Palladium(ii)-selenated Schiff base complex catalyzed Suzuki-Miyaura coupling: Dependence of efficiency on alkyl chain length of ligand

Article abstract of DOI:10.1039/c1dt11695a

The new selenated Schiff bases L1-L4 which differ in the chain lengths (longest in L4) of non-coordinating substituents and their square planar complexes [Pd(L-H)Cl] (1-4) [L = L1-L4, behaving as (Se, N, O^-) ligand] have been synthesized and characterized by multinuclei NMR. The molecular structure of 1 has been elucidated by X-ray diffraction on its single crystal [Pd-Se = 2.3965(9) A]. All the complexes 1-4 (0.5 mol%) have been found suitable to catalyze Suzuki-Miyaura coupling reactions under mild conditions. The activity of 4 which has ligand L4 has been found highest. The formation of palladium(0) nano-particles (NPs) stablilized by organoselenium species appears to be the catalytic pathway. The length of the pendent alkyl chain present in the complex molecule unprecedentedly controls the dispersion and composition of these particles and consequently the catalytic activity.

Full text of DOI:10.1039/c1dt11695a

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An international journal of inorganic chemistry
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Volume 41 | Number 7 | 21 February 2012 | Pages 1905–2196
ISSN 1477-9226
COVER ARTICLE
Singh et al.
Palladium(II)-selenated Schiff base complex catalyzed Suzuki–Miyaura coupling:
Dependence of efficiency on alkyl chain length of ligand

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PAPER
Palladium(II)-selenated Schiff base complex catalyzed Suzuki–Miyaura
coupling: Dependence of efficiency on alkyl chain length of ligand†
Gyandshwar Kumar Rao, Arun Kumar, Bharat Kumar, Dinesh Kumar and Ajai Kumar Singh*
Received 7th September 2011, Accepted 13th October 2011
DOI: 10.1039/c1dt11695a
The new selenated Schiff bases L1–L4 which differ in the chain lengths (longest in L4) of
non-coordinating substituents and their square planar complexes [Pd(L–H)Cl] (1–4) [L = L1–L4,
behaving as (Se, N, O-) ligand] have been synthesized and characterized by multinuclei NMR. The
molecular structure of 1 has been elucidated by X-ray diffraction on its single crystal [Pd–Se = 2.3965(9)
˚
A]. All the complexes 1–4 (0.5 mol%) have been found suitable to catalyze Suzuki–Miyaura coupling
reactions under mild conditions. The activity of 4 which has ligand L4 has been found highest. The
formation of palladium(0) nano-particles (NPs) stablilized by organoselenium species appears to be the
catalytic pathway. The length of the pendent alkyl chain present in the complex molecule
unprecedentedly controls the dispersion and composition of these particles and consequently the
catalytic activity.
bases themselves are versatile ligands widely used for designing
1. Introduction
several types of catalysts due to their capability of fine tuning
the properties of the metal center by varying its immediate and
distant surroundings. Thus the influence of alkyl chains (differing
in lengths and numbers) present on the framework of selenated
Schiff base (L1–L4: Scheme 1) on Suzuki–Miyaura coupling
reactions (eqn (1)) has been studied by catalyzing such reactions
with Pd(II) complexes, [Pd(L–H)Cl] (1–4) (L = L1–L4) which are
pre-catalysts giving palladium(0) nano-particles (appearing to be
protected by organoselenium species) that are responsible for the
activity. Further, our experiments suggest that the chain lengths
influence the dispersion of these nanoparticles (NPs) generated
in situ during catalysis, which in turn affects the efficiency. This
novel observation has been made for the first time for molecular
complexes which are single source palladium catalysts. These
results are presented in this paper.
The palladium-catalyzed carbon–carbon coupling reactions are
essential tools for organic synthesis.1 One of the most important
among them is the Suzuki–Miyaura cross-coupling of aryl halides
with organoboronic acids.2 Palladium complexes of a large number
of phosphorus,3 carbene,4 oxime,5 imine6,7 and other ligands8 have
been reported as catalysts for such coupling. Palladium species
having dendritic macromolecular structure9,10 have been explored
for Suzuki–Miyaura coupling and it has been found that the
catalytic activity increases with the generation of dendrimer.10
This is a very significant observation implying that branching of
the macromolecule controls the activity of the catalytic system.
As parallel to this the length of the pendent/non-coordinating
arm of a ligand may influence the catalytic properties of its
palladium complex. However, it is little known how on increasing
the bulkiness of a multi-dentate ligand while keeping the dentate
character the same, the catalytic efficiency of its complex changes,
and therefore it is worth studying. The chalcogenated Schiff
bases having S, Se or Te in their frame-work at an appropriate
position so that they can act as donor atom have been thought
worthwhile for such a study because of two reasons. First, the
chalcogenated ligands4a,7,11 have been found attractive recently for
designing Pd-complexes which are efficient as catalysts for C–C
coupling reactions even under aerobic conditions. Second, Schiff
Aryl Bromide + PhB(OH)2 → Ar–Ph
(1)
2. Experimental
2.1. Materials and instruments
Diphenyldiselenide, NaBH4, 3-chloropropylaminehydrochloride,
alkyl halides, 2,4-dihydroxybenzaldehyde, sodium tetrachloro-
palladate, potassium carbonate and all aryl halides viz. 1-bromo-
4-nitrobenzene, 4-bromobenzonitrile, 4-bromobenzaldehyde,
4-bromobenzoic acid, bromobenzene, 4-bromotoluene, 4-
bromoanisol, 2-bromopyridine, 5-bromopyrimidine were
procured from Aldrich (USA). Precursor amine H2N(CH2)3SePh
was synthesized according the previously published procedure.12
The benzoate esters of 2,4-dihydroxybenzaldehyde were prepared
Department of Chemistry, Indian Institute of Technology Delhi, New Delhi,
110016, India. E-mail: aksingh@chemistry.iitd.ac.in, ajai57@hotmail.com;
Fax: +91 11 26581102; Tel: 91 11 26591379
† Electronic supplementary information (ESI) available: NMR data of
ligands and complexes 1–4; data for X-ray structure of 1, SEM, SEM-
EDX and TEM-EDX of Pd nano-particles stabilised by organoselenium
species. CCDC reference number 823568. For ESI and crystallographic
data in CIF or other electronic format see DOI: 10.1039/c1dt11695a
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1931–1937 | 1931
©

ticated by matching their spectroscopic data with those reported
in the literature. All reactions were carried out in glassware dried
in an oven, under ambient conditions. The commercial nitrogen
gas was used after passing it successively through traps containing
solutions of alkaline anthraquinone-sodium dithionite, alkaline
pyrogallol, conc. H2SO4 and KOH pellets. Nitrogen atmosphere if
required was created using the Schlenk technique.
