and crystal structure of compounds 15, 10a, 10d
and 10f
d
11e12 ppm) present in salts 8ae8d was absent in the chalcoge-
none derivatives. The significant shift in the 13C NMR signal of
carbene carbon from the precursor salt ( 143 ppm in 8c) to the
chalcogenone compound ( 167 ppm in 10d) suggested the
The molecular structures of compounds 15, 10a, 10d and 10f are
depicted in Fig. 2 (for molecular structures of compounds 10b, 10e
and 10g see the Supporting information) and selected bond lengths
and bond angles are given in Table 2. In compound 15, the CeO
d
d
deshielding of the carbene carbon. It is further observed that the 13C
NMR signal for 10a was downfield shifted compared with 10d and
10f (see Table 1). This was probably due to the decreasing elec-
tronegativity and increasing size of the chalcogen atoms.
ꢀ
distance (1.226(8) A) is closer to the CeO double bond distance
[26]. Both 2-bromo-benzyl rings are trans to each other with
respect to the core benzimidazole ring. The benzimidazole core of
10a is planar and the sulfur atom is also in the same plane. The CeS
After obtaining the chalcogenones, we next set out to study their
oxidation reactions with halogens. Bromination of selenone 10d
with bromine in THF gave a crystalline yellow-colored product 16a
ꢀ
bond distance (1.674(2) A) is shorter than the single bond
ꢀ
ꢀ
(1.789(1) A) and longer than the double bond distances (1.635 A)
Br
Br
Br
Br
δ+
Na
δ+
Na
δ−
E
N
N
N
t-BuOK
E
+ H2O
- NaOH
H
N
R
N
R
N
R
E = S, Se, Te
R = 2-Py, Ph, n-Bu, i-Pr
Scheme 3. Plausible mechanism for the formation of chalcogenones.

64
S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
Br
Br
A/B/C
NH
A/B/C
N
8a
8b
Te
NH
R
N
R
11a
11b
12a R = 2-Py,
12b R = Ph
Reagents and conditions: (A) n-BuLi, Te powder, THF, -78 oC; (B) Na2Te2,
THF, t-BuOK; (C) t-BuOK, Te powder,THF;
Scheme 4. Attempted synthesis of tellurone with electron withdrawing groups.
[27]. This suggested a partial carbonesulfur double bond character.
The CeSe bond distances in the cases of selenones 10b (1.825(2) A),
one carbene carbon. On considering the two equatorial lone pairs of
selenium, the geometry can be regarded as distorted trigonal
bipyramidal. The geometries around the selenium and tellurium in
compounds 16c and 16e respectively resemble to that observed for
compound 16a. In compound 16a, the benzimidazole ring lies in the
equatorial plane and the Br2eSeeBr3 unit is almost perpendicular
ꢀ
ꢀ
ꢀ
10d (1.831(5) A) and 10e (1.833(2) A) are similar and are compa-
rable with the reported value [13]. The CeTe bond distances for 10f
ꢀ
ꢀ
(2.0772(19) A) and 10g (2.062(4) A) are similar. The
carbonechalcogen bond distances, as expected, gradually increase
from O to Te. The carbene CeN bond length of the compounds 10a,
10b, 10d, 10e, 10f and 10g are similar. Also the bond angles around
the carbene carbon in compound 10a (N2eC1eS 127.75(14)ꢁ,
N1eC1eS 125.93(14)ꢁ and N2eC1eN1106.32(16)ꢁ) are comparable
with compounds 10b, 10d and 10f, while in iso-propyl substituted
compounds 10e and 10g, the angle N1BeC1eN1A (107.30(17)ꢁ) is
slightly higher than the other compounds.
ꢀ
to this plane. The Se1eBr2 (2.4944(3) A) bond length is shorter
ꢀ
than Se1eBr3 (2.6529(3) A). Also the bond angles C14eSe1eBr2
(89.18(5)ꢁ) and C14eSe1eBr3 (86.36(5)ꢁ) are not equal. Ragogna
and co-workers [14] have reported a related molecular structure
ꢀ
with equal SeeBr bond lengths (2.5870(10) A) and bond angles
(87.87(3)ꢁ). The Se1eC14 bond length (1.8967(15) A) and
ꢀ
Br2eSe1eBr3 (175.527(8)ꢁ) also resemble with the values reported
in literature [14]. In compound 16c, bond distances I1eSe
ꢀ
The intermolecular CH/O distance (2.324 A) in compound 15
ꢀ
ꢀ
lead to a chain of molecules formed due to two different types of
intermolecular CH/O bond interactions (Fig. 3a). In the crystal
packing of 10f (Fig. 3b), the molecules are linked by intermolecular
Te/Te* and Te/Br interactions giving rise to a ribbon-like struc-
(2.7040(3) A) and I2eSe (2.8982(3) A) are significantly unequal
ꢁ
ꢀ
with a difference of 0.2 A and the bond angle C1eSeeI1 (91.91(7) )
is much larger than C1eSeeI2 (84.22(7)ꢁ). However, in the crystal
structure reported by Kuhn and co-workers [13], only small
ꢀ
ꢀ
ꢀ
ꢀ
ture. The intermolecular Te/Te* (3.675 A) and Te/Br (3.724 A)
differences (0.1 A) in the bond length of SeeI1 (2.854(1) A) and
ꢁ
ꢀ
distances are higher than the sum of covalent radii of two atoms
SeeI2 (2.768(1) A) and bond angles I1eSeeC1 (87.3(1) ) and
I2eSeeC1 (88.2(1)ꢁ) were observed. In compound 16e, the strong
Te/I intermolecular interaction gives rise to a dimeric structure
placing the two tellurium atoms at the diagonal corners of the
distorted square. The two core benzimidazole rings are planar. The
two bond lengths TeeI1 (2.8330(3) A) and TeeI2 (3.0394(3) A) are
significantly different in compound 16e. Also the bond angle
C1eTeeI1 (88.35(8)ꢁ) is quite larger than C1eTeeI2 (80.59(8)ꢁ).
The dimeric molecule reported by Kuhn et al. [13] has two different
bond lengths of TeeI1 (2.989(1) A) and TeeI2 (2.897(1) A) and the
bond angle C1eTeeI1 (83.6(1)ꢁ) is significantly smaller than the
C1eTeeI2 (89.8(1)ꢁ). The monomeric compound reported in the
literature [13] have two equal bond lengths of TeeI1 (2.9446(7) A)
and TeeI2 (2.9333(6) A) and the similar bond angle C1eTeeI1
ꢀ
ꢀ
(2.94 A and 2.51 A) [28]. These are significantly shorter than the
ꢀ
ꢀ
sum of their van der Waals radii (4.12 A and 4.15 A) [29] respec-
tively. The intermolecular CH/Te distance (2.944 A) in crystal
packing of 10g is higher than the sum of covalent radii (1.7 A), but
shorter than the sum of van der Waals radii (3.15 A). This suggested
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
the existence of intermolecular CH/Te interactions (Fig. 3c).
Steiner was the first to report a similar intermolecular CH/Te
hydrogen bonding interaction [30].
ꢀ
ꢀ
2.2.2. Molecularand crystal structureof compounds 16a,16c and 16e
The molecular structures of chalcogen(IV) compounds, 16a, 16c
and 16e are shown in Fig. 4. In compound 16a, the geometry around
selenium is T-shaped where selenium bonded two bromides and
ꢀ
ꢀ
Br
Br
Br
Br
N
Br
Na2Se2, THF
t-BuOK, rt.
N
N
N
N
N
O
O
1,4-dioxane
reflux
Br
Br
13
15
14
Scheme 5. Attempted synthesis of 1,3-bis(2-bromobenzyl)-1H-benzo[d]imidazole-2(3H)-selenone.

S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
65
Table 1
It is clear from the Table 3 that there is not much effect of the
alkyl/aryl substituents at nitrogen atoms on the CeE bond lengths.
Expectedly, there is significant increase in the CeE bond distances
as we move down the chalcogen group from oxygen to tellurium.
Also it is observed that the two SeeX/TeeX bond distances and two
CeSeeX/CeTeeX bond angles in compounds 16a, 16c and 16e are
significantly different.
13C, 77Se and 125Te NMR chemical shift in ppm.
