Palladium(ii) complexes of pyrazolated thio/selenoethers: Syntheses, structures, single source precursors of Pd4Se and PdSe nano-particles and potential for catalyzing Suzuki-Miyaura coupling

Article abstract of DOI:10.1039/c2dt31975f

The reactions of 4-bromo-1-(2-chloroethyl)-1H-pyrazole prepared from 4-bromopyrazole with the in situ generated PhSNa, PhSeNa, Na₂S and Na₂Se have resulted in thio/selenoether ligands L1-L4 respectively. The complexes [PdL1/L2Cl

Full text of DOI:10.1039/c2dt31975f

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Palladium(II) complexes of pyrazolated thio/selenoethers: syntheses,
structures, single source precursors of Pd4Se and PdSe nano-
particles and potential for catalyzing Suzuki-Miyaura coupling
Kamal Nayan Sharma, Hemant Joshi, Ved Vati Singh, Pradhumn Singh and Ajai Kumar Singh*
The Pd(II)-complexes (1-4) of four pyrazolated thio/selenoether have been synthesized and found
efficient catalysts for Suzuki-Miyaura coupling reactions. The in situ generated Pd-chalcogen NPs (size ~
3-19 nm) appear to be real catalysts. Single source one pot synthesis of Pd4Se and PdSe NPs (size ranges
o
8-26 nm), capped with TOP, have been done by thermolysis of 2 and 4 at 200-250 C in TOP. The PdP2
NPs were formed in the attempts made to prepare NPs of palladium-sulfide by thermolysis of 1 and 3 in
TOP.

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Cite this: DOI: 10.1039/c0xx00000x
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ARTICLE TYPE
Palladium(II) complexes of pyrazolated thio/selenoethers: syntheses,
structures, single source precursors of Pd4Se and PdSe nano-particles
and potential for catalyzing Suzuki-Miyaura coupling
Kamal Nayan Sharma, Hemant Joshi, Ved Vati Singh, Pradhumn Singh and Ajai Kumar Singh*
5
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
DOI: 10.1039/b000000x
The reactions of 4–bromo–1–(2–chloroethyl)–1H–pyrazole prepared from 4– bromopyrazole with the in situ generated PhSNa, PhSeNa,
Na2S, and Na2Se have resulted in thio/selenoether ligands L1-L4 respectively. The complexes [PdL1/L2Cl2](1-2) and [PdL3/L4Cl]BF4
(3-4) of these ligands have been synthesized by reacting them with [PdCl2(CH3CN)2] in CH3CN at 70°C. The L1-L4 and their complexes
10 (1-4) have been characterized with spectroscopic techniques viz. 1H, 13C{1H} and 77Se{1H} NMR, IR and HR-MS. Single crystal
structures of 1-4 determined by X-ray diffraction reveal nearly square planar geometry around Pd in each case. Thermally stable,
moisture/air insensitive complexes 1-4 have been found efficient catalysts for Suzuki-Miyaura coupling reactions (Yield up to 96% in 2
h). Nano-particles (NPs) (size ~3-19 nm) were formed in the beginning of these reactions. They are composed of Pd and S or Se with
more % of Pd. These NPs also catalyze Suzuki coupling and appear to be playing important role in catalysis. Single source one pot
15 synthesis of Pd4Se and PdSe NPs (size ranges ~8-26 nm), capped with trioctylphosphine (TOP), have been developed by thermolysis of 2
and 4 at 200-250 ºC in TOP. HR-TEM, SEM, SEM-EDX and powder XRD have been used to authenticate these nano-particles. The NPs
of PdP2 are formed when attempts were made to prepare nano-sized phases of palladium-sulfide by thermolysis of 1 and 3 in TOP.
due to strong donor properties of chalcogen atoms, which make
Introduction
them suitable for designing catalyst for C−C coupling reactions.14
Pyrazolyl groups are among the important building units used in
The potential of pyrazole based ligands in designing metal
20 ligand design1 and supramolecular chemistry.2 The pyrazolates,
50 complexes having good catalytic activity has been already
are known as robust bridging ligands.3 Their metal complexes
recognized. The catalytic processes viz. oxidation,15 ethylene
have been used as precursors for chemical vapor phase deposition
polymerization,16 hydroamination,17-18 redox isomerisation of
and found to show luminescent properties.4 The pyrazole and
allylic alcohols,19 ethylene oligomerization20 and polymerization
pyrazolate moieties can be integrated as part of many polydentate
of rac-lactide21 based on metal complexes of pyrazole based
25 donors.5 The polypyrazolylborates are among the most useful and
55 ligands have been found promising. Thus Pd-complexes of
widely employed ligands.6 In addition to their ligand chemistry,
pyrazole based chalcogen ligands would be worth exploring for
there are reports on their biological importance.7 The antitumor
Suzuki-Miyaura coupling. Platinum group metal chalcogenides
activities of metal-complexes of pyrazolyl ligands have been
have found applications in catalysis.22 Their properties such as
widely investigated and many of them have cytotoxicity
semiconducting nature,23 photoelectrochemical behavior24 etc are
30 comparable or superior than those of standard drugs. For
60 attractive. They have also shown promise for lithiographic
instance, compounds of the type [{AuCl2(L)}2] (L = pyrazole, 3-
films,25 optical disc recording films26 and as light image receiving
methylpyrazole) have been reported more cytotoxic than cis-
material.27 The various important selenides of palladium
platin toward the MOLT-4 and C2C12 tumor cell lines.8 Rocha et
identified are PdSe, Pd17Se15, Pd7Se4, Pd2.5Se, Pd3Se, Pd7Se,
al.9 have reported that the cytotoxic activity of complex
Pd4Se, Pd4.5Se, Pd8Se and PdSe2. Nano-sized forms of some of
35 [PdI2(tdmPz)] (tdmPz = 1-thiocarbamoyl-3,5-dimethylpyrazole)
65 them may become more interesting due to the favorable tuning of
towards mammary adenocarcinoma murine tumor cell line (LM3)
their semiconducting properties.23 The Pd-complexes of pyrazole
is comparable to that of cis-platin. However, chemistry of
based chalcogenated ligands may be used as a single source
pyrazole based organosulfur and selenium based ligands is
precursor for currently important nano-particles of some of these
unexplored. Their Pd(II) complexes may be very interesting
palladium selenides and may abandon presently used volatile
40 because this metal has outstanding application potential for C–C
70 and/or toxic species like H2Se. Nano-particles of PdSe2 and
bond formation,10 for example Suzuki-Miyaura coupling
Pd17Se15 have been recently grown using palladium complex viz.
reaction.11 Pd-complexes of bulky and electron-rich phosphines12
bis(N,N-diethyl-N¢-naphthoylselenoureato)palladium(II) as
a
and carbenes13 are considered to be of immense importance for
such coupling but most of them are air/moisture sensitive.