X-ray diffraction data for crystals of 1, obtained by slow
evaporation of its solution made in chloroform-hexane mixture
(10 : 1), were collected on a BRUKER AXS SMART-APEX
diffractometer equipped with a CCD area detector (Ka =
˚
0.71073 A; monochromator, graphite). Frames were collected at
T = 298(2)K by w, j, and 2q-rotations with full quadrant data
collection strategy (four domains each with 600 frames) at 10 s per
frame with SMART. The measured intensities were reduced to F2
and corrected for absorption with SADABS. Structure solution,
refinement, and data output were carried out with the SHELXTL
package by direct methods. Non-hydrogen atoms were refined
anisotropically. All hydrogen atoms were included in idealized
positions, and a riding model was used for the refinement. Images
were created with the program Diamond.
Scheme 1 Syntheses of ligands L1–L4 and complexes 1–4.
2.2. Syntheses of L1 to L4
by literature methods.13 Other commercially available reagents
were used as received without further purification. The solvents
viz. chloroform, DMF, MeOH and EtOH were dried by the
standard methods.
1H, 13C{ H}, 77Se{ H} and 15N{ H} NMR spectra were
recorded on a Bruker Spectrospin DPX 300 NMR spectrometer
at 300.13, 75.47, 57.24 and 30.41 MHz respectively. 13C DEPT
NMR was used routinely to determine the number of hydrogen
atoms linked to carbon atoms. Assignments of proton and carbon
were done on the basis of 2D COSY and 2D HMQC experiments.
Elemental analyses were carried out with a Perkin-Elmer 2400
Series II C, H, N analyzer. Estimation of the palladium in the
nanoparticles was carried out with an AA7000 Series atomic
absorption spectrophotometer (Lab India).
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 powder in chloroform by ultrasonic
treatment, dropping slurry onto a porous carbon film supported
on a copper grid, and then drying 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 composition of nano-particles at SEM were analyzed
by EDX system, model Quan Tax 200 which is based on the SDD
technology and provides an energy resolution of 127 eV at Mn
Ka. The samples were scanned in different regions in order to
minimize the error in the analysis for evaluating the morphological
parameters.
Melting points were determined in an open capillary and
reported as such. The progress of the ligand’s synthesis was
monitored by a TLC plate coated with an appropriate grade
silica gel. Iodine was used for visualizing the spots. The products
of Suzuki reactions were separated and purified (if required) by
column chromatography using silica gel (60–120 mesh) as the solid
support. n-Hexane and its mixtures with chloroform/ethyl acetate
in variable proportions were used as eluent. They were authen-
2-(Phenylseleno) propylamine (0.428 g, 2.0 mmol) was stirred in
dry ethanol (5 mL) at room temperature for 0.5 h. 4-Methoxy ben-
zoate ester of 2,4-dihydroxybenzaldehyde (0.544 g, 2.0 mmol)/4-
decyloxy benzoate ester of 2,4-dihydroxybenzaldehyde (0.796
g, 2.0 mmol)/2,3,4-trisdecyloxy benzoate ester of 2,4-
dihydroxybenzaldehyde (1.422 g, 2.0 mmol)/4-octadecyloxy ben-
zoate ester of 2,4-dihydroxybenzaldehyde (1.022 g, 2.0 mmol)13
dissolved in dry ethanol (5 mL), was added drop wise with stirring.
The mixture was stirred further at room temperature for 4 h. The
precipitate was filtered off. All ligands L1 to L4 were finally dried
in vacuo (See ESI for numbering of C and H).
1
1
1
L1: Yield: (0.851 g) 91%; m.p. 79 ◦C. Anal. Found: C, 61.43;
H, 4.87; N, 3.04%. Calc. for C24H23NO4Se: C, 61.54; H, 4.95; N,
2.99%. 1H NMR (300 MHz, CDCl3, 25 ◦C, TMS): d (ppm): 2.063–
2.130 (m, 2H, H6), 2.966 (t, J = 7.2 Hz, 2H, H5), 3.674 (t, J = 6.3
Hz, 2H, H7), 3.873 (s, 3H, H20), 6.728 (dd, J = 8.1 & 1.8 Hz, 1H,
H13), 6.806 (d, J = 1.8 Hz, 1H, H11), 6.970 (d, J = 8.7 Hz, 2H,
H18), 7.209–7.257 (m, 4H, H1, H2, H14), 7.484–7.509 (m, 2H, H3),
8.132 (d, J = 8.7 Hz, 2H, H17), 8.253 (s, 1H, ◦H8), 13.773 (bs, 1H,
1
-OH). 13C{ H} NMR (75 MHz, CDCl3, 25 C, TMS): d (ppm):
24.99 (C5), 30.86 (C6), 55.44 (C7), 58.25 (C20), 110.41 (C11), 112.32
(C13), 113.79 (C18), 116.46(C9), 121.48 (C16), 126.91 (C1), 129.07
(C2), 129.75 (C4), 132.07 (C14), 132.27 (C17), 132.66 (C3), 154.08
(C10), 162.86 (C12), 163.91 (C19), 164.31 (C15), 164.72 (C8). 77Se{ H}
1
NMR (57 MHz, CDCl3, 25 ◦C, Me2Se): d (ppm): 285.87.
L2: Yield: (1.012 g) 85%; m.p. 71 ◦C. Anal. Found: C, 66.59;
H, 6.91; N, 2.41%. Calc. for C33H41NO4Se: C, 66.66; H, 6.95; N,
2.36%. NMR: 1H (300 MHz, CDCl3, 25 ◦C, TMS): d (ppm): 0.886
(t, J = 6.9 Hz, 3H, H22), 1.279–1.490 (m, 14H, HY), 1.790–1.838
(m, 2H, H21), 2.071–2.116 (m, 2H, H6), 2.973 (t, J = 7.2 Hz, 2H,
H5), 3.686 (t, J = 6.3 Hz, 2H, H7), 4.032 (t, J = 6.6 Hz, 2H, H20),
6.731 (dd, J = 8.4 & 2.1 Hz, 1H, H13), 6.802 (d, J = 2.1 Hz, 1H, H11),
6.961 (d, J = 9.0 Hz, 2H, H18), 7.216–7.278 (m, 4H, H1, H2, H14),
7.484–7.515 (m, 2H, H3), 8.121 (d, J = 9.0 Hz, 2H, H17), 8.265 (s,
1H, H8), 13.787 (bs, 1H, -OH). 13C{ H} NMR (75 MHz, CDCl3,
1
1932 | Dalton Trans., 2012, 41, 1931–1937
This journal is
The Royal Society of Chemistry 2012
©

25 ◦C, TMS): d (ppm): 14.09 (C22), 22.64, 25.06 (C5), 25.94, 29.28,
29.32, 29.51, 31.86, 29.05 (C21), 30.93 (C6), 58.34 (C7), 68.31 (C20),
110.47 (C11), 112.38 (C13), 114.29 (C18), 116.50 (C9), 121.27 (C16),
126.96 (C1), 129.11 (C2), 129.80 (C4), 132.08 (C14), 132.30 (C17),
132.75 (C3), 154.18 (C10), 162.88 (C12), 163.61 (C19)◦, 164.40 (C15),
(d, J = 1.5 Hz, 1H, H11), 6.840 (d, J = 8.7 Hz, 1H, H14), 6.990
(d, J = 8.7 Hz, 2H, H18), 7.294 (s, 1H, H8), 7.412–7.428 (m, 3H,
H1, H2), 8.140 (d, J = 8.7 Hz, 2H, H17), 8.346–8.374 (m, 2H, H3).
