Acyclic tetrachalcogenoether ligands tethered with bulky substituents: Their syntheses and coordination chemistry

Article abstract of DOI:10.1016/j.jorganchem.2008.01.016

New o-phenylene-bridged tetrachalcogenoether ligands tethered with an extremely bulky substituent, 2,4,6-tris[bis(trimethylsilyl)methyl]phenyl (Tbt) group, [TbtE(o-phenylene)Se]₂(o-phenylene) (3: E = S, 4: E = Se), were synthesized. Complexation reactions of 3 and 4 with Na₂PdCl₄ gave the corresponding dichloropalladium(II) complexes 7 and 8. X-ray structural analysis of 7 and 8 indicated that the central palladium metals are in a distorted octahedral environment, where the two inner selenium atoms and the two chlorine atoms form a square planar arrangement around the palladium metal and the two terminal chalcogen atoms weakly coordinate to the palladium center at the axial positions. The AIM calculations also supported the existence of the interaction between the palladium and the terminal chalcogen atoms in the crystalline state. On the other hand, the ⁷⁷Se NMR spectra suggested that there are no or very weak interactions between the palladium and the terminal chalcogen atoms in solution. The UV/Vis spectra of 7, 8, and related compounds imply the possibility of weak interaction between the terminal selenium atoms and the palladium center in solution.

Full text of DOI:10.1016/j.jorganchem.2008.01.016

Available online at www.sciencedirect.com
Journal of Organometallic Chemistry 693 (2008) 1225–1232
www.elsevier.com/locate/jorganchem
Acyclic tetrachalcogenoether ligands tethered with bulky
substituents: Their syntheses and coordination chemistry
Toru Isobe, Yoshiyuki Mizuhata, Norihiro Tokitoh *
Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
Received 6 December 2007; received in revised form 10 January 2008; accepted 11 January 2008
Available online 17 January 2008
Abstract
New o-phenylene-bridged tetrachalcogenoether ligands tethered with an extremely bulky substituent, 2,4,6-tris[bis(trimethyl-
silyl)methyl]phenyl (Tbt) group, [TbtE(o-phenylene)Se]2(o-phenylene) (3: E = S, 4: E = Se), were synthesized. Complexation reactions
of 3 and 4 with Na2PdCl4 gave the corresponding dichloropalladium(II) complexes 7 and 8. X-ray structural analysis of 7 and 8 indicated
that the central palladium metals are in a distorted octahedral environment, where the two inner selenium atoms and the two chlorine
atoms form a square planar arrangement around the palladium metal and the two terminal chalcogen atoms weakly coordinate to the
palladium center at the axial positions. The AIM calculations also supported the existence of the interaction between the palladium and
the terminal chalcogen atoms in the crystalline state. On the other hand, the 77Se NMR spectra suggested that there are no or very weak
interactions between the palladium and the terminal chalcogen atoms in solution. The UV/Vis spectra of 7, 8, and related compounds
imply the possibility of weak interaction between the terminal selenium atoms and the palladium center in solution.
Ó 2008 Elsevier B.V. All rights reserved.
Keywords: Polychalcogenoether ligand; Selenium; Palladium complex; 77Se NMR spectra; Bulky substituent
1. Introduction
the case of palladium(II) complexes, they generally have
planar four-coordinate structures [3], though some six-
coordinate structures have been reported [4].
Crown ethers are especially significant in the field of
molecular recognition, since they have an effective size-
selectivity for alkali and alkaline earth metals, and their
complexes are soluble in organic solvent; alkali and alka-
line earth metals are generally difficult to solvate in organic
solvent [1].
In contrast to the development of crown ether chemis-
try, the chemistry of cyclic polychalcogenoethers, i.e.,
crown ethers containing sulfur or selenium atoms instead
of oxygen atoms, has not been extensively developed so
far. The synthesis of some cyclic polythio- and polysele-
no-ether ligands and their coordination modes were
reported [2]. In contrast to the crown ethers, cyclic poly-
chalcogenoethers prefer complexation with transition met-
als rather than that with alkali or alkaline earth metals. In
As for acyclic polychalcogenoethers, some examples
have been reported so far [5], but their coordination and
detachment of transition metal complexes are too flexible
[6]. This leads to the difficulty of the synthesis and isolation
of the transition metal complexes with acyclic polychalcog-
enoether ligands. Consequently, the studies of acyclic poly-
chalcogenoether ligands are still elusive and their
properties have not been disclosed yet so far.
