(NHC)-Pd(II) complexes with hydrophilic nitrogen ligands: Catalytic properties in neat water

Article abstract of DOI:10.3906/kim-1302-75

The cleavage reactions of the dimers [(NHC)PdX₂]₂ with hydrophilic N-donors, L, afforded the mixedligand complexes of the type trans-[(NHC)LPdX₂] (X = Cl or Br; NHC = 1,3-dialkylbenzimidazol-2- ylidene (BIm) or bis(imino)a

Full text of DOI:10.3906/kim-1302-75

Turk J Chem
Turkish Journal of Chemistry
(2013) 37: 633 – 642
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http://journals.tubitak.gov.tr/chem/
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c
⃝ TUBITAK
doi:10.3906/kim-1302-75
Research Article
(NHC)-Pd(II) complexes with hydrophilic nitrogen ligands: catalytic properties
in neat water
1
Hayati TURKMEN, Lu¨tfiye GOK, Ibrahim KANI, Bekir C¸ ETINKAYA
1
2
1,∗
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˙
˙
1
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Department of Chemistry, Faculty of Science, Ege University, Bornova, Izmir, Turkey
2Department of Chemistry, Faculty of Science, Anadolu University, Eski¸sehir, Turkey
Received: 28.02.2013
•
Accepted: 12.06.2013
•
Published Online: 12.07.2013
•
Printed: 05.08.2013
Abstract: The cleavage reactions of the dimers [(NHC)PdX2 ]2 with hydrophilic N-donors, L, afforded the mixed-
ligand complexes of the type trans-[(NHC)LPdX2 ] (X = Cl or Br; NHC = 1,3-dialkylbenzimidazol-2-ylidene (BIm)
or bis(imino)acenaphthene-annulated bis(2,6-diisopropylphenyl)imidazol-2-ylidene (BIAN-IPr); L = diethanolamine
(DEA), morpholine (MOR), and 3-pyridinecarboxylic acid (3-PCA)). The new complexes (1–3) were characterized by
elemental analysis and spectroscopic methods and the molecular structure of 1a was determined by X-ray diffraction
studies. These complexes were applied in the Suzuki–Miyaura cross-coupling reaction of phenylboronic acid with aryl
halides in neat water. The activities of catalysts were monitored by gas chromatography–flame ionization detector and
nuclear magnetic resonance. Whereas the complexes with DEA or 3-PCA ligands did not show significant difference in
the activity, the BIAN-IPr complexes 1b and 3b bearing DEA and 3-PCA, displayed the highest catalytic activity at
100 ◦ C.
Key words: Palladium, diethanolamine, N-heterocyclic carbene, water soluble complexes, cross-coupling
1. Introduction
Palladium-catalyzed carbon–carbon coupling reactions constitute a category of the most frequently employed
organic reactions.1 Among these transformations, the coupling of aryl and alkyl halides with arylboronic acids
(Suzuki–Miyaura [S–M] reaction) is an interesting example of unsymmetrical biaryl formation.2 These reactions
are generally carried out in the presence of various ligands, such as tertiary phosphine, which could stabilize
the active palladium intermediates.3 However, traditional phosphines have some drawbacks and, consequently,
N-heterocyclic carbene (NHC)-ligated Pd complexes have also received considerable attention as a class of
moisture- and air-stable catalyst precursors for the coupling reactions. NHC is considered as a strong σ donor
with a weak π-accepting ability; however, the π-acceptor properties of the NHC might influence the catalytic
behavior of these complexes considerably.4 One of the focal points of current research concerns the development
of (NHC)-Pd(II) complexes with a nitrogen ligand, which has been described as a “throw-away” ligand.5 In
these catalysts, steric hindrance of NHC is of crucial importance. For example, the IPent complex in PEPPSI
(pyridine-enhanced precatalyst preparation stabilization and initiation) complexes display higher activity than
IPr.6 Some related Pd(II) complexes bearing triethylamine and IPr or SIPr ligands were reported as active
∗Correspondence: bekir.cetinkaya@ege.edu.tr
This article is dedicated to the memory of Prof Dr A.S. Demir, who was one of the pioneers of frequently used novel catalysts in
organic synthesis.
