Reactions of Di-o-tolyl telluride and selenide with palladium acetate: Isolation of a novel palladium complex of a tellurenic acid anhydride and related trinuclear and tetranuclear palladium complexes

Article abstract of DOI:10.1021/om2000184

The reaction of di-o-tolyl telluride with palladium acetate provided a novel palladium complex of a tellurenic acid anhydride, (o-tolylTe) ₂OPdOAc₂, and a linear trinuclear complex, [Pd(o-tolyl){di-o-tolyl telluride}]₂Pd(μ-OAc)₂. The reaction of di-o-tolyl selenide with palladium acetate afforded a tetranuclear complex of rare geometry, [Pd(OAc)(μ-Se-o-tolyl)]₄.

Full text of DOI:10.1021/om2000184

ARTICLE
pubs.acs.org/Organometallics
Reactions of Di-o-tolyl Telluride and Selenide with Palladium Acetate:
Isolation of a Novel Palladium Complex of a Tellurenic Acid Anhydride
and Related Trinuclear and Tetranuclear Palladium Complexes
Tapash Chakraborty,† Sagar Sharma,† Harkesh B. Singh,*,† and Ray J. Butcher‡
†Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
‡Department of Chemistry, Howard University, Washington, D.C. 20059, United States
S Supporting Information
b
ABSTRACT: The reaction of di-o-tolyl telluride with palladium acetate
provided a novel palladium complex of a tellurenic acid anhydride, (o-toly-
lTe)2OPdOAc2, and a linear trinuclear complex, [Pd(o-tolyl){di-o-tolyl
telluride}]2Pd(μ-OAc)2. The reaction of di-o-tolyl selenide with palladium
acetate afforded a tetranuclear complex of rare geometry, [Pd(OAc)(μ-Se-o-
tolyl)]4.
alladacycles are one of the most important classes of orga-
nometallic compounds which have been used as catalyst
methods. Di-o-tolyl ditelluride prepared from the corresponding
Grignard reagent was detellurated using copper7c to give 2.
Monoselenide 3 was synthesized by reacting the in situ generated
reagent SeCl2 with o-tolyl Grignard reagent.8 However, the
reaction could not be reproduced as a high-yield method.
Instead, the use of the in situ generated reagent SeBr2 provided
3 in much better yield.
P
precursors for coupling reactions.1 Herrmann and co-workers
demonstrated the use of palladacycles derived from Pd(OAc)2
and phosphines such as tri-o-tolylphosphine (1a, Chart 1) in
Heck and Suzuki coupling reactions.2
These thermally stable palladacyclic catalysts showed excellent
catalytic activity and have set a milestone in homogeneous
catalysis. Since then, a wide variety of known and new pallada-
cycles with PC, NC, SC, PCP, PCN, NCN, and SCS coordina-
tion modes have been successfully used in CꢀC coupling
reactions.1a,b,3,4 Sulfur-based palladacycles have also been em-
ployed successfully in CꢀC coupling reactions.5
Reaction between Di-o-tolyl Telluride and Palladium
Acetate: Synthesis of a Palladium Complex of Tellurenic
Acid Anhydride and a Linear Trinuclear Palladium Complex.
The reaction between 2 and palladium acetate in toluene
provided two palladium complexes (4 and 5). Complex 4 has a
bidentate tellurenic acid anhydride ligand, (o-tolylTe)2O, coor-
dinated to a monomeric Pd(OAc)2 fragment, and 5 is coordi-
nated to a tolyl group and tellurium, as shown in Scheme 1. The
coordination chemistry of tellurium and selenium ligands has
continued to be an area of growing interest. The chemistry of
metal complexes of the telluroethers,9 diorganoditellurides,10
and tellurolates11 has been the subject of many reviews and
books. However, to the best of our knowledge, there has been no
report on the coordination behavior of a tellurenic acid anhydride
until now. Complex 4 represents a novel palladium complex with
a tellurenic acid anhydride, which results from trimeric palladium
complex 5. The source of oxygen in the ligand could be
adventitious water from the atmosphere. It has been character-
ized by elemental analysis, NMR (1H, 13C, and 125Te) spectros-
copy, and mass spectrometry.
