Synthesis of Pd(II) complexes of unsymmetrical, hybrid selenoether and telluroether ligands: Isolation of tellura-palladacycles by fine tuning of intramolecular chalcogen bonding in hybrid telluroether ligands

Article abstract of DOI:10.1016/j.poly.2019.03.036

Two novel unsymmetrical selenoether ligands namely, N,N-dimethyl-2-(o-tolylselanyl)aniline (10) and 2-((2,6-dimethylphenyl)selanyl)-N,N-dimethylaniline (11) were synthesized from N,N-dimethylbenzylamine via the ortho-lithiation route. When ligands 10 and 11 were treated with Pd(COD)Cl₂ (COD = 1,5-cyclooctadiene), the reaction afforded novel Pd(II) complexes of the form Pd(2-NMe₂CH₂C₆H₄)(R)SeCl₂, where R = 2-MeC₆H₄ (16) and 2,6-MeC₆H₃ (17) respectively. Similarly, when unsymmetrical telluroether ligands, N,N-dimethyl-2-(phenyltellanyl)aniline (12), N,N-dimethyl-2-(o-tolyltellanyl)aniline (13), 2-((2,6-dimethylphenyl)tellanyl)-N,N-dimethylaniline (14) and 2-((2,6-diisopropylphenyl)tellanyl)-N,N-dimethylaniline (15), which contain one coordinating group with an sp³ N-donor atom, were treated with Pd(COD)Cl₂, the palladium telluroether complexes of the form Pd(2-NMe₂CH₂C₆H₄)(R)TeCl₂, where R = C₆H₅ (18), 2-MeC₆H₄ (19), 2,6-MeC₆H₃ (20) and 2,6-ⁱPrC₆H₃ (21) respectively were obtained. The selenoether complexes 16 and 17 and telluroether complexes 18, 20 and 21 were characterized by single crystal X-ray diffraction studies. In the asymmetric unit of complex 18, two molecules are present and due to the presence of weak, intermolecular Te?Cl interactions, the two molecules exist as symmetrically related dimer. The N-donor substituents, which were involved in intramolecular chalcogen bonding (IChB) with the chalcogen atoms in the free ligand, made six-membered chelating rings in the complexes. Again, when bis(2-phenylazophenyl-C,N′)selenide 22 was treated with Pd(COD)Cl₂, it afforded ortho C–H bond activated cyclopalladated complex 24. However, when bis(2-phenylazophenyl-C,N′)telluride 23 was treated with Pd(COD)Cl₂, due to strong IChB from two N-donor substituents, the reaction afforded cleaved product, [2-(phenylazo)phenyl-C,N′]tellurenyl chloride, 25. All the metal complexes exhibited significant downfield chemical shifts in ⁷⁷Se/¹²⁵Te NMR spectra as compared to the corresponding free ligands. The downfield shifts in the ⁷⁷Se/¹²⁵Te NMR signal in the complexes might be attributed to the coordination of the chalcogen atoms to the electropositive Pd(II) center.

Full text of DOI:10.1016/j.poly.2019.03.036

Accepted Manuscript
Synthesis of Pd(II) complexes of unsymmetrical, hybrid selenoether and tellur-
oether ligands: Isolation of tellura-palladacycles by fine tuning of intramolecular
chalcogen bonding in hybrid telluroether ligands
Anand Gupta, Rajesh Deka, Kriti Srivastava, Harkesh B. Singh, Ray J. Butcher
PII:
S0277-5387(19)30209-8
https://doi.org/10.1016/j.poly.2019.03.036
POLY 13837
DOI:
Reference:
To appear in:
Polyhedron
Received Date:
Revised Date:
Accepted Date:
15 January 2019
19 March 2019
20 March 2019
Please cite this article as: A. Gupta, R. Deka, K. Srivastava, H.B. Singh, R.J. Butcher, Synthesis of Pd(II) complexes
of unsymmetrical, hybrid selenoether and telluroether ligands: Isolation of tellura-palladacycles by fine tuning of
intramolecular chalcogen bonding in hybrid telluroether ligands, Polyhedron (2019), doi: https://doi.org/10.1016/
j.poly.2019.03.036
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Synthesis of Pd(II) complexes of unsymmetrical, hybrid selenoether and telluroether
ligands: Isolation of tellura-palladacycles by fine tuning of intramolecular chalcogen
bonding in hybrid telluroether ligands
a
a
a
a,*
b
Anand Gupta , Rajesh Deka , Kriti Srivastava , Harkesh B. Singh , Ray J. Butcher
aDepartment of Chemistry, Indian Institute of Technology Bombay, Mumbai 400076, India.
bDepartment of Chemistry, Howard University, Washington, D. C. 20059, USA.
*Corresponding Author
E-mail address: chhbsia@chem.iitb.ac.in (H. B. Singh)
Keywords: Intramolecular interaction; Molecular structure; Selenoether; Telluroether;
Palladacycles
Abstract
Two novel unsymmetrical selenoether ligands namely, N,N-dimethyl-2-(o-tolylselanyl)aniline
(
10) and 2-((2,6-dimethylphenyl)selanyl)-N,N-dimethylaniline (11) were synthesized from N,N-
dimethylbenzylamine via the ortho-lithiation route. When ligands 10 and 11 were treated with
Pd(COD)Cl (COD = 1,5-cyclooctadiene), the reaction afforded novel Pd(II) complexes of the
form Pd(2-NMe CH )(R)SeCl , where R = 2-MeC (16) and 2,6-MeC (17)
respectively. Similarly, when unsymmetrical telluroether ligands, N,N-dimethyl-2-
phenyltellanyl)aniline (12), N,N-dimethyl-2-(o-tolyltellanyl)aniline (13), 2-((2,6-
2
2
2
C
H
6 4
2
6
H
4
6
H
3
(
dimethylphenyl)tellanyl)-N,N-dimethylaniline (14) and 2-((2,6-diisopropylphenyl)tellanyl)-N,N-
3
dimethylaniline (15), which contain one coordinating group with an sp N-donor atom, were
treated with Pd(COD)Cl
NMe CH )(R)TeCl , where R = C
iPrC
(21) respectively were obtained. The selenoether complexes 16 and 17 and telluroether
2
, the palladium telluroether complexes of the form Pd(2-
2
2
C
6
H
4
2
6
H
5
(18), 2-MeC (19), 2,6-MeC (20) and 2,6-
6
H
4
6
H
3
6
H
3
complexes 18, 20 and 21 were characterized by single crystal X-ray diffraction studies. In the
asymmetric unit of complex 18, two molecules are present and due to the presence of weak,
intermolecular Te···Cl interactions, the two molecules exist as symmetrically related dimer. The
N-donor substituents, which were involved in intramolecular chalcogen bonding (IChB) with the
chalcogen atoms in the free ligand, made six-membered chelating rings in the complexes. Again,
when bis(2-phenylazophenyl-C,N´)selenide 22 was treated with Pd(COD)Cl , it afforded ortho
2
C-H bond activated cyclopalladated complex 24. However, when bis(2-phenylazophenyl-
1