Compound
77Se/125Te
13C (only NCN)
8a
8b
8c
8d
e
149.1
142.3
143.4
141.9
170.4
168.4
169.1
167.8
167.4
147.5
147.5
150.0
153.1
148.3
151.4
133.4
e
e
e
10a
10b
10c
10d
10e
10f
10g
16a
16b
16c
16d
16e
e
101
95
60
2.3. Computational studies
58
ꢀ130
ꢀ126
293
220
218
219
330
In order to get a better understanding of the bonding mode of
synthesized chalcogenones and the variation in their property with
the change in the chalcogen atoms, density functional calculations
(DFT) were carried out with the Gaussian 03 program [31]. All the
structures were optimized at MPW1PW91 method by using
Lanl2dz(dp) basis set for S, Se, Te, Br and 6-311g(d,p) for the rest of
the atoms. The gas phase optimized geometries obtained on per-
forming DFT calculations were well in conformity with the crystal
structures of the respective compounds. In particular the CeE bond
(E ¼ S, Se, Te) is very much in agreement with the crystal structure
bond lengths. For instance, the CeE bond lengths for 10a, 10d and
10f from the crystal structure are 1.674(2), 1.831(5) and
Br
R
E
X
n-Bu
2-Py
n-Bu
Se Br (16a)
10b
10d
X2, THF
-78 oC (1 h) to
rt. (16-20 h)
Se
Se
Se
Te
I
I
I
I
(16b)
(16c)
(16d)
(16e)
X
E
N
10e
10f
ꢀ
2.0772(19) A respectively and are close to the CeE bond lengths of
i
-Pr
ꢀ
ꢀ
ꢀ
n-Bu
N
R
1.679 A (10a), 1.833 A (10d) and 2.058 A (10f) in the optimized
geometries. In case of dihaloderivatives 16c and 16e the calculated
CeSe and CeTe bond lengths for the optimized structure were
X
ꢀ
Scheme 6. Oxidative addition reactions of chalcogenone compounds.
found to be 1.901 and 2.118 A respectively. These values are also
close to that obtained from the molecular structures of 16c and 16e
ꢀ
(1.902 and 2.128 A for CeSe and CeTe bond lengths respectively).
(84.79(11)ꢁ) and C1eTeeI2 (84.74(11)ꢁ). This molecule showed
very weak intermolecular TeeI interactions.
On analysis of the molecular orbitals (MO’s) of the chalcoge-
nones, it becomes apparent that HOMO’s of these molecules have
significant p-character of chalcogen while the LUMO’s have anti-
The crystal packing of molecule 16a shows two types of
ꢀ
secondary interactions CeH5A/Br3 (2.925(2) A) and Br3/Br1
bonding
responsible for
energy levels while high lying MO’s contribute to the
CeE bond. The frontier orbitals as well as the orbitals that
contribute to the character of CeSe bond of representative
compound 10d are shown in Fig. 6aef. The MO responsible for
character of CeSe bond are the inner MO’s such as HOMO-44 and
p
*
character associated with CeE bond. The MO’s
character of CeE bond are buried deep inside the
character of
ꢀ
(3.618(5) A). In the crystal packing diagram of molecule 16c, two
s
different types of intermolecular secondary interactions
p
ꢀ
ꢀ
CeH17B/I2 (3.062(1) A) and Se/I2* (3.528(2) A) have been
observed. The other two secondary interactions observed in the
s
ꢀ
crystal packing diagram are CH13B/I2 (3.040(9) A) and Te/Te*
s
ꢀ
(4.021(7) A) (Fig. 5aec).
Fig. 2. (a) The molecular structure of compound 15. (b) The molecular structure of compound 10a. (c) The molecular structure of compound 10d. (d) The molecular structure of
compound 10f. Hydrogen atoms are omitted for clarity.

66
S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
Table 2
The model compounds (Fig. 7) were optimized for comparison and
we observed that the negative charge on chalcogen decreases from
S to Te due to gradual decrease in electronegativity from S to Te. In
the case of dihaloderivatives 16c, 16e and the model compound 22,
the NPA charges follow a similar pattern as that of chalcogenones.
The NPA charge on Te, Se and S in 16e, 16c and 22 are 0.455, 0.25
and 0.09 respectively. These high values of NPA charge are in
accordance with the high oxidation state of chalcogens as well as
delocalization of electronic charge to halides in these compounds.
Computation of the total Wiberg bond index on chalcogen
revealed that it is highest for S (1.89e1.92) and lowest for Te
(1.56e1.59). For selenones the values of total Wiberg bond index on
Se were found in the range of 1.76e1.79. Thus CeE bond has more
double bond character for thiones followed by selenones and tel-
lurones. It can be well explained by the proper overlap of similar
energy orbitals of carbon and sulfur atoms. The lowest Wiberg bond
index of tellurium in tellurone is due to the mismatch of the
overlapping carbon and Te orbitals. This also renders CeTe bond
relatively weak as compared to CeS or CeSe bond. Also, it is re-
ported in the literature that the donoreacceptor bonding mode not
Selected bond lengths and bond angles for compounds 10a, 10b, 10de10g, 15, 16a,
16c and 16e.
Bond angles [ꢁ]
ꢀ
Bond lengths [A]
15
O1eC1 1.226(8)
N1eC1 1.376(8)
N1eC1 1.376(2)
N1eC1 1.363(3)
N1eC1 1.364(6)
N1AeC1 1.360(2)
N1eC1 1.360(2)
N1eC1 1.342(5)
Se1eBr2 2.4944(3)
I2eSe 2.8982(3)
O1eC1eN1
127.7(6)
N1eC1eN2
105.5(6)
O1eC1eN2
126.8(6)
N2eC1 1.377(8)
10a
SeC1 1.674(2)
N2eC1eS
127.75(14)
N2eC1eN1
106.32(16)
N1eC1eS
125.93(14)
N2eC1 1.369(2)
10b
SeeC1 1.825(2)
N1eC1eSe
126.51(15)
N1eC1eN2
106.01(19)
N2eC1eSe
127.47(17)
N2eC1 1.383(3)
10d
SeeC1 1.831(5)
N1eC1eSe
126.7(4)
N1eC1eN(2)
106.8(4)
N2eC1eSe
126.5(4)
N2eC1 1.367(6)
only comprises of a
s donation from the carbene, but also signifi-
10e
cant back-bonding from the main group elements [34]. The
p
SeeC1 1.833(2)
N1BeC1eSe
127.42(15)
N1BeC1eN1A
107.30(17)
N1AeC1eSe
125.29(15)
benzimidazolium systems are considered to be more robust in
comparison to the imidazolium as they can provide more stability
by further enhancing conjugation in the system. A comparison of
Wiberg bond index of chalcogen on model imidazolium derivatives
23ae23c reveals that total bond indices of chalcogen is higher for
benzimidazolium systems. As compared to bond indices of 1.89,
1.77 and 1.56 for S, Se and Te in 17ae17c respectively, the corre-
sponding Wiberg bond indices for chalcogens in the imidazolium
systems were 1.81,1.68 and 1.47 respectively, thus pointing towards
stronger CeE bond in benzimidazolium systems.
N1BeC1 1.354(2)
10f
TeeC1 2.0772(19)
N1eC1eTe
127.13(14)
N1eC1eN2
106.71(16)
N2eC1eTe
126.05(13)
N2eC1 1.362(2)
10g
TeeC1 2.062(4)
N1eC1eTe
125.0(3)
N1eC1eN2
107.3(3)
N2eC1eTe
127.7(3)
N2eC1 1.368(5)
16a
3. Conclusions
Se1eC14 1.8967(15)
C14eSe1eBr2
89.18(5)
Br2eSe1eBr3
175.527(8)
C14eSe1eBr3
86.36(5)
In summary, the use of stronger nucleophiles E22ꢀ/E2ꢀ inplace of E,
inthereactionwith benzimidazoliumsalts afforded a highyieldof the
desired benzimidazolin-2-chalcogenones. The plausible mechanism
for the formation of chalcogenone suggested the favorable attack of
E22ꢀ/E2ꢀ nucleophile at the carbene carbon. It is observed that, as the
substitution at nitrogen of benzimidazole varies from electron
donating groups to electron withdrawing groups, the stability of the
chalcogenone compounds decreases. It showed good stability with
electron donating groups. The 13C NMR signal of carbene carbons and
the chalcogens (77Se, 125Te) showed a partial negative charge on the
chalcogen atoms. This is well supported by the DFT calculations. The
DFT calculations also reveal the carbonechalcogen double bond
character and this carbonechalcogen bond in benzimidazolin-2-
chalcogenone system is stronger compared to the simple imidazole-
2-chalcogenone systems. The oxidative addition reactions of chalco-
genone compounds with halogens afforded the halide derivatives
chalcogenones.
Se1eBr3 2.6529(3)
16c
I1eSe 2.7040(3)
C1eSeeI1
91.91(7)
I1eSeeI2
176.109(9)
C1eSeeI2
84.22(7)
SeeC1 1.902(2)
16e
TeeC1 2.128(3)
TeeI1 2.8330(3)
TeeI2* 3.5627(3)
I1eTeeI2
168.938(9)
C1eTeeI2
80.59(8)
C1eTeeI1
88.35(8)
I1eTeeI2*
85.486(7)
TeeI2 3.0394(3)
HOMO-49 while the MO’s such as HOMO-4, HOMO-5 which are
higher in energy are responsible for character of CeSe bond.
p
Natural bond orbital (NBO) analyses [32] on the optimized
geometries of the molecules were performed for the evaluation of
Natural Population Analysis (NPA) charges and Wiberg bond
indices [33] and it revealed some of the expected trends. NPA
results reveal that the net charges on the chalcogen atoms are
negative in chalcogenones whereas it is positive for the carbon
attached to the chalcogen (see Table 4). In case of thiones, the NPA
charge on sulfur atom varies from ꢀ0.318 (19) to ꢀ0.218 (20a)
depending on the substituent attached to the nitrogen of benz-
imidazole ring. Similarly, in cases of selenones and tellurones the
charges on Se and Te are in the range of ꢀ0.212 (10d) to ꢀ0.177
(10c) for Se and ꢀ0.160 (10f) to ꢀ0.129 (20b) for Te respectively. It is
to be noted that þI effect of alkyl groups (Me, Et, i-Pr, n-Bu)
attached to nitrogen leads to a higher negative charge on chalco-
gens when compared with chalcogenones having aryl substituents.