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S–M coupling catalysts.5c,d Most of the catalytic reactions involving these catalysts were carried out in organic
media due to the hydrophobic nature of the ligands surrounding the Pd center.
Recently, a great deal of attention has been paid to the search for water-soluble metal complexes because,
in principle, the advantages of homogeneous and heterogeneous catalysts can be combined.7 Furthermore, water
has a number of favorable properties, such as nontoxicity, nonflammability, and availability in large quantities.
Despite this interest, almost all published aqueous chemistry studies concentrate on tertiary phosphines, and
triphenylphosphine-3,3,3-trisulfonic acid trisodium salt (TPPTS) is the most favored hydrophilic phosphine.7,8
This concept has been successfully extended to the NHC ligands by introducing polar functionalities such as
-SO−3 , -COO− , -OH, or -(CH2 CH2 O)n -H, -NR+4 by various research groups.9 In this context, we have, very
recently, reported the synthesis and catalytic activity of water-soluble complexes A and B obtained by cleavage
of the dimer [(NHC)PdBr2 ]2 with TPPTS and pyridine-2,6-dicarboxylic acid, respectively.8b,10 However, a
sophisticated ligand design mostly resulted in increasingly expensive complexes. Therefore, we have focused
on hydrophilic throw-away ligands analogous to that of PEPPSI catalysts and obtained good results with B,
using aryl halides as substrates. Furthermore, the way they act during the catalytic process remains unknown.
Herein, we attempt to find some information in order to get a better understanding of this question by applying
alternative commercially available and cheap nitrogen ligands. A related objective is to study the role of the
size of the NHC ligand in determining the efficiency in the S–M reaction.
2. Results and discussion
2.1. Synthesis and cleavage of (NHC)-palladium dimers with hydrophilic N ligands
NHCs are not purely σ-donors; π-back donation represents approximately 10%–30% of the character of the
bond.11 The percentage of π-back bonding could significantly increase for more electronrich species such as
(NHC)-Pd(0), which are believed to play an important role in the catalytic cycle.12 Previous studies have shown
that, for the S–M reaction, 4,5-annulation and bulky N-substituents are crucial for high catalytic performances.
In view of this information and for comparative purposes, we have focused on 4,5-annulated imidazolium salts
[BIm].HBr and [BIAN-IPr].HCl as NHC precursors. Rh(I), Ir(I), Ru(II), Ag(I), Au(I), and Pd(II) complexes
bearing the BIAN-IPr ligand have been reported while this work was in progress.13 We previously employed a
saturated version of the BIAN-IMes ligand in Ag(I), Rh(I), and Pd(II) complexes.14 We have chosen surface-
active DEA as a hydrophilic coligand akin to diethylamine, which has been found to inhibit the S–M reaction
at 40 ◦ C, and this inhibition has been attributed to the intramolecular H-bonding between diethylamine and a
chloride attached to the Pd center.5d However, at higher temperatures and longer reaction times, the catalysts
were effective.