C,N´)telluride 23 was treated with Pd(COD)Cl , due to strong IChB from two N-donor
2
substituents, the reaction afforded cleaved product, [2-(phenylazo)phenyl-C,N´]tellurenyl
chloride, 25. All the metal complexes exhibited significant downfield chemical shifts in
7
7
125
Se/ Te NMR spectra as compared to the corresponding free ligands. The downfield shifts in
the 77Se/ Te NMR signal in the complexes might be attributed to the coordination of the
125
chalcogen atoms to the electropositive Pd(II) center.
1
. Introduction
Chalcogenoether ligands, a class of organochalcogen ligands with neutral chalcogen donor atoms
Se, Te), have garnered significant attention over a long time period and their chemistry has been
(
thoroughly reviewed in the literature [1]. These ligands are modest -donors in nature and with
the ease of fine-tuning their auxiliary arms, the coordination compounds of these ligands have
found important applications in various aspects of contemporary organometallic chemistry,
starting from catalysis [2], chemical vapor deposition (CVD) techniques [3], toxicology and drug
design [4], to name a few. While the reactions of selenoether ligands with metal precursors
afforded desired selena-metallacycles, with its heavier congener i.e., telluroether ligands, the
reactions took a different course. It is commonly observed that the reactions of telluroether
ligands with Intramolecular Chalcogen Bonding (IChB) with metal precursors resulted in
complexes with concomitant cleavage of the C-Te bond(s). Such de-alkylation/-arylation of the
telluroether ligands during coordination to a metal was first reported by McWhinnie and co-
workers, wherein they observed that the reaction of 1,6-bis-2-butyltellurophenyl-2,5-diazahexa-
1
,5-diene with a Pt(II) precursor resulted in a complex with the loss of two butyl groups [5]. In
another instance, when 2-(2-pyridyl)phenyl(p-ethoxyphenyl)tellurium(II) was reacted with PdCl
and PtCl , labilisation of the C-Te bond took place resulting in the formation of reverse-
transmetallated products [6]. Similar labilisation of C-Te bonds was also observed when the
ligand was treated with HgCl , CuCl and CuCl [7, 8].
2
2
2
2
As a part of our research on the isolation of metal complexes of IChB stabilized
organochalcogen ligands, we have also observed contrasting ligating behavior of selenoether and
2

telluroether ligands during coordination with metal ions. For example, when the intramolecularly
3
coordinated selenoether ligand, 1 containing one coordinating group with an sp donor atom, was
treated with Pd(CH
3
CN)Cl , it afforded the desired 1:1 palladated complex (Chart 1) [2c].
2
Similar straightforward ligation properties were observed when 22-membered macrocyclic
chalcogenoether ligands 2 and 3 were treated with Pd (II) precursors [9]. Again, when selenaaza
2
macrocycle 4 containing sp donor atoms was treated with Pd (II) ion, it underwent partial
hydrolysis to result in an acyclic product where the Pd(II) ion was coordinated to two selenium
and two nitrogen atoms [10]. The hydrolysis was attributed to the significant ring strain arising
from the mismatch of the cavity size and metal ion. This was further confirmed by the fact that
the larger homologues (i.e., 24 membered Schiff base macrocycle) resulted in the expected 1:1
Pd(II) complex [10]. Interestingly, when the telluraazamacrocycle 5 was treated with Hg(II) and
Pt(II) precursors, a contrasting ligating behavior was observed [11, 12]. In particular, during the
reaction of 5 with HgCl
2
[11] or Pt(COD)Cl (COD = 1,5-cyclooctadiene) [12], concomitant
2
cleavage of C-Te bonds took place resulting in the formation of transmetallated products. A
similar trend in the formation of transmetallated (or cleaved) products was obtained when
N,Te,N- type tridentate ligands 6-8 containing two possible coordinating groups, were treated
with Hg(II) or Pd(II) precursors [13, 14]. It is worth noting that in all these complexes the C-Te
bonds, which were trans to Te···N secondary bonding interactions, underwent cleavage.
Consequently, the labilisation of the C-Te bond in the aforementioned telluroether ligands during
the coordination to a metal, could be explained from the perspective of IChB. IChB can be
2
described as 3c-4e, donor–acceptor type interactions [n (D) → σ*(E–X)] where the donor atom
D (e.g., N, O) donates its lone pair of electrons to the antibonding σ*-orbital of the heavy atom E
(e.g., Se, Te) [15]. While moving down the chalcogen group, the electronegativity decreases, and
the polarizability increases in the order; O < S < Se < Te. As a result, Te atom consists of low-
lying tellurium σ*-orbitals, which in turn reduces the energy difference between σ(E–X) and
σ*(E–X) orbitals in Te atom in comparison to its lighter congeners. Again, the Te-N bond is
significantly polar in comparison to corresponding Se-N (or S-N) bond. Consequently, Te
compounds experience stronger IChB interactions as compared to its lighter congeners (Se and
S), thereby making the trans C-Te bond more labile than that of Se (or S) compounds. The
-1
higher lability of C-Te bond also stems from the fact that the C-Te bond ( ~ 202 KJ mol )
-1
energy is significantly lower in comparison to that of C-Se bond (234 KJ mol ).
3

Chart 1. Examples of selenoether and telluroether ligands.
From the above discussion, it can be inferred that due to the extensive IChB in the cases of
symmetrical telluroether ligands with two possible coordinating groups, the reaction with metal
precursors generally afforded cleaved products instead of the expected 1:1 tellura-metallacycles.
We envisaged that, by fine-tuning the auxiliary donor arms of the telluroether ligands, for
instance taking unsymmetrical telluroether ligands with one coordinating group, the IChB can be
modulated to reduce the lability of the trans C-Te bond. Herein, in this article, we report the
synthesis of a series of palladium(II) complexes of unsymmetrical selenoether and telluroether
3
ligands which contain only one coordinating group with an sp donor atom. In addition, to
further substantiate the effects of IChB, we have treated symmetrical chalcogenoethers 22 and 23
containing two coordinating groups with Pd(II) precursors. In line with our earlier observations,
while selenoether 22 afforded a 1:1 palladacycle without cleavage of a C-Se bond, whereas
telluroether 23 underwent C-Te cleavage to afford [2-(phenylazo)phenyl-C,N´]tellurenyl
chloride 25. The structures of the synthesized complexes are thoroughly studied both in solution
states as well as solid states and compared with the similar reported literature.
2
2
. Experimental section
.1. Materials and methods
4