Palladacycles synthesized from ligands with phosphorus and
nitrogen donor atoms are numerous. There are very few pallada-
cycles with selenium,6 and none have been reported with tell-
urium. Use of heavier chalcogens as ligands for catalysts in the
coupling reactions has high potential. Recently, Yao et al. have
reported that selenium-ligated palladacycles (1b,c, Chart 1) act
as highly active and efficient catalysts for the Heck reaction.6 In
view of the observation that the PC-type palladacycle 1a derived
via activation of a benzylic CꢀH bond as well as selenium
palladacycles have shown high activity in CꢀC coupling reac-
tions, we set out to synthesize palladacycles based on selenium
and tellurium via activation of benzylic CꢀH bonds. Herein we
report the unexpected and interesting outcome of the reactions.
’ RESULTS AND DISCUSSION
The ligands di-o-tolyl telluride (2)7a,b and di-o-tolyl selenide
Received: January 11, 2011
Published: April 05, 2011
(3)8 were prepared by minor modification of the known
r
2011 American Chemical Society
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The complex crystallizes as a toluene solvate (vide infra), and
the calculated value of elemental analysis of the compound is in
good agreement with the observed value when half a molecule of
toluene is considered as part of the formula. The reaction was
tetranuclear palladium selenolato complex having a [PdSeR-
(OAc)]4 framework by the reaction of (PhSe)3Snꢀ(CH2)4ꢀ
Sn(SePh)3 with palladium acetate.13 Transmetalation of ArSe
moiety from tin to palladium has been achieved at ambient
temperature. On the other hand, in our case cleavage of the
CꢀSe bond of (o-tolyl)2Se required more drastic conditions.
Complex 6 has been characterized by elemental analysis, NMR
(1H, 13C, 77Se) spectroscopy, and mass spectrometry. The 77Se
NMR chemical shift appeared at δ ꢀ83 ppm, an upfield shift of
418 ppm compared to selenide 3 (δ 335 ppm).
1
also carried out in benzene, and the H NMR spectrum of the
product was essentially the same as that of 4, barring the signa-
ture peaks due to the solvents toluene and benzene. The 125Te
NMR of the compound in CDCl3 showed two peaks at δ 1325
and 1286 ppm. The 125Te NMR chemical shifts are shifted
upfield as compared with those of a related tellurenic acid
anhydride, bis[(2-(phenylazo)phenyl-C,N0)tellurium] oxide
(1535 ppm).12 The intensity of the latter was almost one-fourth
that of the former. The lower intensity peak was due to some
unidentified species in solution, indicating some sort of decom-
position/dissociation or scrambling in solution.
The trinuclear palladium complex 5 was obtained serendipi-
tously as a minor product in the reaction and could not be
isolated in pure form in sufficient amount for its characterization.
However, a single-crystal X-ray structure (vide infra) of the
complex could be determined. The 1H and 125Te NMR spectra
of the crude product indicated its existence in solution. Several
attempts were made to isolate the complex by varying reaction
conditions such as temperature from 25 to 75 °C and reaction
time from 2 to 30 min. However, in all the attempts the product
was the more stable tellurenic acid anhydride palladium complex
4, presumably formed via fragmentation of the less stable 5 as an
intermediate, as indicated by the 1H NMR (see the Supporting
Information).