13C{ H} NMR (75 MHz, CDCl3, 25 ◦C, TMS): d (ppm): 27.92
1
(C6), 32.56 (C5), 55.53 (C20), 62.15 (C7), 109.76 (C13), 111.63 (C11),
113.89 (C18), 117.01(C9), 121.83 (C16), 129.58 (C1 & C2), 131.23
(C4), 132.34 (C17), 133.93 (C3), 136.67 (C14), 156.68 (C10), 161.15
1
164.76 (C8). 77Se{ H} NMR (57 MHz, CDCl3, 25 C, Me2Se): d
(ppm): 285.91.
1
L3: Yield: (1.34 g) 76%; m.p. < room temperature. Anal. Found:
C, 70.13; H, 9.08; N, 1.60%. Calc. for C53H81NO6Se: C, 70.18; H,
(C8), 164.00 (C12), 164.08 (C19), 164.83 (C15). 77Se{ H} NMR (57
MHz, CDCl3, 25 ◦C, Me2Se): d (ppm): 332.72.
9.00; N, 1.54%. H NMR (300 MHz, CDCl3, 25 ◦C, TMS): d
2 [Pd(L2–H)Cl]: Yield (0.588 g) 80%; m.p. 184 ◦C (d). Anal.
Found: C, 53.93; H, 5.46; N, 1.94%. Calc. for C33H40ClNO4PdSe:
C, 53.90; H, 5.48; N, 1.90%. 1H NMR (300 MHz, CDCl3, 25 ◦C,
TMS): d (ppm): 0.884 (t, J = 6.6 Hz, 3H, H22), 1.280–1.473 (m,
14H, HY), 1.771–1.863 (m, 2H, H21), 2.198–2.290 (m, 1H, H6),
2.543–2.590 (m, 2H, H5, H6), 3.422–3.488 (m, 2H, H5, H7), 4.042
(t, J = 6.6 Hz, 2H, H20), 4.182–4.261 (m, 1H, H7), 6.226 (dd, J =
8.4 & 2.1 Hz, 1H, H13), 6.665 (d, J = 2.1 Hz, 1H, H11), 6.818 (d, J =
8.7 Hz, 1H, H14), 6.971 (d, J = 9.0 Hz, 2H, H18), 7.276 (s, 1H, H8),
7.405–7.426 (m, 3H, H1, H2), 8.121 (d, J = 9.0 Hz, 2H, H17), 8.346–
1
(ppm): 0.880 (t, J = 6.6 Hz, 9H, H22), 1.272–1.486 (m, 42H, HY),
1.715–1.878 (m, 6H, H21), 2.085–2.130 (m, 2H, H6), 2.986 (t, J =
7.2 Hz, 2H, H5), 3.707 (t, J = 6.3 Hz, 2H, H7), 4.022–4.077 (m, 6H,
H20), 6.724 (dd, J = 8.1 & 1.8 Hz, 1H, H13), 6.792 (d, J = 2.1 Hz, 1H,
H11), 7.239–7.264 (m, 4H, H1, H2, H14), 7.386 (s, 2H, H17), 7.499–
1
7.524 (m, 2H, H3), 8.286 (s, 1H, H8), 13.831 (bs, 1H, -OH). 13C{ H}
NMR (75 MHz, CDCl3, 25 ◦C, TMS): d (ppm): 14.08 (C22), 22.65,
25.04 (C5), 26.04, 29.26–29.69, 30.31 (C6), 30.90 (C21), 31.87, 58.31
(C7), 69.22 (C20b), 73.54 (C20a), 108.54 (C17), 110.50 (C11), 112.31
(C13), 116.58 (C9), 123.61 (C16), 126.96 (C1), 129.11 (C2), 129.77
(C4), 132.12 (C14), 132.74 (C3), 143.05 (C19), 152.92 (C18), 154.10
◦
1
8.377 (m, 2H, H3). 13C{ H} NMR (75 MHz, CDCl3, 25 C, TMS):
d (ppm): 14.07 (C22), 22.63, 25.93, 27.80, 29.04, 29.26, 29.31, 29.50,
31.84, 32.69 (C5), 62.08 (C7), 68.33 (C20), 109.65 (C13), 111.45 (C11),
114.31 (C18), 117.01(C9), 121.41 (C16), 129.48 (C1 & C2), 131.39
(C4), 132.27 (C17), 133.94 (C3), 136.83 (C14), 156.56 (C10), 161.07
1
(C10), 162.93 (C12), 164.51 (C15), 164.74 (C8). 77Se{ H} NMR (57
MHz, CDCl3, 25 ◦C, Me2Se): d (ppm): 285.69.
L4: Yield (1.144 g) 81%; m.p. 89 ◦C. Anal. Found: C, 69.61;
H, 8.11; N, 2.03%. Calc. for C41H57NO4Se: C, 69.67; H, 8.13; N,
1.98%. NMR: 1H (300 MHz, CDCl3, 25 ◦C, TMS): d (ppm): 0.880
(t, J = 6.6 Hz, 3H, H22), 1.265–1.473 (m, 30H, HY), 1.773–1.842
(m, 2H, H21), 2.058–2.147 (m, 2H, H6), 2.981 (t, J = 7.2 Hz, 2H,
H5), 3.696 (t, J = 6.3 Hz, 2H, H7), 4.040 (t, J = 6.6 Hz, 2H, H20),
6.739 (dd, J = 8.4 & 2.1 Hz, 1H, H13), 6.803 (d, J = 2.1 Hz, 1H,
H11), 6.963 (d, J = 8.7 Hz, 2H, H18), 7.220–7.291 (m, 4H, H1, H2,
H14), 7.494–7.519 (m, 2H, H3), 8.121 (d, J = 8.7 Hz, 2H, H17),
(C8), 163.58 (C12), 163.75 (C19), 164.92 (C15). 77Se{ H} NMR (57
1
MHz, CDCl3, 25 ◦C, Me2Se): d (ppm): 333.83.