45 Chalcogen ligands have emerged as alternatives to phosphines
single source precursor.28 Thus Pd(II)-complexes of pyrazole
based organochalcogen may be worth exploring on this count
75 also as they may be used for low temperature preparation of
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1

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palladium selenides. The known routes for the preparation of 55 4–Bromopyrazole (2.205 g, 15.0 mmol) was mixed with
such phases typically involve heating of the two constituent
elements in an evacuated sealed tube followed by annealing at
high temperatures for several days.
potassium
carbonate
(4.146
g,
30.0
mmol)
and
tetrabutylammonium bromide (0.484 g, 1.5 mmol). The mixture
5
In present paper we report the synthesis of pyrazole based
sulphur/selenated ligands and their palladium(II) complexes.
These palladium(II) complexes were explored for their potential
as catalyst for Suzuki-Miyaura cross coupling reaction and as
single source precursors of Pd4Se and PdSe nano-particles.
10 Experimental
Physical measurement
The C, H and N analyses were carried out with a Perkin-Elmer
1
2400 Series II C, H, N analyzer. The H, 13C{1H} and 77Se{1H}
NMR spectra were recorded on a Bruker Spectrospin DPX-300
15 NMR spectrometer at 300.13, 75.47 and 57.24 MHz respectively.
IR spectra in the range 4000-400 cm−1 were recorded on a Nicolet
Protége 460 FT-IR spectrometer as KBr pellets. The diffraction
data on single crystals of 1-4 were collected on a Bruker AXS
SMART Apex CCD diffractometer using Mo-Ka (0.71073 Å)
20 radiations at 298(2) K. The software SADABS29 was used for
absorption correction (if needed) and SHELXTL for space group,
structure determination and refinements.30 All non–hydrogen
atoms were refined anisotropically. Hydrogen atoms were
included in idealized positions with isotropic thermal parameters
25 set at 1.2 times that of the carbon atom to which they are
attached. The least-square refinement cycles on F2 were
performed until the model converged. Powder X-ray diffraction
(XRD) patterns of the dried powders were recorded on a Bruker
D8 Advance diffractometer using Ni-filtered Cu-Kα radiation, at
30 a scanning step of 0.0334°, using Cu-Kα radiation (λ = 1.5406 Å)
in the range of θ=20-80°. Samples for high resolution
transmission electron microscopy (HR-TEM) analysis were
prepared by drying a drop of dispersion of nano-crystals in
cyclohexane or ethanol on carbon-coated copper grids. High-
35 resolution TEM characterization revealing particle sizes and
shapes was performed with a Philips Tecnai F20 operated at 200
kV. The morphologies of nano-sized phases were studied with a
Carl ZEISS EVO5O scanning electron microscope (SEM).
Sample was mounted on a circular metallic sample holder with a
40 sticky carbon tape. Elemental composition of these phases has
been obtained by associated EDX system Model QuanTax 200,
which is based on the SDD technology and provides an energy
resolution of 127 eV at Mn-Kα. The melting points determined in
an open capillary are reported as such. Yields refer to isolated
45 yields of compounds which have purity ≥ 95%.
Scheme 1 Synthesis of L1-L4 and 1-4.
60 was added to 40 mL (taken in excess) of 1, 2–dichloroethane and
the resulting reaction mixture was refluxed for 12 h. A light
yellow suspension was formed. Its organic phase was decanted
off. The solid residue was extracted with dichloromethane (2 × 25
mL). All the extracts were combined with the organic phase. The
65 volume of resulting combined organic phase was reduced on a
rotary evaporator to 50%. The concentrated organic phase was
washed with water and dried over sodium sulphate. Its solvent
was removed under reduced pressure on a rotary evaporator
resulting in A as light yellow oil.
70 Yield: 2.828 g, 90%. 1H NMR (CDCl3, 25 ºC, vs Me4Si) : δ
3
3
(ppm): 3.86 (t, JH−H = 6.0 Hz, 2H, ClCH2), 4.40 (t, JH−H = 6.0
Hz, 2H, NCH2), 7.51 (s, 2H, Ha and Hb). 13C{1H} NMR (CDCl3,
25 ºC, vs Me4Si) : δ (ppm): 42.5 (ClCH2), 53.9 (NCH2), 92.9
(BrC), 130.3 (Ca), 140.5 (Cb). IR (KBr, νmax/cm-1): 3128 (m; νC-
75 H(aromatic)), 2959 (s; νC-H(aliphatic)), 1518 (s; νC-N(aromatic)), 1439 (s; νC-
C(aromatic)), 1141 (m; νC-N(aliphatic)), 847 (m; νC-H(aromatic)), 654 (m; νC-
Cl(aliphatic)).
Chemicals and reagents
Syntheis of L1
4–Bromopyrazole,
thiophenol,
diphenyl
diselenide,
Thiophenol (0.441 g, 4.0 mmol) was added to sodium hydroxide
80 (0.160 g, 4.0 mmol) dissolved in 30 mL of EtOH and refluxed for
1h. 4–Bromo–1–(2–chloroethyl)–1H–pyrazole (0.837 g, 4.0
mmol) dissolved in 20 mL of EtOH was added to it. The resulting
reaction mixture was further refluxed for 5 h. Thereafter, the
reaction mixture was stirred for overnight at room temperature. It
85 was poured into cold water (30 mL). The L1 was extracted with
chloroform (4 × 25 mL). The extract was washed with water (3 ×
sulphur/selenium powder, sodium borohydride, palladium
chloride, silver tetrafluoroborate and trioctylphosphine (Technical
50 grade), procured from Sigma-Aldrich (USA) and Fluka were used
as received. All the solvents were dried and distilled before use
by standard procedures.31 The common reagents and chemicals
available commercially within the country were used.
Synthesis of 4–bromo–1–(2–chloroethyl)–1H–pyrazole (A)
2
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40 mL) and dried over anhydrous sodium sulphate. The solvent
was evaporated off under reduced pressure on a rotary evaporator
resulting L1 as light yellow oil.
[M+H]+ (m/z) 378.9232; calc. Value for C10H13Br2N4S; 378.9222
(δ: −2.5 ppm), [M+Na]+ (m/z) 400.9042; calc. Value for
C10H12Br2N4NaS; 400.9027 (δ: 3.7 ppm).
Yield: 1.019 g, 90%. 1H NMR (CDCl3, 25 ºC, vs Me4Si): δ
3
3
5
(ppm): 3.27 (t, JH−H = 6.9 Hz, 2H, H5), 4.19 (t, JH−H = 6.9 Hz, 60 L4: Yield: 0.384 g, 90%. 1H NMR (CDCl3, 25 ºC, vs Me4Si): δ
3
3
2H, H6), 7.16−7.33 (m, 6H, H1,H2,H3 and H7), 7.42 (s, 1H, H9).