Recently, we have succeeded in the syntheses of the
acyclic tetrachalcogenoether ligands 1 and 2, bearing an
extremely bulky substituent, 2,4,6-tris[bis(trimethylsilyl)-
methyl]phenyl (Tbt) group, at both terminal chalcogen
atoms, and their dichloropalladium(II) complexes 5 and
6, respectively [7,8]. These complexes had a pseudo six-
coordinate structure, in which the central two chalcogen
atoms in tetrachalcogenoether ligand and two chlorine
atoms were arranged in a square planar fashion around
*
Corresponding author. Fax: +81 774 38 3209.
E-mail address: tokitoh@boc.kuicr.kyoto-u.ac.jp (N. Tokitoh).
0022-328X/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2008.01.016

1226
T. Isobe et al. / Journal of Organometallic Chemistry 693 (2008) 1225–1232
Scheme 1.
Chart 1.
compound 11 was difficult to isolate, it was used in the next
reaction without further purification. The coupling reac-
tions of 11 or 12 with 1,2-diiodobenzene gave the expected
ligand 3 (3% from 9) or 4 (32% from 12) together with the
mono-coupling products 13 (ꢀ50%) or 14 (56%). Ligand 4
was also obtained by the coupling reaction of 12 with 14
using Cu2O in refluxing 2,4,6-trimethylpyridine.
the palladium(II) atom and the terminal chalcogen atoms
coordinated weakly to the palladium(II) atom. These are
very few examples for six-coordinate structures of neutral
palladium(II) complexes. In addition, selenoethers complex
6 had an advantage that the 77Se NMR spectroscopic anal-
yses of their complexes give useful information in solution
about the characters of the coordination bonds between the
selenium atoms and the transition metal center. Here, we
reported the syntheses of new acyclic tetrachalcogenoether
ligands 3 and 4 and their complexes 7 and 8. Successful iso-
lation of 7 and 8 in addition to the previously reported 5
and 6 enabled us to elucidate the coordination ability of
polychalcogenoethers systematically (see Chart 1).
1
Ligands 3 and 4 were characterized based on H, 13C,
and 77Se NMR and mass spectra together with the result
of elemental analysis.
2.2. Syntheses and structures of palladium(II) complexes 7
and 8
The reactions of ligands 3 and 4 with Na2PdCl4 in eth-
anol at room temperature afforded the corresponding
dichloropalladium complexes 7 and 8, respectively, as
orange crystals (Scheme 2). The structures of 7 and 8 were
fully established by 1H, 13C, and 77Se NMR and mass spec-
tra, elemental analysis, and X-ray crystallographic analysis.
The X-ray structural analysis of complexes 7 and 8
showed C2 symmetrical and distorted octahedral struc-
2. Results and discussion
2.1. Synthesis of 1,2-bis(2-chalcogenaphenylselanyl)benzene
ligands 3 and 4
1,2-Bis(2-chalcogenaphenylselanyl)benzene ligands
3
and 4, in which two or all sulfur atoms in ligand 1 were
replaced with selenium atoms, were synthesized via disele-
nides 11 or 12 (Scheme 1). Although the synthesis of 1
and 2, bearing sulfur atoms at inner positions, were
achieved directly by the reactions of 9 or 10 with ben-
zene-1,2-dithiol [7,8], we selected different methods for 3
and 4 due to the difficulty in the synthesis of benzene-1,2-
diselenol [9]. Diselenides 11 and 12 were obtained in mod-
erate yields by the reaction of 9 and 10 with t-BuLi and
then with an excess amount of elemental selenium followed
by the treatment with LiAlH4, water and air [10]. Since the
Scheme 2.

T. Isobe et al. / Journal of Organometallic Chemistry 693 (2008) 1225–1232
1227
tures, where the inner two selenium atoms of the ligands
and the two chlorine atoms form a square planar arrange-
ment around the palladium(II) atom and the two terminal
chalcogen atoms of 3 and 4 were located at the axial posi-
tions of the palladium center (Fig. 1). Selected bond
lengths, angles, and torsion angles of 7 and 8 are shown
in Table 1. The distances between the terminal chalcogen
six-coordinate structure in the crystalline state as well as
the complexes 5 and 6 [7,8] (see Table 2).
The complexes 5–8 were found to have structures quite
similar to each other. The distances between the terminal
chalcogen and the palladium atoms of 5–8 are shown in
Fig. 2.