3 [Pd(L3–H)Cl]: Yield (0.692 g) 66%; m.p. < room temper-
ature. Anal. Found: C, 60.71; H, 7.71; N, 1.39%. Calc. for
1
C53H80ClNO6PdSe: C, 60.74; H, 7.69; N, 1.34%. NMR: H (300
◦
MHz, CDCl3, 25 C, TMS): d (ppm): 0.797–0.902 (m, 9H, H22),
1.274–1.639 (m, 42H, HY), 1.746–1.866 (m, 6H, H21), 2.128–2.169
(m, 1H, H6), 2.555–2.614 (m, 2H, H5, H6), 3.401–3.476 (m, 2H,
H5, H7), 4.196–4.277 (m, 6H, H20), 6.214 (dd, J = 8.4 Hz & 1.8
Hz, 1H, H13), 6.659 (d, J = 1.8 Hz 1H, H11), 6.828 (d, J = 8.7 Hz,
1H, H14), 7.294 (s, 2H, H17), 7.385–7.429 (m, 3H, H1, H2), 8.356–
1
8.277 (s, 1H, H8), 13.718 (bs, 1H, -OH). 13C{ H} NMR (75 MHz,
CDCl3, 25 ◦C, TMS): d (ppm): 14.10 (C22), 22.66, 25.06 (C5), 25.94,
29.06–29.67, 30.91 (C21), 31.89 (C6), 58.32 (C7), 68.30 (C20), 110.47
(C11), 112.39 (C13), 114.28 (C18), 116.49 (C9), 121.24 (C16), 126.96
(C1), 129.11 (C2), 129.79 (C4), 132.09 (C14), 132.30 (C17), 132.74
(C3), 154.17 (C10), 162.90 (C12), 163.60 (C19), 164.41 (C15), 164.75
◦
1
8.388 (m, 2H, H3). 13C{ H} NMR (75 MHz, CDCl3, 25 C, TMS):
d (ppm): 14.01 (C22), 22.60, 26.02 (C6), 29.26–30.28, 31.83, 31.86
(C5), 62.07 (C7), 69.26 (C20a), 73.53 (C20b),109.46 (C13), 111.43 (C11),
117.13 (C9), 123.74 (C16), 129.44 (C1 & C2), 131.38 (C4), 133.86
(C3), 136.89 (C14), 143.11 (C19), 152.96 (C18), 156.46 (C10), 161.05
◦
1
(C8). 77Se{ H} NMR (57 MHz, CDCl3, 25 C, Me2Se): d (ppm):
286.41.
(C8), 163.76 (C12), 165.04 (C15). 77Se{ H} NMR (57 MHz, CDCl3,
1
25 ◦C, Me2Se): d (ppm): 335.62.
2.3. Syntheses of palladium complexes 1 to 4
4 [Pd(L4–H)Cl]: Yield (0.626 g) 74%; m.p. 185 ◦C (d). Anal.
Found: C, 58.13; H, 6.68; N, 1.64%. Calc. for C41H56ClNO4PdSe:
C, 58.10; H, 6.66; N, 1.65%. NMR: 1H (300 MHz, CDCl3, 25 ◦C,
TMS): d (ppm): 0.878 (t, J = 6.6 Hz, 3H, H22), 1.259–1.472 (m,
30H, HY), 1.795–1.842 (m, 2H, H21), 2.108–2.143 (m, 1H, H6),
2.554–2.588 (m, 2H, H5, H6), 3.407–3.473 (m, 2H, H5, H7), 4.042
(t, J = 6.3 Hz, 2H, H20), 4.149–4.226 (m, 1H, H7), 6.242 (d, J =
8.4 Hz, 1H, H13), 6.684 (s, 1H, H11), 6.832 (d, J = 8.7 Hz, 1H,
H14), 6.969 (d, J = 8.7 Hz, 2H, H18), 7.285 (s, 1H, H8), 7.421–7.427
(m, 3H, H1, H2), 8.118 (d, J = 8.7 Hz, 2H, H◦17), 8.352–8.364 (m,
Na2[PdCl4] (0.294 g, 1.0 mmol) was dissolved in 5 mL of water.
The solution of a ligand from L1 to L4 (1.0 mmol) made in
10 mL of acetone was added to it with vigorous stirring. The
mixture was further stirred for 2 h. The orange red solution was
extracted with chloroform. The chloroform layer was washed with
water, dried with anhydrous Na2SO4, reduced in volume (~5 mL)
under vacuo and mixed with excess hexane to obtain 1 to 4 as
an orange colored powder. Single crystals of 1 were grown from
chloroform (containing a few drops of hexane per 5 mL). See ESI
for numbering of C and H.
1
2H, H3). 13C{ H} NMR (75 MHz, CDCl3, 25 C, TMS): d (ppm):
1 [Pd(L1–H)Cl]: Yield (0.542 g) 89%; m.p. 148 ◦C (d). Anal.
Found: C, 47.35; H, 3.67; N, 2.34%. Calc. for C24H22ClNO4PdSe:
C, 47.32; H, 3.64; N, 2.30%. NMR: 1H (300 MHz, CDCl3, 25 ◦C,
TMS): d (ppm): 2.016–2.178 (m, 1H, H6), 2.553–2.587 (m, 2H,
H5, H6), 3.420–3.483 (m, 2H, H5, H7), 3.899 (s, 3H, H20), 4.174–
4.254 (m, 1H, H7), 6.244 (dd, J = 8.4 & 1.5 Hz, 1H, H13), 6.682
14.09 (C22), 22.06, 25.94, 27.81 (C6), 29.06–29.66, 31.59, 32.70 (C5),
62.07 (C7), 68.33 (C20), 109.68 (C13), 111.47 (C11), 114.30 (C18),
117.00(C9), 121.38 (C16), 129.49 (C1 & C2), 131.37 (C4), 132.28
(C17), 133.94 (C3), 136.81 (C14), 156.56 (C10), 161.07 (C8), 163.58
1
(C12), 163.74 (C19), 164.93 (C15). 77Se{ H} NMR (57 MHz, CDCl3,
25 ◦C, Me2Se): d (ppm): 334.97.
