Bis(chalcogenones) as pincer ligands: isolation and Heck activity of the selone-ligated unsymmetrical C,C,Se-Pd pincer complex

Article abstract of DOI:10.1039/c5dt01565k

The reaction of meta-phenylene-bis(1-methyl-1H-imidazole-2(3H)-selone) with [Pd₂(μ-Cl)₂(2-C₆H₄CH₂NMe₂)₂] in dry benzene and glacial acetic acid resulted in the formation of an un

Full text of DOI:10.1039/c5dt01565k

Dalton
Transactions
View Article Online
View Journal
PAPER
Bis(chalcogenones) as pincer ligands: isolation and
Heck activity of the selone-ligated unsymmetrical
C,C,Se–Pd pincer complex†
Cite this: DOI: 10.1039/c5dt01565k
a
a,b
a
c
Ninad Ghavale, Sudesh T. Manjare, Harkesh B. Singh* and Ray J. Butcher
The reaction of meta-phenylene-bis(1-methyl-1H-imidazole-2(3H)-selone) with [Pd
CH NMe ] in dry benzene and glacial acetic acid resulted in the formation of an unsymmetrical
,6-membered C,C,Se–Pd(II) pincer complex through C–H bond activation and extrusion of one sel-
enium. This is the first example of a C,C,Se–Pd(II) complex wherein the central Pd(II) is simultaneously co-
2 2
(µ-Cl) (2-
C
6
H
4
2
2 2
)
5
ordinated to a selone and an N-heterocyclic carbene. The chelated complex of the type [PdL2] 2[PF6]−
2+
Received 25th April 2015,
Accepted 13th May 2015
(
L = bis(selone)) was isolated from the reaction of the bis(selone) with [PdCl (PhCN) ] and NH PF . The
2
2
4
6
DOI: 10.1039/c5dt01565k
unsymmetrical pincer complex was studied for Heck activity revealing its application as an acceptable
catalyst in coupling of iodobenzene with acrylates and styrene.
www.rsc.org/dalton
4
in Heck catalysis. More recently, Singh and coworkers have
developed a related chelate complex with NHC and selenoether
Introduction
Palladium complexes of pincer ligands of the type D,C,D (D = ligand and shown its catalytic activity for Suzuki–Miyaura
5
N, P, O, S) have attracted considerable current interest in coupling reactions.
various catalytic reactions. However, the pincer ligands invol-
1
The pincer complexes discussed above have generally more
ving Se donors, usually selenoethers, are comparatively few common 5,5-membered ring systems; however, the examples
6
due to difficulty in synthesis, handling and malodorous nature of 6,6-membered Pd(II) pincers are relatively rare, while there
2
of the organoselenium ligands. The first important result was is no evidence of 7,7-membered pincer complexes. We intuited
2
c
demonstrated by Yao et al. wherein the symmetrical Se,C,Se– the use of selones as pincer donors instead of selenoethers. It
Pd(II) catalyst was synthesized through C–H activation of the was envisaged that a strong Pd–Se overlap due to the existence
+
−
bis(selenide). The palladium complex was shown to be an of considerable zwitterionic C –Se character in CvSe may
excellent Heck catalyst with its ability to couple relatively lead to the isolation of stable pincer complexes with higher
9
unreactive aryl bromides and n-butyl acrylate with extremely than five-membered ring. Recently, we reported a series of benz-
high TON (≈240 000) and high yield. The catalytic activity was imidazolin-2-chalcogenones (chalcogen = S, Se, Te). Interest-
not only comparable to the analogous P- and S-donor pincers ingly, the DFT calculation of the chalcogenones suggested the
7
but also outperforms them. Also, the catalytic efficiency of an characteristic negative charge on the chalcogen atoms. Even
air and moisture stable unsymmetrical C,N,Se pincer consist- though the transition metal complexes of selones are reported
8
ing of a Schiff-base ligand scaffold was studied in Suzuki– in the literature, the potential of these ligands as pincers has
3
Miyaura C–C coupling. A recent review highlights the syn- never been explored. Therefore, it was decided to explore the
thesis and catalytic activity of organochalcogen based Pd(II) role of bis(chalcogenone) pincer ligands to access 6,6- and 7,7-
complexes including selenium-ligated Pd(II) pincer complexes membered Pd(II) pincer complexes. The present investigation
reports the formation of an unprecedented C,C,Se unsymme-
trical pincer complex, which was further explored for its cata-
lytic ability in Heck C–C coupling of iodobenzene and alkenes.
a
Department of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076,
India. E-mail: chhbsia@chem.iitb.ac.in; Fax: +091-22-2572 3480, +091-22-25767152;
Tel: +(022) 25767190
b
Department of Chemistry, University of Mumbai, Vidyanagari, Santacruz (E),
Mumbai 400098, India
Results and discussion
c
Department of Chemistry, Howard University, Washington, D. C. 20059, USA
†
Electronic supplementary information (ESI) available: NMR spectra, mass Synthesis of bis(chalcogenones)
spectra and elemental analysis of the compounds. Crystal packing diagrams,
bond lengths and bond angles for 8, 9 and 13. Cif files for 8, 9, 13, 15 and 16.
CCDC 1061740–1061744. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c5dt01565k
1
0
Bis(selone) 7 was prepared from salt 1 through a reported
procedure with slight modification (route A, Scheme 1).
The reactions of salts 2–6 with disodium dichalcogenides
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Scheme 2 Synthesis of bis(dihaloselones).
Scheme 1 Synthesis of pincer bis(chalcogenones).
(
prepared in situ) in the presence of potassium t-butoxide
7
in dry THF afforded bis(chalcogenones) 8–13 (route B). Bis-
1
13
77
(
chalcogenones) 7–13 were characterized by H, C, Se and
1
25
77
Te NMR spectroscopy. The
Se NMR signals for bis-
(
selones) 7, 8 and 10–13 were observed at ∼δ 32, 61, 59, 60, 198
1
25
and 102 ppm, respectively, while the Te NMR signal for bis- Scheme 3 Synthesis of Pd(II) complexes of bis(selones) C = (i) [Pd2-
(
tellurone) 9 at δ −129 ppm. Compounds 8, 9 and 13 were (µ-Cl)
further characterized by single crystal X-ray diffraction studies
2
(2-C
2.2 eq.).
6 4 2 2 2 2 2 4 6
H CH NMe ) ], benzene, 5 h; D = [PdCl (PhCN) ], NH PF
(
(
vide infra).
