Chalcogen-dependent palladation at the benzyl carbon of 2,3-bis[(phenylchalcogeno)methyl]quinoxaline: Palladium complexes catalyzing suzuki-miyaura coupling via palladium-chalcogen nanoparticles

Article abstract of DOI:10.1021/om3006273

The reaction of PhS^-/PhSe^- with 2,3-bis(bromomethyl) quinoxaline has resulted in 2,3-bis[(phenyl-thio/-seleno)methyl]quinoxaline (L1/L2). They react with Na₂PdCl₄, resulting in [Pd ₂(L1-H)₂Cl₂] (1)/[PdL2Cl₂] (2). External base-free activation of the benzyl group's C(sp³)-H results in palladation of L1, forming palladacycle 1, whereas L2 forms a seven-membered chelate ring with Pd(II), resulting in 2. L1, L2, 1, and 2 have been characterized by IR, multinuclear NMR, mass spectrometry, and single-crystal X-ray diffraction. In the case of 1 bond lengths (A) are Pd-C = 2.001(9), Pd-N = 2.048(8), and Pd-S = 2.259(2) A. The Pd-Se bond length in complex 2 is 2.3924(15)-2.3991(15) A. Complexes 1/2 were explored in the catalyzed Suzuki-Miyaura coupling reactions of several aryl bromides (including deactivated ones). The palladacycle 1 shows better catalytic efficiency than complex 2, as its lower reaction time and catalyst loading (up to 0.006 mol %) are sufficient for significantly good conversions. The catalysis appears to be occurring via in situ generated nanoparticles (size <2 nm) composed of palladium and sulfur or selenium and protected by L1 or L2, as nanoparticles after isolation also show catalytic activity. The results of a two-phase test suggest that the catalysis is cocktail type (i.e., homogeneous and heterogeneous in parts).

Full text of DOI:10.1021/om3006273

Article
pubs.acs.org/Organometallics
Chalcogen-Dependent Palladation at the Benzyl Carbon of 2,3-
Bis[(phenylchalcogeno)methyl]quinoxaline: Palladium Complexes
Catalyzing Suzuki−Miyaura Coupling via Palladium−Chalcogen
Nanoparticles
Fariha Saleem, Gyandshwar Kumar Rao, Pradhumn Singh, and Ajai Kumar Singh*
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi 110016, India
S
* Supporting Information
ABSTRACT: The reaction of PhS−/PhSe− with 2,3-bis-
(bromomethyl)quinoxaline has resulted in 2,3-bis[(phenyl-
thio/-seleno)methyl]quinoxaline (L1/L2). They react with
Na2PdCl4, resulting in [Pd2(L1−H)2Cl2] (1)/[PdL2Cl2] (2).
External base-free activation of the benzyl group’s C(sp3)−H
results in palladation of L1, forming palladacycle 1, whereas L2
forms a seven-membered chelate ring with Pd(II), resulting in
2. L1, L2, 1, and 2 have been characterized by IR, multinuclear
NMR, mass spectrometry, and single-crystal X-ray diffraction.
In the case of 1 bond lengths (Å) are Pd−C = 2.001(9), Pd−N
= 2.048(8), and Pd−S = 2.259(2) Å. The Pd−Se bond length
in complex 2 is 2.3924(15)−2.3991(15) Å. Complexes 1/2
were explored in the catalyzed Suzuki−Miyaura coupling reactions of several aryl bromides (including deactivated ones). The
palladacycle 1 shows better catalytic efficiency than complex 2, as its lower reaction time and catalyst loading (up to 0.006 mol
%) are sufficient for significantly good conversions. The catalysis appears to be occurring via in situ generated nanoparticles (size
<2 nm) composed of palladium and sulfur or selenium and protected by L1 or L2, as nanoparticles after isolation also show
catalytic activity. The results of a two-phase test suggest that the catalysis is cocktail type (i.e., homogeneous and heterogeneous
in parts).
ated nitrogen heterocycles as building blocks of phosphine-free
Pd catalysts, an attempt to design chalcogenated quinoxaline-
based palladium(II) catalysts for C−C coupling has been
envisaged worth exploring. The chalcogenation of 2,3-bis-
(bromomethyl)quinoxaline can give ligands that may be
competitive with chalogenated pyridines and related systems
for designing Pd(II) catalysts. In this paper we report seleno-
and thio-ether type ligands (L1 and L2), synthesized from 2,3-
bis(bromomethyl)quinoxaline (Scheme 1). The resulting
multidentate ligands with four potential coordination sites
(two N and two S/Se) may offer some additional advantages,
because it is known for transition-metal complexes that an
additional donor site in the ligand can act as a stabilizing group
during the course of a metal-mediated reaction, which in turn
may improve the catalytic efficiency of the complex.20 Except
silver(I)21 and copper(I)22 complexes of some quinoxaline
derivatives analogous to L1 (having different substituents in
place of Ph on S) nothing else is known about ligation of
chalcogeneted quinoxaline-based ligands and their applications.
It was therefore thought worthwhile to explore the chemistry of
L1 and L2. Palladium(II) forms a seven-membered chelate ring
INTRODUCTION
■
The quinoxaline ring is present in dyes,1 pharmaceuticals,2,3
and electrical/photochemical materials.4−9 It is also present in
various antibiotics such as echinomycin, levomycin, and
actinoleutin.10,11 The quinoxaline-based ligands have not been
explored so far for the designing of Pd complexes catalytically
active for C−C coupling reactions such as Suzuki−Miyaura
coupling, which is one of the most widely used processes for
the synthesis of biaryls, important intermediates in organic
synthesis, and recurring functional groups in natural products.12
Phosphorus ligand based Pd-catalysts commonly used for such
reactions are often air/moisture sensitive, and therefore,
catalysis under phosphine-free conditions is of high importance
currently. The palladacycles of organochalcogen ligands, Pd(II)
complexes of chalcogenated Schiff bases and some other S- or
Se-containing ligands, have emerged13−16 as a family of air-
stable, moisture-insensitive, and efficient catalysts, which can
carry out phosphine-free Suzuki−Miyaura coupling. Chalco-
genated half-pincer and pincer ligands are particularly attractive
for designing catalysts for phosphine-free Heck or Suzuki−
Miyaura coupling. Some important ones among them have
been synthesized from 2-(chloromethyl)pyridine,17 2,6-bis-
(bromomethyl)benzene,15e,18 and 2,6-bis(chloromethyl)-
pyridine.19 Considering the immense potential of chalcogen-
Received: July 6, 2012
Published: January 11, 2013
© 2013 American Chemical Society
387
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
Scheme 1. Synthesis of Ligands and Pd(II) Complexes
atmosphere, if required, was created using Schlenk techniques.