This journal is
The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1931–1937 | 1933
©

2.4. General procedure for Suzuki–Miyaura C–C coupling
reaction
2.9. PPh3 poisoning test
To the coupling reaction of 4-bromobenzaldehyde with phenyl-
boronic acid using 4 (2 mol%) as a catalyst, PPh3 (1 mol%)
was added under optimal conditions. After 24 h of reaction
cross coupling the product 4-biphenylcarboxyldehyde (~100%
conversion) was obtained.
An oven-dried flask was charged with aryl halide (1.0 mmol),
phenylboronic acid (1.2 mmol), K2CO3 (2.0 mmol), DMF (2.0 mL)
and H2O (1.0 mL). A solution of complex of 1–4 in DMF (5 ¥
10-3 mmol, 1 mL, 0.5 mol %) was then added via syringe. The flask
was placed on an oil bath at 100 ◦C for 12 h. The mixture was
extracted with diethyl ether. The extract was washed with water
and dried over anhydrous Na2SO4. The solvent of the extract was
removed with rotary evaporator and the resulting residue was
purified by column chromatography on silica gel.
3. Results and discussion
The syntheses of L1–L4 and 1–4 have been summarized in Scheme
1. In the complexation reaction on varying metal:ligand ratio the
products did not change. The ligands and complexes have been
1
1
1
characterized by H, 13C{ H} and 77Se{ H} NMR spectroscopy
2.5. General procedure for the Suzuki Reaction of aryl bromides
with phenylboronic acid catalyzed by nanoparticles
1
(ESI†). In the 77Se{ H} NMR spectra of L1–L4 the signals appear
almost at the same position (285.8, 285.9, 285.7 and 286.4 ppm
respectively). The assignments in the 1H and 13C{ H} spectra are
1
An oven-dried flask was charged with aryl halide (1.0 mmol),
phenylboronic acid (1.2 mmol), K2CO3 (2.0 mmol), DMF (2.0 mL)
and H2O (1.0 mL). Nanoparticles resulting from 1 or 4 (Pd ~ 2 mol
%) were added. The flask was heated on an oil bath at 100 ◦C with
stirring of the reaction mixture for 8 h. The mixture was extracted
with diethyl ether. The extract was washed with water and dried
over anhydrous Na2SO4. The solvent of the extract was evaporated
off with a rotary evaporator and the resulting residue was purified
by column chromatography using silica gel.
based on correlations with COSY and HMQC experiments (ESI†)
and are consistent with their structures depicted in Scheme 1. The
1
absence of a signal of the phenolic (-OH) proton in H NMR
spectra of complexes 1–4 supports the involvement of O- in the
coordination which is also supported by the crystal structure of 1
1
(Fig. 1). 77Se{ H} NMR signals of 1–4 are at higher frequency (47–
50 ppm) with respect to those of the corresponding free ligands
indicating the involvement of Se in coordination with Pd. In the
1
15N{ H} NMR spectra of L1 and L4 signals appear at 290.52 and
2.6. Isolation of nanoparticles generated from 1 and 4 during
catalytic reactions
290.97 ppm respectively.
A mixture of Pd(II) complex 1/4 (0.5 mmol), phenylboronic
acid (1.0 mmol), 1-bromo-4-nitrobenzene (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 residues were thoroughly washed
with water-acetone(1 : 3) and subjected to various analytical
measurements for their characterization.
2.7. Hot filtration test
The reaction with catalyst 4 was subjected to a hot filtration test.
The reaction mixture of the Suzuki coupling reaction of phenyl-
boronic acid (1.2 mmol) with 4-bromobenzaldehyde (1.0 mmol)
catalyzed with 1 mol % of 4 under optimal reaction conditions
was filtered hot through a G-4 crucible containing 1 g celite, when
26% conversion (monitored by 1H NMR spectroscopy) occurred
(after ~1 h of reaction). The conversion was monitored in the
filtrate with time, continued and reached a maximum (72%) after
15 h.
Fig. 1 ORTEP diagram of 1 with ellipsoids at the 30% probability
level. The solvent molecule (CHCl3) has been omitted for clarity. Selected
˚
bond lengths (A): Pd(1)–O(4) 2.000(5); Pd(1)–N(1) 2.018(6); Pd(1)–Cl(1)
2.305(2); Pd(1)–Se(1) 2.3965(9); Se(1)–C(18) 1.928(7); Se(1)–C(17)
1.951(9). Selected bond angles (◦): O(4)–Pd(1)–Se(1) 167.97(14);
O(4)–Pd(1)–N(1) 92.5(2); O(4)–Pd(1)–Cl(1) 84.95(15); N(1)–Pd(1)–Cl(1)
176.48(19); N(1)–Pd(1)–Se(1) 99.51(19).
2.8. Hg poisoning test
For the mercury poisoning test an excess of Hg (Hg:Pd: 400 : 1) was
taken in the reaction flask before the addition of reactants. There-
after the coupling reaction of 4-bromobenzaldehyde (1.0 mmol)
with phenylboronic acid (1.2 mmol) using 4 (2 mol%) and
nanoparticles isolated from 4 during Suzuki–Miyaura coupling
(4 mol%) as catalyst under optimum conditions was carried out in
the flask. The product biphenyl-4-carboxyldehyde was obtained
in ~100% yield after 24 h even in the presence of excess of
Hg.
3.1. Crystal structure
The structure of 1 has been elucidated by X-ray diffraction on
its single crystals (Fig. 1). The molecular structure of 1 with
its selected bond distances and angles is shown in Fig. 1. The
coordination geometry around Pd is almost square planar. The
ligand is coordinated with Pd in a monoanionic tridentate (Se,
N, O-) mode and forms two six membered chelate rings, one
via O- and N and the other via Se and N. The Pd–N bond
1934 | Dalton Trans., 2012, 41, 1931–1937
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The Royal Society of Chemistry 2012
©

length 2.018(6) in 1 is almost similar to the reported value of
catalytic efficiency of 4 was found to be highest whereas 1 showed
significantly lower efficiency than 2–4. The enhanced efficiency of
4 can also be gauged from the fact that it can give more than
84% conversions in only 6 h (Table 1: Entry No. 3, 5 and 6).
One of the reasons for this variation in catalytic activities of these
Pd-complexes may be the electronic properties of Se and N in
-
2.010(4) A for [PdCl{C6H5(C6H4–2—O )C N–(CH2)2SePh}]7a
˚
7a
˚
and is longer than 1.986(6) A reported for [PdCl{C6H5(C6H4–
2–O-)C N (CH2)3SePh}]. The Pd–O distance 2.000(5) in 1 is
7a
˚
consistent with values 1.993(3) and 1.995(6) A reported for Pd–
O of the Pd(II)-selenated Schiff base complex. The bond distances
1
of Pd–Se 2.3965(9) A and Pd–Cl 2.305(2) A of 1 are found
to be longer than those of [PdCl{C6H5(C6H4–2–O-)C N(CH2)3
SePh}],7a where the ligand is also a tridentate selenated Schiff base.