Synthesis of bis(dihaloselones)
The formation of a planar, more rigid structure with one
Bis(selones) 10 and 11 were further characterized by synthesiz- 5-membered chelate ring and NHC as a ligand may be the
ing their halogen derivatives (14–16) wherein the oxidative driving forces for the extrusion of selenium.
addition derivatives were obtained by the reaction of the
Also, cleavage of the CvSe bond has been reported in the
1
1c
corresponding halogens in THF at −78 °C (Scheme 2). The literature.
Attempts to prepare analogous symmetrical 6,6-
1
3
77
C NMR signals (∼δ 150 ppm) and
Se NMR signals membered PCP-Rh(I) pincer complexes by Chauvin and
(
∼δ 160 ppm) of the iodo-derivatives 15 and 16 suggested that coworkers were unsuccessful, further demonstrating the
the electron density has been shifted from selenium to difficulty in the synthesis of higher ring system pincer com-
carbene carbon with respect to the precursors 10 and 11 plexes.12a Significantly, 18 is the first example of a 5,6-mem-
respectively.
bered selone ligated Pd(II) pincer complex reported to date.
The synthesis of symmetrical 7,7-membered Pd(II) pincer com-
plexes was attempted through extension of the same approach
Synthesis of Pd(II) complexes of bis(chalcogenones)
In an attempt to prepare symmetrical 6,6-membered Pd(II) to bis(selones) 8 and 9 comprising a methylene spacer. This
pincer complex 17, bis(selone) 7 was refluxed with the Pd(II) yielded an intractable mixture of compounds and the attempts
2
c
precursor [Pd (µ-Cl) (2-C H CH NMe ) ] in dry benzene and to purify, isolate or characterize proved futile. The application
2
2
6
4
2
2 2
glacial acetic acid. This resulted in an unprecedented for- of other synthetic strategies such as C–H activation of 8 and 9
mation of 5,6-membered unsymmetrical C–H activated Pd(II) through more electrophilic Pd(II) precursors like Pd(OAc)
pincer complex 18 via extrusion of one selenium (route C, [Pd(CH CN) (BF ] or more facile oxidative addition of the
Scheme 3). The molecular structure was confirmed by single C–Br bond (10–13) to the Pd(0) precursor Pd (dba) also
2
,
)
4 2
3
4
2
3
crystal X-ray crystallography (vide infra). The extrusion of sel- proved unsuccessful. Interestingly, Nicasio-Collazo and co-
enium may take place via the formation of palladium seleni- workers who synthesized an unsymmetrical 5,7-membered
1
1a,b
de.
The extrusion leads to an almost planar pincer NNC-Pd(II) pincer emphasized the difficulty in the synthesis of
complex accompanied with the formation of a 5-membered palladacycles larger than six members due to the facile reduc-
1
2b
chelate ring where a NHC is strongly bonded to palladium. tive elimination pathway.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
2
+
]−
2 6
The cationic Pd(II) complex (19) of the type [PdL ] 2[PF
(
(
L = 7) was isolated by the reaction of 7 with [PdCl (PhCN) ]
2 : 1 ratio) and NH PF (route D, Scheme 3) and characterized
4 6
2
2
by common NMR spectroscopy and single crystal X-ray crystal-
lography (vide infra). The reaction of 7 with [PdCl (PhCN) ] in
2
2
a 1 : 1 ratio and NH
yield. However, attempts to isolate cationic Pd(II) complexes of
–13 with [PdCl (PhCN) ] and NH PF resulted in insoluble
4 6
PF also gives the same product 19 in low
8
2
2
4
6
products, which could not be purified and characterized.
The dissymmetric electronic environment of 18 was evident
1
13
from the H and C NMR spectra. As expected the four imid-
azole protons as well as the two protons (C –H and C –H) of
the phenylene bridge are different from each other. The C –H
proton peak (7.96 ppm) of the phenylene ring of ligand 7 is
3
5
1
1
13
absent in the H NMR spectra of 18. Interestingly, C NMR
spectra for 18 exhibits two different methyl carbons at
∼36 ppm and twelve aromatic carbons as compared to only
one methyl peak and seven aromatic carbons in 7. The obser-
1
3
77
vation of the C peak of CvSe in 18 at 171 ppm and the Se
1
3
peak at 97 ppm much downfield with respect to 7 ( C
156 ppm) and Se (32 ppm)) is the direct outcome of a gen atoms are omitted for clarity.
Fig. 1 Molecular structures of compounds 8 (a), 9 (b) and 13 (c). Hydro-
7
7
(
deshielding effect due to coordinate bonding between Pd and
Se, thereby reducing the electronic density on the selenium.
7
7
A downfield shift of the Se NMR signal (δ 42 ppm) was
observed for complex 19 compared to bis(selone) 7 (δ 32 ppm). the other molecule. The Se1⋯Br* and Se1*–Br distance
(
3.668 Å) is significantly higher than the sum of the single
X-ray crystallography
bond covalent radii for Se (1.22 Å) and bromine (1.21 Å), but
Compounds 8, 9 and 13 crystallize in the P2
1
/c space group shorter than the sum of van der Waals radii (3.75 Å). Also the
with a monoclinic crystal system. The molecular structure of C2A–π interactions have been observed which are responsible
compound 8 is shown in Fig. 1a. The significant bond dis- for the formation of the 1-D network.
tances and angles for 8, 9 and 13 are mentioned in the ESI†
(
The molecular structures of 18 and 19 with atomic number-
Table 1). In compound 8 the bond length Se1–C1 (1.833(4) Å) ing scheme are shown in Fig. 2.
is slightly smaller than Se2–C20 (1.842(5) Å). Interestingly, the
The crystals of 18 were obtained by slow evaporation of an
Se2–C20–N4A (131.0(4)°) bond angle is significantly higher acetonitrile solution of the compound. The Pd(II) metal centre
than the related bond angles Se1–C1–N1 (126.6(3)°), Se1–C1– is bound in a tridentate way to the carbene^C^Se ligand, with
N2 (126.4(3)°) and Se2–C20–N3 (125.5(3)°). In the absence of the fourth site occupied by a chlorine atom. The geometry of
the 1-bromo group on the central aryl ring, the two selenium this cyclometalated complex is distorted square planar as the
atoms are cis to each other. In compound 9 (Fig. 1b) the bond C(4)–Pd–C(10) bond angle of 82.0° and the C(10)–Pd–Se bond
lengths Te1–C1 (2.087(10) Å) and Te2–C20 (2.073(9) Å) are angle of 95.9° deviate from ideal 90° due to the planar and
almost equal. Also all Te–C–N (126.00(1)°) bond angles are rigid framework of the carbene^C^Se ligand (Fig. 2a). The
equal. The two tellurium atoms are cis to each other with Pd–Se bond length of 2.3773(5) Å is significantly shorter than
respect to the middle benzene ring. In compound 13, the that reported (∼2.528 Å) for the selenium-ligated palladacycle
5
bond length Se1–C2B (1.824(4) Å) is slightly smaller than Se2– reported by Singh and coworkers. Moreover, it is also shorter
C2A (1.836(4) Å) (Fig. 1c). However, these bond lengths are than the Pd–Se bond distances of 2.4508(5) and 2.4553(5) Å
7
comparable to the Se–C bond lengths of related compounds.