Single-crystal structure data were collected with a Bruker AXS
SMART-APEX CCD diffractometer using Mo Kα radiation (0.71073
Å) at 298(2) K. The software SADABS was used for absorption
correction (if needed) and SHELXTL for space group, structure
determination, and refinements.25,26 Non-hydrogen atoms were
refined anisotropically. All hydrogen atoms were included in idealized
positions, and a riding model was used for the refinement. The least-
squares refinement cycles on F2 were performed until the model
converged. The melting points were determined in an open capillary
and reported as such. IR spectra in the range 4000−400 cm−1 were
with a selenated derivative of quinoxaline (L2). Palladacycle 1
is formed via an external base-free deprotonation of the C(sp3)
−
H bond of the benzyl group of L1. Only a limited number of
stable palladacycles having a Pd(II)−C(sp3) bond23,24 are
known, but none of them have been synthesized using
Na2PdCl4 as a source of Pd and without using an external
base. The applications of these Pd(II) complexes (1 and 2) in
the Suzuki−Miyaura coupling (Scheme 2) have been explored
Scheme 2. Suzuki−Miyaura Coupling Reaction
́
recorded on a Nicolet Protege 460 FT-IR spectrometer as KBr pellets.
Elemental analyses were carried out with a Perkin-Elmer 2400 Series II
C, H, N analyzer. High-resolution mass spectral (HR-MS) measure-
ments were performed with electron spray ionization (10 eV, 180 °C
source temperature) and using sodium formate as a calibrant on a
Bruker MIcroTOF-Q II, taking samples in CH3CN.
and found promising. It appears that catalysis with 1 and 2
takes place via formation of nanoparticles (NPs) made of
palladium and sulfur or selenium and protected by L1/L2. The
role of NPs in a few Suzuki−Miyaura reactions catalyzed with
palladium(II) complexes of chalogenated ligands has been
reported recently.13f,h,14g The present results are thus
important, as they would further strengthen the understanding
of Suzuki−Miyaura coupling catalyzed with palladium−organo-
chalcogen ligand complexes, such as the role of palladium−
chalcogen NPs. All these results are reported in the present
paper.
TEM studies were carried out with a Technai G2 20 electron
microscope operated at 200 kV. The specimens for TEM were
prepared by dispersing the powdered sample in chloroform by
ultrasonic treatment, dropping the slurry onto a porous carbon film
supported on a copper grid, and then drying it in air. The phase
morphologies of the samples were observed by using a Carl Zeiss
EVO5O scanning electron microscope (SEM). Samples were mounted
on a circular metallic sample holder with a sticky carbon tape.
Elemental compositions of nanoparticles on SEM were analyzed by an
EDX system, model Quan Tax 200, which is based on the SDD
technology and provides an energy resolution of 127 eV at Mn Kα.
The samples were scanned in different regions in order to minimize
the error in the analysis for evaluating the morphological parameters.
Chemicals and Reagents. Thiophenol, diphenyldiselenide,
sodium borohydride, 2,3-bis(bromomethyl)quinoxaline, disodium
tetrachloropalladate, and all other aryl bromides procured from
Sigma-Aldrich (USA) were used as received. All the solvents were
dried and distilled before use by known standard procedures.27
Synthesis of Ligand L1. Thiophenol (0.20 mL, 2.0 mmol) was
added to a refluxing solution of sodium hydroxide (0.16 g, 4.0 mmol)
made in 30 mL of EtOH under a nitrogen atmosphere, and the
mixture was refluxed further for 1 h. 2,3-Bis(bromomethyl)quinoxaline
(0.32 g, 1.0 mmol) dissolved in 20 mL of EtOH was added, and the
EXPERIMENTAL SECTION
■
1
Physical Measurements. The H, 13C{1H}, and 77Se{1H} NMR
spectra were recorded on a Bruker Spectrospin DPX-300 NMR
spectrometer at 300.13, 75.47, and 57.24 MHz, respectively, with
chemical shifts reported in ppm relative to normal standards. Yields
refer to isolated yields of compounds that have a purity of ≥95%. All
reactions were carried out in glassware dried in an oven under ambient
conditions, except the synthesis of L1 and L2. Commercial nitrogen
gas was used after passing it successively through traps containing
solutions of alkaline anthraquinone, sodium dithionite, alkaline
pyrogallol, concentrated H2SO4, and KOH pellets. A nitrogen
388
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
reaction mixture refluxed again for 3 h. Thereafter the reaction mixture
was stirred overnight at room temperature. It was poured into water
(30 mL). The ligand L1 was extracted with chloroform (4 × 25 mL).
The extract was washed with water (3 × 40 mL) and dried over
anhydrous sodium sulfate. The solvent was evaporated off under
reduced pressure on a rotary evaporator to get an off-white product,
which on recrystallization from an EtOH and dichloromethane
mixture (1:1) gave light yellow colored single crystals of L1. Yield:
0.33 g (88%); mp 110 °C. Anal. Found: C, 70.52; H, 4.91; N, 7.46.
(m, 2H, H8). 13C{1H} NMR (DMSO-d6, 25 °C, TMS): δ (ppm), 30.5
(C5), 127.4 (C1), 128.1 (C9), 129.2 (C2), 129.5 (C4), 129.9 (C8),
132.8 (C3), 140.0 (C6), 152.7 (C7). 77Se{1H} NMR (DMSO-d6, 25
°C, Me2Se): δ (ppm), 334.3. IR (cm−1): 464 (m), 687 (s), 743 (s),
1003 (b), 1127 (b), 1220 (b), 1327 (m), 1437 (s), 1478 [s;
νC−C (aromatic)], 1569 (b), 1651 [b; νCN], 2925 [b; νC−H (aliphatic)], 3056
[m; νC−H (aromatic)]. HR-MS: M = [(L2)2Pd] (m/z) 1045.8598, calcd
value for C44H36N4PdSe4 1045.8664 (δ 5.4 ppm).
Procedure for the Suzuki−Miyaura Coupling Reaction. An
oven-dried flask was charged with aryl bromide (1.0 mmol),
phenylboronic acid (1.5 mmol), K2CO3 (2.0 mmol), DMF/H2O
(3.0/2.0 mL), and catalyst 1 (1.0 to 0.006 mol %) or 2 (1 mol %). The
flask was placed on an oil bath at 90 °C under aerobic conditions, and
the reaction mixture was stirred. The reaction monitored by TLC was
carried out until maximum conversion of aryl bromide to product
occurred. The mixture was extracted with diethyl ether, washed with
water, and dried over anhydrous Na2SO4. The solvent of the extract
was removed with a rotary evaporator to obtain the product, which
was purified by column chromatography on silica gel. The products
1
Calcd for C22H18N2S2: C, 70.55; H, 4.84; N, 7.48. H NMR (CDCl3,
25 °C, TMS): δ (ppm), 4.57 (s, 4H, H5), 7.17−7.26 (m, 6H, H1, H2),
7.36−7.38 (m, 4H, H3), 7.67−7.70 (m, 2H, H9), 7.92−7.96 (m, 2H,
H8). 13C{1H} NMR (CDCl3, 25 °C, TMS): δ (ppm), 39.0 (C5), 127.1
(C1), 128.6 (C2), 128.9 (C9), 129.7 (C3), 130.9 (C8), 134.7 (C4),
140.9 (C6), 151.5 (C7). IR (cm−1): 474 (m), 687 (s), 739 [s; C−H
(aromatic) bending], 768 (s), 1087 (m), 1358 (m), 1390 (m), 1478
[s; νC−C (aromatic)], 1575 [m; νCN], 2936, 2979 [s; νC−H (aliphatic)], 3057
[m; νC−H (aromatic)]. HR-MS [M + H]+ (m/z): 375.0970; calcd value for
C22H18N2S2H 375.0984 (δ 3.8 ppm).