Crystallographic Studies. The molecular structure of 4 is
depicted in Figure 1a. The bidentate ligand (o-tolylTe)2O is
coordinated to palladium via two tellurium atoms. The other two
coordination sites of palladium are satisfied by oxygen atoms of the
two acetate groups. The geometry around palladium is essentially
square planar. The PdꢀTebondlength(PdꢀTe#1 = 2.47105(15) Å)
is less than the sum of their covalent radii14 and is slightly shorter
than those in the palladium complexes of telluroether macro-
cycles.15 The bite angle Te#1ꢀPdꢀTe is 78.980(6)°. The pre-
sence of strong Te O secondary bonding interactions between
3 3 3
other two oxygen atoms of the two acetate groups with tellurium
atoms is observed from the bond distances and the geometry. For
example, the Te O1 distance, 2.4022(11) Å, is much shorter than
3 3 3
the sum of their van der Waals radii16 and the angle OꢀTe O1 =
3 3 3
169.12(4)° is close to linearity. This near-planar unit is linked to
Scheme 2. Reaction between 3 and Pd(OAc)2
Reaction between Di-o-tolyl Selenide and Palladium
Acetate: Synthesis of a Tetranuclear Palladium Selenolate
Complex. The reaction between 3 and palladium acetate in
toluene provided the tetranuclear palladium selenolate complex
6, as shown in Scheme 2. Complex 6 represents only the second
example of the [PdSeR(OAc)]4 framework formed via cleavage
of the CꢀSe bond. Dehnen et al. have reported very recently a
Chart 1
Scheme 1. Reaction between 2 and Pd(OAc)2
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Figure 1. (a) Molecular structure of the complex 4. Thermal ellipsoids are drawn at the 30% probability level; hydrogen atoms and solvent molecules are
removed for clarity. Significant bond lengths (Å) and bond angles (deg): TeꢀO = 2.0208(9), TeꢀC1 = 2.1171(14), Te O1 = 2.4022(11), TeꢀPd =
3 3 3
2.47106(15), PdꢀO2 = 2.1096(11), PdꢀO2#1 = 2.1097(11), PdꢀTe#1 = 2.47105(15), Te Te#1 = 3.1429(2) Å; OꢀTeꢀC1 = 92.75(6),
3 3 3
OꢀTeꢀO1 = 169.12(4), C1ꢀTeꢀO1 = 84.84(5), OꢀTeꢀPd = 89.28(3), C1ꢀTeꢀPd = 101.57(4), O1ꢀTeꢀPd = 80.83(3), OꢀTeꢀTe#1 =
38.96(3), C1ꢀTeꢀTe#1 = 96.21(4), O1ꢀTeꢀTe#1 = 130.68(3), PdꢀTeꢀTe#1 = 50.510(3), O2ꢀPdꢀO2#1 = 94.31(6), O2ꢀPdꢀTe#1 =
172.24(3), O2#1ꢀPdꢀTe#1 = 93.34(3), O2ꢀPdꢀTe = 93.34(3), O2#1ꢀPdꢀTe = 172.24(3), Te#1ꢀPdꢀTe = 78.980(6), O2ꢀPdꢀPd#2 =
87.05(3), O2#1ꢀPdꢀPd#2 = 87.05(3), Te#1ꢀPdꢀPd#2 = 94.631(6), TeꢀPdꢀPd#2 = 94.630(6), TeꢀOꢀTe#1 = 102.09(7)°. (b) Pd Pd
3 3 3
interaction between two molecular units. Pd Pd#2 = 3.1993(3) Å.
3 3 3
angle is 102.09(7)°, which is close to that in the water molecule
(104.45°). The aromatic rings of the tolyl groups are nearly
parallel to each other.
Complex 5 represents a linear trinuclear palladium complex
where terminal palladium ions are simultaneously coordinated to
a tellurium and an aromatic carbon. The molecular structure of 5
is shown in Figure 2.
Complex 5 has a perfectly linear arrangement of metal atoms.
The linear arrangement of three palladium atoms has been
observed much less frequently, compared to the triangular
arrangement.17 These structures contain a central Pd3(OAc)4
moiety. The PdꢀPd distance (3.0483(4) Å) is less than the sum
of their van der Waals radii (4.10 Å)16 and indicates the presence
of a metalꢀmetal interaction. The PdꢀPd distances reported in
similar complexes containing a linear array of three palladium
ions fall in the range 2.933ꢀ3.075 Å.18 The molecule has three
palladium ions in two different environments: (i) Pd2 is situated
at the crystallographic inversion center and coordinated by the
oxygen atoms of two pairs of mutually orthogonal acetate groups,
Figure 2. Molecular structure of the complex 5. Thermal ellipsoids are
i.e., the central Pd is perfectly square planar, and (ii) the terminal
palladium ions, Pd1 and Pd1i, are coordinated by the oxygen
atoms of a pair of mutually orthogonal acetate groups, the
tellurium atom of di-o-tolyl telluride, and the carbon atom of
the tolyl group at the ortho position. The geometry around the
terminal palladium ions is slightly distorted square planar with
the angles around the metal ions being in the range of 88.15-
(17)ꢀ94.60(11)°. The square planes generated by the coordina-
tion environment around Pd1 and Pd2 are nearly parallel to
each other with a dihedral angle of ca. 8° between them
(TeꢀPd1ꢀPd2ꢀO12i = 7.47(13)°). The PdꢀC bond length
(1.994(4) Å) islessthanthe sum of the covalent radii of palladium
and sp2-hybridized carbon (1.39 þ 0.73 = 2.12 Å) and fall within
the range reported for these types of compounds.18 The PdꢀTe
bond length (2.5054(5) Å) is slightly shorter than those in the
palladium complexes of tellurium-containing macrocycles,15
drawn at the 30% probability level; hydrogen atoms are removed for clarity.
