Facile one-step synthesis of palladium tellurium alloy nanorods

Article abstract of DOI:10.1016/j.jorganchem.2018.04.024

A palladium-tellurium binary alloy nanomaterial was synthesized by a one-pot reaction of bis(4-methoxyphenyltelluro)methane [(4-CH₃O-C₆H₄Te)₂CH₂](1) and allylpalladium (II)chloride dimer [(η³-C₃H₅)₂Pd₂(μ-Cl₂)] (2) in 1:1 ratio using methylene chloride as solvent at ambient conditions. In addition to the Pd₂₀Te₇ alloy nanomaterial (3) generated, a palliadum (II) tellurolate complex [PdC1(μ-TeC₆H₄-OCH₃)Te(C₆H₄-OCH₃)₂]₂ (6), and other organic and organotellurim compounds were isolated as byproducts using column chromatography. The palladium-tellurium binary alloy nanomaterial and other byproducts from the reaction were characterized by powder X-ray diffraction (PXRD), NMR, GC-MS, transmission electron microscopy (TEM), and single crystal X-ray diffractions (XRD) methods. The palladium-tellurium binary alloy nanomaterial was obtained as single-phase Pd₂₀Te₇ nanorods, under mild conditions. TEM results indicated that the nanorods are less than 15 nm in diameter and range from 40 to 200 nm in length. A nanomaterial mixture was isolated with two binary-phases Pd₂₀Te₇ and Pd₁₀Te₃ when benzene was used as solvent. Compound 6 was successfully tested for catalytic activity for the Heck Reaction and produced a mixture of PdTe₂ with Pd₁₃Te₃ nanomaterials as byproducts.

Full text of DOI:10.1016/j.jorganchem.2018.04.024

Accepted Manuscript
Facile one-step synthesis of palladium tellurium alloy nanorods
Kadarkaraisamy Mariappan, Shelton J.P. Varapragasam, Matt R. Hansen,
Shivatharsiny Rasalingam, Madhubabu Alaparthi, Andrew G. Sykes
PII:
S0022-328X(18)30267-5
10.1016/j.jorganchem.2018.04.024
JOM 20416
DOI:
Reference:
To appear in: Journal of Organometallic Chemistry
Received Date: 13 February 2018
Revised Date: 12 April 2018
Accepted Date: 13 April 2018
Please cite this article as: K. Mariappan, S.J.P. Varapragasam, M.R. Hansen, S. Rasalingam, M.
Alaparthi, A.G. Sykes, Facile one-step synthesis of palladium tellurium alloy nanorods, Journal of
Organometallic Chemistry (2018), doi: 10.1016/j.jorganchem.2018.04.024.
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ACCEPTED MANUSCRIPT
Journal of Organometallic Chemistry
(Article)
Revision, April 2018
Facile one-step synthesis of palladium
tellurium alloy nanorods
∗
Kadarkaraisamy Mariappan , Shelton J. P. Varapragasam, Matt R. Hansen, Shivatharsiny
Rasalingam, Madhubabu Alaparthi, and Andrew G. Sykes
Contribution from the Department of Chemistry
University of South Dakota, Vermillion, SD 57069,
United States of America.
*
To whom correspondence should be addressed: mkadarka@usd.edu

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1
. Introduction
Material chemists are interested in making new alloy nanomaterials [1-2] because of their
industrial applications as catalysts and components in electronic devices. Many
traditional methods are available to make metal nanomaterials and homogeneous binary
nanomaterials [3-7]; however a foremost challenge remains making heterogeneous binary
alloy nanomaterials with multiple compositions and crystallinities [8-10]. Platinum group
elements made with chalcogenides are common [11], while palladium-tellurium binary
mixtures are a class of alloys that have only gained recent interest due to their potential
application as heterogeneous catalysts. Palladium and tellurium form several binary
phases (Pd Te ), including Pd Te [12-14]. These binary phases are typically prepared
x
y
20
7
either by milling a mixture of Pd and Te in appropriate ratios with a planetary-type ball
mill under ambient conditions [15], or by thermolysis of palladium organometallic
complexes [16-17]. Synthetic conditions are crucial for composition and structure of an
alloy. Drastic conditions, solvent and unwanted side product(s) [18-19] may reduce
catalytic activity. Sometimes uneven size may also reduce the lifetime of the catalyst.
Takahasi et al designed a synthetic route for PdTe alloy nanoparticles by controlling the
reaction pH conditions based on metal complex calculations using the critical stability
2
+
constants. They reduced a solution containing specific metal complexes of [Pd (EDTA)]
and Te-citric acid with hydrazine to get well-crystallized Pd20Te alloy nanoparticles of
Pd Te and its chemical composition was confirmed by using EXAFS and PXRD [20].
7
2
0
7
Crystals of Pd Te have produced by chemical vapor transport reactions using palladium
1
3
3
(
II) halide as transport agent by Janetzky et al. The crystal structure of Pd Te was
13 3
established by means of single crystal X-ray diffraction [21]. Recently Singh and
1