1
Synthesis of Ligand L2. Diphenyldiselenide (0.62 g, 2.0 mmol)
dissolved in 30 mL of EtOH was refluxed with stirring under a
nitrogen atmosphere and treated with a saturated solution of sodium
borohydride made in 5 mL of aqueous NaOH (5%) dropwise until it
became colorless due to the formation of PhSeNa. 2,3-Bis-
(bromomethyl)quinoxaline (0.63 g, 2.0 mmol) dissolved in 10 mL
of EtOH was added to the colorless solution with constant stirring,
and the mixture refluxed further with stirring for 3 h. Thereafter the
reaction mixture was stirred overnight at room temperature. It was
poured into water (30 mL). L2 was extracted with chloroform (4 × 25
mL). The extract was washed with water (3 × 40 mL) and dried over
anhydrous sodium sulfate. The solvent was evaporated off under
reduced pressure on a rotary evaporator to get a light yellow solid,
which on recrystallization with an EtOH and dichloromethane mixture
(1:1), gave pale yellow colored single crystals of L2. Yield: 0.75 g
(80%); mp 105 °C. Anal. Found: C, 56.40; H, 3.89; N, 5.94. Calcd for
were authenticated with H and 13C{1H} NMR spectra.
Isolation of Nanoparticles Generated from 1 and 2. A mixture
of Pd(II) complex 1/2 (0.5 mmol), phenylboronic acid (1.5 mmol), 4-
bromobenzonitrile (1.0 mmol), and K2CO3 (2.0 mmol) in DMF (4.0
mL) and water (4.0 mL) was heated at 100 °C for 1.5 h and then
cooled to room temperature. The solvent was decanted, and the black
residue (NPs) was thoroughly washed with a water/acetone mixture
(1:3) and dried in vacuo. Yield: 1, 0.23 g; 2, 0.14 g. The NPs were
characterized by SEM, SEM-EDX, TEM, and TEM-EDX.
Procedure for the Suzuki−Miyaura Coupling Reaction
Catalyzed by NPs Generated from 1 and 2. This was similar to
the one used for complexes 1 and 2 except that the reaction time was 3
h and NPs (10 and 50 mg of those obtained from 1 and 2,
respectively) generated from each complex were used in their place.
Hg Poisoning Test. An excess of Hg (Hg:Pd, 500:1) was taken in
the reaction flask, and thereafter the coupling reactions were carried
out in the same flask. For catalyst 1 coupling of 4-bromoanisole was
carried out under optimum conditions, whereas in the case of 2 the
substrate taken was 4-bromobenzaldehyde. The coupling products
were not obtained after 3 h.
1
C22H18N2Se2: C, 56.42; H, 3.87; N, 5.98. H NMR (CDCl3, 25 °C,
TMS): δ (ppm), 4.44 (s, 4H, H5), 7.15−7.25 (m, 6H, H1, H2), 7.42−
7.45 (m, 4H, H3), 7.62−7.66 (m, 2H, H9), 7.84−7.88 (m, 2H, H8).
13C{1H} NMR (CDCl3, 25 °C, TMS): δ (ppm), 31.3 (C5), 127.8
(C1), 128.4 (C2), 129.0 (C9), 129.5 (C3), 134.2 (C4, C8), 140.8 (C6),
152.5 (C7). 77Se{1H} NMR (CDCl3, 25 °C, Me2Se): δ (ppm), 354.0.
IR (cm−1): 463 (s), 607 (m), 687 (s), 733 [s; C−H (aromatic)
bending], 764 (s), 803 (m), 1013 (m), 1065 (m), 1127 (m), 1173
(m), 1317 (m), 1355 (m), 1435 (s), 1475 [s; νC−C (aromatic)], 1565 [m;
νCN], 2943 (m), 2993 [s; νC−H (aliphatic)], 3056 [m; νC−H (aromatic)].
HR-MS [M + Na]+ (m/z): 492.9707; calcd value for C22H18N2Se2Na
492.9696 (δ 2.1 ppm).
PPh3 Test. This was carried in a manner similar to that of the Hg
poisoning test using identical substrates except the amount of PPh3
was taken as 1 mmol. Even after 3 h of reaction no cross-coupled
product was obtained.
Two-Phase Test. A mixture of 4-bromoacetophenone-immobilized
silica (0.20 g) prepared by standard procedure28 (details in the
Supporting Information), phenylboronic acid (0.36 g, 3 mmol), 4-
bromoacetophenone (0.20 g, 1 mmol), and K2CO3 (0.56 g, 4 mmol)
was heated at 90 °C for 12 h in a DMF/water (8 mL/4 mL) mixture.
The resulting mixture was cooled and filtered through a G-4 crucible.
The residue was washed with 20 mL of H2O followed by diethyl ether
(50 mL). The filtrate and washings were collected together and mixed
with 50 mL of water. The resulting mixture was extracted with diethyl
ether (50 mL). The solvent of the extract was evaporated off on a
Synthesis of Palladium Complexes 1 and 2. A solution of
Na2PdCl4 (0.029 g, 0.1 mmol) made in 5 mL of water was mixed with
L1 (0.037 g, 0.1 mmol) or L2 (0.047 g, 0.1 mmol) dissolved in
acetone (10 mL) with vigorous stirring. An orange precipitate was
obtained instantaneously, which was filtered, washed with water, and
dried. Single crystals were grown from a 1:1 mixture of chloroform and
hexane.
1
rotary evaporator, and the residue subjected to H NMR. The solid
residue was hydrolyzed with KOH (1.68 g dissolved in 10 mL of
EtOH + 5 mL of H2O) at 90 °C for 3 days. The resulting solution was
neutralized with aqueous 20% (v/v) HCl, extracted with dichloro-
methane followed by ethyl acetate. The solvent of the combined
extract was evaporated off, and the resulting residue was analyzed with
1H NMR.
1: Yield: 0.044 g (84%); mp 200 °C (dec). Anal. Found: C, 51.21;
H, 3.35; N, 5.40. Calcd for C44H34Cl2N4Pd2S4: C, 51.27; H, 3.32; N,
5.44. 1H NMR (CDCl3, 25 °C, TMS): δ (ppm), 4.06 (s, 2H, H5, CH),
4.16−4.27 (m, 4H, H5, CH2), 7.28−7.40 (m, 12H, H1, H2), 7.90 (d,
3JH−H = 9 Hz 4H, H8), 8.10−8.27 (m, 2H, H3), 8.17 (m, 4H, H9).
13C{1H} NMR (CDCl3, 25 °C, TMS): δ (ppm), 41.1 (CH2, C5), 60.5
(CH, C5), 128.3 (C1, C2), 129.3 (C9), 130.2 (C3), 130.8 (C8), 140.9
(C6), 142.1 (C4), 151.0 (C7). IR (cm−1): 476 (b), 689 (s), 748 [s;
νC−H (aromatic)], 1022 (b), 1124 (m), 1226 (m), 1330 (s), 1438 [s;
νC−C (aromatic)], 1477 (s), 1625 [m; νCN], 2924 [s, νC−H (aliphatic)], 3056
[m; νC−H (aromatic)]. HR-MS [M − Cl] (m/z) 992.9451; calcd value for
C44H34N4S4Pd2Cl 992.9429 (δ 2.5 ppm).