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The targeted mixed-ligand complexes, 1–3, were obtained as yellow-orange solids from the dimers
[(NHC)PdX2 ]2 according to the synthetic route presented in Scheme. The dimer [(BIm)PdBr2 ]2 has been
prepared using the literature method,15 whereas [(BIAN-IPr)PdCl2 ]2 was obtained via an NHC transfer reac-
tion of [(BIAN-IPr)-Ag-Cl].13b Pyridinecarboxylic (PCA)-derived Pd(II) complexes (such as B) were successfully
used as water-soluble catalysts in the S–M reaction. Our initial attempt to cleave [(BIAN-IPr)PdCl2 ]2 with
2,6-PDCA failed, but 3-PCA readily reacted to give the expected 3b in high yield. Owing to its easy acces-
sibility and formal similarity to 3-chloropyridine, 3-PCA was the ligand of choice for the cleavage reaction to
prepare 3b. The coligands DEA and MOR, a dehydrated form of DEA, are completely soluble/miscible with
water. They are electronically and sterically different from 3-PCA and afforded 1–3 in high yields. Due to their
ability to form strong H-bonds, the DEA complexes 1a and 1b are water-soluble at 100 ◦ C, 3b is soluble in
its deprotonated form (basic conditions) at 25 ◦ C and 2a is the least soluble. The sharp contrast in the water
solubility of complexes 1a and 2a clearly reflects diminished H-bonding characteristics of MOR complex.
The palladium complexes can be stored in air for a long period of time. In some cases, the stabilities of
NHC complexes in water have been described as being low.9i Therefore, we gradually heated and monitored
the solutions of the new complexes by 1 H NMR in wet DMSO-d6 , but no significant changes were observed
((ESI) electronic supporting information). They were characterized by 1 H NMR, 13 C NMR, and elemental
analyses. The NMR spectra of complexes 1a 1b 2a and 3b show that the amine ligands are coordinated to
the palladium center. The 1 H NMR spectra of complexes 1a and 2a clearly indicate benzylic protons at 6.11
and 6.06 ppm, respectively. The signals of the carbene of 1b (δ 163.8) in the 13 C NMR spectrum are slightly
shifted to higher field as compared to their signals from pyridine derivative 3b (δ 168.4).
Scheme. Synthesis of (NHC)-Pd(II) complexes’ conditions and reagents: (i) Pd(OAc)2 , DMSO, 90 ◦ C; (ii) a) Ag2 O,
CH2 Cl2 , 25 ◦ C, b) PdCl2 (MeCN)2 , 40 ◦ C; (iii) DEA, CH2 Cl2 , 25 ◦ C; (iv) MOR, CH2 Cl2 , 25 ◦ C; (v) 3-PCA,
CH2 Cl2 , 25 ◦ C.
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2.2. X-ray structural analyses of the complex
Diffraction data for the complex were collected with a Bruker AXS APEX CCD diffractometer equipped with
˚
a rotation anode at 296(2) K using graphite monochromated Mo Kα radiation at λ = 0.71073 A. Diffraction
data were collected over the full sphere and were corrected for absorption. The data reduction was performed
with the Bruker SMART16 program package. For further crystal and data collection details, see Table 1.
Structure solution was found with the SHELXS-9717 package using the direct methods and were refined with
SHELXL-9718 against F2 using first isotropic and later anisotropic thermal parameters for all nonhydrogen
atoms. Hydrogen atoms were added to the structure model at calculated positions. Geometric calculations were
performed with PLATON.19
2.3. Description of structure
The molecular structure of complex 1a was determined by single-crystal structure X-ray diffraction studies. The
ORTEP view of the complex is shown in the Figure and the crystallographic data are summarized in Table 1.
The complex crystallizes in a monoclinic system with Z = 4 in space group P21/n. The structure determination
of complex 1a reveals a mononuclear square-planar Pd(II) atom coordinated by the NHC, 2 bromide ligands,
and 1 diethanolamine ligand in a trans arrangement (Figure).
Figure. A view of the complex 1a, showing 50% probability displacement ellipsoids and the atom-numbering scheme;
◦
˚
selected bond lengths (A) and angles ( ) for complex 1a: Pd(1)-C(5) 1.959(18), Pd(1)-N(1) 2.134(16), Pd(1)-Br(1)
2.431(2), Pd(1)-Br(2) 2.431(2), C(5)-Pd(1)-N(1) 177.3(7), C(5)-Pd(1)-Br(1) 88.33(5), N(1)-Pd(1)-Br(1) 89.06(5), C(5)-
Pd(1)-Br(2) 88.85(5), N(1)-Pd(1)-Br(2) 93.77(5).