Significant bond lengths (Å) and bond angles (deg): Pd1ꢀC1C = 1.994(4),
Pd1ꢀO11 = 2.102(4), Pd1ꢀO21 = 2.132(3), Pd1ꢀTe = 2.5054(5),
Pd1 Pd2 = 3.0483(4), Pd2ꢀO22 = 1.991(4), Pd2ꢀO12 = 1.999(4)
3 3 3
Å; C1CꢀPd1ꢀO21 = 172.11(18), O11ꢀPd1ꢀO21 = 88.64(15),
C1CꢀPd1ꢀTe = 87.44(13), O11ꢀPd1ꢀTe = 170.21(10), O21ꢀPd1ꢀ
Te = 94.60(11), C1CꢀPd1ꢀO11 = 88.15(17), O22ꢀPd2ꢀO22i =
180.0(2), O22ꢀPd2ꢀO12i = 89.81(18), O22ꢀPd2ꢀO12 = 90.19(18),
O12iꢀPd2ꢀO12 = 180.0(2), Pd1ꢀPd2ꢀPd1i = 180.0.
another such planar structure in an antiparallel fashion via a weak
Pd Pd (Pd Pd#2) interaction (Figure 1b). The distance
3 3 3
3 3 3
between these two palladiums (Pd Pd#2) is 3.1993(3) Å ,which
3 3 3
is slightly shorter than the sum of their van der Waals radii.16
The TeꢀO bond distance (2.0208(9) Å) is slightly shorter
than the sum of the covalent radii,14 and the TeꢀOꢀTe#1 bond
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ARTICLE
however, it is somewhat longer than that in (2-NH2-5-MeC6-
H3)Te(40-C2H5OC6H4)PdCl2.18
The molecular structure of 6 is shown in Figure 3. The
molecule assumes a paddle-wheel type geometry with two pairs
of orthogonal acetate groups and another two pairs of orthogonal
tolylselenolate groups bridging two different pairs of palladium
atoms.
The palladium atoms form a rectangular plane, each of which is
coordinated to two oxygen and two selenium atoms of the acetate
and tolylselenolate groups, respectively, in an essentially square-
planar geometry, as observed in the isostructural complex
[Pd(OAc)(SePh)]4 (6a).13 The short PdꢀPd distance bridged
by two acetate groups in the [Pd2(OAc)2]2þ unit is 2.8805(8) Å.
This distance is less than the sum of their van der Waals radii (4.10
Å)16 and is marginally greater than the sum of their covalent radii
(2.78 Å),14 hence indicating the presence of a significant me-
talꢀmetal interaction. This PdꢀPd distance falls within the range
reported for PdꢀPd bonds.19 The corresponding PdꢀPd distance
in 6a is 2.864(18) Å. The longer Pd Pd contact bridged by two
3 3 3
tolylselenolate groups is 3.438 Å, which is less than the correspond-
ing distance in the isostructural complex 6a (3.496(2) Å). The
PdꢀSe bond lengths (2.3720(17)ꢀ2.3864(15) Å) are shorter
than those in the mesitylselenolato-bridged palladium complex Pd2
(μ-SeMes)2(η3-C3H7)2 (2.4694(17)ꢀ2.4732(18) Å).20
’ CONCLUSION
A novel palladium complex of a tellurenic acid anhydride has
been isolated in good yield from the reaction of di-o-tolyl
telluride with Pd(OAc)2, obtained by the cleavage of the Cꢀ
Te bond. Another telluride-coordinated trinuclear palladium
complex was obtained from the same reaction and could be
characterized by X-ray crystallography. A tetranuclear selenolato-
bridged palladium complex was isolated from the reaction of di-o-
tolyl selenide with Pd(OAc)2.