RESULTS AND DISCUSSIONS
■
The syntheses of L1 and L2 and their complexes 1 and 2 are
summarized in Scheme 1. They are stable under ambient
conditions and can be stored for several months. The solubility
of both ligands was found to be good in common organic
solvents, viz., chloroform, methanol, dichloromethane, and
acetone. The complexes 1 and 2 have good solubility in
chloroform and dichloromethane but moderate only in
2: Yield: 0.056 g (87%); mp 165 °C (dec). Anal. Found: C, 40.90;
H, 2.88; N, 4.30. Calcd for C22H18Cl2N2PdSe2: C, 40.93; H, 2.81; N,
1
4.34. H NMR (DMSO-d6, 25 °C, TMS): δ (ppm), 4.64 (s, 4H, H5),
7.25 (s, 6H, H1, H2), 7.50 (s, 4H, H3), 7.76−7.86 (m, 2H, H9), 7.95
389
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
acetonitrile. L1, L2, and 2 have good solubility in DMSO.
Complex 1 is moderately soluble in DMSO, and the stability of
the solution is poor. Complex 1 is formed via deprotonation of
the benzyl (sp3) group, which results in Pd−C bond formation.
The examples of palladation via activation of the C(sp3)−H
bond of the benzyl group without externally added base are few.
The source of Pd is Pd(OOCCH3)2 in those cases reported23
so far. There is no example to our knowledge in which such
palladation has been carried out by PdCl2 or Na2PdCl4 in the
absence of any external base.24 Thus this is the first example of
activation of C(sp3)−H by Na2PdCl4, in which the nitrogen of
quinoxaline acts as an internal base. This is consistent with the
interaction between nitrogen and benzylic hydrogen in the
structure of 1 (Figure 5). Further the reaction mixture was not
Figure 2. ORTEP diagram of L2 with 30% thermal probability
ellipsoids; H atoms are omitted for clarity. Bond lengths (Å): Se(1)−
C(1) 1.926(8); Se(1)−C(13) 1.982(7); Se(2)−C(7) 1.896(8);
Se(2)−C(14) 1.948(8). Bond angles (deg): C(1)−Se(1)−C(13)
97.6(3); C(7)−Se(2)−C(14) 102.0(3).
Figure 1. ORTEP diagram of L1 with 30% probability ellipsoids; H
atoms are omitted for clarity. Bond lengths (Å): S(1)−C(10)
1.757(4); S(1)−C(9) 1.802(4); S(2)−C(17) 1.774(4); S(2)−C(16)
1.823(4). Bond angles (deg): C(10)−S(1)−C(9) 103.5(2); C(17)−
S(2)−C(16) 100.65(18).
found to be basic, ruling out the possibility of base effect by any
component of the reaction mixture also. This kind of activation
in L2 does not occur, and due to the large size of Se, the seven-
membered chelate is easily stabilized, as observed earlier also.29
NMR Spectra. The 1H, 13C{1H}, and 77Se{1H} NMR
spectra of L1 and L2 as well as their complexes 1 and 2 were
found to be in agreement with their molecular structures
depicted in Scheme 1. They are given in the Supporting
Figure 3. ORTEP diagram of 1 with 30% thermal probability
ellipsoids; H atoms and CHCl3 are omitted for clarity. Bond lengths
(Å): C(10)−Pd(1) 2.001(9); Pd(1)−S(1) 2.259(2); N(2)−Pd(1)
2.048(8); Cl(1)−Pd(1) 2.350(3) C(1)−S(1) 1.758(11); C(11)−S(2)
1.740(10); C(7)−S(1) 1.802(9); C(10)−S(2) 1.780(10). Bond angles
(deg): C(10)−Pd(1)−N(2) 89.3(3); C(10)−Pd(1)−S(1) 91.3(3);
N(2)−Pd(1)−S(1) 177.4(2); C(10)−Pd(1)−Cl(1) 1178.0(3);
N(2)−Pd(1)−Cl(1) 92.7(2); S(1)−Pd(1)−Cl(1) 86.70(9).
1
Information (Figures S1−S10). In the H NMR spectra of L1
and L2, signals of H5 (−SCH2/−SeCH2) appearing at 4.57 and
4.44 ppm, respectively, are at 0.4 ppm lower frequency with
respect to those of 2,3-bis(bromomethyl)quinoxaline. The
signal in the 77Se{1H} NMR spectrum of L2 (at 354 ppm) is at
108 ppm lower frequency with respect to that of
diphenyldiselenide (462 ppm). Further there is one signal in
the 77Se{1H} NMR spectrum of each L2 and 2, implying the
equivalence of two Se atoms in solution. The 1H NMR
spectrum of 1 has two benzyl CH2 signals at 4.06 and 4.16−
4.27 ppm, as expected. Both of them are at lower frequency
relative to that of free L1. This may be due to the influence of
the 4d-electron cloud of palladium on hydrogen. In the
13C{1H} NMR spectrum of 1 two benzyl signals at 41.14 and
60.50 ppm have been observed. The one at higher frequency
arises from the carbon bonded to palladium. These
observations imply that in the solution structure also the Pd−
C bond exists as observed in the single crystal of 1. NMR
spectra of crude and single crystals of 1 are not different,
implying that 1 is not formed from [PdL1Cl2] during
crystallization. There is only one signal in the 77Se{1H} NMR
spectrum of 2, and it is at lower frequency (19.7 ppm) with
respect to that of free L2. This is consistent with earlier report
that on formation of a six-membered chelate ring by a Se ligand
such a signal may show a shift of small magnitude to lower as
390
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
complex [Pd(L2)2](ClO4)2 was prepared and authenticated
by NMR. In its 77Se{1H} (Supporting Information; Figure
S11), only one signal, at 324.2 ppm, appears. It is shielded
nearly 10 ppm with respect to that of 2. In the mass spectrum
of complex [Pd(L2)2](ClO4)2, two peaks, at m/z ≈ 1046 and
574, have been observed (Supporting Information; Figure S17).
The first one probably arises from [Pd(L2)2]+• and the second
one from [PdL2]+•, formed by the fragmentation of the first.
Thus [Pd(L2)2]2+ and [Pd(L2)]2+ are easily converted into
each other in the mass spectrometer. Further the MS/MS
experiment (Supporting Information; Figures S18 and S19) on
the peak at m/z ≈ 1046 of 2 gives a peak at m/z ≈ 574,
supporting the above inference and formulation of complex 2.