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The palladium ion has slightly disordered square planar geometry, principally due to Br1 -Pd-Br2 [176.94
(8)◦ ], and C5-Pd-N1 [177.34◦ ]. The bromide ligands are bent towards the NHC ligand for steric reasons. Pd-Br
˚
bond length [2.431 (2) A] is similar to the equivalent value found in the related complexes trans-[(NHC)LPd(Br2 ]
(L = PCy3 , PPh3).2 The Pd (II)-Ccarbene [1.959 (18) A] and the Pd-N [2.134 (16) A] bond lengths are slightly
shorter than other similar types of Pd(II)-NHC complexes21−24 and also reported Pd-C bonds25 , and this result
is attributed to the π-back bonding interaction of the Pd (II)-carbene bonds for the latter types.
˚
˚
Table 1. Crystal data and structure refinement parameters for complex 1a.
Empirical formula
Formula weight
Temperature
C26H39Br2N3O3Pd
707.80
100(2) K
Wavelength
0.71073 Å
Crystal system, space group
Unit cell dimensions
Monoclinic, P21/n
a = 18.7767(3) Å alpha = 90°
b = 7.51130(10) Å beta = 100.3250(10)°
c = 19.9073(3) Å gamma = 90°
2762.21(7) Å3
Volume
Z, Calculated density
Absorption coefficient
F(000)
4, 1.702 Mg/m3
3.597 mm–1
1424
Crystal size
Theta range for data collection
Limiting indices
0.53 × 0.27 × 0.18 mm
1.65° to 28.41°
–25 ≤ h ≤ 23, –7 ≤ k ≤10, –25 ≤ l ≤ 26
25988 / 6932 [R(int) = 0.0251]
28.41 99.4%
Reflections collected / unique
Completeness to theta
Absorption correction
Max. and min. transmission
Refinement method
Data / restraints / parameters
Goodness-of-fit on F2
Final R indices [I > 2sigma(I)]
R indices (all data)
Integration
0.524 and 0.325
Full-matrix least-squares on F2
6891 / 0 / 328
1.035
R1 = 0.0218, wR2 = 0.0532
R1 = 0.0277, wR2 = 0.0553
0.519 and –0.467 e.Å–3
Largest diff. peak and hole
2.4. Catalytic studies
Early experiments established that coupling reactions proceeded in water at 100 ◦ C in the presence of 1 mol%
NHC-Pd complexes with KOH as a base.8b,10 In this work, we first carried out a catalyst screening by comparing
the activity of 1a, 1b, 2a, and 3b in the coupling of 4-chloroacetophenone and 4-chlorobenzaldehyde with
phenylboronic acid. The reactions were carried out in neat water at 100 ◦ C with 1 mol% palladium complexes
loading in the presence of KOH. Among the complexes, 1a and 1b containing DEA gave the highest yield, while
2a with MOR gave moderate yields. The results from the screening of aryl chlorides with phenylboronic acid
are summarized in Table 2. These observations showed that the presence of DEA ligands in complexes provided
the catalytic enhancement. In separate experiments, we used DEA as a base, which showed higher efficiencies
than KOH (Table 2). It is assumable that DEA increases the rate of the reaction catalyzed by water soluble
catalysts to stabilize catalytically active species in water or/and to act as a mass transfer promoter. Mono- and
triethanolamines were less efficient. Therefore, the rest of the tests were carried out with DEA. Efficiency of
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1b over 3b suggests that DEA may stabilize the active species in 1b due to the “NHC Pdb ” intermediate via
hydrophilic OH groups.