All the manipulations were executed under a nitrogen or argon atmosphere using standard
Schlenk techniques unless otherwise noted. Solvents were purified and dried by standard
1
13
procedures and were distilled prior to use. H (400 MHz, 500 MHz), C NMR (100.56 MHz,
26 MHz), 77Se NMR (76 MHz, 95 MHz) and 125Te (126 MHz, 158 MHz) nuclear magnetic
resonance spectra were recorded on Bruker AV 400 and/or Bruker AV 500 spectrometers at 25
1
1
13
°
C. Chemical shifts are cited with respect to Me
4
Si as an internal standard for H and C, Me
2
Se
7
7
Te for 125Te as external standards. Electron spray mass spectra (ESI-MS) were
for Se and Me
2
performed on a Q-Tof micro (YA-105) mass spectrometer. Elemental analyses were performed
on a Carlo Erba Model 1106 elemental analyzer.
2
.2. X-ray crystal structure determination
The single crystal X-ray diffraction measurements were performed on a Rigaku Saturn 724
diffractometer and 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 [16a] and Fourier methods and refined by full-matrix least
squares with the anisotropic non-hydrogen atoms and hydrogen atoms with fixed isotropic
2
thermal parameters of 0.07 Å using the SHELXL 97 [16b] program. The hydrogen atoms were
partially located from difference electron density maps, and the rest were fixed at predetermined
positions. Scattering factors were from common sources [17]. For 17 the structure contained
disordered acetonitrile on a symmetry element and thus could not be defined and refined and this
was removed using the SQUEEZE routine in Platon [18].
2
2
.3. Synthesis
.3.1 General procedure for the synthesis of selenoether ligands 10 and 11. A stirred solution
of N,N-dimethylbenzylamine 9 (1.95 mL, 1.78 g, 13.16 mmol) in dry Et O (50 mL) was treated
2
dropwise with 1.6 M solution of n-BuLi in hexane (8.23 mL, 13.16 mmol) at 0 °C under nitrogen
atmosphere for 30 min. and the reaction mixture allowed to stir for 30 h at room temperature. A
solution of RSeBr (R = 2-MeC
solution of Br in benzene (10 mL) at -114 °C to a solution of R
MeC ) in 150 mL of Et O [19a]. The solution was stirred for 30 min. in an ice bath. The
6
H
4
, 2,6-MeC
6
H
3
) was prepared in situ by slow addition of a
2
2
Se (R = 2-MeC , 2,6-
2
6
H
4
6
H
3
2
resulting white suspension of the lithiated product was transferred via a cannula to the dark red
RSeBr reagent at -114 °C and the resulting suspension was stirred for 2 h at the same
5

temperature and then at room temperature for 4 h. After completion of the reaction (monitored
by TLC), saturated NH Cl aqueous solution (100 mL) was added. The reaction mixture was
O (25 mL x 3) and the organic phase was washed with H O, dried over
and concentrated over rotary evaporator to afford a semi-solid. The resulting
4
extracted with Et
2
4
2
anhydrous Na SO
2
semi-solid was purified by column chromatography using petroleum ether (60-80 °C) as eluent.
The first fraction isolated was R
2
Se and second fraction was the desired selenoether ligands 10
2
and 11.
Synthesis of 10. Reagents used were 2-MeC
6
H
4
SeBr (in situ) prepared using Br (1.05 mL, 6.58
2
mmol) and 1,2-di-o-tolyldiselenide (2.24 g, 6.58 mmol). The product obtained was a yellowish
1
liquid, yield: 0.71 g (40 %). H NMR (500 MHz, CDCl
3
): δ (ppm) 7.40 (d, 1H, Ar-H), 7.20 (d,
1
2
1
6
H, ArCH
H, ArCH
41.29, 139.76, 135.84, 134.60, 132.24, 131.87, 130.40, 129.86, 128.36, 128.02, 126.77, 126.26,
2
), 7.15 (s, 2H, ArH), 7.05 (t, 1H, ArH), 7.03 (t, 1H, ArH), 6.95 (s, 2H, ArH), 3.45 (s,
1
3
2
), 2.34 (s, 3H, ArCH
3
), 2.15 (s, 6H, NMe
2
). C NMR (100 MHz, CDCl ): δ (ppm)
3
7
7
4.58, 45.03, 22.73. Se NMR (76 MHz, CDCl ): δ (ppm) 347. ESI-MS (positive mode): [M+
3
+
H] m/z = 306.0750 (observed), 306.0756 (calculated).
Synthesis of 11. Reagents used were 2,6-Me
2
C
6
H
3
SeBr (in situ) prepared using Br (1.05 mL,
2
6
.58 mmol) and 1,2-bis(2,6-dimethylphenyl)diselenide (2.43 g, 6.58 mmol). The product
1
obtained was a yellowish liquid (yield: 0.80 g, 45%). H NMR (500 MHz, CDCl
3
): δ (ppm) 7.14
(
(
s, 1H, ArH), 7.10 (m, 1H, ArH), 7.06 (t, 2H, ArH), 6.96 (d, 1H, ArH ), 6.83 (d, 1H, ArH ), 6.61
1
3
d, 1H, ArH), 3.44 (s, 2H, ArCH
2
), 2.34 (s, 6H, ArCH
3
), 2.20 (s, 6H, NMe ). C NMR (100
2
MHz, CDCl
3
): δ (ppm) 143.82, 138.74, 135.95, 132.55, 129.74, 129.35, 129.13, 128.90, 128.44,
7
7
1
28.00, 127.97, 125.24, 64.67, 45.07, 24.49; Se NMR (76 MHz, CDCl
3
): δ (ppm) 283. ESI-MS
+
(
positive mode): [M + H] m/z = 320.0912 (observed), 320.0913 (calculated).
2
.3.2 General procedure for synthesis of complexes 16-21. To a toluene-chloroform (2:5 v/v
0 mL) solution of chalcogenoether ligands (10-11 and 12-15 [20]), a chloroform (5 mL)
1
solution of Pd(COD)Cl
stirred for 4 h at room temperature. The precicpiate formed was filtered and washed with hexane
2 mL x 5) and Et O (10 mL x 5). The resulting solid was dried under vacuum to afford a red
2
was added with stirring at room temperature. The reaction mixture was
(
2
solid (in case of selenoether) and a yellowish solid (in case of telluroether) as the desired
6