13C{1H} NMR (CDCl3, 25 ºC, vs Me4Si): δ (ppm): 33.6 (C5), 51.5
(C6), 92.6 (C8), 126.6 (C1), 128.9 (C2), 129.6 (C7), 129.7 (C3),
134.0 (C4), 139.9 (C9). IR (KBr, νmax/cm-1): 2928 (m; νC-
(ppm): 2.83 (t, JH−H = 6.9 Hz, 4H, H5), 4.26 (t, JH−H = 6.9 Hz,
4H, H4), 7.43 (s, 2H, H3), 7.48 (s, 2H, H1). 13C{1H} NMR
(CDCl3, 25 ºC, vs Me4Si): δ (ppm): 23.4 (C5), 53.2 (C4), 92.9
(C2), 129.7 (C3), 140.2 (C1). 77Se{1H} NMR (CDCl3, 25 ºC, vs
10 H(aromatic)), 2855 (s; νC-H(aliphatic)), 1648 (s; νC-N(aromatic)), 1438 (s; νC- 65 Me2Se): δ (ppm): 144.12. IR (KBr, νmax/cm-1): 2925 (m; νC-
C(aromatic)), 1309 (m; νC-N(aliphatic)), 743 (m; νC-H(aromatic)). HR-MS
[M+Na]+ (m/z) 304.9719; calc. Value for C11H11BrN2NaS;
304.9724 (δ: −3.3 ppm).
H(aromatic)), 2855 (s; νC-H(aromatic)), 1645 (s; νC-N(aromatic)), 1460 (s; νC-
C(aromatic)), 1260 (m; νC-N(aliphatic)), 792 (m; νC-H(aromatic)). HR-MS
[M+H]+ (m/z) 426.8660; calc. Value for C10H13Br2N4Se;
426.8665 (δ: 1.4 ppm).
Synthesis of L2
70 Synthesis of complex 1 and 2
15 Diphenyldiselenide (0.312 g, 1.0 mmol) dissolved in 30 mL of
EtOH was stirred under reflux in N2 atmosphere. Sodium
borohydride (0.080 g, 2.0 mmol) was added to it as solid so that it
became colorless due to the formation of PhSeNa. 4–Bromo–1–
(2–chloroethyl)–1H–pyrazole (0.419 g, 2.0 mmol) dissolved in 10
Solid [Pd(CH3CN)2Cl2] (0.052 g, 0.2 mmol) taken in CH3CN (20
mL) was stirred under reflux until a clear light yellow colored
solution was obtained. The L1/L2 (0.057/0.066 g, 0.2 mmol)
dissolved in CH3CN (5 mL) was added. The reaction mixture was
20 mL of ethanol was added to the colourless solution with constant 75 further refluxed for 5 h. It was cooled thereafter to room
stirring and the mixture was further refluxed for 5 h. It was
extracted with chloroform (4 × 25 mL). The extract was washed
with water (3 × 40 mL) and dried over anhydrous sodium
sulphate. The solvent from extract was evaporated off under
25 reduced pressure on a rotary evaporator to get L2 as yellow oil.
Yield: 0.594 g, 90%. 1H NMR (CDCl3, 25 ºC, vs Me4Si): δ
(ppm): 3.23 (t, JH−H = 6.9 Hz, 2H, H5), 4.28 (t, JH−H = 6.9 Hz,
2H, H6) , 7.22−7.27 (m, 6H, H1, H2), 7.33 (s, 1H, H7), 7.41 (s,
1H, H9), 7.44−7.48 (m, 2H, H3). 13C{1H} NMR (CDCl3, 25 ºC, vs
temperature, concentrated upto 7 mL on a rotary evaporator and
mixed with diethyl ether (10 mL). The 1 or 2 resulting as orange
colored solid was filtered, washed with diethyl ether (10 mL) and
dried in vacuo. Single crystals of 1/2 were grown by slow
80 evaporation of its solution in DMSO.
1: Yield: 0.083 g, 90%. m.p. 230.0 ºC. Anal. Calc. for
C11H11BrCl2N2PdS: C, 28.69; H, 2.41; N, 6.08%. Found: C,
28.51; H, 2.36; N, 6.81%. 1H NMR (DMSO−d6, 25 ºC, vs
Me4Si): δ (ppm): 3.16 (broad singlet, 1H, H5), 3.53 (broad singlet,
3
3
30 Me4Si): δ (ppm): 26.9 (C5), 52.7 (C6), 92.8 (C8), 127.5 (C1), 85 1H, H5) , 4.36 (broad singlet, 1H, H6), 4.78 (broad singlet, 1H,
128.3 (C4), 129.2 (C2), 129.5 (C7), 133.1 (C3), 140.1 (C9).
77Se{1H} NMR (CDCl3, 25 ºC, vs Me2Se): δ (ppm): 282.56. IR
(KBr, νmax/cm-1): 2927 (m; νC-H(aromatic)), 2853 (s; νC-H(aliphatic)),
1645 (s; νC-N(aromatic)), 1474 (s; νC-C(aromatic)), 1254 (m; νC-N(aliphatic)),
H6), 7.41−7.61 (m, 3H, H1, H2), 8.10−8.12 (m, 2H, H3), 8.28 (s,
1H, H7), 8.45 (s, 1H, H9). 13C{1H} NMR (DMSO−d6, 25 ºC, vs
Me4Si): δ (ppm): 36.1 (C5), 49.7 (C6), 92.6 (C8), 129.3 (C4),
129.7 (C2), 130.8 (C1), 133.0 (C3), 135.9 (C7), 143.3 (C9). IR
35 794 (m; νC-H(aromatic)). HR-MS [M+Na]+ (m/z) 352.9160; calc. 90 (KBr, νmax/cm-1): 3131 (m; νC-H(aromatic)), 2978 (s; νC-H(aliphatic)),
1633 (s; νC-N(aromatic)), 1437 (s; νC-C(aromatic)), 1300 (m; νC-N(aliphatic)),
Value for C11H11BrN2NaSe; 352.9180 (δ: −5.6 ppm).
813 (m; νC-H(aromatic)). HR-MS [M+K]+ (m/z) 496.7828; calc.
Value for C11H11BrCl2KN2PdS; 496.7865 (δ: 7.4 ppm).