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coworkers reported the synthesis of palladium-chalcogenide nanoparticles when a Pd(II)
complex containing organochalcogenide ligands was used to catalyze Heck and Suzuki
Miyaura reactions [22-23]. However, the nanomaterial Pd Te phase has not been
2
0
7
synthesized without thermolysis/annealing or the addition of any external agents.
H C
3
Cl
O
Te
Te
O
+
Pd
Pd
CH3
Cl
2
1
CH Cl , RT
2
2
Pd20Te7
3
CH3
H C
3
O
Te
5
O
O
O
H C
CH3
3
4
H C
3
O
CH3
CH3
O
O
CH3
O
O H
7
H C
3
Te
Te
Te
O
Te
Cl
O
Pd
Pd
CH3
Cl
O
6
H C
3
Scheme 1: Synthetic scheme for making Pd Te alloy nanomaterial
2
0
7
Our original aim was to make a paddle wheel type palladium complex of Bis-(4-
methoxyphenyltelluro)methane (1) with the allylpalladium(II) chloride dimer (2), but
ended up isolating a Pd-Te binary alloy nanomaterial instead. Here we report a procedure
7
to make nanorods of Pd20Te alloy in a one-step synthesis using organometallic
precursors under ambient conditions. In this study, we have synthesized and
characterized a palladium-tellurium (Pd Te ) alloy nanomaterial; identified other organic
2
0
7
2

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and organometallic byproducts; and studied the catalytic behavior of an isolated Pd(II)
tellurolate complex.
2
. Experimental section
.1 General procedure
2
1
13
H and C NMR spectra were obtained using a Bruker 400 MHz instrument at room
temperature using deuterated solvents. Mass spectrometry was conducted using a
Shimatzu GC mass spectrometer. Elemental analyses were conducted using an Exeter
CE-440 Elemental analyzer. Melting points were determined using open capillaries and
were uncorrected. Powder X-ray diffraction patterns were measured with a Rigaku
Ultima IV at room temperature using a Ni filtered Cu Kα radiation (λ = 1.5408
Å). These patterns were recorded using at the following operative conditions: voltage of
4
0 kV, current of 44 mA, scan rate 1°/min with the step size of 0.02°, and the two theta
range (2Φ) is from 10° to 80°. Transmission electron microscopy (TEM) data was
obtained using a Technai Spirit G2 Twin (FEI Company) transmission electron
microscope fitted with LaB6 filament operated at 120kV. TEM sample was prepared by
grounding the sample well in hexane followed by dispersion also in hexane. One drop of
this hexane dispersed sample was placed on ultrathin carbon film 200 mesh copper
(Electron Microscopy Sciences), and the hexane was allowed to evaporate, then dropcast
onto carbon film (20-30 nm) on 200 mesh copper grid (Electron Microscopy
Sciences). Electron micrographs were obtained by projection onto an Orius SC200 CCD
Digital Camera and recorded with Digital Micrograph software. A qualitative, direct
surface pXRF measurement was done on the nanomaterial (Pd Te ) by Bruker Tracer III
2
0
7
SD IV contain X-ray tube (Rh target) at room temperature. The pXRF data and spectra
3