observed for chelated complex 19. The Pd–Cl bond length
The two benzimidazole ring planes are perpendicular to the (2.3967(10) Å) is longer than the value of 2.325(16) Å for the
middle benzene ring plane and also the two selenium atoms selenium-ligated palladacycle reported by Singh and co-
3
2
are trans to each other.
workers. This may be due to the increase in s-character in sp
3
The molecular packing diagrams of compounds 8 and 9 hybridised orbitals of selenium compared to sp hybridization
show a 1-D network formed by π–π stacking interactions in selenoethers. This may facilitate a better overlap with d-orbi-
(
3.777(1) Å for 8 (Fig. 78 in the ESI†) and 3.846(2) Å for 9 tals of palladium, resulting in a very strong interaction and
(
Fig. 79 in the ESI†)). Due to these interactions, a supramole- thus a shorter bond length.
cular structure has been formed. The packing diagram of 13
Complex 19 crystallized as red crystals through slow evapor-
showed a centrosymmetric pair due to intermolecular second- ation of acetonitrile solution of the complex. Complex 19 is
ary Se1⋯Br* and Se1*⋯Br interactions (Fig. 80 in the ESI†). symmetrical where the Pd(II) metal centre is chelated to two
One of the selenium atoms interacts with the bromine atom of bis(selone) ligands resulting in a square planar geometry with
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Table 1 Catalytic activity of 18 in Heck C–C coupling of aryl halides and acrylates
Entry
Aryl halide
Alkene
Product
Base
Et
Solvent
Temp.
Time
Yield
1
2
3
4
5
6
7
8
9
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Iodobenzene
Bromobenzene
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
Methyl acrylate
n-Butyl acrylate
t-Butyl acrylate
Styrene
Methyl cinnamate
Methyl cinnamate
Methyl cinnamate
Methyl cinnamate
Methyl cinnamate
Methyl cinnamate
Methyl cinnamate
n-Butyl cinnamate
t-Butyl cinnamate
Stilbene
3
N
DMA
DMA
DMA
DMA
DMA
Xylene
DMSO
DMA
DMA
DMA
DMA
140 °C
140 °C
140 °C
140 °C
140 °C
135 °C
180 °C
140 °C
140 °C
140 °C
140 °C
48 h
48 h
48 h
7 h
48 h
48 h
48 h
8 h
<5%
—
—
95%
75%
—
NaOMe
t
KO Bu
2
K CO
3
Cs CO
2
3
2
K CO
2
K CO
2
K CO
2
K CO
2
K CO
2
K CO
3
3
3
3
3
3
—
96%
95%
94%
—
7 h
20 h
48 h
1
1
0
1
Methyl acrylate
Methyl cinnamate
Catalytic activity of 18
The selone ligated Pd(II) pincer complex 18 was studied as a
catalyst for the Heck C–C coupling reaction and the optimiz-
1
4
ation and catalytic activity data are mentioned in Table 1.
The evaluation of various bases for coupling of iodobenzene
with methyl acrylate in DMA (1 mol% catalyst loading) illus-
trated that Et N is a relatively less active base (entry 1), and
3
t
NaOMe and KO Bu are inactive bases (entries 2 and 3). It was
2 3 2 3
observed that bases like K CO and Cs CO are more active
resulting in 95% and 75% yields (entries 4 and 5) but even-
tually K CO was preferred as a base over Cs CO for further
2
3
2
3
reactions with less reaction time as well as better yields. The
unsuccessful assessment of other solvents like xylene and
DMSO (entries 6 and 7) proved that DMA is a superior solvent
for this reaction. The coupling of iodobenzene with n-butyl
and t-butyl acrylates in DMA (1 mol% catalyst loading) resulted
in high yields (∼95%) in comparatively less reaction times
(
∼7 h) (entries 8 and 9). Almost analogous high yields were
obtained in coupling of iodobenzene with styrene under
similar reaction conditions but moderately prolonged reaction
time of 20 h (entry 10). Attempts to couple less reactive sub-
strates like bromobenzene with acrylates proved futile
(
entry 11). The catalytic activity of 18 is observed to be high
with respect to reactive substrates like iodobenzene, but
has no activity as compared to other selenium-ligated
Pd(II) pincer complexes studied which show better activity
for less reactive and inexpensive substrates like ArBr and
2
c,3
ArCl.
Fig. 2 Molecular structures of compounds 18 (a) and 19 (b). Significant
bond lengths [Å] and angles [°] 15: Pd–C(10) 2.022(4); Pd–C(4) 2.014(4);
Pd–Se 2.3773(5); Pd–Cl 2.3967(10); C(10)–Pd–Cl 178.75(12); C(4)–Pd–
Se 176.36(13). 16: Pd–Se(1) 2.4508(5); Pd–Se(2) 2.4553(5) Se(1)–Pd–Se(1)
#1180.000(1).
Conclusions
In summary, we have demonstrated the application of bis(chalco-
the Se–Pd–Se bond angle in the range of 88–91° (Fig. 2b). The genone) ligands for synthesizing an unsymmetrical, rigid and
two selone ligands are anti with respect to each other and are selone ligated 5,6-membered C,C,Se–Pd(II) pincer complex
arranged in a zig-zag mode to the central metal. The Pd–Se through C–H bond activation. The synthesis of 7,7-membered
bond distances 2.4508(5) and 2.4553(5) Å of 19 are comparable pincer complexes was unsuccessful plausibly due to facile
to those reported for Pd(II) coordination complexes of N,N-di- reductive elimination pathways. The pincer complex has Pd in
1
3
−
methylselenourea. The two PF
6
anions are outside the a dissymmetric electronic environment with a very short Pd–Se
coordination sphere and are involved in hydrogen bonding and long Pd–Cl bond. The complex showed good Heck activity
through fluorine with protons of the imidazole moiety.
with respect to reactive substrates like iodobenzene.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
1
15.4, 115.1, 68.2, 53.2, 52.8, 22.4. Anal. calcd for C28
3 4
H31Br N
Experimental section
(
%): C, 50.70; H, 4.71; N, 8.45. Found: C, 49.70; H, 4.20; N,
All reactions were carried out under a nitrogen or an argon 8.99.