4. Experimental section
4.1. General considerations
All the manipulations were carried out under nitrogen or argon
atmosphere using standard Schlenk techniques unless otherwise
noted. Solvents were purified and dried by standard procedures
and were distilled prior to use. Melting points were recorded on
a Veego VMP-I melting point apparatus in capillary tubes and were
uncorrected. 1H (400 MHz) and 13C (100.56 MHz) nuclear magnetic
resonance spectra were recorded on Varian VXR 400S and Bruker
AV 400 spectrometers at 25 ꢁC. The 77Se (57.22 MHz and 76.3 MHz)

S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
67
Fig. 3. (a) The crystal packing diagram of compound 15 showing two different types of intermolecular hydrogen bonds. (b) The crystal packing diagram of compound 10f showing
the intermolecular Te/Te* and Te/Br interactions. (c) The crystal packing diagram of compound 10g showing the intermolecular hydrogen bond interactions. Hydrogen atoms
(except those are involved in interactions) are omitted for clarity.
and 125Te (94.79 MHz and 157.97 MHz) spectra were recorded on
a Varian VXR 300S and Bruker AV 400 spectrometers. Chemical
shifts are cited with respect to Me4Si as internal standard (1H and
13C) and Me2Se (77Se) and Me2Te (125Te) as external standards.
Elemental analyses were performed on a Carlo Erba Model 1106
elemental analyzer. The ESI mass spectra were recorded on a Q-Tof
micro (YA-105) mass spectrometer.
4.3. General procedure for the synthesis of salts (8ae8d)
A solution of 2-bromobenzylbromide and N-alkylated/arylated
benzimidazole derivative in 1,4-dioxane (40 mL) was refluxed
under nitrogen atmosphere for 16 h. Then the solvent was removed
and the solid residue was washed with THF (10 mL X 2). The white
solid obtained was dried in vacuum.
4.3.1. Synthesis of compound 8a
4.2. Synthesis of compounds 7ae7d
The reagents used are N-pyridyl benzimidazole (0.86 g,
4.40 mmol) and 2-bromobenzylbromide (1.01 g, 4.40 mmol). Yield:
1.61 g (82%). Mp. 199e201 ꢁC (decomposed). 1H NMR (400 MHz,
Precursor salts 7ae7d were synthesized by the reported
procedures and their purity was confirmed by 1H NMR spectros-
copy prior to use [19e21].
CDCl3):
d
(ppm) 12.02 (s, 1H), 8.76 (dd, J ¼ 8.2 Hz, J ¼ 0.8 Hz, 1H),

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S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
4.3.2. Synthesis of compound 8b
The reagents used are N-phenyl benzimidazole (1.01 g, 5.19 mmol)
and 2-bromobenzylbromide (1.29 g, 5.19 mmol). Yield: 0.84 g (37%).
Mp. 202e204 ꢁC. 1H NMR (400 MHz, CDCl3):
(ppm) 11.04 (s,1H), 8.01
d
(d, J ¼ 7.6 Hz, 1H), 7.95e7.92 (m, 1H), 7.85e7.80 (m, 1H), 7.73e7.61 (m,
7H), 7.41 (t, J ¼ 7.2, 1H), 7.30e7.25 (m, 2H), 6.24 (s, 2H). 13C NMR
(100 MHz, CDCl3): d(ppm)142.3(NCHN),133.3,132.7,132.0,131.7,131.2,
131.0, 130.6, 130.5, 128.5, 127.7, 127.6, 124.8, 123.9, 114.1, 113.5, 51.3. ESI-
MS: (m/z) 363 [M ꢀ Br]þ. Anal. Calcd. for C20H16Br2N2 (%): C, 54.08; H,
3.63; N, 6.31. Found: C, 53.68; H, 3.30; N, 6.42.
4.3.3. Synthesis of compound 8c
The reagents used are N-butyl benzimidazole (2.74 g, 15.73 mmol)
and 2-bromobenzylbromide in (3.93 g,15.73 mmol). Yield: 4.73 g (71%).
1H NMR (400 MHz, CDCl3):
d(ppm) 11.54 (s,1H), 7.71e7.56 (m, 6H), 7.39
(t, J ¼ 7.6 Hz, 1H), 7.32e7.25 (m,1H), 6.01 (s, 2H). 4.65 (t, J ¼ 7.6 Hz, 1H),
2.11e2.04 (m, 2H), 1.53e1.44 (m, 2H), 1.01 (t, J ¼ 7.6 Hz, 3H). 13C NMR
(100 MHz, CDCl3): d(ppm) 143.4 (NCHN),133.6,132.0,131.5,131.4,131.2,
128.8, 127.5, 127.4, 123.9, 114.1, 113.4, 51.4, 47.8, 31.4, 19.9, 13.7. ESI-MS:
(m/z) 344 [M ꢀ Br]þ. Anal. Calcd. for C18H20Br2N2 (%): C, 50.97; H,
4.75; N, 6.60. Found: C, 50.62; H, 4.80; N 6.39.
4.3.4. Synthesis of compound 8d
The reagents used are N-iso-propyl benzimidazole (1.50 g,
9.37 mmol) and 2-bromobenzylbromide (2.34 g, 9.37 mmol). Yield:
2.61 g (68%). Mp.169e171 ꢁC. 1H NMR (400 MHz, CDCl3):
d (ppm) 11.38
(s,1H), 7.88e7.85 (m, 1H), 7.67e7.53 (m, 5H), 7.35 (td, J ¼ 7.3, J ¼ 1.2 Hz,
1H), 7.24 (td, J ¼ 7.9, J ¼ 1.8 Hz, 1H), 6.10 (s, 2H), 5.12 (m, 1H), 1.86 (d,
J¼ 6.8 Hz, 6H).13C NMR (100 MHz, CDCl3):
d(ppm) 141.9 (NCHN),133.5,
132.0,131.5,131.3,130.9,130.7,128.6,127.3,127.2,123.7,114.1,113.7, 52.1,
51.1, 22.4. ESI-MS: (m/z) 329 [M ꢀ Br]þ. Anal. Calcd. for C18H20Br2N2 (%):
C, 49.78; H, 4.42; N, 6.83. Found: C, 48.29; H, 4.45; N, 6.24.
4.4. General procedure for the synthesis of chalcogenone
compounds (10ae10g and 12b)
The chalcogenone compounds were synthesized using four
different methods.
Method (A): In a round bottom flask, salt (8c) was taken in dry THF
(40 mL) under nitrogen atmosphere. n-BuLi (at different concentra-
tions 1 eqv/2 eqv/3 eqv) wasadded atꢀ78ꢁCandthereactionmixture
was stirred for 1e2 h. Then elemental powder (Se or Te) was added to
the reaction mixture at room temperature and stirred for 8e10 h. The
reaction mixture was quenched in water (30 mL) and extracted with
dichloromethane, dried over anhydrous sodium sulfate and evapo-
rated. The residue obtained was dissolved in toluene (5 mL) and
petroleum ether (15 mL) to separate the impurity from the solution.
The solution was filtered, evaporated and the residue was recrystal-
lized from slow evaporation of diethyl ether and petroleum ether
(3:1) to afford the product in moderate yield.
Method (B): The salt (8ae8d, 1 eqv) was added into the brown
solution of Na2E2 (E ¼ S, Se, Te: prepared in situ; 1 eqv) [31] in THF
(30 mL) under nitrogen atmosphere and stirred for 6e10 h at room
temperature. Thenpotassium tert-butoxide (1 eqv) was added tothe
above reaction mixture and stirred for further 5e7 h. The reaction
mixture was quenched in water (50 mL) and extracted with diethyl
ether, dried over sodium sulfate and evaporated. The residue was
recrystallized from slow evaporation of diethyl ether and petroleum
ether (3:1) to afford the crystalline product in good yield.
Method (C): In a round bottom flask containing salt (8c, 1 eqv)
was taken in THF (40 mL) under nitrogen atmosphere and chal-
cogen powder (S, Se or Te; 1 eqv) followed by addition potassium
tert-butoxide (1 eqv). The reaction mixture was stirred for 5e6 h at
room temperature. The reaction mixture was quenched in water
(50 mL) and extracted with dichloromethane, dried over sodium
Fig. 4. (a) The molecular structure of compound 16a. (b) The molecular structure of
compound 16c. (c) The molecular structure of compound 16e. Hydrogen atoms are
omitted for clarity.