The Cl ◊ ◊ ◊ H (aromatic), Cl ◊ ◊ ◊ H (-OCH3) and C–H ◊ ◊ ◊ p secondary
interactions in the crystal of 1 result in the formation of a three
dimensional chain structure shown in Fig. 2 and the ESI† (Fig.
S2.1 to Fig. S2.8).
L1–L4. As mentioned earlier the 77Se{ H} NMR signals of all
˚
˚
the four ligands appear at almost the same position (from 285.41
to 286.87 ppm), implying that the lengths of alkyl chains present
on the ligand framework do not affect significantly the electronic
1
property of the selenium donor site. The signals in 15N{ H} NMR
spectra of ligands L1 and L4 appear at 290.52 and 290.97 ppm
respectively (Fig. S4.1 and S4.2 in ESI†) and indicate that the
electronic environment of nitrogen is also almost unaffected by
alkyl chains. As the electronic properties of the donor atoms
remain unaffected with chain length, the variation in the catalytic
activities of 1–4 with the nature of the alkyl chain has to be ascribed
to some other factor.
In the course of Suzuki reactions black particles appear. There-
fore, it is possible that 1–4 are pre-catalysts and give nanosized
Pd(0) species during the reaction. The observed variation in
catalytic efficiency may be due to some difference in these species
generated in situ during the course of catalysis by 1–4. Thus
the species obtained from 1 and 4 in the course of catalysis of
the coupling reaction of 1-bromo-4-nitrobenzene with PhB(OH)2
under optimum reaction conditions, were analyzed so that a
possible correlation between the length of alkyl chains present
on the ligand’s framework, catalytic activity and nature of these
species (possibly true catalysts) can be understood. The black
particles were isolated and characterized by HRTEM (Fig. 3),
TEM-EDX (Fig. S1.1 and S1.4 in ESI†) and SEM-EDX (Fig.
S1.3 and S1.6 in ESI†). These studies revealed that spherical
shaped nano-particles of average size ~3 nm were formed in case
of both the complexes. The nanoparticles, formed in the case of 4
(Fig. 3) are much more uniformly dispersed than those formed
from 1 (Fig. 3).
Fig. 2 Molecular packing of 1 showing Cl ◊ ◊ ◊ H (aromatic) and Cl ◊ ◊ ◊ H
(OMe) interactions.
3.2. Suzuki-Miyaura C–C coupling reaction catalyzed by 1–4
1–4 have been explored as catalysts for Suzuki–Miyaura C–C
coupling reactions (Table 1) of several aryl bromides. K2CO3 has
been found the most appropriate base as with the alternatives
viz. Cs2CO3, CH3COONa, Et3N or Na2CO3, a longer reaction
time was necessary for reasonable conversions. Among the various
solvents explored the best results were obtained in a DMF–H2O
mixture. The optimum concentration of 1–4 for catalysis was found
to be 0.5 mol%. The reaction time was optimized as 12 h. The
Table 1 Suzuki coupling reactions catalyzed by 1–4a
Aryl Bromide + PhB(OH)2 → Ar–Ph
Yield (%)
Entry No.
Aryl Bromide
1b
2b
3b
4c
1.
2.
3.
4.
5.
6.
7.
8.
9.
1-Bromo-4-nitrobenzene
4-Bromobenzonitrile
4-Bromobenzaldehyde
4-Bromobenzoic acid
Bromobenzene
4-Bromotoluene
4-Bromoanisol
25
28
26
23
29
23
20
17
19
85
82
83
81
80
77
79
85
84
86
82
84
83
85
80
79
84
81
90
88
95d
87
Fig. 3 HRTEM images of nanoparticles obtained in catalytic reactions
with 1 and 4 respectively.
86d
84d
87
The -CH3 group is present on the ligand framework of 1 and the
linear -C18H37 group on that of 4. The large size of alkyl chain in the
case of 4 appears to have made the nanoparticles more uniformly
dispersed resulting in its higher catalytic activity.
Such an influence in systems like dendrimers is reported10
because palladium is fully encapsulated by the dendritic ligand
structure, whereas in non-dendritic molecular Pd(II) complexes it
is observed for the first time.
2-Bromopyridine
5-Bromopyrimidine
93
90
a Reaction conditions: 1.0 equiv. of aryl bromide, 1.3 equiv. of phenyl-
boronic acid, and 2 equiv of base (K2CO3), 0.5 mol% of catalyst, aqueous
DMF as solvent and temperature of bath 100 ◦C. Reaction time 12 h.
b NMR % Yield. c Isolated yield after column chromatography. d Reaction
time 6 h.
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The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1931–1937 | 1935
©

Table 2 Suzuki coupling reactions catalyzed by nanoparticlesa
protected by organoselenium species. Most probably the difference
in catalytic efficiency occurs due to variation in the dispersion and
composition of these nanoparticles with alkyl chain lengths.
Yield (%)b
Pd NPs obtained Pd NPs obtained
from 1 from 4
Entry No. Aryl Halide
Acknowledgements
1.
2.
3.
4-Bromobenzaldehyde 30
94
90
91
Bromobenzene
4-Bromoanisol
26
25
The work was supported by Council of Scientific and Industrial
Research India through the award of SRF/RA and project
01(2421)10/EMR-II. The authors thank Professor A. K. Ganguli
of IIT Delhi for HRTEM facility.
a Reaction conditions: 1.0 equiv. of aryl bromide, 1.3 equiv. of phenyl-
boronic acid and 2.0 equiv. of base (K2CO3), catalyst: nanoparticles (Pd
~ 2 mol%), aqueous DMF as solvent and temperature of bath 100 ◦C.
Reaction time 8 h. b Isolated yield after column chromatography.
References
The EDX (SEM as well as TEM) has revealed that Pd:Se ratios
in nanoparticles generated from 1 and 4 are ~51 : 49 and 40 : 60
respectively. The nanoparticles obtained from 4 are richer in Se.
Thus the effect of alkyl chain lengths on the catalytic activity
appears to occur due to their influence on the nature of the real
catalyst, the nanoparticles.
This is shown independently by the catalytic activity of nanopar-
ticles for Suzuki coupling (Table 2). However, to attainan efficiency
similar to the one shown by in situ generated particles, the quantity
of isolated nanoparticle (i.e. mol% of Pd) needed is higher, which
is very much expected. The % yields in Table 1 also indicate that
chain length has a greater influence than their number on the
benzene ring.