To estimate the effect of terminal chalcogen atoms, the
comparison of 6 with 5, both of which have inner sulfur
atoms, was examined. The distances between Se(t) and
˚
and the palladium atoms [7: PdÁ Á ÁS(t) = 3.2309(9) A, 8:
˚
PdÁ Á ÁSe(t) = 3.1934(2) A] are shorter than the sum of the
˚
van der Waals radii of palladium and sulfur atoms
Pd [3.14240(17) A] in 6 were shorter than those between
˚
˚
˚
(3.43 A) or that of palladium and selenium atoms
S(t) and Pd [3.1755(8) A] in 5, despite the van der Waals
(3.53 A), respectively. This result suggests that complexes
radius of selenium is larger than that of sulfur. This result
indicated the interaction between Se(t) and Pd in 6 was
stronger than that between S(t) and Pd in 5. The bond
7 and 8 have weak interactions between the palladium
and the terminal chalcogen atoms leading to the pseudo
˚
lengths of Se(t)–C9 [1.9104(17) A] of 6 are longer than
˚
those of S(t)–C9 [1.762(3) A] of 5, therefore, terminal
selenium atoms of 6 should be able to approach more
closely to the palladium metal center than the terminal
sulfur atoms of 5. Similar trend was observed in the com-
˚
parison of 7 [S(t)Á Á ÁPd = 3.2309(9) A] with 8 [Se(t)Á Á ÁPd =
˚
3.1934(2) A], both of which have inner selenium atoms.
The effect of inner chalcogen atoms could be estimated
from the comparing between 7 with 5, both of which have
terminal sulfur atoms. We can accept easily the fact that
bond-stretchings in 7 of E(i)–C4 and E(i)–Pd (E = S or
Se) make the terminal sulfur atoms difficult to approach
to the palladium metal center. Similar trend was confirmed
in the relation between 6 and 8, both of which have termi-
nal selenium atoms.
These results suggested that the distances between the
terminal chalcogen atoms and the palladium metal center
got shorter in the case of the complex having inner sulfur
or terminal selenium atoms. Therefore, those in complex
6, which has inner sulfur and terminal selenium atoms,
were the shortest among these complexes.
2.3. Atoms in molecule (AIM) analysis for the Se (or
S)Á Á ÁPd interactions
To estimate the interactions between the terminal chal-
cogen atoms and the palladium metal of complexes 5–8,
the topological analysis using Bader’s theory of atoms in
molecules (AIM) was examined [11]. In the AIM analysis,
chemical bondings can be identified by the presence of a
bond critical point (BCP), where the electron density
becomes a minimum along the bond path. For the interac-
tion between the terminal selenium (or sulfur) atoms and
the palladium metal centers [E(t)Á Á ÁPd (E = Se or S)] of
complexes 5–8, the BCPs could be located. The electron
density (q) at a BCP correlates with the strength of atomic
interaction. The q values of E(t)Á Á ÁPd interaction of com-
plexes 5–8 (qE(t)Á Á ÁPd) were 0.017, 0.020, 0.016, and
0.019 ea0À3, respectively (Table 3). The q values of 5–8
were smaller than those for normal covalent bonds, and
larger than those for the practical boundary of molecules
(q = 0. 001 ea0À3) [12], and these values are in good agree-
ment with the interaction of E(t)Á Á ÁPd in 5–8. In addition,
Fig. 1. ORTEP drawings of [7 Á C2H5OH Á 0.5C6H14] (a) and [8 Á C6H14
]
(b) with thermal ellipsoid plots (50% probability). Hydrogen atoms and
solvent molecules are omitted for clarity.
Table 1
˚
Selected bond lengths (A), angles (°), and torsion angles (°) of
[7 Á C2H5OH Á 0.5C6H14] and [8 Á C6H14] (E = S or Se)
[7 Á C2H5OH Á 0.5C6H14
]
[8 Á C6H14
]
E(i)–Pd
Pd–Cl
2.3499(5)
2.3220(11)
1.902(4)
1.763(4)
3.2309(9)
2.3725(3)
2.3222(6)
1.930(2)
1.912(2)
3.1934(2)
E(i)–C4
E(t)–C9
E(t)Á Á ÁPd
Cl–Pd–Cl*
E(i)–Pd–Cl
E(i)–Pd–E(i)*
C4–C9–E(t)–C10
C9–E(t)–C10–C11
96.05(6)
87.17(3)
91.08(3)
178.1(3)
95.6(3)
95.41(4)
87.381(18)
91.066(15)
177.40(19)
97.82(16)

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T. Isobe et al. / Journal of Organometallic Chemistry 693 (2008) 1225–1232
Table 2
Crystal data for [7 Á C2H5OH Á 0.5C6H14] and [8 Á C6H14
[7 Á C2H5OH Á 0.5C6H14
72H130Cl2PdS2Se2Si12ÁC2H5OH Á 0.5C6H14
]
]
[8 Á C6H14
]
Formula
Mw
C
C72H130Cl2PdSe4Si12ÁC6H14
1821.33
Orange, plate
Monoclinic
C2/c (#15)
41.6556(9)
12.8854(3)
19.2760(7)
106.8433(14)
9902.5(5)
4
1912.15
Crystal color, habit
Crystal system
Space group
Orange, plate
Monoclinic
C2/c (#15)
42.2464(6)
