Facile one-step synthesis of palladium tellurium alloy nanorods

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

DOI:

10.1016/j.jorganchem.2018.04.024

Reference:

JOM 20416

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. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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Journal of Organometallic Chemistry

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Revision, April 2018

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(Article)

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Facile one-step synthesis of palladium tellurium alloy nanorods

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Kadarkaraisamy Mariappan∗, Shelton J. P. Varapragasam, Matt R. Hansen, Shivatharsiny Rasalingam, Madhubabu Alaparthi, and Andrew G. Sykes

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Contribution from the Department of Chemistry University of South Dakota, Vermillion, SD 57069, United States of America.

*To whom correspondence should be addressed: [email protected]

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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

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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

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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

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application as heterogeneous catalysts. Palladium and tellurium form several binary phases (PdxTey), including Pd20Te7 [12-14]. These binary phases are typically prepared 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

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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.

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Takahasi et al designed a synthetic route for PdTe alloy nanoparticles by controlling the

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reaction pH conditions based on metal complex calculations using the critical stability constants. They reduced a solution containing specific metal complexes of [Pd2+(EDTA)] and Te-citric acid with hydrazine to get well-crystallized Pd20Te7 alloy nanoparticles of Pd20Te7 and its chemical composition was confirmed by using EXAFS and PXRD [20]. Crystals of Pd13Te3 have produced by chemical vapor transport reactions using palladium (II) halide as transport agent by Janetzky et al. The crystal structure of Pd13Te3 was 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 Pd20Te7 phase has not been

H3C

Cl

O

Te

Te

+

O

Pd

1

2

Pd20Te7

CH3

H3C

H3 C O

O

O

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O

CH3

Te

Te

Pd

Te

Pd

Cl

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Te

H3 C

O

5

H3 C

CH3

CH3

Te

O

O 4

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3

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CH2Cl2, RT

O

Pd

Cl

CH3

H3 C

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synthesized without thermolysis/annealing or the addition of any external agents.

O

CH3

O H 7

O CH3

Cl

O 6

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Scheme 1: Synthetic scheme for making Pd20Te7 alloy nanomaterial Our original aim was to make a paddle wheel type palladium complex of Bis-(4methoxyphenyltelluro)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 to make nanorods of Pd20Te7 alloy in a one-step synthesis using organometallic precursors under ambient conditions. In this study, we have synthesized and characterized a palladium-tellurium (Pd20Te7) alloy nanomaterial; identified other organic 2

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and organometallic byproducts; and studied the catalytic behavior of an isolated Pd(II) tellurolate complex. 2. Experimental section

1

H and

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2.1 General procedure

C NMR spectra were obtained using a Bruker 400 MHz instrument at room

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temperature using deuterated solvents. Mass spectrometry was conducted using a Shimatzu GC mass spectrometer. Elemental analyses were conducted using an Exeter

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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

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40 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

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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

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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 (Pd20Te7) by Bruker Tracer III 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 200 atomic absorption spectrometer equipped with deuterium background correction was

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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

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adjusted in order to obtain the maximum absorbance signal while aspirating the Pd(II)

2.2 Crystallography

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solution in water.

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 MoKα radiation. The data reduction

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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

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ideal positions and refined as riding atoms with relative isotropic displacement parameters. Platon Squeeze removed a disordered diethyl ether solvent from the structure

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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 1823651.

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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

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single crystal X-ray diffraction [31] studies (SI Fig. 1-3). Allylpalladium (II) chloride dimer (2) was purchased from Sigma-Aldrich and its purity was checked by 1H NMR spectroscopy (SI Fig.4) each time prior to use. Both the organotellurium and

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organopalladium precursors are long lasting in solid form under ambient conditions as well as solution form with halogenated solvents such as CH2Cl2 and CHCl3. CH2Cl2 was

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purchased from Aldrich and purified using a PURE SOLVTM solvent purification system. Benzene and CHCl3 were purchased from Aldrich and purified by available procedures [32].