Synthesis of L3 and L4
Sulphur powder (0.032 g, 1 mmol)/selenium powder (0.078 g, 1
mmol) added in 30 mL of ethanol were stirred under reflux in N2
40 atmosphere. Solid sodium borohydride (0.151 g, 4.0 mmol) was
added to it so that it became colorless. 4–Bromo–1–(2–
chloroethyl)–1H–pyrazole (0.418 g, 2 mmol) dissolved in 10 mL
of ethanol was added with constant stirring and the mixture
stirred with refluxing for further 5 h. It was extracted with
45 chloroform (4 × 25 mL). The extract was washed with water (3 ×
40 mL) and dried over anhydrous sodium sulphate. The solvent
was evaporated off under reduced pressure on a rotary evaporator
to get L3/L4 as yellow oil.
95 2: Yield: 0.091 g, 90%. m.p. 235.0 ºC. Anal. Calc. for
C11H11BrCl2N2PdSe: C, 26.04; H, 2.19; N, 5.52%. Found: C,
26.10; H, 2.12; N, 5.69%. 1H NMR (DMSO−d6, 25 ºC, vs Me4Si):
δ (ppm): 2.93 (m, 1H, H5), 3.45 (m, 1H, H5), 4.77 (m, 1H, H6),
4.90 (m, 1H, H6), 7.32-7.511 (m, 3H, H1+ H2), 7.98-8.00 (m, 2H,
100 H3), 8.14 (s, 1H, H9), 8.37 (s, 1H, H7). 13C{1H} NMR
(DMSO−d6, 25 ºC, vs Me4Si): δ (ppm): 31.48 (C5), 51.16 (C6),
92.6 (C8), 129.1 (C4), 129.9 (C2), 130.2 (C1), 133.1 (C3), 135.7
(C7), 143.5 (C9). 77Se{1H} NMR (DMSO-d6, 25 ºC, vs Me2Se): δ
(ppm): 366.93. IR (KBr, νmax/cm-1): 3129 (m; νC-H(aromatic)), 2968
105 (s; νC-H(aliphatic)), 1633 (s; νC-N(aromatic)), 1437 (s; νC-C(aromatic)), 1246
(m; νC-N(aliphatic)), 815 (m; νC-H(aromatic)). HR-MS [M+K]+ (m/z)
544.7311; calc. Value for C11H11BrCl2KN2PdSe; 544.7285 (δ: 4.8
ppm).
1
L3: Yield: 0.323 g, 85%. H NMR (CDCl3, 25 ºC, vs Me4Si): δ
3
3
50 (ppm): 2.80 (t, JH−H = 6.3 Hz, 4H, H5), 4.19 (t, JH−H = 6.6 Hz,
4H, H4), 7.42 (s, 2H, H3), 7.50 (s, 2H, H1). 13C{1H} NMR
(CDCl3, 25 ºC, vs Me4Si): δ (ppm): 31.8 (C5), 52.2 (C4), 92.7
(C2), 129.8 (C3), 140. (C1). IR (KBr, νmax/cm-1): 2924 (m; νC-
H(aromatic)), 2854 (s; νC-H(aromatic)), 1643 (s; νC-N(aromatic)), 1460 (s; νC-
55 C(aromatic)), 1261 (m; νC-N(aliphatic)), 898 (m; νC-H(aromatic)). HR-MS
Synthesis of complex 3 and 4
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Hg poisoning test
Solid [Pd(CH3CN)2Cl2] (0.052 g, 0.2 mmol) taken in CH3CN (20
mL) was stirred under reflux until a clear light yellow colored
solution was obtained. The solution of ligand L3 (0.076 g, 0.2
mmol)/L4 (0.085 g, 0.2 mmol) dissolved in CH3CN (5 mL) was
added. The reaction mixture was further refluxed for 5 h.
Thereafter solid AgBF4 (0.038 g, 0.2 mmol) was added and the
mixture refluxed further for 2 h. It was cooled to room
temperature and precipitated AgCl was filtered off through celite.
The filtrate was concentrated to 5 mL on a rotary evaporated and
For the mercury poisoning test an excess of Hg (Hg:Pd: 400 : 1)
55 was taken in the reaction flask before the addition of reactants.
Thereafter the coupling reaction of 4-bromobenzaldehyde (1.0
mmol) with phenylboronic acid (1.2 mmol) using catalyst (1.0
mol%) as catalyst was carried out in the flask under optimum
conditions. The conversion was not observed even after 2 h of
60 reaction. This may be ascribed to Hg poisoning.
5
PPh3 poisoning test
10 mixed with diethyl ether (10 mL) to obtain 3/4 as yellow solid,
which was filtered and dried in vacuo. The single crystals of 3/4
were grown by slow evaporation of its solution in CH3CN.
3: Yield: 0.103 g 85%; m.p. 170.0 ºC (d). ΛM = 158.2 S cm2
mol−1. Anal. Calc. for C10H12Br2ClN4PdS.BF4.: C, 19.73; H, 1.99;
15 N, 9.20%. Found: C, 19.71; H, 1.99; N, 9.22%. 1H NMR
(DMSO-d6, 25 ºC, vs Me4Si): δ (ppm) 3.31−3.60 (m, 4H, H5,
merged with DMSO), 5.01−5.06 (m, 2H, H4), 5.27−5.35 (m, 2H,
H4), 8.13 (s, 2H, H1), 8.43 (s, 2H, H3). 13C{1H} NMR (DMSO-d6,
25 ºC, vs Me4Si): δ (ppm): 36.0 (C5), 53.3 (C4), 93.4 (C2), 136.6
20 (C1), 143.8 (C3). IR (KBr, νmax/cm-1): 3169 (m; νC-H(aromatic)), 2962
(s; νC-H(aliphatic)), 1627 (s; νC-N(aromatic)), 1443 (s; νC-C(aromatic)), 1259
(m; νC-N(aliphatic)), 810 (m; νC-H(aromatic)). HR-MS [{M−BF4}+H]+
(m/z) 519.7945; calc. Value for C10H13Br2ClN4PdS; 519.7944 (δ:
0.3 ppm).
To the coupling reaction of 4-bromobenzaldehyde with
phenylboronic acid, PPh3 (0.5 mol%) was added under optimal
conditions before addition of catalyst (1.0 mol%). Even after 2 h
65 of reaction no cross-coupled products were obtained.
Isolation of nano-particles generated from 1-4 during Suzuki-
Miyaura coupling
A mixture of Pd(II) complex 1/2/3/4 (0.5 mmol), phenylboronic
acid (1.5 mmol), 4−bromobenzaldehyde (1.0 mmol) and K2CO3
70 (2.0 mmol) in DMF (4.0 mL) and water (4.0 mL) was heated at
100◦C for 2 h and then cooled to room temperature. The solvent
was decanted and the black residue (NPs) was washed with
water-acetone mixture (1:3) and dried in vacuo. The NPs were
characterized by SEM-EDX, and TEM.