12.8876(2)
19.2391(6)
106.2999(19)
10053.8(4)
4
˚
a (A)
˚
b (A)
˚
c (A)
b (°)
3
˚
V (A )
Z
T (K)
103(2)
1.222
1.201
103(2)
1.263
1.864
qcalcd (g cmÀ1
)
l (mmÀ1
)
Independent reflections
Number of parameters
Goodness-of-fit on F2
R1 [I > 2r(I)]
8696
475
1.071
0.0441
9364
483
1.062
0.0272
wR2 (all data)
0.1056
0.0613
Table 3
The electron densities (q/ea0À3) and their Laplacians ($2q/ea0À5) of
EÁ Á ÁPd in complexes 5–8
5
6
7
8
qE(t)Á Á ÁPd
0.017
0.043
0.099
0.249
0.020
0.049
0.097
0.246
0.016
0.040
0.092
0.191
0.019
0.046
0.088
0.185
$2qE(t)Á Á ÁPd
qE(i)Á Á ÁPd
$2qE(i)Á Á ÁPd
$2q indicates that the electron density is locally concen-
trated, while a positive value of $2q means that the electron
density is locally depleted. The $2qE(t)Á Á ÁPd values of 5–8
were 0.043, 0.049, 0.040, and 0.046 ea0À5, respectively
(Table 3). These positive values of $2qE(t)Á Á ÁPd suggest that
the E(t)Á Á ÁPd interaction is dominantly electrostatic in
nature.
2.4. 77Se NMR spectra of dichloropalladium complexes
In order to estimate the interactions between the chalco-
gen atoms and the palladium metal in solution, the 77Se
NMR of complexes 7 and 8 were measured. The 77Se
NMR chemical shifts of dichloropalladium complexes
coordinated with selenide have been reported to show dis-
tinct down-field shifts (about 130–250 ppm) compared with
those of the corresponding selenide ligands [13].
Actually, the 77Se NMR signal of selenium atoms in
complex 7 in chloroform-d solution at 24 °C was observed
at 523.2 ppm, which was down-field shifted by about
130 ppm compared with that of ligand 3 (390.0 ppm). This
result indicated that complex 7 has coordinate bonds
between the inner selenium atoms and the palladium metal
in solution.
Fig. 2. Distances between the terminal chalcogen atoms and the
palladium atom in complexes 5–8.
the q values of E(t)Á Á ÁPd of 5–8 corresponded to the dis-
tances of E(t)Á Á ÁPd of 5–8 in the crystalline state. As the
q values are larger, the distances of E(t)Á Á ÁPd in these com-
plexes are shorter. The Laplacian ($2) of q denotes the
curvature of electron density in the 3D-topological space
for two interacting atoms. In general, a negative value of
The 77Se VT NMR spectra of complex 8 in chloroform-d
or 1,1,2,2-tetrachloroethane-d2 solution were measured at
100, 24, and À50 °C. In all cases, the inner selenium signals

T. Isobe et al. / Journal of Organometallic Chemistry 693 (2008) 1225–1232
1229
of 8 (100 °C: 564.5 ppm, 24 °C: 561.7 ppm, À50 °C:
558.1 ppm) were down-field shifted by about 150–
160 ppm compared with those of ligand 4 (100 °C:
410.8 ppm, 24 °C: 400.8 ppm, À50 °C: 393.6 ppm). By con-
trast, very little chemical shift change was observed for the
terminal selenium atoms in each temperature (Fig. 3). In
solution, complex 8 was considered to have coordination
bonds between the inner selenium atoms and the palladium
metal and very weak or no interactions between the termi-
nal selenium atoms and the palladium metal. These results
suggested that complex 8 in solution had a four-coordina-
tion structure, where the two inner selenium atoms of 8 and
two chorine atoms coordinated to the palladium metal.
These trends in the terminal selenium atoms were also
observed for complex 6 (Scheme 3) [8].
Fig. 4. UV/Vis spectra of dichloropalladium complexes 5–8. [5] = [6] =
[7] = [8] = 1.0 Â 10À4 mol dmÀ3 in CH2Cl2.
Table 4
2.5. UV/Vis spectrum of dichloropalladium complexes
The wavelengths at absorption maxima (kmax) and the molar extinction
coefficients (e) of UV/Vis spectrum of complexes 5–8
The UV/Vis spectra of dichloropalladium complexes 5–
8 were measured in CH2Cl2 (Fig. 4). The wavelengths at
absorption maxima (kmax) and the molar extinction coeffi-
cients (e) are shown in Table 4. The kmaxs of 5–8 were
observed at 391, 417, 396, and 421 nm, respectively. The
kmax (nm)
e (dm3 molÀ1 cmÀ1
)
5
6
7
8
391
417
396
421
3.7 Â 103
2.8 Â 103
2.0 Â 103
3.1 Â 103
k
maxs of selenoethers complexes (6–8) showed a red shift
compared with that of thioether complexes 5. Particularly,
complexes 6 and 8, bearing Tbt–Se moieties in ligands,
showed a considerable red shift of kmax. These results imply
the possibility of weak interaction between the terminal
selenium atoms and the palladium center in solution.