complex. Suitable crystals for single crystal X-ray diffraction analysis were obtained by slow
diffusion of Et O into CH CN at room temperature.
2
3
Synthesis of compound 16. The reagents used are 10 (0.10 mg, 0.34 mmol), Pd(COD)Cl
2
(0.97
): δ
), 7.15 (m, 2H, ArH), 7.05
1
mg, 0.34 mmol). Yield: 80 mg (80%); m.p. 177-180 °C. H NMR (500 MHz, DMSO-d
6
(ppm) 7.50 (d, 2H, Ar-H), 7.46 (d, 1H, ArCH
2
), 7.36 (d, 1H, ArCH
2
1
3
(
d, 2H, ArH), 3.58 (d, 2H, Ar-CH ), 3.25 (s, 3H, Ar-CH
2
3
), 2.50 (s, 6H, NMe ). C NMR (100
2
MHz, DMSO-d ): δ (ppm) 140.29, 136.76, 134.84, 133.99, 132.14, 130.86, 130.26, 128.85,
6
7
7
1
3
4
27.98, 127.50, 125.58, 124.27, 64.55, 40.12, 23.62. SeNMR (126 MHz, DMSO-d ): δ (ppm)
6
47. Anal. Calcd. for [C16
H19Cl
2
NPdSe] (%): C, 39.90; H, 3.98; N, 2.91;. Found: C 40.14; H
+
.02; N 3.08. ESI-MS (positive mode): [M+Na] m/z = 503.8989 (observed), 503.8992
(calculated).
Synthesis of compound 17. The reagents used are 11 (0.10 mg, 0.31 mmol), Pd(COD)Cl (88
2
1
mg, 0.31 mmol). Yield: 84 mg (84%); m.p. 202-205 °C. H NMR (400 MHz, CDCl
3
): δ (ppm)
7
1
.53 (s, 2H, Ar-H), 7.37-7.43 (m, 1H, ArCH
H, Ar-CH ), 3.43 (d, 1H, Ar-CH ), 3.16 (s, 6H, Ar-CH
): δ (ppm) 283. Anal. Calcd. for [C17
2
), 7.28 (d, 2H, ArH), 7.20 (d, 2H, ArH), 4.21 (d,
7
7
2
2
3
), 2.34 (s, 6H, NMe ). Se NMR (126
2
MHz, DMSO-d
6
H21Cl
2
NPdSe] (%):C 41.20; H 4.27; N
+
2
.83;. Found: C 40.88; H 4.06; N, 2.51. ESI-MS (positive mode): [M+Na] m/z = 517.9146
(observed), 517.9149 (calculated).
Synthesis of compound 18. The reagents used are 12 [20] (0.1 g, 0.29 mmol), Pd(COD)Cl
2
1
(
0.083 g, 0.29 mmol). Yield: 0.75 g (85%); m.p. 154-157 °C. H NMR (400 MHz, DMSO-d
6
): δ
),
): δ (ppm) 140.44, 138.55, 133.23, 130.12,
29.22, 128.33, 126.87, 125.55, 123.11, 120.43, 68.56, 44.22. 125TeNMR (126 MHz, DMSO-d
):
NPdTe] (%):C 34.90; H 3.32; N 2.71. Found: C, 35.08;
(
ppm) 7.63 (d, 1H, Ar-H), 7.43-7.61 (m, 6H, Ar-H), 7.03 (d, 2H, ArH), 4.04 (s, 2H, ArCH
2
1
3
2
1
.72 (s, 6H, NMe
2
). C NMR (100 MHz, DMSO-d
6
6
δ (ppm) 754. Anal. Calcd. for [C15
H, 3.46; N, 2.97. ESI-MS (positive mode): [M+Na] m/z = 539.8702 (observed), 539.8732
calculated).
H17Cl
2
+
(
Synthesis of compound 19. The reagents used are 13 [20] (0.10 mg, 0.28 mmol), Pd(COD)Cl
2
1
(
0.079 g, 0.28 mmol). Yield: 85 mg (85%); m.p. 158-160 °C. H NMR (500 MHz, CDCl
3
): δ
(ppm) 8.17-8.05 (bd, 2H, Ar-H), 7.59-7.45 (bd, 1H, Ar-H), 7.40-7.30 (bd, 4H, ArH), 7.24 (t, 1H,
Ar-H), 3.67 (s, 1H, Ar-CH
2
), 3.34 (s, 1H, Ar-CH
2
), 3.11 (s, 3H, Ar-CH
3
), 2.55 (d, 6H, NMe
2
).
7

