Synthesis of selenium bridged metallacycles via oxidative addition of diaryl diselenide across Re-Re bond: Novel one-pot reaction approach

Article abstract of DOI:10.1016/j.jorganchem.2011.01.026

One-pot synthesis of novel M₂E₂L₂ type metallacycles [L(CO)₃Re(μ-SeR)₂Re(CO)₃L] (1-5) was accomplished by oxidative addition of diaryl diselenide to low-valent transition metal carbonyl with monodentate pyridine ligands. In metallacycles 1-5, where L = pyridine ligand, R = C₆H₅, CH ₂C₆H₅, the pyridyl groups bonded to metal centres invariably adopted cis conformation due to π-π interaction whereas, in compounds 1a and 2a, the pyridyl ligands were oriented in trans conformation. When bulky phenyl groups are introduced at para position of pyridyl rings, as in case of metallacycle 3, the steric hindrance disrupts the soft interaction and resulted into the expansion of space in between two phenylpyridyl groups and created a void. The Metallacycles 1-5 have been characterised by elemental analysis, NMR, IR, absorption and emission spectroscopic techniques. Molecular structures of 1, 1a, 2, 2a, 3 and 4 were determined by single crystal X-ray diffraction analysis and the structural studies of 1, 2, 3 and 4 revealed that the pyridyl groups attached to the metal centres exhibited cis conformation, while 1a, 2a displayed trans conformation.

Full text of DOI:10.1016/j.jorganchem.2011.01.026

Journal of Organometallic Chemistry 696 (2011) 1609e1617
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Synthesis of selenium bridged metallacycles via oxidative addition of diaryl
diselenide across ReeRe bond: Novel one-pot reaction approach
,
A. Vanitha a, Shaikh M. Mobin b, Bala. Manimaran a
*
a Department of Chemistry, Pondicherry University, Puducherry 605 014, India
b National Single Crystal X-ray Diffraction Facility, Indian Institute of Technology Bombay, Powai, Mumbai 400 076, India
a r t i c l e i n f o
a b s t r a c t
Article history:
One-pot synthesis of novel M2E2L2 type metallacycles [L(CO)3Re(m-SeR)2Re(CO)3L] (1e5) was accom-
plished by oxidative addition of diaryl diselenide to low-valent transition metal carbonyl with mono-
Received 19 October 2010
Received in revised form
14 January 2011
dentate pyridine ligands. In metallacycles 1e5, where L ¼ pyridine ligand, R ¼ C6H5, CH2C6H5, the pyridyl
groups bonded to metal centres invariably adopted cis conformation due to pep interaction whereas, in
Accepted 20 January 2011
compounds 1a and 2a, the pyridyl ligands were oriented in trans conformation. When bulky phenyl
groups are introduced at para position of pyridyl rings, as in case of metallacycle 3, the steric hindrance
disrupts the soft interaction and resulted into the expansion of space in between two phenylpyridyl
groups and created a void. The Metallacycles 1e5 have been characterised by elemental analysis, NMR,
IR, absorption and emission spectroscopic techniques. Molecular structures of 1, 1a, 2, 2a, 3 and 4 were
determined by single crystal X-ray diffraction analysis and the structural studies of 1, 2, 3 and 4 revealed
that the pyridyl groups attached to the metal centres exhibited cis conformation, while 1a, 2a displayed
trans conformation.
Keywords:
Rhenium carbonyl
Diaryl diselenide
Pyridine ligands
Oxidative addition
Molecular recognition
Metallacycles
Ó 2011 Elsevier B.V. All rights reserved.
1. Introduction
cleavage of SeeSe bond was not observed [26,27]. Dinuclear sele-
nium bridged Re2(m-SePh)2(CO)8 compound was obtained from Re
The design and study of well arranged metal-containing cyclic
compounds have emerged as promising research area in modern
supramolecular chemistry [1e10]. Metallacyclic compounds have
a significant impact in the area of molecular sensing, catalysis,
molecular electronics and hydrogen fuel technologies [11e18].
Binuclear metallacyclic structures with synthetically tailorable
chemical and physical properties are potentially useful in molecular
assemblies [19e23]. Earlier, sulphur bridged dinuclear rhenium
and manganese complexes [M(CO)4(SC6H5)]2 (M ¼ Mn, Re) were
prepared by Osborne and Stone from metal pentacarbonyl hydride
with benzene thiol [24]. Liaw et al. have reported that the reaction of
diphenyl diselenide with [Mn(CO)5]ꢀ proceeds to form cis-[Mn
(CO)4(SePh)2]ꢀ via oxidative addition. Similarly, the oxidative addi-
tion reaction of diphenyl ditelluride with [Mn(CO)5]ꢀ afforded cis-
[Mn(CO)4(TePh)2]ꢀ which further transformed into a dinuclear
(CO)5Cl and (PhSe)2 by two-step process via oxidative addition
reaction and the crystal structure was reported by Liaw and co-
workers [28]. The oxidative addition reaction of (PhSe)2 with
Re2Cl4(dppm)2 yielded the doubly bonded Re2C14(m-SePh)2(m-
dppm)2 with bridging SePh groups [29]. Treatment of the tetranu-
clear ruthenium(II) complex [Cp*Ru(m3-Cl)]4 and [CpRu(CH3CN)3]
PF6 with diphenyl diselenide afforded the benzeneselenolate-
bridged diruthenium complexes [Cp*RuCl(m2-SePh)]2 and [CpRu
(CH3CN)(
and co-workers have reported the dinuclear molybdenum complex
[Cp*2Mo2(CO)4( -SePh)2] from [Cp*2Mo2(CO)4] and benzene sele-
nol [32]. Reaction of [ -C5H5(CO)2Mn^CC6H5]BBr4 with [Et3NH]
[Fe2( -CO)( -SeC6H5)(CO)6] yielded FeeFe bridged dinuclear
complex [Fe2( -SeC6H5)2(CO)6] [33]. Cyclopentadienyl chromium
m-SePh)2(CH3CN)RuCp](PF6)2 respectively [30,31]. Petillon
m
h
m
m
m
chalcogenide complex [CpCr(SePh)]2Se was obtained from the
reaction of [CpCr(CO)3]2 with Ph2Se2 [34]. Hupp and co-workers
have reported the preparation of sulphur bridged rhenium
compounds [(CO)4Re(m-SR)]2 for the synthesis of thiolate bridged
molecular rectangles and in the same report they have also
mentioned the stepwise synthesis of selenium bridged rhenium
compound [(CO)4Mn(m-TePh)2Mn(CO)4] [20]. Marsden and Shel-
drick have reported the crystal structure of CF3Se bridged manga-
nese compound [CF3SeMn(CO)4]2 [25]. In literature, the compounds
[M2Br2(CO)6(Se2Ph2)] (M ¼ Mn, Re) containing a Se2Ph2 unit
bridging with two metal centres were reported where, the oxidative
dimers [(CO)4Re(m-SeR)]2 from selenol and Re(CO)5OTf and used as
precursors for synthesising molecular rectangles [35]. Later, 2,20-
bisbenzimidizolate bridged 4-Phpy containing rhenium compounds
* Corresponding author. Tel.: þ91 4132654414; fax: þ91 4132654987.