25 4: Yield: 0.112 g 85%; m.p. 160.0 ºC (d). ΛM = 149.9 S cm2
75 Procedure for Suzuki-Miyaura coupling catalyzed by NPs
obtained from 1-4
mol−1. Anal. Calc. for C10H12Br2ClN4PdSe.BF4: C, 18.32; H,
1
1.84; N, 8.54%. Found: C, 18.13; H, 1.92; N, 9.01%. H NMR
The coupling reactions of 4-bromobenzaldehyde and 4-
bromoanisole under optimum conditions similar to those used
with complexes 1-4 (except that 0.01 g of NPs obtained from 1-4
80 replaced them) were carried out. All coupling products were
authenticated by 1H and 13C{1H} NMR spectra.
(DMSO-d6, 25 ºC, vs Me4Si): δ (ppm): 3.24–3.31 (m, 2H, H5),
3.58–3.61 (m, 2H, H5), 5.17–5.22 (m, 2H, H4), 5.33–5.38 (m, 2H,
30 H4), 8.07 (s, 2H, H3), 8.42 (s, 2H, H1). 13C{1H} NMR
(DMSO−d6, 25 ºC, vs Me4Si): δ (ppm): 32.3 (C4), 54.3 (C5), 93.5
(C2), 136.4 (C3), 143.6 (C1). 77Se{1H} NMR (DMSO−d6, 25 ºC,
vs Me2Se): δ (ppm): 342.42. IR (KBr, νmax/cm-1): 3133 (m; νC-
H(aromatic)), 3017 (s; νC-H(aliphatic)), 1631 (s; νC-N(aromatic)), 1447 (s; νC-
35 C(aromatic)), 1256 (m; νC-N(aliphatic)), 844 (m; νC-H(aromatic)). HRMS
[M−BF4]+ (m/z) 566.7311; calc. Value for C10H12Br2ClN4PdSe;
566.7308 (δ: −0.5 ppm).
Synthesis of Pd4Se and PdSe nano-particles
A mixture of 5.0 mL (11.0 mmol) of tri–n–octylphosphine (TOP)
and 2/4 (0.507 / 0.655 g, 1.0 mmol) was heated to 200-250 ºC
85 under N2 atmosphere in a three neck flask for 2 h with continuous
stirring. The colour of the mixture changed from yellowish to
red-brown within 30 min and brown-black precipitate started
appearing thereafter. The mixture was cooled to room
temperature and 20 mL of acetone was added into the flask to
90 obtain a brown-black precipitate which was separated by
centrifugation. The precipitate was washed three times with
methanol (20 mL) and dried in vacuo.
Procedure for the Suzuki-Miyaura coupling reaction
An oven-dried flask was charged with aryl bromide (1.0 mmol),
40 phenylboronic acid (1.5 mmol), K2CO3 (2.0 mmol), DMF (3.0
ml), H2O (2.0 ml) and complex 1-4. The flask was placed on an
oil bath at 90°C with air condensor and the reaction mixture was
stirred. The reaction monitored by TLC was carried out until
maximum conversion of aryl halide to product occurred. The
45 mixture was extracted with diethyl ether (2 × 20 mL), washed
with water and dried over anhydrous Na2SO4. The solvent of the
extract was completely removed with a rotary evaporator to
obtain the product, which was further purified by a column
chromatography on silica gel. All coupling products were
50 authenticated by 1H and 13C{1H} NMR spectra.
Scheme 2 Suzuki-Miyaura Coupling Reaction
95
Scheme 3 Synthesis of Pd4Se and PdSe Nano-Particles
4
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Results and discussion
55
The syntheses of 4–bromo–1–(2–chloroethyl)–1H–pyrazole (A)
is shown in equation (1), The synthesis of L1-L4 and their Pd(II)-
complexes 1-4 are summarized in (Scheme 1). The molar
conductance values in acetonitrile indicate a 1:1 electrolyte nature
of 3-4. All the ligands were found soluble in common organic
solvents. The solubility of complexes 1 and 2 was good in DMF
and DMSO, moderate in CH3CN and almost negligible in
CH2Cl2, CHCl3, CH3OH, diethyl ether, THF and hexane. On
5
10 other hand complexes 3-4 showed good solubility in DMF,
DMSO and CH3CN and were found sparingly soluble in CH2Cl2,
CHCl3 and CH3OH. In diethyl ether and hexane they were found
insoluble.
Figure 1. ORTEP diagram of 1 with ellipsoids at the 30%
probability level; H atoms are omitted for clarity. Bond
length(Å): Pd(1)—S(1) 2.273(11), Pd(1)—N(2) 2.028(2),
60 Pd(1)—Cl(1) 2.277(11), Pd(1)—Cl(2) 2.292(11); bond angle(o):
Cl(1)—Pd(1)—S(1) 86.6(5), Cl(2)—Pd(1)—S(1) 175.7(3),
N(2)—Pd(1)—S(1) 94.2(8), N(2)—Pd(1)—Cl(1) 179.1(7),
N(1)—Pd(1)—Cl(2) 89.3(8), Cl(2)—Pd(1)—Cl(1) 89.9(5).
NMR and IR spectra
15 The 77Se{1H} NMR spectra of ligands (L2 and L4) and their
corresponding complexes (2 and 4) are given in Figures S3-S6 of
ESI†. The signals in the 77Se{1H} NMR spectra of 2 and 4
appear shifted to higher frequencies by 84.2 and 198.3 ppm
respectively with respect to those of free L2 and L4, implying
1
20 coordination of Se with palladium center. The H and 13C{1H}
NMR spectra (see ESI†, Figures S7-S22) of L1-L4 and their
complexes 1-4 have been found consistent with their molecular
1
structures (Scheme 1). The signals in the H and 13C{1H} NMR
spectra of L1 and L2 have been found shifted to lower
25 frequencies upto 0.59 and 8.86 ppm and 0.63 and 15.56 ppm
respectively with respect to 4−bromo–1–(2–chloroethyl)–1H–
1
pyrazole (A), as Se is less electronegative than Cl. In H and
13C{1H} NMR spectra of complexes 1-4 signals of various
protons and carbon atoms generally appear at higher frequency
30 relative to those of free ligands which coordinate with palladium
in a bidentate (1 and 2) or tridentate (3 and 4) mode. In 13C{1H}
NMR spectra of 1 and 2 signals of C5 and C9 are more
deshielded relative to those of other carbon atoms present in the
molecules. Same is true for C1 and C5 in case of 3 and 4. The
35 protons attached to all these carbon atoms also appear somewhat
more deshielded than other protons of the four complex
molecules. The high magnitude of shift for these four carbon
atoms is probably due to the fact that they are very close to donor
sites.