3. Conclusion
We have succeeded in the synthesis of new acyclic tetra-
chalcogenoether ligands 3 and 4 tethered with two Tbt
groups and their complexes 7 and 8. The molecular struc-
tures of 7 and 8 were discussed systematically in compari-
son with those of related compounds 5 and 6 on the
basis of their NMR and UV/Vis spectra, and X-ray crystal-
lographic analysis.
The X-ray structural analyses of 5–8 showed their struc-
tures quite similar to each other. The distances between the
terminal chalcogen atoms and the palladium metal center
in 5–8 were shorter than the sum of the van der Waals radii
of sulfur or selenium and palladium atoms. Therefore,
complexes 5–8 were expected to have a weak interaction
between the terminal chalcogen atoms and the palladium
metal, and have a pseudo six-coordinate structure in the
crystalline state. The AIM calculations also suggested the
six-coordination characters of 5–8.
Fig. 3. The 77Se NMR spectra of ligand 4 and complex 8 in chloroform-d
at 24 °C.
On the other hand, the 77Se NMR spectra of 6–8 indi-
cated that the terminal selenium atoms in complexes 6
and 8 have no interactions to the palladium metal center,
and they have a four-coordination structure in solution.
4. Experimental
4.1. General experimental details
All reactions were carried out under an argon
atmosphere, unless otherwise noted. THF was purified
prior to use by using an Ultimate Solvent System (Glass
Contour Company) Laguna Beach, CA, USA [14], and
Scheme 3.

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T. Isobe et al. / Journal of Organometallic Chemistry 693 (2008) 1225–1232
other solvents were used without purification. Preparative
gel permeation liquid chromatography (GPLC) was per-
formed on an LC-908 or LC-918 instruments with JAI
gel 1H + 2H columns (Japan Analytical Industry) using
chloroform as an eluent. Short column chromatography
was performed with Nacalai Tesque Silica Gel 60. The
1H NMR (300 MHz) and 13C NMR (75 MHz) spectra were
measured in CDCl3 with a JEOL AL-300 spectrometer
using CHCl3 (7.25 ppm) as internal standards for 1H
NMR spectroscopy, and CDCl3 (77.0 ppm) as those for
13C NMR spectroscopy. The 77Se NMR (95 MHz) spectra
were measured in CDCl3 or C2D2Cl4 with a JEOL JNM
AL-300 spectrometer using diphenyl diselenide (460 ppm)
as an external standard. Mass spectral data were obtained
on a JEOL JMS-700 spectrometer. All melting points were
determined on a Yanaco micro melting point apparatus
and are uncorrected. Elemental analyses were performed
at the Microanalytical Laboratory of the Institute for
Chemical Research, Kyoto University. Tbt-substituted sul-
fide (9) [7] and selenide (10) [8] were prepared according to
the reported procedure.
ice water was added to the residue under air. The mixture
was extracted with hexane (200 mL). MgSO4 was added
to the solution to remove the remaining water. After
removal of the solvents under vacuum, the residue was sub-
jected to GPLC (CHCl3) to give diselenide 12 (126 mg,
0.0801 mmol, 44%) as yellow crystals. Compound 12:
m.p. 89.7–90.1 °C; 1H NMR (300 MHz, CDCl3) d 0.00
(72H, br s), 0.07 (36H, br s), 1.36 (2H, br s), 2.87 (4H, br
s), 6.41 (2H, br s), 6.55 (2H, br s), 6.91–7.06 (6H, m),
3
7.55 (2H, d, JHH = 6 Hz); 13C NMR (75 MHz, CDCl3) d
0.7 (q), 29.4 (d), 30.5 (d), 122.1 (d), 127.1 (d), 127.8 (d),
128.2 (s), 131.2 (d), 131.4 (s), 131.9 (d), 136.6 (s), 144.3
(s), 150.0 (s); 77Se NMR (57 MHz, CDCl3) d 278.0,
438.6; LRMS (FAB) m/z 787 [12M]+.