atmosphere using standard Schlenk techniques. Solvents were
4: The reagents used are 2,6-bis(bromomethyl)-1-bromo-
purified and dried by standard procedures and were distilled phenylene (0.50 g, 1.45 mmol) and N-butyl benzimidazole
1
prior to use. Melting points were recorded on a Veego VMP-I (0.51 g, 2.91 mmol). Yield: 0.84 g (87%). H NMR (400 MHz,
3
melting point apparatus in capillary tubes and were un- CDCl ): δ (ppm) 11.12 (s, 2H), 8.04 (d, 2H), 7.75 (d, 2H),
1
13
corrected. The H (400 MHz) and C (100.56 MHz) NMR spectra 7.69–7.50 (m, 4H), 7.29 (s, br, 3H), 5.92 (s, 4H), 4.62 (t, J =
were recorded on Varian VXR 400S and Bruker AV 400 spectro- 7.2 Hz, 4H), 2.02 (quint, J = 7.2 Hz, 4H), 1.44 (sext, J = 7.2 Hz,
7
7
125
13
meters at 25 °C. The Se (57.22 MHz and 76.3 MHz) and Te 4H), 0.91 (t, J = 7.2 Hz, 6H). C NMR (CDCl
94.79 MHz and 157.97 MHz) NMR spectra were recorded on 131.1, 130.8, 129.8, 129.6, 129.3, 127.1, 126.9, 114.3, 112.8,
Varian VXR 300S and Bruker AV 400 spectrometers. Chemical 50.2, 47.5, 30.9, 19.6, 13.3.
shifts are cited with respect to Me Si as the internal standard 5: The reagents used are 2,6-bis(bromomethyl)-1-bromo-
H, C) and Me Se ( Se) and Me Te ( Te) as external phenylene (1.55 g, 4.52 mmol) and N-tert-butyl benzimidazole
3
): δ 141.8, 133.9,
(
4
1
13
77
125
(
2
2
1
standards. Elemental analyses were performed on a Carlo Erba (1.73 g, 9.94 mmol). Yield: 2.6 g (83%). Mp. 227–229 °C. H
Model 1106 elemental analyzer. The ESI mass spectra were NMR (400 MHz, CDCl ): δ (ppm) 9.84 (s, 2H), 8.30 (d, J =
3
recorded on a Q-Tof micro (YA-105) mass spectrometer.
8.7 Hz, 2H), 7.72–7.68 (m, 4H), 7.60 (t, J = 7.1 Hz, 2H), 7.43 (t,
J = 8.6 Hz, 1H), 7.35 (d, J = 7.5 Hz, 2H), 6.02 (s, 4H), 1.95 (s,
Synthesis of salts 1
13
3
18H). C NMR (100 MHz, CDCl ): δ (ppm) 142.9 (NCN), 135.6,
Salt 1 was obtained by stirring a mixture of acetonitrile solu- 133.9, 132.0, 131.7, 130.1, 128.2, 128.1, 125.3, 118.0, 117.9,
tion of 1,3-di(1H-imidazol-1-yl)benzene (1.35 g, 6.42 mmol) 115.3, 63.3, 52.7, 29.4, 29.3, 29.2. Anal. calcd for C30
with methyl iodide (5 eq.) (4.55 g, 2 mL, 32.1 mmol) at room 1H O (%): C, 50.80; H, 5.26; N, 7.90. Found: C, 50.78; H, 4.46;
temperature for 8 h by slightly modifying a reported pro- N, 8.54.
H
3 4
35Br N +
2
1
0
cedure. The white precipitate formed was washed with
6: The reagents used are 2,6-bis(bromomethyl)-1-bromo-
1
diethyl ether and dried. Yield: 2.95 g (93%). H NMR phenylene (5.00 g, 14.57 mmol) and N-pyridyl benzimidazole
400 MHz, DMSO): δ (ppm) 9.80 (s, 2H), 8.36 (m, 2H), 8.25 (m, (6.15 g, 31.5 mmol). Yield: 9.58 g (84%). H NMR (400 MHz,
H), 8.00–7.90 (m, 4H), 3.95 (s, 6H). C NMR (100 MHz, CDCl
1
(
1
3
1
3
): δ (ppm) 10.69 (s, 2H), 8.80 (d, J = 2.7 Hz, 2H), 8.51 (d,
DMSO): δ (ppm) 136.3, 135.6, 132.2, 124.7, 122.8, 121.0, 115.9.
J = 8.3 Hz, 2H), 8.30 (t, J = 7.3 Hz, 1H), 8.12 (d, J = 8.2 Hz, 2H),
7
6
.95 (d, J = 8.3 Hz, 2H), 7.81–7.72 (m, 6H), 7.49–7.42 (m, 4H),
.07 (s, 4H). C NMR (100 MHz, CDCl ): δ (ppm) 149.3 (NCN),
3
General procedure for the synthesis of salts 2–6
13
Salts 2–6 were synthesized by dissolving 2,6-bis(bromomethyl)- 147.1, 143.2, 140.5, 133.6, 131.3, 130.5, 129.6, 128.5, 127.8,
-bromophenylene (1 eq.) in 1,4-dioxane and the corres- 127.4, 125.2, 123.9, 117.3, 116.1, 114.0, 51.2. Anal. calcd for
ponding N-alkyl or N-aryl benzimidazole (2.2 eq.). The reaction (%): C, 52.41; H, 3.44; N, 11.46. Found: C, 51.76;
1
32 3 6
C H25Br N
mixtures were refluxed for 14 h under a nitrogen atmosphere. H, 2.92; N, 12.54.
The white solids formed were filtered and washed with THF
Synthesis of bis(selone) 7
and diethyl ether to afford salts 2–6.