8.69e8.64 (m, 2H), 8.16e8.11 (m, 1H), 7.87 (dd, J ¼ 8.3, J ¼ 1.5 Hz,
1H), 7.74 (dd, J ¼ 8.5, J ¼ 0.9 Hz, 1H), 7.71e7.61 (m, 3H), 7.55e7.52
(m, 1H), 7.41e7.36 (m, 1H), 7.29e7.25 (m, 1H), 6.23 (s, 2H). 13C
NMR (100 MHz, CDCl3):
d (ppm) 149.1 (NCHN), 148.0, 142.1, 140.7,
133.5, 131.7, 131.6, 131.2, 130.1, 128.7, 128.2, 127.9, 125.0, 123.9, 117.7,
117.5, 113.7, 51.4. ESI-MS: (m/z) 366 [M ꢀ Br]þ. Anal. Calcd. for
C19H15Br2N3 (%): C, 51.26; H, 3.40; N, 9.44. Found: C, 49.84; H,
3.02; N, 9.26.

S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
69
Fig. 5. (a) The crystal packing diagram of compound 16a showing CH5A/Br3 and Br1/Br3 intermolecular interactions. (b) The crystal packing diagram of compound 16c showing
CH17B/I2 and Se/I2* intermolecular interactions. (c) The crystal packing diagram of compound 16e. Hydrogen atoms (except those are involved in interactions) are omitted for clarity.
sulfate and evaporated. The residue obtained was purified as given
in method A to afford the product.
Method (D): The salt 8c (1 eqv) was added into the solution of
Na2Se (prepared in situ; 1 eqv) [31] in THF (30 mL) under nitrogen
atmosphere and stirred for 6e10 h at room temperature. Then
potassium tert-butoxide (1 eqv) was added to the above reaction
mixture and stirred for further 5e7 h. The reaction mixture was
quenched in water (50 mL) and extracted with diethyl ether, dried
over sodium sulfate and evaporated. The residue was recrystallized
from slow evaporation of diethyl ether and petroleum ether (3:1) to
afford the crystalline product in excellent yield.
Table 3
CeE, EeX bond lengths and CeEeX, XeEeX bond angles.
Compound
C]E bond
Distance/angle
The yields reported for the compounds are by method B.
15
C]O
C]S
C]Se
C]Se
C]Se
C]Te
C]Te
CeSe
SeeBr(2)
SeeBr(3)
C14eSeeBr2
C14eSeeBr3
Br2eSeeBr3
CeSe
SeeI1
SeeI2
C1eSeeI1
C1eSeeI2
I1eSeeI2
CeTe
1.226(8)
1.674(2)
1.825(2)
1.831(5)
1.833(2)
2.0772(19)
2.062(4)
1.8967(15)
2.4944(3)
2.6529(3)
89.18(5)
86.36(5)
175.527(8)
1.902(2)
2.7040(3)
2.8982(3)
91.91(7)
84.22(7)
176.109(9)
2.128(3)
10a
10b
10d
10e
10f
10g
16a
4.4.1. Synthesis of compound 10a
The reagents used are salt 8c (0.46 g, 1.08 mmol), Na2S2 (in situ
prepared,1.08 mmol), potassium tert-butoxide (0.12 g,1.08 mmol) in
dry THF (30 mL). Yield: 0.19 g (43%). Mp. 84e86 ꢁC. 1H NMR
(400 MHz, CDCl3):
d
(ppm) 7.61 (dd, J ¼ 7.2 Hz, J ¼ 1.6 Hz,1H), 7.23 (d,
J ¼ 4 Hz, 2H), 7.13 (m, 3H), 7.00 (d, J ¼ 8 Hz, 1H), 6.85 (dd, J ¼ 7.2 Hz,
J ¼ 2.4 Hz, 1H), 5.69 (s, 2H), 4.4 (t, J ¼ 7.6 Hz, 2H), 1.89e1.84 (m, 2H),
1.51e1.45 (m, 2H),1.01 (t, J ¼ 7.6 Hz, 3H). 13C NMR (100 MHz, CDCl3):
d
(ppm) 170.4 (NCN), 134.6, 132.9, 132.2, 131.9, 129.2, 128.0, 127.9,
123.3, 123.2, 122.6, 109.8, 109.3, 48.1, 45.2, 30.1, 20.3, 13.9. ESI-MS:
(m/z) 377 [M]þ, 342 [M ꢀ S]þ. Anal. Calcd. for C18H19BrN2S (%): C,
57.60; H, 5.10; N, 7.46. Found: C, 57.80; H, 4.91; N, 7.76.
16c
16e
4.4.2. Synthesis of compound 10b
Reagents used are salt 8a (0.96 g, 2.17 mmol), Na2Se2 (in situ
prepared, 2.17 mmol), potassium tert-butoxide (0.24 g, 2.17 mmol), in
dry THF. Yield: 0.55g (57%). Mp.142e144 ꢁC.1HNMR(400MHz,CDCl3):
TeeI1
TeeI2
C1eTeeI1
C1eTeeI2
I1eTeeI2
2.8330(3)
3.0394(3)
88.35(8)
80.59(8)
168.938(9)
d
(ppm) 8.73 (td, J ¼ 4.9 J ¼ 0.6 Hz, 1H), 8.16 (d, J ¼ 8 Hz, 1H), 8.01 (dt,
J ¼ 7.7 Hz, J ¼ 1.8 Hz, 1H), 7.64 (dd, J ¼ 8 Hz, J ¼ 1.6 Hz, 1H), 7.50e7.47 (m,
1H), 7.42e7.39 (m, 1H), 7.23e7.11 (m, 5H), 7.01 (dd, J ¼ 7.2 Hz, J ¼ 2.4 Hz,

70
S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
Fig. 6. MO’s of compound 10d. a) HOMO. b) LUMO. c) HOMO-49. d) HOMO-44. e) HOMO-5. f) HOMO-4.
1H), 5.91 (s, 2H),13C NMR (100 MHz, CDCl3):
149.3, 138.3, 134.0, 133.6, 133.1, 129.4, 128.4, 128.0, 124.5, 124.3, 124.2,
d
(ppm) 168.4 (NCN),150.4,
for C20H15BrN2Se (%): C, 54.32; H, 3.42; N, 6.33. Found: C, 54.11; H,
3.29; N, 6.45.
123.9, 122.6, 111.9, 110.3, 50.1. 77Se NMR (57 MHz, CDCl3):
d (ppm) 101.
ESI-MS: (m/z)444[Mꢀ Br]þ. Anal. Calcd. forC19H14BrN3Se (%): C, 51.49;
4.4.4. Synthesis of compound 10d
H, 3.18; N, 9.48. Found: C, 52.60; H, 2.60; N, 9.87.
The reagents used are salt 8c (0.96 g, 2.28 mmol), Na2Se2 (in situ
prepared, 2.28 mmol) and potassium tert-butoxide (0.26 g,
2.28 mmol) in dry THF. Yield: 0.71 g (74%). Mp. 93e95 ꢁC. 1H NMR
4.4.3. Synthesis of compound 10c
Reagents used are salt 8b (0.24 g, 0.54 mmol), Na2Se2 (in situ
prepared, 0.54 mmol) and potassium tert-butoxide (0.06 g,
0.54 mmol) in dry THF. Yield: 0.15 g (63%). Mp. 161e163 ꢁC. 1H NMR
(400 MHz, CDCl3):
d
(ppm) 7.62 (dd, J ¼ 7.2 Hz, J ¼ 1.6 Hz, 1H), 7.32
(d, J ¼ 8 Hz, 1H), 7.27 (dd, J ¼ 12 Hz, J ¼ 0.8 Hz, 2H), 7.19e7.11 (m,
2H), 7.08 (d, J ¼ 8.0 Hz, 1H), 6.86 (dd, J ¼ 6.4 Hz, J ¼ 2.4 Hz, 1H), 5.83
(s, 2H), 4.51 (t, J ¼ 8 Hz, 2H), 1.93e1.89 (m, 2H), 1.57e1.47 (m, 2H),
(400 MHz, CDCl3):
d
(ppm) 7.66e7.57 (m, 6H), 7.23e7.13 (m, 5H),
(ppm)
7.08e7.05 (m, 2H), 5.92 (s, 2H). 13C NMR (100 MHz, CDCl3):
d
1.02 (t, J ¼ 8 Hz, 3H). 13C NMR (100 MHz, CDCl3):
d (ppm) 167.8
169.1 (NCN), 136.7, 134.6, 134.1, 133.0, 132.9, 129.8, 129.5, 129.4,
(NCN), 134.4, 133.3, 133.0, 129.3, 128.3, 127.9, 123.7, 123.6, 122.6,
128.4, 128.3, 128.0, 124.2, 124.1, 122.6, 110.6, 110.3, 50.2. 77Se NMR
110.4, 109.8, 50.0, 47.0, 30.3, 20.3, 13.9. 77Se NMR (57 MHz, CDCl3):
(57 MHz, CDCl3):
d
(ppm) 95. ESI-MS: (m/z) 443 [M]þ. Anal. Calcd.