Crystal Structures. The crystal structures of L1, L2, 1, and
2 have been solved. The crystal data and refinement parameters
are given in the Supporting Information (Table S1). The
ORTEP diagrams of L1, L2, 1, and 2 are given in Figures 1 to 4
with selected bond lengths and angles. More bond angles and
lengths are given in the Supporting Information (Tables S2−
S5). In L1 the S−C (aryl) bond [1.757(4) Å] is somewhat
shorter than the S−C (alkyl) bond [1.802(4) Å]. The Se−C
(aryl) bond [1.896(8) Å] in L2 is also shorter than the Se−C
(alkyl) bond [1.948(8) Å]. However all these bond lengths are
consistent with the reported values.14d,29 In 1 the Pd−C and
Pd−S bond lengths of 2.001(9) and 2.259(2) Å, respectively,
are consistent with the values 2.190(9)24a and 2.2644(11) Å,14d
respectively, reported earlier. The Pd−Cl bond length in 1,
2.350(3) Å, is also not much different from the earlier reported
value of 2.3091(11) Å.14d Similarly the Pd−N bond length of
2.048(8) Å is consistent with the value of ∼2.0 Å reported for
Pd complexes of tridentate selenated Schiff bases.14d−g
In complex 2 the Se−C (aryl) and Se−C (alkyl) bond
lengths of 1.938(11) and 1.981(11) Å, respectively, are longer
than the corresponding bond lengths of L2. This may be due to
coordination of the Se atom with Pd. The two Pd−Se bond
lengths, 2.3924(15) and 2.3991(15) Å, of 2 are similar but
differ from the values 2.4567(15) and 2.4627(14) Å reported
for the Pd(II) complex of the bis-pincer ligand 1,2,4,5-
tetrakis[(phenyseleno)methyl]benzene,29 which also has a
seven-membered chelate ring. The Pd−Cl bond length of
2.318(3) Å in 2 is consistent with the value, 2.325(16) Å,
reported in the case of a selenated palladacycle.13h The crystals
of complexes 1 and 2 have N(1)···H(7A)−C(7) (2.742 Å) and
Cl···H(3)−C(3) (aromatic) (2.797 Å) secondary interactions,
Figure 4. ORTEP diagram of 2 with 30% thermal probability
ellipsoids; H atoms are omitted for clarity. Bond lengths (Å): Cl(1)−
Pd(1) 2.318(3); Cl(2)−Pd(1) 2.317(3); Pd(1)−Se(1) 2.3924(15);
Pd(1)−Se(2) 2.3991(15); C(1)−Se(1) 1.919(12); C(7)−Se(2)
1.938(11); C(13)−Se(1) 1.986(11); C(14)−Se(2) 1.981(11). Bond
angles (deg): Cl(2)−Pd(1)−Cl(1) 90.81(14); Cl(2)−Pd(1)−Se(1)
172.25(10); Cl(1)−Pd(1)−Se(1) 81.46(11); Cl(2)−Pd(1)−Se(2)
82.66(10); Cl(1)−Pd(1)−Se(2) 169.95(10); Se(1)−Pd(1)−Se(2)
105.08(5).
well as higher frequency.14f The crystal structure of 2 indicates
that both Se donor sites of L2 are engaged in coordination with
Pd in an almost equivalent manner, supporting the occurrence
of a single signal in the 77Se{1H} NMR. In the case of 2 the
chelate ring is seven membered, and therefore shifting to lower
frequency of the signal is not surprising. The signal of C5 in the
13C{1H} NMR spectrum of 2 appears somewhat shifted to
lower frequency relative to that of free L2. However the small
higher frequency shift in the H5 signal in the 1H NMR
spectrum is consistent with the formation of a Pd−Se bond in
2, as shown by the single-crystal structure. The signal of C4(Se)
in the 13C{1H} NMR spectrum of 2 also appears at a lower
frequency (4.6 ppm) in comparison to that of free L2.
The high-resolution mass spectra of both the ligands and
complex 1 authenticate them. The spectrum of complex 2 has
one peak at m/z ≈ 1046 (Supporting Information; Figures S15
+•
̇
and S16), which may correspond to [Pd(L2)2] . Thus
Figure 5. C(7)−H(7A)···N(1) interactions in 1.
391
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
Figure 6. Helical chain of 2 arising by an (aromatic) C(3)−H(3)···Cl(1) interaction.
as shown in Figures 5 and 6, which result in the formation of a
helical chain in the case of 2.
Table 2. Suzuki−Miyaura Coupling Reaction Catalyzed by
a
a
Catalysts 1 and 2
Suzuki−Miyaura Coupling Reaction Catalyzed by 1
and 2. The complexes 1 and 2 have been explored as catalysts
for the Suzuki−Miyaura C−C coupling reactions of several aryl
bromides. To optimize the reaction conditions, the coupling
reaction of 4-bromoanisole with phenylboronic acid in the
presence of 1 was studied. K2CO3 has been found to be a better
base for the coupling reaction than cesium carbonate, sodium
acetate, or sodium methoxide, as lower yields were obtained
with them under similar reaction conditions (Table 1). Further
catalyst 1
catalyst 2
b
entry no.
1
aryl bromide
mol % t (h) yield t (h) yield
b
4-bromobenzaldehyde
1
3
3
95
100
100
100
75
3
90
c
0.1
0.02
0.006
1
c
3
c
12
4
b
c
2
3
4
4-bromotoluene
4-bromobenzonitrile
4-bromoanisole
12
3
33
93
0.1
1
12
3
83
c
94
c
ab
,
0.01
1
12
3
66
Table 1. Effect of Base on the Suzuki−Miyaura Coupling
b
c
88
c
entry no.
base
K2CO3
yield (%)
0.1
0.02
1
4
85
24
3
c
1
2
3
4
88
47
28
16
4
83
b
c
Cs2CO3
5
4-bromonitrobenzene
3
96
93
CH3COONa
CH3ONa
0.01
0.2
0.2
12
3
50
b
b
6
7
4-bromobenzoic acid
4-bromoacetophenone
91
a
3
95
Reaction conditions: 1.0 equiv of ArBr, 1.5 equiv of phenylboronic
acid, and 2 equiv of base, catalyst 1; 1 mol %, solvent aqueous DMF,
a
Reaction conditions: 1.0 equiv of ArBr, 1.5 equiv of phenylboronic
acid, and 2 equiv of base (K2CO3), solvent aqueous DMF and bath
temperature 90 °C. Isolated yield after column chromatography,
b
c
and bath temperature 90 °C. Reaction time 3 h. NMR (%) yields.
b
c
NMR % yields.
for the reaction, a solvent mixture of DMF and water was found
to give the best result. No product was obtained when THF or
an ethanol−water mixture was used as solvent system.