To establish the nature of the real catalysts, hot filtration
experiments14 were carried out. The catalytic reaction is expected
to be quenched or drastically reduced in the filtrate. The latter
happened in our case as the maximum conversion dropped
(Table 1) from 95% (6 h) to 72% (15 h). The catalytic reaction
continued because some of the palladium was leached from in
situ generated NPs. The palladium leaching estimated by AAS,
was found to be 5.9% of initial catalyst loading. A mercury
poisoning test14 performed on a representative coupling reaction of
4-bromobenzaldehyde was found negative. The catalysis by NPs,
obtained as a by-product during the course of catalysis, is also
not quenched by Hg. The triphenyphosphine poisoning test14 was
performed. The biaryl product was obtained in 100% yield when
the reaction was carried out for 24 h in the presence of PPh3.
These results suggest that Pd(0) nanoparticles are protected by
organoselenium species as the presence of Se is indicated by EDX
results. The weight loss (%) in TGA (Fig. S5.1 to S5.3 in ESI†) up
to 500 ◦C was 22.56, 47.97 and 67.20 in the case of NPs obtained
during Suzuki-coupling by 1, 2 and 4 respectively, which is most
likely due to organselenium skeletons present. However the nature
of the organic entity could not be established unequivocally by
spectroscopic methods.
1 (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.
2 (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.
3 (a) T. Kinzel, Y. Zhang and S. L. Buchwald, J. Am. Chem. Soc., 2010,
ˇ
132, 14073; (b) P. Steˇpnicˇka, J. Schulz, T. Klemann, U. Siemeling and I.
C´ısarˇova´, Organometallics, 2010, 29, 3187; (c) R. Ghosh, N. N. Adarsh
and A. Sarkar, J. Org. Chem., 2010, 75, 5320; (d) J. I. van der Vlugt, M.
A. Siegler, M. Janssen, D. Vogt and A. L. Spek, Organometallics, 2009,
28, 7025; (e) J. Ma, X. Cui, L. Gao and Y. Wu, Inorg. Chem. Commun.,
2007, 10, 762; (f) C. A. Fleckenstein and H. Plenio, Organometallics,
2007, 26, 2758; (g) S. Teo, Z. Weng and T. S. A. Hor, Organometallics,
2006, 25, 1199; (h) A. F. Littke and G. C. Fu, Angew. Chem., Int. Ed.,
2002, 41, 4176.
4 (a) C. Fliedel and P. Braunstein, Organometallics, 2010, 29, 5614; (b) H.
V. Huynh, C. H. Yeo and Y. X. Chew, Organometallics, 2010, 29, 1479;
(c) B. Karimi and P. F. Akhavan, Chem. Commun., 2009, 3750; (d) H.
Tu¨rkmen, R. Can and B. C¸ etinkaya, Dalton Trans., 2009, 7039; (e) O.
Diebolt, P. Braunstein, S. P. Nolan and C. S. J. Cazin, Chem. Commun.,
2008, 3190; (f) C. Fleckenstein, S. Roy, S. Leutha¨ußer and H. Plenio,
Chem. Commun., 2007, 2870; (g) S. K. Yen, L. L. Koh, H. V. Huynh
and T. S. A. Hor, Dalton Trans., 2007, 3952; (h) R. Singh, M. S. Viciu,
N. Kramareva, O. Navarro and S. P. Nolan, Org. Lett., 2005, 7, 1829;
(i) O. Navarro, H. Kaur, P. Mahjoor and S. P. Nolan, J. Org. Chem.,
2004, 69, 3173; (j) G. Altenhoff, R. Goddard, C. W. Lehmann and F.
Glorius, J. Am. Chem. Soc., 2004, 126, 15195; (k) V. C. Vargas, R. J.
Rubio, T. K. Hollis and M. E. Salcido, Org. Lett., 2003, 5, 4847; (l) C.
W. K. Gstottmayr, V. P. W. Bo¨hm, E. Herdtweck, M. Grosche and W.
A. Herrmann, Angew. Chem., Int. Ed., 2002, 41, 1363.
5 (a) D. A. Alonso, C. Na´jera and M. C. Pacheco, J. Org. Chem., 2002,
67, 5588; (b) D. A. Alonso, C. Na´jera and M. C. Pacheco, Org. Lett.,
2000, 2, 1823.
6 (a) J. Zhou, X. Li and H. Sun, J. Organomet. Chem., 2010, 695, 297;
(b) A. D. Zotto, F. I. Prat, W. Baratta, E. Zangrando and P. Rigo, Inorg.
Chim. Acta, 2009, 362, 97; (c) B. Mu, T. Li, W. Xu, G. Zeng, P. Liu and
Y. Wu , Tetrahedron, 2007, 63, 11475; (d) C. Xu, J.-F. Gong, S.-F. Yue, Y.
Zhu and Y.-J. Wu, Dalton Trans., 2006, 4730; (e) D. Domin, D. Benito-
Garagorri, K. Mereiter, J. Fro¨hlich and K. Kirchner, Organometallics,
2005, 24, 3957; (f) C.-L. Chen, Y.-H. Liu, S.-M. Peng and S.-T. Liu,
Organometallics, 2005, 24, 1075; (g) J. Cui, M. Zhang and Y. Zhang,
Inorg. Chem. Commun., 2010, 13, 81; (h) C. Rocaboy and J. A. Gladysz,
Org. Lett., 2002, 4, 1993.
7 (a) A. Kumar, M. Agarwal and A. K. Singh, Inorg. Chim. Acta,
2009, 362, 3208; (b) A. Kumar, M. Agarwal and A. K. Singh, J.
Organomet. Chem., 2008, 693, 3533; (c) P. R. Kumar, S. Upreti and A.
K. Singh, Polyhedron, 2008, 27, 1610; (d) I. D. Kostas, B. R. Steele,
A. Terzis, S. V. Amosova, A. V. Martynov and N. A. Makhaeva,
Eur. J. Inorg. Chem., 2006, 2642; (e) I. D. Kostas, G. A. Heropoulos,
D. K. -Demertzi, P. N. Yadav, J. P. Jasinski, M. A. Demertzis, F. J.
Andreadaki, G. Vo-Thanh, A. Petit and A. Loupy, Tetrahedron Lett.,
4. Conclusions
The complexes [Pd(L–H)Cl] (1–4; L = Schiff base ligands of (Se,
N, O-) type) have been synthesized. The crystal structure solved
for 1 indicates that selenated Schiff bases (L1–L4) ligate in a
tridentate mode. Suzuki–Miyaura coupling reactions have been
catalyzed by 1–4. The catalytic efficiency depends on the length
of the pendent alkyl chain present on the ligand, and is highest
for 4. It appears that Pd-complexes are pre-catalysts, generating
in situ real catalytic species, ~3 nm size nanoparticles of Pd(0)
1936 | Dalton Trans., 2012, 41, 1931–1937
This journal is
The Royal Society of Chemistry 2012
©

2006, 47, 4403; (f) I. D. Kostas, F. J. Andreadaki, D. K. -Demertzi,
C. Prentjas and M. A. Demertzis, Tetrahedron Lett., 2005, 46, 1967;
(g) M.-T. Chen, C.-A. Huang and C.-T. Chen, Eur. J. Inorg. Chem., 2006,
4642.