d
(ppm) 60. ESI-MS: (m/z) 422 [M]þ, 342 [M ꢀ Br]þ. Anal. Calcd. for

S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
71
C18H19BrN2Se (%): C, 51.20; H, 4.54; N, 6.63. Found: C, 51.98; H, 4.59;
N, 6.82.
afforded a white precipitate. The precipitate was collected, washed
with THF and characterized as 14. Yield: 1.20 g (50%). The
compound 14 was also synthesized in a direct reaction between
two equivalent of 1-bromo-2-(bromomethyl)benzene and benz-
imidazole. Mp. 191 ꢁC (decomposed). 1H NMR (400 MHz, CDCl3):
4.4.5. Synthesis of compound 10e
The reagents used are salt 8d (0.58 g, 1.43 mmol), Na2Se2 (in situ
prepared, 1.43 mmol) and potassium tert-butoxide (0.16 g,
1.43 mmol) in THF. Yield: 462 g (79%). Mp. 178e180 ꢁC. 1H NMR
d
(ppm) 11.29 (s, 1H), 7.70 (dd, J ¼ 7.6 Hz, J ¼ 1.6 Hz, 2H), 7.64e7.59
(m, 4H), 7.51 (dd, J ¼ 6.4 Hz, J ¼ 3.2 Hz, 2H), 7.36 (td, J ¼ 7.6 Hz,
(400 MHz, CDCl3):
d
(ppm) 7.61 (dd, J ¼ 8 Hz, J ¼ 1.6 Hz, 1H), 7.55 (d,
J ¼ 1.2 Hz, 2H), 7.24 (td, J ¼ 8 Hz, J ¼ 1.6 Hz, 2H), 6.01 (s, 4H). 13C
J ¼ 8 Hz, 1H), 7.25e7.08 (m, 5H), 6.84 (dd, J ¼ 7.2 Hz, J ¼ 2.4 Hz, 1H),
NMR (100 MHz, CDCl3): d (ppm) 144.5 (NCN), 133.6, 131.8, 131.6,
5.96e5.91 (m, 1H), 5.84 (s, 2H), 1.67 (d, J ¼ 6.8 Hz, 6H). 13C NMR
131.4, 131.2, 128.8, 127.4, 123.9, 113.9, 51.6. ESI-MS: (m/z) 456
[M ꢀ Br]þ. Anal. Calcd. for C21H17Br3N2 (%): C, 46.96; H, 3.19; N, 5.22.
Found: C, 47.47; H, 2.88; N, 5.74.
(100 MHz, CDCl3):
d (ppm) 167.4 (NCN), 134.4, 133.6, 133.0, 131.6,
129.3, 128.2, 128.0, 123.4, 123.2, 122.6, 111.4, 110.6, 52.3, 50.4, 20.3.
77Se NMR (57 MHz, CDCl3): (ppm) 58. ESI-MS: (m/z) 408 [M]þ.
d
Anal. Calcd. for C17H17BrN2Se (%): C, 50.02; H, 4.20; N, 6.86. Found:
C, 49.91; H, 3.89; N, 7.28.
4.6. Synthesis of compound 15
Compound 14 (0.51 g, 1.1 mmol) was added to a brown solution
of Na2Se2 (in situ prepared, 1.1 mmol) in THF (25 mL) at room
temperature under nitrogen atmosphere and the reaction mixture
was stirred for 7 h. Then potassium tert-butoxide (0.12 g, 1.1 mmol)
was added to the above reaction mixture and stirred further 5 h.
The reaction mixture was quenched with water (50 mL), extracted
with dichloromethane and dried over anhydrous Na2SO4. The
solvent was evaporated to give a semi-solid, which was dissolved in
toluene and small amount of petroleum ether was added. The
solution was evaporated to afford the solid. Recrystallization of the
solid from diethyl ether and petroleum ether (4:1) afforded pure
crystalline product of 15 instead of the desired compound 1,3-
bis(2-bromobenzyl)-1H-benzo[d]imidazole-2(3H)-selenone.
Yield: 0.19 g (43%). Mp. 137e139 ꢁC. 1H NMR (400 MHz, CDCl3):
4.4.6. Synthesis of compound 10f
The reagents used are salt 8c (0.48 g, 1.13 mmol), Na2Te2 (in situ
prepared, 1.13 mmol) and potassium tert-butoxide (0.13 g,
1.13 mmol) in THF. Yield: 0.33 g (62%). Mp. 130e132 ꢁC. 1H NMR
(400 MHz, CDCl3):
d
(ppm) 7.64e7.60 (m, 1H), 7.41 (d, J ¼ 8 Hz, 1H),
7.29e7.25 (m, 1H), 7.20e7.11 (m, 4H), 6.81 (dd, J ¼ 5.6 Hz, J ¼ 3.6 Hz,
1H), 5.91 (s, 1H), 4.57 (t, J ¼ 8 Hz, 2H), 1.97e1.89 (m, 2H), 1.55e1.50
(m, 2H), 1.04 (t, J ¼ 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3):
d (ppm)
147.5 (NCN), 134.4, 134.1,133.1,129.4,128.5,128.0, 124.1,122.6, 111.2,
110.6, 53.4, 50.4, 30.8, 20.3, 14.0. 125Te NMR (95 MHz, CDCl3):
d
(ppm) ꢀ130. ESI-MS: (m/z) 393 [M ꢀ Br]þ, 343 [M ꢀ Te]þ. Anal.
Calcd. for C18H19BrN2Te (%): C, 45.91; H, 4.07; N, 5.95. Found: C,
46.25; H, 3.89; N, 6.16.
d
(ppm) 7.60 (dd, J ¼ 8 Hz, J ¼ 1.2 Hz, 2H), 7.22 (dt, J ¼ 7.2 Hz,
4.4.7. Synthesis of compound 10g
J ¼ 0.8 Hz, 2H), 7.14 (dt, J ¼ 7.6 Hz, J ¼ 1.6 Hz, 2H), 7.07 (d, J ¼ 7.6 Hz,
2H), 7.01 (dd, J ¼ 5.6 Hz, J ¼ 3.2 Hz, 2H), 6.88 (dd, J ¼ 5.6 Hz,
The reagents used are salt 8d (0.26 g, 0.65 mmol), Na2Te2 (in situ
prepared, 0.65 mmol) and potassium tert-butoxide (0.07 g,
0.65 mmol) in THF. Yield: 0.17 g (59%). Mp. 185 ꢁC (decomposed). 1H
J ¼ 3.2 Hz, 2H), 5.25 (s, 4H). 13C NMR (100 MHz, CDCl3):
d (ppm)
154.9 (NCN), 135.6, 133.2, 129.7, 129.5, 128.8, 127.9, 123.0, 121.9,
108.7, 45.3. ESI-MS: (m/z) 473 [M]þ, 457 [M ꢀ O]þ. Anal. Calcd. for
C21H16Br2N2O (%): C, 53.42; H, 3.42; N, 5.93. Found: C, 53.19; H,
3.00; N, 6.48.
NMR (400 MHz, CDCl3):
d (ppm) 7.67e7.61 (m, 2H), 7.27e7.12 (m,
5H), 6.82e6.79 (m, 1H), 5.94 (s, 2H), 5.98e5.89 (m, 1H), 1.70 (d,
J ¼ 7.2 Hz, 6H). 13C NMR (100 MHz, CDCl3):
d (ppm) 147.5 (NCN),
134.9, 134.0, 133.0, 132.4, 129.4, 128.4, 127.9, 123.9, 123.5, 122.5,
111.9, 111.5, 56.8, 53.9, 20.3. 125Te NMR (95 MHz, CDCl3):
4.7. General procedure for the synthesis of compounds 16ae16e
d
(ppm) ꢀ126. ESI-MS: (m/z) 457 [M]þ, 379 [M ꢀ Br]þ, 328
[M ꢀ Te]þ. Anal. Calcd. for C17H17BrN2Te (%): C, 44.69; H, 3.75; N,
In a round bottomed flask containing the solution of selenone or
tellurone (10b or 10de10f; 1 eqv) in THF (40 mL), halogen (Br2, I2;
1 eqv) in dry THF (15 mL) was added dropwise at ꢀ78 ꢁC under
nitrogen atmosphere. The reaction mixture was stirred for 16e20 h
at room temperature. The solvent was evaporated to one third of
original volume and n-pentane (15e20 mL) was added and kept in
fridge at ꢀ23 ꢁC for overnight to afford the crystalline product.
6.13. Found: C, 44.81; H, 3.58; N, 6.05.
4.4.8. Synthesis of compound 12b
The reagents used are salt 8b (0.34 g, 0.76 mmol), Na2Te2 (in situ
prepared, 0.76 mmol) and potassium tert-butoxide (0.08 g,
0.76 mmol) in THF. The reaction, after work up led to the formation
of hydrolyzed diamine product 12b, instead of the desired tellurone
11b. Yield: 0.05 g (19%). 1H NMR (400 MHz, CDCl3):
d
(ppm) 8.15 (m,
4.7.1. Synthesis of compound 16a
1H), 7.54 (dd, J ¼ 7.6 Hz, J ¼ 1.2 Hz, 1H), 7.43 (m, 1H), 7.32 (m, 1H),
7.23 (m, 2H), 7.11 (m, 2H), 6.71 (m, 2H), 6.61 (dd, J ¼ 8 Hz, J ¼ 1.2 Hz,
1H), 6.40 (m, 1H), 6.15 (s, 1H), 4.83 (d, J ¼ 5.6 Hz, 1H), 4.41 (d,
J ¼ 6 Hz, 2H).