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are uncorrected. Quantitative determination of palladium was determined using atomic
absorption spectroscopy [24] and tellurium by titration method [25]. A Varian SpectrAA
2
00 atomic absorption spectrometer equipped with deuterium background correction was
used. The system has an automatic pc controlled 4-lamp turret, gas control, slit and
wavelength selection. The instrumental parameters were adjusted according to the
manufacturer’s recommendations. The air-acetylene flow rate and the burner height were
adjusted in order to obtain the maximum absorbance signal while aspirating the Pd(II)
solution in water.
2
.2 Crystallography
X-ray quality crystals of compound 6 was obtained by slow evaporation of a methylene
chloride:methanol (96:4) solution. Crystallographic data for 6 was collected at 273 K
using a Bruker SMART APEX II diffractometer by MoK radiation. The data reduction
α
and refinement were completed using the WinGX suite of crystallographic software [26
and 27]. The structure was solved using SIR97 [28]. All hydrogen atoms were placed in
ideal positions and refined as riding atoms with relative isotropic displacement
parameters. Platon Squeeze removed a disordered diethyl ether solvent from the structure
equal to ~67 electrons/cell equal to approximately 1.5 ether molecules [29]. Table S1 lists
additional crystallographic and refinement information. One of the methoxy groups in 6
was found disordered and modelled over two positions 50:50. The cif file of structure 6
has been deposited at Cambridge Crystallographic Data Center and its CCDC number is
1
823651.
4

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2
.3 Chemicals and reagents
Bis-(4-methoxyphenyltelluro)methane (1) has been synthesized using an available
procedure [30] and its purity was checked by NMR and its structure was confirmed by
single crystal X-ray diffraction [31] studies (SI Fig. 1-3). Allylpalladium (II) chloride
1
dimer (2) was purchased from Sigma-Aldrich and its purity was checked by H NMR
spectroscopy (SI Fig.4) each time prior to use. Both the organotellurium and
organopalladium precursors are long lasting in solid form under ambient conditions as
2 2 3 2 2
well as solution form with halogenated solvents such as CH Cl and CHCl . CH Cl was
TM
purchased from Aldrich and purified using a PURE SOLV solvent purification system.
Benzene and CHCl were purchased from Aldrich and purified by available procedures
3
[32].
2
.4 Synthesis of Pd Te Nanomaterial (3)
20 7
Bis-(4-methoxyphenyltelluro)methane, 1 (0.05 mg, 0.104 mmol) dissolved in 10 mL of
CH Cl was mixed with a solution of 0.038 mg (0.104 mmol) of allylpalladium(II)
2
2
2 2
chloride dimer (2) in 10 mL of CH Cl . A clear red solution was obtained as soon as 1
and 2 were mixed and the solution was stirred at room temperature. A cloudy red solution
formed overnight under ambient conditions (SI Fig.5), and the solution was centrifuged
to isolate a black solid. The black solid was washed two times with fresh CH Cl and
2
2
allowed to dry. Yield is 0.031g, ~10%. Elemental analyses calculated for Pd Te . C,
2
0
7
0
6
.00; H, 0.00; N, 0.00; Pd, 70.44; Te, 29.56 %. Found: C, 0.11; H, 0.04; N, 0.01; Pd,
9.76; Te, 28.96 %.
The filtrates were pooled, loaded into a silica gel column and eluted using methylene
chloride, methylene chloride:Ethyl acetate (90:10) and methylene chloride:methanol
5

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(96:4)
mixture.
1-methoxy-4-(4-methoxyphenyl)benzene
(4),
bis-(4-
methoxyphenyl)telluride (5) and 4-methoxybenzyl alcohol (7) were the byproducts
isolated from the filtrate along with the organomettalic Pd(II) tellurolate complex (6).
Compounds 4-7 were characterized by GC-MS, NMR spectroscopy (SI Fig.6-13) and X-
ray crystallography.
2
.5 Palladium(II) tellurolate complex (6)
Compound 6 was obtained as a red solution eluted by CH
2
2 3
Cl : CH OH (96:4) while
isolating compound 3. The red solution was evaporated slowly to obtain X-ray quality
crystals. Yield is 0.005g (as crystals), ~4% with melting point = 115-117 °C (dec).
Elemental analyses calculated for C H O Pd Te Cl . C, 35.01; H, 3.22; Te, 35.42 %.
4
2
42
6
2
4
2
1
Found: C, 34.97; H, 3.25; Te, 33.94 %. H NMR (at 25 °C, CDCl
3
): δ 3.81 s, 12H, CH
3
-
O from telluride); 3.87 (s, 6H, CH -O from tellurolate); 6.85-6.91 (m, 6H, ArH); 7.01-
3
7
.03 (m, 4H, ArH); 7.29-7.31 (m, 6H, ArH); 7.70 -7.72 (d, 4H, J=8Hz, ArH); 7.96 -7.98
d, 4H, J=8Hz, ArH).
.6 Catalytic Heck Reaction of 6
(
2
A solution of styrene (0.137 mL, 1 mmol), bromobenzene (0.12 mL, 1.1 mmol) and
triethylamine (0.280 mL, 2 mmol) in 5 mL of DMF with a catalytic amount (0.001 g,
~0.001 mmol) of 6 was refluxed for 24 hours and monitored by TLC. After completion, a
black solid was separated by centrifugation from the reaction mixture. The filtrate was
diluted with 10 mL of H O and extracted with methylene chloride (3 x 10 mL), and the
2
organic layer was combined, dried over anhydrous MgSO , and the solvent was removed
4
under reduced pressure. Stilbene formation was confirmed by GC-MS. Yield (~30%) was
calculated on the basis of styrene. The black solid that remained after the reaction was
6