65 Figure 2. ORTEP diagram of 2 with ellipsoids at the 30%
probability level; H atoms are omitted for clarity. Bond
length(Å): Pd(1)—Se(1) 2.381(7), Pd(1)—N(2) 2.035(3),
Pd(1)—Cl(1) 2.287(11), Pd(1)—Cl(2) 2.315(11); bond angle(o):
Cl(1)—Pd(1)—Se(1) 85.4(4), Cl(2)—Pd(1)—Se(1) 175.0(3),
70 N(2)—Pd(1)—Se(1) 94.4(9), N(2)—Pd(1)—Cl(1) 179.8(9),
N(2)—Pd(1)—Cl(2) 89.8(9), Cl(2)—Pd(1)—Cl(1) 90.9(4).
40
IR spectra of L1-L4 have bands at 1254–1269 and
1643–1648 cm-1 may be ascribed to C—N (aliphatic) and C
N
(aromatic) stretching. On complex formation both these bands
show red shift upto 8 and 16 cm-1 respectively.
Crystal structure
45 The single crystal structures of complexes 1-4 have been solved.
The details of crystal data and refinements are given in Tables S1
of ESI†. The ORTEP diagrams of 1-4 are given in Figures 1-4
with selected bond lengths and angles (more values are given in
Table S2 of ESI†). The 1 and 2 are iso-structural. The geometry
50 around Pd in complexes 1-4 is nearly square planar and the
ligands are coordinated with Pd in a bidentate (S/Se, N) or
tridentate (N, S/Se, N) mode forming one (in case of 1 and 2) and
two (in case of 3 and 4) six membered chelate rings respectively.
Figure 3. ORTEP diagram of 3 with ellipsoids at the 30%
probability level; H atoms, solvated CH3CN and BF4¯ are omitted
75 for clarity. Bond length(Å): Pd(1)—S(1) 2.288(4), Pd(1)—N(2)
2.010(10), Pd(1)—N(4), 2.007(10) Pd(1)—Cl(1) 2.305(4); bond
angle(o): Cl(1)—Pd(1)—S(1) 176.4(15), N(2)—Pd(1)—S(1)
90.0(3), N(4)—Pd(1)—S(1) 89.8(3), N(2)—Pd(1)—Cl(1)
90.8(3), N(4)—Pd(1)—Cl(1) 89.4(3), N(2)—Pd(1)—N(4)
80 179.7(5).
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The bond angles at the coordinating S/Se and N atoms are as
35 expected for nearly trigonal-pyramidal and tetrahedral
geometries, respectively.
Figure 4. ORTEP diagram of 4 with ellipsoids at the 30%
probability level; H atoms and BF4¯ are omitted for clarity. Bond
length(Å): Pd(1)—Se(1) 2.385(5), Pd(1)—N(2) 1.993(5),
Pd(1)—N(4), 2.005(5) Pd(1)—Cl(1) 2.284(16); bond angle(o):
Cl(1)—Pd(1)—Se(1) 177.2(5), N(2)—Pd(1)—Se(1) 90.3(14),
N(4)—Pd(1)—Se(1) 91.5(15), N(2)—Pd(1)—Cl(1) 89.2(14),
N(4)—Pd(1)—Cl(1) 89.1(15), N(2)—Pd(1)—N(4) 177.5(2).
Figure 6. Inter and intra-molecular Cl···H, Br···H, B−F···H
40 interactions in 4.
5
In the crystals of 1-4, due to secondary interactions (See
Table S3 of ESI† for inter-atomic distances) several supra-
molecular structural patterns (see ESI†, Figures S23-S26 and
Figures 5-6) have been observed. The inter-molecular/intra-
45 molecular Cl···H [2.722(1)–2.954(1) Å], Br···H [2.873(4)–
2.838(5) Å] C–H···π [3.077(1)–3.150(1) Å] and π···π [3.948(4)–
3.951(7) Å] interactions result in chain structures for complexes 1
and 2. In Figure 5 such structure for 2 is shown. In complexes 3
and 4 out of above four secondary interactions π···π one is absent
50 and an additional B–F···H interaction exists (See Figure 6 for
complex 4). Each BF4¯ group is caged between complex cations.
In 1 and 2, one-dimensional (1D) chain structures are formed
along b-axis. The C–H···π interactions in 3 [3.304(49)–3.405(62)
Å] (see ESI†, Figure S24) are shorter than those of 4 [3.443(6)–
55 3.815(3) Å].
10 The Pd−S bond lengths of complexes 1/3 are 2.2731(11)/2.288(4)
Å,
consistent
with
earlier
reported
values14p,32
2.270(16)−2.286(12) Å for [PdCl(O¯, N, S)ligand] and [PdCl(S,
N, Se)ligand]+. These values are shorter than the reported values
[2.299(3)-2.2976(10)
Å ]
for [PdCl2(S, N)ligand].34 This
15 difference may be due to combined effect of difference in chelate
ring size, substituent on S, donor strength of nitrogen and ligand
architecture. The Pd−Se bond lengths of complex 2, 2.3806(7) Å
and 4, 2.3854(5) Å are similar, probably because coordinating
skeletons are identical in their ligand systems, but somewhat
20 shorter than the sum of covalent radii 2.44 Ǻ. They are consistent
with earlier reported value14i 2.3891(7) Å for [PdCl(Se, N,
Se)ligand]+ and somewhat longer than 2.353(2)−2.3669(11) Å
reported for [PdCl(O¯, N, Se)ligand] and [PdCl2(N,
Se)ligand].14k–l,14p–q The Pd−N bond lengths of complexes 1-4 are
25 from 1.993(5) to 2.035(3) Å consistent with the sum of covalent
radii 2.03 Å. Further the present Pd−N bond distances are within
the range 1.985(3)−2.045(1) Å reported for [PdCl(Se, N,
Se)ligand]+16i and [PdCl2(S, N)ligand].23-24 The Pd−Cl bond
lengths in 1-4 are also normal (in the range
30 2.2770(11)−2.3152(11) Å).14i, 14k–l,14p–q, 32-34
Application in Suzuki-Miyaura coupling reaction
Suzuki-Miyaura reaction (Scheme 2) an important palladium
catalyzed cross coupling is of wide interest.11 In view of air and
moisture sensitivity of complexes of phosphorus ligands, there is
60 a current interest in palladium complexes of phosphine-free
ligands for the Suzuki-Miyaura reaction.35-37 Complexes 1-4 have
been explored for Suzuki-Miyaura reaction of aryl bromide with
phenylboronic acid, as they offer the advantage of stability under
ambient conditions. In Table 1 substrates, reaction time, mol% of
65 Pd used and percentage yield are given.
For carrying out Suzuki-Miyaura reactions of aryl
bromide with phenylboronic acid the reaction conditions used
were similar to those used for analogous phosphine-free
systems.14e,14k The complexes 1-4 were found to show promising
70 catalytic activity14e for several aryl bromides (Table 1) including
electron rich ones, as their low catalyst loading (~0.01 mol%)
was found sufficient for good conversion in several cases. The
highest yield (96%) was obtained in case of 4–bromobenzonitrile
and 1–bromo–4–nitrobenzene both, when 4 was used as catalyst.