and S22), SEM-EDX, and HR-TEM. They are of nanosize and
spherical in shape. The size of those obtained from complex 1 is
∼1−2 nm, whereas 2 gives nanoparticles of size ∼1 nm (Figure
7). The EDX (SEM as well as TEM) has revealed that they are
composed of palladium and chalcogen. The Pd:S ratio in
nanoparticles generated from 1 is 43:57, while in 2, the Pd:Se
ratio is 38:62 (Supporting Information; Figure S21 and Figures
S23−S25). The mercury poisoning test31 and triphenylphos-
phine test31 were performed on representative reactions of 4-
bromoanisole (1: 0.1 mol %) and 4-bromobenzaldehyde (2: 1
mol %). A 500 equivalent amount of Hg with respect to that of
catalyst was added at the initial stage of the reaction. After 3 h
no significant conversion to product was obtained. The PPh3
test was also positive. As these two poison tests are not enough
to fully affirm the heterogeneous nature of catalyst and the
possibility of involvement of surface atoms of heterogeneous
nanoparticles of Pd in oxidative addition to form soluble Pd(II)
intermediate32 Ar−Pd−Br exists, a two-phase test (Scheme 3)
was performed to understand the nature of the reaction
(heterogeneous vs homogeneous) further.33,34 This test (called
a three-phase test when the catalyst is a solid phase), developed
by Rebek and co-workers, is considered more definitive for
establishing whether the nature of catalytically active metal
The results of investigations on catalytic activities of
complexes 1 and 2 for Suzuki−Miyaura coupling are given in
Table 2. The efficiency of palladacycle 1 appears to be better
than that of 2, in which L2 has formed a seven-membered
chelate ring with palladium. The coupling of 4-bromoanisole
was negligible when 1 mol % of 2 was used as a catalyst. On
increasing the reaction time the amount of catalyst 1 required
was reduced (Table 2). The 4-bromobenzaldehyde in 12 h is
coupled nearly quantitatively even at 0.006 mol % loading of
catalyst. The performance of 1 is comparable with or better
than many well-known Pd-based catalysts for Suzuki−Miyaura
coupling, for example, palladium complexes of tridentate (S, N,
O−),14a (S/Se/Te, N, O−),14c,e−g bidentate (S, N),14b
(SNS)15c,f/(SCS)15d,e pincer, and (P, N) donor.30 In the
course of the Suzuki−Miyaura coupling reaction, black particles
appear, which suggest that catalysts 1 and 2 are probably
precatalysts and dispense real catalyst during the reaction. Such
species obtained from 1 and 2 during the course of catalysis of
the coupling reaction of 4-bromobenzonitrile with phenyl-
boronic acid under optimum reaction conditions were isolated
and analyzed to understand their nature. The black particles
were subjected to SEM (Supporting Information; Figures S20
392
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
Figure 7. TEM image of Pd NPs obtained from complexes 1 (a) and 2 (b) during Suzuki−Miyaura coupling.
loss in the temperature range 110−400 °C, whereas NPs
obtained from 2 show a weight loss of 58% in the temperature
range 150−400 °C (Supporting Information; Figures S28 and
S29). All these observations are consistent with the protection
of these NPs with ligands. These NPs appear to be real
catalysts. This is supported by the fact that even after isolation
they continue to catalyze Suzuki−Miyaura coupling, of course
with lower efficiency than those generated in situ, which is not
unexpected. For catalytic activity of these NPs, the Suzuki−
Miyaura coupling reaction was carried out under optimum
conditions (Table 3). 4-Bromobenzaldehyde and 4-bromoni-
Scheme 3. Two-Phase Test on Suzuki−Miyaura Coupling
with Catalyst 1
species is homogeneous or heterogeneous.33 If the catalyst
behaves in a heterogeneous fashion, the supported aryl halide is
not expected to be converted to a coupled product. When Pd is
released (i.e., catalysis is homogeneous), the supported
substrate can be converted to product. The addition of a
soluble aryl halide to the reaction mixture ensures the presence
of a catalytic process and its real active species. A two-phase test
made with an immobilized aryl bromide is shown in Scheme 3.
4-Bromoacetophenone and immobilized 4-bromobenzoic acid
(as amide) were reacted with phenylboronic acid under
optimum reaction conditions. The soluble part was separated
Table 3. Suzuki−Miyaura Coupling Reaction Catalyzed by
a
a
NPs Obtained from Complexes 1 and 2
b
yield (%)
entry
no.
NPs obtained from NPs obtained from
c d
aryl bromide
complex 1
complex 2
1
2
3
4-bromobenzaldehyde
4-bromonitrobenzene
4-bromoanisole
94
91
75
89
85
a
Reaction conditions: 1.0 equiv of ArBr, 1.5 equiv of phenylboronic
acid, and 2 equiv of base (K2CO3), solvent aqueous DMF and bath
b
1
temperature 90 °C, reaction time 3 h. Isolated yield after column
chromatography. 10 mg of NPs was used, 50 mg of NPs was used.
by filtration and analyzed after workup with H NMR. The
yield of the cross-coupled product (4-acetylbiphenyl) has been
c
d
found to be ∼93%. The solid phase was hydrolyzed, and
1
trobenzene react smoothly with PhB(OH)2 in aqueous DMF in
the presence of these NPs. The NPs obtained from 1
considerably convert 4-bromoanisole to coupled product,
whereas in the presence of NPs generated from 2 no cross-
coupled product has been obtained.
resulting products after workup were analyzed with H NMR.
Of the immobilized 4-bromobenzoic acid (as amide), ∼41%
was converted to the cross-coupled product (biphenyl-4-
carboxylic acid), whereas ∼59% remains unreacted (Supporting
Information; Figure S27). This observation suggests that the
catalytically active Pd leachs from the in situ generated
nanoparticles and is responsible for homogeneous catalysis.
Thus, it appears that in the case of 1 and 2 coupling is catalyzed
with nanosized Pd species homogeneously as well as
heterogeneously. Recently such a possibility has been described
as “cocktail”-like mixtures of the catalysts.35
CONCLUSION
■
Two potentially tetradentate ligands, 2,3-bis[(phenylthio)-
methyl]quinoxaline (L1) and 2,3-bis[(phenylseleno)methyl]-
quinoxaline (L2), and their Pd(II) complexes (1 and 2) have
been synthesized and characterized. Complex 1 is a palladacycle
formed by unexpected palladation of the benzyl group of L1
with Na2PdCl4 in the absence of external base. On the contrary
L2 behaves in 2 as a bidentate ligand via formation of a seven-
membered chelate ring with a Pd(II) center. The mass
spectrometric investigation on [Pd(L2)2](ClO4)2 prepared
separately has suggested that 2 can be an easy source of
1
The H and 77Se{1H} NMR spectral studies on these NPs
show that they are protected by L1 or L2. In the 77Se{1H}
NMR spectrum of the NPs obtained from 2 the signals at
348.3, 353.9, and 416.3 ppm have been observed. The first two
2−
seem to originate from L2 and third one from Se2 species.
The TGA of NPs obtained in the case of 1 shows 60% weight
393
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
[Pd(L2)2]+•, a transient species in the mass spectrum. The
catalytic activity of complexes 1 and 2 for Suzuki−Miyaura
coupling reactions has been studied. It was found that the
palladacycle 1 shows promising catalytic activity, which is also
much better than that of complex 2. On the basis of two-phase
tests the catalysis of Suzuki−Miyaura coupling with 1 and 2 via
palladium−sulfur or −selenium nanoparticles (size <2 nm)
protected by corresponding ligands appears to be of cocktail
type (i.e., homogeneous and heterogeneous in parts). Few
examples have been established so far where palladium−
chalcogen NPs have been recognized as a real catalyst for
Suzuki−Miyaura coupling. The present results further add a
new dimension to it.
187. (e) Suzuki, A. J. Organomet. Chem. 1999, 576, 147. (f) Kotha, S.;
Lahiri, K.; Kashinath, D. Tetrahedron 2002, 58, 9633.
(13) (a) Gruber, A. S.; Zim, D.; Ebeling, G.; Monteiro, A. L.;
Dupont, J. Org. Lett. 2000, 2, 1287. (b) Zim, D.; Gruber, A. S.;
Ebeling, G.; Dupont, J.; Monteiro, A. L. Org. Lett. 2000, 2, 2881.
(c) Xiong, Z.; Wang, N.; Dai, M.; Li, A.; Chen, J.; Yang, Z. Org. Lett.
2004, 6, 3337. (d) Chen, M.-T.; Huang, C.-A.; Chen, C.-T. Eur. J.