13C NMR (100 MHz, CDCl
): δ (ppm) 148.09, 145.66, 144.27, 139.60, 135.12, 130.12, 130.01,
27.50, 126.13, 124.22, 123.55, 68.80, 49.01, 30.11. 125TeNMR (126 MHz, DMSO-d
): δ (ppm)
17. Anal. Calcd. for [C16 NPdTe] (%): C 36.24; H 3.61; N 2.64. Found: C 36.08; H 3.36;
3
1
6
6
H19Cl
2
+
N 2.28. ESI-MS (positive mode): [M+Na] m/z = 553.8886 (observed), 553.8889 (calculated).
Synthesis of compound 20. The reagents used are 14 [20] (0.10 mg, 0.27 mmol), Pd(COD)Cl
2
1
(
(
(
0.078 g, 0.27 mmol). Yield: 80 mg (80%); m.p. 178-179 oC. H NMR (400 MHz, CDCl
3
): δ
ppm)7.54-7.50 (m, 2H, Ar-H), 7.40(t, 1H, Ar-H), 7.38 (t, 1H, Ar-H), 7.26 (d, 2H, Ar-H), 7.17
s, 1H, Ar-H), 4.11 (d, 1H, Ar-CH ), 3.53 (d, 1H, Ar-CH ), 2.79 (s, 6H, Ar-CH ), 2.72 (d, 6H,
). 13C NMR (100 MHz, DMSO-d
): δ (ppm) 147.15, 144.50, 138.44, 131.85, 130.56,
29.85, 128.01, 127.38, 126.14, 124.15, 70.14, 50.11, 31.55. 125TeNMR (126 MHz, DMSO-d
):
δ (ppm) 611. Anal. Calcd. for [C17 NPdTe] (%):C 37.51; H 3.89; N 2.57. Found: C 37.78;
H, 4.06; N, 2.94. ESI-MS (positive mode): [M+Na] m/z = 567.9041 (observed), 567.9045
calculated).
2
2
3
NMe
2
6
1
6
H21Cl
2
+
(
Synthesis of compound 21. The reagents used are 15 [20] (0.10 mg, 0.24 mmol), Pd(COD)Cl
2
1
(
0.068 g, 0.24 mmol). Yield: 85 mg (85%); m.p. 188-190 °C. H NMR (500 MHz, DMSO-d
6
): δ
(ppm) 7.54 (m, 4H, Ar-H), 7.53 (t, 2H, Ar-H), 6.87 (d, 1H, Ar-H), 4.21 (d, 2H, Ar-CH), 3.57 (d,
1
3
2
H, Ar-CH
2
), 2.37 (s, 6H, NMe
): δ (ppm) 158.13, 145.55, 139.56, 135.15, 130.38, 129.31, 128.87, 127.20,
25.13, 124.59, 70.55, 47.78, 40.48, 28.46. 125TeNMR (126 MHz, DMSO-d
): δ (ppm) 586.
Anal. Calcd. for [C21 NPdTe] (%): C, 42.01; H, 4.87; N, 2.33. Found: C, 41.98; H, 4.66; N,
2
), 1.38 (d, 6H, iso-propyl), 1.25 (d, 6H, iso-propyl). C NMR
(100 MHz, DMSO-d
6
1
6
H
29Cl
2
+
2
.23. ESI-MS (positive mode): [M+Na] m/z = 623.9645 (observed), 623.9671 (calculated).
2
.3.3 Synthesis of compound 24. To the stirred solution of 22 [21] (0.10 g, 0.23 mmol) in
(0.065 g, 0.23 mmol) at room temperature. The
acetonitrile (15 mL), was added Pd(COD)Cl
2
reaction mixture was allowed to reflux for 7.5 h. A reddish-brown colored precipitate started to
appear as the reaction progressed. After the completion of reaction (monitored by TLC), the
reaction mixture was allowed to cool to room temperature. The precipitate was filtered off and
was triturated with hexane and ether mixture (1.0:0.5) to give deep red powder of 24. Yield:
1
0
7
7
.062 g, 44%. H-NMR (400 MHz, CDCl
3
):  8.32 (d, 1H), 8.13 (d, 2H), 7.98-7.95 (m, 2H),
.86-7.81 (m, 1H), 7.74 (d, 1H), 7.64 (t, 2H), 7.57 (td, 1H), 7.52-7.49 (m, 3H), 7.44 (t, 2H), 7.31-
.27 (m, 1H), 7.16 (d, 1H). 77Se NMR (400 MHz, CDCl
):1111. Anal. Calcd. for
3
8

C
24
H
17
N
4
ClPdSe: C, 49.51; H, 2.94; N, 9.62. found C, 48.97; H, 2.73; N, 9.14. ESI-MS (positive
+
mode): [(M-Cl)+H] m/z = 546.9707 (observed), 547.9740 (calculated).
3
3
. Results and discussion
.1. Synthesis and characterization
In order to synthesize metal complexes 16-21, first selenoethers 10 and 11 and telluroethers 12-
5 were synthesized by the ortho-lithiation route as reported in the literature (Scheme 1) [19-20].
1
In particular, N,N-dimethylbenzylamine, 9 was treated with n-BuLi to afford the aryllithium
intermediate. When arylselenyl bromide, RSeBr [19a] (generated in situ by slow addition of dry
°
benzene solution of Br
2
to the Et
2
O solution of R
2
Se
2
at -114 C; R = 2-MeC
6
H
4
, 2,6-MeC
6
3
H ),
was added to the lithiated intermediates, nucleophilic substitution reactions took place at the
selenium centers to afford selenoether ligands, 10 and 11. Selenoethers 10 and 11 were purified
by column chromatography using petroleum ether (60-80%) as eluent. The first fraction was
isolated as the corresponding diorganodiselenide (R
2
Se ) and the second fraction obtained was
2
the desired 10 and 11 with the yield of 40 and 45% respectively. It is worth mentioning that the
formation of diselenides significantly reduces the yield of desired selenides 10 and 11. Similarly,
i
when aryltellurenyl bromide, RTeBr (R = C
6
H
5
, 2-MeC
6
H
4
, 2,6-MeC
6
H
3
, 2,6- PrC
6
3
H ) was
added to the lithiated intermediate, telluroether ligands 12-15 were obtained [20]. When
chalcogenoethers 10-15 were treated with equimolar amount of Pd(COD)Cl in toluene-
2
chloroform mixture at room temperature, the desired palladacycles 16-21 were observed in
quantitative yield.
Scheme 1. Synthesis of palladium complexes 16-21 of unsymmetrical chalcogenoether ligands
1
0-15.
9

The chalcogenoethers 22 and 23 were prepared by the reaction of 2-iodoazobenzene with
n-BuLi followed by SeCl and TeBr as reported in the literature report [21, 22]. When
selenoether 22 was treated with Pd(COD)Cl in CH CN under reflux conditions, it resulted in the
formation of deep colored precipitate which was characterized as ortho C-H bond activated
cyclopalladated complex, 24 (Scheme 2). When telluroether 23 was treated with Pd(COD)Cl
under similar condition, as expected, it underwent C-Te bond cleavage to afford [2-
phenylazo)phenyl-C,N´]tellurenyl chloride, 25 [21]. A subsidiary product was also observed
2
4
2
3
2
(
during the reaction. However, its insolubility in common organic solvents precluded
identification.
Scheme 2. Reaction of chalcogenoether ligands 22-23 with Pd(COD)Cl .
2
1
In the H NMR spectra of newly synthesized ligands 10 and 11, recorded in deuterated
chloroform (CDCl
corresponded to the –N(CH
singlet observed at ~3.45 ppm for both these ligands could be assigned to benzylic (-ArCH
protons attached to the –N(CH group. In comparison to the free ligands, small but perceptible
changes in chemical shifts were observed for the –N(CH and benzylic protons of the
3
) at room temperature, a singlet resonance was observed at ~2.2 ppm, which
)
3 2
protons from the N,N-dimethylbenzylamine moiety. The sharp
2
)
)
3 2
)
3 2
complexes and the values lie in the ranges 2.3-2.7 and 3.5-4.2 ppm, respectively. The aromatic
protons and the protons corresponding to the substituents on the ancillary phenyl ring showed
resonance in the expected regions with proper integration values. Similarly, in the 13C NMR
1
0