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completed was found to be a mixture of Pd-Te nanomaterial binary phases.
Results and Discussion
2
.7 Synthesis of Pd Te Nanomaterial and organic and organometallic
20 7
byproducts
The reaction of Bis-(4-methoxyphenyltelluro)methane (1) with allylpalladium (II)
chloride (2) led to the formation of a pure Pd20Te binary alloy nanomaterial (3) with
other byproducts. A silica gel column using CH Cl , CH Cl :Ethyl acetate (90:10) and
7
2
2
2
2
CH Cl :CH OH (96:4) as eluents were used to isolate other byproducts. Formation of
2
2
3
compounds 3-7 when 1 mixes with 2 in CH Cl does not depending upon light or oxygen.
2
2
The yield of byproducts and the composition of Pd-Te alloy nanomaterials depended on
the reaction time, the purity of precursors (1 and 2), the choice & purity of solvent. Other
byproducts isolated were 1-methoxy-4-(4-methoxyphenyl)benzene (4); bis-(4-
methoxyphenyl)telluride (5); a binuclear palladium(II) tellurolate complex (6), and 4-
methoxybenzyl alcohol (7) (Scheme 1). Formation of these neutral organic and
organometallic compounds shows there is a remarkable structural change in 1 and 2. By
products 1-methoxy-4-(4-methoxyphenyl)benzene (4) (SI Fig. 6-8), bis-(4-
methoxyphenyl)telluride (5) ( SI Fig. 9-10) and 4-methoxybenzyl alcohol (7) (SI Fig. 11-
1
3) have been characterized by GC-MS and NMR spectroscopy. Apart from compounds
3
-7, a chloropropane and 4-methylanisole were also identified (SI Fig. 14) in the mother
liquor and characterized by GCMS.
.8 Possible mechanism for the formation of compounds 3-7
2
A variety C-C coupling reactions in aqueous media has been discussed previously by
Chao [33]. Compound 1 underwent a drastic structural change through a series of free
7

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radical reactions when it mixes with 2. Even though anhydrous solvents were used in
these studies, it is likely moisture is present as well since the reaction was carried out at
ambient conditions for a length period of time. Polarity by trace amount of water might
have helped stabilizing the intermediates [34, 35] that were formed in the reaction
progress. Compound 1 might have formed an unstable Pd complex (SI Fig.5a) with
allylpalladium(II) chloride dimer by displacing allyl ligand. A reductive elimination of
unstable Pd complex lead the formation of elemental palladium, and it also triggered the
2
-
oxidation of tellurium as Te in compound 1 through free radical reaction. A peak
observed for chloropropane (combination allyl portion + HCl) (SI Fig. 14) in the GCMS
of the mother liquor before column chromatography clearly supports the reductive
elimination process. Free radical recombination is the driving force behind the formation
of compounds 4 and 5. Free radical formation may also lead the formation of elemental
tellurium [36-37]. The methylene group (-TeCH Te-) in 1 might have formed a triplet
2
carbene (:CH ) after homolytic cleavages. Our speculation is 4-methoxyphenyl radical
2
underwent a disproportionation reaction to yield a 4-methoxybenzyl carbocation and 4-
methoxybenzyl carbanion. The 4-methoxybenzyl carbocation reacts with water followed
by deprotonation to yield compound 7 and a proton, and the resulting proton reacts with
4
-methoxybenzyl carbanion to generate 4-methylanisole. Observation of a peak for 4-
methylanisole (SI Fig. 14) in the GCMS of the mother liquor before column
chromatography supports the disproportionation reaction of 4-methoxyphenyl radical.
This mechanism is shown in the supplementary materials. Chloropropane and 4-
methylanisole were not included as one of the products in reaction scheme since both
haven’t been isolated by column chromatography.
8