Figure 3. Molecular structure of the complex 6. Thermal ellipsoids are
drawn at the 30% probability level; hydrogen atoms are removed for clarity.
Significant bond lengths (Å) and bond angles (deg): Pd1ꢀO21 =
2.079(11), Pd1ꢀO11 = 2.080(10), Pd1ꢀSe1 = 2.3748(16), Pd1ꢀSe2 =
2.3868(17), Pd1ꢀPd2 = 2.8939(12), Pd2ꢀO12 = 2.092(11), Pd2ꢀO22 =
2.075(11), Pd2ꢀSe2i = 2.3720(17), Pd2ꢀSe1i = 2.3864(15), Se1ꢀC1BA
= 1.912(11) Å; O21ꢀPd1ꢀO11 = 91.1(5), O21ꢀPd1ꢀSe1 = 175.8(3),
O11ꢀPd1ꢀSe1 = 91.9(3), O21ꢀPd1ꢀSe2 = 94.1(4), O11ꢀPd1ꢀSe2 =
174.5(3), Se1ꢀPd1ꢀSe2 = 83.04(5), O22ꢀPd2ꢀO12 = 91.8(6),
O22ꢀPd2ꢀSe2i = 176.2(4), O12ꢀPd2ꢀSe2i = 92.1(4), O22ꢀPd2ꢀSe1i
= 93.1(4), O12ꢀPd2ꢀSe1i = 174.1(4), Se2iꢀPd2ꢀSe1i = 83.11(5),
C1BAꢀSe1ꢀPd1 = 101.5(5).
’ EXPERIMENTAL SECTION
All reactions were carried out under nitrogen or argon using standard
vacuum-line techniques. Solvents were purified and dried by standard
procedures and were distilled prior to use. Melting points were recorded
on a Veego VMP-I melting point apparatus in capillary tubes and were
Table 1. Crystal Data and Structure Refinement Details for 4ꢀ6
4
1/2C7H8
5
6
3
empirical formula
fw
C
43H48O10Pd2Te4
C50H54O8Pd3Te2
1357.33
C36H40O8Pd4Se4
1342.12
monoclinic
C2/c
1448.01
monoclinic
I2/m
cryst syst
space group
a (Å)
triclinic
P1
7.8457(2)
15.1119(4)
19.1215(4)
90
10.1676(2)
10.3479(3)
14.0427(3)
71.258(3)
87.1053(19)
64.937(3)
1261.07(5)
1
18.1021(12)
13.1486(9)
18.6113(12)
90
b (Å)
c (Å)
R (deg)
β (deg)
γ (deg)
V (Å3)
Z
91.798(2)
90
104.214(7)
90
2265.99(10)
2
4294.2(5)
4
Dcalcd (Mg mꢀ3
)
2.121
1.787
2.076
temp (K)
200(2)
200(2)
293(2)
θ range (deg)
abs coeff (mmꢀ1
4.81ꢀ34.77
3.372
4.61ꢀ34.71
2.242
4.54ꢀ77.55
17.558
)
final R(F) (I > 2σ(I))a
Rw(F2) indices (I > 2σ(I))
no. of data/restraints/params
goodness of fit on F2
a Definitions: R(Fo) = ∑||Fo| ꢀ |Fc||/∑|Fo| and Rw(Fo ) = {∑[w(Fo ꢀ Fc2)]2/∑[w(Fc2)2]}1/2
0.0214
0.0578
0.0975
0.0294
0.0915
0.1281
4740/0/164
9337/0/291
1.078
4370/15/226
1.356
1.028
2
2
.