E-mail address: manimaran.che@pondiuni.edu.in (Bala. Manimaran).
0022-328X/$ e see front matter Ó 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2011.01.026

1610
A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
have been reported by Dinolfo and co-workers [36]. Recently we
have accomplished the sulphur bridged dinuclear rhenium metal-
lacycles from oxidative addition reaction of diaryl disulphides to
rhenium carbonyl with monodendate pyridine ligands [37]. Herein,
we report on the novel one-pot synthesis of selenium bridged
phenyl group proton signals were shifted towards downfield in 1. 13C
NMR of compound 1 showed signals for terminal carbonyl groups at
d
200.2 and 195.1 ppm with 1:2 ratio and the signals at around
d
157.1e126.8 ppm were attributed to pyridyl group and the phenyl
group carbons resonated at
d
133.9e127.2 ppm. Similarly, 1H NMR
neutral metallacycles [L(CO)3Re(
m
-SeR)2Re(CO)3L] (L ¼ pyridine
spectrum of compound 2 displayed, two doublets for pyridyl protons
and methyl group protons showed a singlet. When compared to free
picoline (8.39, 7.02 and 2.27) ligand, the proton signals of 2 were
shifted towards downfield. 1H NMR spectrum of compound 3 dis-
played, three doublets, one triplet and one multiplet for phenyl-
pyridine protons and the phenyl protons of aryl selenide appeared as
one doublet, one triplet and one multiplet. Compared with free
phenylpyridine (8.63, 7.61, 7.48, 7.46, and 7.43) and diphenyl dis-
elenide (7.61 and 7.27) ligands, the phenylpyridine proton signals of
metallacycle were shifted towards downfield and aryl group proton
signals were shifted towards upfield except one doublet. The 1H NMR
spectrum of compound 4 showed one doublet, one triplet, one
multiplet for pyridyl group protons and the benzyl group protons
appeared as one doublet, one triplet, one multiplet and a singlet for
CH2 group. In compound 4, the pyridyl and aryl group proton signals
were shifted towards downfield when compared with free pyridine
and dibenzyl diselenide (7.29, 7.26, 7.22 and 3.83) ligands. 13C NMR
spectrum of compound 4 showed signals for terminal carbonyl
ligand) (1e5) via oxidative addition of SeeSe bond across ReeRe
bond by a facile reaction of rudimentary metal precursor with diaryl
diselenide and monodentate pyridine ligands.
2. Results and discussion
2.1. Synthesis of selenium bridged metallacycles 1e5 from rhenium
carbonyl, diaryl diselenide and monodendate pyridine ligands
Synthesis of selenium bridged Re(I) metallacycles proceeded
with Orthogonal-bonding approach, [38e40] i.e., simultaneous
incorporation of two aryl selenolate ligands to the equatorial sites of
fac-Re(CO)3 core with substitution of CO groups by rigid monotopic
N-donor ligands to the orthogonal axial site, resulting into hetero-
topic molecular tweezers. The formation of cis-[L(CO)3Re(m-SeR)2Re
(CO)3L] (1e5) was accomplished by the reaction of rhenium
carbonyl with diphenyl/dibenzyl diselenides and monodentate
ligands (L) like pyridine (py), 4-picoline (pic) and 4-phenylpyridine
(Phpy) in mesitylene medium (Scheme 1). Synthesis of metalla-
cycles 1 and 2 were also accompanied by the formation of trace
amount of trans isomers 1a and 2a respectively. Metallacycles 1e5
were soluble in common organic solvents and stable at room
temperature and they were characterised by spectroscopic and
crystallographic techniques to arrive the structural details.
groups at
around
benzyl group carbons resonated at
d
202.4 and 194.0 ppm with 1:2 ratio and the signals at
156.6e126.7 ppm were attributed to pyridyl group and
142.7e127.5 ppm andthe benzyl
d
d
CH2 was appeared at 31.1 ppm. Likewise, 1H NMR spectrum of
compound 5 displayed, two doublets for picolyl group protons and
two singlets for methyl and CH2 group protons. When compared to
uncoordinated ligand, the protons signals were shifted towards
downfield. 13C NMR spectrum of compound 5 exhibited signals
similar to that of compound 4 in addition to the CH3 group signal
observed at alkyl region. The UVeVis absorption spectra of 1e5 in
CH2Cl2 showed intense bands in the higher energy region at around
2.2. Spectroscopic characterisation of compounds 1e5
The IR spectra of compounds 1e5 in CH2Cl2 exhibited carbonyl
stretching at the region of 2027e1897 cmꢀ1 characteristic of facial
assembly of three terminal carbonyl groups (fac-Re(CO)3) in an
octahedrally coordinated metal centre [41]. 1H NMR spectra of
compounds 1e5 displayed appropriate signals for the pyridine
ligands andaryl groups bonded to bridging seleniumandthespectral
datawere includedin Experimental section. The 1H NMR spectrum of
compound 1 displayed, one doublet, two triplets for pyridyl group
protons and the phenyl group protons showed one doublet and two
triplets. When compared with free pyridine (8.60, 7.65 and 7.26 ppm)
and diphenyl diselenide (7.61 and 7.27) ligands, the pyridyl and
lmax 226e275 nm, that were assigned to
pep
* transition of the
ligands [18,37,42,43]. Metallacycles 1e5 upon excitation at their
respective ligand centred transitions exhibited moderate emissions
observed at around lmax 382e429 nm due to pep
* excited state of
the ligands [44,45].
2.3. Structural characterisation of 1, 1a, 2, 2a, 3 and 4
Single crystals of compounds 1, 1a, 2, 2a and 4 were obtained
by slow diffusion of hexane into concentrated solution of the
Scheme 1. Synthesis of selenium bridged dinuclear metallacycles 1e5.