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2
.9 Powder X-ray Diffraction
A PXRD study was used to provide information about the crystalline structure and
chemical composition of the black material isolated from CH Cl and benzene as
2
2
solvents. The PXRD pattern in Figure 1 shows a crystalline material that matches well
with single-phase Pd Te (PDF: 01-089-2014) when CH Cl was used as solvent [13],
2
0
7
2
2
and SI Fig. 15 shows the PXRD spectrum of Pd Te with complete indexing list. The
2
0
7
crystal system is trigonal with the space group R-3 (148). The cell parameters are a =
1.7970; b = 11.7970 and c = 11.1720; α = β = 90° ; and γ = 120°. A mixture of phases
Pd Te & Pd Te [38] is obtained when benzene (SI Fig. 16) was used as solvent and
1
2
0
7
10
3
mixture formation was confirmed by comparing peak indexes (SI Fig. 17). The peaks of
Pd Te are moderately sharp, and several trials involving the combination of 1 and 2 in
2
0
7
CH
2
Cl
2
7
as solvent in a 1:1 ratio produced only the single phase of Pd20Te .
Pd Te : Synthesized
20
7
Pd Te : (PDF:01-089-2014)
7
20
10
20
30
40
50
60
70
80
2 θθ Degree
Figure 1: PXRD of nanomaterial obtained from CH Cl as solvent vs standard phase of
2
2
Pd Te from reference 13.
2
0
7
9

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2
.10 Transmission Electron Microscopy:
The size and morphology of the Pd Te nanomaterial was examined further by
2
0
7
transmission electron microscopy (TEM) studies, and select TEM images of Pd Te are
2
0
7
given in Figure 2A as well as in SI Figure 18. Calcination was done on the binary alloy
nanomaterials at 450 °C for 5 h to remove organic moieties before conducting TEM
studies. TEM indicates that the black binary Pd Te obtained from CH Cl solution is a
2
0
7
2
2
highly uniform, mono-dispersed nanomaterial. TEM also revealed that the majority of
nanomaterials are nanorods. Nanorod lengths vary in a range from 50 nm to 200 nm with
under 10 nm thickness. TEM images (Fig. 2B) were collected in the similar fashion for
the binary Pd-Te alloy mixture obtained when benzene was used as solvent (Pd Te +
2
0
7
Pd Te ), which are also uniform, mono-dispersed nanoparticles. Size of the nanomaterial
1
0
3
is ~ 15-30 nm from benzene solution.
A
B
Figure 2: A) TEM image of Pd20Te
7
2 2
nanomaterial obtained from CH Cl as solvent. B)
Nanomaterial obtained from benzene as solvent. Both images are in identical resolution.
1
0

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2
.11 X-Ray Fluorescence Spectroscopy:
X-Ray fluorescence spectroscopy was used to find the qualitative chemical composition
of the nanomaterials. Selective and self-labelling XRF spectrum is shown in SI Fig. 19.
Relative peak intensities in pXRF of Pd Te alloy nanomaterial support the chemical
2
0
7
composition. A peak observed at 21.18 keV corresponding to palladium K and peaks at
α1
2
3.8 keV and 24. 3 keV are due to Kβ1 and Kβ2 for palladium respectively. Peaks
appeared at 27.5 keV, 30.9 keV and 31.7 keV are due to tellurium’s Kα1,
Kβ1 and Kβ2
correspondingly. CHN elemental analyses of 3 also confirmed that there is no carbon,
hydrogen or nitrogen present in the palladium-tellurium nanomaterial. Quantitative
amount of palladium (Pd%) in 3 was determined by atomic absorption spectroscopy
using sodium tetrachloropalladate as standard. Tellurium percentage in 3 was determined
by treating 3 with nitric acid and 70% perchloric acid (1:1), followed a back titration of
ferrous ammonium sulfate and potassium dichromate. Percentage data of Pd and Te in
compound 3 is given under elemental analyses in experimental section 2.4. Atomic
absorption spectroscopic data for palladium; and titration data for tellurium in 3 matches
well with the accepted value.
2
.12 NMR spectroscopy of 6
The aliphatic and aromatic proton ratio matches the structure proposed for 6 in Scheme 1.
The splitting pattern observed in the aromatic region suggests that 6 retains its structure
in solution as well. Two singlets which appear at 3.81 ppm and 3.87 ppm are due to the
methoxy groups from the bis-(4-methoxyphenyl)telluride (5) ligand and the 4-
methoxyphenyltellurolate bridging ligand which are coordinated to Pd(II) respectively.
Aromatic protons appear from 6.85-7.98 ppm as multiplets and doublets.
1
1