2.4 Synthesis of Pd20Te7 Nanomaterial (3)

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Bis-(4-methoxyphenyltelluro)methane, 1 (0.05 mg, 0.104 mmol) dissolved in 10 mL of CH2Cl2 was mixed with a solution of 0.038 mg (0.104 mmol) of allylpalladium(II) chloride dimer (2) in 10 mL of CH2Cl2. A clear red solution was obtained as soon as 1

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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

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to isolate a black solid. The black solid was washed two times with fresh CH2Cl2 and allowed to dry. Yield is 0.031g, ~10%. Elemental analyses calculated for Pd20Te7. C, 0.00; H, 0.00; N, 0.00; Pd, 70.44; Te, 29.56 %. Found: C, 0.11; H, 0.04; N, 0.01; Pd, 69.76; 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

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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).

ray crystallography. 2.5 Palladium(II) tellurolate complex (6)

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Compounds 4-7 were characterized by GC-MS, NMR spectroscopy (SI Fig.6-13) and X-

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Compound 6 was obtained as a red solution eluted by CH2Cl2: CH3OH (96:4) while isolating compound 3. The red solution was evaporated slowly to obtain X-ray quality

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crystals. Yield is 0.005g (as crystals), ~4% with melting point = 115-117 °C (dec). Elemental analyses calculated for C42H42O6Pd2Te4Cl2. C, 35.01; H, 3.22; Te, 35.42 %. Found: C, 34.97; H, 3.25; Te, 33.94 %. 1H NMR (at 25 °C, CDCl3): δ 3.81 s, 12H, CH3O from telluride); 3.87 (s, 6H, CH3-O from tellurolate); 6.85-6.91 (m, 6H, ArH); 7.01-

(d, 4H, J=8Hz, ArH).

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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

2.6 Catalytic Heck Reaction of 6

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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,

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~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 H2O and extracted with methylene chloride (3 x 10 mL), and the organic layer was combined, dried over anhydrous MgSO4, and the solvent was removed 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

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completed was found to be a mixture of Pd-Te nanomaterial binary phases. Results and Discussion

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2.7 Synthesis of Pd20Te7 Nanomaterial and organic and organometallic byproducts

The reaction of Bis-(4-methoxyphenyltelluro)methane (1) with allylpalladium (II)

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chloride (2) led to the formation of a pure Pd20Te7 binary alloy nanomaterial (3) with other byproducts. A silica gel column using CH2Cl2, CH2Cl2:Ethyl acetate (90:10) and

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CH2Cl2:CH3OH (96:4) as eluents were used to isolate other byproducts. Formation of compounds 3-7 when 1 mixes with 2 in CH2Cl2 does not depending upon light or oxygen. 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 isolated

were

1-methoxy-4-(4-methoxyphenyl)benzene

(4);

bis-(4-

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byproducts

methoxyphenyl)telluride (5); a binuclear palladium(II) tellurolate complex (6), and 4methoxybenzyl alcohol (7) (Scheme 1). Formation of these neutral organic and

products

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organometallic compounds shows there is a remarkable structural change in 1 and 2. By 1-methoxy-4-(4-methoxyphenyl)benzene

(4)

(SI

Fig.

6-8),

bis-(4-

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methoxyphenyl)telluride (5) ( SI Fig. 9-10) and 4-methoxybenzyl alcohol (7) (SI Fig. 1113) 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. 2.8 Possible mechanism for the formation of compounds 3-7 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

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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

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unstable Pd complex lead the formation of elemental palladium, and it also triggered the oxidation of tellurium as Te2- in compound 1 through free radical reaction. A peak

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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

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tellurium [36-37]. The methylene group (-TeCH2Te-) in 1 might have formed a triplet carbene (:CH2) after homolytic cleavages. Our speculation is 4-methoxyphenyl radical underwent a disproportionation reaction to yield a 4-methoxybenzyl carbocation and 4-

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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

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4-methoxybenzyl carbanion to generate 4-methylanisole. Observation of a peak for 4methylanisole (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 4methylanisole were not included as one of the products in reaction scheme since both haven’t been isolated by column chromatography.

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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 CH2Cl2 and benzene as

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solvents. The PXRD pattern in Figure 1 shows a crystalline material that matches well with single-phase Pd20Te7 (PDF: 01-089-2014) when CH2Cl2 was used as solvent [13], and SI Fig. 15 shows the PXRD spectrum of Pd20Te7 with complete indexing list. The

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crystal system is trigonal with the space group R-3 (148). The cell parameters are a = 11.7970; b = 11.7970 and c = 11.1720; α = β = 90° ; and γ = 120°. A mixture of phases

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Pd20Te7 & Pd10Te3 [38] is obtained when benzene (SI Fig. 16) was used as solvent and mixture formation was confirmed by comparing peak indexes (SI Fig. 17). The peaks of Pd20Te7 are moderately sharp, and several trials involving the combination of 1 and 2 in

Pd20Te7: Synthesized

Intensity (a.u.)

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(0 2 4)

(3 14)

(1 24) (1 4 0)

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CH2Cl2 as solvent in a 1:1 ratio produced only the single phase of Pd20Te7.