: The reagents used are 2,6-bis(bromomethyl)benzene A mixture of 1 (1.43 g, 2.89 mmol), Se powder (0.48 g,
2.01 g, 7.59 mmol) and N-butyl benzimidazole (2.91 g, 6.0 mmol) and K CO (0.88 g, 6.36 mmol) was refluxed in dry
2
(
1
2
3
1
3
6.71 mmol). Yield: 4.6 g (99%). H NMR (400 MHz, CDCl ): δ methanol (50 mL) for 6 h after which the solvent was evapor-
(
(
ppm) 11.13 (s, 2H), 8.30 (s, 1H), 8.04 (d, J = 8.1 Hz, 2H), 7.75 ated and the residual solid was extracted with chloroform. The
d, J = 8.0 Hz, 2H), 7.63 (d, J = 7.7 Hz, 2H), 7.59–7.51 (m, 4H), chloroform extract was concentrated to 4 mL and 1 mL of
7
.29 (t, J = 7.7 Hz, 1H), 5.92 (s, 4H), 4.63 (t, J = 7.3 Hz, 4H), methanol was added to yield a white crystalline solid of 7
1
2
.06–1.99 (m, 4H), 1.48–1.39 (m, 4H), 0.95 (t, J = 7.7 Hz, 6H). (0.644 g, 56%) Mp. 247 °C (dec.). H NMR (400 MHz, CDCl
3
):
1
3
13
C NMR (100 MHz, CDCl ): δ (ppm) 141.8 (NCN), 134.0, δ (ppm). C NMR (100 MHz, CDCl ): δ (ppm) 156.9 (NCN),
3
3
77
1
6
31.1, 130.8, 129.8, 129.7, 129.4, 127.1, 126.9, 114.3, 112.8, 139.1, 129.7, 126.3, 124.6, 120.9, 120.3, 37.6.
6.8, 50.2, 47.5 (1,4-dioxane), 30.9, 19.6, 13.3. Anal. calcd for (57 MHz, CDCl ): δ (ppm) 32.2. Anal. calcd for C14
Se NMR
Se
2
3
H
14
N
4
C H Br N + 1H O (%): C, 57.15; H, 6.08; N, 8.89. Found: C, (%): C, 42.44; H, 3.56; N, 14.14. Found: C, 42.64; H, 3.66; N,
3
0
36
2
4
2
+
5
7.35; H, 6.04; N, 8.24.
: The reagents used were 2,6-bis(bromomethyl)-1-bromo-
phenylene (4.59 g, 13.38 mmol) and N-iso-propyl benzimid-
14.67. HRMS: (m/z) 398.9647 [M + 1] .
3
General procedure for the synthesis of bis(chalcogenones)
1
8–13
azole (4.71 g, 29.43 mmol). Yield: 7.8 g (88%). H NMR
(
2
2
400 MHz, CDCl
3
): δ (ppm) 9.88 (s, 2H), 9.82 (d, J = 6.4 Hz, Bis(chalcogenones) 8–13 were synthesized by addition of
H), 8.10 (d, J = 8.2 Hz, 2H), 7.78–7.70 (m, 2H), 7.66–7.61 (m, respective salts 2–6 (1 eq.) into a brownish red solution of
H), 7.50–7.42 (m, 3H), 5.97 (s, 4H), 5.21–5.10 (m, 2H), 1.76 (d, Na (3 eq.; E = Se, Te) (prepared in situ) under a nitrogen
): δ (ppm) 142.4 atmosphere and the reaction mixture was stirred for 8–10 h at
NCN), 135.6, 133.1, 132.6, 132.5, 130.3, 128.6, 128.4, 126.1, room temperature. Potassium tert-butoxide was added to the
2 2
E
1
3
J = 6.7 Hz, 12H). C NMR (100 MHz, CDCl
(
3
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
reaction mixture and the reaction was further stirred for 5–7 h Anal. calcd for C32
H
23BrN
6
Se
2
(%): C, 52.69; H, 3.18; N, 11.52.
at room temperature. The reaction mixture was quenched by Found: C, 52.21; H, 4.76; N, 6.73.
adding water (50 mL) and extracted with diethyl ether/chloro-
General procedure for the synthesis of bis(dihaloselones)
4–16
The bis(selenones) 10 or 11 (1 eq.) was taken in dry THF
form, dried over sodium sulfate. Combined organic layer was
evaporated under reduced pressure to obtain bis(chalcogen-
1
ones) 8–13.
1
8
: Yield: 0.47 g (58%). Mp. 120–122 °C. H NMR (400 MHz, (15 mL) and iodine/bromine (2 eq.) in THF was added at
CDCl ): δ (ppm) 7.44 (s, 1H), 7.24 (m, 6H), 7.11 (m, 5H), 5.67 −78 °C under a nitrogen atmosphere. The reaction mixtures
3
(
s, 4H), 4.47 (t, J = 7.7 Hz, 4H), 1.87 (m, 4H), 1.49 (m, 4H), 1.00 were stirred for 16–20 h at room temperature. The reaction
1
3
(t, J = 7.4 Hz, 6H). C NMR (100 MHz, CDCl
3
): δ (ppm) 167.2 mixtures were concentrated in a vacuum and n-pentane
(
1
NCN), 136.2, 133.3, 132.9, 129.5, 127.3, 127.2, 123.5, 110.5, (15–20 mL) was added. Crystalline compounds were obtained
7
7
09.7, 50.1, 47.0, 30.3, 20.3, 13.9. Se NMR (57 MHz, CDCl
Se (%): C, 59.21; H,
.63; N, 9.21. Found: C, 59.61; H, 5.49; N, 9.95.
3
): at −30 °C.
1
δ (ppm) 60.7. Anal. calcd for C30
5
H
34
N
4
2
14: Yield: 0.65 g (87%). Mp. 208 °C (decomposed). H NMR
(400 MHz, CDCl ): δ (ppm) 7.92 (d, J = 7.7 Hz, 2H), 7.58 (m,
3
1
9: Yield: 0.61 g (34%). Mp. 160–162 °C. H NMR (400 MHz, 4H), 7.45 (d, J = 7.7 Hz, 2H), 7.22 (d, J = 7.0 Hz, 2H), 7.16 (t, J =
CDCl ): δ (ppm) 7.43 (s, 1H), 7.37 (d, J = 8.2 Hz, 2H), 7.29–7.10 6.2 Hz, 1H), 6.19 (s, 4H), 5.95 (m, 2H), 1.92 (d, J = 7.0 Hz,
3
7
7
(
1
m, 9H), 5.75 (s, 4H), 4.55 (t, J = 7.7 Hz, 4H), 1.94–1.86 (m, 4H), 12H). Se NMR (57 MHz, CDCl ): δ (ppm) 290.4. ESI-MS: m/z
.56–1.46 (m, 4H), 1.02 (t, J = 7.3 Hz, 6H). C NMR (100 MHz, 738.9 [M − Br
3
1
3
+
+
+
3
] , 685.9 [M − C
4
H
10Br
3
5
] , 581.1 [M − Br ] ;
CDCl
23.8, 123.7, 111.2, 110.4, 53.2, 50.2, 30.6, 20.2, 13.9.
3
): δ (ppm) 146.2 (NCN), 135.6, 134.2, 133.8, 129.4, 127.3, Anal. calcd for C28
H
29Br
5
N
4
Se
2
(%): C, 34.35; H, 2.99; N, 5.72.