Inorg. Chem. 2006, 4642. (e) Kozlov, V. A.; Aleksanyan, D. V.;
Nelyubina, Yu. V.; Lyssenko, K. A.; Gutsul, E. I.; Puntus, L. N.;
Vasil’ev, A. A.; Petrovskii, P. V.; Odinets, I. L. Organometallics 2008,
27, 4062. (f) Zim, D.; Nobre, S. M.; Monteiro, A. L. J. Mol. Catal. A:
Chem. 2008, 287, 16. (g) Kozlov, V. A.; Aleksanyan, D. V.; Nelyubina,
Y. V.; Lyssenko, K. A.; Vasil’ev, A. A.; Petrovskii, P. V.; Odinets, I. L.
Organometallics 2010, 29, 2054. (h) Rao, G. K.; Kumar, A.; Ahmed, J.;
Singh, A. K. Chem. Commun. 2010, 46, 5954. (i) Aleksanyan, D. V.;
Kozlov, V. A.; Nelyubina, Y. V.; Lyssenko, K. A.; Puntus, L. N.; Gutsul,
E. I.; Shepel, N. E.; Vasil’ev, A. A.; Petrovskii, P. V.; Odinets, I. L.
Dalton Trans. 2011, 40, 1535.
ASSOCIATED CONTENT
■
S
* Supporting Information
NMR data, mass spectral data of ligands and complexes, SEM
image, SEM-EDX, and TEM-EDX of nanoparticles obtained
from complexes 1 and 2, crystal and structural refinement data,
bond lengths and bond angles for ligands and complexes, and
CIFs are included. This material is available free of charge via
the Internet at http://pubs.acs.org.
(14) (a) Kostas, I. D.; Andreadaki, F. J.; Demertzi, D. K.; Prentjas, C.;
Demertzis, M. A. Tetrahedron Lett. 2005, 46, 1967. (b) Kostas, I. D.;
Heropoulos, G. A.; Demertzi, D. K.; Yadav, P. N.; Jasinski, J. P.;
Demertzis, M. A.; Andreadaki, F. J.; Thanh, G. V.; Petit, A.; Loupy, A.
Tetrahedron Lett. 2006, 47, 4403. (c) Kostas, I. D.; Steele, B. R.; Terzis,
A.; Amosova, S. V.; Martynov, A. V.; Makhaeva, N. A. Eur. J. Inorg.
Chem. 2006, 2642. (d) Kumar, P. R.; Upreti, S.; Singh, A. K.
Polyhedron 2008, 27, 1610. (e) Kumar, A.; Agarwal, M.; Singh, A. K. J.
Organomet. Chem. 2008, 693, 3533. (f) Kumar, A.; Agarwal, M.; Singh,
A. K. Inorg. Chim. Acta 2009, 362, 3208. (g) Rao, G. K.; Kumar, A.;
Kumar, B.; Kumar, D.; Singh, A. K. Dalton Trans. 2012, 41, 1931.
(15) (a) Dai, M.; Liang, B.; Wang, C.; Chen, J.; Yang, Z. Org. Lett.
2004, 6, 221. (b) Dai, M.; Liang, B.; Wang, C.; You, Z.; Xiang, J.;
Dong, G.; Chen, J.; Yang, Z. Adv. Synth. Catal. 2004, 346, 1669.
(c) Bai, S.-Q.; Hor, T. S. A. Chem. Commun. 2008, 3172. (d) Rui, L.;
Wei, C.; Jianyou, S.; Lijuan, C.; Yingchun, C.; Lisheng, D.; Yuquan, W.
J. Mass Spectrom. 2008, 43, 542. (e) Kruithof, C. A.; Berger, A.;
Dijkstra, H. P.; Soulimani, F.; Visser, T.; Lutz, M.; Spek, A. L.;
Gebbink, R. J. M. K.; van Koten, G. Dalton Trans. 2009, 3306.
(f) Kozlov, V. A.; Aleksanyan, D. V.; Nelyubina, Y. V.; Lyssenko, K. A.;
Gutsul, E. I.; Vasilev, A. A.; Petrovskii, P. V.; Odinets, I. L. Dalton
Trans. 2009, 8657. (g) Singh, P.; Singh, M.; Singh, A. K. J. Organomet.
Chem. 2009, 694, 3872.
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
ACKNOWLEDGMENTS
■
A.K.S. thanks the Council of Scientific and Industrial Research
(CSIR) India for financial support through project 01(2421)
10/EMR-II and the Department of Science and Technology for
research project SR/S1/IC-40/2010. F.S. thanks the University
Grants Commission (UGC) for JRF. G.K.R. thanks CSIR,
India, for SRF.
REFERENCES
■
(1) Brock, E. D.; Lewis, D. M.; Yousaf, T. I.; Harper, H. H. (The
Procter & Gamble Company USA) WO 9951688, 1999.
(2) Gazit, A.; App, H.; McMahon, G.; Chen, J.; Levitzki, A.; Bohmer,
F. D. J. Med. Chem. 1996, 39, 2170.
(16) (a) Zim, D.; Monteiro, A. L.; Dupont, J. Tetrahedron Lett. 2000,
41, 8199. (b) Bergbreiter, D. E.; Osburn, P. L.; Wilson, A.; Sink, E. M.
J. Am. Chem. Soc. 2000, 122, 9058. (c) Zhang, W.; Shi, M. Tetrahedron
Lett. 2004, 45, 8921. (d) Piechaczyk, O.; Doux, M.; Ricard, L.; le
Floch, P. Organometallics 2005, 24, 1204. (e) Das, D.; Singh, M.;
Singh, A. K. Inorg. Chem. Commun. 2009, 12, 1120. (f) Yuan, D.;
Huynh, H. V. Organometallics 2010, 29, 6020. (g) Das, D.; Singh, P.;
Singh, A. K. J. Organomet. Chem. 2010, 695, 955. (h) Fliedel, C.;
Braunstein, P. Organometallics 2010, 29, 5614.
(3) Sehlstedt, U.; Aich, P.; Bergman, J.; Vallberg, H.; Norden, B.;
Graslund, A. J. Mol. Biol. 1998, 278, 31.
(4) Dailey, S.; Feast, J. W.; Peace, R. J.; Sage, I. C.; Till, S.; Wood, E.
L. J. Mater. Chem. 2001, 11, 2238.
(5) O’Brien, D.; Weaver, M. S.; Lidzey, D. G.; Bradley, D. D. C. Appl.
Phys. Lett. 1996, 69, 881.
(17) (a) Canovese, L.; Visentin, F.; Santo, C.; Chessa, G.; Uguagliati,
P. Polyhedron 2001, 20, 3171. (b) Jones, R. C.; Madden, R. L.; Skelton,
B. W.; Tolhurst, V.-A.; White, A. H.; Williams, A. M.; Wilson, A. J.;
Yates, B. F. Eur. J. Inorg. Chem. 2005, 1048. (c) Jones, R. C.; Canty, A.
J.; Gardiner, M. G.; Skelton, B. W.; Tolhurst, V.-A.; White, A. H. Inorg.
Chim. Acta 2010, 363, 77.
(6) Yamamoto, T.; Sugiyama, K.; Kushida, T.; Inoue, T.; Kanbara, T.