4.4. Synthesis of 1,2-bis(2-thiophenylselanyl)benzene (3)
The diselenide (11) (4.06 g), Cu2O (5.00 g, 34.9 mmol),
and 1,2-diiodobenzene (2.35 g, 7.12 mmol) in 2,4,6-trimeth-
ylpyridine (55 mL) was refluxed for 7.5 h. The mixture was
washed with a 1.0 M aqueous solution of HCl four times
(100 mL Â 4). The organic layer was passed through a
short column (SiO2, CHCl3) to remove water and inorganic
salts, and then the eluate was evaporated. After the residue
was subjected to GPLC (CHCl3), the reprecipitation from
CH2Cl2/CH3CN gave 1,2-bis(2-thiophenylselanyl)benzene
3 (177.6 mg, 0.114 mmol, 3% from 9) as a colorless solid.
4.2. Synthesis of diselenide (11)
To a THF solution (150 mL) of Tbt-substituted sulfide
(9) (6.28 g, 7.99 mmol) was gradually added t-BuLi
(1.58 M pentane solution, 11.7 mL, 17.6 mmol) at
À78 °C. After stirring for 1.5 h at this temperature, elemen-
tal selenium (4.3 g, 54 mmol) was added to the dark brown
solution. The reaction mixture was stirred at À78 °C for
47 h and then at room temperature for 59 h. The resulting
dark brown solution was added to a THF solution (20 mL)
of LiAlH4 (1.0 g, 26 mmol) at 0 °C. The reaction mixture
was stirred for 24 h at room temperature. After EtOH solu-
tion of NaOH was added to the solution at 0 °C, the reac-
tion mixture was stirred for 12 h. Then removal of the
solvents under reduced pressure, water was added to the
residue under air. The mixture was extracted with chloro-
form (500 mL). The solution was passed through a short
column (SiO2, CHCl3) to remove water and inorganic salts.
The eluate was evaporated, and the residue was subjected
to GPLC (CHCl3) to give diseleide (11) as a mixture of
compounds (4.06 g).
1
Compound 3: m.p. 101.4–101.6 °C; H NMR (300 MHz,
CDCl3) d À0.03 (72H, s), 0.07 (36H, s), 1.38 (2H, s), 2.67
(4H, br s), 6.42 (2H, br s), 6.55 (2H, br s), 6.65 (4H, d,
3JHH = 7 Hz), 6.88–7.04 (4H, m), 7.08–7.18 (2H, m),
7.27–7.33 (2H, m); 13C NMR (75 MHz, CDCl3) d 0.8 (q),
26.4 (d), 30.6 (d), 122.7 (d), 125.6 (d), 127.4 (d), 127.6
(d), 127.83 (d), 127.84 (s), 128.3 (d), 128.6 (s), 133.1 (d),
133.8 (d), 136.0 (s), 142.4 (s), 143.4 (s), 150.2 (s); 77Se
NMR (57 MHz, CDCl3) d 390.0; HRMS (FAB) m/z calcd
for C72H130S2 80Se2Si12 [M]+ 1554.5196. Found: 1554.5151.
Anal. Calc. for C72H130S2Se2Si12: C, 55.62; H, 8.43. Found:
C, 55.68; H, 8.39%.
4.5. Synthesis of 1,2-bis(2-selanylphenylselanyl)benzene (4)
A mixture of Tbt-substituted diselenide (12) (248 mg,
0.158 mmol), Cu2O (50 mg, 0.35 mmol), and 1,2-diiodo-
benzene (52.1 mg, 0.158 mmol) in 2,4,6-trimethylpyridine
(19 mL) was refluxed for 6 h. The mixture was washed with
a 1.0 M aqueous solution of HCl four times (100 mL Â 4).
The organic layer was passed through a short column
(SiO2, CHCl3) to remove water and inorganic salts, and
then the eluate was evaporated. The residue was subjected
to GPLC (CHCl3) to give 1,2-bis(2-selanylphenylsela-
nyl)benzene (4) (84.6 mg, 0.0513 mmol, 32%) as a colorless
solid, and mono-Tbt-substituted selenide (14) was also
obtained (87.1 mg, 0.0880 mmol, 56%). Compound 4:
m.p. 184.3–184.7 °C; 1H NMR (300 MHz, CDCl3) d
À0.03 (72 H, s), 0.07 (36H, s), 1.37 (2H, s), 2.77 (4H, br
s), 6.42 (2H, br s), 6.56 (2H, br s), 6.82 (2H, dd,
4.3. Synthesis of diselenide (12)
To a THF solution (10 mL) of Tbt-substituted selenide
10 (300 mg, 0.360 mmol) was gradually added t-BuLi
(1.58 M pentane solution, 0.53 mL, 0.79 mmol) at
À78 °C. After stirring for 40 min at this temperature, ele-
mental selenium (320 mg, 4.05 mmol) was added to the
dark brown solution. The reaction mixture was stirred at
À78 °C for 19 h and then at room temperature for 43 h.