In order to evaluate the role of NHC ligands, we included other water-soluble palladium complexes. In
this context, we decided to examine trans-[PdCl2 (DEA)2 ], 4.24 However, the efficiency of 4 was much lower
(45% yield), and therefore further experiments were abandoned. This observation clearly suggests that NHC
ligands play an important role in the catalysis. In the catalytic studies, phenyldioxazaboracane was also used
as a substrate (Table 2, entry 1), because DEA and PhB(OH)2 are known to form phenyldioxazaboracane.26
However, a lower yield was observed.
Table 2. Palladium-catalyzed C-C coupling reaction of phenylboronic acid with aryl halides.
Cat.
R
1a
1b
100b,d
2a
34b
16b
-
-
-
3b
91b
4
45b
37b
-
-
-
COCH3 85a(97)b(62)b,c
CHO
CN
NO2
OMe
CH3
82a(89)b
80a(91)b
78a(89)b
61a(70)b
53a(67)b
100b,d
97b
100b,d
100b,d
94b(85)b,d
91b(82)b,d
100b
100b
87b(78)b,d
89b(76)b,d
-
-
Yields were determined by gas chromatography for an average of 2 runs. a KOH was used as a base. b Diethanolamine
was used as a base. c Phenyldioxazaboracane was used instead of phenylboronic acid. d Reaction time is 2 h.
2.5. Catalyst recycling
We examined the possibility of reusing catalysts 1a 1b or 3b for the S–M reaction of 4-chloroacetophenone
and phenylboronic acid and the reactions were conducted under the same conditions. After the first reaction,
the solid product was separated by filtration (100% yield). To the filtrate containing 1b fresh substrates DEA
(2.0 mmol) and sufficient distilled water were added to bring the volume to 6.0 mL. The yields for the 2nd, 3rd,
and 4th cycles were 92%, 87%, and 77% respectively (Table 3). Catalyst 1b appears to be reusable for 6 cycles
for the reaction of 4-chloroacetophenone; however, on the sixth cycle, the yield dropped to 54%.
Table 3. Reusability of catalyst B, 1a, 1b, and 3b for the S–M reaction of 4-chloroacetophenone and phenylboronic
acid.
Cat./Cycles 1st 2nd 3rd 4th 5th 6th
B
99
97
100
91
67
88
92
84
63
83
87
79
48
70
77
71
41
65
69
63
30
40
54
50
1a
1b
3b
Yields (%) at 100 ◦C for 4 h; DEA used as base.
3. Conclusion
We showed that the cleavage reaction of [(NHC)PdX2 ]2 is a suitable synthetic procedure for the incorporation
of hydrophilic ligands such as DEA, MOR, or 3-PCA onto the Pd-center to prepare water-soluble complexes.
The DEA coordinates to palladium through its N, while the ethanolic groups are pendant and ready to interact
with phenylboronic acids or to give H-bonds with water.
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The attempt to improve the catalytic efficiency of the S–M reaction by combining bulky BIAN-IPr with
DEA or 3-PCA is highly successful, particularly in view of the commercial availability of these hydrophilic
ligands and ease of synthesis of the (BIAN-IPr).HCl precursor. Again, the combination of BIAN-IPr and DEA
as ligands is found to be beneficial in water for the S–M reaction. The strategy may have further implications
in large-scale operations. Work is also in progress to extend this system to other C-C and C-N cross-coupling
reactions catalyzed by (NHC)Pd complexes.
4. Experimental
4.1. General procedures
The complexes [BIm].HBr, [BIAN-IPr].HCl, and 4 were prepared according to the literature methods.13b,14,24
NMR spectra were recorded at 297 K on a Varian Mercury AS 400 at 400 MHz (1 H) and 100.56 MHz (13 C).
Elemental analyses were carried out by the analytical service of the Scientific and Technological Research Council
of Turkey with a Carlo Erba Strumentazione Model 1106 apparatus. The yields of C-C coupling products were
determined using GC and NMR.