A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
1611
compounds in dichloromethane at 5 ꢁC. Crystals of 3 were obtained
Table 2
Crystallographic data and structure refinement of 1a and 2a.
by slow cooling of warm and concentrated solution of 3 in mesi-
tylene to room temperature. A good quality single crystals of 1, 1a,
2, 2a, 3 and 4 were subjected to single crystal X-ray diffraction
studies. Details about data collection, solution and refinement were
summarized for 1e4 in Table 1 and for 1a and 2a in Table 2,
respectively. The molecular structure of 1, 1a, 2, 2a, 3 and 4 dis-
played a dinuclear metallacyclic structure, where each rhenium in
fac-Re(CO)3 is bonded to one pyridine ligand and two aryl seleno-
late groups and hence Re centres attained a distorted octahedral
geometry [38,41,46e48].
Compound
1a
2a
Empirical Formula
Formula weight
Crystal system
Temperature (K)
Space group
a (Å)
C42H30N3O9Re3Se3
1516.17
Triclinic
120(2) K
Pe1
9.4900(8)
10.2246(9)
23.7518(13)
95.082(6)
94.608(6)
107.080(8)
2180.6(3)
2
C30H24N2O6Re2Se2
1038.83
Triclinic
120(2)
Pe1
9.1312(4)
10.2140(4)
10.2958(4)
113.624(4)
109.647(4)
100.546(3)
3860.8(5)
1
484
2.239
10.257
ꢀ10, 10; ꢀ12,
11; ꢀ12, 12
3.31e25.00
b (Å)
c (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
Crystal structure of cis-[py(CO)3Re(m-SeC6H5)2Re(CO)3py] (1)
Volume (Å3)
Z
consists of Re2Se2 ring that is non-coplanar with a dihedral angle of
4.34ꢁ between the Re(1)eSe(1)eRe(2) and Re(1)eSe(1)#eRe(2)
planes. The Re/Re distance in Re2Se2 ring is 4.024 Å. The rhenium
metal centre has the bond distances of 2.6315(9) Å for Se(1)eRe(1),
2.18(1) Å for N(1)eRe(1), 1.92(1) Å for C(1)eRe(1) and 1.921(9) Å for
C(2)eRe(1). The octahedral geometry is associated with the bond
angles of 80.41(4)ꢁ for Se(1)eRe(1)eSe(1)#1, 84.7(2)ꢁ for N(1)eRe
(1)eSe(1), 93.4(4)ꢁ for C(1)eRe(1)eC(2), 91.3(3)ꢁ for C(1)eRe(1)e
Se(1), 174.7(4)ꢁ for C(1)eRe(1)eN(1), 90.4(3)ꢁ for C(2)eRe(1)eN(1)
and 173.5(3)ꢁ for C(2)eRe(1)eSe(1). The two pyridyl groups were
oriented in a cis conformation and stabilised by weak faceeface
F(000)
1404
2.309
10.867
Dcalc (mg mꢀ3
)
m
(mmꢀ1
)
h, k, l collected
ꢀ11,11; ꢀ11,
12; ꢀ28,28
3.00e25.00
Theta range for data
collection (ꢁ)
Crystal size (mm)
Reflections collected/unique
Rint
0.32 ꢂ 0.28 ꢂ 0.22
17078/7668
0.0752
0.23 ꢂ 0.21 ꢂ 0.17
7146/2707
0.0164
2707/0/191
R1 ¼ 0.0147,
wR2 ¼ 0.0374
1.065
R1 ¼ 0.0165,
wR2 ¼ 0.0384
1.103 and ꢀ0.669
Data/restraints/parameters
Final R indices
7668/0/541
R1 ¼ 0.0395,
wR2 ¼ 0.1266
1.102
R1 ¼ 0.0603,
wR2 ¼ 0.1385
2.934 and ꢀ2.330
pep stacking interaction with a distance of 3.638 Å at C(7) and C
[I > 2sigma(I)]
(10) carbons of two pyridyl groups (Fig. 1) [49e52]. The two phenyl
groups bonded to bridging selenium are present in a plane
perpendicular to that of pyridyl groups and bent away from the
Goodness-of-fit on F2
R indices (all data)
Largest difference in peak
Re2Se2 ring and pyridyl groups. Intermolecular CeH/
p interac-
and hole (e Åꢀ3
)
tions were observed in between C(6)eH(6) of pyridyl and C(11) and
C(12) of phenyl selenolate group of adjacent molecules with
a distance of 2.586 Å and 2.783 Å [38,53e55]. CeH/Se interactions
were observed between Se(1) present in the Re2Se2 ring and C(6)e
H(6) of pyridyl ring with a distance of 3.089 Å [56e58]. CeH/O
hydrogen bondings were viewed among C(8)eH(8) and C(9)eH(9)
of pyridyl ligand and C(4)eO(4), C(2)eO(2) of carbonyl groups with
a distance of 2.698 Å, 2.602 Å [59e61]. CeO/C (lp/p) interactions
were observed between C(4)eO(4) of carbonyl oxygen and C(5)
carbon of pyridyl ring with a distance of 3.079 Å [62].
Molecular structure of trans-[py(CO)3Re(m-SeC6H5)2Re(CO)3py]
(1a) showed that the two pyridyl ligands bonded to two rhenium
centres were oriented in a trans conformation. The crystal structure
of 1a consists of two sets of orientation for the phenyl selenolate
groups, where one set of arrangement displays the pyridyl and
phenyl selenolate groups trans to each other, whereas another set
of arrangement exhibits both phenyl groups in a cis position with
Table 1
Crystallographic data and structure refinement of 1e4.