75 When Suzuki coupling was started a black precipitate appeared
causing curiosity about the role of this precipitate in catalytic
reaction. It is possible that 1-4 are only pre-catalysts and give
nano-sized Pd(0) containing species during the reaction which in
turn are responsible for catalysis. The black precipitates appeared
Figure 5. Inter and intra-molecular Cl···H, Br···H, C–H···π and
π···π interactions in 2.
6
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during
the
course
of
catalysis
of
coupling
of
30
Further in comparison to several complex catalysts14
which are giving good conversions at lower loading than the
present one, the required reaction time in our case is very short.
The additional advantage of using these catalysts is that they are
air stable and also not moisture sensitive.
4−bromobenzaldehyde with phenylboronic acid under optimum
reaction conditions by 1-4, were isolated, washed, dried and
subjected to SEM-EDX (see ESI†; Figure S47 and S50) and TEM
(Figure 7). They are of nano-size and spherical in shape. The
sizes of NPs are ~19, ~2, ~5 and ~3 nm obtained from 1-4
respectively. The SEM-EDX has revealed that they can be
approximately formulated as Pd4S, Pd2Se, Pd5S2 and PdSe
respectively for complexes 1-4. These NPs were found
5
10 catalytically active as shown by results of representative coupling
reactions given in Table 2. As expected isolated NPs appear to be
somewhat deactivated in comparison to those generated in situ as
their amount needed for comparable conversions is more than
those of 1-4. Thus real catalysts appear to be NPs formed from 1-
15 4, which are their dispensers only. This explains the little effect
of change in ligand on catalytic efficiency also. To identify
whether the reaction is heterogeneous or homogeneous Hg-
poisoning14a and triphenylphosphine14a tests were carried out.
Both the tests were positive further suggesting heterogeneous
20 nature of catalysis, which proceeds most probably via NPs
composed of Pd-S/Se.14a,e The present results of catalytic
coupling were found comparable with the earlier reports viz.
Suzuki C−C coupling catalyzed with [PdCl2(N, S/Se) ligands)]14k
and [PdCl(O¯, N, Se)ligand],14p The short reaction time, 2 h in
25 present case is much lower than 24 h reported earlier for other
catalysts14 used for Suzuki coupling. The catalyst loading (0.01
mol %) in the present case is also lower compared to some
previously reported complex catalysts [PdCl2(N, S/Se)
ligands)]14k and [PdCl(O¯, N, Se)ligand].
35
(a)
(b)
(c)
Figure 7. TEM images palladium-chalcogenide (Pd-S/Se) NPs
40 (a, b, c and d) obtained from 1-4 respectively.
(d)
Table 1 Suzuki-Miyaura coupling reactions catalyzed by 1-4.
Entry Aryl Bromides
No.
Mol %
Pd
1
2
3
4
Time
(h)
Yield
(%)
Time
(h)
Yield
(%)
Time
(h)
Yield
(%)
Time
(h)
Yield
(%)
1
NO2
0.01
2
90
2
92
2
94
2
96
Br
2
CHO
Br
0.01
0.01
2
2
88
90
2
2
90
94
2
2
93
94
2
2
95
96
3
CN
Br
4
0.01
1.0
2
86
2
90
2
92
2
94
Br
5
12
24
12
65
75
60
12
24
12
65
78
62
12
24
12
67
82
65
12
24
12
72
85
68
CH3
Br
6
OCH3
Br
1.0
24
70
24
74
24
85
24
80
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ARTICLE TYPE
stronger. Consequently TOP substitutes sulphur ligand and
decomposition of Pd-TOP complex results in PdP2. Since TOP is
40 absent during coupling reaction, formation of palladium sulphide
phases is not hindered. On the other hand Se is a strong donor and
TOP fails to substitute Se lgands. Thus thermolysis of 2 and 4 has
resulted palladium selenide nano-particles (Pd4Se and PdSe
respectively). Probably formation of PdP2 is not due to
45 decomposition of TOP otherwise it would have been observed as
a serious impurity with Pd-selenide phases. The PdP2 nano-
particles are of size 21 nm and authenticated by powder XRD,
SEM-EDX and HR-TEM (see ESI†, Figures S35, S37, S39, S41,
S43, S45, S51 and S52).
Table 2 Suzuki-Miyaura coupling catalyzed by NPs (10 mg)
isolated from 1-4.
Entry
No.
Aryl Bromides
Time NP1 NP2 NP3 NP4
(h)
CHO
Br
Br
2
92
1
92
95
96
OCH3
OCH3
2
3
2
64
64
87
68
95
70
97
Br
12
85
One pot single source synthesis of Pd4Se and PdSe nano-
particles
5
50
The synthesis of nano-structured palladium selenides important
due their potential applications (see Introduction) requires harsh
condition or sophisticated experimental set up. We have observed
that high quality TOP capped nano-particles of two such
60
50
40
30
20
10
0
10 selenides Pd4Se and PdSe may be synthesized by thermolysis of
complexes 2 and 4 respectively (Scheme 3) at lower temperature
◦
(200-250 C) as compared to other synthetic procedure reported
in literature.28a Further our synthesis is one pot, based on single
source precursor (for both Pd and Se). TOP acts potentially
15 surface ligand that stabilizes and mediates the growth of these
NPs. It appears that palladium selenide phases formed are
somewhat dependent on structure of precursor complexes. There
are not many such examples reported earlier.38 The NPs of Pd4Se
and PdSe were authenticated by powder XRD patterns which
20 have been found matching with those reported for such phases
(See ESI†, Figure S35-S38 and text below them). Both types of
nano-particles are tetragonal. The sharp nature of the powder
XRD patterns (see ESI†, Figures S35-S38) is consistent with their
high crystallinity and nano-size. SEM-EDX and HR-TEM have
25 supported their compositions. The morphology of these nano-
particles as revealed by SEM is shown in Figure S31-S34 of
ESI†. The results of SEM-EDX show that they are capped with
TOP (see ESI†, Figures S35-S38). HR-TEM images have
revealed size of TOP capped nano-particles spherical in shape,
30 obtained from 2 and 4 is in the range 8-26 nm (Figures 8 and 9).
Attempts to synthesize palladium sulfide phases in
4
6
8
10
12
14
16
Particle size (nm)
Figure 8. TEM image and distribution of Pd4Se NPs.