4.2. General procedure for the preparation 1a, 1b, 2a, and 3b; cleavage of the [(NHC)PdX2 ]2
with DEA, MOR, or 3-PCA
A sample of [(NHC)PdX2 ]2 (0.5 mmol) and DEA, MOR, or 3-PCA (1.0 mmol) were dissolved in 10 mL of
CH2 Cl2 . The mixture was stirred at ambient temperature for 1 h. The volume of the solution was reduced to
about 5 mL in vacuo. Diethyl ether (10 mL) was added to the solution to obtain a bright cream precipitate,
which was collected by filtration, washed with 10 mL of diethyl ether, and dried in vacuo. The product was
recrystallized from CH2 Cl2 /Et2 O. Complexes 1a, 1b, 2a, and 3b were synthesized according to this procedure.
[(BIAN-IPr)PdCl2 ]2, b: To a solution of (BIAN-IPr).HCl (500 mg, 0.9 mmol) in CH2 Cl2 (20 mL),
Ag2 O (310 mg, 1.35 mmol) was added. The mixture was stirred at 35 ◦ C for 48 h in the dark and filtered through
Celite. [Pd(CH3 CN)2 Cl2 ] (468 mg, 1.8 mmol) was added and, after stirring for 24 h at 35 ◦ C, the product was
separated by column chromatography (CH2 Cl2). The product was recrystallized from CH2 Cl2 /Et2 O, yield:
404 mg, 65%. 1 H NMR (CDCl3): δ 7.75–7.62 (m, 4 H, Naph-H , Ar-H), 7.44 (d, J = 7.6 Hz, 4 H, Ar-H),
7.27 (dd, J = 14.5, 7.2 Hz, 2 H, Naph-H), 6.71 (d, J = 7.6 Hz, 2 H, Naph-H), 3.00 (dt, J = 13.4, 6.7 Hz, 4
H, -CH), 1.29 (d, J = 6.5 Hz, 12 H, -CH3), 0.80 (d, J = 6.5 Hz, 12 H, -CH3). 13 C NMR: δ 153.2 (C -Pd),
147.2, 140.5, 133.4, 130.9, 129.7, 129.1, 128.4, 127.4, 126.0, 125.1, 122.4 (Ar-C , Naph-C), 29.0 (-C H3), 25.8
(-C H), 24.3 (-C H3). Anal. Calc. for C74 H80 Cl4 N4 Pd2 (1380,11): C 64.40, H 5.84, N 4.06; Found C 64.37,
H 5.80, N 4.01%.
1a: Yield: 0.57 g, 80%. 1 H NMR (CDCl3): δ 7.46 (d, J = 8.4 Hz, 1 H, Benz-H), 7.12 (t, J = 7.2
Hz, 1 H, Benz-H), 6.85 (t, J = 8.0 Hz, 1 H, Benz-H), 6.18 (d, J = 8.4 Hz, 1 H, Benz-H), 6.11 (s, 2 H,
CH2 C6 (CH3)5), 4.96 (t, J = 5.6 Hz, 2 H, NCH2 CH2 OCH3), 4.83 (t, J = 10.4 Hz, 2 H, NH(CH2 CH2 OH)2),
4.12 (t, J = 5.6 Hz, 2 H, NCH2 CH2 OCH3), 3.93 (d, J = 11.2 Hz, 2 H, NH(CH2 CH2 OH)2), 3.51 (br,
1 H, NH (CH2 CH2 OH)2), 3.36 (s, 3 H, CH2 CH2 OCH3), 2.61 (m, 2 H, NH(CH2 CH2 OH)2), 2.27 (m,
2 H, NH(CH2 CH2 OH)2), 2.33 (s, 3 H, CH2 C6 (CH3)5p), 2.28 (s, 6 H, CH2 C6 (CH3)5m), 2.26 (s, 6 H,
CH2 C6 (CH3)5o). 13 C NMR: δ 164.6 (C-Pd), 136.4, 135.7, 134.6, 134.7, 133.3, 127.3, 123.1, 122.6, 111.7, 111.0
(Benz-C , CH2C6 (CH3)5), 71.3 (NH(CH2C H2 OH)2), 60.6 (NH(C H2 CH2 OH)2), 59.3 (NCH2 CH2 OC H3),
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54.3 (NCH2C H2 OCH3), 52.5 C H2 C6 (CH3)5), 48.6 (NC H2 CH2 OCH3), 17.6 (CH2 C6(C H3)5m), 17.3
(CH2 C6(C H3)5o), 16.8 (CH2 C6(C H3)5p). Anal. Calc. for C26 H39 Br2 N3 O3 Pd (707.83): C 44.12, H 5.55,
N 5.94; Found C 44.11, H 5.51, N 5.97%.