spectra, the free ligands and the complexes showed expected number of signals within the
chemical shift region  = 0-220 ppm supporting the formulation of the compounds.
A comparative study of the 77Se and 125Te NMR chemical shifts of the free ligands with the
respective metal complexes is given in Table 1. The Se/ 125Te of the free ligands as well as
77
their complexes displayed single resonances suggesting the purity and stability of the synthesized
7
7
compounds. Selenoether ligands 10 and 11 showed Se NMR resonances at 347 and 283 ppm
respectively. These chemical shift values are comparable with the values reported for similar
IChB stabilized diorganoselenides [23]. The respective metal complexes 16 and 17 exhibited
77Se NMR resonances at 632 and 500 ppm respectively, which are significantly downfield
shifted in comparison to the free ligands. Similarly, all the palladated telluroether complexes 18-
2
1
1 showed significant downfield shift in 125Te NMR resonance as compared to the free ligands
2-15 [20]. The significant downfield shifts of the complexes as compared to their free ligands
7
7
are attributed to the coordination of the chalcogen atom to the electropositive Pd(II) ion. The Se
NMR signal for compounds 24 appeared at 1111 and significantly downfield shifted in
comparison to that of free ligand 22 (383 ppm). Again, the considerable difference in the
chemical shift of complex 24 as compared to that of 16 and 17 might be attributed to the fact that
in complex 24, while one azo group was involved in coordination to the Pd center, the other azo
group exhibited strong intramolecular Se···N secondary bonding interaction as evident from the
single crystal X-ray diffraction study (vide infra). As expected, [2-(phenylazo)phenyl-
C,N´]tellurenyl chloride, 25 showed significant downfield shift (1462 ppm, Fig. S13) as
compared to telluride 23 (667 ppm).
Table 1. 77Se/ 125Te NMR chemical shifts for chalcogenoether 10-15, 22-23 and metal
complexes 16-21, 24-25
Chalcogenoether Chemical shift ()
Ref
Complex
Chemical shift
() in ppm
632
in ppm
1
1
1
1
1
1
2
2
0
1
2
3
4
5
2
3
347
283
633
549
410
350
383
667
16
17
18
19
20
21
24
25
500
754
617
611
586
1111
1462
20
20
20
20
22
2
1
1
1

The identity of the new ligands and the metal complexes could be established by High
Resolution Electrospray Ionization Mass Spectrometry (HRMS). In the mass spectra, taken in the
+
positive ion mode, the molecular ion peaks at m/z 306.0750 (Calc. 306.0756 [M+H] ) (10),
+
+
3
20.0912 (Calc. 320.0913 [M+H] ) (11), 503.8989 (Calc. 503.8992 [M+Na] ) (16), 517.9146
+
+
(
Calc. 517.9149 [M+Na] ) (17), 539.8702 (Calc. 539.8732 [M+Na] ) (18), 553.8886 (Calc.
+
+
5
53.8889 [M+Na] ) (19), 567.9041 (Calc. 567.9045 [M+Na] ) (20), 623.9645 (Calc. 623.9671
+
+
[
M+Na] ) (21), 546.9707 (Calc. 547.9740 [(M-Cl)+H] ) (24) substantiated the formation of the
respective compounds. It is worth mentioning that the observed patterns in HRMS for the
compounds were in agreement with the simulated isotopic patterns.
3
.2 Description and Discussion of the Crystal Structures
The identity of the complexes was further validated by single crystal X-ray diffraction study. The
molecular structure of complex 16 is shown in Fig. 1(a). In the molecular structure of 16, the
Pd(II) center is coordinated to one Se atom, one N atom and two cis-chlorido ligands. Deviations
of respective cis- and trans- bond angles around Pd center from 90º and 180º signify the distorted
square planar geometry of the Pd center as indicated by the cis and trans- angles. The N1-Pd1-
Cl1 is 178.74°, the other trans-angle Se1-Pd1-Cl1 [172.91(2)°] deviates slightly more from
linearity while the cis angles vary from 83.898(16) to 95.91(5). The geometry around Se atom is
distorted trigonal pyramidal with C1-Se1-C10 bond angle of 102.6 (1)°. Of particular interest is
the Pd1-Se1 bond distance of 2.4023 (5) Å. This distance is in agreement with the observed
values in similar reported palladated selenoether complexes [2c, 10, 24a-d]. The N-donor atom
makes a six membered chelating ring with the Pd center with a bite angle (N1-Pd1-Se1) of 95.90
(5)°. It is worth mentioning that the chelating ring is puckered and adopts a boat-like
conformation [puckering amplitude (Q) = 0.8252 Å; θ = 93.14º; φ = 236.14º] [24e]. The Pd1-Cl2
bond distance [2.3241(6) Å] trans to Se atom is slightly longer than the Pd1-Cl1 bond distance
[
2.2969(7) Å] trans to N atom. This difference is attributed to the trans influence of selenium
and the chloride ligand. Both Pd-N and Pd-Cl distances are in agreement with the values reported
for similar complexes [2c, 24a-d]. In the packing of 16, there are π···π and C-H···Cl interactions
which link the molecules into a complex 3-D array (Supplementary Information, Fig. S12).
1
2

(a)
(b)
Fig. 1. Molecular structures of (a) 16 and (b) 17 at 50% probability level. Selected metrical
parameters for 16 are: Pd-N1 2.1095(18) Å, Pd-Se1 2.4022(5) Å, Pd-Cl1 2.2969(7) Å, Pd-Cl2
2
.3241(7) Å, N1-Pd1-Cl1 178.74(5)°, N1-Pd1-Cl2 91.16(5)°, Cl1-Pd1-Cl2 89.02(2)°, N1 Pd1
Se1 95.91(5)°, Cl1-Pd1-Se1 83.898(16)°, Cl2-Pd1-Se1 172.905(16)°; and for 17 are: Pd-N1
2
1
.1095(18) Å, Pd-Se1 2.4022(5) Å, Pd-Cl1 2.2969(7) Å, Pd-Cl2 2.3241(7) Å, N1-Pd1-Cl1
75.80(4)°, N1-Pd1-Cl2 91.25(5)°, Cl1-Pd1-Cl2 89.39(2)°, Cl1-Pd1-Se1 85.385(19)°, Cl2-Pd1-
Se1 174.755(15)°.
The molecular structure of compound 17 [Fig. 1(b)] is similar to that of 16, except the
fact that in the place of 2-methylphenyl ring, 2,6-dimethylphenyl ring unit is bonded to the
selenium atom. Due to the steric constrains of the 2,6-dimethylphenyl unit, the environment
about the central Pd in 17 is not as planar as in 16. The Pd1-Se1 bond distance is 2.3910 (7) Å,
which closely resembles the respective bond distance in complex 16 [2.4023 (5) Å]. The N1-
Pd1-Se1, N1-Pd1-Cl1, Se1-Pd1-Cl1 bond angles are 94.00 (4)°, 175.71 (4)° and 174.76 (2)°
respectively. All these bond angles are in line with that of the previous structure, 16 and the
chelate ring also adopts a boat-like conformation with similar puckering, θ, and φ values.
Similarly, Pd1-N1, Pd1-Cl1 and Pd1-Cl2 are comparable to the values observed in complex 16
and similar reported complexes [2c, 24a-d]. In the packing of 17 there are π···π and C-H···Cl
1
3