Compound
1
2
3
4
Empirical Formula
Formula weight
Crystal system
Temperature (K)
Space group
a (Å)
C28H20N2O6Re2Se2
1010.78
Orthorhombic
150(2)
P n m a
23.467(2)
C30H24N2O6Re2Se2
1038.83
Orthorhombic
150(2)
P n m a
26.1649(10)
C40H28N2O6Re2Se2
1162.96
Monoclinic
150(2)
I 2/a
13.9147(11)
C30H24N2O6Re2Se2
1038.83
Monoclinic
120(2)
P 21/n
9.4734(2)
b (Å)
13.4773(12)
9.3549(10)
90
90
90
2958.7(5)
4
12.9805(4)
9.1883(4)
90
90
90
3120.7(2)
4
12.5534(10)
22.255(2)
90
107.737(11)
90
3702.7(6)
4
18.5774(5)
17.9572(7)
90
95.119(2)
90
c (Å)
a
b
g
(ꢁ)
(ꢁ)
(ꢁ)
Volume (Å3)
Z
3147.70(16)
4
F(000)
1872
2.269
10.679
1936
2.211
10.128
2192
2.086
6.424
1936
2.192
10.041
Dcalc (mg mꢀ3
)
m
(mmꢀ1
)
h, k, l collected
ꢀ27, 27; ꢀ16, 15; ꢀ11, 11
ꢀ31,31; ꢀ15, 15; ꢀ10, 10
ꢀ16, 16; ꢀ14, 14; ꢀ22, 26
ꢀ11, 11; ꢀ22, 22; ꢀ21, 21
3.08e25.00
0.32 ꢂ 0.30 ꢂ 0.27
22017/5529
0.0305
Theta range for data collection (ꢁ)
Crystal size (mm)
3.02e25.00
3.11e25.00
3.07e25.00
0.34 ꢂ 0.28 ꢂ 0.22
20008/2710
0.1993
0.33 ꢂ 0.28 ꢂ 0.21
23724/2860
0.0509
0.23 ꢂ 0.18 ꢂ 0.14
14024/3259
0.1066
Reflections collected/unique
Rint
Data/restraints/parameters
Final R indices [I > 2sigma(I)]
Goodness-of-fit on F2
2710/0/196
2860/7/211
3259/0/235
5529/0/379
R1 ¼ 0.0220, wR2 ¼ 0.0464
1.016
R1 ¼ 0.0577, wR2 ¼ 0.1435
R1 ¼ 0.0699, wR2 ¼ 0.1795
R1 ¼ 0.0431, wR2 ¼ 0.1261
1.040
1.157
1.211
R indices (all data)
R1 ¼ 0.0634, wR2 ¼ 0. 1484
4.270 and ꢀ3.475
R1 ¼ 0.0738, wR2 ¼ 0.1813
11.131 and ꢀ2.296
R1 ¼ 0.0597, wR2 ¼ 0.1756
2.917 and ꢀ4.630
R1 ¼ 0.0303, wR2 ¼ 0.0491
Largest difference in peak and hole (e Åꢀ3
)
0.965 and ꢀ1.194

1612
A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
Molecular structure of cis-[pic(CO)3Re(m-SeC6H5)2Re(CO)3pic]
(2) consists of Re2Se2 ring that is non-coplanar with a dihedral
angle of 4.67ꢁ between the Re(1)eSe(1)eRe(2) and Re(1)eSe(1)
#1eRe(2) planes. The Re/Re distance in Re2Se2 ring is 3.967 Å.
The rhenium metal centre has the bond lengths of 2.617(1) Å for Re
(1)eSe(1), 2.22(2) Å for Re(1)eN(1), 1.61(2)Å for Re(1)eC(1) and
1.90(2) Å for Re(1)eC(2). The octahedral geometry is associated
with the bond angles of 98.39(5)ꢁ for Re(1)eSe(1)eRe(2), 81.55(6)ꢁ
for Se(1)eRe(1)eSe(1)#1, 85.6(4)ꢁ for N(1)eRe(1)eSe(1), 83.6(1)ꢁ
for C(1)eRe(1)eC(2), 171.2(1)ꢁ for C(1)eRe(1)eN(1), 101.1(1)ꢁ for C
(1)eRe(1)eSe(1), 173.4(5)ꢁ for C(2)eRe(1)eSe(1) and 90.3(6)ꢁ for C
(2)eRe(1)eN(1). The two picoline groups are oriented in a cis
conformation and stabilised by weak faceeface
pep stacking
interaction with a distance of 3.818 Å at C(13) and C(17) carbons of
two picoline groups (Fig. 3). The two phenyl groups bonded to
bridging selenium are oriented in a plane perpendicular to that of
two picoline groups and bent away from the Re2Se2 ring and
picoline groups. The existence of CeH/p interactions were found
in between methyl group present in the picoline ligand and phenyl
selenolate carbon with a distance of 2.898 Å (C(18)eH(18C)/C(5)),
2.860 Å (C(18)eH(18C)/C(7)), 2.836 Å (C(18)eH(18A)/C(7)) and
2.855 Å (C(18)eH(18A)/C(6)). The Re2Se2 ring containing sele-
nium atom interacted with C(16)eH(16) of picoline moiety by
CeH/Se interaction with a distance of 2.989 Å. CeH/O inter-
molecular contacts were observed among the carbonyl groups and
C(11)eH(11), C(12)eH(12) and C(14)eH(14A) of picoline ligand
with a distance of 2.535 Å, 2.627 Å and 2.612 Å respectively.
Fig. 1. Molecular structure of 1. The thermal ellipsoids are drawn at the 50% probability
level.
the pyridyl groups occupying the trans positions (Fig. 2). The
rhenium metal centre has the bond lengths of 2.650(1) Å for Re
(1)eSe(1), 2.659(1) Å for Re(1)eSe(2), 2.228(8) Å for Re(1)eN(1),
1.91(1) Å for Re(1)eC(1), 1.93(1) Å for Re(1)eC(2) and 1.940(1) Å for
Re(1)eC(3). The octahedral geometry is associated with the bond
angles of 80.86(3)ꢁ for Se(1)eRe(1)eSe(2), 93.1(2)ꢁ for N(1)eRe
(1)eSe(2), 91.9(2)ꢁ for N(1)eRe(1)eSe(1), 89.2(4)ꢁ for C(1)eRe(1)e
C(3), 88.4(3)ꢁ for C(1)eRe(1)eSe(1), 178.4(4)ꢁ for C(1)eRe(1)eN(1),
88.5(3)ꢁ for C(1)eRe(1)eSe(2), 91.5(4)ꢁ for C(2)eRe(1)eC(3), 91.5
(4)ꢁ for C(2)eRe(1)eN(1) and 93.0(3)ꢁ for C(2)eRe(1)eSe(1).
CeO/C (lp/p) interactions were observed between C(15) and C
(16) carbons of pyridyl ring with carbonyl group oxygen by the
distances of 2.992 Å and 3.158 Å.