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Pd20Te7: (PDF:01-089-2014)

10

20

30

40

50

60

70

80

2θ Degree

Figure 1: PXRD of nanomaterial obtained from CH2Cl2 as solvent vs standard phase of Pd20Te7 from reference 13. 9

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2.10

Transmission Electron Microscopy:

The size and morphology of the Pd20Te7 nanomaterial was examined further by transmission electron microscopy (TEM) studies, and select TEM images of Pd20Te7 are

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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 Pd20Te7 obtained from CH2Cl2 solution is a

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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

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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 (Pd20Te7 + Pd10Te3), which are also uniform, mono-dispersed nanoparticles. Size of the nanomaterial

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is ~ 15-30 nm from benzene solution.

A

B

Figure 2: A) TEM image of Pd20Te7 nanomaterial obtained from CH2Cl2 as solvent. B) Nanomaterial obtained from benzene as solvent. Both images are in identical resolution. 10

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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.

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Relative peak intensities in pXRF of Pd20Te7 alloy nanomaterial support the chemical composition. A peak observed at 21.18 keV corresponding to palladium Kα1 and peaks at 23.8 keV and 24. 3 keV are due to Kβ1 and Kβ2 for palladium respectively. Peaks

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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,

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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

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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

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well with the accepted value.

NMR spectroscopy of 6

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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 4methoxyphenyltellurolate bridging ligand which are coordinated to Pd(II) respectively. Aromatic protons appear from 6.85-7.98 ppm as multiplets and doublets.

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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-TeC6H4-OCH3)Te(C6H4-OCH3)2]2

(6)

is

represented

in

Figure

3.

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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

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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); Pd32.5985(14))

are

slightly

longer

than

the

negatively

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Te6:

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

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range from 81°-102° (SI Fig. 20).

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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. 12

B

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All the phenyl groups of the 4-CH3O-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

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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(4methoxyphenyl)telluride (5), and this supports the formation and isolation of 5 from the

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reaction between 1 and 2. C-Te-C bond angle of telluride ligand (5) in 6 measured as 96.5(5)° (C26-Te6-C42) and 95.0(5)° (C2-Te1-C32) which is somewhat shorter than

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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)

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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

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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 K2PdCl4 or

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PdCl2(PhCN)2, and there is no report about isolation of any combination of Pdx-Tey metal chalcogenide during synthesis. In fact Pd(II) complex of 1 was very stable even in hot DMSO since crystallization of PdCl2.1 was done using hot DMSO. A few intramolecular chlorine-hydrogen (aromatic) interactions in complex 6 were observed with distances of 2.864 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

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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

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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----

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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

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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

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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

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Br

6

+

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Styrene

TEA, DMF

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 30%. In addition to stilbene, a fine black solid was also isolated. The black nanomaterial

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residue isolated from the Heck reaction catalyzed by 6 was subjected to various analyses and identified as a mixture of PdTe2 [46] (more than 95%) & Pd13Te3 [21] (5% or less) binary phases and confirmed from peak indexes (SI Fig. 23). Several trials of the Heck

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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

PdTe2 + Pd13Te3

600

200

0

20

40

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400

60

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2θ Degree

80

A

Figure 4: PXRD (A) and TEM (B) of nanomaterial obtained from a Heck reaction catalyzed by 6.

4

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Intensity (a. u.)

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1000

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dispersed nanoclusters (Fig. 4B).

Conclusions

In summary, palladium-tellurium binary alloy nanoparticles have been synthesized and characterized under mild conditions. Monodispersed Pd20Te7 is produced when CH2Cl2 is used as the solvent and a mixture of Pd20Te7 & Pd10Te3 are produced when benzene is

15

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used as the solvent.

Resulting nanoparticles produced from CH2Cl2 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

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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

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Reaction with decent yield. A mixture of different PdxTey binary nanomaterials was obtained after the Heck Reaction was run with 6. Currently we are working on the

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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

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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-MRICHE-1229035. Purchase of the TEM was made possible by funding from the National

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Science Foundation (CHE-0840507). MH thankfully acknowledges support from NSFREU (CHE-1460872) for summer research support. KM acknowledges Professor David

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Hawkinson for the useful discussions regarding possible reaction mechanisms. References

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Research Highlights: Pd20Te7 binary nanomaterial was has been synthesized under ambient condition.

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Palladium(II) tellurolate complex was one of the products while isolating Pd20Te7.

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Palladium(II) tellurolate is a as heterogeneous catalyst for the Heck reaction.

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TEM analyses reveal that the Pd20Te7 binary nanomaterial is nanorod shape.

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