The reagents used are bromine (0.11 g, 0.71 mmol) and 10d
(0.30 g, 0.71 mmol). Yield: 0.37 g (89%). Mp. 210e212 ꢁC (decom-
posed). 1H NMR (400 MHz, CDCl3):
d
(ppm) 7.68 (dd, J ¼ 6.7 Hz,
J ¼ 1.2 Hz, 2H), 7.59 (t, J ¼ 7.9 Hz, 1H), 7.48 (t, J ¼ 8.4 Hz, 1H), 7.40
(dd, J ¼ 7.3 Hz, J ¼ 2.4 Hz 1H), 7.34 (d, J ¼ 8.2 Hz 1H), 7.26e7.20 (m,
2H), 6.09 (s, 2H), 4.78 (t, J ¼ 7.9 Hz 2H), 2.25e2.17 (m, 2H),1.62e1.57
4.5. Synthesis of compound 14
(m, 2H), 1.09 (t, J ¼ 7.6 Hz 3H). 13C NMR (100 MHz, CDCl3):
d (ppm)
The synthesis of compound 13 was attempted by treating (1H-
benzo[d]imidazol-1-yl)(phenyl)methanone (1.00 g, 4.50 mmol)
with 1-bromo-2-(bromomethyl)benzene (1.13 g, 4.50 mmol) in 1,4-
dioxane (30 mL) under nitrogen atmosphere. The reaction mixture
was refluxed with stirring for 24 h, no formation of 1-benzoyl-3-(2-
bromobenzyl)-1H-benzo[d]imidazol-3-ium bromide was observed.
Thereafter, additional 1-bromo-2-(bromomethyl)benzene (1.13 g,
4.50 mmol) was added to the reaction mixture and continued
reflux for 12 h. The reaction mixture when kept aside for 15 days,
150.0 (NCN), 133.3, 132.3, 131.9, 130.5, 130.3, 128.6, 127.5, 127.4,
122.9, 114.2, 113.2, 52.8, 49.7, 30.7, 20.5, 13.9. 77Se NMR (57 MHz,
CDCl3):
d
(ppm) 293. ESI-MS: (m/z) 571 [M
ꢀ
CH3]þ, 448
[M ꢀ C4H9Br]þ, 423 [M ꢀ Br2]þ. Anal. Calcd. for C18H19Br3N2Se (%):
C, 37.14; H, 3.29; N, 4.81. Found: C, 36.76; H, 2.94; N, 4.73.
4.7.2. Synthesis of compound 16b
The reagents used are 10b (0.08 g, 0.18 mmol) and iodine (0.05 g,
0.18 mmol). Yield: 0.11 g (87%). Mp. 150e152 ꢁC (decomposed). 1H

72
S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
217. MS: m/z 423 [M ꢀ I2]þ, 343 [M ꢀ SeI2]þ, 345 [(Mþ2) ꢀ SeI2]þ.
Anal. Calcd. for C18H19BrI2N2Se (%): C, 31.98; H, 2.83; N, 4.14. Found:
C, 32.52; H, 2.59; N, 4.45.
Table 4
Charge and Wiberg bond index of chalcogenone compounds.
Compound
Charge on C atom
Charge on
chalcogen atom
Total Wiberg
bond index on E
17a
17b
17c
18a
18b
18c
19
10e
10g
10a
10d
10f
20a
10c
20b
21a
10b
21b
22
0.247
0.198
0.129
0.248
0.199
0.129
0.295
0.205
0.137
0.249
0.202
0.133
0.250
0.196
0.138
0.250
ꢀ0.244
ꢀ0.204
ꢀ0.149
ꢀ0.248
ꢀ0.208
ꢀ0.154
ꢀ0.318
ꢀ0.211
ꢀ0.156
ꢀ0.248
ꢀ0.212
ꢀ0.160
ꢀ0.218
ꢀ0.177
ꢀ0.129
ꢀ0.222
ꢀ0.187
ꢀ0.133
0.210
1.8921
1.768
1.564
1.888
1.763
1.560
1.886
1.764
1.561
1.887
1.762
1.559
1.919
1.794
1.582
1.918
1.790
1.585
4.7.4. Synthesis of compound 16d
The reagents used are 10e (0.10 g, 0.25 mmol) and iodine (0.06 g,
0.25 mmol). Yield: 0.11 g (70%). 1H NMR (400 MHz, DMSO-d6):
d
(ppm) 7.81 (d, J ¼ 8.1 Hz, 1H), 7.72e7.60 (m, 2H), 7.57e7.50 (m,
2H), 7.32e7.17 (m, 2H), 6.64 (d, J ¼ 7.0 Hz, 1H), 5.83 (s, 2H),
5.57e5.50 (m, 1H), 1.71 (d, J ¼ 7.0 Hz, 6H). 13C NMR (100 MHz,
DMSO-d6):
d (ppm) 151.4 (NCN), 133.2, 132.7, 130.5, 129.9, 128.2,
127.8, 126.8, 126.1, 125.9, 121.8, 114.1, 112.9, 54.4, 51.2, 19.8. 77Se
NMR (76.3 MHz, DMSO-d6):
d (ppm) 214. ESI-MS: (m/z) 408
[M ꢀ I2]þ, 328 [M ꢀ SeI2]þ, 331 [M ꢀ SeI2]þ.
4.7.5. Synthesis of compound 16e
The reagents used are 10f (0.10 g, 0.21 mmol) and iodine (0.05 g,
0.21 mmol). Yield: 0.14 g (91%). Mp. 224e226 ꢁC (decomposed). 1H
0.203
0.133
0.164
NMR (400 MHz, CDCl3):
d
(ppm) 7.69 (d, J ¼ 7.2 Hz, 2H), 7.57 (t,
J ¼ 8 Hz, 1H), 7.46 (t, J ¼ 8 Hz, 1H), 7.35 (d, J ¼ 8 Hz, 1H), 7.31e7.22
(m, 3H), 6.08 (s, 2H), 4.80 (t, J ¼ 8 Hz, 2H), 2.25e2.19 (m, 2H),
1.65e1.58 (m, 2H),1.11 (t, J ¼ 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3):
I1 ꢀ0.419, ꢀ0.395
16c
16e
0.275
0.250
0.455
2.159
2.077
I1 ꢀ0.400, ꢀ0.363
0.195
d
(ppm) 133.4, 132.8, 132.4, 132.3, 131.7, 130.7, 130.5, 128.6, 127.4,
127.3, 122.8, 114.2, 113.4, 56.3, 52.8, 31.1, 20.6, 13.9. 125Te NMR
I1 ꢀ0.454, ꢀ0.428
23a
23b
23c
0.100
ꢀ0.216
ꢀ0.344
ꢀ0.378
1.81
1.68
1.47
(126.2 MHz, CDCl3):
d
(ppm) 330. ESI-MS: (m/z) 598 [M ꢀ I]þ, 392
0.136
0.120
[M ꢀ BrI2]þ, 343 [M ꢀ TeI2]þ. Anal. Calcd. for C18H19BrI2N2Te (%): C,
29.83; H, 2.64; N, 3.87. Found: C, 30.20; H, 2.26; N, 4.12.
NMR (400 MHz, CDCl3):
d
(ppm) 8.79 (d, J ¼ 4.4 Hz, 1H), 8.16e8.14
5. Single crystal X-ray crystallographic data
(m, 2H), 7.68 (dd, J ¼ 6.9 Hz, J ¼ 1.4 Hz, 1H), 7.65e7.62 (m, 1H),
7.56e7.53 (dd, J ¼ 7.0 Hz, J ¼ 1.3 Hz, 1H), 7.49e7.42 (m, 2H),
7.35e7.32 (dd, J ¼ 7.3 Hz, J ¼ 2.5 Hz, 1H), 7.27e7.22 (m, 2H),
7.08e7.05 (dd, J ¼ 7.3 Hz, J ¼ 2.6 Hz, 1H), 5.99 (s, 2H). 13C NMR
The single crystal X-ray diffraction measurements were per-
formed on an Oxford Diffraction Gemini diffractometer. The data
were corrected for Lorentz, polarization, and absorption effects. The
structures were determined by routine heavy-atom methods using
SHELXS 97 [35] and Fourier methods and refined by full-matrix
least squares with the non-hydrogen atoms anisotropic and
hydrogen with fixed isotropic thermal parameters of 0.07 A using
the SHELXL 97 [36] program. The hydrogens were partially located
from difference electron density maps, and the rest were fixed at
predetermined positions. Scattering factors were from common
sources [37]. Details of the X-ray data collection parameters are
given in Tables 5 and 6.