40
30
20
10
0
nano-size by thermolysis of 1 and 3 in TOP (following a
procedure analogous to one given in Scheme 3) has resulted in
PdP2 instead of palladium sulphide. The phosphorus present in
35 PdP2 nano-particles probably has come from capping ligand TOP.
The phosphorous donors are considered stronger than sulphur
ones and presence of three alkyl groups makes TOP further
10
12
14
16
18
20
22
24
26
28
30
Particle size (nm)
55
Figure 9. TEM image and distribution of PdSe NPs.
[journal], [year], [vol], 00–00 | 8
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60 7 (a) A. C. Moro, A. E. Mauro, A. V. G. Netto, S. R. Ananias, M.B.
Quilles, I. Z. Carlos, F. R. Pavan, C. Q. F. Leite and M. Hörner, Eur.
J. Med. Chem., 2009, 44, 4611; (b) A. M. Bego, R. C. G. Frem, A. V.
G. Netto, A. E. Mauro, S. R. Ananias, I. Z. Carlos and M. C. da
Rocha, J. Brazil Chem. Soc., 2009, 20, 437; (c) R. A. de Souza, A.
Conclusions
The four pyrazolated thio/selenoethers (L1-L4) have been
synthesized by reaction of 4–bromo–1–(2–chloroethyl)–1H–
pyrazole with the in situ generated PhSNa, PhSeNa, Na2S, and
Na2Se and characterized by using 1H, 13C{1H} and 77Se {1H}
NMR, IR and HRMS. Their Pd(II) complexes (1-4) have been
synthesized by reacting them with [PdCl2(CH3CN)2] in CH3CN at
70 °C and also authenticated with H, 13C{1H} and 77Se {1H}
NMR, IR, HRMS and single crystal X-ray diffraction. The
10 complexes 1−4 were found efficient pre-catalysts for the Suzuki-
Miyaura coupling reaction, as the yield was found upto 96% in
just 2 h. TOP capped nano-particles of Pd4Se and PdSe (size
ranges 8-26 nm) have been obtained under mild conditions by
65
Stevanato, O. Treu-Filho, A. V. G. Netto, A. E. Mauro, E. E.
Castellano, I. Z. Carlos, F. R. Pavan and C. Q. F. Leite, Eur. J. Med.
Chem., 2010, 45, 4863.
5
8
D. Fan, C. Yang, J. D. Ranford and J. J. Vittal, Dalton Trans., 2003,
4749.
1
70 9 (a) F. V. Rocha, C. V. Barra, A. V. G. Netto, A. E. Mauro, I. Z.
Carlos, R. C. G. Frem, S. R. Ananias, M. B. Quilles, A. Stevanato
and M. C. da Rocha, Eur. J. Med. Chem., 2010, 45, 1698; (b) J. S.
Casas, E. E. Castellano, J. Ellena, M. S. García-Tasende, M. L.
Pérez-Parallé, A. Sánchez, A. Sanchéz-Gonzázlez, J. Sordo and A.
75
80
85
Touceda, J. Inorg. Biochem., 2008, 102, 33.
10 (a) Recent selected books: J. Tsuji, Palladium Reagents and
Catalysts, John Wiley & Sons, Chichester, 1995; (b) F. Diederich and
P. J. Stang, Metal-Catalyzed Cross-Coupling Reactions, Wiley-VCH,
Weinheim, 1998; (c) M. T. Reetz, Transition Metal Catalysed
Reactions (ed.: S. G. Davies, S.-I. Murahashi), Blackwell Science,
Oxford, 1999; (d) N. Miyaura, Cross-Coupling Reactions, Springer,
Berlin, 2002.
11 (a) A. Suzuki, Pure Appl. Chem., 1991, 63, 419; (b) S. Kotha, K.
Lahiri and D. Kashinath, Tetrahedron, 2002, 58, 9633; (c) A. Suzuki,
J. Organomet. Chem., 1999, 576, 147; (d) S. P. Stanforth,
Tetrahedron, 1998, 54, 263; (e) N. Miyaura and A. Suzuki, In
Advances in Metal–Organic Chemistry, L. S. Liebeskind, Ed.; JAI:
London, 1998, 6, 187; (f) N. Miyaura and A. Suzuki, Chem. Rev.,
1995, 95, 2457.
◦
thermolysis 1-4 at 200-250 C. HRTEM, SEM, SEM-EDX and
15 powder XRD have authenticated these nano-particles. Attempt to
prepare nano-particles composed of palladium and sulphur by a
procedure similar to the one used for palladium-selenide phases
resulted in PdP2 nano-particles.
Acknowledgements
20 Authors thank Council of Scientific and Industrial Research
(CSIR), New Delhi, India for the project no. 01(2421)10/EMR−II
and JRF/SRF to KNS. Department of Science and Technology
(India) is acknowledged for research projects (SR/WOS–A/CS–
22/2009 and SR/S1/IC-40/2010), financial support for single
25 crystal X-ray (FIST) and HR-TEM (NSIT) facilities at IIT Delhi.
HJ thanks University Grants Commission (India) for JRF.
90 12 (a) T. Kinzel, Y. Zhang and S. L. Buchwald, J. Am. Chem. Soc.,
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Notes and references
Department of Chemistry, Indian Institute of Technology Delhi, New
Delhi 110016, India.
30 *Corresponding author. Fax: +91-01- 26581102; Tel: +91-011-
26591379;
100 13 (a) C. Fliedel and P. Braunstein, Organometallics, 2010, 29, 5614;
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E-mail: aksingh@chemistry.iitd.ac.in, ajai57@hotmail.com (A. K. Singh)
† Electronic Supplementary Information (ESI) available: NMR spectra
(Figures S1−S22), Crystal data and refinement parameters (Table S1),
35 bond lengths and angles (Table S2), distances of non–covalent
interactions (Table S3), non-covalent interactions with bond lengths
(Figures S23–S26), Mass spectra (Figures S27–S34), PXRD (Figures
S35–S38), SEM images (Figures S39–S42), SEM–EDX images (Figures
S43–S50) and TEM images (Figures S51–S52). CIFs for 1−4. CCDC
40 numbers: 885700 (For 1), 885701 (For 2), 885702 (For 3) and 885703
(For 4). For ESI† and crystallographic data in CIF or other electronic
formate see DOI: 10.1039/b000000x/
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Palladium(II) complexes of pyrazolated thio/selenoethers: syntheses,
structures, single source precursors of Pd4Se and PdSe nano-
particles and potential for catalyzing Suzuki-Miyaura coupling
Kamal Nayan Sharma, Hemant Joshi, Ved Vati Singh, Pradhumn Singh and Ajai Kumar Singh*
Pd(II)-complexes (characterized by X-ray crystallography) give Pd4Se/PdSe nano-particles and
efficiently catalyze Suzuki-Miyaura coupling via in situ generated Pd-S/Se NPs
.