J. Am. Chem. Soc. 1996, 118, 3930.
(7) Yamamoto, T.; Zhou, Z.-H.; Kanbara, T.; Shimura, M.; Kizu, K.;
Maruyama, T.; Nakamura, Y.; Fukuda, T.; Lee, B.-L.; Ooba, N.;
Tomaru, S.; Kurihara, T.; Kanno, T.; Kubota, K.; Sasaki, S. J. Am.
Chem. Soc. 1996, 118, 10389.
(18) Yao, Q.; Kinney, E. P.; Zheng, C. Org. Lett. 2004, 6, 2997.
(19) Das, D.; Rao, G. K.; Singh, A. K. Organometallics 2009, 28, 6054.
(20) (a) Reetz, M. T.; Waldvogel, S. R.; Goddard, R. Tetrahedron
Lett. 1997, 38, 5967. (b) Jung, I. G.; Son, S. U.; Park, K. H.; Chung, K.-
C.; Lee, J. W.; Chung, Y. K. Organometallics 2003, 22, 4715.
(c) Kostas, I. D.; Steele, B. R.; Terzis, A.; Amosova, S. V. Tetrahedron
2003, 59, 3467.
(8) Nurulla, I.; Yamaguchi, I.; Yamamoto, T. Polym. Bull. 2000, 44,
231.
(9) Yamamoto, T.; Lee, B.-L.; Kokubo, H.; Kishida, H.; Hirota, K.;
Wakabayashi, T.; Okamoto, H. Macromol. Rapid Commun. 2003, 24,
440.
(10) Dell, A.; William, D. H.; Morris, H. R.; Smith, G. A.; Feeney, J.;
Roberts, G. C. K. J. Am. Chem. Soc. 1975, 97, 2497.
(11) Bailly, C.; Echepare, S.; Gago, F.; Waring, M. J. Anti-Cancer Drug
Des. 1999, 15, 291.
(21) Zhang, S.-M.; Hu, T.-L.; Li, J.-R.; Du, J.-L.; Bu, X.-H.
CrystEngComm 2008, 10, 1595.
(22) Zhang, S.-M.; Hu, T.-L.; Du, J.-L.; Bu, X.-H. Inorg. Chim. Acta
2009, 362, 3915.
(23) (a) Ceder, R. M.; Granell, J.; Sales., J. J. Organomet. Chem. 1986,
(12) (a) Suzuki, A. Pure Appl. Chem. 1991, 63, 419. (b) Miyaura, N.;
Suzuki, A. Chem. Rev. 1995, 95, 2457. (c) Stanforth, S. P. Tetrahedron
1998, 54, 263. (d) Miyaura, N.; Suzuki, A. In Advances in Metal−
Organic Chemistry; Liebeskind, L. S., Ed.; JAI: London, 1998; Vol. 6, p
307, 44. (b) Alsters, P. L.; Engel, P. F.; Hogerheide, M. P.; Copijn, M.;
394
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395

Organometallics
Article
Spek, A, L.; van Koten, G. Organometallics 1993, 12, 1831. (c) Ohff,
M.; Ohff, A.; Van Der Boom, M. E.; Milstein, D. J. Am. Chem. Soc.
1997, 119, 11687. (d) Herrmann, W. A.; Brossmer, C.; Reisnger, C.-
̈
P.; Riermeier, T. H.; Ofele, K.; Beller, M. Chem.Eur. J. 1997, 3,
1357. (e) Brunel, J. M.; Hirlemann, M. H.; Heumann, A.; Buono, G.
Chem. Commun. 2000, 1869. (f) Canty, A. J.; Patel, J.; Skelton, B. W.;
White, A. H. J. Organomet. Chem. 2000, 607, 194. (g) Keuseman, K. J.;
Smoliakova, I. P. Organometallics 2005, 24, 4159. (h) Luo, F.-T.; Xue,
C.; Ko, S.-L.; Shao, Y.-D.; Wu, C.-J.; Kuo, Y.-M. Tetrahedron 2005, 61,
6040. (i) Guo, R.; Portscheller, J. L.; Day, V. W.; Malinakova, H. C.
Organometallics 2007, 26, 3874. (j) Mawo, R. Y.; Mustakim, S.; Young,
V. G., Jr.; Hoffmann, M. R.; Smoliakova, I. P. Organometallics 2007, 26,
1801. (k) Joshaghani, M.; Daryanavard, M.; Rafiee, E.; Nadri, S. J.
Organomet. Chem. 2008, 693, 3135. (l) Stepanova, V. A.; Kukowski, J.
E.; Smoliakova, I. P. Inorg. Chem. Commun. 2010, 3, 653. (m) García,
D. V.; Fernan
Viader, C.; Vila, J. M.; Fernan
(n) Vicente, J.; Llamas, I. S.; Lop
4320.
́
dez, A.; Torres, M. L.; Rodríguez, A.; Blanco, N. G.;
dez, J. J. Organometallics 2010, 29, 3303.
ez, J.-A. G. Organometallics 2010, 29,
́
́
(24) (a) Newkome, G. R.; Puckett, W. E.; Gupta, V. K.; Fronczek, F.
R. Organometallics 1983, 2, 1247. (b) Newkome, G. R.; Evans, D. W.;
Kiefer, G. E.; Theriot, K. J. Organometallics 1988, 7, 2537.
(c) Newkome, G. R.; Gupta, V. K. Makromol. Chem., Rapid Commun.
1988, 9, 609. (d) Yoneda, A.; Hakushi, T.; Newkome, G. R.; Fronczek,
́
F. R. Organometallics 1994, 13, 4912. (e) Lοpez, C.; Caubet, A.;
Bosque, R.; Solans, X.; Bardia, M. F. J. Organomet. Chem. 2002, 645,
146.
(25) Sheldrick, G. M. Acta Crystallogr., Sect. A: Found. 1990, 46, 467.
(26) Sheldrick, G. M. SHELXL-NT, Version 6.12; University of
Gottingen: Germany, 2000.
(27) Furniss, B. S.; Hannaford, A. J.; Smith, P. W. G.; Tatchell, A. R.
Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; ELBS/
Longman Group U K Ltd., 1989.
(28) Webb, J. D.; MacQuarrie, S.; McEleney, K.; Crudden, C. M. J.
Catal. 2007, 252, 97.
(29) Das, D.; Singh, P.; Singh, M.; Singh, A. K. Dalton Trans. 2010,
39, 10876.
̌
(30) Step
Organometallics 2010, 29, 3187.
(31) Widegren, J. A.; Finke, R. G. J. Mol. Catal. A: Chem. 2003, 198,
317.
̌ ̌ ̌ ́
nicka, P.; Schulz, J.; Klemann, T.; Siemeling, U.; Císarova, I.
(32) Hu, J.; Liu, Y. B. Langmuir 2005, 21, 2121.
(33) (a) Rebek, J.; Gavina, F. J. Am. Chem. Soc. 1974, 96, 7112.
(b) Rebek, J.; Brown, D.; Zimmerman, S. J. Am. Chem. Soc. 1975, 97,
454.
(34) Davies, I. W.; Matty, L.; Hughes, D. L.; Reider, P. J. J. Am. Chem.
Soc. 2001, 123, 10139.
(35) Ananikov, V. P.; Beletskaya, I. P. Organometallics 2012, 31, 1595.
395
dx.doi.org/10.1021/om3006273 | Organometallics 2013, 32, 387−395