1
25
1
Te Found: C, 34.17; H, 2.84; N, 6.00.
1
NMR (126.2 MHz, CDCl
3
): δ (ppm) −129.1. HRMS: (m/z)
15: Yield: 0.12 g (68%). Mp. 119–129 °C. H NMR (400 MHz,
CDCl ): δ (ppm) 7.86 (d, J = 6.7 Hz, 2H), 7.53 (m, 4H), 7.45 (d,
3
+
7
11.0993 [M] .
1
1
0: Yield: 0.35 g (54%). Mp. 114–116 °C. H NMR (400 MHz, J = 7 Hz, 2H), 7.17 (t, J = 7.8 Hz, 1H), 6.95 (d, J = 7.6 Hz, 2H),
CDCl
3
): δ (ppm) 7.55 (d, J = 8 Hz, 2H), 7.22 (m, 4H), 7.10 (d, J = 6.00 (s, 4H), 5.79 (t, J = 7.1 Hz, 2H), 1.87 (d, J = 7.1 Hz, 12H).
1
3
8
Hz, 2H), 6.98 (t, J = 7.8 Hz, 1H), 6.60 (d, J = 8.0 Hz, 2H), 5.92
3
C NMR (100 MHz, CDCl ): δ (ppm) 150.0 (NCN), 133.6,
13
(
(
1
2
m, 2H), 5.90 (s, 4H), 1.67 (d, J = 7.1 Hz, 12H). C NMR 133.5, 131.1, 129.4, 128.7, 127.1, 126.6, 122.8, 114.2, 113.6,
7
7
100 MHz, CDCl
3
): δ (ppm) 167.2 (NCN), 135.1, 133.5, 131.5, 55.8, 53.2, 20.7. Se NMR (57 MHz, CDCl
3
): δ (ppm) 154.6.
16: Yield: 0.42 g (81%). H NMR (400 MHz, CDCl ): δ (ppm)
0.2, 15.4. Se NMR (57 MHz, CDCl ): δ (ppm) 59.3. Anal. 7.80 (d, J = 8 Hz, 1H), 7.48–7.34 (m, 4H), 7.05 (t, J = 8 Hz, 1H),
1
28.1, 126.9, 123.5, 123.3, 122.3, 111.5, 110.7, 52.3, 50.9, 20.3,
3
7
7
3
calcd for C28
4 2
H29BrN Se (%): C, 51.00; H, 4.43; N, 8.50. Found: 6.38 (d, J = 8 Hz, 1H), 5.85 (s, 2H), 4.51 (t, J = 7.2 Hz, 2H), 1.79
1
3
C, 50.67; H, 4.50; N, 8.06.
(m, 2H), 1.40 (m, 2H), 0.93 (t, J = 7.2 Hz, 3H). C NMR
1: Yield: 0.85 g (57%). Mp. 193–195 °C. H NMR (400 MHz, (100 MHz, CDCl ): δ (ppm) 156.4 (NCHN), 134.7, 132.5, 127.9,
1
1
3
3
CDCl ): δ (ppm) 7.96 (d, J = 7.6 Hz, 1H), 7.35–7.17 (m, 4H), 126.6, 125.3, 121.9, 112.1, 111.9, 50.8, 47.1, 30.0, 19.4, 13.6.
7
7
7
.04 (d, J = 8 Hz, 1H), 6.66 (dd, J = 0.8 Hz, 7.2 Hz, 1H), 5.79 (s,
3
Se NMR (57 MHz, CDCl ): δ (ppm) 166.09. Anal. calcd
2
H), 4.50 (t, J = 7.6 Hz, 2H), 1.91 (m, 2H), 1.50 (m, 2H), 1.02 (t, for C H BrI N Se (%): C, 30.15; H, 2.78; N, 4.69. Found:
3
0
33
4
4
2
1
3
J = 7.2 Hz, 3H). C NMR (100 MHz, CDCl
3
): δ (ppm) 167.5 C, 30.07; H, 2.46; N, 5.21.
(
NCN), 135.1, 133.2, 132.9, 128.0, 127.0, 123.8, 123.7, 122.3,
7
7
Synthesis of 18
(%): C, The reaction mixture of 7 (0.215 g, 0.54 mmol) and [Pd
2.42; H, 4.84; N, 8.15. Found: C, 52.56; H, 4.58; N, 8.94. Cl) (2-C CH NMe ] (0.179 g, 0.32 mmol) in benzene
2: Yield: 0.58 g (87%). Mp. 203 °C (decomposed). H NMR (30 mL) and glacial acetic acid was refluxed for 5 h. The reac-
400 MHz, CDCl ): δ (ppm) 7.86 (m, 2H), 7.16 (m, 4H), 7.03 tion mixture was evaporated to dryness and washed with
m, 2H), 6.95 (t, J = 7.7 Hz, 1H), 6.49 (d, J = 8.0 Hz, 2H), 5.99 (s, diethyl ether to isolate the crude product. The solid was
1
10.4, 109.8, 50.5, 47.0, 30.3, 20.3, 13.9. Se NMR (57 MHz,
): δ (ppm) 60.2. Anal. calcd for C30 33BrN Se
CDCl
5
3
H
4
2
2
(µ-
2
6
H
4
2
2 2
)
1
1
(
(
3
1
3
4
H), 2.23 (s, 18H). C NMR (100 MHz, CDCl ): δ (ppm) 165.9 extracted with chloroform and filtered through celite pad. The
3
(
1
(
NCN), 134.9, 133.9, 133.4, 127.9, 126.6, 123.4, 123.1, 122.2, solvent was evaporated and the residue was treated with
7
7
3
14.5, 110.6, 64.6, 50.2, 30.8. Se NMR (57 MHz, CDCl ): δ diethyl ether to yield a reddish brown solid. Yield: 0.105 g
1
ppm) 197.6. Anal. calcd for C H BrN Se (%): C, 52.42; H, (42%). Mp. 205 °C (dec.). H NMR (400 MHz, DMSO): δ (ppm).
30 33 4 2
4
.84; N, 8.15. Found: C, 52.22; H, 4.77; N, 6.73.