8 (a) C. Najera, J. Gil-Molto, S. Karlstrom and L. R. Falvello, Org. Lett.,
2003, 5, 1451; (b) A. Schnyder, A. F. Indolese, M. Studer and H.-U.
Blaser, Angew. Chem., Int. Ed., 2002, 41, 3668; (c) Z. Xiong, N. Wang,
M. Dai, A. Li, J. Chen and Z. Yang, Org. Lett., 2004, 6, 3337; (d) C. A.
Kruithof, A. Berger, H. P. Dijkstra, F. Soulimani, T. Visser, M. Lutz,
A. L. Spek, R. J. M. K. Gebbink and G. V. Koten, Dalton Trans., 2009,
3306; (e) M. Dai, B. Liang, C. Wang, J. Chen and Z. Yang, Org. Lett.,
2004, 6, 221.
9 (a) T. Fujihara, S. Yoshida, H. Ohta and Y. Tsuji, Angew. Chem.,
Int. Ed., 2008, 47, 8310; (b) P. Servin, R. Laurent, A. Romerosa, M.
Peruzzini, J.-P. Majoral and A.-M. Caminade, Organometallics, 2008,
27, 2066; (c) A. K. Diallo, C. Ornelas, L. Salmon, J. R. Aranzaes and
D. Astruc, Angew. Chem., Int. Ed., 2007, 46, 8644.
10 (a) A. Fihri, M. Bouhrara, B. Nekoueishahraki, J.-M. Basset and V.
Polshettiwar, Chem. Soc. Rev., 2011, 40, 5181; (b) L. Wu, Z.-W. Li,
F. Zhang, Y.-M. He and Q.-H. Fan, Adv. Synth. Catal., 2008, 350,
846; (c) L. Wu, B. L. Li, Y. Y. Huang, H. F. Zhou, Y. M. He and Q.-
H. Fan, Org. Lett., 2006, 8, 3605; (d) N. T. S. Phan, M. Van Der
Sluys and C. W. Jones, Adv. Synth. Catal., 2006, 348, 609; (e) D.
Astruc, F. Lu and J. R. Aranzaes, Angew. Chem., Int. Ed., 2005, 44,
7852.
Rao, A. Kumar, J. Ahmed and A. K. Singh, Chem. Commun., 2010,
46, 5954; (e) D. Das, P. Singh, M. Singh and A. K. Singh, Dalton
Trans., 2010, 39, 10876; (f) D. Das, P. Singh and A. K. Singh, J.
Organomet. Chem., 2010, 695, 955; (g) D. Das, G. K. Rao and A.
K. Singh, Organometallics, 2009, 28, 6054; (h) D. Das, M. Singh and A.
K. Singh, Inorg. Chem. Commun., 2009, 12, 1120; (i) P. Singh, M. Singh
and A. K. Singh, J. Organomet. Chem., 2009, 694, 3872; (j) V. A. Kozlov,
D. V. Aleksanyan, Y. V. Nelyubina, K. A. Lyssenko, E. I. Gutsul, A. A.
Vasil’ev, P. V. Petrovskii and I. L. Odinets, Dalton Trans., 2009, 8657;
(k) S.-Q. Bai and T. S. A. Hor, Chem. Commun., 2008, 3172; (l) V. A.
Kozlov, D. V. Aleksanyan, Yu. V. Nelyubina, K. A. Lyssenko, E. I.
Gutsul, L. N. Puntus, A. A. Vasil’ev, P. V. Petrovskii and I. L. Odinets,
Organometallics, 2008, 27, 4062; (m) D. Zim, S. M. Nobre and A. L.
Monteiro, J. Mol. Catal. A: Chem., 2008, 287, 16; (n) O. Piechaczyk,
M. Doux, L. Ricard and P. le Floch, Organometallics, 2005, 24, 1204;
(o) W. Zhang and M. Shi, Tetrahedron Lett., 2004, 45, 8921; (p) Q. Yao,
E. P. Kinney and C. Zheng, Org. Lett., 2004, 6, 2997; (q) A. S. Gruber,
D. Zim, G. Ebeling, A. L. Monteiro and J. Dupont, Org. Lett., 2000,
2, 1287; (r) D. Zim, A. S. Gruber, G. Ebeling, J. Dupont and A. L.
Monteiro, Org. Lett., 2000, 2, 2881; (s) D. Zim, A. L. Monteiro and J.
Dupont, Tetrahedron Lett., 2000, 41, 8199; (t) D. E. Bergbreiter, P. L.
Osburn, A. Wilson and E. M. Sink, J. Am. Chem. Soc., 2000, 122, 9058.
12 A. Khanna, A. Bala and B. L. Khandelwal, J. Organomet. Chem., 1995,
494, 199.
13 (a) K. Kimura, S. Kohama and Y. Yamashita, Macromolecules, 2002,
35, 7545; (b) M.-A. Guillevic, M. J. Danks, S. K. Harries, S. R.
Collinson, A. D. Pidwell and D. W. Bruce, Polyhedron, 2000, 19, 249;
(c) J. Barbera, R. Gimenez, M. Marcos, J. L. Serrano, P. J. Alonso and
J. I. Martinez, Chem. Mater., 2003, 15, 958.
11 (a) D. V. Aleksanyan, V. A. Kozlov, Y. V. Nelyubina, K. A. Lyssenko,
L. N. Puntus, E. I. Gutsul, N. E. Shepel, A. A. Vasil’ev, P. V. Petrovskii
and I. L. Odinets, Dalton Trans., 2011, 40, 1535; (b) D. Yuan and H.
V. Huynh, Organometallics, 2010, 29, 6020; (c) V. A. Kozlov, D. V.
Aleksanyan, Y. V. Nelyubina, K. A. Lyssenko, A. A. Vasil’ev, P. V.
Petrovskii and I. L. Odinets, Organometallics, 2010, 29, 2054; (d) G. K.
14 J. A. Widegren and R. G. Finke, J. Mol. Catal. A: Chem., 2003, 198,
317.
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The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 1931–1937 | 1937
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