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2
.13 Single-crystal X-ray crystallography of 6
The molecular structure (side view) of the palladium(II) tellurolate binuclear complex
PdCl(µ-TeC H -OCH )Te(C H -OCH ) ] (6) is represented in Figure 3.
[
6
4
3
6
4
3 2 2
Crystallographic data are given in Table S1, and selected bond lengths and bond angles
are summarized in Table S2. The structure consists of two square planar Pd(II) atoms
bridged by two 4-methoxyphenyltellurolate ligands (-1 oxidation state), two terminal
chloride atoms, and two terminal neutral bis-(4-methoxyphenyl)tellurium ligands (Figure
3
). The bis-(4-methoxyphenyl)telluride’s Pd-Te bond lengths (Pd1-Te1: 2.6291(13); Pd3-
Te6: 2.5985(14)) are slightly longer than the negatively charged 4-
methoxyphenyltellurolate’s Pd-Te bonds (Pd1-Te2: 2.5446(15); Pd3-Te2: 2.5368(13)) in
6
and match closely with the literature [16, 39-40]. The Pd(II) atoms have a slightly
distorted square planar geometry in 6 since the bond angles around Pd(II) metal centers
range from 81°-102° (SI Fig. 20).
A
B
Figure 3: A) The molecular structure of 6. Selective atoms are labelled for clarity. B)
Dimeric packing in the structure of 6 (as viewed from the side) and hydrogens are
omitted for clarity.
1
2

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-
All the phenyl groups of the 4-CH
3
O-PhTe ligands adopt a syn-configuration above the
planar, four-membered Pd2Te2 rhombus ring (SI Fig. 20). Pd-Te rhombus angles (acute
on Pd and obtuse on Te) are closely matching with the literature [16, 39-40]. All the
ligands in complex 6 are facing in one direction which is due to the formation of a
dimeric structure as seen in Figure 3B. The terminal ligand in 6 is bis(4-
methoxyphenyl)telluride (5), and this supports the formation and isolation of 5 from the
reaction between 1 and 2. C-Te-C bond angle of telluride ligand (5) in 6 measured as
9
6.5(5)° (C26-Te6-C42) and 95.0(5)° (C2-Te1-C32) which is somewhat shorter than
found in the literature [41]. The distances between the two Pd atoms (Pd1-Pd3) between
the rhombus in dimeric form is 3.454 Å, and within the rhombus is 3.884 Å which
indicates that there is no metal–metal interaction observed, but a substantial Te-Te
secondary interaction is observed in complex 6 with a distance of 3.327 Å (Te4-Te2)
within the rhombus, and 3.625 Å (Te4-Te2) is the distance for between rhombus in
dimeric form. In the literature a Te-Te bond distance of unsubstituted diphenylditelluride
(PhTe-TePh) is reported as 2.7073(5) Å [42]. This Te-Te interaction in 6 has a covalent
character, since the Van der Waals radius of a Te atom is 2.06 Å [43]. Khandelwal [44]
and his coworkers have made a palladium(II) complex of 1 with K PdCl or
2
4
PdCl (PhCN) , and there is no report about isolation of any combination of Pd -Te metal
2
2
x
y
chalcogenide during synthesis. In fact Pd(II) complex of 1 was very stable even in hot
DMSO since crystallization of PdCl .1 was done using hot DMSO. A few intramolecular
chlorine-hydrogen (aromatic) interactions in complex 6 were observed with distances of
.864 Å (C3-H3----Cl2); 2.953 Å (C10-H10----Cl1); 2.693 Å (C41-H41----Cl1) & 3.027
Å (C12-H12----Cl2), and these are typical C-H----Cl hydrogen bonds since the Van der
2
2
1
3