Molecular structure of trans-[pic(CO)3Re(m-SeC6H5)2Re(CO)3pic]
(2a) showed that the two picolyl ligands bonded to two rhenium
centres are oriented in a trans conformation. The two phenyl
selenolate groups are oriented towards two picolyl ligands. Overall,
the two picoline and two phenyl groups are arranged trans to each
other (Fig. 4). The rhenium metal centre has the bond distances of
2.6205(4) Å for Re(1)eSe(1), 2.6493(3) Å for Re(1)eSe(1)#1, 2.227
(3) Å for Re(1)eN(1), 1.910(3) Å for Re(1)eC(1), 1.910(3) Å for Re
(1)eC(2) and 1.904(3) Å for Re(1)eC(3). The octahedral geometry is
associated the bond angles of 99.43(1)ꢁ for Re(1)eSe(1)eRe(1)#1,
80.57(1)ꢁ for Se(1)eRe(1)eSe(1)#1, 82.21(7)ꢁ for N(1)eRe(1)eSe
(1), 175.6(1)ꢁ for C(1)eRe(1)eN(1), 95.9(1)ꢁ for C(1)eRe(1)eSe(1),
92.1(1)ꢁ for C(2)eRe(1)eC(1), 91.9(1)ꢁ for C(2)eRe(1)eN(1) and
93.3(1)ꢁ for C(2)eRe(1)eSe(1). Intermolecular CeH/O contacts
were observed among the carbonyl groups and picoline moiety
CeH/p interactions were observed in between pyridyl and phenyl
selenolate group of adjacent molecules with a distance of 2.711 Å
(C(7)eH(7)/C(40)), 2.697 Å (C(27)eH(27)/C(18)) and 2.803 Å
(C(27)eH(27)/C(19)). CeH/O hydrogen bondings were viewed
among the carbonyl groups and phenyl selenolate ligand with
a distance of 2.683 Å (C(10)eH(10)/O(9)), 2.588 Å (C(11)eH(11)/
O(7)) and 2.449 Å (C(12)eH(12)/O(8)). CeH/Se interactions
were observed at C(35)eH(35) and C(19)eH(19) of pyridyl group
with selenium atom with a distance of 3.075 Å and 3.094 Å
respectively. CeO.C (lp/p) interactions were observed among
the carbonyl and pyridine groups with the contact distances of
3.177 Å (O(5)/C(18)) and 3.215 Å (O(6)/C(6)).
Fig. 2. Molecular structure of 1a. The thermal ellipsoids are drawn at the 50% probability level.

A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
1613
ligands with a distance of 2.684 Å and 2.551 Å. In addition, hydrogen
bonding interactions were observed between C(7)eH(7) of benzyl
moiety and carbonyl group with a distance of 2.491 Å. Further,
CeO/C (lp/p) interaction was observed between C(18) carbon of
phenylpyridine ligand and oxygen atom of carbonyl group with
a distance of 3.214 Å. Packing diagram of metallacycle 3 was given in
Fig. 7.
While comparing the molecular structures of 1, 2 and 3, when
the size of substituent is changed from hydrogen, methyl to bulky
phenyl group at para position of the pyridine ligands, the space
between two phenyl rings has been found largely increased in 3.
Here, the steric hindrance imposed by phenyl groups, predomi-
nates the pep stacking interaction and resulted in the expansion of
space between phenyl rings with creation of a void in between two
phenylpyridine ligands. The increase in size of void in between
Phpy ligands, imparts V shape to cis-[Phpy(CO)3Re(m-SeC6H5)2Re
(CO)3Phpy] (3). The Re/Re distance has decreased from 1 to 3 as
4.029 Å, 3.967 Å to 3.910 Å. Also, the planarity of Re2Se2 metal core
has been distorted and bent outwards. The dihedral angle between
the planes of Re(1)eSe(1)eRe(2) and Re(1)eSe(2)eRe(2) has
increased from 1 to 3 as 4.34ꢁ, 4.67ꢁ to 27.92ꢁ. In compound 3, Re
(1)eSe(1)eRe(1)#1 bond angle is decreased to 95.69(3)ꢁ from
99.56ꢁ(3) as in 1 and Se(1)eRe(1)eSe(1)#1 bond angle is decreased
to 77.35(4)ꢁ from 80.41(4)ꢁ as in 1. The phenyl groups at para
position of the pyridyl ring has been twisted by angle of 30.02ꢁ with
respect to the pyridyl groups.
The void present in metallacycle 3 has potential to serve as
a host site to exhibit molecular recognition capabilities with some
planar aromatic molecules and few metal ions. The hosteguest
interaction studies of phenylpyridine based rhenium metallacycle
have been carried out with aromatic hydrocarbons like pyrene and
triphenylene using 1H NMR spectroscopic technique. The chemical
shift values of pyridyl protons of metallacycle 3 were shifted
towards upfield on treatment with planar guest molecules such as
pyrene and triphenylene. Similar upfield shifts have been observed
in the binding of aromatic guests to the Pd cage, Au and Re rect-
angle [63]. In metallacycles 3, the pyridyl protons of Phpy are
affected more than other protons, indicating that pyridyl protons
Fig. 3. Molecular structure of 2. The thermal ellipsoids are drawn at the 50% proba-
bility level.
with a distance of 2.536 Å (C(14)eH(14)/O(1)), 2.372 Å (C(11)eH
(11)/O(3)), 2.645 Å (C(7)eH(7)/O(1)) and 2.533 Å (C(13)eH
(13B)/O(2)). Packing diagram of metallacycle 2a was given in
Fig. 5.
Molecular structure of cis-[Phpy(CO)3Re(m-SeC6H5)2Re(CO)3Phpy]
(3) consists of Re2Se2 ring that is non-coplanar with a dihedral angle
of 27.92ꢁ between the Re(1)eSe(1)eRe(1)#1 and Re(1)eSe(1)#1eRe
(1)#1 planes and the Re/Re distance is 3.910 Å. The rhenium metal
centre has the bond distances of 2.630(1) Å for Re(1)eSe(1), 2.644
(1) Å for Re(1)eSe(1)#1, 2.221(7) Å for Re(1)eN(1), 1.91(1) Å for Re
(1)eC(1) and Re(1)eC(2), 1.86(1) Å for Re(1)eC(3). The octahedral
geometry isassociated with the bondangles of 77.35(4)ꢁ for Se(1)eRe
(1)eSe(1)#1, 95.69(3)ꢁ for Re(1)eSe(1)eRe(1)#1, 84.7(2)ꢁ for N(1)e
Re(1)eSe(1), 88.6(2)ꢁ for N(1)eRe(1)eSe(1)#1, 92.1(4)ꢁ for C(1)eRe
(1)eN(1), 94.8(4)ꢁ for C(1)eRe(1)eSe(1), 89.2(4)ꢁ for C(2)eRe(1)eC
(1), 176.1(4)ꢁ for C(2)eRe(1)eN(1), 99.0(4)ꢁ for C(2)eRe(1)eSe(1),
91.2(5)ꢁ for C(3)eRe(1)eC(1) and 92.8(4)ꢁ for C(3)eRe(1)eN(1). The
crystal structure of 3 exhibits a cis orientation of two phenylpyridine
rings with expansion of distance about 6.781 Å at C(12)eC(12)
are more shielded by the
p ring of the guests. These observations
reveal that the added pyrene and triphenylene interact with pyridyl
protons of Phpy ligand of metallacyle 3. The binding constants (K)
for pyrene and triphenylene with 3 have been found as 6.8 and
10.5 Mꢀ1 respectively that indicate the weak binding of metalla-
cycle 3 with guest molecules.