(100 MHz, CDCl3):
d (ppm) 153.1 (NCN), 149.9, 148.4, 139.5, 133.5,
132.6, 132.2, 130.3, 128.9, 128.4, 126.9, 125.7, 123.6, 126.9, 125.7,
123.6, 122.8, 113.8, 112.5, 52.2. 77Se NMR (57 MHz, CDCl3):
d (ppm)
219. ESI-MS: (m/z) 570 [M ꢀ I]þ, 444 [M ꢀ I2]þ, 364 [M ꢀ SeI2]þ.
Anal. Calcd. for C19H14BrI2N3Se (%): C, 32.74; H, 2.02; N, 6.03. Found:
C, 32.86; H, 1.55; N, 7.06.
2
ꢀ
4.7.3. Synthesis of compound 16c
The reagents used are iodine (0.03 g, 0.12 mmol) and 10d (0.05 g,
0.12 mmol). Yield: 0.07 g (87%). Mp. 170e172 ꢁC (decomposed). 1H
The solvents for growing the crystals are listed below.
NMR (400 MHz, CDCl3):
d
(ppm) 7.67 (dd, J ¼ 7.1 Hz, J ¼ 1.6 Hz, 1H),
Compound 10a: diethyl ether and petroleum ether (4:1) slow
evaporation, 10b: dichloromethane and petroleum ether (2:1) slow
evaporation, 10d: diethyl ether and petroleum ether (4:1) slow
evaporation, 10e: diethyl ether and petroleum ether (4:1) slow
evaporation, 10f: diethyl ether and petroleum ether (5:1), 10g:
diethyl ether and petroleum ether (5:1), 12a: diethyl ether and
petroleum ether (3:1) slow evaporation, 15: chloroform-d, 16a:
7.60 (d, J ¼ 8.0 Hz, 1H), 7.52 (t, J ¼ 7.4 Hz, 1H), 7.42 (t, J ¼ 7.3 Hz, 1H),
7.29 (d, J ¼ 8.2 Hz, 1H), 7.25e7.20 (m, 2H), 7.04 (d, J ¼ 5.6 Hz, 1H),
5.90 (s, 2H), 4.63 (t, J ¼ 8 Hz, 2H), 2.11e2.03 (m, 2H), 1.60e1.49
(m, 2H), 1.07 (t, J ¼ 7.2 Hz, 3H). 13C NMR (100 MHz, CDCl3):
d
(ppm) 148.3 (NCN), 132.9, 132.5, 129.7, 127.6, 125.6, 121.8, 112.1,
109.4, 50.6, 47.4, 30.0,19.4,13.5. 77Se NMR (57 MHz, CDCl3):
d (ppm)
17a R = Me, E = S
17b R = Me, E = Se
17c R = Me, E = Te
18a R = Et, E = S
18b R = Et, E = Se
18c R = Et, E = Te
19 R = iPr, E = S
20a R = Ph E = S
20b R = Ph, E = Te
21a R = Py, E = S
21b R = Py, E = Te
Br
Br
N
Br
N
I
N
N
S
E
E
N
R
N
R
I
23a R = Me, E = S
23b R = Me, E = Se
23c R = Me, E = Te
22
Fig. 7. Optimized model compounds.

S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
73
Table 5
Details of the X-ray data collection parameters.
Compound
10a
10b
10d
10e
10f
Formula
Mr
C18H19BrN2S
375.32
C19H14BrN3Se
443.20
C18H19BrN2Se
422.22
C17H17 25
410.45
.
BrN2 O0.13 Se
C18H19BrN2Te
470.86
System
Space group
Monoclinic
P21/n
10.0157(5)
16.2939(9)
11.1665(6)
90
114.245(6)
90
1661.57(16)
4
Monoclinic
P21/n
13.0639(6)
9.7597(4)
14.0421(5)
90
109.427(5)
90
1688.43(12)
4
Monoclinic
P 21/n
11.2184(7)
10.1733(6)
16.2720(9)
90
109.599(6)
90
1749.50(18)
4
Monoclinic
C2/c
19.9209(18)
9.6353(6)
18.3953(16)
90
110.262(10)
90
3312.4(5)
8
Triclinic
P-1
ꢀ
a[A]
8.943(2)
10.518(2)
10.978(2)
118.43(2)
94.420(17)
97.033(18)
890.4(3)
2
ꢀ
b[A]
ꢀ
c[A]
a
[ꢁ]
[ꢁ]
b
g
[ꢁ]
3
ꢀ
V[A ]
Z
Crystal size [mm3]
0.51 ꢂ 0.38 ꢂ 0.32
0.44 ꢂ 0.38 ꢂ 0.29
0.51 ꢂ 0.35 ꢂ 0.30
0.47 ꢂ 0.41 ꢂ 0.32
0.49 ꢂ 0.34 ꢂ 0.29
rcalcd [Mg/m3]
1.500
1.744
1.603
1.646
1.756
m
[mmꢀ1
]
2.598
4.595
4.428
4.676
3.912
Refls. collected
Observed reflns [I > 2
R1 observed reflns
wR2, all
12,894
5475
0.0719
0.0648
13,522
5428
0.0880
0.0780
12,537
5257
0.1549
0.1855
13,719
5407
0.1080
0.0597
14,536
5891
0.0494
0.0509
s
(I)]
Table 6
Details of the X-ray data collection parameters.
Compound
10g
15
16a
16c
16e
Formula
Mr
C
17H17BrN2Te
C21H16Br2N2O
472.18
Triclinic
P-1
7.5360(5)
9.3672(10)
13.6128(10)
98.940(7)
105.933(6)
96.726(7)
899.80(13)
2
C18H19Br3N2Se
582.04
Triclinic
P-1
8.3025(6)
10.9155(8)
11.1023(8)
84.187(4)
79.706(4)
89.314(4)
984.85(12)
2
C18H19BrI2N2Se
676.02
Monoclinic
P21/n
12.2722(2)
11.8520(2)
14.5483(2)
90
95.6851(15)
90
C18H19BrI2N2Te
724.66
Monoclinic
P21/n
12.3800(3)
11.9892(3)
14.5863(4)
90
95.313(2)
90
456.84
Monoclinic
C2/c
21.162(6)
9.556(8)
18.413(6)
90
112.18(4)
90
3448(3)
8
System
Space group
ꢀ
a[A]
ꢀ
b[A]
ꢀ
c[A]
a
[ꢁ]
[ꢁ]
b
g
[ꢁ]
3
ꢀ
V[A ]
2105.64(6)
4
2155.69(10)
4
Z
Size [mm3]
rcalcd [Mg/m3]
0.47 ꢂ 0.38 ꢂ 0.31
0.55 ꢂ 0.21 ꢂ 0.15
0.42 ꢂ 0.33 ꢂ 0.27
0.53 ꢂ 0.47 ꢂ 0.36
0.53 ꢂ 0.42 ꢂ 0.37
1.760
1.743
1.963
2.132
2.233
m
[mmꢀ1
]
4.038
4.517
7.995
6.616
6.101
Refls. collected
Observed reflns [I > 2
R1 observed reflns
wR2, all
17,305
6882
0.1327
0.1691
8601
8604
0.1391
0.2416
30,208
8351
0.0437
0.0601
32,446
8595
0.0625
0.0560
17,583
7203
0.0414
0.0550
s
(I)]
chloroform and diethyl ether (3:1), 16c: THF and n-pentane (2:3)
at ꢀ23 ꢁC, 16e: chloroform-d slow evaporation.
References
[1] W.A. Herrmann, Angew. Chem. Int. Ed. 41 (2002) 1290.
[2] J.C.Y. Lin, R.T.W. Huang, C.S. Lee, A. Bhattacharyya, W.S. Hwang, I.J.B. Lin,
Chem. Rev. 109 (2009) 3561;
Acknowledgment
I.J.B. Lin, C.S. Vasam, Coord. Chem. Rev. 251 (2007) 642;
D. Martin, M. Melaimi, M. Soleilhavoup, G. Bertrand, Organometallics 30
(2011) 5304;
H.B.S. gratefully acknowledges the Department of Science and
Technology, NewDelhi, fortheRamannaFellowship. S.T.M. isthankful
to CSIR, New Delhi for SRF and SAIF, IITB for spectral data analysis.
D. Bourissou, O. Guerret, F.P. Gabbaï, G. Bertrand, Chem. Rev. 100 (2000) 39.
[3] G.C. Vougioukalakis, R.H. Grubbs, Chem. Rev. 110 (2010) 1746.
[4] K.M. Hindi, M.J. Panzner, C.A. Tessier, C.L. Cannon, W.J. Youngs, Chem. Rev. 109
(2009) 3859.
[5] O. Kose, S. Saito, Org. Biomol. Chem. 8 (2010) 896;
J. Monot, M.M. Brahmi, S.-H. Ueng, C. Robert, M.D.-E. Murr, D.P. Curran,
M. Malacria, L. Fensterbank, E. Lacôte, Org. Lett. 11 (2009) 4914;
N. Marion, S.P. Nolan, Acc. Chem. Res. 41 (2008) 1440;
V.P.W. Böhm, C.W.K. Gstöttmayr, T. Weskamp, W.A. Herrmann, J. Organomet.