1
8.21 (d, J = 2.4 Hz, 1H), 8.09 (d, J = 1.9 Hz, 1H), 7.77 (d, J = 2.3
3: Yield: 0.7 g (74%). Mp. 240–242 °C. H NMR (400 MHz, Hz, 1H), 7.53 (d, J = 7.2 Hz, 1H), 7.47 (d, J = 7.9 Hz, 1H), 7.37
CDCl ): δ (ppm) 8.73 (dd, J = 4.9 Hz, J = 1.9 Hz, 2H), 8.16 (d, (d, J = 1.9 Hz, 1H), 7.32 (t, J = 7.8 Hz, 1H), 4.10 (s, 3H), 3.74 (s,
1
3
1
3
J = 8.3 Hz, 2H), 8.01 (dt, J = 7.6 Hz, J = 1.8 Hz, 2H), 7.48 (m, 3H). C NMR (100 MHz, DMSO): δ (ppm) 171.6, 148.4, 143.1,
2
7
H), 7.42 (m, 2H), 7.25 (m, 4H), 7.12 (m, 2H), 7.05 (t, J = 139.2, 132.7, 125.9, 123.4, 122.6, 119.4, 117.1, 115.1, 111.2,
1
3
77
.7 Hz, 1H), 6.80 (d, J = 7.6 Hz, 2H), 5.98 (s, 4H). C NMR 37.1, 36.6. Se NMR (57 MHz, DMSO): δ (ppm) 97.8. ESI-MS:
+
+
3
(100 MHz, CDCl ): δ (ppm) 168.2 (NCN), 150.3, 149.4, 138.4, m/z 422.9 [M − Cl] , 343.0 [M − (Se + Cl)] , 317.0 [M − (Pd + Se
+
1
1
34.8, 133.5, 133.0, 128.2, 127.2, 124.6, 124.4, 124.2, 123.9, + Cl)] . Anal. calcd for C14
H
13ClN
4
PdSe (%): C, 36.70; H, 2.86;
7
7
11.9, 110.4, 50.7. Se NMR (57 MHz, CDCl ): δ (ppm) 102.1. N, 12.23. Found: C, 36.82; H, 2.95; N, 12.60.
3
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015

View Article Online
Dalton Transactions
Paper
Table 2 Details of the X-ray data collection parameters
Compound
Formula
8
9
13
18
19
C
30
H
33
N Se
4 2
C
30
H
34
4
N Te
2
C
32
H
23BrN
Se
6 2
C
14
H
13ClN
4
PdSe
28 28 12 8 2 4
C H F N P PdSe
1188.76
M
r
607.52
705.81
729.39
458.09
System
Space group
a [Å]
b [Å]
c [Å]
Monoclinic
P21/c
9.74100(10)
21.5258(5)
13.7748(2)
90.00
Monoclinic
P21/c
9.7586(3)
21.6201(13)
14.0678(5)
90.00
Monoclinic
P121/c1
13.4416(4)
20.7586(7)
12.6712(4)
90.00
Monoclinic
P21/c
8.0559(2)
13.1124(3)
13.8977(3)
90.00
Monoclinic
P21/c
6.82075(19)
10.9648(3)
25.1631(6)
90.00
α [°]
β [°]
94.4040(10)
90.00
2879.81(8)
4
93.418(3)
90.00
2962.8(2)
4
0.44 × 0.39 ×
0.22
1.582
1.993
12 138
5995
107.462(4)
90.00
3372.69(19)
4
0.49 × 0.32 ×
0.15
1.436
3.406
36 999
11 354
96.673(2)
90.00
1458.10(6)
4
0.4159 × 0.1574 ×
0.1395
2.087
14.786
8995
2978
95.769(2)
90.00
1872.38(9)
2
0.3662 × 0.1823 ×
0.0907
2.109
10.132
6718
3731
γ [°]
V [Å ]
3
Z
3
Size [mm ]
0.48 × 0.41 ×
.24
0
−3
ρcalcd [Mg m
]
1.401
3.391
1 1694
5827
−
1
μ [mm
Reflections collected
Observed reflns [R(int) =
]
0
R
.0615]
observed reflns
wR , all
1
0.0636
0.1959
0.0896
0.2995
0.0493
0.1285
0.0402
0.1107
0.0450
0.1226
2
Synthesis of 19
(2 mmol) and solvent (5 mL) and the reaction mixture was
heated in a preheated oil bath for a specified time at the given
temperature. After completion of the reaction, it was cooled to
room temperature. The reaction mixture was filtered through a
celite pad and washed with water and extracted with dichloro-
methane. The organic layer was dried over anhydrous sodium
sulfate and filtered. The sample was injected in the gas chro-
matographic column using a microsyringe and run for 30 min
under the preset temperature program. Yields were calculated
from the conversion of the aryl halides.
To a solution of selone 7 (0.133 g, 0.33 mmol) in acetonitrile,
PdCl (PhCN) (0.064 g, 0.16 mmol) and NH PF (0.061 g,
2
2
4
6
0
.36 mmol) were added and the mixture was refluxed with stir-
ring for 3 h. The reaction mixture was then evaporated to
dryness and the residual solid was washed with methanol fol-
lowed by diethyl ether. The solid was extracted with aceto-
nitrile and filtered. The filtrate was evaporated to dryness to
yield a reddish brown solid. Yield: 0.165 g (83%). Mp. 217 °C
1
(
dec.). H NMR (400 MHz, CD
3
CN): δ (ppm). 7.95 (t, J = 1.2 Hz,
2
8
H), 7.75 (t, J = 8.7 Hz, 2H), 7.66 (d, J = 1.5 Hz, 4H), 7.56 (d, J =
General method for Heck coupling of iodobenzene and
bromobenzene
7
7
.1 Hz, 4H), 7.41 (d, J = 1.9 Hz, 4H), 3.53 (s, 12H). Se NMR
): (ppm) 42.8. Anal. calcd for
(%): C, 28.29; H, 2.37; N, 9.43. Found: C,
(57 MHz, CDCl
3
δ
A round-bottom flask was charged with aryl halide (1 mmol),
alkene (1.5 mmol), catalyst 18 (1 mol%), base (2 mmol), and
solvent (5 mL). The reaction mixture was heated in a preheated
oil bath for a given time at a specified temperature. After the
completion of the reaction, it was worked up as described
above and purified by column chromatography (silica: 60–120,
hexane–ethyl acetate).
C
2
28 28 12 8 2 4
H F N P PdSe
8.41; H, 2.11; N, 8.71.
X-Ray crystallographic study
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 and Fourier methods and refined
by full-matrix least squares with the non-hydrogen atoms aniso-
tropic and hydrogen with fixed isotropic thermal parameters
of 0.07 Å using the SHELXL 97 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. Details of the X-ray data
collection parameters are given in Table 2.
1
5
Acknowledgements
H. B. S. gratefully acknowledges the Department of
Science and Technology, New Delhi, for J. C. Bose
Fellowship. S. T. M. is thankful to the Council of Scientific and
Industrial Research (CSIR), New Delhi for SRF.