carbons of pyridyl groups (Fig. 6) Intermolecular CeH/p links were
observed betweenphenylpyridine and phenyl selenolate groups with
a distance of 2.825 Å (C(8)eH(8)/C(12)) and 2.852 Å (C(11)eH(11)/
C(5)). CeH/O hydrogen bondings were observed among the
carbonyl group and C(19)eH(19), C(16)eH(16) of phenylpyridine
Molecular structure of cis-[py(CO)3Re(m-SeCH2C6H5)2Re
(CO)3py] (4) consists of Re2Se2 ring that is non-coplanar with
a dihedral angle of 8.09ꢁ between the Re(1)eSe(1)eRe(2) and Re
(1)eSe(2)eRe(2) planes. The Re/Re distance in Re2Se2 ring is
3.954 Å. The rhenium centres has bond lengths of 2.6292(4) Å for
Re(1)eSe(1), 2.6316(4) Å for Re(1)eSe(2), 2.236(3) Å for Re(1)eN
(2), 1.921(5) Å for Re(1)eC(1), 1.917(5) Å for Re(1)eC(2) and 1.908
(5) Å for Re(1)eC(3). The octahedral geometry is associated with
the bond angles of 81.91(1)ꢁ for Se(1)eRe(1)eSe(2), 93.4(2)ꢁ for C
(1)eRe(1)eN(2), 94.0(1)ꢁ for C(1)eRe(1)eSe(1), 175.2(1)ꢁ for C(1)e
Re(1)eSe(2), 91.3 (1)ꢁ for C(2)eRe(1)eN(2), 175.4 (1)ꢁ for C(2)eRe
(1)eSe(1), 92.1(1)ꢁ for C(3)eRe(1)eSe(1) and 91.0(1)ꢁ for C(3)eRe
(1)eSe(2). The two pyridyl groups are oriented in a cis conforma-
tion and stabilised by weak faceeface
pep stacking interaction
with a distance of 3.876 Å at C(9) and C(21) carbons of two pyridine
groups (Fig. 8). The two benzyl groups bonded to bridging sele-
nium are oriented in a plane perpendicular to that of the two
pyridyl groups and bent away from the Re2Se2 ring and pyridine
groups. The intermolecular CeH/p interactions were observed
between pyridyl and benzyl selenolate groups by a distance of
Fig. 4. Molecular structure of 2a. The thermal ellipsoids are drawn at the 40% prob-
ability level.
2.725 Å (C(24)eH(24A)/C(15)) and 2.867 Å (C(21)eH(21)/C(15)).

1614
A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
Fig. 5. Packing diagram of compound 2a viewed along a axis with CeH/O hydrogen bonding interactions.
CeH/O hydrogen bonding interactions were observed between
the carbonyl groups and benzyl selenolate and pyridyl moiety with
a distance of 2.710 Å (C(18)eH(18)/O(5)), 2.634 Å (C(21)eH(21)/
6700 FT-IR spectrometer. 1H and 13C NMR were recorded on a Avans
Bruker 400 MHz spectrometer. Absorption spectrawererecorded on
a Shimadzu UV-2450 UVeVis spectrophotometer. Emission spectra
were recorded on a Fluorolog Horiba jobin Yuvon SPEX-F311 spec-
trometer. Elemental analyses were performed using Elementar
Micro Cube CHN analyzer.
O(2)) and 2.457 Å (C(22)eH(22)/O(4)). CeO/C (lp/p) interac-
tions were observed between C(4)eO(4), C(5)eO(5) of carbonyl
oxygen and C(11) and C(7) carbons of pyridyl ring with a distance
of 3.089 Å, 3.140 Å.
3. Experimental
3.2. Synthesis of [L(CO)3Re(m-SeR)2Re(CO)3L], general procedure
3.1. Instruments and materials
A mixture of Re2(CO)10 (0.6 mmol) and diaryl diselenide
(0.4 mmol) were taken in a 50 ml two neck Schlenk flask and fitted
with a reflux condenser. The system was evacuated and purged with
N2. Monodentate pyridine ligand (L) (0.8e150 mmol) and 40e50 ml
of mesitylene was added under N2 atmosphere. The reaction
mixture was heated to 130 ꢁC under N2 for 16e39 h and allowed to
cool to room temperature. The mesitylene was removed by vacuum
distillation and the solid mixture was washed with hexane, chro-
matographed on silica gel column using dichloromethane and
All reactions were carried out under dry, oxygen-free N2 atmo-
sphere using standard schlenk techniques. The starting materials
were purchased from Strem Chemicals, Inc. and SigmaeAldrich
Chemicals. Rhenium carbonyl, diphenyl diselenide, dibenzyl dis-
elenide, 4-phenylpyridine were used as received. Pyridine, 4-pico-
line, mesitylene and other solvents were dried using literature
procedure prior to use. IR spectra were taken on a Thermo Nicolet
Fig. 6. Molecular structure of 3. The thermal ellipsoids are drawn at the 50% probability level.

A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
1615
Fig. 7. Packing diagram of 3 viewed along a axis.
hexane as eluent to gave white colour solids of [L(CO)3Re(
(CO)3L] metallacycles.
m
-SeR)2Re
flask and fitted with a reflux condenser. The system was evacuated
and purged with N2. Freshly distilled pyridine (4 ml, 49 mmol) and
mesitylene (45 ml) were added under N2 atmosphere. The reaction
mixture was heated to heated to 130 ꢁC under N2 for 17 h and
allowed to cool to room temperature. The solvent was removed by
vacuum distillation and the reaction mixture was washed with
hexane, chromatographed on silica gel column using dichloro-
methane and hexane as eluent (2:3) to gave white colour solid of
3.3. Synthesis of cis-[py(CO)3Re(m-SeC6H5)2Re(CO)3py] (1)
A mixture of Re2(CO)10 (392 mg, 0.6 mmol) and diphenyl dis-
elenide (124 mg, 0.4 mmol) were taken in a 50 ml two neck Schlenk
cis-[py(CO)3Re(m-SeC6H5)2Re(CO)3py] (1). Yield: 278 mg, 56%
(based on Re2(CO)10). Anal. Calcd. for C28H20N2O6Re2Se2: C 33.27; H
1.99; N 2.77. Found: C 33.32; H 1.96; N 2.74%. 1H NMR (400 MHz,
CD3COCD3, ppm):
d
9.15 (d, 4H, H2 (py), 3J ¼ 6.8 Hz), 8.01 (t, 2H, H4
(py), 3J ¼ 7.6 Hz) 7.92 (d, 4H, H2 (ph), 3J ¼ 7.2 Hz), 7.48 (t, 4H, H3 (py),
3J ¼ 6.4 Hz), 7.35 (t, 4H, H3 (ph), 3J ¼ 7.4 Hz), 7.26 (t, 2H, H4 (ph),
3J ¼ 7.4 Hz). 13C NMR (100 MHz, CD3COCD3, ppm):
d 200.2, 195.1
(1:2, CO group),157.1,139.8,126.8 (py) 133.9,131.5,129.5,127.2 (ph).