The resulting darkbrown solution was added to a THF
solution (5 mL) of LiAlH4 (200 mg, 5.26 mmol) at 0 °C.
The reaction mixture was stirred for 8 h at room tempera-
ture. After removal of the solvents under reduced pressure,

T. Isobe et al. / Journal of Organometallic Chemistry 693 (2008) 1225–1232
1231
4
3JHH = 6 Hz, JHH = 3 Hz), 6.96–7.02 (4H, m), 7.13 (2H,
(70.0 mg, 0.238 mmol) in 20 mL of EtOH. The mixture
was stirred for 5.5 h at room temperature, and the resulting
orange suspension was filtered. After the addition of
CHCl3 to the precipitates, the mixture was filtered. The
orange filtrate was evaporated to give dichloropalladium
complex 8 (226 mg, 0.123 mmol, 73%) as orange crystals.
Complex 8: m.p. 257.2–257.7 °C. (dec.); 1H NMR
(300 MHz, CDCl3) d À0.07 (72H, s), 0.07 (36H, s), 1.39
(2H, s), 2,57 (4H, br s), 6.43 (2H, br s), 6.56 (2H, br s),
dd, 3JHH = 6 Hz, 4JHH = 4 Hz), 7.24 (2H, dd,
4
3
3JHH = 6 Hz, JHH = 3 Hz), 7.32 (2H, dd, JHH = 6 Hz,
4JHH = 4 Hz); 13C NMR (75 MHz, CDCl3) d 0.8 (q), 29.2
(d), 30.5 (d), 122.0 (d), 126.4 (d), 126.9 (d), 127.3 (s),
128.3 (d), 130.4 (d), 130.5 (s), 132.8 (d), 134.4 (d), 136.0
(s), 139.9 (s), 144.3 (s), 150.8 (s); 77Se NMR (57 MHz,
CDCl3) d 292.5, 400.8; HRMS (APCI) m/z Calcd for
C72H130 78Se80Se3Si12 [M]+: 1648.4098. Found: 1648.4042.
Anal. Calc. for C72H130Se4Si12: C, 52.45; H, 7.95. Found:
C, 52.62; H, 7.88%.
3
4
6.71 (2H, dd, JHH = 6 Hz, JHH = 3 Hz), 7.12–7.16 (4H,
3
4
m), 7.46 (2H, dd, JHH = 6 Hz, JHH = 3 Hz), 7.61 (2H,
3
4
3
dd, JHH = 6 Hz, JHH = 3 Hz), 7.86 (2H, dd, JHH = 6
4
4.6. Synthesis of 1,2-bis(2-selanylphenylselanyl)benzene (4)
[by the reaction of diselenide (12) with selenide (14)]
Hz, JHH = 3 Hz); 13C NMR (75 MHz, CDCl3) d 0.7 (q),
30.7 (d), 122.4 (d), 125.4 (s), 126.0 (d), 128.4 (s), 130.4
(d), 131.4 (d), 131.7 (d), 133.2 (d), 134.3 (s), 136.1 (d),
139.2 (s), 145.7 (s), 150.7 (s); 77Se NMR (57 MHz, CDCl3)
d 293.2, 561.7; LRMS (FAB) m/z 1792 [MÀCl]+. Anal.
Calc. for C72H130Cl2PdSe4Si12 C, 47.36; H, 7.18. Found:
C, 47.31; H, 7.17%.
A mixture of Tbt-substituted diselenide (12) (248 mg,
0.158 mmol), selenide (14) (297 mg, 0.300 mmol), and
Cu2O (50 mg, 0.35 mmol) in 2,4,6-trimethylpyridine
(55 mL) was refluxed for 8 h. The mixture was washed with
a 1.0 M aqueous solution of HCl four times (100 mL Â 4).
The organic layer was passed through a short column
(SiO2, CHCl3) to remove water and inorganic salts, and
then the eluate was evaporated. The residue was subjected
to GPLC (CHCl3) to give 1,2-bis(2-selanylphenylsela-
nyl)benzene (4) (282 mg, 0.0607 mmol, 62%) as colorless
solid.
4.9. X-ray crystallography
Single crystals of [7 Á C2H5OH Á 0.5C6H14] and [8 Á C6-
H14] were grown by the slow evaporation of the saturated
dichloromethane/hexane/ethanol solution. Their intensity
data were collected on a Rigaku/MSC Mercury CCD
diffractometer with graphite monochromated Mo Ka radi-
˚
4.7. Synthesis of diseleno-dithio-dichloropalladium complex
(7)
ation (l = 0.71071 A) to 2hmax = 50° at 103 K. Their
structures were solved by direct method (SHELXS-97) and
refined by full-matrix least-squares procedure on F2 for
all reflections (SHELXL-97) [15]. All the non-hydrogen atoms
were refined anisotropically, and all hydrogens were placed
using AFIX instruction.