interactions which link the molecules into an octameric unit (Supplementary Information, Fig.
S13).
The molecular structure of complex 18 is shown in Fig. 2. In the molecular structure of 18, the
geometry around the Pd(II) center is distorted square planar and is coordinated to one Te atom,
one N atom and two cis-chlorido ligands. There are two molecules in the asymmetric unit (Z´ =
2
) with no statistically significant differences in their internal bond lengths but significant
differences in their bond angles and conformations adopted due to differences in their
intermolecular contacts. For molecule A, angles and conformation adopted are very similar to 16
and 17. However, for molecule B the deviations from planarity for the donor atoms are
significant. In fact, atoms Pd2, Te2, N1B, and Cl1B form the best plane with C1B and Cl2B
significantly deviating from this plane (0.505 (2) Å and 0.814 (2) Å, respectively). The
coordination environment around metal center in each is similar to the selenoether complexes 16
and 17. The geometry around Te atom is distorted trigonal pyramidal [the sums of the angles are
2
97.3° and 299.1°, respectively). The Pd-Te distances are 2.5165 (10) and 2.5021 (8) Å,
respectively. These distances are comparable to the values reported for palladated telluroether
complexes [25]. As in complexes 16 and 17, the N-donor atom makes a six membered chelating
ring with the Pd center with bite angles (N-Pd-Te) of 94.28 (4)° and 96.29 (5)°, respectively.
Both chelating rings are puckered and adopt boat-like conformations [for A; puckering amplitude
(Q) = 0.9739 Å, θ = 81.25°, φ = 3.69°: for B; puckering amplitude (Q) = 0.8030 Å, θ = 91.24°, φ
=177.81°: expected values for boat are θ = 90.0; φ = k x 60] although it can be seen that A
deviates more from this idealized conformation than B. The differences between the two
molecules are due to the different intermolecular contacts each makes. In A these are between
the Pd and Te of adjoining molecules, which link A into symmetrically related dimers while in B
there are Te···Cl intermolecular interactions which link B into symmetrically related dimers. The
Pd-N distances are comparable to the values observed in similar reported complexes [25]. Due to
the difference in the trans influence of the tellurium and chloride ligands, there are two different
Pd-Cl bond distances observed in the complex. In particular, the Pd1-Cl2 bond [2.3695 (10) and
2
.3797 (8) Å] trans to the Te atom is considerably longer than that of Pd1-Cl1 bond [2.3003 (9)
and 2.3100 (9) Å] trans to the nitrogen atom. From the Pd-Cl bond distances in all the
selenoether and telluroether complexes, it is observed that the Pd-Cl bond trans to Te atom is
significantly longer in comparison to that of the Pd-Cl bond trans to Se atom. This observation
1
4

indicated that Te atom exhibited higher trans influence in comparison to that of Se atom. The
Te1-Pd1-Cl2 and N1-Te1-Cl1 bond angles exhibit slight deviation from linearity with angles of
1
74.231 (14)°/ 167.565(16) and 175.86 (4)°/ 175.10(5) respectively. In the packing of A and B
both are involved in π···π, C-H···Cl and the above mentioned Pd…Te and Te···Cl interactions
which link the molecules into a complex 3-D array (Supplementary Information, Fig. S14).
Fig. 2. Molecular structures of the two molecules for 18 showing their differences in
intermolecular contacts and drawn at the 50% probability level. Selected metrical parameters:
Pd1-Te1 2.5165(10), Pd1…Te1 3.7544(9) Å, Pd1-Cl1A 2.3003(9) Å, Pd1-Cl2A 2.3695(11) Å,
Pd1-N1A 2.1101(16) Å, Pd2-Te2 2.5021(8) Å, Te2···Cl1B 3.3861(12) Å, Pd2-Cl1B 2.3100(9)
Å, Pd2-Cl2B 2.3797(8) Å, Pd2-N1B 2.1019(17) Å, N1A-Pd1-Cl1A 175.86(4)°, N1A-Pd1-
Cl2A 91.30(5)°, Cl1A-Pd1-Cl2A 90.54(3)°, N1A-Pd1-Te1 94.28(5)°, Cl1A-Pd1-Te1 83.99(3)°,
Cl2A-Pd1-Te1 174.231(14)°, N1B-Pd2-Cl1B 175.10(5)°, N1B-Pd2-Cl2B 92.22(5)°, Cl1B-Pd2-
Cl2B 90.11(3)°, N1B-Pd2-Te2 96.29(5)°, Cl1B-Pd2-Te2 82.11(3)°, Cl2B-Pd2-Te2
1
67.565(16)°.
The molecular structures of complexes 20 and 21 are shown in Fig 3 (a) and Fig 3 (b)
respectively. It should be noted that in the case of 21 there are 2 molecules in the asymmetric
unit (Z´ = 2) but with no significant differences in their metrical parameters. Both these
structures are isostructural with 18 except the fact that in the place of phenyl ring in complex 18,
2
,6-dimethylphenyl and 2,6-diisopropylphenyl rings are bonded to the tellurium atom in
complexes 20 and 21 respectively. In both structures the chelate rings are boat-like [20:
1
5