ab
UVeVis. {
l
(CH2Cl2)/(nm) (
3
) dm3 molꢀ1 cmꢀ1}: 227 (33550)
max
em
(LIG), 267 (23550) (LIG). Emission:
l
max
(CH2Cl2)/(nm) 406. IR
(CH2Cl2): n(CO) 2027 (m) 2011 (vs) 1927 (m) 1901 (vs) cmꢀ1. The
trans isomer of [py(CO)3Re( -Se C6H5)2Re(CO)3py] (1a) was isolated
m
in trace amount. IR (CH2Cl2): n(CO) 2013(vs), 1914(vs) cmꢀ1. 1H NMR
(400 MHz, CDCl3, ppm):
d
8.95 (d, 4H, H2 (py), 3J ¼ 6.4 Hz), 7.72
(t, 2H, H4 (py), 3J ¼ 7.6 Hz), 7.44 (d, 4H, H3 (py), 3J ¼ 6.4 Hz), 7.31
(t, 2H, H4 (ph), 3J ¼ 7.2 Hz), 7.15 (t, 4H, H2 (ph), 3J ¼ 6.8 Hz), 7.08
(t, 4H, H3 (ph)).
3.4. Synthesis of cis-[pic(CO)3Re(m-SeC6H5)2Re(CO)3pic] (2)
Compound 2 was prepared using Re2(CO)10 (392 mg, 0.6 mmol),
diphenyl diselenide (124 mg, 0.4 mmol) and 4-picoline (2 ml,
20 mmol) in mesitylene (45 ml) by following the procedure adopted
Fig. 8. Molecular structure of 4. The thermal ellipsoids are drawn at the 40% proba-
bility level.
for 1. It was isolated as white solid of cis-[picRe(CO)3(m-SeC6H5)2Re

1616
A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
(CO)3pic] (2). Yield: 268 mg, 55% (based on Re2(CO)10). Anal. Calcd.
3.7. Synthesis of cis-[pic(CO)3Re(m-SeCH2C6H5)2Re(CO)3pic] (5)
for C30H24N2O6Re2Se2: C 34.68, H 2.32, N 2.69. Found: C 34.60, H
2.35, N 2.64%. 1H NMR (400 MHz, CD3COCD3, ppm):
d
8.91 (d, 4H, H2
Compound 5 was prepared using Re2(CO)10 (392 mg, 0.6 mmol),
dibenzyl diselenide (136 mg, 0.4 mmol) and 4-picoline (1 ml,
10 mmol) in mesitylene (50 ml) by following the procedure
adopted for 1. It was isolated as pale yellow colour solid of cis-[picRe
(pic), 3J ¼ 6.8 Hz), 7.86 (t, 4H, H2 (ph), 3J ¼ 7.2 Hz), 7.27 (t, 4H, H3 (ph),
3J ¼ 7.6 Hz), 7.23 (m, 6H, H3 (pic), & H4 (ph)), 2.44 (s, 6H, CH3).
ab
UVeVis. {
l
(CH2Cl2)/(nm) (
3
) dm3 molꢀ1 cmꢀ1}: 228 (35000)
max
em
(LIG), 267 (25200) (LIG). Emission:
l
max
(CH2Cl2)/(nm) 410. IR
(CO)3(m-SeCH2C6H5)2Re(CO)3pic] (5). Yield: 16 mg, 9% (based on
(CH2Cl2): n(CO) 2026(s), 2011(vs), 1926(m), 1900(vs) cmꢀ1. The trans
isomer of [picRe(CO)3( -SeC6H5)2Re(CO)3pic] (2a) was isolated in
Re2(CO)10). Anal. Calcd. for C32H28N2O6Re2Se2: C 36.02, H 2.64,
m
N 2.62. Found: C 36.13, H 2.59, N 2.64%. 1H NMR (400 MHz, CDCl3,
trace amount. IR(CH2Cl2): n(CO) 2012(vs), 1911(s) cmꢀ1
.
1H NMR
ppm):
d
8.59 (d, 4H, H2 (pic), 3J ¼ 6.4 Hz), 7.48 (d, 4H, H2 (ph),
(400 MHz, CDCl3, ppm):
d
8.75 (d, 4H, H2 (pic), 3J ¼ 6.8 Hz), 7.44
3J ¼ 6.8 Hz), 7.31 (t, 4H, H3 (ph), 3J ¼ 7.2 Hz), 7.25 (t, 2H, H2 (ph),
3J ¼ 7.2 Hz), 6.82 (d, 4H, H3 (pic), 3J ¼ 6.4 Hz), 4.43 (s, 4H, CH2
(benz)), 2.30 (s, 6H, CH3 (pic)). 13C NMR (100 MHz, CDCl3, ppm):
(d, 4H, H3 (pic)), 7.07 (dt, 6H, H2 & H4 (ph)), 6.94 (d, 4H, H3 (ph),
3J ¼ 6.4 Hz), 2.34 (s, 6H, CH3).
d
201.0, 193.4 (1:2, CO group), 155.6, 149.2, 125.8, 21.2 (pic) 142.1,
ab
129.0, 128.7, 126.7 (ph) 30.8 CH2 (benz). UVeVis. {
l
max
(CH2Cl2)/
3.5. Synthesis of cis-[Phpy(CO)3Re(m-SeC6H5)2Re(CO)3Phpy] (3)
(nm) (
3
) dm3 molꢀ1 cmꢀ1}: 227 (39550), 275 (16550). Emission:
(CH2Cl2)/(nm) 429. IR(CH2Cl2): n(CO) 2019(m), 2004(vs), 1915
em
l
max
Compound 3 was prepared using Re2(CO)10 (392 mg, 0.6 mmol),
diphenyl diselenide (124 mg, 0.4 mmol) and 4-phenylpyridine
(4 ml, 49 mmol) in mesitylene (50 ml) following the procedure
(m), 1897(s) cmꢀ1
.
3.8. Crystal structure determinations
adopted for 1. It was isolated as white solid of cis-[Phpy(CO)3Re(m-
Se C6H5)2Re(CO)3Phpy] (3). Yield: 102 mg, 30% (based on
Re2(CO)10). Anal. Calcd. for C40H28N2O6Re2Se2: C 41.31, H 2.43, N
2.41. Found: C 40.97, H 2.46, N 2.44%. 1H NMR (400 MHz, CDCl3,
Crystals of 1, 1a, 2, 2a and 4 suitable for single crystal X-ray
crystallography were obtained by slow diffusion of hexane into
CH2Cl2 solution. Crystals of 3 were grown from mesitylene solution.