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uncorrected. 1H (400 MHz) and 13C (100.56 MHz) nuclear magnetic
resonance spectra were recorded on a Varian Mercury Plus 400 MHz
spectrometer and 77Se (57.22 MHz) and 125Te (94.79 MHz) spectra on
a Varian VXR 300S spectrometer. Chemical shifts are cited with respect
to Me4Si as internal standard (1H, 13C) and Me2Se (77Se) and Me2Te
Analytical Instrument Facility (SAIF), Indian Institute of Technol-
ogy Bombay, for 300 MHz NMR spectroscopy is gratefully acknowl-
edged. T.C. and S.S. are also grateful to the Council of Scientific and
Industrial Research of India and University Grant Commission of
India, respectively, for providing fellowships.
(
125Te) as external standards. Elemental analyses were performed on a
Carlo Erba Model 1106 elemental analyzer. The ESI mass spectra were
recorded on a Q-Tof micro (YA-105) mass spectrometer.
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Synthesis of 6. To a pale yellow solution of di-o-tolyl selenide (705
mg, 1.35 mmol) was added palladium acetate (225 mg, 1.00 mmol) in
25 mL of toluene. The mixture was heated at ca. 100 °C for 90 min. The
reaction was monitored by TLC. A metallic mirror was observed when the
reaction was stopped. Then the reaction mixture was filtered through a short
Florisil column to remove the insoluble black particles formed and
concentrated under vacuum to ca. 5 mL. A gray precipitate was obtained
on adding hexane (10 mL). The precipitate was filtered off, washed with
hexane, and dissolved in toluene (2 mL) and this solution layered with
diethyl ether to give dark red crystals of the title compound at room
temperature after 2 days. Yield: 75 mg. Mp: 177ꢀ179 °C. Anal. Calcd for
C36H40O8Pd4Se4: C, 32.21; H, 3.00. Found: C, 31.57; H, 2.43. 1H NMR
(CDCl3):δ2.03 (s, CH3COO, 12H), 2.75 (s, CH3C6H4, 12H), 6.68ꢀ6.71
(m, 4H), 6.98 (m, 4H), 7.10ꢀ7.13 (m, 4H), 8.82 (m, 4H). 13C NMR
(CDCl3): δ 23.9, 24.2, 126.4, 128.4, 128.9, 130.8, 137.8, 140.9, 181.1. 77Se
NMR (CDCl3): δ ꢀ83. ESI-MS: m/e 628.99 [C15H12O4Pd2Se2þ, 20%].
X-ray Crystallography. The diffraction measurements were per-
formed on an Oxford Diffraction Gemini diffractometer. The data were
corrected for Lorentz, polarization, and absorption effects. The struc-
tures were determined by routine heavy-atom methods using SHELXS
9721 and Fourier methods and refined by full-matrix least squares with
the non-hydrogen atoms anisotropic and hydrogen with fixed isotropic
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ꢀ2
thermal parameters of 0.07 Å by means of the SHELXL 9722 program.
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The hydrogens were partially located from difference electron density
maps, and the rest were fixed at predetermined positions. Scattering
factors were from common sources.23 Some details of the data collection
and refinement are given in Table 1.
’ ASSOCIATED CONTENT
S
Supporting Information. CIF files giving crystal data and
b
figures giving spectroscopic data (1H, 13C, 125Te, and 77Se NMR
and ESI-MS) for 4ꢀ6. This material is available free of charge via
the Internet at http://pubs.acs.org.
’ ACKNOWLEDGMENT
We thank the Department of Science and Technology (DST)
of India for funding this work. Additional help from the Sophisticated
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Organometallics
ARTICLE
(20) Ghavale, N.; Dey, S.; Wadawale, A.; Jain, V. K. Organometallics
2008, 27, 3297.
(21) Sheldrick, G. M. SHELXS 97, Program for the Solution of Crystal
Structures; University of G€ottingen, G€ottingen, Germany, 1997.
(22) Sheldrick, G. M. SHELXL 97, Program for Refining Crystal
Structures; University of G€ottingen, G€ottingen, Germany, 1997.
(23) Cromer, D. T.; Waber, J. T. International Tables for X-ray
Crystallography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV, pp
99, 149.
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