puckering amplitude (Q) = 0.954 Å, θ = 82.52°, φ = 4.40°; 21: puckering amplitude (Q) = 0.867
Å, θ = 94.19°, φ = 179.21° and puckering amplitude (Q) = 0.839 Å, θ = 87.10°, φ =358.84°]. The
Pd1-Te1 distances in the molecular structures of 20 and 21 are 2.52423 (15) Å and 2.4990 (3)/
2
.4973 (3) Å respectively. Both these distances are in agreement with the value observed in
complex 18. The N1-Pd1-Te1 bite angles in 20 and 21 are 94.17 (3)° and 94.71 (6) °/ 95.45 (6)°
respectively and are consistent with the corresponding bond angle observed in complex 18
[
94.28 (4)°]. The Pd1-N1 distances in 20 and 21 respectively are agreement with the values
observed in complex 18 and palladated selenoether complexes 16 and 17. Similarly, the Pd-Cl
bond distances in complex 20 and 21 are comparable to the values observed in 18 and show the
same trends. Interestingly, in the case of 21 where there are 2 molecules in the asymmetric unit,
they form loosely associated dimers through Pd···Te interactions. In the packing of 20 and 21
only 20 is involved in π···π interactions probably due to the steric bulk of the iso- propyl
substituents in 21 while both are involved in extensive C-H···Cl intermolecular interactions
(Supplementary Information, Fig. S15-S16).
Fig. 3. Molecular structures of (a) 20 and (b) 21 at 50% probability level. Selected metrical
parameters for 20: Pd1-Cl1 2.3079(4) Å, Pd1-Cl2 2.3628(4) Å, Pd1-N1 2.1110(13) Å , Pd1-Te1
2
.52423(15) Å, N1-Pd1-Cl1 174.82(4)°, N1-Pd1-Cl2 91.08(4)°, Cl1-Pd1-Cl2 89.912(16)°, N1-
Pd1-Te1 94.17(3)°, Cl1-Pd1-Te1 85.078(12)°, Cl2-Pd1-Te1 174.168(12)°. Selected metrical
parameters for 21: Pd1-Cl1 2.3043(7) Å, Pd1-Cl2 2.3476(8) Å, Pd1-N1 2.110(2) Å, Pd1-Te1
2
.4990(3) Å, Pd1···Cl1A 3.6423(3) Å, PdA-Cl1A 2.3084(6) Å, PdA-Cl2A 2.3426(7) Å, PdA-
N1A 2.109(2) Å, PdA-Te1A 2.4973(3) Å, N1-Pd1-Cl1 176.12(6)°, N1-Pd1-Cl2 93.19(6)°, Cl1-
Pd1-Cl2 89.58(3)°, N1-Pd1-Te1 94.71(6)°, Cl1-Pd1-Te1 82.61(2)°, Cl2-Pd1-Te1 171.93(2)°,
1
6

N1A-PdA-Cl1A 176.23(6)°, N1A-PdA-Cl2A 92.63(7)°, Cl1A-PdA-Cl2A 90.21(3)°, N1A-PdA-
Te1A 95.45(6)°, Cl1A-PdA-Te1A 81.779(18)°, Cl2A-PdA-Te1A 171.81(2)°.
The molecular structure of complex 24 with symmetrical selenoether ligands is shown in Fig.
4
. As in previous cases, in 24 the Pd center is four-coordinated and adopts a distorted square
planar geometry. The coordination sites around Pd center are occupied by one selenium atom,
mutually trans-N and Cl atoms and the fourth coordination site is provided by carbon atom of the
phenyl ring metallated at the ortho-position and in this case results in a five-membered chelate
ring. The spatial arrangement around Se atom is distorted tetrahedral, taking the Se···N
intramolecular interaction into account. It is worth noting that, the spatial arrangement of the
ligands around the Pd center and the associated bond lengths and bond angles are in close
agreement with the molecular structure of a palladium complex of the azobenzene based
selenoether ligand reported by Jones et al [26]. In particular, the Pd-Se bond distance in complex
2
4 is 2.5222 (3) Å. This distance is comparable to the value observed by Jones et al. in their
complex [2.4995 (4) Å], but significantly longer than the values observed in complex 16 and 17
and similar reported palladacycles [2c, 10, 24a-d]. The Pd1-C12 bond distance of 1.984 (2) Å in
complex 24 is consistent with the value observed by Jones et al. [1.987 (3) Å]. Similarly, the
Pd1-N1 distance of 1.9888 (19) Å is comparable with the value reported by Jones et al. [1.989
(2) Å]. The N4 atom from the second azobenzene group is involved in a secondary bonding
interaction with the Se atom with Se1···N4 bond distance of 2.623 (3) Å. This intramolecular
Se1···N4 bond distance is much shorter than Σ rvdw (Se, N) i.e. 3.45 Å but is longer than Σ rcov
(Se, N) i.e. 1.91 Å [27, 28]. In the packing there are intermolecular π…π interactions involving
the chelate ring and C1B – C6B phenyl ring (Supplementary Information, Fig. S17).
1
7

Fig. 4. Molecular structure of 24 at 50% probability level. Selected metrical parameters for 24:
Pd-Cl 2.2903(6) Å, Pd-N1A 1.9888(19) Å, Pd-C12A 1.984(2) Å, Pd-Se 2.5222(3) Å, Se···N2B
2
.617(2) Å, C12A-Pd-N1A 79.59(9)°, C12A-Pd-Cl 94.01(7)°, N1A-Pd-Cl 172.56(6)°, C12A-
Pd-Se 164.11(7)°, N1A-Pd-Se 85.84(6)°, Cl-Pd-Se 100.919(18)°.
4
. Conclusion
In conclusion, we have reported the synthesis of a series of palladium(II) complexes of IChB
stabilized unsymmetrical selenoether ligands which contain one coordinating group with sp3
donor atom. As evident from the literature, due to the strong IChB in case of symmetrical
telluroether ligands containing two possible coordinating groups, the attempted metallation
afforded transmetallated or cleaved product. Herein, by fine tuning the IChB, in particular, using
unsymmetrical telluroether ligand containing one coordinating group, we have succeeded in
isolating 1:1 palladated telluroether complexes. In comparison to the symmetrical telluroether
ligand with two coordinating groups, when unsymmetrical telluroether ligands are used which
contain one coordinating group, the lability of Te-C bond trans to Te···N IChB interaction is
reduced. This results in the isolation of desired 1:1 palladium complex. In all synthesized
palladium chalcogenoether complexes, the N-donor atom which was involved in IChB
interactions with the chalcogen atom in the free ligands, makes a six membered chelating ring
with the metal center. It is worth noting that the telluroether complexes reported in this paper are
first of their kind for ligand containing N,N-dimethylbenzylamine moiety.
Acknowledgements
1
8

H. B. S. gratefully acknowledges the Department of Science and Technology, New Delhi, for the
J. C. Bose Fellowship. A. G is thankful to the UGC.
Conflicts of interest
The authors declare no conflict of interest.
Appendix A. Supplementary data
CCDC 1510104 (16), 1510105 (17), 1510106 (18) 1510107 (20) 1510108 (21) and 1890222 (24)
contains the supplementary crystallographic data for this paper. These data can be obtained free
of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-
0
33; or e-mail: deposit@ccdc.cam.ac.uk.
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2
0

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2
2

The synthesis of a series of palladium(II) complexes of unsymmetrical, hybrid selenoether and
telluroether ligands is reported. While the reaction of Pd(II) precursors with symmetrical
telluroether ligands containing two coordinating groups results in cleavage of Te-C bond, no
such labilisation is observed using unsymmetrical ligands containing one coordinating group.
2
3