Single crystal X-ray structural studies were performed on Oxford
Diffraction XCALIBUR-S CCD equipped diffractometer with an
Oxford Instruments low-temperature attachment. Data were
ppm):
d
9.15 (d, 4H, H2 (Phpy), 3J ¼ 6.8 Hz), 7.89 (d, 4H, H2 (ph),
3J ¼ 8.4 Hz), 7.68 (d, 4H, H3 (Phpy), 3J ¼ 6.8 Hz), 7.58 (d, 4H, H20
(Phpy), 3J0¼ 8.4 Hz), 7.40 (t, 2H, H40 (ph), 3J ¼ 7.4 Hz), 7.32 (m, 8H, H3
ab
(ph) & H3 (Phpy)), 7.22 (t, 2H, H4 (Phpy), 3J ¼ 7.8 Hz). UVeVis. {
l
max
collected at 150(2) K using graphite-monochromated Mo Ka radi-
(CH2Cl2)/(nm) (
(LIG). Emission:
3
) dm3 molꢀ1 cmꢀ1}: 226 (36550) (LIG), 266 (43650)
ation (lf ¼ 0.71073 Å). The strategy for the Data collection was
evaluated by using the CrysAlisPro CCD software. The data were
collected by the standard ‘phi-omega scan’ techniques, and were
scaled and reduced using CrysAlisPro RED software. The structures
were solved by direct methods using SHELXS-97 and refined by full
matrix least squares with SHELXL-97 [64], refining on F2. The
positions on all the atoms were obtained by direct methods. All
non-hydrogen atoms were refined anisotropically. The hydrogen
atoms were placed in geometrically constrained positions and
refined with isotropic temperature factors, generally 1.2 ꢂ Ueq of
their parent atoms.
em
l
(CH2Cl2)/(nm) 405 and 428. IR(CH2Cl2) : n(CO)
max
2026(s), 2011(vs), 1927(m), 1901(vs) cmꢀ1. The trans isomer of
[Phpy(CO)3Re( -Se C6H5)2Re(CO)3Phpy] was isolated in trace
amount. IR(CH2Cl2) : n(CO) 2012(vs), 1912(s) cmꢀ1
Molecular recognition properties of cis-[Phpy(CO)3Re(
m
.
m-
SeC6H5)2Re(CO)3Phpy] (3) with pyrene and triphenylene have been
studied using 1H NMR spectroscopic technique by keeping the host
(3) concentration (0.46 ꢂ 10ꢀ3 M) as constant and increasing the
guest (pyrene) concentration (35.7 ꢂ 10ꢀ4e38.0 ꢂ 10ꢀ3 M) and
(triphenylene) (6.9 ꢂ 10ꢀ3e36.8 ꢂ 10ꢀ3 M) respectively in CDCl3.
The chemical shift values of pyridyl protons of metallacycle 3 have
been found to be shifted towards upfield by adding pyrene and
triphenylene. The binding constant (K) (pyrene, K ¼ 6.8 Mꢀ1; tri-
phenylene, K ¼ 10.5 Mꢀ1) for these hosteguest interactions were
evaluated on the basis of BenesieHildebrand relationship by using
curve fitting method [63].
4. Conclusion
In conclusion, we have demonstrated the spontaneous associ-
ation of six components into a metallacycle containing pyridyl
ligands, via the tandem addition of SeeSe bond across ReeRe bond.
The molecular structure of compounds 1, 1a, 2, 2a, 3 and 4 have
been elucidated by single crystal X-ray diffraction analysis. Studies
towards the change of substituents at para position of pyridyl ring,
by bulky phenyl groups pursues disruption of soft interaction
leading to the expansion of void in compound 3. We have
concluded that this methodology is an effective and comparatively
expedient route the class of compounds and the novel metallacycle
having a shape of a molecular tweezer exhibit molecular recogni-
tion properties. The one-pot synthetic methodology paves strategy
for the design and synthesis of novel metallacyclophanes, when
multidentate pyridine ligands are used and the research works in
this direction are in progress.
3.6. Synthesis of cis-[py(CO)3Re(m-SeCH2C6H5)2Re(CO)3py] (4)
Compound was prepared using Re2(CO)10 (392 mg,
4
0.6 mmol), dibenzyl diselenide (136 mg, 0.4 mmol) and pyridine
(12 ml, 150 mmol) in mesitylene (40 ml) by following the
procedure adopted for 1. It was isolated as white solid of cis-
[pyRe(CO)3(m-Se CH2C6H5)2Re(CO)3py] (4). Yield: 149 mg, 69%
(based on Re2(CO)10). Anal. Calcd. for C30H24N2O6Re2Se2: C 34.69,
H 2.33, N 2.70. Found: C 34.78, H 2.31, N 2.74%. 1H NMR
(400 MHz, CD3COCD3, ppm):
d
8.82 (d, 4H, H2 (py), 3J ¼ 6.4 Hz),
7.86 (t, 4H, H3 (py), 3J ¼ 7.6 Hz), 7.51 (d, 4H, H2 (ph), 3J ¼ 8.4 Hz),
7.32 (m, 8H, H3 (py & ph)), 7.25 (t, 2H, H4 (ph), 3J ¼ 7.2 Hz), 4.46
(s, 4H, CH2 (benz)). 13C NMR (100 MHz, CD3COCD3, ppm):
d
202.4,
Acknowledgement
194.0 (1:2, CO group), 156.6, 139.4, 126.7 (py) 142.7, 129.6, 129.5,
ab
127.5 (ph), 31.1 CH2 (benz). UVeVis. {
l
(CH2Cl2)/(nm) (
3
)
We thank the Department of Science and Technology, Govern-
ment of India for financial support. We are grateful to the Central
Instrumentation Facility, Pondicherry University for providing
spectral data.
max
dm3 molꢀ1 cmꢀ1}: 227 (36950) (LIG), 272 (16850) (LIG). Emis-
em
sion:
l
(CH2Cl2)/(nm) 382. IR (CH2Cl2): n(CO) 2017(m), 2000
max
(vs), 1917(m), 1902(s) cmꢀ1
.

A. Vanitha et al. / Journal of Organometallic Chemistry 696 (2011) 1609e1617
1617
[31] E. Becker, K. Mereiter, R. Schmid, K. Kirchner, Organometallics 23 (2004)
2876e2883.
Appendix A. Supplementary material
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Organometallics 14 (1995) 2277e2287.
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