1b: Yield: 0.72 g, 91%. 1 H NMR (CDCl3): δ 7.74–7.64 (m, 4 H, Naph-H , Ar-H), 7.50 (d, J = 7.8
Hz, 4 H, Ar-H), 7.36 (dd, J = 8.3, 7.1 Hz, 2 H, Naph-H), 6.95-6.93 (m, 2 H, Naph-H), 4.08 (t, J = 11.7
Hz, 2 H, NH(CH2 CH2 OH)2), 3.41 (br, 1 H, NH (CH2 CH2 OH)2), 3.24 (dt, J = 13.4, 6.7 Hz, 4 H, -CH),
3.08 (br, 2 H, NH(CH2 CH2 OH)2), 2.73 (t, J = 11.5 Hz, 2 H, NH(CH2 CH2 OH)2), 2.53 (t, J = 10.5 Hz, 2
H, NH(CH2 CH2 OH)2), 2.26 (d, J = 11.5 Hz, 2 H, NH(CH2 CH2 OH)2), 1.39 (d, J = 6.6 Hz, 12 H, -CH3),
0.93 (d, J = 6.6 Hz, 12 H, -CH3). 13 C NMR: δ 163.8 (C -Pd), 147.5, 140.6, 133.7, 131.0, 129.8, 129.4, 128.4,
127.5, 126.2, 124.7, 122.6 (Ar-C, Naph-C), 60.3 (NH(C H2 CH2 OH)2), 53.3 (NCH2C H2 OH), 29.1 (-C H3),
26.1 (-C H), 24.0 (-C H3). Anal. Calc. for C41 H51 Cl2 N3 O2 Pd (795,19): C 61.93, H 6.46, N 5.28; Found C
61.89, H 6.42, N 5.24%.
2a: Yield: 0.62 g, 90%. 1 H NMR (CDCl3): δ 7.46 (d, J = 8.4 Hz, 1 H, Benz-H), 7.11 (t,
J = 8.0 Hz, 1 H, Benz-H), 6.87 (t, J = 8.0 Hz, 1 H, Benz-H), 6.23 (d, J = 8.4 Hz, 1 H, Benz-H),
6.06 (s, 2 H, CH2 C6 (CH3)5), 4.94 (t, J = 6.0 Hz, 2 H, NCH2 CH2 OCH3), 4.13 (t, J = 6.0 Hz, 2 H,
NCH2 CH2 OCH3), 3.84 (d, J = 7.2 Hz, 2 H, NH(CH2 CH2)2 O), 3.46 (m, 4 H, NH(CH2 CH2)2 O), 2.94
(d, J = 7.2 Hz, 2 H, NH(CH2 CH2)2 O), 2.53 (br, 1 H, NH (CH2 CH2)2 O), 2.31 (s, 3 H, CH2 C6 (CH3)5p),
2.26 (s, 6 H, CH2 C6 (CH3)5m), 2.24 (s, 3 H, CH2 C6 (CH3)5o). 13 C NMR: δ 164.5 (C -Pd), 136.3, 135.9,
135.0, 134.9, 133.3, 127.8, 123.2, 122.7, 111.6, 111.3 (Benz-C , CH2C6 (CH3)5), 71.5 (NH(CH2C H2)2 O),
68.3 (NH(C H2 CH2)2 O), 59.3 (NCH2 CH2 OC H3), 54.4 (NCH2C H2 OCH3), 52.4 C H2 C6 (CH3)5), 48.9
(NC H2 CH2 OCH3), 17.8 (CH2 C6(C H3)5m), 17.5 (CH2 C6(C H3)5o), 17.1 (CH2 C6(C H3)5p). Anal. Calc.