To EtOH (20 mL) and chloroform (1 mL) solution of
diselenodithioether (3) (51.5 mg, 0.0331 mmol) was added
a solution of Na2PdCl4 (14.1 mg, 0.0479 mmol) in 20 mL
of EtOH. The mixture was stirred for 1.5 h at room tem-
perature, and the resulting orange suspension was filtered.
After the addition of CHCl3 to the precipitates, the mixture
was filtered. The orange filtrate was evaporated to give
4.10. Theoretical calculations
The calculations of the wave function of 5–8 were carried
out using the GAUSSIAN 03 program [16] with density func-
tional theory at the B3LYP level with TZV [17] (for Pd),
6-311+G(2d,p) (for S and Se), and 6-31G(d) (for C, Cl, H,
and Si) basis sets. The atomic coordinates obtained by the
X-ray crystallography of 5–8 were used as those for the
calculations. Computation time was provided by the Super-
computer Laboratory, Institute for Chemical Research,
Kyoto University. The atoms in molecules (AIM) analysis
was performed by using the AIM2000 package [18].
dichloropalladium complex
7 (24.8 mg, 0.0143 mmol,
43%) as orange crystals. Complex 7: m.p. 226.7–227.3 °C
(dec.); 1H NMR (300 MHz, CDCl3) d À0.19 (18H, s),
À0.11 (18H, s), À0.06 (18H, s), 0.07 (36H, s), 0.16 (18H,
s), 1.40 (2H, s), 2.85 (4H, s), 6.36 (2H, br s), 6.50 (2H, d,
3JHH = 7 Hz), 6.58 (2H, br s), 7.09 (2H, t, JHH = 7 Hz),
3
3
7.19 (2H, t, JHH = 7 Hz), 7.40–7.51 (2H, m), 7.55–7.65
(2H, m), 7.90 (2H, d, JHH = 7 Hz); 13C NMR (75 MHz,
3
CDCl3) d 0.8 (q), 1.2 (q), 1.5 (q), 26.5 (d), 30.9 (d), 121.1
(d), 125.0 (d), 125.4 (s), 127.7 (d), 131.3 (d), 131.6 (d),
133.1 (d), 134.1 (s), 136.1 (d), 142.3 (s), 144.0 (s), 145.8
(s), 150.1 (s); 77Se NMR (57 MHz, CDCl3) d 523.2;
LRMS (FAB) m/z 1696 [MÀCl]+. Anal. Calc. for
C72H130Cl2PdS2Se2Si12 C, 49.92; H, 7.56. Found: C,
49.66; H, 7.63%.
Acknowledgements
This work was partially supported by Grants-in-Aid for
Creative Scientific Research (No. 17GS0207), Science Re-
search on Priority Areas (No. 19027024, ‘‘Synergy of Ele-
ments”), Young Scientist (B) (No. 18750030), and the
21st Century COE and the Global COE Programs, Kyoto
University Alliance for Chemistry from the Ministry of
Education, Culture, Sports, Science and Technology,
Japan.
4.8. Synthesis of tetraseleno-dichloropalladium complex (8)
To an EtOH solution (20 mL) of tetraselenoether (4)
(282 mg, 0.171 mmol) was added a solution of Na2PdCl4

1232
T. Isobe et al. / Journal of Organometallic Chemistry 693 (2008) 1225–1232
[9] K. Shimada, K. Goto, T. Kawashima, N. Takagi, Y.-K. Choe, S.
Nagase, J. Am. Chem. Soc. 126 (2004) 13238–13239.
Appendix A. Supplementary material
[10] (a) E. Block, V. Eswarakrishnan, M. Gernon, G. Ofori-Okai, C.
Saha, K. Tang, J. Zubieta, J. Am. Chem. Soc. 111 (1989) 658–665;
(b) S. Ogawa, T. Kikuchi, S. Niizuma, R. Sato, J. Chem. Soc., Chem.
Commun. (1994) 1593–1594;
CCDC 670083 and 670084 contains the supplementary
crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif. Supplementary data associated with this article
can be found, in the online version, at doi:10.1016/
j.jorganchem.2008.01.016.
`
(c) A. Krief, L. Defrere, Tetrahedron Lett. 40 (1999) 6571–6575.
[11] (a) R.F.W. Bader, Atoms in Molecules: A Quantum Theory, Oxford
University Press, New York, 1990;
(b) M. Iwaoka, H. Komatsu, T. Katsuda, S. Tomoda, J. Am. Chem.
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(e) R.F. Nalewajski, R.G. Parr, Proc. Nat. Acad. Sci. USA 97 (2000)
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