2
16
1
7
References
General method for optimization of the catalytic reaction
conditions using gas chromatography
1
(a) N. Selander and K. J. Szabó, Chem. Rev., 2011, 111,
2048–2076; (b) G. van Koten and R. J. M. K. Gebbink, guest
editors, Pincers and other Hemilabile ligands, Dalton
A two-necked round-bottomed flask was charged with aryl
halide (1 mmol), alkene (1.5 mmol), catalyst 18 (1 mol%), base
This journal is © The Royal Society of Chemistry 2015
Dalton Trans.

View Article Online
Paper
Dalton Transactions
Trans., 2011, 35, 8713–9052; (c) G. van Koten and
P. L. Gupta and A. K. Singh, Organometallics, 2014, 33,
3629–3639; (c) M. M. Kimani, C. A. Bayse, B. S. Stadelman
and J. L. Brumaghim, Inorg. Chem., 2013, 52, 11685–11687
and references therein; (d) J. Jin, H.-W. Shin, J. H. Park,
J. H. Park, E. Kim, T. K. Ahn, D. H. Ryu and S. U. Son, Orga-
nometallics, 2013, 32, 3954–3959; (e) M. M. Kimani,
H. C. Wang and J. L. Brumaghim, Dalton Trans., 2012, 41,
5248–5259.
D. Milstein, guest editors, Organometallic Pincer Chem-
istry. Topics in Organometallic Chemistry, Springer-Verlag,
Berlin Heidelberg, 2013, vol. 40, p 1–352; (d) S. Humphrey,
guest editor, The Carbon–Metal Bond and C–H Metalation,
Dalton Trans., 2014, 43, 9834 and references therein;
(
e) B. G. Anderson and J. L. Spencer, Chem. – Eur. J., 2014,
0, 6421–6432; (f) Y. Imanaka, H. Hashimoto, I. Kinoshita
and T. Nishioka, Chem. Lett., 2014, 43, 687–689;
2
9 Y. Rong, A. Al-Harbi, B. Kriegel and G. Parkin, Inorg. Chem.,
2013, 52, 7172–7182.
(
g) R. E. Andrew and A. B. Chaplin, Dalton Trans., 2014, 43,
1
413–1423; (h) X.-Y. Yang, W. S. Tay, Y. Li, S. A. Pullarkat 10 V. C. Vargas, R. J. Rubio, T. K. Hollis and M. E. Salcido,
Org. Lett., 2003, 5, 4847–4849.
(a) A. Kumar, G. K. Rao, S. Kumar and A. K. Singh, Organo- 11 (a) A. Kumar, G. K. Rao, S. Kumar and A. K. Singh, Organo-
and P.-H. Leung, Organometallics, 2015, 34, 1582–1588.
2
metallics, 2014, 33, 2921–2943; (b) A. Kumar, G. K. Rao,
S. Kumar and A. K. Singh, Dalton Trans., 2013, 42, 5200–
metallics, 2014, 33, 2921–2943; (b) G. K. Rao, A. Kumar,
J. Ahmed and A. K. Singh, Chem. Commun., 2010, 46, 5954–
5956; (c) N. Ghavale, S. Dey, A. Wadawale and V. K. Jain,
Organometallics, 2008, 27, 3297–3302; (d) Á. Kozma,
J. Petuškova, C. W. Lehmann and M. Alcarazo, Chem.
Commun., 2013, 49, 4145–4147.
5
6
223; (c) Q. Yao, E. P. Kinney and C. Zheng, Org. Lett., 2004,
, 2997–2999; (d) O. A. Wallner and K. J. Szabó, J. Org.
Chem., 2005, 70, 9215–9221; (e) S. Sebelius, V. J. Olsson and
K. J. Szabó, J. Am. Chem. Soc., 2005, 127, 10478–10479;
(
f) J. Kjellgren, H. Sundén and K. J. Szabó, J. Am. Chem. 12 (a) C. Barthes, C. Lepetit, Y. Canac, C. Duhayon,
Soc., 2005, 127, 1787–1796; (g) Q. Yao and M. Sheets, J. Org.
Chem., 2006, 71, 5384–5387; (h) J. Aydin and K. J. Szabó,
Org. Lett., 2008, 10, 2881–2884; (i) L. T. Pilarski and
K. J. Szabó, Angew. Chem., Int. Ed., 2011, 50, 8230–8232.
G. K. Rao, A. Kumar, J. Ahmed and A. K. Singh, Chem.
Commun., 2010, 46, 5954–5956.
D. Zargarian and R. Chauvin, Inorg. Chem., 2013, 52, 48–58;
(b) J. Nicasio-Collazo, E. Álvarez, J. C. Alvarado-Monzón,
G. Audreu-de-Riquer, J. O. C. Jimenez-Halla, L. M. D. León-
Rodriguez, G. Merino, U. Morales, O. Serrano and
J. A. López, Dalton Trans., 2011, 40, 12450–12453.
13 D. Fregona, R. Graziani, G. Faraglia, U. Caselato and
S. Sitran, Polyhedron, 1996, 15, 2523–2533.
14 T. Chakraborty, K. Srivastava, H. B. Singh and R. J. Butcher,
J. Organomet. Chem., 2011, 696, 2559–2564.
15 G. M. Sheldrick, SHELXS 97, Program for the Solution of
Crystal Structures, University of Göttingen, Göttingen,
Germany, 1997.
3
4
5
6
7
8
A. Kumar, G. K. Rao, J. Ahmed and A. K. Singh, RSC Adv.,
2
012, 2, 12552–12574.
K. N. Sharma, H. Joshi, A. K. Sharma, O. Prakash and
A. K. Singh, Organometallics, 2013, 32, 2443–2451.
F. E. Hahn, M. C. Jahnke and T. Pape, Organometallics,
2
007, 26, 150–154.
S. T. Manjare, S. Sharma, H. B. Singh and R. J. Butcher, 16 G. M. Sheldrick, SHELXL 97, Program for Refining Crystal
J. Organomet. Chem., 2012, 717, 61–74.
(a) D. J. Nelson, F. Nahra, S. R. Patrick, D. B. Cordes,
Structures, University of Göttingen, Göttingen, Germany,
1997.
A. M. Z. Slawin and S. P. Nolan, Organometallics, 2014, 33, 17 D. T. Cromer and J. T. Waber, International Tables for X-ray
3
640–3645; (b) A. K. Sharma, H. Joshi, K. N. Sharma,
Crystallography, Kynoch Press, Birmingham, U.K, 1974.
Dalton Trans.
This journal is © The Royal Society of Chemistry 2015