for C26 H37 Br2 N3 O2 Pd (689.82): C 45.27, H 5.41, N 6.09; Found C 45.22, H 5.37, N 6.17%.
3b: Yield: 0.73 g, 90%. 1 H NMR (CDCl3): δ 9.30 (s, 1 H, C5H4 NCOOH), 8.86 (d,J = 5.5 Hz, 1 H,
C5H4 NCOOH), 8.20 (d,J = 7.9 Hz, 1 H, C5H4 NCOOH), 7.73–7.58 (m, 4 H, (2 H + 2 H) Naph-H , Ar-H),
7.49 (d, J = 7.7 Hz, 4 H, Ar-H), 7.33 (t, J = 7.6 Hz, 2 H, Naph-H), 7.25 (d, J = 1 Hz, 1 H, C5H4 NCOOH),
6.80 (d, J = 7 Hz, 2 H, Naph-H), 4.51 (br, 1 H, C5 H4 NCOOH ), 3.42 (sept, 4 H, -CH), 1.47 (d, J =
6.5 Hz, 12 H, -CH3), 0.93 (d, J = 6.8 Hz, 12 H, -CH3). 13 C NMR: δ 168.4 (C -Pd), 159.7, 155.7, 153.5,
147.5, 140.6, 139.1, 134.1, 130.9, 129.8, 129.3, 128.2, 127.4, 126.3, 126.1, 124.9, 123.9, 122.4 (Ar-C , Naph-C ,
C5 H4 NC OOH), 29.1 (-C H3), 26.0 (-C H), 24.5 (-C H3). Anal. Calc. for C43 H46 Cl2 N3 O2 Pd (814.17): C
63.43, H 5.69, N 5.16; Found C 63.38, H 5.66, N 5.21%.
Supplementary data: Crystallographic data can be obtained from the Cambridge Crystallographic
Data Centre by quoting the reference number CCDC - 798814. The data can be obtained free of charge at
www.ccdc.cam.ac.uk/data request/cif.
4.3. General procedure for the Suzuki coupling reactions
Catalytic studies were performed under aerobic conditions. A 2-necked 25-mL flask was charged with aryl
chlorides (1.0 mmol), 2 mmol KOH or DEA, phenylboronic acid (1.5 mmol), and 1.0% 1a, 1b, 2a, 3b, or 4 in
6 mL of H2 O. The flask was placed in a preheated oil bath under air atmosphere and temperature of 100 ◦ C
for 2 or 4 h.
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4.4. Recycling of catalyst
The flask was charged with catalyst 1a, 1b, 3b 4-chloroacetophenone (1.0 mmol), 2 mmol DEA, phenylboronic
acid (1.5 mmol), and diethyleneglycol-di-n-butylether (0.6 mmol, internal standard). The reaction was carried
out in water at 100 ◦ C. After cooling to room temperature, the organic products were removed by filtration.
The aqueous phase was then transferred to a new reaction flask for the next cycle. Yields were determined by
gas chromatography for an average of 2 runs.
Acknowledgments
¨
The authors are grateful to Ege University (Project 2012-BIL-42) and TUBA for financial support and to the
Medicinal Plants and Medicine Research Center of Anadolu University, Eski¸sehir, Turkey, for the use of the
X-ray diffractometer. They also thank Dr S Astley at the Ege University Chemistry Department for reading
the manuscript.
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