Chem. 595 (2000) 186;
W. Huang, J. Guo, Y. Xiao, M. Zhu, G. Zou, J. Tang, Tetrahedron 61 (2005) 9783.
[6] C. Samoj1owicz, M. Bieniek, K. Grela, Chem. Rev. 109 (2009) 3708;
C.W. Bielawski, R.H. Grubbs, Angew. Chem. Int. Ed. 39 (2000) 2903;
T. Weskamp, W.C. Schattenmann, M. Spiegler, W.A. Herrmann, Angew. Chem.
Int. Ed. 37 (1998) 2490.
Appendix A. Supplementary material
CCDC 878413, 878414, 878415, 878416, 878417, 878418, 759105,
878419, 878420 and 878421 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
[7] Q. Xu, X. Gu, S. Liu, Q. Dou, M. Shi, J. Org. Chem. 72 (2007) 2240;
L.-J. Liu, F. Wang, M. Shi, Organometallics 28 (2009) 4416;
S. Díez-González, H. Kaur, F.K. Zinn, E.D. Stevens, S.P. Nolan, J. Org. Chem. 70
(2005) 4784.
Appendix B. Supplementary material
[8] M.R. Buchmeiser, Chem. Rev. 109 (2009) 303.
Supplementary Information associated with this article can be
found, in the online version, at http://dx.doi.org/10.1016/j.
jorganchem.2012.07.025.
[9] Y. Wang, G.H. Robinson, Inorg. Chem. 50 (2011) 12326;
M. Asay, C. Jones, M. Driess, Chem. Rev. 111 (2011) 354;
N. Kuhn, A. Al-Sheikh, Coord. Chem. Rev. 249 (2005) 829;

74
S.T. Manjare et al. / Journal of Organometallic Chemistry 717 (2012) 61e74
C.J. Carmalt, A.H. Cowley, Adv. Inorg. Chem. 50 (2000) 1;
A.J. Arduengo III, C.J. Carmalt, J.A.C. Clyburne, A.H. Cowley, R. Pyatib, Chem.
Commun. (1997) 981.
[21] F.E. Hahn, M.C. Jahnke, T. Pape, Organometallics 26 (2007) 150.
[22] T. Takata, D. Saeki, Y. Makita, N. Yamada, N. Kihara, Inorg. Chem. 42 (2003)
3712;
[10] G.B. Ansell, D.M. Forkey, D.W. Moore, J. Chem. Soc. Chem. Commun. (1970) 56.
[11] B.L. Benac, E.M. Burgess, A.J. Arduengo III, Org. Synth. 64 (1986) 92.
[12] A.J. Arduengo III, F. Davidson, H.V.R. Dias, J.R. Goerlich, D. Khasnis,
W.J. Marshall, T.K. Prakasha, J. Am. Chem. Soc. 119 (1997) 12742.
[13] A. Abu-Rayyan, C. Piludu, M. Steimann, N. Kuhn, Heteroatom Chem. 16 (2005)
316;
D.P. Thompson, P. Boudjouk, J. Org. Chem. 53 (1988) 2109.
[23] S.T. Manjare, H.B. Singh, R.J. Butcher, Acta Crystallogr. E65 (2009) o2640.
[24] T.H. File, R. Natarajan, M.H. Werner, J. Org. Chem. 52 (1987) 740.
[25] R.L. Clark, A.A. Pessolano, J. Am. Chem. Soc. 80 (1958) 1657.
[26] B.V.R. Murthy, Z. Kristallogr. 113 (1960) 445.
[27] J.G. Garcia, S.N. Haydar, A.P. Krapcho, F.R. Fronczek, Acta Crystallogr. C51
(1995) 2333.
[28] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, Wiley, 1962, 93;
F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, Wiley, 1962, 104.
[29] A. Bondi, J. Phys. Chem. 68 (1964) 441.
K. Eichele, M. Walker, N. Kuhn, Z. Anorg. Allg. Chem. 628 (2002) 2026;
R. Fawzi, T. Kratz, M. Steimann, N. Kuhn, Phosphorus, Sulphur, Silicon Relat.
Elem. 108 (1996) 107;
R. Fawzi, T. Kratz, M. Steimann, N. Kuhn, Phosphorus, Sulphur, Silicon Relat.
Elem. 112 (1996) 225;
[30] T. Steiner, J. Mol. Struct. 447 (1998) 39.
N. Kuhn, T. Kratz, G. Henkel, Z. Naturforsch. 51b (1996) 295;
T. Kratz, G. Henkel, N. Kuhn, Chem. Ber. 127 (1994) 849;
G. Henkel, T. Kratz, N. Kuhn, Chem. Ber. 126 (1993) 2047;
T. Kratz, G. Henkel, N. Kuhn, Z. Naturforsch. 48b (1993) 973.
[14] J.L. Dutton, P.J. Ragogna, Inorg. Chem. 48 (2009) 1722;
J.L. Dutton, R. Tabeshi, M.C. Jennings, A.J. Lough, P.J. Ragogna, Inorg. Chem. 46
(2007) 8594;
J.L. Dutton, H.M. Tuononen, M.C. Jennings, P.J. Ragogna, J. Am. Chem. Soc. 128
(2006) 12624.
[15] F. Bigoli, A.M. Pellinghelli, P. Deplano, F.A. Devillanova, V. Lippolis,
M.L. Mercuri, E.F. Trogu, Gazz. Chim. Ital. 124 (1994) 445.
[16] F. Cristiani, F.A. Devillanova, A. Diaz, G. Verani, Phosphorus, Sulphur, Silicon
Relat. Elem. 20 (1984) 231;
[31] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, J.A. Montgomery Jr., T. Vreven, K.N. Kudin, J.C. Burant,
J.M. Millam, S.S. Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi,
G. Scalmani, N. Rega, G.A. Petersson, H. Nakatsuji, M. Hada, M. Ehara,
K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao,
H. Nakai, M. Klene, X. Li, J.E. Knox, H.P. Hratchian, J.B. Cross, V. Bakken,
C. Adamo, J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin,
R. Cammi, C. Pomelli, J.W. Ochterski, P.Y. Ayala, K. Morokuma, G.A. Voth,
P. Salvador, J.J. Dannenberg, V.G. Zakrzewski, S. Dapprich, A.D. Daniels,
M.C. Strain, O. Farkas, D.K. Malick, A.D. Rabuck, K. Raghavachari, J.B. Foresman,
J.V. Ortiz, Q. Cui, A.G. Baboul, S. Clifford, J. Cioslowski, B.B. Stefanov, G. Liu,
A. Liashenko, P. Piskorz, I. Komaromi, R.L. Martin, D.J. Fox, T. Keith, M.A. Al-
Laham, C.Y. Peng, A. Nanayakkara, M. Challacombe, P.M.W. Gill, B. Johnson,
W. Chen, M.W. Wong, C. Gonzalez, J.A. Pople, GAUSSIAN03, Revision C.02,
Gaussian, Inc., Wallingford, CT, 2004.
J.S. Warner, J. Org. Chem. 28 (1963) 1642.
[17] F.E. Hahn, L. Wittenbecher, R. Boese, D. Bläser, Chem. Eur. J. 5 (1999) 1931.
[18] A.J. Mukherjee, S.S. Zade, H.B. Singh, R.B. Sunoj, Chem. Rev. 110 (2010) 4357;
H. Gornitzka, S. Besser, R. Herbst-Irmer, U. Kilimann, F.T. Edelmann,
J. Organomet. Chem. 437 (1992) 299;
[32] A.E. Reed, L.A. Curtiss, F. Weinhold, Chem. Rev. 88 (1988) 899;
E.D. Glendening, A.E. Reed, J.E. Carpenter, F. Weinhold, NBO Version 3.1.
[33] A.B. Sannigrahi, T. Kar, J. Chem. Educ. 65 (1988) 674.
Y. Nishibayashi, J.D. Singh, S.-i. Fukuzawa, S. Uemura, J. Org. Chem. 60 (1995)
4114;
S.R. Wilson, P.A. Zucker, R.-R.C. Huang, A. Spector, J. Am. Chem. Soc. 111
(1989) 5936;
[34] G. Frison, A. Sevin, J. Chem. Soc. Perkin Trans. 2 (2002) 1692.
[35] G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Structures,
University of Göttingen, Göttingen, Germany, 1997.
[36] G.M. Sheldrick, SHELXL 97, Program for Refining Crystal Structures, University
of Göttingen, Göttingen, Germany, 1997.
S.S. Zade, H.B. Singh, R.J. Butcher, Angew. Chem. Int. Ed. 43 (2004) 4513.
[19] F.E. Hahn, M.C. Jahnke, Angew. Chem. Int. Ed. 47 (2008) 3122.
[20] A.K. Varma, J. Singh, V.K. Sankar, R. Chaudhary, R. Chandra, Tet. Lett. 48 (2007) 4207.
[37] D.T. Cromer, J.T. Waber, International Tables for X-ray Crystallography,
Kynoch Press, Birmingham, U.K, 1974.