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Waals radii of Cl-H is 3.0 [43]. These intramolecular H-bonding interactions may be due
to crystal packing of 6 in solid form. Tellurium-chlorine secondary interaction is common
in organotellurium compounds especially in metal complexes contain organotellurium as
ligands. Both intra and intermolecular Cl----Te bond interactions have been observed in
6
. Intramolecular distances are 3.568Å; 3.566Å; 3.379 Å; 3.432 Å for Te4----Cl1, Te4----
Cl2, Te1----Cl1 and Te2----Cl6 respectively. Intermolecular distances between Te1----
Cl2; Te6----Cl1 are 3.539Å; 3.429Å respectively. Van der Waals radius of a Te---Cl
atoms is ~4Å [43]. Both intra and intermolecular interactions between Te-Cl are closely
matching with literature values [45] and shorter than Van der Waals radius of a Te---Cl.
These intermolecular Te----Cl interactions might be one of the reasons for the dimeric
form of 6 in solid state (SI Fig. 21). We have measured the Pd-Te bond lengths (both
terminal as well as bridging) in dimeric form and all of these are close to 4.0Å, hence the
intermolecular Pd-Te interactions are not the reason for formation of the dimeric form. A
unit cell diagram is given in SI Fig. 22.
3
.7 Heck reaction of 6
Br
6
+
TEA, DMF
Styrene
Bromobenzene
Stilbene
Scheme 2: The Heck reaction
Catalytic quantity of the organometallic palladium(II) tellurolate binuclear complex 6
was heated in DMF with styrene and bromobenzene in the presence of triethylamine
(Scheme 2) used as a catalyst in the Heck reaction. Stilbene was isolated with a yield of
3
0%. In addition to stilbene, a fine black solid was also isolated. The black nanomaterial
1
4

ACCEPTED MANUSCRIPT
residue isolated from the Heck reaction catalyzed by 6 was subjected to various analyses
and identified as a mixture of PdTe [46] (more than 95%) & Pd Te [21] (5% or less)
2
13
3
binary phases and confirmed from peak indexes (SI Fig. 23). Several trials of the Heck
reactions catalyzed by 6 yielded similar nanomaterial mixture of Pd-Te binary phases.
Peaks in the PXRD (Fig. 4A) of this nanomaterial mixture are pretty sharp, and TEM
image showed that the mixture is neither rod nor spherical shaped but obtained as well
dispersed nanoclusters (Fig. 4B).
1000
PdTe + Pd13Te3
2
8
6
4
2
00
00
00
00
0
20
40
60
80
2
θ Degree
B
A
Figure 4: PXRD (A) and TEM (B) of nanomaterial obtained from a Heck reaction
catalyzed by 6.
4
Conclusions
In summary, palladium-tellurium binary alloy nanoparticles have been synthesized and
characterized under mild conditions. Monodispersed Pd20Te is produced when CH Cl is
used as the solvent and a mixture of Pd20Te & Pd10Te are produced when benzene is
7
2
2
7
3
1
5

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2 2
used as the solvent. Resulting nanoparticles produced from CH Cl as solvent are
morphologically relatively pure nanorods. Apart from these nanomaterials, and
respective organic and organometallic compounds (4, 5 and 7), a palladium(II) tellurolate
dimeric complex (6) was also isolated from the mother liquor and it is structurally solved.
Homolytic cleavage in 1 followed by recombination of free radicals might be responsible
for the formation of compounds 3-7. Complex 6 can also act as a catalyst for the Heck
x y
Reaction with decent yield. A mixture of different Pd Te binary nanomaterials was
obtained after the Heck Reaction was run with 6. Currently we are working on the
catalytic behavior of 3.
Acknowledgements
The authors thank NSF-EPSCOR (EPS-0554609) and the South Dakota Governor's 2010
Initiative for financial support and the purchase of a Bruker SMART APEX II CCD
diffractometer and NSF-URC (CHE-0532242) funding for the purchase of the elemental
analyzer. The 400 MHz Bruker NMR was also provided by funding from NSF-MRI-
CHE-1229035. Purchase of the TEM was made possible by funding from the National
Science Foundation (CHE-0840507). MH thankfully acknowledges support from NSF-
REU (CHE-1460872) for summer research support. KM acknowledges Professor David
Hawkinson for the useful discussions regarding possible reaction mechanisms.
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Research Highlights:
•
•
•
•
Pd Te binary nanomaterial was has been synthesized under ambient condition.
20 7
Palladium(II) tellurolate complex was one of the products while isolating Pd Te .
2
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Palladium(II) tellurolate is a as heterogeneous catalyst for the Heck reaction.
TEM analyses reveal that the Pd Te binary nanomaterial is nanorod shape.
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